mil-h-6875h heat treatment of steel

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~NOT MEASUREMENT SENSITIM L-H-6875H1 March 1989SUPERSEDI NGML-H-6875G16 September 1983

MLITARY SPECI FI CATI ONHEAT TREATMENT OF STEEL, PROCESS FOR

Thi s specl f l cat l on i s approved for useby al l Departments and Agenci es of theDepartment of Defense.1. SCOPE1. 1 Scope. Thi s spec fl catl on covers the requi rements for heat- treatmentfour cl asses of steel (see 1. 2) and the requi rements for furnace equi pment, teprocedures and i nformati on for heat- treati ng procedures, heat- treati ngtemperatures and mater ial (see 6. 11) test procedures. I t i s appl i cabl e to al lheat treatment of parts and to onl y the heat treatment of ml l products whi chcoul d af fect I t s fabr icab l ty or the proper ti es of par ts. Thi s speci fi cati onal so descri bes procedures whi ch, when fol l owed, w 1l produce the desi redpropert ies and mater ial qual i t l es w thi n the l i mtat i ons of the respect i veal l oys tabul ated I n Tabl es IA, IB, IC and ID. A11OYS other than thosespeci f i cal l y covered herei n may be heat treated usi ng al l appl i cabl erequi rements of thi s speci fi cati on.1.1.1 Li mtat ions. Unl ess otherwse specl f l ed, thi s speci f i cat i on i s notappl i cabl e to heati ng or to i ntermedi ate (non-f i nal ) heat treatment, of rawmateri al , e. g. for hot worki ng. Processes not covered I ncl ude del i beratesurface heat- treati ng and spectal tzed heat- treati ng, such as inductionhardeni ng, fl ame hardeni ng, carburi zl ng, nl tri di ng; however, this specificationmay be referenced for equi pment and control s. Austemperl ng, ausbay quenchi ngand martemperl ng may be used when speci f i ed by the cogni zant engtneer ngorgani zati on.1. 2 Cl assi f i cat i on. Steel s covered by thi s speci f i cat i on are cl assi f i edi nto the fol l ow ng four cl asses. Unl ess otherw se speci fi ed, the process andequi pment requi rements I n thi s speci f i cat i on refer to al l cl asses of steeltabul ated I n Tabl es I A, IB, IC and ID, respecti vel y.

Cl ass A - Carbon and l ow al l oy steelCl ass B - Martensl ti c corrosi onresi stant steelCl ass C - Austeni tl c corrosi onresi stant steelCl ass D - Prectpi tatl on- hardeni ng and maragi ng steel

8enef l cl al comments (recommendati ons, addi ti ons, del etl ons) and any perti nentdata With may be of use in improving this document should be addressed to:Systems Engi neeri ng and Standardi zati on Department (Code 53), Naval Ai rEngi neeri ng Center, Lakehurst , NJ 08733-5100, by usi ng the sel f- addressedStandardi zati on Document Improvement Proposal (DD Form 1426) appeari ng at theend of thi s document or by letter.AMSCN/A FSC 95GPDI STRI BUTION ~TATEMFN~ A Approved for publ i c r r?l ease; di st ri but ion Is unl i m. =. .- - - - - -

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?-. APPLI CABLE DOCUMENTS2. 1 Government documents.2. 1. 1 Speci fi cati ons. The fol l ow ng specdocument to the extent specof these documents shal i beDefense I ndex of Specl fl catci ted i n the ~cfl tc:tat?on.

SPECI FI CATIONSFederal

ficatlons, form a part of thi sfi ed nerein. Unl ~ss otherw se speci fi ed, the issuesthose l i sted In the i ssue of the Department ofons and Standards 0001SS) and suppl ement thereto,

QQ-N- 290 - Ni ckel Pl ati ng (El ectropl ated)M l ~tary

ML- C- 14550 - Copper Pl ati ng, (El ectrodeposl ted).(Unl ess otherw se I ndi cated, copi es of federal and ml l tary specl f l cat l ons,standards. and handbooks are avatl abl e f rom the Naval Publ l catl ons and FormsCenter, (ATTN: NPODS), 5801 Tabor Avenue, Phi 2. 2 Non-Government publ i cati ons. The fol thi s document to the extent speci fi ed herei n.i ssues of the documentsthe DoDI SS ci ted i n thedocuments not l l sted i nsol i ci tati on.AMERI CAN SOCI ETY FOR

which are DoD adoptedsol i ci tati on. Unl ess

adel phl a, PA 19120-5099).ow ng documents form a part ofUnl ess otherw se specl fl ed, theare those l l st ed In the I ssue ofotherw se specl f l ed, the I ssues ofthe DoDI SS are the I ssues of the documents c ted \ n the

TESTI NG AND MATERI ALS (ASTMASTM A 262 - Detecti ng Susceptlbillty to Intergranular Attack I n Austenl tl cStai nl ess Steel s.ASTM A 370 - Mechani cal Testi ng of Steel Products, Methods andDefi ni ti ons for.ASTM C 848 - Young s Modul us, Shear Modul us, and Poi sson s Rat o forCeramc Nhl tewares by Resonance, Test Method for.ASTM D 3520 - Test Method for Quenchi ng Ti me of Heat Treati ng Fl uI ds(Magneti c Quenchometer Test)ASTM E 3 - Metal l ographi c Specimens, preParat~On of .ASTM E 8 - Tensi on- Tekt l ng of Metal l l c Materi al s.ASTM E 10 - Brl nel l Hardness of Metal l i c Materi al s.ASTM E 18 - Rockwel l Hardness and Rockwel l Superf l cMetal l i c Materi al s.ASTM E 384 - Mcrohardness of Materi al s.(Appl l catl on forTesti ng and Materl a

al Hardness of

copi es shoul d be addressed to the Amer can Soci ety fors, 1916 Race Street, Phi l adel phi a, PA I 9103. )



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Soci ety of Automoti ve Engi neers (SAE)MIS 2418 - Copper Pl ati ngAMS 2424 - Ni ckel Pl ati ng, Low Stressed Deposi tAMS 2750 - Pyromety.AMS 2759 - Heat Treatment of Steel Parts, General Requi rementsAMS 2759i 3 - Heat Treatment of Preci pi tati on Hardeni ng Corrosi onRes~stant and Maragl ng Steel Parts

(Appl l catl on for copi es shoul d be addressed to SAE, 400 Commonweal th Dri ve,14arrendal e, PA 15096. )(Nongovernment standards and other publ i cati ons are normal l y avai l abl e fromthe organi zati ons whi ch prepare or wh~ch di stri bute the documents. Thesedocuments al so may be avai l abl e I n or through I l brarl es or other I nformati onalservi ces).2.3 Order of precedence. In the event of a conf l l ct between the text of

thi s document and the references ci ted herei n except for associ ated detai ldocument, speci f i cat i on sheets or MS standards, the text of thi s specl f l cat l ontakes precedence. Nothi ng i n thi s speci fi cati on, however, supersedes appl i cabl el aws and regul ati ons unl ess a specl fl c exempti on has been obtai ned.2.3.1 Order of precedence for ml l products. In the event of a conflictbetween the requi rements of thi s document and specl fl catl ons for ml l productswhi ch reference i t , the ml l product speci f cat l on shal l take precedence.3. REQUIREMENTS3. 1 Equi pment.3. 1. 1 Furnace medi a and protecti ve coati ngs.3.1.1.1 Atmosphere for Cl asses A, 8, C and D steel par ts. The gaseousmedi um for heat treat ing Cl asses A, B, C and D steel parts above 1250eF shal l beai r/ products of combusti on, argon, hel i um hydrogen, ni trogen, or bl ends ofthese gases, vacuum exothermc, endothermc, ni trogen based, or di ssoci atedammon a conformng to the requi rements bel ow Suppl ementary protecti vecoati ngs, i n accordance w th 3. 3. 1. 3, may be used where necessary.Atmosphere Cl ass A ~1 Cl ass B~/ Cl ass C ~/ Cl ass D 1/Ai r/ Products x gl x g/ x xof Combusti onArgon j l x x x xHel i um j / x x x xHydrogen ~1 x x 7/ x x ~/

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Ni trogen ~1 gi x gl xVacuum x xExothermc ~/ x xN~trogen based orendothermc J I x f l / xDi ssoci atedAmmoni a ~/ $/ No No

x - Denotes atmosphere acceptabl e forsteel w th or w thout I l tnl tat ions.

x Nox xx NoNo No

x NOuse on that desi gnated cl ass of

Unl ess otherw se spec~f i ed, an ai r/ product of combusti on atmosphereshal l be l i mted to preci pi tat i on hardeni ng, temperi ng, stressrel l evl ng and 1400F transformati on treatments. An ai r/ product ofcombusti on atmosphere may be used for treatment above 1400F forCl asses A and B mater ial whi ch w l l have a mnl mum of 0.020 i nch metalremoved from al l surfaces after heat treatment or whi ch have beenprotected by el ectropl ates.Dew poi nt shal l be not hi gher than -40F at the exi t of the worki ngzone.

Atmosphere shal l be refi ned or bl ended to avoi d a change I n carboncontent at the sur face of the mater ial as specl f l ed In 3.3.3. A productof combusti on at - 40F maxi mum dew poi nt (e. g. endothermc) may be usedfor cl ass A mater al wh~ch al l ows 0. 003 I nch maxi mum parti aldecarbur zatl on at the surface. Exothermc atmosphere permssi bl e onl yfor heat t reatment of cl ass A ml l products.Acceptabl e up to 1950F.Ni trogen atmosphere does not i ncl ude ni trogen from di ssoci ated ammoni aOnl y acceptabl e when tempered at 1000oF or above. Acceptabl e foranneal i ng.Cl ass A steel s may be f i ne grai n copper pl ated 0.002 to 0.005 Inchthi ck I n accordance w th ML-C-14550 or AMS 2418 or ni ckel pl ated perAUS 2424 or QQ-N-290 or equi val ent as a suppl ementary surfaceprotecti on. Other suppl ementary protecti ve coati ngs may be used I fapproved by the cogni zant engi neeri ng organi zati on.Permssi bl e onl y for anneal l ng of ml l products provi di ng resi dualammoni a at the outl et of the generator does not exceed 15 ppm



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3. 1. 1. 2 AtrnosRheres for ml l products. Furnaces for ml l products shal l besuppl l ed w th gases of a consi stent anal ysi s such that the product meets therequi rements of the appropri ate materi al speci f~catfon. Furnaces, gases, andgas generators shal l be control l ed. Ducts and worki ng zones shal l be seal ed toprevent contamnati on by outsi de gases. Vacuum furnaces shal l have a cal i bratedrecordi ng i nstrument for sensi ng the vacuum I n the vacuum chamber. Al latmosphere furnaces and gas suppl y l i nes shal l be purged w th the desi gnated andapproved atmosphere gas for the speci f i c steel to be heat treated.3.1.1.3 Salt baths. Salt baths may be used for the heat treatment ofCl asses A and 6steel s. Sal t bat hs shal l be t est ed Inl t l al l y and at l east onceeach week and shal l be adj usted to assure that par t sur faces shal l be f ree f romgeneral corrosi on, carburi zati on and decarburl zatl on or I ntergranul ar attack I nexcess of l l mts specl f l ed In 3.3.3. Addi t ves used for adj ustments shal l bel i mted to sal ts i n bath and rect i f i ers recommended by the sal t manufacturer.3. 1. 1. 4 Temperature uni formty. The desi gn and constructi on of heat ngequi pment shal l be such that the temperature at any poi nt i n the furnace worki ngzone or work l oad shal l compl y w th AMS 2750.3. 1. 1. 5 Temperature range and set temperature. The set temperature on thefurnace control I nstrument shal l be such that the l oad temperature fal l s w thl nthe spec f l ed range, taki ng fnto account the temperature uni formty of thefurnace. In conti nuous furnaces used to anneal and normal i ze ml l products, athermal head may be used. The temperature of the ml l product shal l not exceedthe maximum processi ng temperature.

3. 1. 2 Pyrometry and furnace temperature control . The requi rements andprocedures for control and test i ng of furnaces, ovens, sal t baths, vacuumfurnaces, refri gerati on equi pment and al l i ed pyrometri c equi pment used for heattreatment shal l be I n accordance w th AMS 2750 and the appendi x thereto (see4. 2. 1 and 4. 2. 2). Equi pment whi ch cannot be control l ed and tested i n accordancew th AMS 2750 shal l be control l ed and tested as di rected by the cogni zantengi neeri ng organi zati on.

3. 1. 3 Quenchi ng equi pment.3. 1. 3. 1 Quench baths. Quench bathsmateri al , provi de for adequate ci rcul at shal l permt compl ete Immersi on ofon of the media or agl t at on ofmateri al , provi de a means for i ndi cati ng the temperature of the medi a and forcool l ng and heati ng, as appl i cabl e. Baths shal l be adequate to produce therequfred properti es I n the most massi ve materi al to be quenched.3. 1. 3. 1. 1 Oi l - quenchi ng baths. The ol l - quenchi ng medi um shal l be between6C@F and 160F at the begi nni ng of the quenchi ng operati on and shal l not

exceed 2000F at any ti me duri ng the quenchi ng operati on, unl ess otherw seapproved by the cogni zant engi neeri ng organi zati on. The temperature of the oi lquenchi ng medi a shal l not exceed the manufacturers recommended operati ng range.Quench oi l useo i n i ntegrai quench vacuum furnace systems, where the quenchchamber I s bel ow atmospheri c pressure, shal l be vacuum degassed at approxi matel ythe maxi mum recommended temperature for the quenchant I ni ti al l y and aft er eachmaj or addi t ion of oi l .

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s. ~. ~, l , z A~ueo~ po~ymer ~uenc~ nts Aqueous pol ymer quenchants may beused as permtted I n Tabl es IA through ID. The temperature of the aqueouspol ymer quenchant baths shal l not exceed the manufacturers recommended operati ngrange. These baths shall also be adequately circulated to assure homogenei ty ofthe aqueous pol ymer quenchant medi a.3. 1. 3. 1. 3 Quenchi ng from sal t bath furnaces. Hater- quenchi ng baths empl oyedi n cool i ng steel parts whi ch have been heated i n sal t-bath furnaces shoul d beprovi ded ti i than ~nfl ow of fresh water to prevent a concentrat i on of di ssol vedsal ts i n the tanks. Pol ymer quenchi ng baths when used i n conj unct i on w th sal tbath furnaces shal l be moni tored weekl y so that the sal t content of the bathshal l not exceed 62 by wei ght of the bath. Al l sal t resi dues shal l be removedfrom parts processed I n sal t-bath furnaces or quenched I n bri ne, duri ng ori mmedi atel y fol l ow ng quenchi ng.3. 1. 3. 1. 4 Al ternati ve Quenchants. In l i eu of the stated methods i n Tabl esIA through ID, steam ai r ,water sprays, i nert gases, pol ymers, mol ten sal ts orother commerci al quenchi ng medi a or processes may be used when approved by the

cogni zant engi neeri ng organi zati on, provl dfng equi val ence w th respect tomechani cal properti es and corrosi on resi stance, as appl i cabl e to the materi aland I ts appl i cati on, can be substanti ated. Equi val ence tests shal l be asspec f l ed by the cogni zant engi neeri ng organi zati on. bl hereai r quenchi ng i spermtted I n the Tabl es I A- I D, argon and hel l um may be used; other I nert gasesmay be substi tuted when approved by the cogni zant engi neeri ng organ zatl on.3. 1. 3. 2 Locati on of quenchi ng equi pment. Quenchi ng equi pment shal l bel ocated In such a manner and handl i ng faci l i t ies shal l funct ion w th suf f i ci entspeed to prevent the I nl t l at \on of transformat i on or sensi t i zat i on pr ior toquenchi ng.3. 1. 4 Mscel l aneous equi pment. Sui tabl e j i gs, f i xtures, trays, hangers,

racks, vent i l ators, and so on, shal l be empl oyed as necessary for the properhandl l ng of the work and for mai ntenance of the maj or I tems of equi pment. Theuse of heat -t reat i ng f xtures or f txture mater ial s where the contact w th orproxi mty to the materi al coul d contamnate the materi al reduce the heati ng,cool i ng or quenchi ng rates to l ess than requi red for compl ete transformati on orthrough-hardeni ng of the materi al shal l not be permtted.3.1.5 Cl eani ng Equi pment . Equi pment shal l be provi ded to cl ean mater ial I naccordance w th 3. 3. 1. 1. Hhere toxi c or harmul cl eaners are empl oyed, theyshal l be used I n compl i ance w th the appl i cabl e heal th and safety regul at i ons.3. 2 Thermal treatment.3.2.1 Rate of heat ing. Heat ing rates shal l be cont rol l ed to prevent damageto the mater ial (see 6.2) . Pre-heati ng at 1000F-1200F i s recommended beforeheati ng materi al above 13000F I f the materi al :

a. Has been previ ousl y hardened above Rc 35, or I S made of steel of0.50 (nomnal ) ~ercent carbon or over , orb. Has abrupt changes of sect i on, or sharp re-entrant angl es, orc. Hds been f i ni sh machi ned,

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3,2.2 Hardeni ng of Cl asses A and B mater ial . Cl asses A and B matertalshal l be hardened by austenl tl zl ng, quenchi ng and temperi ng.3.2.2.1 Pr ior condi t i on of Cl ass A steel par ts.3.2.2 .1.1 H-n mater ial . H- I I parts shal l be I n the anneal ed condl t l on,~ri or to hardeni ng, unl ess i t has been hot headed. HGt headed H-1: materi alshal l be anneal ed; pri or to hardeni ng, by furnace cool i ng from 1625F ~ 25F toat l east 1000CF, at a maxi mum rate of 50F per hour.3. 2. 2. 1. 2 52100 and 1095 materi al . Parts made of 52100 or 1095 steelshoul d be hardened from the spherol dl ze anneal ed condi ti on.3.2.2.1.3 Other Cl ass A parts. Parts made from other Cl ass A steel s to behardened and tempered to 220 ksi and above shal l be ei ther normal i zed,normal i zed and tempered, or normal i zed and sub-cri t i cal anneal ed, pri or toi ni ti al austeni tl zi ng. Parts that have been wel ded shal l be normal i zed, pri orto hardeni ng. Parts i dent~fi ed as damage tol erant, mai ntenance cri ti cal orfracture cri ti cal shal l be normal i zed, normal i zed and tempered or normal i zed andsubcri ti cal anneal ed, regardl ess of the strength to whi ch they are subsequentl yto be heat- treated.3. 2. 2. 2 Austenl tl z ng. The austen ti zl ng temperature shal l conform toTabl es I A and IB, as appl i cabl e. Part s shal l be hel d w thi n the specl f l edtemperature range for suff i ci ent ti me for the necessary transformati on anddi ffusi on to take pl ace. The recommended hol di ng ti mes at temperature arel i sted in Table 11A.3. 2. 2. 3 Quenchi ng. Materi al shal l be quenched from the austeni ti zi ngtemperature I n the quenchant speci fi ed I n Tabl es IA or 15, as appl ~cabl e.Materi al shal l be cool ed to or bel ow the quenchant temperature beforetemperi ng. Materi al shoul d be tempered w thi n two hours after quench or w thi n

two hours aft er reachi ng room temperature aft er col d treatment. If hardenedparts cannot be tempered w~thl n 2 hrs. of quenchi ng, they can be snap temperedfor one hour at 400F ~ 25F or as appropr iate to prevent cracki ng. M l lproducts shal l be quenched I n a manner consi stent w th commerci al practi ce whereTabl es IA 16 are not appl i cabl e. They shal l be cool ed suf f i ci ent l y andtempered w thi n a peri od of ti me adequate to prevent quench cracki ng orcondi ti ons del eteri ous to end product mechani cal properti es and corrosi onresi stance.3.2.2.4 Temperi ng. Materi al shal l be tempered I n accordance w th Tabl e111. I +4henmul tl pl e temperi ng I s used, materi al shal l be cool ed to roomtemperature between temperi ng treatments. The temperi ng temperatures l l sted I nTabl es IA or I B are recommended, unl ess fndi cated as mandatory by the fcotnotes.3.2.3 Hardeni ng Cl ass D steel . Cl ass D steel par ts shal l be hardened bypreci pi tati on heat- treatment of materi al whi ch has been ei ther sol ut~on-treated, austeni te condi t i oned, or col d worked. Cl ass D materi al i s normal l yacqui red i n the sol ut l on treated or sol ut l on treated and col d worked (I .e.Sprto theng temper) condi ti on. Thermal treatment for Cl ass D materi al shal l conformabl e ID. The agi ng temperature I n Tabl e ID may be adj usted hi gher to meetspeci fi ed tensi l e strength.



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3. 2. 4 Other thermal treatment.3.2.4.1 Normal i zi ng (appl i cabl e to Cl ass A steel onl y) . Normal i zi ng shal lbe accompl i shed by cool ~ng from Tabl e 1A temperatures I n ci rcul ated ai r or I n aci rcul ated protecti ve atmosphere. The recommended mni mum hol dl ng ti mes at

temperature are I l sted i n Tabl e 11A.3.2.4.2 Anneal i ng Cl asses A and B steel . Anneal l ng (ful l anneal i ng) ofCl asses A and B materi al shal l be accompl i shed I n accordance w th Tabl es 1A orIB, as appl i cabl e, and at suggested hol di ng ti mes i n Tabl e 11A. Sub-cri t i cal(part ial ) anneal l ng of Cl ass A mater ial shal l be accompl i shed by heat i ng to1200F-1250F and hol di ng i n that temperature range for two hours. Sub- crl tl calanneal i ng of Cl ass B materi al shal l be accompl i shed as specl f l ed I n Tabl es IBand 11A, as appl i cabl e.3.2.4.3 Anneal i ng Cl ass C steel . Anneal i ng of Cl ass C mater ial shal l beaccompl i shed as speci f i ed I n Tabl es I C and IIB, as appl i cabl e.3.2.4.4 St ress rel l evl ng. St ress rel i evi ng before hardeni ng of Cl ass Amateri al shal l be accompl i shed at any temperature between 1000 F and 1250F.Stress rel l evi ng after hardeni ng of Cl asses A and B mater ial shal l beaccompl i shed by heati ng to a maxi mum temperature of 50F bel ow the temperi ngtemperature. The recommended mni mum hol di ng ti mes at temperature are l i sted i nTabl e 11A. Stress rel i evi ng after hardeni ng i s prohi bi ted on parts whi ch havebeen peened or col d deformed; e.g. , rol l threaded. St ress rel i evi ng of Cl ass Cmateri al shal l be accompl i shed by ei ther heati ng to 875 ~ 25*F maxi mum or to1900F and rapi d cool i ng. Hardened cl ass D materi al shal l be stress rel i eved fora mni mum of one hour at 30F bel ow the agi ng temperature.3. 2. 5 Thermal treatment of ml l products. Unl ess otherw se speci f i ed i n thecontract or purchase order , processi ng of ml l products for whi ch the tabl es are

not appl i cabl e (e. g. raw materi al whi ch I s conti nuousl y heat-treated) shal l beanneal ed, austeni ti zed, quenched and tempered w th proven commerci al practi ces.Such practi ces shal l provtde equi val ence w th respect to end product mechani calproperti es, corrosi on resi stance, and mcrostructure, as requi red by theappl i cabl e materi al speci f i cat i on or engi neeri ng draw ng, and shal l besubstanti ated by tests or methods determned by the cogni zant engi neeri ngorgani zati on.3. 3 Process requi rements.3. 3. 1 General . The equi pment and processi ng techni ques empl oyed i n theheat-treatment of materi al shal l be ful l y capabl e of provi di ng the combi nati onof mechani cal properti es, corrosi on resi stance and mcrostructure i n the productas speci fi ed i n the appropri ate procurement document.3. 3. 1. 1 Cl eani ng. Materi al shal l be cl eaned pri or to heat-treatment asrequi red to remove contamnants and l eave no substance that coul d have adel eter ious ef f ect . Cl eani ng pr ior to heat t reatment of ml l product s i s notrequi red provi ded no surface condi t i on i s retai ned whi ch coul d have adel eter ious ef fect on the product .

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3.3.1.2 SM. Materi al shal l be racked or supported to al l ow ci rcul at i onof heati ng and quenchi ng medi a; to ensure exposure of surfaces to heati ng andquenchi ng medi a; and to mni mze warpage duri ng heati ng and quenchi ng.3.3.1.3 Approval for use of coat lnqs or pl at tngs. Except for copper orntckel Dl at inq as descr ibed i n footnote 8/ cf 3.1.1.1, a~proval f rom thecognizant engineering organi zat i on shal l -be obtai ned pri or to the use ofcoati ngs or pl ati ng for protecti on of surfaces duri ng heat-treatment.3. 3. 2. Mechani cal properti es. Parts made from Cl asses A and B steel s shal l ,after heat treatme~, be hardness tested I n accordance w th 4. 3. 2. 1. Hardnesstest data shal l be converted to equi val ent tensi l e strengths as specl f l ed byASTM A 370 (see 6.5) and the tensi l e strengths shal l conform to the desi gnrequi rements. Where a di spute exi sts i n the hardness test , the tensi l e testshal l be performed I n accordance w th ASTM E8 and the test results shall conformto the desi gn requi rements. Parts made from the fol l ow ng Cl ass D steel s shal lbe accompani ed through heat treatment by a mni mum of one tensi l e speci men ofthe same al l oy form and condi ti on: AM 350 (thi cker than . 015 I nch thi ckness), AM355, al l parts heat -t reated to an RH temper, parts that are re-sol utton

heat-treated, and al l parts made from 17-4 PH and 15-5 PH heat treated to H11OOand H1150 tempers. Tensi l e speci mens shal l be tested I n accordance w th 4. 3. 2. 2and shal l meet the requi rements of the appl i cabl e draw ng, ci esl gnspeci fi cati on,or materi al speci fi cati on. Al l other cl ass D steel par ts shal l be hardnesstested to the requi rements of AMS 2759 and MS 275913. Hhen speci f i ed i n thecontract or purchase order, a mni mum of one tensi l e speci men shal l accompanyanY Cl ass D Steel sol ut i on heat-treated, aged or both. Consi derati on shal l begi ven so that the tensi l e speci men Is representat ive of the par ts that are to bemanufactured, i . e. they are of sl m lar si ze and of the same al l oy form andcondi ti on.3.3.2.1 Permssl bl e var iat ions of Cl asses A and B steel f rom desi gn ul t lmatestrength. When a mni mum acceptabl e strength l evel and no maxi mum strength

l evel I s s~ecl f l ed by desi gn or the appl i cabl e mater ial speci f l cat lon, themaxi mum strength shai l be 20 ksi above the mnl mum except for Hy-Tuf and H-11steel s for whi ch a maxi mum strength of 30 ksl above the mnl mum I s acceptabl e.For 300 M steel , a maxi mum strength of 30 ksi above the mnl mum i s acceptabl e,provi ded the maxi mum tensi l e strength does not exceed 305 ksl .3. 3. 3 Surface contamnati on. When materi al i s hardened, normal i zed beforehardeni ng or i s rehardened after hardeni ng, the requi rements of 3. 3. 3. 1, 3. 3. 3. 2and 3.3.3.3 shal l appl y, These requi rements do not appl y provi ded I t I sdef i ni tel y known that suff i ci ent materi al w l l subsequentl y be removed toel tmnate any ci el eterl ous surface condi ti ons.3. 3. 3. 1 Decarburi zat i on of Cl asses A and B materi al . The heati ng medi um I n

furnaces used for normal i zi ng Cl ass A materi al and for hardeni ng Cl asses A and Bmateri al shal l be so control l ed as not to produce excessi ve decarburl zati on.For furnaces used to heat-treat materi al whose f i nal hardness w 1l be HRC 46(220 ksi ) and above, part i al decarbur~zati on shal l be j udged excessi ve I fgreater than 0, 003 i nch deep on any ffni sh machi ned surface. For furnaces usedto heat - t reat mater ial whose f i nal hardness w l l be l ess than t iRC46 (220 ksi )decarburi zatl on shal l be not greater than 0. 005 i nch deep on any f ni sh machi nedsurface. The extent of decarburl zat l on shal l be determned i n accordance w th4. 3. 3. 1. Any total decarburl zat i on at the surface i s not acceptabl e.9



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3. 2. 3. 2 Larburizatim and ni tri di ng. The heati ng med a i n furnaces used forheati ng materi al shal l be control l ed to precl ude carburl zat i on and ni tr i dl ng.The eyi ent O= c rburiz tlon and nl trl di ng shal l be determned I n accordance-w th4. 3, 3. 1,3. 3. 3. 3 Inte~granu?ar attack. The heati ng medi a I n furnaces used forheati ng materi al to temperatures above 125CJ oFshal l be control l ed to precl udeI ntergranul ar attack. exceedi ng 0, 0007 I nch on materi ai under 220 ksi and 0. 0005I nch on other materi al . l he depth of i ntergranul ar attack shal l be determnedby test i ng the speci mens as speci f i es i n 4. 3. 3. 2.3. 3. 4. Consi stency of quench ef fecti veness. Shal l be determned by test i ngeach quenchant i n each tank I ni t i al l y and quarter ly thereafter , by one of themethods I n 4. 4, and compari ng the resul ts w th those obtai ned previ ousl y by thesame method. The heat t reat ing fac l l ty shal l establ i sh cont rol I l mts for eachquenchi ng system If the resul ts I ndi cate that a quenchant i s outsi de theestabl i shed l i mts, cor rect i ve act i on shal l be taken and the test shal l berepeated to veri fy restorat i on of the pri or condi t i on.

4. QUALI TY ASSURANCE PROVI SI ONS4. 1 Responsi bi l i ty for i nspecti on. Unl ess otherw se speci f i ed I n thecontract or purchase order, the contractor i s responsi bl e for the performance ofal l I nspecti on requi rements (examnati ons and tests) as speci fi ed herei n.Except as otherw se speci f i ed I n the contract or purchase order, the contractormay use hi s own or any other faci l i t ies sui tabl e for the per formance of thei nspecti on requi rements spectfi ed herei n, unl ess di sapproved by the Government,The Government reserves the ri ght to perform any of the I nspecti ons set forth i nthi s speci fi cati on where such I nspecti ons are deemed necessary to ensuresuppl l es and servi ces conform to prescri bed requi rements.4. 1. 1 Responsi bl l l ty for compl i ance. Al l i tems shal l meet al l requi rementsof sect i on 3. The Inspect ion set for th In thi s speci f i cat ion shal l become apart of the contractor s overal l i nspect i on system or qual i ty program Theabsence of any I nspecti on requi rements I n the specl f l cat l on shal l not rel i evethe contractor of the responsi bi l i ty of ensur ing that al l products or suppl i essubmtted to the Government for acceptance compl y w th al l requi rements of thecontract. Sampl i ng i nspecti on, as part of manufacturi ng operati ons, I s anacceptabl e practi ce to ascertai n conformance to requi rements, however, thi s doesnot authori ze submssi on of known defecti ve matertal , ei ther I ndi cated oractual , nor does i t commt the Government to accept defecti ve materi al .4. 1. 2 Control records. Records of system accuracy tests, furnacetemperature surveys, cal i brati on of control and recordi ng I nstruments and date,

ti me, temperature, and quenchant used i n heat treat i ng mater ial shal l be on f i l eand avai l abl e for revi ew by contractors and Government representati ves for fi ve(5) years. In addl t l on heat treaters of f i nal parts shal l keep furnace recorderchar ts ?or f :ve (5) years.

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4. 1. 3 Noncompl i ance. If any test result fails to meet the requirementsspeci f i ed herei n, t he cause of f ai l ure shal l be determned. I f at tri butable toequi pment , repai r shal l be compl eted before the equi pment i S used foraddi ti onal processi ng. The qual i ty assurance organi zati on responsi bl e for theraw mater i al I n the case of m l ? processing, or f or part s In the case offi ni shed or sem- fi ni shed parts processi ng, shal l eval uate possi bl e effects ofthe def i ci ency on mater i al processed si nce the l ast successful test . Theeval uati on and correcti ve acti ons shal l be documented.

4. 2 Equi pment Cal i brati on and tests.4. 2. 1 Pyrometri c cal i brati on. Pyrometri c equi pment shal l be cal i brated I naccordance w th AMS 2750 and appendi x thereto (see 3. 1. 2).4. 2. 2 Test procedures for equi pment. Heat- treati ng equi pment shal l betested I n accordance w th AMS 2750 and appendi x thereto (see 3. 1. 2).4. 3 Test procedure for materl a~.4. 3. 1 Surface contamnati on tests. Each furnace used for any of thefol l ow ng treatments shal l be tested for conformance w th 3. 3. 3: normal i zi ngand austenl t l z ng of cl asses A and B mater ial , and sol utfon treat i ng andausteni te condi ti oni ng of cl ass D materi al . A furnace used excl usi vel y for heat- treatment of mater i al where al l contamnati on on that mater i al w l lsubsequentl y be removed need not be tested.4.3.1.1 Speci mens of Cl asses A and B mater ial , except H- I I , shal l be testedei ther i n the tempered or i n the untempered condl t l on at the opt i on of thecogni zant engi neeri ng organi zati on. H-n speci mens and speci mens of Cl ass Dmateri al shal l be tested after compl eti on of heat treatment. Speci mens shal l bemetal l ographi cal l y prepared per 4. 3. 3 and tested per 4. 3. 3. 1 and 4. 3. 3. 2 for

conformance to 3. 3. 3.4.3.1.2 For mater ial made from Cl ass A steel s w th a f i nal st rength of220ksi or hardness of Rc 46 or hi gher , at l east one speci men of the same al l oyshal l be heat t reated w th each l oad. For materi al that I s damage tol erant orf racture cr i t i cal , a mni mum of one speci men of the same al l oy shal l beheat - t reated w th each l oad regardl ess of the f i nal st rength or hardness. I fsuch mater ial i s reheat- treated, the ori gi nal speci men, or a port ion of theori gi nal speci men must accompany the materi al and be tested aft er thereheat- treatment i n accordance w th 3. 3. 3.4. 3. 1. 3 For l ower strength materi al , under 220 ksl . made from Cl ass A steel sand mater i al made from Cl asses B and D steel s, at l east one speci men shal l be

tested In accordance w th 3.3.3 as fol l ows w th the f i r st l oad of each al l oygroup as defi ned i n 4. 3, 1. 3. 1:a. Each month for atmosphere furnaces,b. Each week for sal t baths, and

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c. Each occurrence that purge cycl es are run for Cl ass Osteel as requi red by 3. 1.1. 2.4.3.1 .3.1 For the purposes of the monthl y and weekl y tests of 4.3.1.3,steel s w thl n the fol l ow ng groups may be consi dered to be the same al l oy:

a. Cl ass A steel s of 0.45 percent carbon and l ower .b. Cl ass A steel s of above 0. 45 percent carbon.c. Cl ass B steel s: 403, 410 and 416.d. Cl ass D steel s: 17-4 PH, 15-5 PH and PH 13-8 Mo.e. Cl ass D steel s: 17-7 PH, PH 15-7 Mo and PH 14-8 Mo.

4. 3. 2 Mechani cal Properti es.4.3.2,1 Hardness test of heat treated matertal made from Cl asses A, B and Dsteel s. The frequency of hardness testi ng for materi al whi ch has been fi nalheat- treated, shal l be I n accordance w th the sampl i ng requi rements of At4S2759. The test i ng shal l be performed I n the heavi est sect i on whi ch 1s sui tabl eand not detr imental to the functi on of the materi al . bl henheat treati ngstandard components such as nuts and bol ts or ml l products, the sampl i ng andhardness test reaul rements of the apc)l i cabl e conmonent and steel speci fi cati onsshal l take precedence.4.3,2.2 Tensi l e Tests, Hhere specl f l ed, speci mens of the same al l oy formand condl t l on w thi n cl ass D steel , heat treated and aged i n the same furnacecharge, shal l be tensi on tested i n accordance w th ASTM E 8. The test ing shaencompass, as a mnl mum one speci men representati ve of the part. 14henspecl f l ed, Cl asses A and B materi al shal l be sl m lar l y tensi on tested Inaccordance w th ASTM E 8. Hhen test i ng of a si ze representat i ve of the parti mpracti cal because of I nabl l l ty to make a representati ve speci men suff i ci entsmal l whi l e st i l l usi ng an accepted tensi l e speci men or excessi ve i n cost duewasted steel from a bl ank whi ch I s much l arger than that needed to produce astandard si ze tensi l e speci men, then a sam~l e suff i ci ent to accommodate one

sYto

standard tensi l e bar I naccordance w th ASTM E-8 w l l be heat treated and agedw th the furnace charge and consi dered to be a representati ve sampl e.4. 3. 3 Metal l oqraphi c tests. Specimens shal l be metal l ographl cal l y preparedI n accordance w th ASTM E 3. Determnati on of decarburl zatl on, carburi zatl on,nl t r idl ng and I ntergranul ar attack shal l be I n accordance w th 4.3.3.1 and4. 3. 3. 2.4. 3. 3. 1 Determnati on of surface chemstry changes. The depth ofdecarburi zatl on shal l be determned by maki ng a mcrohardness traverse per ASTME 384 usi ng at l east 250X magnl fl catl ~n and ~ecordi ng hardness versus depthbel ow surf ace. The boundary of the decarburl zat i on shal l be at the depth atwhi ch the hardness ri ses to the equi val ent of 20 poi nts Knoop bel ow the corehardness. I n addi ti on, the mcrohardness and mcrostructure shal l show noevi dence of carburl zatl on or n tr di ng. The traverse shal l show no evi dence ofI ncreased hardness at the surface as I ndi cated by (20) poi nts knoop orequi val ent above the core hardness.

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4. 3, 3. 2 I ntergranul ar attack. I ntergranul ar oxl dat~on of Cl ass A materi alshal l be determned by tnetal l ographlcal l y etchi ng speci mens of these steel s for7 - 20 mnutes In a f reshl y prepared bol l l ng sol ut ion consi st ing of 16 grams ofchromic acid and 80 grams of sodi um hydroxi de I n 145 ml l l l l ters of water .I ntergranul ar oxl datl on of Cl asses 8 and O materi al shal l be determnedmetal l ographi cal l y by etchi ng speci mens of these steel s for 1 - 2 mnutes In af reshl y prepared sol ut i on consi st ing of 1 gram of pi cr i c aci d In 5 ml l i l i t er sof hydrochl or ic aci d and 100 ml l l l i ters of ethanol . Al ternate etchants may beused provi ded thei r eff ecti veness w th respect to reveal l ng i ntergranul ar attacki s substanti ated.4. 4 Test procedures for quench rate control .4. 4. 1 Comparati ve cool i ng curve eval uati on. Vari at on i n the quenchi ngeff ecti veness of an oi l , water, or aqueous pol ymer quenchant bath may bemoni tored usi ng a sui tabl e cool i ng curve eval uati on procedure approved by thecogni zant engi neeri ng organl zat on.4. 4, 2 Maqnetl c quenchometer. Var ati on i n the quenchi ng eff ecti veness of

011 quenchi ng medi a may be moni tored usi ng a magneti c quenchometer test asdescri bed i n ASTM D3520.4. 4ef fectfol l ow4. 4Heat ow thi n

3 Hot w re test . Hhen thi s test i s used var iat i on In the quenchi ngveness of oi l quenchi ng medi a shal l be performed i n accordance w th theri g.3. 1 Procedure. Pour 150 m of otl to be tested I n cl ean 250 m beaker.1 to 60C by pl aci ng thermometer i n oi l and heat ing on a hot pl ate (heat5 mnutes). Pl ace precut w re (No. 28 Cupron- 55%Copper, 45% Nl ckel -w re cut I n 2.5 i nch l engths) i n cl amps such that the w re I s st rai ght andtaut. Hi res that have been ki nked or I n any way f l attened shoul d not be used.Uhen oi l i s at 60 ~2C, remove thermometer and transfer beaker to Hot Y/ i re

Tester setup. The Hot bl l reTester consi sts of a dual spr ing cl amp for hol di ngthe w re (1. 0 i nch of ef f ect i ve w re l ength) , el ect ri cal l eads t o t he cont rolbox whi ch suppl l es 60 cycl e A.C. current to each cl amp. The current I s stead~l yI ncreased from O to 35 amperes i n 4. 5 seconds usi ng sol l d state cl r cul t ry w t h athyrl stor (tr l ac) opti cal l y coupl ed to a stai r case generator. Maxi mum currentthrough the w re i s di spl ayed on a LED Dl gl tal Read Out . I mmedi atel y i mmersecl amped w re and hol der I n oi l and turn on contro?s. Readi ng i s compl etedw~th~n 10 seconds. The maxi mum current f l ow I s read from the LED dl gl tal readout and recorded. Fresh w re can be pl aced I n cl amps and test repeated asqui ckl y as mani pul ati ons can be performed. Tests must be performed I ntr i pl i cate and the 3 resul ts averaged. Readi ngs shoul d fal l w thl n ~0.5 ampsto be val l d. Otherw se test shoul d be repeated.4. 4. 4 Mechani cal properti es test of al l quenchi ng medi a Shal l beperformed by quenchi ng speci mens of al l oy steel , of appropri ate hardenabl l l tyand di mensi ons and testi ng a mechani cal property ( e. g. , hardness, strength,modul us) whi ch vari es directly or inversely with the effectiveness of quench.The speci fi c test shal l veri fy quenchant eff ecti veness by compari ng the testedmechani cal property resul ts w th those propert i es l i sted \ n the appl i cabl edraw ng or materi al speci fi cati on.



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4. 4. 4. 1 Speci men sel ectl on for mechani cal properti es test of al l quenchl n~medi a. Sel ecti on of the specimen di mensi ons/ hardenabl l l ty combi nati on shoul d be_ at achtevi ng approxi matel y ful l hardeni ng (e.g. 95%martensl te) on thesurface and si gni f i cantl y l ess hardeni ng (e. g. , l ess than 5(I Zmartens te Pl uSbai ni te) at the center.4. 4. 4. 2 Temperi ng speci men for machi ni ng. Specimensmay be temperedl i ght l y (e. g, , at 500F (260C)) aft er quenchi ng to faci l i tate machl nl ng.4. 4. 4. 3 Testfng area. Tests may be performed on (1) surface, sub-surface,md- radi us or center materi al , or ( 2) the ent i r e sect i on or any port i on of i t .4. 4. 4. 4 Conformance of testi ng. Hardness testi ng shal l conform to ASTM E18for Rockwel l hardness testi na and ASTM E1O for Brl nel l hardness testi ng.Tensi l e testi ng shal l confor~ to ASTM E8. Modul us testi ng sha(resonant f requency) method slml ar to ASTM C848.5. PACKAGI NG - Thi s sect ion Is not appl i cabl e to thi s spec6. NOTES

1 be by-a dynamc

f l cati on.

6. 1 I ntended use. Heat- treati ng processes are used to obtai n desi redproper ti es w thi n the l i mtat ion of the respect ive cl asses of steel ( see 1.2) .6. 2 Rate of heati nq. kl hent he st eel , si ze, desi gn of parts, or t heoperat ng condi ti ons are such that no cracki ng or excessi ve warpage resul ts, themateri al may be charged i nto the heat-treati ng furnace or bath at any desi redtemperature not exceedi ng the maxi mum temperature speci f i ed for the operati onand the materi al i nvol ved. I n conti nuous furnaces used to anneal and normal i zeml l products, a thermal head may be used. The temperature of the ml l productshal l not exceed the maxi mum processi ng temperature.6. 3 Hol di ng-ti me i nterval s and protecti ve coatfngs. The hol dl ng-ti mei nterval s I ndi cated by Tabl es 11A and 118 are approxi matel y correct for heati ngi n ai r , i n a gaseous atmosphere, or i n sal t baths. The proper t ime i nterval

wI1l vary w th the type of steel , capaci ty of heat ing el ements, and si ze ofcharge, as wel l as w th the thi ckness of the i ndi vi dual mater ial andprotecti ve coati ngs.6. 4 Shape i nfl uence. Much of the publ i shed l i terature and the data In thi sspeci f l cat~on refers to round speci mens of vari ous di ameters. I n order to usethe data successful l y on actual parts, I t 1s f i r st necessary to vi sual i ze theparts as si mpl e geometri c shapes such as rounds, hexagons, squares. Pl ates ortubes. These shapes can then be consi dered as the round si ze whi ch w1l l have

approxi matel y the same cool l ng rate as that of the si mpl e shape. Therel ati onshi p between the vari ous si mpl e shapes and the correspondi ng round si ze1s I ndi cated on Fi gure 1.6. 5 Hardness-tensi l e rel ati onshi p. The normal rel ati onshi p between thetensi l e st rength and hardness of carbon and l ow al l oy steel i s i ndi cated i n thehardness conversi on tabl e of ASTM A 370. The tabl e I s to be used as a gui de asthe rel at i onshi p i s not preci se.

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6.5.1 Narrow strength range (+ 5 ksi ) . Nhen a narrow range ~n strength i srequi red, tests to determne the rel ati onshi p between hardness anc strengthshoul d be made on the actual part. Hardness val ues shoul d be consi dered as theaverage val ue obtai ned by at l east three determnati ons, each of whi ch shoul dchecu w~thl n 2 poi nts Rockwel l , or 20 poi nts Br lnel l or Vthe other two val ues.6. 5. 2 Thi n-wal l ed tubi ng hardness tests. On rel at i veor parts whi ch cannot be f i rmy supported on the anvi l ofmethods wni ch measure the area of the i mpressi on (Vi ckersacceptabl e. Any process whi ch aff ects the surface, such i

ckers, or ei ther of.

y thi n-wal l ed tublngsthe test machi ne, onl yor Knoop) ares buff i ng and pl ati ng,or the presence of decarbur lzed or porous areas and hard spots w 1l af fect thehardness and the correspondi ng rel ati on between hardness and tensi l e strength.6. 6 Heati ng baths. Mater ial i nserted i n sal t baths shoul d be free froml l aul ds and coatl nas whi ch may subl l me or become aaseous and thereby s~l atter orexpl ode the conten~s of theheat- treati ng corrosi onres

recti f i ers have been added.steel , may carburl ze corrosand resi stance to corrosi on

b~th. Precauti ons sh~ul d be taken when- stant steel I n sal t baths to whi ch carbonaceousSuch baths, whi l e neutral to carbon and l ow al l oyon-resi stant steel and l ower the I mpact properti es

6.7 Ver l f l cat ion of heat - t reat ing procedures. Hardness I s not the onl ycri teri on of sati sfactory heat- treatment si nce excessi vel y coarsened grai ns,over- heated, or I mproperl y tempered steel may show adequate hardness, - but may bedef~c ent I n ducti l i ty and other mechani cal properti es. Parts are acceptabl eonl y when the requi rements of thi s speci fi cati on and appl i cabl e des~gnrequi rements are met.6. 8 Cl assi f i cat i on of strength. Al l references herei n to strength ortensi l e strength refer to ul t i mate tensi l e strength.6. 9 Hol dl ng at temperature. Hol di ng at temperature refers to materi alt{me at temperature.6. 10 Cl asses A and B fi ni sh machi ned surfaces. Hhen parts made f rom Cl assesA and B steel contai ni ng fi ni sh machi ned surfaces are normal i zed or rehardenedand these operat i ons are not i mmedi atel y before or after hardeni ng, i t i s themanufacturers responsi bi l i ty to assure that the combi ned effects of thetreatment meet the requi rements of 3. 3. 3. Fi ni sh machi ned surfaces are thosefrom whi ch l ess than 0.020 Inch (Cl ass A) and 0.010 I nch (Cl ass B) w1l lsubsequentl y be removed.

6.11 Defi nl tl ons of terms:6.11.1 Mater ial I ncl udes al l forms of steel products descr ibed w thl n thespeci f i cati on (ml l products and parts).6.11.2 Ml l product s def i ned herei n as a product whi ch I s commonl yproduced I n: f i ni shed form as pl ate, sheet , st ri p, bar , rod, and structuralshapes; sem- fi ni shed form as bl ooms, bi l l ets, sl abs and tube rounds, and wh~chare not suppl i ed i n heat treated form forgi ngs, casti ngs and extrusi ons.

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6. 11. 3 Part I s a rough machi ned or f i ni sh machi ned I ndl vl dual pi ece madefrom wrought or cast stock heat treated by the user duri ng the fabrl cat~onprocess, fo~ qual i f i cat i on of response to heat treatment, or any other operati onwhere achi evement of fi nal physi cal or mechani cal properti es i s i ntended.6. 11. 4. Cogni zant engi neeri ng organi zat i on i s the termappl l ed to theengi neeri ng organi zati on responsi bl e for the desi gn of the i tembei ng heattreated.6. 12 Al l requi rements for 431 stai nl ess steel have been del eted from thi sspeci f i cati on (see ML-S-18732) .6.13 Subj ect term (Key Nerd) l i st i ng

Anneal l ngAustenl t~z ngFurnace atmosphereHeat TreatmentNormal i zi ngPyrometryQuenchi ngSteel Al l oysTemperi ng6. 14 Changes from the previ ous draft. The margi ns of thi s speci f i cat i on aremarked w th asteri sks to i ndi cate where changes (addi ti ons, modl fl catl ons,correcti ons) from the previ ous draft were made.

Custodi ansArmy - MRNavy - ASAl r Force - 20Revi ew act v tl es:Army - AR, AV, EA, MNavy - OSA r Force - 82, 84, 99DLA - I S

Prepari ng acti vi ty:Navy - AS(Proj ect 95GP-0096)

User actl vl ti es:Army - AT

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ML-H-6875K

TABLE I C. Anneal l ng Procedure for Cl ass C (austeni t{c corrosi on-resl stant steel .

SAE I Anneal i ng treatment IAI SI orproducer sdes gnat\ on Heati ng F Cool i ng 16/201 and 1850 to Nater quench202 17/ 2050

302 and 1850 to ti di er quench303 17/ 2050I ,

304 I I 304L and 1850 to Hater quench308 17/ 2050 1I I t309 El 1900 to Nater quench2050310316 and I 1900 to Hater quench I316L 17/ 2050 I, I

321 l J / I Ai r or water quench347 and 13/ 1800 to Ai r or water quench348 2050

Footnotes to Tabl es I A, 16 and I C:~t For the purpose of thi s specl f l cat lon, normal tzl ng descri bes a metal -l urgi cal process rat her than a set of propert i es. Al l st eel s are ai rquenched f rom temperature range.~/ Furnace cool to 1000F or bel ow except furnace cool 4330V, 4335V to800F, 4640 to 750F, 4340 to 800F and 300M to 600F. Rate of furnacecool for al l oy steel s, except 4130, 8630, 4037 and 8735 shoul d be 50Fper hour or sl ower.j l Recommended subcri ti cal anneal temperature I s 1250F.

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ML-H-6875H

Footnotes to Tabl es I A, IB and IC - Conti nuedCool to- l OOF for 1 hour mni mum w thi n 2 hours after quenchi ng andbefore temperi ng,Steel al l oys l i sted are the more freuuent ones used. A11OYS not l l stedshoul d beI n generaI n genera

~eat treated as recommended by thei r manufacture~s.- for spr ing temper , temper at 700 - 800F for Rc 40-45.- for spr ing temper , temper at 725 - 900F for Rc 43-47.

For antl fr ctl on beari ngs, temper to Rc 58 to 65 at 300 - 450F.The fol l ow ng anneal l ng treatment for 52100 steel shoul d be used:

Heat to 1430F, hol d for 20 mnutes, and cm at cont rol l ed rates,as fol l ows:1430 to 1370F at a rate not to exceed 20F per hour,1370 to 1320F at a rate not to exceed 10F per hour .1320 to 1250F at a rate not to exceed 20F per hour.

Absence of val ues I ndi cates the respecfor th s tensi l e strength range.Temper 420 steel : 300F for Rc 52 rei n600F for Rc 48 mni mum

~ve steel I s not recommended

mum 400F for Rc 50 mni mum

Control l ed atmosphere quench I s opti onal for smal l parts. The quenchfor 440C shal l be fol l owed by ref r igerat ion to -1OOF or l ower for 2hours. Doubl e temper to remae retai ned austeni te.When stress rel l evi ng after wel dl ng i s specl ftecf , hol d for 1/ 2 hourmnl murnat temperature specl f l ed I n Tabl e XC or hol dl ng for 2 hoursat 1650F t 25F.a. 4340, 260 - 280 temperi ng must be between 425F and 500F.b. 300M and Hy Tuf - temperi ng temperature I s mandatory.Fi nal temperi ng shal l be at or above 1000F. No temperi ng temperatureshal l be l ess than that of previ ous temper nor more than 25F hi gherthan the previ ous temper.Other means of cool l ng permtted provi ded I t I s substanti ated by teststhat the rate I s rapi d enough to prevent carbi de precl pl tatl on.

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ML-H-6875H

Footnotes to Tabl es IA, 18 and I C - Conti nued17/

18/19/

20/21/

221231

Stress rel i evi ng of unstabi l i zed grades, except 304L and 316Lbetween 875 ~ 25F andstabi l i zed grades shouMul ti pl e cycl i c anneal

1500 F l s-prohi bi ted. Stress rel i evtng ofd be at 1650F for 1 hour.ng may be permtted to prevent grai n growth.

Si ze stabi l i ty may be enhanced by refri gerati on. Hhen requi red, cooto - 100oF for 1 hour w thi n 2 hours after quenchi ng andbefore temperi ng.Normal i zi ng I s not recommended practi ce for 52100 steel .Dupl ex anneal - hol d 4 hrs. ~ 0. 25 hrs. at 1250F ~25F, al r cool toroom temperature, then reheat to l 150~25F and hol d for 8 hrs ~0. 25hrs and al r cool to room temperature.Overage to faci l i tate machl nl ng by normal i zi ng pl us 1250F ~ 25*F fornot l ess t han 6 hrs. and al r cool .Mhen approved by the cogni zant engi neeri ng organtzatl on, parts may betempered I n 1000-10500F range when 135- 145 ksi tensi l e strength i srequi red provl dl ng the parts are not subj ect to substanti al i mpactl oadi ng or stress- corrosi on condi ti ons. Temperi ng these al l oys I n thrange I sted resul ts i n decreased i mpact strength and al so reducedcorrosi on resi stance. However, temperi ng i n thi s range i s someti mesnecessary to obtai n the strength and ducti l i ty requ red. Hhen approvby the purchaser, materi al may be tempered i n thi s range.



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TABLE 10. Heat- tr eatment procedure for Class D (preci pi tati on-hardeni ngand maraql ng) steel .~1 Treatment Ccmdl tl on:

A = Sol ut i onT= Transformati on at 1400FR, SR, SC = Transformati on at 1700 - 1750F, al so at -90 to - l OOFHC = Homogeni zat i on of cast i ng, 2100F, al r cool to bel ow 90F pri orto soluticm treatment.~1 For appl i cat ions where stress corrosi on cracki ng i s a possl bi l l ty, 17-4materi al shoul d be aged at the hi ghest temperature compati bl e w th thestrength requi rements and a temperature not l ower than 1000*F (wrought) ,935F (cast) and not l ess than four hours hol d t i me.j / Bri ng furnace charge to uni form temperature~/ For Sheet and St ri p, hol d 3 mnutes pl us 1 mnute for each 0. 01 I nchthi ckness.~f Hol d 90 mnutes mni mum for forgi ngs, bars, pl ates.$/ Hold 10 mnutes pl us 1 mnute for each 0.01 Inch thi ckness.~/ Hold 15 mnutes per i nch of thi ckness.~/ Hol d for a tl rnecommensurate w th thi ckness and heati ng equi pment andprocedure used.~/ Cool to bel ow 90F.10/ Cool to bel ow 60*F.11/ Cool to rcom temperature. Start transformati on treatment w thl n 1 hour.El Cool to -1OOF Immedi atel y after water quenchi ng, after austenl tecondl tl onl ng.13/ Col d worked mater ial (condl t l on C) shal l be heat-t reated to spr ing temper (condi ti on CH 900) by age-temperi ng at 900F for 60 mnutes to90 mnutes.~/ Col d work mater ial (condl t l on C) shal l be heat-t reated to spr ing temper(condi ti on CH 850) by age-temperi ng at 850F for 30 mnutes.15/ 18 percent ni ckel (Nl ) maragl ng steel .16/ Agi ng the maragl ng al l oys at 900F for 4 hours shoul d produce the fol l ow ng mni mum y~el d strengths:

Mar 200 - 200 kslMar 250 - 240 ksiMar 300 - 275 ksl23



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ML-H-6875H

TABLE ID. Heat- treatment procedure for Cl ass D (precl pl tatl on-hardenl n~and maraqi ng) steel . - Conti nued17/ Ti mes: pl us 15 mnutes, mnus O mnutes.18/ Ai r quench may be appl l ed to mater ial s up to 0,500 I nch thi ck. Hater quenchi ng i s recommended for materi al s over 0. 500 I nch thi ck.19/ When approved by the cogni zant eng neerl ng organi zati on, al ternatequf i chants may be used provi di ng thei r equi val ence w th respect to mechani calproperti es and corros~on properti es of parts i s substanti ated. Parts may bequenched i n an aqueous pol ymer sol utl on i f speci fi ed on the engi neeri ngdrawng.201 Condi ti on H1150 M may be achi eved after sol uti on treati ng by heati ng to14~ F ~ 25F and hol di ng for 2 hours, al r cool l ng bel ow 90F, and then agi ngfor 4 hours at 1150F ~ 25F.

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TABLE 11A. Heati ng and hol di ng ti me for anneal i ng, normal i zi ng, austenl ti zi nqand st ress rel l evi nq Cl ass A steel and Cl ass B steel .Suggested heat- up ti me Recommended mnimum(mnutes) 4/ hol dl ng ti me ~1 ~1Thi ckness (i nches) ~/ Furnace ~1 Sal t bath (mnutes)

0. 250 & under 20 10 150, 251 - 0. 500 30 10 250.501 - 1.000 45 10 301. 001 - 1. 500 60 15 301. 501 - 2. 000 75 20 302.001 - 2. 500 90 25 402.501 - 3. 000 105 30 453. 001 - 3. 500 120 35 553. 501 - 4. 000 135 40 604.001 - 5.000 165 50 755. 001 - 6. 000 195 60 906. 001 - 7.000 225 75 1057. 001 - 8.000 255 90 120

~/ For unpl ated parts onl y. Copper pl ated parts requi re at l east f i f typercent l onger heat-up ti me and the heat-treati ng faci l i ty shoul d: (a)determne the appropri ate heat- up ti me as a functi on of maxi mum partthi ckness and (b) establ i sh sui tabl e process control s for ensuri ng thatthe parts reach the requi red heat-treat temperature prtor to start ofhol dl ng ti me.gl Maxfmum hol di ng ti me shoul d not exceed tw ce the recommended mnl mumti me.In al l cases, hol d ng t ime shal l not start unt i l par ts or mater i al

have reached speci f i ed heat- treat temperature.jl Mnl mum stress rel l evl ng t i me shal l be one hour for stress rel l evl ngtemperatures up to 850F, i ncl ustve, and 2 hours for hi gher stressrel l evi ng temperatures.~1 Heat -up t ime start s when al l t emperature Indi cator s r i se to w thln 10Fof set temperature. These ti mes are sui tabl e for si mpl e sol i d shapesheated f rom al l - surf aces. Longer ti mes are necessary for compl exshapes andl or parts not uni formy heated.~/ Th ckness I s mni mum di mensi on of heavi est secti on.25



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ML-H-687SH

TABLE I I B, Hol di ng ti me for Cl ass C (corrosi on-resi stant) steel .

Mni mum hol dl ng ti me I n mnutesfor ful l anneal i ng ~/Di ameter or thi cknessof maxi mum secti on(i nches) ~/ Atmospherefurnace

up too. l oo 200. 101 too. 250 250. 251 to 0. 500 450.501 to 1. 00 601.01 to 1.50 751. 51 to 2.00 902.01 to 2.50 1052.51 to 3.00 120

~/ Thi ckness i s the mni mum di mensi on of heavi est sect ion of a part orthe mnl mum dl mensl on of the heavi est secti on of a mul ti - l ayer l oad.~1 Hol dl ng t ime starts when al l temperature i ndi cators r ise to w thl n10*F of set temperature. For conti nuous and repet t~vebatch heat treatment, the hol dl ng ti me may be l owered provi ded thesol uti on of carbi des 1s assured per ASTM A 262.

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SAE, AI SIx producer sdesi gnati onH-11

9N -4C0-. 2OC9Ni - 4Co-. 3OC

Hy-TufD6AC

AF 1410 ~/f )thers 220 ksitnd over ~1Others, under~20 ksi

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ML-H-6B75H

TABLE III. Requi red temperi ng condi ti ons.Mnimum Mnl mum numtemperi ng Under 220 kslti me (hours

Two hours pl l J 5an addit~onalhour for eachI nch of metalthi ckness orf racti on thereofgreater than 1 i nch.

1 hour per inchmni mum 1 hour

22

2

1 I

- of tempers220 ksl and over

3

212

12

1/ AF 1410 requi res agi ng for 4-7 hrs. at 500F t250F because ofI ts secondary hardeni ng characteri sti cs.2/ Doubl e temper i s not appl i cabl e to 1095, 6150, 420, 440C, and 52100.

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SOLIDS, LENGTH LROUND HEXAGON SQUARE RECTANGULAR OR PLATE

Oj ~ n~ ~i ~

ER~=T ER=I. IT ER=I,25T ER.I,5TWHEN L IS LESS THAN T, CONSIDER SECTtON AS A PLATE OF L THICKNESS

TUBE (ANY SECTION)OPEN BOTH ENDS RESTRICTED OR CLOSED AT ONE OR BOTH ENDS

cq li ~~~~~~~~:

-

f+,4 T T 2/

ER = 2TNOTE: WHEN L IS LESS THAN ER= 2.5 T WHEN D IS LESS THAN 2.5D, CONSIDER AS A PLATE OF T INCHES.THICKNESS, WHEN L tS LESS ER = 3.5 T WHEN D IS GREATER THAN 2.5THAN T, CONSIDER SECTION AS INCHES.A PLATE OF L THICKNESS,

~/ ER = EQUIVALENT ROUND, USE MAXIMUM THICKNESS FOR CALCULATION.

FI GURE ). Equi val ent rounds for si mpl e shapes.

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mil-h-6875h heat treatment of steel

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