Microstructure of Carbon and Alloy Steels of H igh Car bon Content

By the ASM Committee on Metallography of High-c,,rbon steet:

CONTENTS

Plain High-Carbon Steels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Loi.y-Alloy Hígh-Carbon Steels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Compositions of High-Carbon Steels for Which Micrographs Are Presented in This Section

Alloy steetsrc) 5160 ... 0.56-0.64 e, 0.75-1.00 Mn, 0.035 max P,

0.040 max S, 0.20-0.35 SI, 0.70-0.90 Cr 51B60 ... Same as 5160, out wíth 0.0005 min l� 52100 .. 0.98-1.10 e, 0.25-0.45 Mn, 0.025 max P,

0.025 max S, 0.20-0.35 Si, 1.30-1.60 Cr 6150 .. 0.48-0.53 e, 0.70-0.90 Mn, 0.20-0.35 Si,

0.80-1.10 Cr, 0.15 min V(d) 9254 0.51-0.59 e, 0.60-0.80 Mn,

1.20-1.60 Si, 0.60-0.80 Cr(d) (a) Ali carbón steels have a maximum phos­

phorus content o! 0.040% and a maxtmum sut­ rur content of 0.050%. (b) Contains i'. mínimum of 0.0005% boron. (e) oompostttons or two non­ standard alloy steels are grven with the micro­ graphs. (d) Also 0.04 max P, 0.04 max S.

then air cooled (air patenting). Patent­ ing usually results in míxed structures (see pages 44, 45 and 46). As-patented wire and rod have sorne commercial applications, but patentíng is . usually done before cold dra wing and between drawing operations. Many coil springs are made of cold drawn patented wíre with no further heat treatment.

For subsequent processíng (for in­ stance, machining) of hígh-carbon steels, especíally those havíng more than 0.70% carbon, the unresolved and lamellar pearlite structures are not satísfactory. Spheroidal cementite in a matríx of ferrite is the desired struc­ ture (see the mícrographs on page 47).

Except in the thinnest sectíons, car­ bon steeís requíre a water quench from the austenítízíng temperature to de­ velop a" fully martensítíc structure (see mícrographs 363 and 364). Oíl quench­ íng usually results in a slack-quenched conditíon (see mícrograph 362).

Austempering can be applied to very thin sectíons of plaín hígh-carbon steel, but It is geners.lly better suited to the hígh-carbon alloy steels,

Alloy Steels, The hígh-carbon alloy steels transform rnuch more slowly on cooling from the austenitíc conditíon than do carbon steels. To develop a fully martensitíc struéture in hígh­ carbón alloy steel, oil quenching is usu­ ally suffi<.:iently rapid.

Pages 49 to 54 of this section show microstructures of 5160, 52100, 6150 and 9254, four extensively used high-ca::bon alloy steels. Large quantitie1; of 5160 steel are used for coil springs for auto­ mobiles. Very often tht: hot rolled prod­ uct is hot coíled and 1:hen heat treated. by austenitizing a.t llOO F (871 C) and o:l quenching. After this treatment, the structure is fully martensit1c, with n•) 1o free carbide (no!R micrograph 382). This structure will then be altered by tem­ pering at about 800 F d,27 C) for mc)st spring appiications (note the mie.ro­ stru<.:ture, other than the dec:l.l'buriza­ tion, in micrograph 384).

Microstructures of 52100 stee1 n.re presented on pages 50 to 53, beginning with a macroP,raph of i;be hot rollcd product (391). Micrographs 396 through 405 show the efiects of various heat treatments on spheroidal ca.rbide in 52100 steel. A structure of spherc!.dal carbide in ferrite (396) is usually the starting structure when machining or further heat treating is to be performed. The structures that res11lt from various quenching and tempering procedures start with micrograph 397. A skuctur<:l consisting of martensite with a disper­ sion of ñne carbide particles, which ii:: obtained by austenitizing; oíl qucnch­ ing, and tempering at approxlmately 350 F ( 177 C), is common in ball bear­ ings and other wear-resistant products made of 52100 steel (thfs typP. of st.ruc­ tur" is showi: in micrograp!i 398).

Steel 6150 is wídely used for coi! springs, including aircraft-e .1gine valve springs. Tempered martensite obtained . by conventional quenchir.g and temper­ ing is an acceptable (often a preferred) structure ior alloy sp,.ing steels.

Mn

0.60-0.90 0.60-0 90 0.6'1-0.90 0.50-0.80 0.60-0.9G 0.60-0.90 0.50-0.80 0.30-0.60 0.60-0.90 0.60-0.90 0.30-0.50

e

GEORGE F. KFITH, Technkal Scrvices Man:iger, Westdox Div., G�11e1::l Time Corp.; J. M. KIEFER, Manager, V::'ire and Rod Met..ilur�y Lv,ain· Cuyahoga Worb, Unitcd States Steel Cor¡-.

EnwA .. D R. MA1"TBL, Resea··ch laboratórics, Gencr�I .!\fotor� Cor;: : Jt.'LIUS l'URK, M, tal.Ju1¡,;ist, Paulo· ProJucts Cu.; HOWARD E. BoYEr, Se.ret,1ry, Managing Editor, Metals Handbook..

Steel

Carbon steeisra) 1055 . . . . . . . . . . . . . 0.50-0.60 1060 . . . . . . . . . . . . . 0.55-0.65 10B61 (b) . . . . . . . . 0.56··0.66 1064 . . . . . . . . . . 0.60-0.70 1065 . . . . . . . . . . . . . 0.60-0.70 1070 . . . . . . . . . . . . . 0.65-0.75 1074 . , . . . . • . . . . . . 0.70-0.80 1078 . . • . . . . . . . . . . 0.72-0.85 1080.............. 0.75-0.88 1090 . . . . . . . . . . . . . 0.85-0.9� 1095 . . . . . . . . . . . . . 0.90-1.03

*RooERT F. MEHL, Chairman, Professor Emeritus, Carnegie-Mellon UniYersity; GEORGB H. BAILE, Supervisor, MetalJurgy Scction, Engir:cer­ ing and Research Center, SKF Industries, Inc.; RoBERT H. BlllGGS (retired), formcrly Metallurgist, Suspension Div., E.tton ,<'orp.; H. B. CHESS, Cbief Metallurgist, Torrington Co.; ERNEST .'\.. EVANC!C, Chief Metallurgist, Simc.nds Saw and Steel Div., Wal!;'lce-Mur:�, Co:p.;

THE MICROGRAPHS presented in this section show varíous structural types - as rolled, quenched and tem­ pered, patented, decarburized - of plain carbon and alloy steels of hígh carbon content. They also show welded struc­ tures and give a mícroprobe analysís of an inclusion (micrographs 418 to 425).

The composítíons of the steels for which micrographs are presented are given in the table below. Tool steels, most of whích also have a hígh carbon content, are dealt wlth in the section on Tool Materials (see page 101).

Hígh-carbcn steels are most com­ monly available as wire, bar, strip and plate. Commercial applications of these steels ínclude antifriction bearíngs, spríngs, sorne knives, and tillage tools. steel 52100 is used extensively for ball bearíngs, both balls and races. Most of the steels listed in the table below ha ve been used for spríngs - from small clock springs to the Iarge spríngs used in railroad equipment. Steels 1090 and 1095 are used far tillage tools (hand and power), and for knives for lawn mowers and hay and grain-cutting machines.

Far properties of the hígh-carbon steels, see Volume 1 of this Handbook, especially the artícles "Hardenable Car­ bon Steels" (beginning on page 94) and "Steel Springs" (beginning on page 160).

Carbon Steels. As the carbon content of steel increases, the mícrostructure becomes more complex and more diffi­ cult to interpret. For instance, a whíte­ etching constituent at grain boundaries in a steel that has been rapidly cooled can be eíther ferrite or cementite.

Hígh-carbon steels are seldom used in the as-rolled, normalized or annealed condition, although they are usually purchased in one of these conditions. Treatments specified for varseus applí­ cations include quenchíng and temper­ íng, patenting, patenting and cold drawíng, and austempering.

Patenting is a heat treatment where­ in wire (and orten rod) is austenítízed, quenched in a molten bath (usually, molten Jead) at a subcrltlcal tempera­ ture, and cooled in air. Small-diam­ eter wire or rod can be austenitized and

Plcral lOOOX 3�2 1055 steeí rod, •.,�-In. dlam, patented by ' � a!.lstenltlzlng 2!1.3 mín at 1710 F (932 C), quenchlng 35 see In a lead bath at 1020 F (549 C), aír coolíng. Unresolved pearlite (dark) ; fer­ rite (whlte) at prior austeníte graín boundarles.

1055 and 1060 Steels

Pi eral lOOOX 333 1055 steel wíre, 0.132-in diam, alr patented

by austenitlzing H� mín at 1890 F (1032 C), and air coolíng In strand form. Fine lamel­ lar pearlite wlth dlscontinuous preclpltatlon of ferrlte at prior austeníte grain boundaries.

�ral rooox 334 1060 steel red, 1'!íH-in. diam, air cooled

frorn hot rolllng In a 1000-lb coll. Dark areas are unresolved pearlite, with sorne dlst!nct lamellar pearlite; whlte áreas are ferrlte partly outllning prior austenlte graín boundaries.

�� l�X 335 1060 steel rod, 1/¡-in. diam. cooled frorn

hot rolling in a single strand by a hígh­ ··elo:�ty aír blast. Strucvure is mostly unresolved pearlíte, wlth sorne dlstlnctly lamellar pearlite; the few scattered whlte áreas are ferrlte partly outllnlng prior austeníte graíns,

f'jcrn• IOOOX 338 1060 steel wire, 0.099-in. díam, air patented

by ·inr.�c1,1tizing at 1850 F (1016 C) for l. l'·\t• ... nd au coc•l1!1g In strand form. Structure: ,lt : pr�.rl!te (dark) , mostly unresolved, and fer­ ,!� , somo �t prior austenlte graín boundarles

Picral lOOOX 336 1060 steel rod, 1'U;4-ln. díarn, patented by

austenítízíng at 1730 F (943 C) for 2% mín, quenching in a lead bath at 990 F (532 C) for 55 sec, and alr coolíng. The structure consísts of pearlite (dark) and rerr-te (white) e.t prior austenlte grain boundarles.

Picral 100 X 339 Decarburlzed 1060 steel, heated at 2200 F

(1204 C) for 1 h.r before rolling to síze. Note thin Iayer of scale at the surface (top of mícrograprn , decarbur ízed layer (whlte, near top), unresolved pearllte, and ferrlte.

Picral lOOOX 337 1060 steel wlre, 0.281-ln. díam, that was

alr patented by austenltlzlng at 1930 F (1054 C) for 3 mín, and aír coollng In strand form. The dark áreas are partly resolved pearl­ íte; the white áreas are ferrite at prior austen­ íte grain boundaríes.

Picral SOOX

340 Decarburized 1060 steel, heated at 1600 to 1700 F (871 to 927 C) for 12 mín arul

cooled in air, Note scale (top of micrograph), partly decarburízéd Iayer (below scale), pearlite (dark), and sorne graín-boundary ferrite.

10B61, 1064, í.065, 1070 and 1074 Steels

1% nital 1500X 341 10B61 steel, austenitized in a salt bath

at 1450 F (788 C) for 3 mín, quenched in a salt bath at 525 F (274 C), held 36% mín.iaír cooled. Small white areas are ferrite; massíve gray areas, martensite; dark áreas, lower bainite.

45

soox 1064 cold rolled steel strip, austenítízed at 1500 F (816 C), quenched to 600 F

(316 C) and held (to complete isothermal trans­ fonnation), air cooled, tempered at 700 F (371 C). Mixture of bainite and tempered martensíte,

Plcral 500X 344 1064 steel strip given same heat treat-

ment as for 343. Surface decarburization <near top of mícrograph) was Intentionally produced to increase formablllty. Remaining structure is balnite and tempered martensite.

nital lOOX 7 1070 hard drawn steel valve-spring wire.

Lcngítudína; sectíon. Tensile strength of .000 psi <1689 MPa) was obtained by 80% re­

Ion. Prior structure was fine lamellar pearl­ ; structure shown is deformed pearlite.

Picral 500X 345 1065 steel wire, 0.135-in. diam, patented

by austenitizing at 1710 F (932 C) for 11�

mín, quenching in a lead bath at 1010 F (543 C) for �2 min, aír coolíng. Structure: mostlv- unre­ solved pearlite; sorne grain-boundary ferrite.

2% nital 348 1070 stcel valve-sprlng wire,

and tempered. Austenítízed at 1600 F (871 C). oil quencL.ed, tempered at 850 F (454 C). Structure is maínly tempered martensite. wlth sorne free ferrite (whlte areas) .

2% n,tal 500" 346 1065 steel sprmg wír>, quenched and

tempered. Austenitized, t 1600 F (871 CJ, o!l quenched, tempered 2 mín at 850 F (454 C). Structure: mostly tempered martensitc; rerrtte at the surface (top) Is due to decarburlzation.

349 1074 cold rolled steel sheet, at•;;•eni�iz � at 1500 F ('11€ C) for 5 ;,, in. oil qncr cned.

The microstructu::e consíst- p:cdo:11''1antly o'.'. untempered martenstte, T.ith scattered !'!?'le ri, r­ tlcles of cementíte (ponrly resolved).

46

Picra! sso x

10i8, 1080 a.o.d 1090 Steels

Picral 2ooox 351 1080 hot rolled steel bar, austenitized at

1920 F (1049 C) for 1/1 hr and furnace cooled to room temperature at 50 F (27.7 C) per hour. Structure is mostly pearlite, with sorne spheroídal cement!te parttcles .

350 1078 hot rolled steel bar, cooled in air ' from the rolllng temperature. Structure

conslsts predominantly of pearllte (note large amount of partly resolved lamellar pearlite) , wlth sorne graín-boundary ferr!te.

..... - ... �-- ... . ....

. ,.

. .. . . ' . ' ':" ' . :1 '

As polished (not etched) 250X 353 Inclus!ons in 1080 steel flat spríng, about

0.008 in. thíck. A longitudinal sectíon (thíckness shown as height in mlcrograph). The black spots are !ron alumínide; the thln gray stríngers near center are sulñde,

Picral 2000X 354 1090 hot rolled steel bar, t-ín, d!am, as

cooled from the finish-rollíng tempera­ ture of 1600 to 1650 F (871 to 899 C). A,replica electrón mícrograph, The structuie consists en­ tlrely of larnellar pearlite.

Picral lOOOX 355 1090 steel rod, 0.343-ln. dlam, patented

by austenítízíng at 1750 F (954 C) for 4% mín, quenchíng in a lead bath at 940 F (504 CJ for 70 sec, air coolíng. The structure is mostly unresolved pearllte with bainlte.

Picral 8000X '.:¡ !16 1090 steel strip, cold reduced 80% after ·.,- · hot rolllng. Rolling direction is vertical .n th� abcve replica electron micrograph. Struc­ tnre fa tl�formed lamellar pearlite.

2% nital / lOOX 357 1090 mod steel (0.3S'% Mn) musíc wíre,

cold drawn to 263,000-psi (1813-MPaJ ten­ sile strength by 75% reductlon. Deformed pearl­ íte (prior structure was fine pearllte) . See 358.

2% nital SOOX 358 Same as 357, but shown at a hlgher

magníñcatíon, As in 357, drawing dírec­ tlon is horizontal In above mícrograph. Prior structure was produced by lead patenting.

Heat Treated Structures m 1095 Steel 47

Picral lOOOX 359 1095 steel bar, normalízed by austenitiz­

íng at 1600 F (871 C) and cooling in aír. Structure is partly unresolved pearlite (black) , partly lamellar pearlite.

2% nital 500X 362 1095 steel wire, austenitized at 1725 F

(941 C), and oíl quenched. Dark areas are a mixture of fine pearlite and lower bainite; light areas are untempered martenslte. Thls structure resulted from slack quenching.

Kn� �X 365 }g9J g:elfot;�· �r���i�i��d ªfo 1m � (329 C), held 5 min, oll quenched, Lower balnite (darkl ; untempered martensite (light) .

Nital lOOOX 360 1095 hot rolled steel bar, 114-in. diam,

spheroidized by holding at 1250 F (677 C) for 15 hr, and aír coo!ing. Structure is spheroidal cementíte partlcles in a ferr!te matrix.

Picral lOOOX 363 1095 steel, austenitized at 1600 F (871 C)

and air cooled (nonnalized), austenitized at 1500 F (816 C) and water quenched. Fine, untempered martensíte, caused by more -severe quench (see 362) ; sorne spheroidal cementíte.

�� l�X 361 1095 cold rolled and annealed steel strtp,

spherold!zed by holding at 1340 F (727 C) for 30 hr. Lap seam at surrace was 1101led over in cold drawíng.

' .. Picral 1000·)� 364 Same steel and heat treatment as ror

363, but tempered at 300 F ,149 C) after the quench. Structure is tempered martensíte (darker, comparert with 363) and sorne spheroi­ dal cementite parbícles.

2% nital 55.J '>(

367 Same steel and austenítdzing treatment as for 365 and 366, b;,¡:; held ror : br in

an 850 F (454 C) quench and aír c0:>Je,l taus­ ternpered) . Structure is mainly upper bi,\rlite.

48 Heat Treated and Cold Worked Structures m 1095 Steel

4% nltal 11,000X 368 1095 steel wire, %-In. dlam, austenitized

5 mín at 1525 F (829 C), quenched in oil at 450 F {232 C), aír cooled, and tempered at 350 F (177 C) for :.J hr. Replica electrón micro­ graph, A mixture of tempered martensite and balnlte, wlth sorne spheroidal cementite.

4% nital 10.000X 369 1095 steel wíre, 1rl-in. diam, heat treated

by austenitizing at 1550 F (843 C) , quenching in Iead at 650 F (343 C), holding for 2 hr, and air cooling to room temperature. A replica electron mícrograph, showing -a structure that consists primarily of lower bainite.

4% nital 5500X 370 1095 steel wlre, 'A-in. díam, heat treated

by austenitizlng at 1625 F {885 C) for 11.l hr, quenchlng in lead at 625 F (329 C), holding for 2 mín, and oíl quenchíng. Replica electron rnícrograph. Structure consísts of lower balnite Cmottled áreas) and martensíte (clear areas).

4Yo nital 11,000X -::i71 Same steel and austenítízing treatment ... , "" as for 370, but quenched in lead at 1250 F (677 C), ne.d for 10 rnin, and oil quenched. A replica electrón mícrograpn, The structure consísts ot larnellar pearlite.

Thin·foif specimen 83,000X 372 1095 steel wíre, cold drawn, with 98.5%

reductíon, to 0.042-in. díam. A thin-foil transmission electrón micrograph of a section transversa to the longitudinal axis of the wire. Structure: deformed pearlíte. See 373.

Thin-foil specimen 83,000X 373 Same as 372, but a longitudinal sectlon

of the wire (axis Is horizontal) . Initial structure (also for 372) was fine pearlite - from austenitizing, then holding at 970 F (521 C) for 10 sec. A tnín-toü electron micrograph.

Ni:�1 500X Nital · lOOOX

37 4 1095 die steel, induction hardened to a depth of 0.10 in. Micro­ grapas show transítíon-zone constituents from sorne fine rnartens­ .3 :�5 íte ,top or 374) to prior structure of spheroidal cementite in a matríx of rerríte aower portien of 374). Microgra¿h 375 (right)

.s "Í u .. same area, but ata magníñcatíon o� lOOOX.

Nital 500X Nital IOOOX

375 Same specímen as for mícrographs 374 and 375, but showlng an area nearer the surface of the steel, where the structure consísts 377 of fine martensíte (gray constituent) and fine unresolved pearlíte (black constituent) . Small white particles are spheroíds or cernent­

ite remaining from the prior structure.

Structures m 0.55C-2.40Mn and 5160 Sreels 4S

2% nital UOX 379 5160 hot rolled steel, 0.635-in.-diam, aír

cooled from ñnísh-rollíng temperature of 1800 F (982 C). Structure is unresolved pearlite (dark constítuent) and ferrite (light constitueut).

2% nital 550X 380 Same as 379, but at a nígher m .. gníñca­ . tion. The pearl!te is still unresolved, Whíte áreas ere ferrite. HarJness is Rockwell e 32, and ASTM austenític graín size is 6 to 8

4% picral with 0.05% HCI 500X 381 5160 hot rolled coü-spríng steel, austenít-

ízed at 1600 F (871 C) for 30 min and oíl uenched. Structure is untempered martensíte

(dark, needlelike constltuent) a.nd retalned austenite (light constituent).

% nital llOX 384 5160 spring steel, 0.632-in. díam, aus-

tenítized at 1600 F (871 C) for 5 mín, hot coiled, oil quenched at 140 F (60 C), tem­ pered at 800 F (427 C) for 40 mín, Note tem­ pered martensíte and decarburization.

4% nital. 4% picral. mixed 1 to 1 lOOOX 382 Same steel and heat treatment as for

381, but at a higher magníñcatíon. The untempered martensite (dark gray constituent) and the retained austeníte (light constítnenc) are now more clearly resolved.

, , 1' . .,,.:

2% nital 275 X 385 Same steel and treatment as for 384, but

at a hígher .nr.gntñcatíon. Surface decar­ burization (white area near top of micrograph) occurred in the bar mili. while the steel was ¡:¡+ a temperature of about 2100 F (1149 C).

4% nit: ,, 4% picral, mixed 1 te 1 lOOOX 383 Same steel as !or 381, but tempered at

400 F (204 C) for 1 hr after austenínzíng and quenchíng. Structure Is predomíncntly tem­ pered martensíte (dark), but there are small partícles of ferrlte cwhíte) ,

,,�, 4% nital, 4% picral, mixed l to 1 lOOOX 386 5160 hot rolled steel. austPr.::i2HI at 1500 F

18':l C) fo, 30 mm, c,J quenehed, tero­ percd at 1000 F (538 e fo.· 1 hr. 'I'he · tr- ., t. ·t. consísts predominantly of terr.pered m vrrenstt­ (dark) wlth sorne ferrite twhíte) .

50 1.2% C Low-Alloy Steel, and 51B60 and 52100 Steels

fu� �X 387 Hot rolled:::. C, 0.5 Cr, 0.9 Mo, 0.2 V steel

� ar, austenitlzed at 1700 F (927 C) for :.o ruin, and 011 quenched. Structure consists of un· mpered martensíte (dark, needlelike con­ stuuent) and retained austeníte (white areasr.

Picral llOOX 388 Same steel and heat treatment as for

387, but at a higher magníñcatíon, The large amount of retained austenite (white con­ stttuent) índícates that the austenítízíng tem­ perature was too high for this steel.

Pi eral lOOOX 389 51B60 hot rolled steel bar, rn-in. díam,

austeníttzed at 1600 F (871 C) , alr cooled (normalized) ; austenitlzed at 1500 F (816 C), wa­ ter quenched. Untempered martensíte, sorne re­ tained austeníte (white), fine spheroidal carblde.

N;tal lOOOX HCl, water, mixed 1 to 1 Actual size 391 52100 steel bar, 41;-in. diam. Cross sectíon

after bot rolling wíthín the temperature range of 2150 to 1700 F (1177 to 927 C) and aír cooling to room temperature. Plts (cluster of small dark spots) in center are íncíusíons.

4% picral, 4% nltal, mixed 1 to 1 lOOX 392 Microstructure of a specimen taken from

bar section sbown in 391. Structure is predomínantly pearlite (light and dark gray), with thin films of carbíde (black línes) outlírung prior austenite graín boundarles.

3�0 51B60 hot rolled steel bar, 11.\-in. díam, austerunzed and quenched to obtain a

martensitrc structure, t ,en heated to 1250 F (57'i C) for 15 hr. Structure consísts of sphe- • Mdal carbide particles in a matrix of ferríte.

�, picral, 4 • nital, mixed 1 to 1 500X -::93 S:,,me specunen as shown in 392, but at � " higher magnifica, ion. The grain- 1, .. C"TY 'arbide rejected from solid solution cur '!? coolin¡; from rolling is now more clearly , 1,:, t <! r ,r:1 'l.iJPP.rn·s as white lines.

4% picrat, 4% nital, mixed 1 to 1 lOOOX 3q4 Sarne specímen as shown in 392 and 293,

v but at " still higher magmñcation. In sorne Iocatíons, the · graín-ooundary carbide (whíte constituent) now shows as arcas rather iban as rhín lincs. Matrix is pearhte.

4% picral, 4% nital, mixed 1 to 1 100" 395 Same steel and processíng as for 391 to

394, but a sectíon through the bar surface (top). White · areas of ferrite near the surfaee show that sorne decarburtzatdon occurred during rolling and cooling f'rom the rolling temperature.

Spheroidízed and Quenched-and-Tempered 52100 Steel 51

4% nital, 4% picral, mixed 1 to 1 500X 397 52100 steel rsee 396), austenitized at 1450

F (788 C) for 1.,fi hr, oíl quenched, tem­ pered at 350 F (177 C} for 1 hr. The black areas are baíníte, the gray areas are tempered mar­ tensíte, and the white dots are carbide partícles that did not dissolve during austenitizing.

4% nitat, 4% picral, mixed 1 to 1 500X 398 52100 steel (see 396). auster.ittzed 1,� hr

at 1550 F �843 C) and oíl quenched, thor, tempered same as 397. Tempered marrez,.,;�e. and carbíde partícles (white) undíssolved during austenittsíng. Ghost lines are due to ínhomo­ geneous distribution of carbon and chromlum.

4% nital, 4% picral, mixed 1 to l 500X 399 52100 steel (see 396), austenitized at

1575 F (857 C) for �íi hr, oil quenched, tempered at 500 F (260 C) for 1 hr. Structure Is tempered martensite and undíssolved carbide particles. Ghost lines are less prominent, because o! the hígher austenitizing and temperíng tem­ peratures (see mícrograph 398) .

4% nital, 4% picral, rnixed 1 to 1 500X 400 52100 steel (see 396), austenitized at

1550 F (843 C) for 1,i! hr, oil quencned, tempered at 750 F (399 C) for 1 hr. Strncture is tempered rnarí.ensíte and a dispersión of car­ bide particles not dissolved during austenítízíng. Ghost lines have nearly disappeared (compare with mícrographs 398 and 399).

4% nital, 4% picral, rnixed 1 to 1 500X 401 5211;0 steel tsee 396), austenítízed at

1700 ¡., (927 C) for J2 hr, oil quenched, tempered at 350 F (177 C) ror 1 hr. Structure is maínly tempered martcnslte. High austenítíz­ íng temperature resulted in sorne retained aus­ tenite (angular, white ai eas) and a re: carbíde partícles, (Compare with 398 to 400.)

1% mtal, 4% picral, mixed 1 to 1 lOOOX 402 Same specímen as used for 401, but shown

at a higher magníñcatíon. Dark areas are tempered martensite; retaíned austeníte angular, light-gray áreas) is well resolved. A

.ew undíssolved carbide partlcles remaín from the original structure (mícrograph 396) .

4% nital, 4% picrar, mixed l to 1 rooox 403 52100 steel rsee 396), austenitized at

1800 F (982 C) for �2 hr, oil quenched, tempered st 350 F (l'n C) for 1 hr. Stru,;tu1e consists e[ coarse places (needles) of ternpered martensite and retained austenite (white). Car­ bide particles are almost wholly díssolved.

4% nital, 4% picral. mix'°d 1 to 1 500X 404 52100 steel (see 396), auscenítízed at

15'75 F (857 C) for t� hr, quenched In a salt bath at 500 F (260 C), held ror is h,·, aír cooled to room temperature. Struc:ure e· , •h\;. of spheroídal carbíde particles in lower b¡,,mt.e, and sorne retained austeníte.

Heat Trcared Structures and Defects in 5210G Steel

, V. mta' 4% picr• mixed 1 to 1 lODDX "105 521!>0 ste (see 396•. austenitized at

1750 F 19 ,4 C) for 2 hr, cooled slowly to 1300 F <704 e oil quenched. Note dark-gray needles of mart ·nsite, carbide rejectcd to graín boundaríes (light gray), bainite (black), and reta ned austenlte ,s1.1all, light areas).

4% nital SOOX 406 52100 steel rod that was austenltlzed at

1650 F (899 C) for 20 min and slack quenched in oll to room iemperature. The dark

áreas (etched) are a mixture or fine pearlite and baíníte. The Iíght áreas (alrnost unetched) are rntempered martensíte.

4% nital 407 52100 steel rod, austenítízed at

(1127 C) ror 15 mín, oil quenched. An electrón mlcrograph of a replica rotarv-snad­ owed wíth chromium. Structure Is coarse, un­ tempered martenslte. Note cracks 1n martenslte platelets (upper left, upper rlght).

4º'• n1hl SOOOX 408 5210C steel rod, austenitlzec at 1800 F

(982 e, fat 1 hr, quenched in a lead bath ut 6í F (357 ci held for 2 hr, o ír cooled. An ele tron mícrograph of a ·eplica rotary-shad­ oweo with ch cnuum. struccure is bainite (prob­ nbJ,· upper baíníte) .

l % ita lOOX 4' crack In a 52100 steel roller, aft r aus-

... cnít ízíng. water qu"r � ung. and tcmper- 1· 1'.,t crack, extending .rown frum the sur ,,e was cm .. ed by a searn in the bar stock.

.,.. , �uctn�:! ís martensíte. SPe also -412.

4% nital 10,000X 409 52100 steel wire, austenltlzed at 1650 F

(899 C) fer 30 sec, quenched in a lead bath at 985 F (529 C). held for 30 sec, air cooled. An electrón micrograph of a replica rotary­ shadowed with chromíum. Structure is lamellar pearltte and bainite.

1 % nital 750X 412 f.1me crack as 'n 4:1• hw at a hígher

,ilt .. gnírteatton. Decarbu.ri..ation (white areas) along the sídes of the crack Is evldence that the crack was there bffore heat treatn ,.nt (surtace Is not decarburized) .

4% nital 10,000X 41 O 52100 steel rod that was austenltlzed at

2100 F (1149 C) for 3 mín, quenched In " lead bath at 1070 F (577 C), held for 5 mm air cooled .. An electron mícrograph of a replíc; statlc-shadowed with chromium. The structur, is fine, lamellar pearlite.

1 % nitai lC- 413 Hardened 52100 steel damaged by ai:

abrasíve cutoff wheel. Dark áreas an martensíte tempered by overheating. Light area are untempered martensíte, which had been ll· austernttzed by rríctíonal heat.

Fr.ction Weld and Indusion in 5210(• Sreel 53

4% picral, 0.05% HCI 3X :J.14 Friction weld between two

0.6-in.-diam rods of 52100 -teel, See mícrograph 396 tor prior scructure of rods. Weld zone (white) ?• the eenter Is bounded by tran­ e tíon zones (black) .

4% picrat, 0.05% HCI 500X 415 Weld zone of frietion weld

in 52100 steel (central, white area in macrograph 414). Struc­ ture is mainly untempered martens­ lte, wíth sorne retained austenite and residual carblde particles.

4% picral, 0.05% HCI 500X 416 Transition zone of friction

weld in 52100 steel (see ma­ crograph 414). Structme ís bainlte (blaek). untempered martenslte (gray), and sorne spheroldal ce­ mentite from the prior structure,

4% picral, 0.05% HC, SOOX 417 Outer part of transítíon

zone in friction weld (414). Scattered carbide particles Irom prior structure <whltE: fine mar­ tensite (medium-gray). and bamíte (dark-gray or black).

;s polished (not etched) lOOOX l 18 Inelusion typical of those • found in 52100 steel. For

,,-,,r¡position of such mclusíons, see results of mícroprobe analyses in iícrographs 419 to 425.

As polished (not etched) lOOOX 419 Result of microprobe sean

for iron in inelusion in 52100 steel. Note un!form dístríbutíon of !ron 1n the surroundíng steel, but absence of !ron in the ineluslon.

As polished (not etched) !OOOX 420 Result of microprobe sean

for manganese in ínclusíon in 52100 steel. Note high concentra­ tíon in rím, but little at center or in surrounding steel.

As polished (not etched) �ooox 421 Result of mieroprobe · set n

for sulfur in ínclusíon in 52100 ste el. :'lote high concentratíon in rirn. but little in eenter or in surroundíng steel.

•s pclished (not etched} lOOOX 422 Result of rnícroprobe sean

for oxygen in inclusion in 52100 steel. Note high eoncentration ':: core, and low concentration in m and in surroundíng s.eel.

As polished (not etched) lOOOX 423 Result of mícroprobe sean

for calcíum in inc!\J! 'cr, in 52100 steel. High concemratíon or Mn, S and ca in rlm (see 420, 421) suggests a <M L,Ca) s compound .

As poiished (not etched) IOOOX 424 Result of mícroprobe se· n

for alur-Inum '"l ínclusíon in 52100 steel. 'I'h�re is a high cor-cen­ tration in the core, buz livcle in the rim or ir. the surroundíng steel.

As polishcc (n.Jt etct,Pd1 lOOCX 425 Result of mícroprobe sean

tor chromíurn in íncius • 1 in 52100 :::t,�e:. '.i'here is v-ry !,t'e i'' thc mcrusíon, bu; �.tnifvnr. 1i->t"' ......... tíon in the SWTOUildlL1� stecl.

54 Heat Treated Srructures m 6150 and 9254 Sreels

2% n; .,;I 550X · "'5 6150 steel wire, austenítízed at 1650 F

·.'"" (1'99 C) for 20 min ar-, s iack quene: :?d In oíl to room temperature. Lower baíuíte .d"-rK1 and untempcred martensíte <l!ght.).

Picral 550X 427 6150 steel, austenitized at 1620 F (882 C)

for 1,� hr, cooled to 1350 F (732 C), held 5 hr, cooled to 1200 F (649 C) at 50 F (28 C) per he .r, held 1 hr, aír cooled, Pearltte and ferrlte.

4% nital sor 428 6150 steel wíre, austenitized at 1625 l

(885 C) for 20 mín, quenched to 1250 F (677 C), held 20 mín, oil quenched to room tem perature. Structure consísts malnly of pearllte.

1% "itzl 5000X

·+2� ¡�if 6}i�r !r�r. a�t�����d�\e�J�re� ;.t :.>OO F' (149 C) .tl.ll eleccron mícrograph of ..1 replica rotary-shadowed with o+rorr-um. The tructure is temoered marten; :te and sorne re­

;idual spherc. lal carbide partícles.

4% nitat io.ooo x 430 6150 steel wlre, aústenítízed at 1600 F

(871 C) for 2 hr, quenched in lead to 1200 F (649 C), held for 2 hr, water quenched. An electrón mícrograph of a replica• i.,tarf­ " iadowed wíth chromlum. Structure is partly spheroídízed carbíde in a ferrite matrix.

4% nital 10,000X 431 6150 steel wire, austenítízed at 1600 F

(871 C) for 2 hr, quenched in lead vi 1325 F (718 C), held 2 hr, water queuched An electrón mícrograph of a replica rotarv­ shadowed with chromíum. Partly spheroídízer' and partly !amellar pearhte in ferrite.

J.,a. ';35X lOOOX 43;� .same sc..eí, rod uíame+cr, and :. ·.1.t ereat­

ment as ror mícro jraph 432, but shown at " higher m,.,g'1.ification. �'he heat treatrnent ,.sect if. commonly :..nown as auctemperme.

'!% nital 1000)' 434 9254 steel, austenitized at 1600 F (871 CJ,

oil quenched, tempered at 850 F (4.l4 -::). 'l:J-,e nucror tructure -onsísts ruaínly of temr¡e-.,' martensit·. a few ares,s are f :rrite.

Íi-32 ·1150 steel ro+, �'Í-in. díam, ,,ui;..erütized t1.t lt:'..'' ::-' (843 C) for 1 hr, quenched to

, O' I' ,316 .'), neld :6 mL1, aír cooled. S,1•1ctt1re · , 10. ';ly oa.i;·ite (p.obably, íower baL'l�t. \.