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Carbon and Alloy Steels of High Carbon Content

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Text of Carbon and Alloy Steels of High Carbon Content

  • 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 Hgh-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 wth 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 carbn steels have a maximum phos-

    phorus content o! 0.040% and a maxtmum sut- rur content of 0.050%. (b) Contains i'. mnimum 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 mxed structures (see pages 44, 45 and 46). As-patented wire and rod have sorne commercial applications, but patentng is . usually done before cold dra wing and between drawing operations. Many coil springs are made of cold drawn patented wre with no further heat treatment.

    For subsequent processng (for in- stance, machining) of hgh-carbon steels, especally those havng more than 0.70% carbon, the unresolved and lamellar pearlite structures are not satsfactory. Spheroidal cementite in a matrx of ferrite is the desired struc- ture (see the mcrographs on page 47).

    Except in the thinnest sectons, car- bon stees requre a water quench from the austentzng temperature to de- velop a" fully martenstc structure (see mcrographs 363 and 364). Ol quench- ng usually results in a slack-quenched conditon (see mcrograph 362).

    Austempering can be applied to very thin sectons of plan hgh-carbon steel, but It is geners.lly better suited to the hgh-carbon alloy steels,

    Alloy Steels, The hgh-carbon alloy steels transform rnuch more slowly on cooling from the austenitc conditon than do carbon steels. To develop a fully martensitc struture in hgh- carbn alloy steel, oil quenching is usu- ally suffi

  • Plcral lOOOX 32 1055 stee rod, .,-In. dlam, patented by ' a!.lstenltlzlng 2!1.3 mn at 1710 F (932 C), quenchlng 35 see In a lead bath at 1020 F (549 C), ar coolng. Unresolved pearlite (dark) ; fer- rite (whlte) at prior austente gran boundarles.

    1055 and 1060 Steels

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

    by austenitlzing H mn at 1890 F (1032 C), and air coolng In strand form. Fine lamel- lar pearlite wlth dlscontinuous preclpltatlon of ferrlte at prior austente grain boundaries.

    ral rooox 334 1060 steel red, 1'!H-in. diam, air cooled frorn hot rolllng In a 1000-lb coll. Dark areas are unresolved pearlite, with sorne dlst!nct lamellar pearlite; whlte reas are ferrlte partly outllning prior austenlte gran boundaries.

    lX 335 1060 steel rod, 1/-in. diam. cooled frorn hot rolling in a single strand by a hgh- elo:ty ar blast. Strucvure is mostly unresolved pearlte, wlth sorne dlstlnctly lamellar pearlite; the few scattered whlte reas are ferrlte partly outllnlng prior austente grans,

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

    by inr.c1,1tizing at 1850 F (1016 C) for l. l'\t ... nd au cocl1!1g In strand form. Structure: ,lt : pr.rl!te (dark) , mostly unresolved, and fer- ,! , somo t prior austenlte gran boundarles

    Picral lOOOX 336 1060 steel rod, 1'U;4-ln. darn, patented by austentzng at 1730 F (943 C) for 2% mn, quenching in a lead bath at 990 F (532 C) for 55 sec, and alr coolng. The structure conssts 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 sze. Note thin Iayer of scale at the surface (top of mcrograprn , decarbur zed layer (whlte, near top), unresolved pearllte, and ferrlte.

    Picral lOOOX 337 1060 steel wlre, 0.281-ln. dam, that was alr patented by austenltlzlng at 1930 F (1054 C) for 3 mn, and ar coollng In strand form. The dark reas are partly resolved pearl- te; the white reas are ferrite at prior austen- te grain boundares.

    Picral SOOX

    340 Decarburized 1060 steel, heated at 1600 to 1700 F (871 to 927 C) for 12 mn arul cooled in air, Note scale (top of micrograph), partly decarburzd Iayer (below scale), pearlite (dark), and sorne gran-boundary ferrite.

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

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

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

    45

    soox 1064 cold rolled steel strip, austentzed 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 martenste,

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

    ment as for 343. Surface decarburization

  • 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 spherodal 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 gran-boundary ferr!te.

    ..... - ... -- ... . ....

    . ,.

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

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

    0.008 in. thck. A longitudinal secton (thckness shown as height in mlcrograph). The black spots are !ron alumnide; the thln gray strngers near center are sulde,

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

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

    Picral lOOOX 355 1090 steel rod, 0.343-ln. dlam, patented by austentzng at 1750 F (954 C) for 4% mn, quenchng in a lead bath at 940 F (504 CJ for 70 sec, air coolng. 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 tlformed lamellar pearlite.

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

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

    2% nital SOOX 358 Same as 357, but shown at a hlgher magncaton, As in 357, drawing drec- tlon is horizontal In above mcrograph. Prior structure was produced by lead patenting.

  • Heat Treated Structures m 1095 Steel 47

    Picral lOOOX 359 1095 steel bar, normalzed by austenitiz-

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

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

    (941 C), and ol 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; riid fo 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 ar coo!ing. Structure is spheroidal cementte 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 martenste, caused by more -severe quench (see 362) ; sorne spheroidal cementte.

    lX 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 drawng.

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

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

    2% nital 55.J '>( 367 Same steel and austentdzing treatment as for 365 and 366, b;,:; held ror : br in an 850 F (454 C) quench and ar 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 mn at 1525 F (829 C), quenched in oil at 450 F {232 C), ar cooled, and tempered at 350 F (177 C) for :.J hr. Replica electrn micro- graph, A mixture of tempered martensite and balnlte, wlth sorne spheroidal cementite.

    4% nital 10.000X 369 1095 steel wre, 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 mcrograph, showing -a structure that consists primarily of lower bainite.

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

    by austenitizlng at 1625 F {885 C) for 11.l hr, quenchlng in lead at 625 F (329 C), holding for 2 mn, and ol quenchng. Replica electron rncrograph. Structure conssts of lower balnite Cmottled reas) and mar

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