Frsed, rent have brmation i matflx lar tem bnless, athe ld quenched rtite, that I temperatures' rcsthat, after riloYs). IloY is heated pneous single- zurrounding r raPidlY cooled po without the kment than the e of martensrre t fhis leads to le time required lgrarn assumes ; matrix when crYstal structures' Problens 431 3*t- A groupof ferrousalloysa'uys ffiro*ion resistance. thattnat c,contain at least 1l% Cr,providing extraordinary martensite The I"to"* microconstituent---v'u!rruelrl ofor ftrernte tempered. and cemendteformed when martensiteis l::j,'"t::::i,,i'iJ:J:,:i"intn?.T,n"j:,n"provide combinations orhighhardness, tough- Vermiculargraphite Th rhis that tii,-i,',,,.is the ;'.J#:*j#iT:#::::1ji*hiteintendedshape rormsduring -i"'"^'r^"]"liuurcauonthe sori idification ductile:i:1,11*.last.jron. im compacted-graphite ofo1 iron. iron.rn, buthrrt itt- is a defectiveshape in White cast iron Castiro cementiterarher white irons n*Jl"i"il.i1lJ.produces than graphiteduring "* soridification.The Section 13-l Designationsand Steefs Classificationof Section l3-2 SimpleHeat Treatments I3-l Whar is the differencebetween SectionI3_3 steels? cast iron and lsothermat Heatlreatments l3-7 Explain I3-2 what do the following heat Ar, At, A"^temperatures cess treatments:(a) pro_ Are ?nd refbrto? anneal,(b) thesetemperatures constant? normatizins,aiJ,St'#:i'fif;(c)annealine,(d) I3'3 Calculatethe amounrc of^r fe'ite'F---:.^ cementite' I mary microcorri,:'::-t: pri- 3'8 cttuent' and pearlite lowing in the iol- diagrams sbels: "?fii,:jtr..'jl^.1*:*"'*treatments "' only. (a) l3-g 1015 (b) 1035 In a pearlitic,,ttotn"*u' (c) 10e5 (d) 10r30 platelets 13-4 Estimate ate4 xto-' .Jt-o'"^1:tl'-'h:tftck, :t-totite the AISI-SAE and the ferrite .rlut.l.t, number for steelshaving arc 14 x f O_, the following microstructures: a spheroidl'"d steel,the ..rn.|'llt:o'In"rt toso lm peattite_62%o are 4 x to-3 \1! pnmary fenite it d;";.;.'u#:-"olttts cm 93% o/opii_"ry,.._.ri,, the total interface lb! pearlite_7 b.tw...r-tt" illi"lt area in a 1".! ??% feffite-3yocementrte centimeteror.uJtl-uTo*cementite cubic g6% Determinethe percent- @) ferite_!4?ocementite agereduction t, :.::::l areawhen the oearlitic l3-5 Completethe following steelis .ph..oidit*tuce table: 7.87 densityof ferrite is g/crnz rit-o^Jleol "ro cementiteis 7.66g/cm3, 13-10 Describethe mic 1035 steelafter.u.n in a 1050 t0l t5 ,rfltltulture,presentep tn the following Steet Steel ments: heat ffeat_ 41 temperature (a) 820"C,quench 43 or As^ temperature i^.::^., ro 650"C and hold ror 9Us, and quench Fullannealing to 25.C temperature (b) near at 920.C, t"tormalizing quenchr 450'c and temperature for eos, il;u.]ii|ro hold rrocessannealing (c) temperarure andquench tpneroidizingtemperature (d) f:]"1820.C, ro25"C 820"C,quench b 720.C rorl*1:, 100 andhotd 13-5 s,and quench to 25.C What do the terms low_, (e) medium_, and high- zzo"c carbon steelsmean? 1".,",,;l:ro::t'q,u;;;h"to ";1::.';j:andhord 500 ;"ffi". in:':-:s, and quench :1*:h,o ZSIC 13-4 Suenchand femperHeat Treatments 401 Primary x 100:36% -: HZ:ilL] (0.5- 0.0218 Pearlite: x 100:64ok I(0.77- 0.0218)il 3. Cool in air to room temperature,preserving the equilibrium amounts of primary ferrite and pearlite. The microstructureand hardnessare uniform becauseof the isothermalanneal. Interruptingthe lsothermalTransformation Complicatedmicrostructures are pro- ducedby interrupting the isothermalheat treatment.For example,we could austenitize t the 1050steel (Figure 13-B)at 800"C,quench to 650"C and hold for 10 s (permitting I someferrite and pearliteto form), then quenchto 350'C and hold for I h (3600s). Whateverunstable austenite remained before quenching to 350'C transformsto bainite. d The flnal structureis ferrite, pearlite, and bainite. We could complicatethe treatment i- further by interrupting the treatment at 350'C after 1 min (60 s) and quenching.Any lr austeniteremaining after I min at 350'C forms martensite.The final structure now id contains ferrite, pearlite, bainite, and martensite. Note that each time we change the temperature,we start at zero time! In practice, temperaturescan not be changed of instantaneously(i.e., we cannotgo instantlyfrom 800to 650or 650to 350"C).This is f-.' ru why it is better to usethe continuouscooling transformation(CCT) diagrams. 900 Figurel3-8 Producingcomplicated structures by 800 interruptingthe isothermalheat --f"-z' 700 treatmentof a 1050 steer. 9 ooo I 500 b 400 Ferrite + pearlite+ bainite F :oo F 200 100 + bainite + 0 0.51 2 510 102 103 104 105 106 Time (s) lx-4 0uenchandIemper l|eal Trentments Quenching hardens most steels and tempering increases the toughness. This has been known for perhaps thousands of years. For example, a series of such heat treatments has been used for making Damascus steel and JapaneseSamurai swords. 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What micro- 13-25 A steelpart must havean as-quenched structurewould be obtained hardness if we used a 4340 of HRC 35 in order steel? to avoid excessive_wear rates during use.