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7/22/2019 Tng hp Thp

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1.Thnh phn ha hcKhc vi thp cacbon, thp hp kim l loi thp m ngi ta c a thm vo (khng phi do

yu cu thng thng ca cng ngh luyn kim) cc nguyn t c li vi lng ln lmthay i t chc v ci thin tnh cht (c, l, ha).

Cc nguyn t c li c a vo mt cch c bit vi lng ln nh vy c gi lnguyn t hp kim, chng bao gm cc nguyn t vi hm lng ln hn cc gii hn cho tngnguyn t (khng c gi tr chung cho mi nguyn t) nh sau: Mn 0,80 - 1,00%, Si 0,50 - 0,80%, Cr 0,50 - 0,80%,Ni 0,50 - 0,80%, W 0,10 - 0,50%, Mo 0,05 - 0,20%,Ti 0,10%, Cu 0,30, B 0,0005%.

Nh hn gii hn di k trn c coi l tp cht. Tuy nhin cc gii hn trn cng ch l quyc v khng cng nhc mt cch qu cht ch.

Thp hp kim l loi c cht lng t tt tr ln nn cha t v rt t cc tp cht c hi.

2.c c tnh ca thp hp kim y ni k hn cc c tnh tri hn hn ca thp hp kim so vithp cacbon (thp cacbon

tng ng c mang ra i chng phi l loi c cng thnh phn cacbon vi thp hp kim cho).

C tnhDo mt s yu t m ch yu l do tnh thm ti cao hn nn thp hp kim c bn cao hnhn so vi thp cacbon, iuny th hin c bit r rng thp sau khi ti + ram. Khi ht sctn dng u im ny cn ch n n cc h qu sau y:

- trng thi khng ti + ram (v d trng thi ), bn ca thp hp kim khng cao hnthp cacbon bao nhiu. Cho nn dng thp hp kim th phi qua nhit luyn ti + ram. Nudng thp hp kim trng thi cung cp (sau cn nng, gn nh thng ha) hay l s lng phln v bn.

- u vit v bn cao ca thp hp kim cng r khi tit din ca thp cng ln v lng hpkim bo m ti thu. Khi tit din nh ( 20mm) u vit ny ca thp hp kim khng th

hin c (v vi tit din nh nh vy thp cacbon cng c ti thu).- Do tnh thm ti tt, dng mi trng ti chm (du) nn khi ti t bindng v nt hn so

vi thp cacbon lun phi ti nc. Do vy cc chi tit c hnh dng phc tp phi qua ti (doi hi v bn) u phi lm bng thp hp kim.

- Khi tng mc hp kim ha lm tng c thm ti lm tng cng, bn songthng lm gim do, dai nn lng hp kim cn thit ch cn va bo m ti thu titdin cho l , khng nn dng tha (dng thp hp kim qu cao va t va kh gia cng li


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d b ph hy gin hn). Do vy c nguyn tc l chn mc thp hp kim cao hay thp l phthuc kch thc (tit din).

- Tuy t bn cao hn nhng thng c do, dai thp hn. Do vy phi ch n miquan h ngc ny c x l thch hp (bng ram).

Mc dc u im v bn, ni chung thp hp kim c tnh cng ngh km hn thp cacbon(tr tnh thm ti).

Tnh chu nhit caoCc nguyn t hp kim cn tr s khuch tn ca cacbon do lm mactenxit kh phn ha v

cacbit kh kt t nhit cao hn 200oC, do vy ti cc nhit ny thp hp kim bn hn.Mt s thp hp kim vi lp vy xyt to thnh nhit cao kh xt cht, c tnh bo v tt.

Tnh cht vt l, ha hc c bitBng cch a vo thp cc nguyn t khc nhau vi lng ln quy nh c th to ra cho thp

cc tnh chtc bit:- Khng g, chng n mn trong axit, bad, mui.- T tnh c bit hoc khng c t tnh.- Gin n nhit c bit...

Qua thy rng thp hp kim l vt liu cn thit, khng th thiu cho nhng ngnh k thutquan trng i hi cc tnh cht cao hoc khc vi thng thng.

3.Tc dng ca nguyn thp kim n tchc cathp

Mt cch n gin c th xem mt thp hp kim n gin (ch c mt nguyn t hp kim) la thm nguyn t hp kim vo hp kim Fe - C. Vy hy xem nguyn t hp kim nh hngnh th no n hp kim Fe - C m ta nghin cu, c th l n cc t chc chnh: cc dungdch rn ferit, austenit, hp cht xmentit (pha cacbit), t chc peclit (hn hp ferit - cacbit)...Cc nguyn t khi a vo thp cng khngngoi hai tc dng: ha tan vo st thnh dung dchrn v kt hp vi cacbon thnh cacbit. Cng kh phn loi rch ri song c th tm chia thnhhai dng nguyn t hp kim tin kho st: dng ch yu ha tan vo st v dng c i lcmnh vi cabon to nn cacbit. Hy xt tng kh nng.Ha tan vo st thnh dung dch rn

l trng hp ca phn ln nguyn t m in hnh v thng gp l Mn, Si, Cr, Ni.Vi lng t nguyn t hp kim (khong vi %) chng khng lm thay i ng k cu hnh

ca gin pha Fe - C, chng ha tan vo st tc ferit nhit thp v austenit nhit cao. Khi ha tan (tt nhin l dng thay th) vo ferit, cc nguyn t hp kim lm x lch mng

do lm tng cng, bn v thng lm gim do, dai. nh hng ca bn nguynt trn n hai ch tiu in hnh l cng v dai c trnh by trn hnh 5.2. Qua thyr c hai nhm khc nhau: Mn v Si, Cr v Ni. Hai nguyn t Mn v Si lm tng rt mnh cng ( bn) song cng lm gim mnh dai ( do), c bit khi thp cha 2%Si hoc


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3,5%Mn ferit c dai rt thp ( 500kJ/m2) lm thp gin khng cho php s dng. Do vymc du c li th l r hn, kh nng ha bn cao Mn v Si ch c dng vi hm lng hnch 1 - 2%. Nh th khng th dng thp Mn, Si vi thm ti cao v b hn ch bi lng avo. Cn Ni v Cr (cho ti hm lng 4%) trong khi lm tng cng chng nhng khng lmgim cn lm tng cht t dai. Do vy hp kim ha thp bng Cr, Ni hay ng thi bng c

hai l rt tt v ngoi lm tng thm ti, bn thn chng nng cao cng, bn m vn duytr tt do, dai ca ferit. V th thp c thm ti cao thuc nhm c hp kim ha bngCr -Ni. Mc du gi thnh c cao hn (do Cr v c bit Ni ngy cng t, him) loi thp nyvn c a chung trong ch to cc chi tit i hi tin cy cao.

Vi lng nhiu (>10%) Cr, Ni, Mn chng lm thay i hn cu hnh ca gin pha Fe - C,c bit r l lm thay i cc khu vc ca ferit v austenit. Trn hnh 5.3 trnh by nh hngca hm lng Mn v Cr n khu vc (austenit) ca gin pha Fe - C. Thy rt r Mn (v cNi na) m rng (nhit tn ti ca) khu vc (tng ng thu hp khu vc ). Vi hm lngln trong khong 10 - 20% t chc austenit tn ti c nhit thng (khng biu th hnh5.3a), tc l khi nung nng hay lm ngui khng c chuyn bin pha nh thng gp, thp cgi l thp austenit. Cn Cr ngc li thu hp khu vc (tng ng m rng khu vc nh

hnh 5.3b). Vi hm lng Cr ln (khong gn 20%) khu vc khng cn tn ti, t chcferit tn ti c nhit cao cho ti khi chy lng. Thp ny cng khng c chuyn bin pha vc gi l thp ferit. Nhng trng hp nh vy ch gp thp c bit. R rng l cc thpny khng th p dng ha bn bng ti.
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Hnh 5.2. nh hng ca ha tan ca cc nguyn t hp kim ch yu trong dung dch rn feritn cng (a) v dai va p (b)

To thnh cacbitTr cc nguyn t Si, Ni, Al, Cu, Co khng to thnh c cacbit trong thp (ch c th ha

tan vo st), cc nguyn t hp kim cn li gm Mn, Cr, Mo, W, Ti, Zr, Nb ngoi kh nng hatan vo st cn c th kt hp vi cacbon thnh cacbit.Ngi ta nhn thy rng s in t ca phn lp nd (3d, 4d, 5d) trong nguyn t ca nguyn t

no cng b thiu th nguyn t cng c i lc mnh vi cacbon v tt nhin l trong thp (chyu l st) ch nguyn t no c s in t ca phn lp nd t hn ca Fe (l 6) th mi c khnng to thnh c cacbit.

Ph hp vi s thiu ht ca in t, cc nguyn t to thnh cacbit trong thp theo th t tyu n mnh nh sau:Fe (6), Mn (5), Cr (5), Mo (5), W (4), V (3), Ti (2), Zr (2), Nb (2)[s trong ngoc l s in t trong phn lp nd], trong : - Mn v Cr l cc nguyn t to thnh cacbit trung bnh.

- Mo v W l cc nguyn t to thnh kh mnh.- V l nguyn t to thnh cacbit mnh, v- Ti, Zr, Nb l cc nguyn t to thnh cacbit rt mnh.

Hnh 5.3. nh hng ca Mn (a) v Cr (b) n cc vng a v g trn gin Fe -C.
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Khi a vo thp cc nguyn t ny, cacbon s u tin kt hp vi cc nguyn t mnh trc.Ty theo nguyn t hp kim (Me) a vo v hm lng ca n, trong thp hp kim c cc phacacbit sau.

- Xmentit hp kim (Fe, Me)3C. Khi thp cha mt lng t (1 - 2%) cc nguyn t to cacbit

trung bnh v kh mnh l Mn, Cr, Mo, W chng ha tan thay th v tr cc nguyn t Fe trongxmentit to nn xmentit hp kim(Fe, Me)3C. Xmentit hp kim c tnh n nh cao (kh phnhy, kt t khi nung) hn xmentit cht t. Nhit ti c tng i cht.- Cacbit vi kiu mng phc tp. Khi hp kim ha n gin (ch bng mt nguyn t hp kim)song vi lng ln (> 10%) Cr hoc Mn (c dC / dMe > 0,59) chng to nn vi C loi cacbitvi kiu mng phc tp nh: Cr7C3, C23C6, Mn3C. Cc c tnh ca cacbit ny l: + C cng cao (hn xmentit mt cht).+ C nhit chy khng cao lm, trong khong 1550 - 1850oC (cao hn xmentit), nn c tnhn nh cao hn. Nhit ti ca thp phi cao hn 1000oC.

- Cacbit kiu Me6C. Trong cc thp cha Cr vi W hoc Mo s to nn cacbit loi Me6C vikiu mng phc tp, trong Me l cc nguyn t Cr, W, Mo v c Fe. Loi cacbit ny cn khha tan vo austenit hn v n nh hn loi trn. Nhit ti ca thp trong khong 1200 -1300oC.

- Cacbit vi kiu mng n gin MeC (Me2C). Cc nguyn t to thnh cacbit mnh v rt mnhl V, Ti, Zr, Nb khi a vo thp vi lng t (0,1%) cng c kh nng lin kt ht vi cacbonthnh cacbit nh VC, TiC, ZrC, NbC, chng chnh l pha xen k vi kiu mng n gin (vdC/dMe < 0,59). Cc c tnh ca loi cacbit ny l:+ C cng cao nhng t gin hn xmentit.+ C nhit chy rt cao (trn di 3000oC) nn rt kh phn hy v ha tan vo austenit khi

nung. Cc nguyn t ny khng c tc dng tng thm ti, cacbit ca chng thng ng vaitr gi cho ht nh v nng cao tnh chng mi mn.Nh vy cc cacbit hp kim cng hn, n nh hn, kh ha tan vo austenite hn so vixmentit lm thp hp kim cng, bn nng hn v c nhit ti cao hn thp cacbon. Do cc nhm thp s dng cc loi nguyn t hp kim v lng cha khc nhau nn ni chungmi nhm thp thng ch gp 1 - 2 loi cacbit k trn, c th l:+ Xmentit hp kim trong thp kt cu.+ Cacbit vi kiu mng phc tp trong thp khng g v bn nng (thuc nhm thp c bit). + Cacbit kiu Me6C trong thp gi (thuc thp dng c). + Cacbit vi kiu mng n gin MeC c to thnh vi lng t trong cc nhm thp khcnhau.

Vai tr ca cacbit hp kim- Ging nh xmentit, cacbit hp kim cng c tc dng lm tng cng, tnh chng mi mnca thp song c phn mnh hn. Nh sau ny s thy thp lm dng c tt nht phi l loi thpc cacbon cao v hp kim cao.- Do kh ha tan vo austenit khi nung nng nn mt mt nng cao nhit ti mt khc li gi


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c ht nh khi nung, iu ny gip nng cao dai v c tnh ni chung. - Khi ram, cacbit hp kim tit ra khi mactenxit v kt t li nhit cao hn so vi xmentit trong thp cacbon, do gi c cng cao ca trng thi ti nhit cao hn 200oC, ikhi ti 500 - 600oC, tc c tnh cng hay bn nng.

4.nh hng ca nguyn thp kim n qu trnhnhit luyn

Cc nguyn t hp kim c nh hng ln n qu trnh nhit luyn, c bit l ti + ram, do vys nh hng ln n c tnh, y l c tnh ni bt ca thp hp kim. Hy xt ti tng mt vtng qu trnh ca nhit luyn.Chuyn bin khi nung nng tiTr mt s thp c bit, cc thp hp kim thng thng cn li vn c t chc peclit, nn khi

nung nng ti vn c cc chuyn pha: peclit austenit, cacbit ha tan vo austenit, htaustenit pht trin (nh thp cacbon vi pha cacbit l xmentit) song c cc im c trng sau: - S ha tan cacbit hp kim kh hn, i hi nhit ti cao hn v thi gian gi nhit di hnso vi xmentit trong thp cacbon. Hy so snh cc thp cng c 1,00%C nhng vi lng hpkim cao thp khc nhau:+ Thp cacbon 1,00%C (mc CD100), Fe3C, nhit ti khong 780oC.+ Tthp hp kim thp 1,00%C + 1,50%Cr (thp ln), (Fe,Cr)3C, nhit ti khong 830oC. + Thp hp kim cao 1,00%C + 12,0%Cr (thp khun dp), Cr23C6, nhit ti > 1000oC. - Cacbit hp kim do kh ha tan vo austenit, nm bin gii ht, nh hang ro gi cho ht nh.Tc dng ny rt mnh vi Ti, Zr, Nb, mnh vi V, tng i mnh vi W, Mo. Ring thp cMn li c khuynh hng lm to ht austenit. Cc nguyn t hp kim cn li Cr, Ni, Si, Al ccoi l trung tnh. Chnh v vy thp hp kim thng gi c ht nh hn thp cacbon khi c haicng b nung nng cng nhit (v d khi thm cacbon). S phn ha ng nhit ca austenit qu ngui v thm tiy l tc dng quan trng nht v inhnh nht, cn nm vng v tn dng trit .S phn ha ng nhit ca austenit qu ngui. Khi ha tan vo austenit, tt c cc nguyn thp kim (tr Co) vi cc mc khc nhau u lm chm tc phn ha ng nhit caaustenit qu ngui tc l lmng cong ch "C" dch sang phi do lm gim tc ti tihn Vt.h (hnh 5.4a). Trong ng : cc nguyn t c tc dng rt mnh l Mo (khi ringr) v Cr -Ni (khi kt hp), mnh l Cr, Mn, B. Vi cng tng lng hp kim, khi hp kim haphc tp lm gim Vth mnh hn khi hp kim ha n gin.Cn ch l khi nguyn t hp kim khng ha tan vo austenit m dng cacbit khng nhngkhng lm tng m cn lm gim tnh n nh ca austenit qu ngui, dn ti tng Vth. thm ti. Do lm gim Vt.h, cc nguyn t hp kim (tr Co) khi ha tan vo austenit u lmtng thm ti (hnh 5.4b). Nh thy r t hnh v, do ng cong ch "C" trong thp hp kimdch sang phi nn c Vt.h2 < Vt.h1 ca thp cacbon, tng ng 2 l thm ti ca thp hpkim, 1- thm ti ca thp cacbon, ta lun c 2> 1.Nh hiu qu ny trong thp hp kim c th xy ra cc trng hp sau m ta khng th gptrong thp cacbon:


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- Vth b n mc nh hn c Vngui ca li, do sau khi ti li cng c t chc mactenxit,y l trng hp ti thu.

Hnh 5.4. So snh gin T - T - T, Vth (a) v thm ti (b) gia thp cacbon v thp hp kim.

- Vngui trong khng kh cng c th ln hn Vt.h, do thng ha cng t c t chcmactenxit, l hin tng t ti (trong khi thng ha thp cacbon ch t c xoocbit lcng).

Do thm ti tng ln s c hai hiu qu chnh sau y:1) Hiu qu ha bn ca ti + ram tng ln r rt, c bit khi ti thu s t ti c tnh cao vng nht trn ton tit din, nng cao mnh sc chu ti ca chi tit. V th:- pht huy ht kh nng chu ti ca chi tit bng thp hp kim, phi s dng n trng thiti + ram, c nh vy mi t hiu qu kinh t (v thp hp kim t hn).- Vi tit din cng ln cng phi dng thp hp kim v dng n cng hiu qu. Do vy phi cnc vo tit din v c tnh yu cu m chn mc thp: tit din cng ln, bn i hi cngcao, lng hp kim trong thp cng phi cao c th ti thu.2) Khi ti c th dng cc mi trng ngui chm m vn t c mactenxit nh ti trong du,trong mui nng chy (phn cp hay ng nhit), iu ny dn n cc u vit sau:
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- Chi tit, dng c vi hnh dng phc tp khi ti khng s gy, nt. Trong khi nu lm bngthp cacbon phi ti trong nc d sinh v.- t bin dng, trong nhiu trng hp c cong vnh di mc cho php, c bit khi ti phncp hay ng nhit.Chuyn bin mactenxit

Khi ha tan vo austenit, cc nguyn t hp kim (tr Co, Al, Si) u h thp nhit chuynbin austenit thnh mactenxit, do lm tng lng austenit d sau khi ti.C 1% nguyn t hp kim lm gim Ms nh sau: Mn - 45oC, Cr - 35oC, Ni - 26oC, Mo - 25oC,cn Co lm tng 12oC, Al lm tng 18oC, Si khng nh hng g.Do austenit d tng mnh cc thp c cacbon cao - hp kim cao, cng sau khi ti c th bst 1 - 10 n v HRC so vi mc cao nht c th t c. Tuy y l nhc im song honton c th khc phc c bng gia cng lnh hay ram nhiu ln nhit thch hp austenit d mactenxit, cng li t c mc cao nht.

5.Chuyn bin khi ramNi chung cc nguyn t hp kim ha tan trong mactenxit u cn tr s phn ha ca pha nykhi ram hay ni c th hn l lm tng cc nhit chuyn bin khi ram. S d nh vy l v ccnguyn t hp kim cn tr s khuch tn ca cacbon. c bit W, Mo, Cr c i lc kh mnh vicacbon c xu hng gi cacbon li trong mactenxit, do duy tr cng cao nhit caohn. V d, s tit ra cacbit hp kim ra khi mactenxit cc nhit sau:

- Xmentit Fe3C 200oC.- Xmentit hp kim (Fe,Me)3C 250 - 300oC.- Cacbit crm Cr7C3, Cr23C6 400 - 450oC.- Cacbit Fe3W3C loi Me6C 550 - 600oC.(VC, TiC, ZrC, NbC khng ha tan khi nung nng nn khng tit ra). Nh vy dn n cc hiu ng sau.-Nng cao tnh chu nhit cao, tnh bn nng, tnh cng nng. - Do khuch tn kh khn cacbit to thnh rt phn tn v nh mn, lm tng cng v tnhchng mi mn, c gi l ha cng phn tn. S tng cng khi ram thp hp kim nhit thch hp lm cho austenit d mactenxit v cacbit tit ra dng phn tn, nh mn c

gi l cng th hai.- Cng ram hay cng lm vic mt nhit , thp hp kim bao gi cng c cng, bn caohn. iu ny cng c ngha cng t cng bn nh nhau, phi ram thp hp kim nhit cao hn nn kh b c ng sut bn trong nhiu hn v th thp c th bo m dai tt.Tm tt cc tc dng tt ca nguyn t hp kim l:+ Khi ha tan vo dung dch rn:


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Ferit lm tng x lch mng gy ha bn (cacbon cng c tc dng ny song ch trng thiti, sau khi ram b gim rt mnh),

Austenit lm tng tnh n nh ca austenit qu ngui, gim Vt.h, tng thm ti, thp ti tbin dng v gy v hn nh dng du v cc mi trng ngui chm hn.

+ Khi to thnh cacbit hp kim: Bn thn pha ny cng v chng mi mn hn xmentit, kh ha tan khi nung gi cho ht nh. Kh tit ra khi mactenxit hn nn gy nn bn nng v cng nng. Khi ram c tit ra di dng phn t nh mn, phn tn gy ha bn.

6.Cc khuyt tt ca thp hp kimTuy c nhiu u vit, thp hp kim i khi cng th hin mt s khuyt tt cn bit phngtrnh.Thin tchThp hp kim, c bit l loi c hp kim ha cao vi nhiu thnh phn ha hc phc tp, saukhi kt tinh s c t chc khng ng nht, khi cn s to nn t chc th lm c tnh chnh lchmnh gia cc phng dc v ngang (c khi chnh lch ti 50 - 70% hay hn na). Khc phcbng khuch tn ri em cn nng, song nhiu khi cc bn thnh phm c tit din ln vncn thy dng khuyt tt ny. R rng tit din ca sn phm cn cng nh dng khuyt tt nycng t th hin. Tuy cc nh my luyn kim phi chu trch nhim v loi khuyt tt ny songnu b lt li, cc nh my c kh phi tin hnh bin dng nng li vi mc ln.m trng

l dng khuyt tt: trn mt ca mt s thp hp kim c cc vt nt nh dng m trng.Nguyn nhn l hyr ha tan vo thp lng ri nm li trong thp rn. trng thi rn do gimt ngt ha tan di 200oC, hyr thot ra mnh, gy ra nt. m trng l ph phmkhng cha c, n ch th hin trong thp c thm ti cao nh Cr - Ni, Cr - Ni - Mo, Cr -Ni - W khi cn nng (khi c khng xut hin m trng do cc r co phn tn l ti chahyr). nh my luyn kim ngi ta ngn nga khuyt tt ny bng cch gim hi nc trongkh quyn, sy kh m luyn (c m liu - st thp vn ln tr dung - vi) v lm ngui thtchm sau khi cn hyr kp thot ra.Hai dng khuyt tt trn phi c kh b ngay nh my luyn kim, rt t gp nh my ckh, ni ch gia cng tip tc cc bn thnh phm cn thnh sn phm c kh vi hnh dng, kchthc, c tnh theo quy nh.

Gin rami vi thp cacbon, khi tng nhit ram dai tng ln lin tc cho n 650oC (vt qu sto ra peclit - hn hp ferit - xmentit th, dai gim i), cn i vi thp hp kim thy c haicc tiu v dai hai khong nhit ram (hnh 5.5) m ta gi l gin ram, ng vi hai cctiu l hai loi gin ram. Nguyn nhn ca chng cha xc nh c r rng. Gin ram loi I(khng thun nghch, khng cha c). Loi gin ram ny th hin rt r trong thp hp kim khi ram khong 280 - 350oC (mi mc c mt khong hp hn trong phmvi ny), khi thy dai rt thp, i vi mt s loi thp n cn thp hn c trng thi mi


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ti. Cc thp cacbon cng b gin ram loi ny v xy ra nhit thp hn. Nguyn nhn cth l do trong khong nhit ny cacbit c tit ra khi mactenxit c dng tm haydM, lm thp tr nn gin.

y l loi gin khng th trnh c, tt hn c l trnh ram khong nhit gy ra gin ramny cho mi mc (khong hp hn, ch 10 - 20oC so vi 70oC k trn).

Hnh 5.5. nh hng ca nhit n dai va p ca thp hp kim (c i chng vi thpcacbon).

Gin ram loi II (thun nghch hay c th cha c). Loi ny ch xy ra trong thp c hpkim ha bng Cr, Mn, Cr - Ni, Cr - Mn khi ram khong 500 - 600oC vi cch lm ngui thngthng sau (trong khng kh). Cng ram ti nhit song li lm ngui nhanh sau (trong du hay nc ch hn) th cng khng c cc tiu th hai ny (ng chm chm trnhnh v). Nguyn nhn c th l ngui chm sau khi ram cao thc y tit ra cc pha gin bingii ht. Gin ram loi II l thun nghch tc l c th b li nu em ram ln na cng vi ch nhit nh trn (500 - 600oC, ngui chm).y l loi gin ram c th trnh c. Bin php phng trnh nh sau: - Vi cc chi tit nh v trung bnh: lm ngui nhanh trong du, trong nc sau khi ram cao. - Vi cc chi tit ln lm ngui nh vy vn khng nhanh lm mt gin ram, lc ny phidng thp c hp kim ha thm bng 0,20 - 0,50%Mo hay 0,50 - 1,00%W.

7.Phn loi thp hp kim

i vi thp hp kim c nhiu cch phn loi hn v mi loi cng cho bit mt c trng cnbit s dng tt hn.Theo t chc cn bngTheo t chc cn bng ( trng thi ), vi lng cacbon tng dn c th ln lt c cc thpvi t chc sau:- Thp trc cng tch: peclit + ferit t do.
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- Thp cng tch: peclit.

- Thp sau cng tch: peclit + cacbit t do.- Thp lburit (cacbit): c lburit.Ring trng hp thp c hp kim ha cao ch yu bng mt trong hai nguyn t Cr, Mn hayCr -Ni, s c:

- Thp ferit: loi c Cr rt cao (> 17%) v thng rt t cacbon.- Thp austenit: loi c Mn cao (> 13%) v thng c cacbon cao, v loi c Cr (> 18%) + Ni(>8%).

Theo t chc thng haTheo t chc thng ha cc mu nh 25, theo lng nguyn t hp kim tng ln s c ccthp sau y (hnh 5.6):- Thp h peclit: loi hp kim thp, ng cong ch "C" st trc tung, ngui trong khng khc hn hp ferit-xmentit tc peclit, xoocbit, trxtit; phn ln thp thuc loi ny.

Hnh 5.6. T chc sau khi thng ha ca cc thp vi lng hp kim tng dn: a. peclit, b.mactenxit, c. austenit.

- Thp h mactenxit: loi hp kim ha trung bnh (> 4 - 6%) v cao, ng cong ch "C" dchsang phi kh mnh, ngui trong khng kh cng c mactenxit.- Thp h austenit: loi c cha Cr cao v Ni cao (> 8%) hoc Mn (> 13%) cao, chng m rngkhu vc v h thp im Ms (< 0oC) nn lm ngui trong khng kh (ch n nhit thng,cao hn Ms) cng khng c chuyn bin g, gi nguyn t chc austenit .Cch phn loi ny cho bit t chc ca thp trng thi cung cp (sau cn nng lm nguitrong khng kh).

Theo nguyn t hp kimDa vo tn nguyn t hp kim chnh a vo gi, nh:- Thp ch c mt nguyn t hp kim chnh nh Cr, Mn c ln lt gi l thp crm, thpmangan, chng l cc thp hp kim (ha) n gin. - Thp c hai hay nhiu nguyn t hp kim nh Cr - Ni, Cr - Ni - Mo c ln lt gi l thpcrm - niken, thp crm - niken - mlipen, chng l cc thp hp kim (ha) phc tp. Theo tng lng nguyn t hp kim
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Theo tng (hm) lng ca cc nguyn t hp kim c trong thp t thp n cao, ngi ta chiara:

- Thp hp kim thp: loi c tng lng < 2,5% (thng l thp peclit).- Thp hp kim trung bnh: loi c tng lng t 2,5 n 10% (thng l thp h t peclit nmactenxit).

- Thp hp kim cao: loi c tng lng >10% (thng l h mactenxit hay austenit) y dng theo cch phn loi trn quen thuc nc ta, theo OCT. Tuy nhin cc nctrn th gii quan nim hp kimha cao thp khng ging nhau. Trung Quc cng c ba loinh trn song ranh gii gia thp v trung bnh l 5% ch khng phi l 2,5%. Cc nc Ty uch phn bit hai loi thp v cao, trong hp kim thp l loi khng cha nguyn t hp kimno nhiu hn 5%, cn hp kim cao l loi c t nht mt nguyn t nhiu hn 5%.Theo cng dngTheo cng dng ngi ta chia thp hp kim ra lm ba nhm:- Thp hp kim kt cu.

- Thp hp kim dng c v- Thp hp kim c bit.Trong hai nhm u cng c trongloi thp cacbon, cn nhm th ba th khng c. y lnhm vi tnh cht vt l - ha hc c bit, thng cha tng lng hp kim cao v rt cao(>20%).

Cc cch phn loi trn thng c quan h vi nhau v cho bit mt s c trng ca thp. Thpaustenit, ferit bao gi cng l loi thp c bit, hp kim cao hoc rt cao, t v kh gia cngct. Thp mactenxit l loi thp rt d ti song rt kh gia cng ct phi trng thi cung cp.Thp lburit bao gi cng thuc nhm hp kim cao - cacbon cao, rt cng lm dng c.Thp Cr -Ni bao gi cng l thp kt cu qu v c thm ti cao v dai tt...

8.Tiu chu n thp hp kimTiu chun Vit NamTCVN 1759 - 75 quy nh nguyn tc k hiu thp hp kim theo trt t nh sau: - S ch hm lngcacbon trung bnh theo phn vn, nu 1% c th khng cn biu th.

- Cc nguyn t hp kim theo k hiu ha hc v ngay sau l hm lng theo phn trm trungbnh (thng c quy trn thnh s nguyn), khi lng cha ca nguyn t khong 1% thkhng cn biu th (bng s).V d:- Thp c 0,36 - 0,44%C, 0,80 - 1,00%Cr s c k hiu l 40Cr.- Thp c 0,09 - 0,16%C, 0,60 - 0,90%Cr, 2,75 - 3,75%Ni s c k hiu l 12CrNi3.


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- Thp c 1,25 - 1,50 %C, 0,40 - 0,70 %Cr, 4,5 - 5,5 %W s c k hiu l 140CrW5 hay ngin ch l CrW5.

- Thp c 0,85 - 0,95%C, 1,20 - 1,60 %Si. 0,95 - 1,25 %Cr s c k hiu l 90CrSi.Nh vy trn nguyn tc rt d hiu ny c th k hiu mi thp theo thnh phn ca chng m

khng c nhng trng lp quan trng. Nguyn tc ny c s dng k hiu cc thp khi cnthit phi rt gn cch biu th thnh phn ha hc.TCVN cha ph ht cc thp hp kim thng dng.Tiu chun NgaOCT k hiu thp hp kim theo trt t sau y:- S ch hm lng cacbon trung bnh theo phn vn (nu l thp kt cu) v phn nghn (nu lthp dng c, loi c cacbon cao), khi 1,00% khng biu th. - Cc nguyn t hp kim theo ch ci Nga (thng l ch u theo tn gi, nu trng phi lych khc) nh sau:Theo ch ci u tin c: X cho crm, H cho niken, B cho vonfram, M cho mlipen, T chotitan, K cho cban;

Theo ch ci tip sau c: cho mangan, C cho silic, cho vanai, cho ng, cho nhm, Pcho bo,

- Thnh phn ca tng nguyn t c biu th theo phn trm t ngay sau mi ch ci tngng, khi lng cha < 1,5% khng biu th.- Cc thp chuyn dng nh thp gi, ln, k thut in... c quy c ring. Theo bn k hiu thp trn ca TCVN s tng ng vi OCT nh sau: 40Cr l 40X,12CrNi3 l 12XH3, 140CrW5 hay CrW5 l XB5, nhng 90CrSi l 9XC. Qua thy c nhngsai khc nh, song cch k hiu thp ca TCVN v c bn l ca OCT, rt d vit chuyn i

cho nhau.Tiu chun Hoa Ki vi thp hp kim kt cu, Hoa K thng s dng AISI v SAE, chng c cch biu thging nhau bng bn s xxxx nn c vit l AISI/SAE xxxx, trong hai s cui biu thlng cacbon theo phn vn trung bnh. Sau y l mt s quy c:thp cacbon 10xx,

thp cacbon c mangan nng cao 15xx,

thp d ct (2 loi) 11xx, 12xx,thp mangan 13xx,

thp niken (2 loi) 23xx, 25xx,

thp niken-crm (4 loi) 31xx, 32xx, 33xx, 34xx,thp mlipen (2 loi) 40xx, 44xx,thp crm-mlipen 41xx,thp niken-crm-mlipen (11 loi)43xx, 43BVxx, 47xx, 81xx, 86xx,87xx, 88xx, 93xx, 94xx, 97xx, 98xx,

thp niken-mlipen (2 loi) 46xx, 48xx,thp crm (2 loi) 50xx, 51xx,


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thp crm vi 0,50 1,50%C 501xx, 511xx, 521xx, thp crm-vanai 61xx,

thp vonfram-crm 72xx,

thp silic-mangan 92xx,

thp bo xxBxx,i vi thp dng c, Hoa K thng s dng AISIvi k hiu gm mt ch ci ch nhm thpv s th t. Sau y cc ch ci (thng ly theo ch ci u tin ch nhm thp) : W cho thp ti nc (water),O cho thp ti du (oil),S cho thp dng c chu va p (shock), T cho thp gi vonfram (tungsten),

M cho thp gi mlipen - vonfram,H cho thp lm dng c bin dng nng (hot),D cho thp lm dng c bin dng ngui (cold),

A cho thp lm dng c bin dng ngui, t ti, trong khng kh (air), i vi thp khng g v bn nng, Hoa K dng AISI vi k hiu l nhm ba s xxx, trong :2xx v 3xx l thp austenit,

4xx l thp ferit,

4xx v 5xx l thp mactenxit.

Tiu chun Nht BnJIS cng k hiu thp hp kim bt u bng ch S song tip theo c nhng ch ci biu th loithp hp kim v cui cng l ba s xxx (trong hai s cui ch phn vn cacbon trung bnh)hay mt hoc hai s theo th t:

SCrxxx - thp kt cu crm, SNCxxx - thp kt cu niken - crm,SMnxxx - thp mangan, SCMxxx - thp kt cu crm - mlipen,SACMxxx - thp nhm - crm - mlipen,SNCMxxx - thp kt cu niken - crm - mlipen,SUJx - thp ln, SUMx - thp d ct,SUPx - thp n hi, SUSxxx - thp khng g (xxx ly theo AISI),SUHx - thp bn nng, SKx - thp dng c cacbon,SKHx - thp gi, SKSx, SKDx, SKTx - thp dngc hp kim.


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1.Thnh phn ha hcNh ni thp l hp kim st - cacbon vi lng cacbon nh hn 2,14% vi c tnh l c tnhdo nn c th cn nng c (do khi nung nng ln nhit cao c t chc hon ton austenit -dung dch rn vi mng A1, rt do). Song trong thc t thp khng ch l hp kim st vicacbon m cn vi nhiu nguyn t khc. Do yu cu thng thng ca cng ngh luyn kim,nhiu nguyn t i vo thnh phn ca thp m khng cn phi kh b i do c li hockhng cn phi kh b trit mc du c hi do qu tn km khng cn thit. Thp cacbon l thp thng thng (thp thng), ngoi cacbon ra cn cha mt s nguyn t vihm lng gii hn m trong thp no cng c, chng c gi l tp cht thng c hay chtln v khng phi do c a vo. Trong s cc tp cht c mt s c li v mt s c hi. Hyxem xt cc nguyn t .

Tp cht c li: mangan v silicBt k thp no d n gin n u cng c mangan v silic vi lng khng vt qu 1%,chng i vo thnh phn ca thp l do:- Qung st c ln cc hp cht (khong vt) khc nh xyt mangan, xyt silic, trong qu trnhluyn gang chng b hon nguyn (MnO Mn, SiO2 Si) i vo gang ri vo thp. - Khi luyn thp phi dng fer mangan v fer silic kh xy, phn khng tc dng ht vixy s i vo thnh phn ca thp {fer l loi hp kim trung gian, d luyn v c nhit chytng i thp, l nguyn liu pha ch, s dng trong qu trnh luyn kim; n cha st,cacbon (> 1%) v lng ln nguyn t hp kim tng ng. V d fer mangan 80 l loi c

khong 80%Mn}.Trong cc iu kin thng thng ca qu trnh luyn, cc thp u c cha 0,80%Mn,0,40%Si. Chng l cc nguyn t c ch, c tc dng tt n c tnh: nng cao cng, bn(cng lm gim do, dai), song vi lng t nh vy khng c nh hng ng k n ctnh ca thp cacbon.Tp cht c hi: phtpho v lu hunhHai nguyn t ny i vo thnh phn ca gang v thp qua con ng qung st v nhin liu(than coke khi luyn gang). Chng lm thp gin do phi c kh b n gii hn cho php,song thng thng cao nht cng khng c vt qu 0,05% cho mi nguyn t. Vy thp no ngoi st ra cng u c cha:

C 2,14%, Mn 0,80%, Si 0,40%, P 0,050%, S 0,050%. cng l thnh phn ha hc c bn ca thp cacbon hay thp thng. Cc tp cht khcNgoi phtpho v lu hunh, trong thp cng lun cha cc nguyn t hyr, xy, nitdo chngha tan vo thp lng t kh quyn ca l luyn. Chng c bit c hi v lm thp khng ngnht v t chc (gy tp trung ng sut) v gin (ring nit c tnh hai mt s trnh by sau) songvi lng cha qu nh (v d: 0,006 - 0,008% i vi xy) nn rt kh phn tch, do vy thng


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"du mt" trong bngthnh phn nn c gi l tp cht n nu.c trng ca cng nghip luyn kim hin i l s dng li (ti ch) ngy cng nhiu vi t lcao thp, gang v hp kim ph liu m trong c mt phn l loi cha cc nguyn t c li(nguyn t hp kim). Do vy ngay trong thp cacbon luyn ra cng c th cha hm lng thpcc nguyn t sau:- Crm, niken, ng 0,30% cho mi nguyn t song tng lng ca chng khng c vtqu 0,50%.

- Vonfram, mlipen, titan 0,05% cho mi nguyn t.ng ch xu th ny ngy mt mnh nn hm lng cho php ca cc nguyn t trn trongthp thng cng tng ln.Song d nh vy ngi ta vn ch coi chng l tp cht (cht ln vo) v: - Khng c a vo.- Vi lng t nh vy, chng khng c nh hng ng k n t chc v c tnh ca hp kimFe - C, v c bn thp to thnh c t chc ph hp vi gin pha Fe - C.

2.nh hng ca cacbon n tchc, tnh cht v cngdng ca thp thng

Tuy l nguyn t ha hc rt bnh thng song c th ni cacbon l nguyn t quan trng nht,quyt nh ch yu n t chc, tnh cht (c tnh), cng dng ca thp (c thp cacbon ln thphp kim thp).T chc t viNh thy r t gin pha Fe-C, khi hm lng cacbon tng ln t l xmentit l pha gin trongt chc cng tng ln tng ng (c thm 0,10%C s tng thm 1,50% xmentit) do lm thayi t chc t vi trng thi cn bng ().- C 0,05% - thp c t chc thun ferit (hnh 3.19a), coi nh st nguyn cht. - C = 0,10 - 0,70% - thp c t chc ferit + peclit,khi %C tng ln lng peclit tng ln (cchnh 3.22a,b,c), l cc thp trc cng tch.- C = 0,80% - thp c t chc peclit (hnh 3.20a,b), l thp cng tch. - C 0,90% - thp c t chc peclit + xmentit II (hnh 3.23), khi %C tng ln lng xmentit IItng ln tng ng, l cc thp sau cng tch.Chnh do s thay i t chc nh vy c tnh ca thp cng bin i theo.


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Hnh 5.1. nh hng ca cacbon n c tnh ca thp thng ( trng thi ).

C tnhnh hng ca cacbon n c tnh ca thp thng trng thi c trnh by trn hnh 5.1. Cacbon c nh hng bc nht (theo quan h ng thng) n cng HB. V mt nh lngthy rng c tng 0,10%C cng HB s tng thm khong 25 n v. Thot tin cacbon lm gim rt mnh do (, ) v dai va p (aK) lm cho cc ch tiuny gim i nhanh chng, song cng v sau mc gim ny cng nh i. V d: c tng 0,10%Ctrong phm vi cacbon thp ( 0,25%) gim 6%, aKgim 300kJ/m2, cn trong phm vi cacbontrung bnh (0,30 - 0,50%) tng ng l 3% v 200kJ/m2...Nh vy hm lng cacbon cng caothp cng cng, cng km do dai v cng gin. C th d dng gii thch iu ny l do lngpha xmentit cng v gin tng ln.

nh hng ca cacbon n gii hn bn bkhng n gin nh i vi cng. Thy rng ctng 0,10%C trong khong 0,10 - 0,50%C btng khong 70 - 90MPa, trong khong 0,60 -0,80%C btng rt chm v t n gi tr cc i trong khong 0,80 - 1,00%C, khi vt qugi tr ny bli gim i. C th gii thchnh sau: thot tin tng s phn t xmentit trong nnferit s lm tng s cht cn trt cho pha ny do vy btng ln cho n khi c t chc honton l peclit, khi vt qu 0,80 - 1,00%C ngoi peclit (tm) ra bt u xut hin li xmentit II(hnh 3.23) gin li dng lin tc (li) lm cho thp khng nhng gin m cn lm gim giihn bn.Vai tr ca cacbon. Cng dng ca thp theo thnh phn cacbon Chnh do cacbon c nh hng ln n c tnh nh vy nn n quyt nh phn ln cng dngca thp. Mun dng thp vo vic g iu cn xem xt trc tin l hm lng cacbon sau mi ti cc nguyn t hp kim. iu kh k diu l ch cn thay i cht t hm lng cacbon(chnh lch nhau khng qu 0,50%) c th to ra cc nhm thp c c tnh i lp nhau mkhng nguyn t no c c. Theo hm lng cacbon c th chia thp thnh ba -bn nhm vic tnh v cng dng rt khc nhau nh sau. - Thp c cacbon thp (0,25%) c do, dai cao nhng bn, cng li thp, hiu qu
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nhit luyn ti + ram khng cao, c dng lm kt cu xy dng, tm l dp ngui. Munnng cao hiu qu ca nhit luyn ti + ram nng cao bn cng phi qua thm cacbon. - Thp c cacbon trung bnh (0,30 - 0,50%) c bn, cng, do, dai u kh cao mcdu khng phi l cao nht, c hiu qu ti + ram tt, tm li c c tnh tng hp cao nn cdng ch yu lm cc chi tit my chu ti trng tnh v va p cao. - Thp c cacbon tng i cao (0,55 - 0,65%) vi u im l c cng tng icao, giihn n hi cao nht, c dng lm cc chi tit n hi.- Thp c cacbon cao (0,70%) vi u im l c cng v tnh chng mi mn u cao, cdng lm cng c nh dao ct, khun dp, dng c o. Trong mt s kiu phn loi, nhm thp ccacbon trung bnh c lng cacbon thay i t 0,30n 0,65%. Tht ra cc gii hn v thnh phn cacbon k trn nh ranh gii gia cc nhmcng khng hon ton cng nhc, c th x dch i cht. Tnh cng nghTnh hn v kh nng dp ngui, dp su ca thp ph thuc nhiu vo hm lng cacbon. Thp

cng t cacbon cng d hn chy v dp. Hm lng cacbon cng c nh hng n tnh gia cng ct ca thp. Ni chung thp cng cngcng kh ct nn thp c hm lng cacbon c tnh gia cng ct km. Song thp qu mm v docng gy kh khn cho ct gt, nn thp c cacbon thp cng c tnh gia cng ct km. Ni chung tnh c ca thp khng cao.

3.nh hng ca cc tp cht thng cManganMangan c cho vo mi thp di dng fer mangan kh xy thp trng thi lng tc l loi tr FeO rt c hi:

Mn + FeO Fe + MnO(MnO ni ln i vo x v b co ra khi l)

Ngoi ra mangan cng loi tr c tc hi ca lu hunh.Mangan c nh hng tt n c tnh, khi ha tan vo ferit n nng cao bn v cng capha ny (hnh 5.2a), do vy lm tng c tnh ca thp, song lng mangan cao nht trong thpcacbon cng ch nm trong gii hn 0,50 - 0,80% nn nh hng ny khng quan trng. Mn cnc tc dng lm gim nh tc hi ca lu hunh.SilicSilic c cho vo nhiu loi thp di dng fer silic kh xy trit thp trng thi lng:

Si + FeO Fe + SiO2(SiO2 ni ln i vo x v b co ra khi l)

Ging nh mangan, silic ha tan vo ferit cng nng cao bn v cng ca pha ny (hnh 5.2a) nn lm tng c tnh ca thp, song lng silic cao nht trong thp cacbon cng ch tronggii hn 0,20 - 0,40% nn tc dng ny cng khng r rt.


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Phtpho

L nguyn t c kh nng ha tan vo ferit (ti 1,20% hp kim thun Fe - C, cn trong thpgii hn ha tan ny gim i mnh) v lm x lch rt mnh mng tinh th pha ny lm tngmnh tnh gin; khi lng phtpho vt qu gii hn ha tan n s to nn Fe3P cng v gin.Do phtpho l nguyn t gy gin ngui hay b ngui ( nhit thng). Ch cn c

0,10%P ha tan, ferit tr nn gin. Song phtpho l nguyn t thin tch (phn b khng u)rt mnh nn trnh gin lng phtpho trong thp phi t hn 0,050% ( ni tp trung caonht lng phpho cng khng th vt qu 0,10% l gii hn gy ra gin). Lu hunhKhc vi phtpho, lu hunh hon ton khng ha tan trong Fe (c Fe ln Fe) m to nn hpcht FeS. Cng tinh (Fe + FeS) to thnh nhit thp (988oC), kt tinh sau cng do nm bin gii ht; khi nung thp ln cn, ko (thng 1100 - 1200oC) bin gii b chy ra lmthp d b t, gy nh l thp rt gin. Ngi ta gi hin tng ny l gin nng hay b nng. Khi a mangan vo, do c i lc vi lu hunh mnh hn st nn thay v FeS s to nn MnS.

Pha ny kt tinh nhit cao, 1620oC, di dng cc ht nh ri rc v nhit cao c tnhdo nht nh nn khng b chy hoc t, gy. Sunfua mangan cng c li cho gia cng ct.

4.Phn loi thp cacbonC nhiu cch phn loi thp cacbon m mi cch cho bit mt c trng ring bit cn s dng thp c tt hn.Theo sch tp cht c hi v phng php luyn R rng l thp cng t tp cht c hi (P, S) v cc kh (H, O, N) c do, dai cng cao tcc c tnh tng hp cao, cht lng cngcao. Cc phng php luyn thp khc nhau c khnng loi tr tp cht c hi khc nhau ny cc mc cao thp khc nhau do to cho thp

cht lng tt, xu khc nhau. C nhiu phng php luyn thp song cho n hin nay trn thgii ch cn tn tiba phng php chnh l l mactanh, l in h quang v l thi xy t nh(l L-D) (nc ta ch bng l in h quang), ngoi ra cn cc phng php lm sch tp chtngoi l.

Theo mc sch tp cht t thp n cao c cc mc cht lng sau. - Cht lng thng, lng P, S ch c kh n mc 0,050% (hay cao hn mt cht) cho minguyn t. Phng php luyn thp L-D thng ch t c cp cht lng ny mc du n chonng sut rt cao v gi thnh thp r. Cp cht lng ny thng ch p dng cho nhm thp cyu cu khng cao nh mt s thp xy dng thng dng. - Cht lng tt, lng P, S c kh n mc 0,040% cho mi nguyn t. Phng php luynthp bng l mactanh v l in h quang d dng t c cp cht lng ny. Cp cht lng

ny thng p dng cho cc nhm thp dng trong ch to my thng dng, tc c yu cu caohn.- Cht lng cao, lng P, S c kh kh cn thn, n mc 0,030% cho mi nguyn t. Vicc bin php k thut b sung (dng cht kh mnh, tuyn chn nguyn liu vo...) vn c tht c cp cht lng ny bng phng php luyn thp trong l in h quang. - Cht lng rt cao, lng P, S c kh mc trit nht: 0,020% cho mi nguyn t. Chvi cc l in h quang khng th t c gii hn ny. Thp sau khi luyn l ny c tinhluyn tip tc: kh tp cht ngoi l bng x tng hp, bng in x. Ngoi ra gim ti a


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lng kh cha trong thp ngi ta phi p dng c rt thp trong chn khng. Cc thp cacbon c th c cung cp ba cp cht lng: thng, tt v cao (t gp). Cc thphp kim khng c cp cht lng thng, ch c cc cp: tt, cao v rt cao. Thp xy dngthng ch yu cu cht lng thng, trong khi thp ch to my phi c cht lng t tttr ln. Ring thp lm ln phi t cp cht lng rt cao.

Theo phng php kh xyTheo mc kh xy c trit hay khng ngi ta chia ra hai loi thp si v thp lng. Thp si l loi khng c kh xy trit , tc ch bng cht kh khng mnh l fer mangan,nn trong thp lng vn cn FeO v do c phn ng:

FeO + C Fe + CO

Kh CO bay ln lm mt thp lng chuyn ng nh th b "si" vy (nn c tn l thp si) vto ra bt (r) kh trong thi c. Khi cn nng tip theo phn ln bt kh c hn kn li (ch l v bc kh nm trong thi c, khng tip xc vi khng kh nu khng lu kho qu lu scha b xy ha nn cc nguyn t st d khuch tn, hn kn li khi cn nng) nn ni chung

khng nh hng xu n c tnh ca thp qua bin dng nng. Cc c im ca thp si l: - Do khng c kh bng fer silic nn cha rt t silic, thng l 0,05 - 0,07%, nn ferit cathp rt mm v do, rt d dp ngui.- Khng cho php dng thp si ch to cc vt c nh hnh v cc r kh lm gim mt ,tp trung ng sut gy nh hng rt xu n c tnh.- Khng cho php dng thp si lm cc kt cu hn chy, do trong thp vn cn xy (FeO)nn khi chy lng phn ng to CO li xy ra, mi hn cha nhiu bt kh. - Khng cho php dng thp si lm chi tit thm cacbon do khng c kh xy trit nnthuc loi thp ht bn cht ln.Thp lng l loi c kh xy trit bng c fer mangan ln fer silic l cht kh mnh v

nhm, nn trong thp lng khng xy ra phn ng trn, mt thp lng lun "phng lng" (nn ctn l thp lng). Cc c im ca thp lng l:- Do c kh bng fer silic nn cha mt lng nht nh silic, thng trong khong 0,15 -0,35%, v th ferit ca thp cng v bn hn, kh dp ngui hn. - Trong t chc khng c r kh nn c cu trc xt cht hn, c c tnh cao hn thp si, cc vtc bng thp phi c ch to bng thp lng, tuy nhin lm co trong thp lng kh ln (phnny phi ct b i lm gim hiu qu kinh t).- Trong cc kt cu hn chy chc php dng thp lng.- Cc chi tit thm cacbon ch c lm bng thp lng.

Do cc c tnh tri hn thp si, thp lng c s dng rng ri hn. Nm trung gian gia hai thp trn l thp na lng, n ch c kh xy bng fer mangan vnhm. Tnh cht ca n nm trung gian gia thp si v thp lng. Tuy xut hin sau song thpna lng c khuynh hng thay th cho thp si.Thp hp kim ch c loi thp lng, song thp cacbon c th c ba loi: si, lng v na lng. Theo cng dngTheo mc ch s dng hay theo cng dng c th chia thp cacbon thnh hai nhm thp kt cu


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v thp dng c.- Thp kt cu l loi c dng lm cc kt cu, chi tit chu ti (lc) do ngoi yu cu v bn bo m cn cn phi c do, dai yu cu tcl c tnh tng hp. y l nhmthp c s dng thng xuyn nht vi khi lng ln nht. Trong nhm ny cn c th phntip thnh hai nhm nh hn l xy dng v ch to my:- Thp xy dng l loi ch yu c dng trong xy dng lm cc kt cu thp di dngcc thanh di, tm rng ghp li, chng i hi c tnh tng hp song khng cao. Thp xy dngtuy c cn bn song phi c do cao d un khi lp ghp v dai cao kh b ph hygin, c tnh hn tt.- Thp ch to my i hi c tnh tng hp mc cao hn nn ni chung i hi cht lngcao hn, c bit l bn phi cao trong khi vn phi bo m tt do, dai. Thp dng cl loi ch chuyn dng lm cng c nn c yu cu ch yu l cng v chng mimn.

Trong thc t ngi ta s dng tt c cc cch phn loi trn.

5.Tiu chun thp cacbonTiu chun Vit NamTiu chun Vit Nam quy nh nhng loi thp cacbon chnh.TCVN 1765 - 75 quy nh cc mc thp kt cu cacbon cht lng thng lm cc kt cuxy dng, c s dng trng thi cung cp, khng qua nhit luyn. Do yu cu cht lngkhng cao lng nn lng P, S cho php kh ln: P l 0,040 - 0,070%, S l 0,050 - 0,060%.Thp c k hiu bng CT (vi ngha l thp cacbon cht lng thng) vi cc ch saucng: s ch thp si, n ch thp na lng, nu khng c ch g l thp lng.

Trong nhm thp ny li quy nh c ba phn nhm A, B v C, trong phn nhm th nht Al ch yu. Phn nhm A phn loi cc mc theo gii hn bn ko ti thiu t c tnh theon vkG/mm2 - CTxx. Cch k hiu theo b(min) nh vy kh tin cho vic tnh ton s bsc bn cng nh tit din thp. V d CT38, CT38n, CT38s l ba mc cng c b 38kG/mm2 hay 380MPa song vi ba phng php kh xy khc nhau: lng, na lng v si nncc ch tiu c tnh khc c khc nhau i cht. Tiu chun cng quy nh t m v cht ch ccch tiu khc nh 0,2, , , aK. Cc phn nhm B v C v c bn gi nguyn k hiu nh phn nhm A song u k hiu tng ng c thm ch B v C l BCTxx v CCTxx. Phnnhm B khng quy nh c tnh song li quy nh thnh phn ha hc, cn phn nhm C li quynh c hai: c tnh ln thnh phn ha hc, v d: mc CCT38 c c tnh ca CT38 cn thnh

phn ca BCT38.TCVN 1766-75 quy nh cc mc thp kt cu cacbon cht lng tt ch to my qua nhitluyn, do vy phi c bo m (quy nh) c thnh phn ha hc ln c tnh (phi tra bng),cc mc c k hiu bng ch C v s phn vn cacbon trung bnh - Cxx. V d: C40 l mc ckhong 0,40%C (0,38 - 0,45%) v cc tp cht trong gii hn trnh by. Do cht lng tt nnlng P v S l 0,040% cho mi nguyn t, cc mc c cht lng cao (P, S 0,030% cho minguyn t) cui k hiu c ch A, v d C40A.


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TCVN 1822-76 quy nh cc mc thp dng c cacbon bng CD (C l cacbon, D l dng c) vis tip theo ch lng cacbon trung bnh tnh theo phn vn - CDxx hoc CDxxx. V d, CD80v CD80A l hai mc cng c khong 0,80%C (0,75 - 0,84%) song vi cht lng tt v cao.

Tiu chun cc nc

OCT quy nh cc thp kt cacbon cht lng thng bng CT vi cc s t 0, 1 n 6 ch cp bn (s cng to bn cng cao). Cng c cc phn nhm theo th t A, , B ln lt tngng vi cc phn nhm A, B, C ca TCVN. V thp kt cu cacbon cht lng tt OCT quynh cc mc k hiu theo s phn vn cacbon trung bnh, nh mc 40 c khong 0,40%C nhmc C40 ca TCVN. V thp cacbon dng c OCT quy nh cc mc bng vi s tip theoch lng cacbon theo phn nghn cacbon trung bnh nh 12 c khong 1,20%C. Tuy c mts khc bit nh v c bn TCVN v thp cacbon vn theo cc nguyn tc c bn ca OCT,nn c s trng hp hon ton gia hai tiu chun ny. Hoa K s dng nhiu tiu chun chothp cacbon. ASTM c dng cho thp xy dng. AISI v SAE cho cc thp ch to my v

dng c.JIS quy nh cc thp kt cu cht lng thng bng SS hay SM vi s tip theo ch gii hnbn ko ti thiu tnh theo n v MPa - SSxxx, SMxxx; cc thp kt cu cacbon cht lng ttbng SxxC trong xx l s ch lng cacbon trung bnh theo phn vn, cc thp cacbon dngc bng SK vi cc s th t t 1 n 7 - SKx.

6.u nhc im ca thp cacbonu imThp cacbon c dng rt rng ri trong k thut ni chung v ch to my v ba u im sau:

1) R, d kim khng phi dng cc nguyn t hp kim t tin. 2) C c tnh tng hp nht nh ph hp vi cc iu kin thng dng. 3) C tnh cng ngh tt: d c, cn, rn, ko si, hn, gia cng ct (so vi thp hp kim). Nhc imThp cacbon cng c nhiu nhc im, trong ng ch nht l: 1) thm ti thp nn hiu qu ha bn bng nhit luyn ti + ram khng cao, do nhhng xu n bn, c bit i vi tit din ln.2) Tnh chu nhit cao km: khi nung nng bn cao ca trng thi ti gim i nhanh chngdo mactenxit b phn ha trn 200oC, trn 570oC b xy ha mnh. 3) Khng c cc tnh cht vt l ha hc c bit nh: cng nng, chng n mn.

Cc thp hp kim trnh c cc nhc im ny.Do vy trong thct thp cacbon c dng lm cc chi tit vi mt ct ngang nh, hnh dngn gin, chu ti trng nh v va phi, lm vic nhit thng; trong khi cc thp hpkim c dng cho cc trng hp ngc li.


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1.Cc yu cu chungMt c my d to n u cng do nhiu chi tit, b phn nh ghp li vi cc i hi c tnhkh khc nhau cho nn thp lm chi tit my c yu cu cao hn v phi tha mn cc yu cukhc nhau v c tnh, chnh xc v hnh dng, kch thc cng nh bng b mt lp rp. tha mn c yu cu , cc chi tit my vi cc iu kin lm vic khc nhau thngc lm bng nhiu mc thp khc nhau vi ch nhit luyn ti + ram khng ging nhau.

C tnh

Tnh cht c bn ca chi tit my l kh nng chu ti trng tnh v ng, do vy yu cu c bnl c bn cao v dai tt ph hp vi iu kin ca ti trng. bn cao s gip to ra cc my khe (c cng sut ln) hn, nh v nh gn hn v gi thnhh hn. t c yu cu ny phi dng thp ph hp v nhit luyn bo m. Tuy nhintrong ch to my, v bn ngi ta ngy cng coi trng gii hn chy, v l cc chi tit my dng lp ghp khng cho php c bin dng do khi lm vic. dai va p rt quan trng i vi chi tit chu ti trng ng do phi tng ti mt cch tngt. Chnh ch tiu ny quyt nh tin cy khi lm vic, n bo m kh b ph hy gin, yucu c bit quan trng i vi cc phng tin giao thng.Ngoi hai ch tiu c bn trn nhiuchi tit my cn i hi cng b mt cao bo m tnhchng mi mn khi lm vic b ma st hay c st. Rt nhiu chi tit my lm vic di ti trngthay i theo chu k (trc, bnh rng...) nn i hi gii hn mi cao.

Tnh cng ngh

tr thnhchi tit thnh phm thp bn thnh phm phi qua nhiu khu gia cng. Trc tin thng l bin dng nng (rn) to phi, to ra hnh dng gn ng nhng mt skch thc bao u ln hn bn v. Hn na cc nh my c kh khng bao gi c michng loi phi ph hp vi chi tit sn xut cho d l loi chi tit n gin nh trc trn, cht.Ngoi ra bin dng nng cng gip to ra t chc tt hn (lm nh mn ht, to th ph hp...).Tip phi thp to thnh phi qua ct gt to ra hnh dng, kch thc chnh xc v bng yu cu nh quy nh. Hu nh khng mt chi tit my no li khng phi qua ct gt, ni

chung y l nguyn cng tn km nht trong gia cng c kh, chim t trng ln trong githnh.Tt c cc yu cu trn c th t c nhchn ng mc thp v ch nhit luyn thch hp.


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Tnh kinh t

Do sn lng ln, thp ch to my ni chung phi r, nn ni chung thng dng thp cacbonv hp kim thp, trong trng hp tht quan trng mi dng n hp kim ha trung bnh, khngdng hp kim ha cao.

2.Thnh phn ha hcDo cc yu cu v c tnh, tnh cng ngh, kinh t nh trn, thp phi c thnh phn ha hc phhp.Cacbon v thp cacbon

Nh bit cacbon l nguyn t c bn nht quyt nh c tnh v c tnh cng ngh ca thp,nn chn ng hm lng cacbon l yu t quan trng hng u khi xc nh mc thp. Cacbonha bn thp song lm gim do, dai, lm xu tnh gia cng p lc, gia cng ct v tnhhn.

Do tc dng nh vy lng cacbon trong thp kt cu ch to my thng gp c quy nhkh cht ch: 0,10 - 0,65% v ty theo cc yu cu khc nhau li chia ra ba nhm nh nh sau: -Nhm yu cu nng v do, dai: thnh phn cacbon thp 0,10 - 0,25%. Mun c bncao phi ti + ram thp, cng b mt cao phi qua thm cacbon. -Nhm yu cu nng v gii hn chy v dai: thnh phn cacbon trung bnh 0,30 - 0,50%Cv ti + ram cao. Mun c cng b mt cao phi qua ti b mt. -Nhm yu cu nng v gii hn n hi: thnh phn cacbon tng i cao 0,55 - 0,65% v ti+ ram trung bnh.

Cch phn chia ba phn nhm v thnh phn cacbon nh trn cng ch c tnh cht tng i, c

th x dch i cht.Ni chung thp cacbon kt cu ch to my c tnh cng ngh tt v r, chim t l ti 80 - 90%trong c kh, c dng ph bin trong ch to my thng dng lm cc chi tit chu ti trngthp hay trung bnh, c tit din nh (< 20mm), hnh dng n gin ( khi phi ti trong nckhng b nt). Trong nhng iu kin dng thp cacbon khng khc g thp hp kim, tc thiu qu kinh t - k thut cao hn.Tuy nhin thp cabon cng c nhc im quan trng, l: - Khi c tit din ln (> 30 - 40mm) khng th t c bn tt nh tit din nh,- Khng th ch to chi tit c hnh dng phc tp (tit din thay i t ngt),- Tnh chng ram km, khng duy tr c bn, cng cao sau khi ti khi b nung nng n

200oC v cao hn, nn ni chung khng lm vic c cc nhit . Ngc li thp hp kim li th hin u vit ba mt trn.Thnh phn hp kim v thp hp kimSo vi thp cacbon, thp hp kim tuy c t hn, tnh cng ngh km hn, song b li c bncao hn, l u im quan trng nht. Nguyn nhn ca n nh ni trc ht l do nng thm ti, ngoi ra cn do ha bn ferit, to ra cacbit phn tn, gi cho ht nh.


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Trong thp kt cu ch to my, theo tc dng v hm lng, cc nguyn t hp kim c chiathnh hai nhm chnh v ph.Nhm cc nguyn t hp kim chnh chim t l ch yu trong cc nguyn t a vo, c tcdng lm tng bn nh nng cao thm ti, l cc nguyn t Cr, Mn, Si v Ni (ngoi rac B), vi cc c tnh:- R, d kim (ring Ni tuy t song vn phi dng khi tht cn), song tng lng ca chng avo thng ch khong 1,0 - 3,0%, rt t khi gp loi 5 - 6%,- C tc dng nng cao thm ti. nng cao thm ti, ngi ta thy rng vi mt tng lng hp kim nh nhau khi chia radng nhiu nguyn t (hp kim ha phc tp) c tc dng mnh hn khi ch dng mt nguyn t(hp kim ha n gin). V d khng dng thp vi 3%Cr v cho thm ti (bn) km hn1%Cr + 2%Ni hay 1%Cr + 1%Mn +1%Si. Thng gp:- Khi tng lng hp kim ~1% dng mt nguyn t, v d thp crm;- Khi tng lng hp kim ~2% hay dng hai nguyn t, v d thp crm - niken;

- Kkhi tng lng hp kim ~3% dng hai hoc ba nguyn t, v d thp crm - mangan - silic;- Khi tng lng hp kim 4% dng hai, ba hoc bn nguyn t.Nhm cc nguyn t hp kim phc a vo thp vi lng rt t, thng < 0,1%, cao nhtthng khng qu 0,2% vi mc ch ci thin mt nhc im no do nguyn t chnh avo, l Ti, Zr, Nb, V v Mo.- Ti, Zr, Nb, V l cc nguyn t gi cho thp c ht nh khi nung, c bit trong thp Cr - Mn(Mn c khuynh hng gy ht ln), t mc ch ny thng dng khong 0,10%Ti.- Mo (~ 0,20%) trnh c gin ram loi II, thng c a vo thp Cr -Ni vi thm ticao c lng cacbon trong khong 0,20 - 0,40% (nh sau ny s bit l loi thp ha tt ti thuvi tit din ln phi qua ti + ram cao, rt nhy cm vi gin ram loi II m khng trnh c

bng bin php n gin lm ngui nhanh trong nc hoc du). W cng c tc dng ny nhngphi dng nhiu hn (~ 0,50%) nn t dng. Ngoi tc dng chng gin ram loi II cc nguyn tny cn c tc dng nng cao thm ti, nn thp crm - niken - mlipen (hoc vonfram)c coi nh thp ch to my tt nht.Nh vy thp hp kim ch to my c nhng c im sau:- Tuy c gi thnh t hn song v c tnh n c bn cao hn, iu ny th hin rt r khi titdin ln nh tnh thm ti cao, c bit l khi ti thu s t c c tnh cao v ng nht trnton tit din.- Do ti du, thm ch c th p dng ti phn cp nn c th lm c cc chi tit c hnh dngphc tp m khng s nt hoc b bin dng ln.- Tnh chng ram tt nn mt mt gi c bn nhit cao hn, mt khc trong iu kinnh nhau thp hp kim c ram nhit cao hn do ng sut bn trong thp hn.


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3.Quan hgia tng lng hp kim v ng knh tithu

bo m c tnh cao v ng nht trn tit din thp phi c ti thu, mun vy phi c

hp kim ha mt cch hp l hay ni khc i trong trng hp ny tit din thp c chn theo thm ti hay tng lng nguyn t hp kim. Cng c th ni rng mi mc thp ch bo mc tnh cao v ng nht ti tit din nht nh. Mc thp vi tng lng hp kim cng cao chophp lm cc chi tit c tit din cng ln. Theo thm ti cc thp kt cu c chia thnhbn nhm:- Thp c thm ti thp, ch ti thu ti ng knh 15mm, l loi khng hp kim ha tcthp cacbon.

- Thp c thm ti trung bnh, ti thu ti ng knh 35mm, l loi c hp kim ha thpv n gin nh c 1%Cr hoc 2%Mn hoc 1%Cr + 0,5%Si.- Thp c thm ti tng i cao, ti thu ti ng knh 75mm, l loi c hp kim ha

thp nhng phc tp nh crm - niken thng, crm - mlipen, crm - mangansilic.- Thp c thm ti cao, ti thu ti ng knh 100mm, l loi c hp kim ha phc tp ti5 - 6% nh thp crm-niken cao hay crm-niken-mlipen.

4.Cc nhm thp chto myC ba nhm thp kt cu ch to my chnh vi cc c im khc nhau v thnh phn cacbon,hp kim, ch nhit luyn, c tnh v cng dng:- Thp thm cacbon c thnh phn cacbon thp (do, dai), t bn cao phi ti + ram thp,cn mun t cng b mt cao phi qua thm cacbon. - Thp ha tt c thnh phn cacbon trung bnh (kh bn, do, dai), nng cao c tnh hn naphi ti + ram cao, cn mun t cngb mt tt cui cng phi qua ti b mt.- Thp n hi c thnh phn cacbon tng i cao (km do, dai nhng kh cng, rt n hi), t gii hn n hi cao phi ti + ram trung bnh.Cn ch l trong mi nhm c nhiu mc khc nhau, chng khc nhau ch yu v thm tido c dung cho cc ln tit din khc nhau; ngoi ra cc nguyn t hp kim cng an cho thp nhng tnh cht c trng nh Cr -Ni va tng mnh thm ti va gi c dai cao, lm xu tnh gia cng ct, gy ginram, Mn - Si lm thp bn, cng, nhng li gy gin.

1.c im vthnh phn ha hc

Thp thm cacbon l loi thp c thnh phn cacbon thp: 0,10 - 0,25% (c bit c th ti0,30%) ch to cc chi tit chu ti trng tnh v va p cao nhng b mt b mi mn mnhnh bnh rng, cam, cht... t c yu cu thp phi qua thm cacbon (bao gm c ti +


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ram thp sau khi thm), nn c t tn nh trn.CacbonLng cacbon trong thp c quy nh trong khong 0,10 - 0,25% bo m do, daicao ca li c trng thi ti + ram thp t c bn cao nht. Dng gii hn di khicn dai cao hn, dng gii hn trn khi cn bn cao hn. Trong mt s trng hp cn t

bn cao hn na c th dung ti0,30%C. Nu dng cao hn na dai ca li s thp khi ti+ ram thp, khng chu c ti trng va p.Cc thp cacbon c thm ti thp, ch dng cho chi tit nh ( < 10 - 20) v hnh dng ngin (v phi ti nc), ch chu mi mn bnh thng. Do phi chu nung lu nhit cao khithm cacbon, cc thp thm cacbon phi l loi c kh xy trit (thp lng), tt nht l loiht nh ht khng b to, lm thp gin.Hp kimNgc li, u th ca thp hp kim l c thm ti cao, dng cho chi tit ln (> 30 - 50),hnh dng phc tp v chu mi mn cao. bo m cc yu cu trn cc nguyn t hp kim dng trong thp thm cacbon phi bo mc hai tc dng: va lm tng tnh thm ti nng cao bn li va thc y qu trnh thm

cacbon (hoc t ra cng khng cn tr). Vi ngha ngi ta khng dng silic v gy thotcacbon nn cn tr qu trnh thm cacbon. Nguyn t hp kim c bn c mt trong mi thp hpkim thm cacbon l crm, c th dng n ring r hay kt hp vi niken, mangan. Cng khngdung thp ch hp kim ha bng mangan do nguyn t ny thc y ht austenit pht trin khithm cacbon.


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Bng 5.3. Thnh phn ha hc (trung bnh, %) ca mt s mc thp thm cacbon
https://sites.google.com/site/truongvanchinhvatlieucokhi/home/gang-va-thep-1/thep/thep-che-tao-may/thep-tham-cacbon/dhac-diem-ve-thanh-phan-hoa-hoc/99.bmp?attredirects=0


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u vit ca thp hp kim thm cacbon so vi thp cacbon l cc mt sau:- bn cao do thm ti cao, u vit ny cng r rt khi tit din chi tit cng ln.- Tnh chng mi mn cao nh sau khi thm cacbon to nn cc cacbit hp kim n nh hn,phn tn hn v cng c phn cng hn i cht.- bn, tnh chng mi mn cao k trn duy tr c nhit cao hn 200oC. - t bin dng, nt khi ti do c lm ngui trong du, nn lm c cc chi tit c hnh dngphc tp.- C kh nng nng cao nhit thm, do rt ngn c thi gian thm. Bng 5.3 trnh by thnh phn ha hc ca mc thp thm cacbon theo mt s tiu chun.

2.Thp cacbonDo cc yu cu trn, thp cacbon thm cacbon phi l loi thp lng, khng c dng thpsi hay na lng v chng c khuynh hng pht trin ht mnh. Ph hp vi cc yu cu rach dng cc mc thp cacbon sau:C10, C15, C20, C25 v i khi cCCT38 (nh ni trong iu kin thng thng ca sn xutluyn kim mc thp ny c khong 0,20%C).(tng ng vi OCT l 10, 15, 20, 25, BCT3, SAE/AISI l 1010, 1015, 1020, 1025, JIS lS10C, S15C, S20C, S25C).

Chng c c im:- Sau khi thm cacbon t c yu cu thp k trn tit din nh: cng b mt HRC 60 -62, chng mi mn tng i tt, li HRC 30 - 40, dai cao, bn tt, btrong khong 500 -600MPa.

- Do bt buc phi ti nc, thm ti thp nn khng th lm c cc chi tit c hnh dng

phc tp v ln.- Khi thm cacbon khng th nng cao qu 900oC (trong thp khng c cc yu t cn tr htpht trin), tc thm ko di, ni chung ht vn b to. Do ht ln sau khi thm khng th titrc tip m phi qua thng ha ri mi ti (mt hoc hai ln) nn thng b bin dng ln.Nh vy thp cacbon vi cc mc trn ch p dng cho cc chi tit nh ( < 20mm), hnh dngn gin, tnh chng mi mn yu cu bnh thng, tm li thng l cc chi tit khng quantrng nh mt s phtng xe p, xe ci tin (trc, cn v bi). Chi tit d nh nhng hnh dngphc tp (nhiu gc cnh) cng khng th lm bng thp cacbon. Khi dng thp ny phi ch tun th ng quy trnh thm do tnh phc tp hn ca n.

3.Thp crmNh bit, crm l nguyn t tng i r, n khng nhng nng cao thm ti cn xc tinqu trnh thm cacbon (do c i lc vi cacbon mnh hn), do vy c dng trong mi thphp kim thm cacbon.Thp crm n gin l thp c khong 1%Cr, c dng kh ph bin trong c kh lm ccchi tit loi nh, c hnh dng khng qu phc tp. Thng dng cc k hiu sau (nh ni


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TCVN cha quy nh cho thp kt cu hp kim nn y ch l k hiu theo TCVN 1659-75)15Cr, 20Cr, 15CrV, 20CrV

(tng ng vi OCT l cc mc 15X, 20X, 15X, 20X, SAE/AISI l 5015, 5115, 5120, JISl SCr415, SCr420).

So vi thp thng, thp crm c nhng c im sau:- Sau khi thm cacbon cng t cng HRC 60 - 62 song c tnh chng mi mn cao hn icht.

- Do nng cao cht t thm ti v dng mi trng ti du nn c th lm c chi tit c hnhdng tng i phc tp.- bn cao hn i cht, btrong khong 700 - 800MPa.-Nhit thm cacbon trong khong 900 - 920oC, tc thm nhanh hn, ht bnh thng,sau thm khng cn thng ha song vn phi p dng cch ti nh thp cacbon (mt hoc hailn). Ngoi ra thp ny cn c khuynh hng qu bo ha cacbon to nn li cacbit gy ra gin(iu ny d xy ra khi thm th rn).

Cng dng: lm cc chi tit nh ( 20 - 40) song hnh dng tng i phc tp nh bnh rng,trc bc, cht vi i hi tnh chng mi mn tng i cao. nng cao thm ti v trnhqu bo ha lp thm ca thp crm, ngi ta thng hp kim ha thm bng niken hay manganl cc nguyn t khngto thnh cacbit (Ni) hay to cacbit yu (Mn).

4.Thp crm - niken v crm - nikenmlipenNh ni s kt hp ca crm v niken khng nhng lm tng mnh thm ti nh tng bn m cn duy tr c dai. Vi c trng bn v dai thp crm - niken c dng chocc chi tit quan trng, cn tin cy cao nh trong t, my bay...

C hai loi:- Crm - niken thng ~ 1%Cr + 1%Ni, v- Crm-niken cao ~ 1%Cr + 3%Ni.

Ngoi ra nu a thm mt lng nh mlipen vo hai loi trn s nng cao thm ti thmna.Thp crm - niken thngL loi thp hp kim thp, trong crm 0,50 - 1,00% cn niken > 1%, nhng cng ci thinng k thm ti, ti rt d trong du. Tuy nhin loi ny khng c hiu qu kinh t cao nnhu nh khng c dng cc nc phng Ty (trc y AISI / SAE c lot mc 3115,3120, 3215, 3220 3316 v 3415 thuc loi crm-niken nhng b t lu, trc 1945). Mc

thp in hnh hin cn c dng Nga l 20XH, c dng lm cc chi tit hnh dng phctp vi kch thc trung bnh (50 - 75mm), chu ti trng va p cao nh cc bnh rng t tinh v du lch.Thp crm - niken cao

L loi thp trong niken cao hn 2% v c th ti 4% cn crm cng ch trn di 1%, tc ct l Ni / Cr = 3 hay 4. Nh bit vi lng crm - niken nh th thm ti rt cao, ti thuc cc tit din n 100mm v cao hn, trong thc t c th coi c thm ti bt k. Vi


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ngay tit din ln nh vy cng rt d dng ti trong du, cn vi tit din nh hn c th pdng ti phncp, nh gim mnh bin dng. Thp c dng lm cc chi tit thmcacbon rt quan trng: chu ti trng nng v b mi mn mnh, hnh dng ln v phc tp, yucu tin cy cao nh cc chi tit trong my bay, t m cc h hng c th gy tai ha chongi.

Mc thp in hnh ca loi ny l 12XH3A v 20X2H4A ca OCT (SNC415 v SNC815 caJIS) c th t c t hp c tnh cao ti b = 1000 - 1200MPa, aK = 900 - 1000kJ/m2.Tuy nhin khi s dng thp ny phi tnh n cc yu t sau: - t (theos liu ca Nga t gp ba thp cacbon), - Tnh gia cng ct km do thp qu do (do cacbon thp, niken cao), phoi khng gy vn, - Phi p dng quy trnh nhit luyn sau khi thm cacbon kh phc tp. ci thin phn no tnh gia cng ct thp phi qua thng ha. Quy trnh nhit luyn thp ny kh phc tp do sau khi thm cacbon b mt vi hm lngcacbon cao v nguyn t hp kim kh cao lm h thp im Ms nn nu ti bnh thng cn li

nhiu austenit d (ti 50 - 60%) v cng ch t HRC 45 - 55, khng chng mi mn. Vth sau khi thm tin hnh:- Thng ha trc tip ri ram cao 600 - 650oC trong thi gian di t 2 n 6h lm cacbit phntn tit ra khi cc dung dch rn lm cho chng ngho hp kim i, - Ti: khi nung nng c hai pha austenit ngho hp kim (nng cao im Ms) v cacbit phntn nn sau lm ngui c nhiu mactenxit, cacbit phn tn v t austenit d nn va bo m cng cao (HRC > 60) va chng mi mn cao, - Ram thp (nh thng l gim ng sut).Thp crm - niken - mlipenCh yu l nhm thp crm-niken cao (cng c c thp crm niken thng) k trn nhng c

thm 0,10 - 0,40%Mo vi tc dng ch yu l nng cao hn na thm ti ( y khng ctc dng chng gin ram do ch phi ram thp), chng c coi l thp thm cacbon tt nht,c dng vo cc mc ch quan trng nht v cho tit din ln nht. Cc mc thp in hnh ca loi ny l 20XH2M, 18X2H4MA ca OCT (SNCM415,SNCM815 ca JIS, 4320, 4720, 8115, 8615, 8822, 9310, 94B17 ca AISI / SAE). c tnh cacc mc thp ny cng ging nh cc mc crm niken cng loi song c tnh thm ti cao hn(v d SNCM415 c tnh thm ti cao hn SNC415, cn cch nhit luyn ging nhSNC415). Ccmc tt nht (v d nh18X2H4MA) l loi t ti, tc loi mactenxit, phi p dng trit cchnhit luyn k trn.

5.Thp crm - mangantitanNhm thp ny c cc ch tiu kinh t - k thut cao c dng rt rng ri Nga cng nh nc ta trong ch to bnh rng t ti nh v trung bnh. V mt kinh t, n l loi thp tng i r v hp kim ha thp ch yu bng cc nguyn t r(Mn) v khng t (Cr) khng phi dng n niken t. V bn, i vi cc chi tit trung bnh (< 50mm) n c bn tng ng nh thp crm -


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niken do c th ti thu (b= 1100 - 1150MPa), tuy do, dai c km hn i cht (aK=600 - 900kJ/m2).

u im chnh ca nhm thp ny l tnh cng ngh.Trc ht thp khng qu do, dai m vn mm c th ct gt tt. Sau l cng nghthm cacbon ca thp c kh nhiu u vit:- Do c mangan nn b mt thp khng b qu bo ha cacbon, - Tuy c mangan l nguyn t lm ht ln, song nh c titan (d vi lng nh) nn to ra ccc phn t cacbit titan TiC rt nh nm bin ht austenit, ngn tr ht ln ln, nn thp c htnh. Chnh do iu ny s dn ti ba u im sau,- Cho php thm nhit cao hn 900oC (v d 930 - 950oC) nn rt ngn c thi gianthm,- C th ti trc tip ngay sau khi thm v khng cn cc nguyn cng lm nh ht nh thngha, ti ln th nht. Nhit luyn sau thm l n gin nht: ti trc tip vi h nhit cn khong850 - 880oC ri ram thp,

- Do quy trnh n gin nh vy nn bin dng rt thp.OCT quy nh hai mc thp lm bnh rng rt ph bin l 18XT (ngoi ra c 25XT, 30XT)v 25XM. Trong mc u dng trong trng hp thm cacbon nh trnh by cn mc saudng cho trng hp thm cacbon - nit th kh vi nhit thm 850oC, thi gian thm vnrt ngn thm, ti trc tip + ram thp, bin dng t c gi trnh nht. Do thm nhit thp hn, khng gy ra ht ln nn khng cn dng titan m thay vo l mlipen cithin thm thm ti. Trong hai, ba mi nm tr li y, Nga phng n dung thp mc25XM lm bnh rng hp s t, qua thm cacbon - nit th kh, ti trc tip phn cp trongdu nng 180oC c coi l hon ho hn c v va cho cng cao, tnh chng mi mn cao(hn thm cacbon), bin dng di mc cho php (ch 0,08 - 0,12mm, cho php l 0,12mm)

nh nng cao gn gp i tui th.

Thp ha tt l thp c thnh phn cacbon trung bnh, 0,30 - 0,50%C, chto cc chi tit mychu ti trng tnh v va p tng i cao m bmt c thbmi mn nh trc, bnh rng,cht..., t c c tnh tng hp cao nht thp phi qua nhit luyn ha tt (ti + ram cao)nn c tn nh trn.

1.c im vthnh phn ha hcCacbon

Lng cacbon trung bnh trong gii hn 0,30 - 0,50% s bo m s kt hp tt nht ca cc chtiu c tnh: bn, do, dai (c tnh tng hp) sau khi ti + ram cao v cng, tnhchng mi mn tng i cao sau khi ti b mt, tha mn tt cc yu cu trn. Nu dng lngcacbon khc i khng th t c c tnh tng hp tt, tuy rng dng lng cacbon cao hn tc cng b mt v tnh chng mi mn cao hn. Thng dng ph bin lng cacbon


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trong khong 0,35 - 0,45%.Hp kim bo m c c tnh tng hp cao v ng nht trn ton tit din, thp phi c hp kim hathch hp t ti thm ti mong mun, do tit din cng ln lng hp kim a vocng phi cao.

Nguyn t hp kim chnh dng trong thp ha tt l cc nguyn t Cr, Mn vi lng cha 1 -2%, Ni - 1 - 4% nh nhm thp thm cacbon, ngoi ra cn cho php dng c Si vi lng chakhng qu 1% (v khng qua thm cacbon nn khng phi hn ch nh trng hp trn). Trongmy chc nm gn y ngi ta cng ch dng bo (B), vi lng rt nh, khong 0,0005 -0,003%, cng c tc dng nh 1% Ni hay 0,5%Cr (khi dng < 0,0005% khng c tc dng,>0,003% to nn cc borit st FeB, Fe2B li lm gim thm ti). Khng dng B mt cch nc v tc dng ca B c tng cng khi dng n cng vi Cr, Ni, Mn. Nguyn t hp kim ph thng dng trong thp ha tt l Mo v W, chng cng c tc dngtng thm ti, song ch yu l khc phc gin ram loi II khi ram cao nhng tit din ln

(khng th khc phc bng ngui nhanh sau khi ram).Cc thp cacbon v hp kim ha tt cng c nhng c im chung tng ng nh trong thpthm cacbon tr v thm cacbon.

2.c im vnhit luynNu nh thp thm cacbon thng qua hai bc nhit luyn: s b l thng ha v kt thc lthm cacbon vi thi gian kh di th vic nhit luyn thp ha tt c coi l n gin hn. ci thin tnh ct gt, sau khi rn, dp nng to phi, thp c qua hon ton (tr thpcrm - niken) t cng HB 180 - 220 d gia cng ct th.

Nhit luyn kt thc thpha tt c chia lm hai bc:- Bc u tin l to cho li c c tnh tng hp cao chu c ti trng tnh v va p bngcch ti + ram cao t t chc xoocbit ram vi cng HB 240 - 280 (HRC 25 - 30). Ngoi ra tchc ny cn c hai tc dng ph nhng kh quan trng l:

+ Gip to ra bng cao khi gia cng tinh tip theo ng nh hnh dng, kch thc yu cuv

+ Gip chuyn bin nhanh v to mactenxit kim nh khi ti b mt tip theo do vi hn hpferit-xmentit nh mn s to ra rt nhiu mm austenit khi nung nng. iu ng ch l khi ram cao cho thp hp kim (loi khng cha Mo hay W) phi ch trnhgin ram (loi II).

Vi cc tit din nh c th thay ti + ram cao bng thng ha cng t hiu qu tng t mcng ngh thc hin n gin v r hn.- Bc th hai l to cho b mt cng v tnh chng mi mn m khng ph hy c tnh tnghp va t c trn ton tit din. Mun vy sau khi gia cng tinh, chi tit thnh phm cqua ti b mt v ram thp. Vi lng cacbon ca thp nh trn sau ti b mt d dng t c cng HRC 52 - 58, cng vi cng li HRC 25 - 30 t c yu cu ra. Ring cc thpvi lng cacbon trong khong 0,30 - 0,35%, ti b mt khng t c cng cao hn RC50


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nn phi thay bng thm cacbon - nit nhit thp (550 - 560oC) tc nhit khng vtqu nhit ram cao khng lm hng t chc xoocbit ram ca li vi c tnh tng hp cao.

3.Thp cacbonPh hp vi cc yu cu ra l cc mc thp C30, C35, C40, C45, C50 v C40Mn song dngnhiu hn c l hai mc gia (tng ng vi cc mc 40, 45, 40, 58 ca OCT, 1040, 1045 caAISI/SAE, S45C ca JIS). Cc mc ny thng c dng lm cc chi tit my nh ( 20 - 30),hnh dng n gin nh cc trc, cht phng, thanh truyn lc. Chng c c im l t cyu cu ra nhng mc thp b= 750 - 850MPa.Trong my chc nm gn y Nga (v gn y Trung Quc) dng kh nhiu mc thpcacbon c bit c gi l thp vi thm ti thp (thp hn c thp cacbon thng), n chart t hai nguyn t Mn ( 0,20% thay v 0,50 - 0,80%) v Si ( 0,15% thay v 0,30 - 0,35%) vimc 58 (hay 55). c tnh ca thp ny l d ti th tch cng t c hiu ng nh ti bmt v lp ti ch dy trn di 2mm nn li khng b ti vn gi c dai nht nh v vilng cacbon cao hn 0,55% cng b mt t c khong HRC 60 vi tnh chng mi mncao. Nhiu hng ch to t ca Nga dng thp ny ch to bnh rang b ng (thng ckch thc ln hn, quay chm hn v t b mn hn loi ch ng) vi cng ngh ti th tchhay ti cm ng vi nung nng su (su hn chiu su lp ti) m vn t hiu qu gn nhdung thp cacbon thp em thm cacbon.

4.Thp crmmlipena thm vo thp crm k trn khong 0,25%Mo s ci thin thm thm ti v chng c

gin ram loi II. Thp crm - mlipen c dng lm cc chi tit my trung bnh ( > 50mm)hnh dng tng i phc tp nh bnh rng. Thng dng cc mc 38XMA ca OCT (tngng vi 4140 ca AISI / SAE, SCM440 ca JIS).

5.Thp crm - mangan v crm - mangansilicThp c cha 1%Cr + 1%Mn hay 1%Cr + 1%Mn + 1%Si l loi hp kim ha phc tp nn c thm ti cao, dng lm chi tit kh ln ( 50 - 60mm). Tuy nhin thp ny do hp kim ha bngc Mn ln Si nn cng hn v cng gin hn cc loi thp hp kim khc v vy khng c phbin tt c cc nc. Nga c dng thp ny vi mc 40X, 30XC, song khng c dng

Hoa K, Nht.

6.Thp crm - niken v crm - nikenmlipenNh hp kim ha bng c crm v niken, thp c thm ti cao m vn gi c do, dai tt, nht l trong trng hp niken cao ti 3% v c chaMo.


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Thp crm - niken thngThp thng cha khong 1%Cr + 1%Ni, do niken thp nn cha c thm ti cao, ch clm cc chi tit vi tit din 50 - 60mm vi bkhong 700MPa v aKkhong 700kJ/m2. Nhtnh ti tt nn thp c lm cc chi tit c hnh dng kh phc tp. OCT quy nh mc thpin hnh l 40XH, thng dng lm cc chi tit truyn lc hay h thng li trong t (Hoa k v

Nht khng c thp loi ny). Nhc im quan trng ca thp ny l b gin ram loi II v tnhgia cng ct hikm. trnh gin ram loi II phi lm ngui nhanh sau khi ram hay dng thp40XHM hay 8640 (cho tit ln hn). ci thin tnh gia cng ct thp c em ram cao. Thp crm - niken cao

Thp thng cha khong 1 - 2%Cr + 3 - 4%Ni (vi t l Ni / Cr vokhong 3 - 4) thuc nhmthp hp kim trung bnh vi thm ti cao, ti thu vi tit din trn 100mm, thc t c coil ti thu vi tit din bt k (n thuc loi mactenxit). Nh vy thp c c tnh tng hp rtcao: b= 1100MPa, 0,2= 1000MPa, aK = 800kJ/m2. OCT dng thp ny vi mc in hnhl 30XH3A (tng ng vi SNC631 v SNC836 ca JIS, Hoa K khng c thp ny). Tuy

nhin thp ny cng c hai nhc im l b gin ram v tnh gia cng ct km nh trn. Thp crm - niken cao vi mlipeny l loi thp ha tt ch to my tt nht v so vi loi trn a them mt lng nh (0,15 -0,40%) mlipen khng nhng lm tng thm ti, lm cc chi tit vi hnh dng phc tp, titdin ln ( 100mm) m cn loi tr c gin ram loi II (ivi loi chi tit ln nh th nylm ngui nhanh trong du, nc sau khi ram khng nhanh lm mt gin ram). Thp thucnhm mactenxit, c coi nh ti thu vi tit din bt k. Thp c c tnh tng hp cao nht:b= 1200MPa, 0,2= 1100MPa, aK = 800kJ/m2. Hu nh mi nc u c nhm thp ny.OCT dng thp ny vi cc mc 38X2H2MA, 38XH3MA (cng vi 4340 ca AISI/SAE,SNCM439 ca JIS). Thp vn cn nhc im l tnh gia cng ct km.

7.hp dng thm nitNh bit, thp thm nit phi l thp hp kim c bit trong c cc nguyn t nh crm(~1,6%), mlipen (~ 0,30%), nhm (~1,00%) to nn nitrit cng, phn tn v n nh hn nitritst. Lng cacbon ca thp ny l trung bnh, khong 0,40% nn c nhit luyn ha tt toc tnh tng hp cao cho li trc khi thm nit nng cao cng b mt. iu cn ch lnhit thm nit bao gi cng phi thp hn nhit ram cao khi ha tt.OCT dng mc 38X2MA (tng ng vi mc 7140 ca SAE v SACM645 ca JIS). Ch nhit luyn ha tt cc mc thp ny gm ti 930 - 950oC trong du, ram 640 - 680oC c

tnh t b= 1030MPa, 0,2= 880MPa, aK = 600kJ/m2. Thm nit 520 - 540oC t cngHV850 - 1050 (~HRC 63 - 72).


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Nh tn gi, thp n hi l thp kh cng, c tnh n hi cao, c thnh phn cacbon tng icao, trong khong 0,55 - 0,65%, dng chto nhp, l xo v cc chi tit n hi khc. t

gii hn n hi cao nht thp c nhit luyn ti + ram trung bnh t tchc trxtit ram.

1.iu kin lm vic v yu cu i vi thp n hic im lm vic ca cc chi tit n hi l chu ti trng tnh v va p cao m khng chophp b bin dng do. Vi c im nh vy ngoi phi c hnh dng thch hp ra, cc thp emdng phi t c:- Gii hn n hi cao, tc kh nng chng bin dng do cao ( y gii hn bn khng c ngha v khng cho php c bin dng do), t l h / bcng gn ti 1 cng tt, thng ttrong gii hn 0,85 - 0,95.

- cng kh cao trong khong HRC 35- 45 hay HB 350 - 450 l thch hp; do, dai thpkhng xy ra bin dng d trong qu trnh lm vic, song khng qu thp d b ph hygin.

- Gii hn mi cao thch ng vi iu kin ti trng thay i theo chu k.

2.c im vthnh phn ha hc v nhit luynThnh phn ha hcLng cacbon thch hp bo m cc yu cu trn l trong gii hn 0,50 - 0,70% song ttnht l 0,55 - 0,65%, khi lng nguyn t hp kim tng ln thnh phn cacbon c th gim i i

cht.Cc nguyn t hp kim a vo thp n hi phi t c cc yu cu sau: -Nng cao gii hn n hi v cng, vi yu cu ny dng mangan v silic l tt nht.-Nng cao thm ti bo m gii hn n hi cao v ng nht trn tit din, vi ngha dng crm - niken l tt nht, song silic, mangan cng c tc dng ny. Trong thp n hi ngi ta dng 1%Mn, 2%Si, 2% (Cr + Ni) v tit din ca chng khng ln,nu qu mc c bit l Mn, Si thp s qu cng v gin.c im v nhit luyn t c gii hn n hi cao nht thp phi c nhit luyn c t chc trxtit ram bngcch ti + ram trung bnh vi t l h/ b 0,90. bo m gii hn n hi, gii hn mi

cao khi nhit luyn cng nh khi gia cng phi ch n cht lng b mt: - Chng thot cacbon, v khi thnh phn cacbon b mt thp hn gii hn quy nh c th tchring nh hn, chu ng sut ko v do d pht sinh vt nt mi. - To nn ng sut nn trn b mt. Bin php c hiu qu hn c l tin hnh phun bi, ln p,thm ch cn, ko ngui sau khi nhit luyn ti + ram trung bnh, nh tui bn tng 50 -100%.


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-Nng cao nhn bng b mt, loi b cc vt xc l mm mng ca nt mi, mun vy phiqua cn, ko tinh, thm ch qua mi.

3.c mc thp v c imCc mc thp nhi ca nc ta c quy nh TCVN 1767 - 75.Thp thng v thp manganThp thng c tnh n hi tt l loi thp cacbon vi cc mc C65, C70 v ngay c CD80,CD100. Thp vi khong 1%Mn vi mc 65Mn cng c dng rng ri. c im ca loithp ny l:

- Gii hn n hi thp h 800MPa do hu nh khng c hp kim ha (v thp cacboncng c th c 0,80%Mn).- thm ti thp, ch ti thu vi ng knh ti 15mm. Dng ph bin nht ca chng l dy(ng knh 0,15 n 8mm) c cung cp trng thi ti ch (xem li mc 4.4.4d) ri sau ko ngui vi bin dng khng nh hn 70%. Do tc dng ca c hai hiu ng m gii hnn hi tng ln gp bi (v d hca dy b ko ngui vi bin dng 95% - dy c ngknh < 1,4mm - c th ln hn 2000MPa), Nh vy dy c tnh n hi cao, nn lm l xoch cn qua qun ngui to hnh ri thp (200 - 300oC) kh b ng sut bn trong va tothnh l m khng cn ti + ram tip tc.Thp silic v cc thp hp kim khcy l nhm c gii hn n hi cao c dng vo cc mc ch quan trng hn. Mc thp silic60Si2 thng c dng vi 2%Si l mc ph bin vi cc c im sau:- Gii hn n hi cao, h 1000MPa vi gi thnh tng i r.- thm ti tt hn (ti thutrong du vi tit din dy 20 - 30mm).

- D thot cacbon khi nung nng ti, v vy phi ch bo v b mt khi nhit luyn. khc phc nhc im trn v nng cao thm ti ngi ta hp kim ha thm bng crm,mangan, niken v vanai vi cc mc 50CrMn, 60Si2CrVA, 60Si2Ni2A. 60Si2 c dng chyu lm l xo trong toa xe, nhp t, trc mm. 50CrMn c dng lm nhp t vi tnh cngngh tt hn. 60Si2CrVA v 60Si2Ni2A c tnh thm ti cao, gii hn n hi cao hn1500MPa nn c dng lm nhp, lxo ln, chu ti trng nng, ring loi chu va p mnhnn dng 60Si2Ni2A. Cc thp hp kim n hi thng c cung cp di dng bn thnhphm (dy > 6, thanh, bng) cha qua nhit luyn. Qu trnh ti + ram trung bnh to tnhn hi cao c tin hnh ngay sau khi to hnh (qun, dp, un) trng thi nng. OCT c cc mc tng t nh 65,70, 8, 10, 65, 60C2, 50X, 60C2XA, 60C2H2A....

AISI / SAE khng c k hiu ring, cc mc c thnh phn cacbon trong gii hn quy nh ul thp n hi nh: AISI/SAE 1065, AISI/SAE 1070, AISI/SAE 1566, SAE 9255, AISI/SAE9260, AISI/SAE 4161, AISI/SAE 50B60, AISI/SAE 5160 v 51B60, AISI/SAE 8655... JIS k

hiu thp n hi bng SUP vi s th t tip theo, c SUP3 (thp cacbon), SUP6 v SUP7 (thpsilic), SUP9 v SUP9A (thp crm - mangan), ngoi ra cn SUP10, SUP11A, SUP12 v SUP13.


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1.Cc yu cu chungTrong sn xut c kh cc dng c hay cng c gia cng, ch bin, to hnh cc vt liu (thnhcc sn phm, chi tit my, kt cu) c ngha quyt nh n nng sut, cht lng v gi thnhca sn phm c kh. Ni chung vic chun b dng c lun lun phi i trc mt bc v chon thin trit trc khi sn xut hng lot. Vic s dng vt liu c tnh nng lmvic ngycng cao c ngha rt quan trng i vi cc nh my ch to c kh.

Phn loi

Theo bn cht ca qu trnh gia cng, c th chia cc dng c thnh ba nhm ln sau y: - Dng c ct (gi tt l dao) vi c trng to hnh l to ra phoi, nh dao tin, phay, bo, tut... - Dng c bin dng vi c trng to hnh bng bin dng do nh trc cn, khun dp, khunp chy... c trng thi ngui ln trng thi nng.- Dng c o nh palme, thc cp, dng... tuy khng lm thay i hnh dng, kch thc snphm, nhng cng khng th thiu trong sn xut c kh.

C tnh

Tnh cht c bn ca dng c l tc ng lc vo phi, sn phm m khng hay t b mn, do vyyu cu c bn l c cng cao v tnh chng mi mn cao. cng cao v phi cao hn hn cng ca phi, sn phm; do vy ty tng loi dng c cn cng yu cu ti thiu khcnhau. Tnh chng mi mn cao bo m cho dng c lm vic c lu di, gia cng c

khi lng ln sn phm m khng b gim hay mt cp chnh xc. Tuy nhin trong khi quantm ch yu n hai yu cu c bn ny cng phi ch n dai va p, khng cho php thpqu gi tr quy nh trnh gy v. Ngoi ra cn quan tm n tnh chu nhit khi dng c lmvic vi nng sut cao v trng thi nng.

Tnh cng nghvtnh kinh t

Trong loi thp ny hai yu t ny khng tht quan trng v khng yu cu cao nh nhm thpkt cu bi v khi lng s dng rt t. Tuy nhin thp cng phi c kh nng bin dng do trng thi nng v mm trng thi ct gt c. V kinh t tuy t hn song phi

b li do ko di tui bn v tang nng sutThnh phn ha hc

Cacbon.

Nh bit, cacbon quyt nh cng v tnh chng mi mn nn nhng loi dng c cnyu cu ny cao nh dao ct, dng c bin dng ngui v dng c o c yu cu cacbon ti thiucao hn, 0,70 - 1,00%, song ni chung l 1,00%, thm ch c loi ln ti trn, di 2%. Cn


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i vi cc dng c gia cng phi mm hay trng thi nng c th thp hn, khong 0,30 -0,50%.

Cng vi l do trnh by, thp dng c cacbon ch ph hp vi cc loi c kch thc nh,hnh dng n gin (do thm ti thp) v nng sut thp, ch yu l cc dng c bng tay. Hp kim.

a nguyn t hp kim vi lng t vo thp ch yu l tang tnh thm ti do vy lm ccc dng c nh vi hnh dng tng i phc tp hay phc tp. Cc nguyn t hp kim a vocng lm tng tnh chng ram do nng cao tnh cng nng, song do vi lng t hiu qu nykhng ng k. a nguyn t hp kim (ch yu l W, Mo) vi lng nhiu vo thp, ngoi tcdng tng mnh tnh thm ti cn c mc ch chnh l gy cn tr mnh qu trnh ram do nngcao mnh nhit phn ha ca mactenxit, nng cao tnh cng nng. Chnh v vy hu nh ccdng c lm vic trn my u lm bng thp hp kim.

2.Thp lm dng cctTrong cc nh my c kh, ct gt l nguyn cng c khi lng ln hn c, tiu ph nhiu nnglng, my mc, nhn cng v chim t l cao trong gi thnh sn phm. Do to ra cc dngc ct c thct gt vi tc cao (nng sut cao) l yu cu thng xuyn.

Yu cu i vi vt liu lm dng cct

iu kin lm vic ca dao tin v yu cu c tnh

Hnh 5.12. S tin (a) v s mt ct khi tin (b): 1. phi, 2. phoi, 3. rnh lm, 4. dao, 5.mt trc, 6. mt sau.

Cc loi dao lm vic trong iu kin tin, phay, bo, doa... tuy c nhng nt khc bit song vc bn l ging nhau v c th coi tin l nguyn cng in hnh (hnh 5.12). 1) to phoi, li ct chu p lc rt ln to ra cng c hc ph hy (tch) kim loi. V vy daophi c cng cao hn hn phi. Trng hp thong dng (ct thp, gang thng thng vi HB
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trn di 200) dao phi c cng HRC 60. Cc trng hp khc c th thp hn (khi ct hpkim mu) hoc cao hn (khi ct thp bn nng, khng g, bn cao) gi tr trn. t cyu cu ny dao phi c lm bng thp vi lng cacbon ti thiu l 0,70% v qua ti cng +ram thp thnh mactenxit ram.2) Dao b mi st: mt trc vi phoi, mt sau vi phi, c bit l trn mt trc s to nn rnh

lm do phi bin dng v b gy phoi. Ti lc hai mt ny b mn mnh, khong cch hp li,li ct b gy v tr nn "cn" phi mi li. V vy dao phi c tnh chng mi mn cao chng to thnh rnh lm, yu cu ny c bit quan trng i vi trng hp gia cng chnhxc. Tnh chng mi mn ca thp ph thuc vo cc yu t sau: - cng: c gi tr cng cao tnh chng mi mn cng tt. Thng l khi cng HRC mccao hn 60, c tng thm 1 n v tui bn ca dao tng them khong 25 - 30%.- Lng cacbit d: cng cao tnh chng mi mn cng cao. Cc thp cng tch v sau cng tchsau khi ti tuy hu nh c cng nh nhau, song tnh chng mi mn khc nhau, cng xa cngtch (tc cng nhiu cacbon) tnh chng mi mn cng cao do cng nhiu cacbit. Chnh v l do

ny phn ln thp lm dng c ct c lng cacbon 1%, i khi ti 1,50%, c bit ti 2% vhn.3) Cng tch phoi v ma st bin thnh nhit v phn ln li tp trung li ct lm cho phnny nng ln r rt, do s lm xu kh nng ct gt ca dao. c bit khi ct gt vi tc cao, nhit li ct cao vt qu 200 - 300oC, mactenxit b phn ha, cng HRC thp di60, dao khng cn kh nng ct gt. Do vy vi dao ct cn nng sut cao, phi a vo thpnhng nguyn t to cho thp tnh cng nng: chng ha tan vo st (trong austenit rimactenxit) v do c i lc mnh vi cacbon nn gi nguyn t ny li trong mactenxit ti 500 -600oC. V vy khi ct gt vi tc cao, dao tuy vn b nng ln song vn gi c t chcmactenxit vi cng cao (HRC > 60) ct. Khc vi cng, (tnh) cng nng c

xc nh bng nhit (ram) cao nht m cng HRC ca thp vn cn cao ti 58. Ngoi ba yu cu chnh ra cc thp lm dng c ct cng phi tha mn cc yu cu khc: bn (un khi tin, xon khi khoan... nh kt hp vi thit k), dai bo m (tuy khng yu cucao trnh m, gy li ct).Thp lm dng c ct cng phi c tnh cng ngh nht nh. - Tnh thm ti tt bo m cng cao v ng nht khi ti trong du, nht l cc dao chnh dng phc tp nh phay tut, mi khoan... phi ti phn cp trnh nt v bin dng. - C kh nng chu gia cng p lc trng thi nng.- C kh nng chu giacng ct trng thi (HB 265).- C tnh mi tt sau khi ti.

Thp lm dao c nng sut thp

l loi thp lm dao ch ct c vi tc 5 - 10m/min.Thp cabon

Theo TCVN 1822-76 c cc mc CD70, CD80, CD80Mn, CD90, CD100, CD110, CD120 v

CD130 vi cht lng tt (P 0,035, S 0,030) v cng cc mc nh vy nhng c cht lng


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cao (P 0,030, S 0,020) c thm ch A sau cng nh t CD70A n CD130A. Chng c ccc tnh nh sau:- Sau khi ti + ram thp c th t HRC 60 ct. Ch ti ca cc thp nh sau: CD70,CD80 - ti hon ton 800 - 820oC, 780 - 800oC, CD90 - CD130 - ti khng hon ton 760 -780oC. Tuy tt c u t cng HRC 60 - 62 song cc thp sau cng tch CD100 - CD130 c

nhiu XeIId nn chng mi mn tt hn ccmc cn li.- D bin dng nng, gia cng ct v r.Song cng l nhiu nhc im quan trng.+ thm ti thp (ch ti thu cc tit din trn di 10mm). Vi cc dao ln hn, lp timng, sau thi gian lm vic khi mi li khng cn cng nn phi ti li, do khngthun tin khi s dng.+ Tnh cng nng thp do mactenxit khng c hp kim ha, c tnh chng ram km. Tnhcng nng khng vt qu 200 - 250oC, do ch t nng sut thp, tc ct khng qu5m/min. Chnh iu ny hn ch s dng.

Cng dng: do nhng nhc im k trn nn rt t dng thp cacbon lm dao ct. Nu c sdng cng ch lm dao nh, hnh dng n gin vi nng sut thp hay bng tay. Dng cin hnh lm bng thp dng c cacbon l gia (hi t kh y cc iu kin va nu cch to vi mc CD120).Thp hp kim l nhm thp c thnh phn cacbon cao (~ 1% v cao hn) v c hp kim ha thp v vaphi vi c tnh c thm ti tt hn hay tnh chng mi mn cao.Loi c tnh thm ti tt l loi c hp kim ha thp bng 1%Cr (c th thm 1%Si) vi mcin hnh 90CrSi (TCVN 1823-76). Thnh phn hp kim nh vy c tc dng: - Ci thin tnh thm ti: mi trng ti du vn bo m cng HRC cao hn 60. Cng chnh

v vy c th lm dao nh vi hnh dng phc tp nh mi khoan, doa, tar, bn ren, lc ren,phay..

-Nng cao cht t tnh cng nng. Silic cng vi crm cn cn tr mnh qu trnh ram di250 - 300oC, v th c tnh cng nng n trn di 300oC, c th ct vi tc 10 m /min hayhn mt cht.90CrSi tng i r vi tnh nng lm vic tt hn thp cacbon nn c dng tng i phbin trong ch to cc loi dao ct k trn. Tuy nhin mc 90CrSi cng c nhc im m ngk nht l d thot cacbon khi nung (do c nhiu silic) nn phi ch bo v khi ti. Thp cti 840 - 860oC trong du, ram 150 - 200oC, cng HRC t trong khong 62 - 64.Loi c tnh chng mi mn cao l loi c cacbon rt cao (> 1,30%) vi 0,50%Cr v 4,0 -5,0%W mc CrW5 (140CrW5). Do c cacbon rt cao v nhiu vonfram l nguyn t to thnhcacbit mnh nn trong thp tn ti mt lng ln cacbit lm tng rt mnh tnh chng mi mn.Thp c tnh thm ti thp (do t crm v nhiu cacbit thc y chuyn bin thnh hn hp ferit -cacbit) nn mi trng ti l nc. cng HRC sau khi ti (800 - 820oC) ram (~ 150oC) tti 66 - 68, nn thp c dng lm dao tin, phay vi tc ct khng ln lm (do khng ctnh cng nng) ct sa cc phi cng (v d b mt trc cn ti).


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Thp lm dao c nng sut cao - thp gi

y l loi thp lm dao quan trng nht, tt nht, tha mn cao nht cc yu cu i vi vt liulm dao:

- Tc ct 35 - 80m/min (3 - 7 ln so vi loi trn).- Tnh chng mi mn v tui bn cao (8 - 10 ln).- thm ti c bit cao (ti thu vi tit din bt k).Thnh phn ha hc v tc dng ca cc nguyn tThp gi l tn gi Vit Nam (cc nc thng gi l thp ct nhanh: high speed steel - Anh,acier coupe rapide - Php, -Nga) ca loithp dng ct ti (c th ldo t ti, ti trong khng kh (gi) cng t c mactenxit cng nn ta thp c gi l thpgi) c nng sut ct cao c tng lng hai nguyn t vonfram v mlipen cao (> 10%) vlng kh ln crm (4%), ngoi ra cn c th c thm vanai v cban. Cc nguyn t trong thp gi c tc dng nh sau. Cacbon bin i trong gii hn kh rng t 0,70 n 1,50%, ha tan vo mactenxit v tothnh cacbit vi cc nguyn t to thnh cacbit mnh l W, Mo v c bit l V. Khi thm 1%Vphi a thm 0,10 - 0,15%C vo thp. C hai tc dng lm cho thp gi cng v lm tngmnh tnh chng mi mn.Crm c trong mi thp gi vi lng ging nhau, khong 4% (3,8 - 4,4%) c tc dng lm tngmnh thm ti. Nh tng lng (Cr + W + Mo) cao (> 15%) nn thp gi c kh nng t ti,ti thu vi tit din bt k v c th p dng ti phn cp.Vonfram l nguyn t hp kim quan trng nht khng nhng v c t l cao nht (6 - 18%) mchnh l do to ra tnh cng nng cao, nn cnng sut cao. L nguyn t to thnh cacbit mnh,vonfram ch yu nm dng Me6C hay Fe3W3C, khi nung nng n ha tan vo austenit nnsau khi ti mactenxit cha nhiu vonfram. Khi nung nng li hay khi ram Me6C ch tit ra khimactenxit khong 550 - 570oC, nn duy tr c cng cao sau khi ti n ti 600oC.Mlipen c dng thay th vonfram t li c t l qu cao. Mlipen c cu trc tinh thv tnh cht rt ging vonfram nn c th thay th cho nhau theo t l nguyn t l 1 : 1, song domlipen r hn li nh hn (vi khi lng ring 10,3 so vi 19,3g/cm3), v mt khi lng1%Mo thay th c gn 2%W, v th s thay th em li hiu qu kinh t cao (mc d khngci thin tnh ct gt).Vanai l nguyn t to thnh cacbit rt mnh. VC rt t ha tan vo austenit khi nung, trongthp n dng cc phn t cng, phn tn, lm tng tnh chng mi mn v gi cho ht nh khiti. Mi thp gi u c t nht 1%V, khi vt qu 2% tnh chng mi mn tng ln, song khngnn dng qu 5% v lm xu mnh tnh mi.Cban khng to thnh cacbit, n ch ha tan vo st dng dung dch rn v vi hm lngvt qu 5% tnh cng nng ca thp gi tng ln r rt. OCT ch c cc mc thp gi chahoc 5 hoc 10%Co, AISI c nhiu mc thp gi vi lng cban thay i trong phm vi 5 -12%. Nhc im ca thp gi cha cban l d b thot cacbon khi ti v khi cha qu nhiu(>10 - 12%) thp b gin.T chc t vi v nhit luynV t chc t vi, do thnh phn hp kim cao, 10 - 20% v cacbon cao nn thp gi thuc loilburit (khi ), mactenxit (khi thng ha, trng thi cung cp). Thp cha nhiu cacbit (15 -25%), sau khi c cacbit ch yu dng cng tinh lburit hnh xng c nn rt gin v philm nh chng bng bin dng nng (cn, rn). Thng thng phi c cung cp c tit dincng nh chng t c cn vi bin dng () mnh nn c cacbit nh mn v phn bu. cc nh my c kh thng tin hnh rn li cc phi ln ( > 40). Sau khi rn b bin


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cng, thp c qua khng hon ton 840 - 860oC t cng HB 241 - 269 vi t chcpeclit (dng xoocbit) + cacbit nh mn phn b u, c th chu gia cng ct c.Nhit luyn kt thc bng ti + ram quyt nh cng, tnh chng mi mn cao c bit l tnhcng nng theo yu cu.Ti l nguyn cng quyt nh tnh cng nng ca thp gi vi c im l nhit ti rt cao

(gn 1300oC) khong dao ng li kh hp (ch 10oC), khng cho php ti nhit thp hnhoc cao hn gii hn quy nh v:1) Khi nung thp hn, austenit cha bo ha W nng cao tnh cng nng: + Khi nung qu Ac1 (khong 850oC) trong thp gi mi c chuyn bin peclit thnh austenit, dovy ti 850 - 900oC ch t HRC 45 - 50 cha ct.+ Tip tc nng cao nhit , cacbit hp kim bt u ha tan v ha tan cng nhiu vo austenitlm pha ny cng giu nguyn t hp kim (v c cacbon) nh biu th hnh 5.13a. Ti 1000oC bo ha crm do Cr23C6 d ha tan hn c. VC hu nh khng tan vo austenit. CnFe3W3C (loi cacbit ch yu) bt u ha tan mnh trn 1150oC v ngay c ti gn 1300oCaustenit cng ch ha tan c 8%W.Nguyn l chn nhit ti ca thp gi l tn lng chn nhit ti cao austenit cha

nhiu vonfram nht mactenxit to thnh c tnh cng nng cao nht. Ti nhit ti vn cnkh nhiu cacbit Fe3W3C v ton b VC cha ha tan s cn tr ht pht trin, gi cho ht nhv lm tng tnh chng mi mn.

Hnh 5.13. ha tan ca cc nguyn t hp kim vo austenite ca thp gi (a) v t chc t vicathp gi sau khi ti (b).

2) Tuy nhin khi vt qu nhit quy nh, cacbit ha tan nhiu, ht li pht trin mnh, thpb gin, thm ch c trng hp bin ht b chy.V th ti sao cho thp gi t c tnh cng nng cao nht i hi phi t nhit cao mtcch kh chnh xc. Nu ch cn t cng cao (HRC > 60) th nhit ti ch cn hn 1000oCl .T chc t vi ca thp gi sau khi ti ng (hnh 5.13b) gm mactenxit giu vonfram, austenitd (30%) v cacbit d (15 - 20%) vi cng HRC khong 62, song cha phi l cao nht.Cacbit d c nh hng tt n tnh chng mi mn song lng ln austenit d lm gim cng ca thp ti vi n v HRC. S d austenit d nhiu nh vy v ti nhit cao, austenit
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c hp kim ha cao mt mt to nn mactenxit cng nng cao mt khc lm h thp im Mf.Do austenit qu ngui c tnh n nh rt cao nn c th p dng nhiu cch ti cho thp gi. - Ti trong du nng (> 60oC) p dng cho cc dao c hnh dng n gin. - Ti phn cp trong muinng chy (400 - 600oC) vi thi gian gi nhit 3 - 5min, p dng chocc dao nh, hnh dng phc tp, c yu cu cong vnh rt nh nh mi khoan.

- Gia cng lnh kh austenit d sau khi ti, p dng khi cn n nh kch thc. - Ti trong khng kh (t ti) tuy vn t cng cao i vi dao mng, song c th cho cng khng u ( cng thp hn ch dy), d b xy ha, thot cacbon b mt, tit cacbitkhi austenit lm gim tnh cng nng, nn rt t dng.- Ti ng nhit ra bainit (gi 240 - 280oC hng h) cho bin dng nh nht song cng HRCkhng qu 60, nng sut thp, t dng.Ram thp gi l nhm lm mt ng sut bn trong, kh b austenite d, tng cng ( cngHRC tng thm 2 - 3 n v, hin tng ny c gi l cng th hai). Thp gi c ram 2 -4 ln (thng l 3) 550 - 570oC, mi ln trong 1h. Chuyn bin xy ra nh sau. Khi nung ti550oC cacbit vonfram Fe3W3C nh mn mi bt u tit ra khi dung dch rn lm austenitngho hp kim i, nng cao im Ms v lm gimng sut nn ln austenit d lm pha ny

chuyn bin thnh mactenxit, cng tng ln. Sau mi ln ram ch c mt t l nht nh(khong 50 - 75%) austenit d chuyn bin v li gy ra ng sut bn trong mi, nn sau phiram thm 1 - 3 ln na qu trnh xy ra c hon ton hn.

Hnh 5.14. Quy trnh ti + ram thp gi 80W18Cr4V (P18, T1, SKH2) cng nh s thay i calng austenit d v cng HRC.

Ch ti + ram thp gi in hnh cng nh s bin i lng austenit d v cng ctrnh by hnh 5.14. nng cao kh nng ct ca thp gi, sau khi mi c th c ha - nhit luyn: thm cacbon -nit nhit thp (550 - 570oC) th lng trong 2 - 3h to ra lp thm mng c cng rt cao(HRC ~ 70) tui bn c th tng 50% song hi gin, ch thch hp vi loi dao t va p.
https://sites.google.com/site/truongvanchinhvatlieucokhi/home/gang-va-thep-1/thep/thep-dung-cu/thep-lam-dung-cu-cat/thep-lam-dao-co-nang-suat-cao---thep-gio/110.bmp?attredirects=0


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Cc mc v cng dngTCVN cha quy nh cc mc thp gi. Bng 5.7 gii thiu bn trong s cc loi thp githng gp ca Nga, M v Nht.Thp gi vi nng sut thng l loi c tnh cng nng n 615 - 620oC, loi khng cha hay

cha rt t cban v c < 2% vanai, gm cc k hiu nh 80W18Cr4V (P18, T1, SKH2) v85W6Mo5Cr4V2 (P6M5, M2, SKH51). Hin nay loi k hiu sau c a chung v cha tvonfram

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