cast stainless steels

8/12/2019 Cast Stainless Steels

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Cast Stainless SteelsIntroduction

The heat treatment of stainless steel castings follous closely in purposeand procedure the thermal process ing of comparable wrought materials.However, the differences in detail warrant separate consideration.

In work-hardenable ferritic alloys. machining and grinding stresses arerelieved at temperatures from approximately 260 to 5-tO C (500 to 1000F). Castings of the martensitic grades CA-IS and CA-JO do not requiresubcritical annealing to remove the effects of cold working, because theyare not cold worked or cold fo rmed. Casting stresses in other martensiticgrades should be relieved by subcritical annealing, before further heattreatment. For hardened martensitic castings, the stress-relieving tempera-ture must be kept below the final tempering or aging temperature.Homogenization. Alloy segregation and dendritic structures mayoccur in castings . They may be particularly pronounced in heavy sections.Also. mechanical reduction and soaking treatments are required in the millprocessing of wrought alloys. Therefore. it is frequently necessary tohomogenize some alloys at temperatures above 10 95 C (2005 F). topromote uniformity of chemical composition and microstructure. Fullannealing of martensitic castings results in recrystallization and maximumsoftness. but it is less effective than homogenization in eliminating segre-gation. Homogenization is a common procedure in the heat treatment ofprecipitation-hardening castings.Ferritic and Austenitic Grades. The fenitic. austenitic, andmixed ferritic-austenitic grades are not hardenable by heat treatment. Theymay be used in the as-cast condition. if maximum resistance to corrosion isnot required. They can be annealed or stress relieved to improve theircorrosion resistance and machining characteristics .

The fenitic alloys CB-30 and CC-50 are annealed to relieve stressesand reduce hardness by being heated above 790 C (1455 R. as shown inthe table included in this section.

The austenitic grades achieve maximum resistance to intergranularcorrosion by the high-temperature heating and quench ing procedure knownas solution annealing. As-cast structures or castings exposed to tempera-tures in the range from 425 to 870 C (795 to I600 F) may contain complexchrom ium carbides precipitated preferentially along gram boundaries inwholly austenitic grades. This microst ructure is susceptible to intergranularcorrosion, especially in oxidizing solutions. In partially ferritic grades.carbides tend to precipitate in the discontinuous ferrite pools. Thus, thesegrades are less susceptible to intergranular attack. The purpose of solutionannealing is to ensure complete solution of carbides in the matrix and toretain these carbides in solid solution.

Solution annealing procedures for all austenitic grades are similar.They consist of heating to a temperature of approximately 1095 C (2005F). holding for a time sufficient to accomplish complete solution ofcarbides. and quenching at a rate fast enough to prevent reprecipitation ofthe carbides, particularly while cooling through the range from 870 to 540

C (1600 to 1000 F). Temperatures to which castings should be heabefore quenching vary somewhat . depending on the alloy.

As shown in the table included in this section, a two-step heat treatiprocedure may be applied to the niobium-containing CF-8C alloy. The ftreatment consists of solution annealing. This is followed by a stabilizintreatment at 870 to 925 C ( I600 to 1695 F), which precipitates niobiucarbides, prevents formation of the damaging chromium carbides, provides maximum resistance to intergranular attack.Because of their low carbon contents. CF-3 and CF-3M do not contaenough chromium carbides to cause selective intergranular attack hence do not require solution annealing.Martensitic Grades. The hardening procedures for CA- IS caings are similar to those used for the comparable wrought alloy, type 4Recommended practice for annealing. austenitizing, and tempering CA-are in the article on this alloy wh ich follows. In addition, operating infomation on two other martensitic grades. CA-40 and CA-6NM. is presentin articles.CompositiOns. Alloy Casting Institute (ACI) compositions corrosion resistant cast steels are in the adjoining table, along with infomation on comparable wrought, and ASTM grades, plus the most comon end-use micros tructure for each alloy.

In addition. I5 articles on representative individual alloys are psented. They include:Ferritic and Austenit ic grades

CB-30CC-SOCE-30CF.3CF-ICCF-BMblartensitic grades

CA-ISCA-40CA-6NM

CF-12CF- I6CF.20CM-2CK-20CN-7M

Applications and welding conditions for corrosion resistant alloys listed in adjoining tables.Heat-Resisting Grades. Information on these casting alloys tfollow include AC1 composit ions; general corrosion charac teristics acreep stress values: room temperatu re properties: short-term tensile proerties at elevated temperatures: approximate rates of corrosion in air aflue gas; and corrosion resistance at 980 C ( I800 F) in various atmopheres.


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Cast Stainless Steels / 78

ACI Type: Compositions and Typical Microstructures of Alloy Casting Institute (ACI) Corrosion-Resistant CastSteelswrought ASTM Most common end-use Composition, S(b)

ACltype alloy type(a) specfications microstructure C hltt Si Cr Ni Others(c)Chromium steelsCA-IS 110CA-I5MCA-I.0 320CA--lOFCB-30 431.4-Ecc-so 446Chromium-nickel steelsCA-6NCA-6NMCA-28MWVCB-7Cu- ICB-7Cu-2CD-IMCu(X-30CF-3(e)CF-3M(ebCF.3MNCF-8(e)CF-8CCF43hICF-IOCF- IOMCF-IOMCCF-IOSMnNCF-I2M

312304L316L30-l317316

316CF-16FCF-20CC-6hlhfN

CG-8MCG-I2CH-8CH-IOCH-20CK-3hlCuNCK-20

303302

317

309

310Nickel-chromium steelCN-3MCN-7hlCN-7MSCT-ISC

A743.A217,A187A 733A 743A 713A 743A 743

A743A 713. A187A7.l3A747A747A351,A743.A744.

A 890A 713A351.A7-l3,A7UA351.A743,A744A 743A351.A743,A711A3Sl.A7-13.A744A351,A743.A744A351A351A351A351.A743

A 743A713A35l.A743

A351.4743.A7UA 743A3.51A351A3Sl.A7-l3A3Sl.A7-13.A7UA 713

A 7-13A35l,A713.A7-UA 713. A 7-UA351

MartensiteMartensiteMartensiteMartensiteFerrite and carbidesFerrite and carbides

Rlartensi teMartensitehlartensitehlartensite. age hardenableMartensite. age hardenableAustrnitc in ferrite. age

hardenableFemtr in austenitrFerrite in austeniteFerrite in austeniteFerrite in austeniteFerrite in austeniteFerrite in austeniteFerrite in austcniteFerrite in austeniteFemte in austeniteFemtr in austenitrFerrite in austcniteFemtrt in austemte orausteniteAustcoitrAusteniteFerrite in austenitc

Ferrite in austeniteFerrite tnausteniteFerrite in austenitcFerrite in austrntteAustrniteFerrite tn austeniteAustetute

AusteniteAusteniteAusteniteAustenitr

0.15 1.000.15 1.000.10 1.00

0 -0.1 1000.30 I .OO0.30 1.00

0.06 0.500.06 loo

0.20-O 28 O.SO- I .oO0.07 0.700.07 0 700.04 I .(X10.30 I so0.03 I so0.03 I.500.03 I .so0.08 I.500.08 I.500.08 I so

0 04-O. IO I 500.04-O. IO I.50

0. IO I so0.10 7.00-9 000. I 2 I .500.16 I.500.20 I.500.06 1.00-h 00

0.08 I .500.12 I 500.08 I.50

00-1-o IO I.SO0.20 I.500.025 1.200.20 2.00

0.03 XKJ007 I.500.07 I so

0.05-O. IS 0.15-1.50

I.90065I.50I.50I.501.50

I .OOI.00I .OOI .OOlooI.002.00002.001.502.002.002.002.00I.50I 50

3.50-4.502.00.oil200I .OO

I.502.00I .502.002.wI SM2.00

I.00I..503.501,gr

0.m I .so

I I.%l-l.011.5-11.011.5.IJ.0II.S-14.018.0-72.026.0-30.0

I.0I.0I .oI .O2.0-I.0

O.SOMo(d)0. IS-I.OOMoO.SMo(d)

10.5-17 511.9-11.011.0-125

6.0-8.03.5-4.50.50-I 00

0.4-I .OMo ..

15.5-17 7 3.6-1.6l-3.0-IS.5 1 s-s.525.0-26 5 4.75-6.0

0.9-I .25Mo: 0.9- I .25W:0.2-0.3v

2.S-3.2Cu;0.20-0.3SNh:O.OSN max2.S-3.3Cu:0.20-0.3SNb:

0.05N maxI 752.2Shlo: 2.75.3.2SCu

26.0-30.0 8.0. I I .Ol7.0-I.0 8.0-13.017.0.I.0 8.0-12.017.0-z I .o 9.0- 13.018.0-2 I .O 8.0. I I .O18.0-21 0 9.0-12.0l80-Il.0 9.0- 12.0180-21.0 80-11.018.0-21.0 9.0- I2 015.0-18.0 13.0-16.0lhOl8 0 8.0-9.0I8 O-21.0 9.0-12.0

2.0-3.OMo2.0-3.OMo: 0. IO-EONNMf)2.0-3.Ohlo2.0-3.OMo1.75-2.25Mo0.08-O. I8N2.0.3.Ohlo

18.0-21.0 ).(I- 12.018.0-2 I .O 8.0-I I .O20.5-23 5 I 1.5-l 3.5

I .SOhlo max: 0.20-0.3SSe

IY.O-21.0 9.0- 13.020.0-23 0 l(J.O-I3 022.0-26.0 12.0-15.022.0-26 0 12.0-15.022.0-7-6.0 I2.0- IS.019.5-20.5 17519.5

I SO-3.OOhlo: 0. IO-0.30Nb; 0. IO-30V;0.20~-ION

3.01.0hlo

6.0-7.OV: 0. I8-0.24N:o.so- I OOCU

23.0-27.0 19.0-22.0

20 O-12.0 13.0-27.0 -155Shlo19.0-X 0 17.5-30.5 2.0-3.OMo: 3 03.OCuI8 O-20.0 22 o-3.0 2.s-3.OMo: I .s-XCU19.0-Z I .o 3 I .o-34.0 0.5-l sv

(a) Qpe numbers of wrought alloys are listed only for nominal identification of corresponding wrought and cast grades. Composition ranges of cast alloys are not the same ascorresponding wrought alloys; cast alloy designations should be used for castings only. tb) hlaumum unless a range is given. The balance of all compositions is iron. (c)Sulfcontent is 0.04% in all grades except: CG-6hlMN. 0.030% S (mast: CF-IOSh4nN. 0.035, S tmax): CT-ISC. O.O3cc,S (ma\): CK-3hlCuN . O.OlOQ S (max): CN-3hl. 0.0306 (m~):CA-6N.0.0206S(max):CA-28hlWV.0.03O ~~S(m~):CA-U)F.0.20-O10~S:CB-7Cu-I and-2.0.03%S(m a~.). Phosphoruscontent isO.O4%~max~ inallgradesex cept.CF-l6F. 0.176 P (max); CF-IOSMnN. 0.060%, P rmax): CT-ISC. 0.0304 P tmax): CK-3h lCuN. 0.045~ P tmax): CN-3hl. 0.03Oc1 P (mar): CA-6N. 0.0204 P tmax): C28MWV. 0.030% P (max): CB-7Cu- I and -2.0.0354 P (mrlr;). td) Molbbdenutn not intrnoonall) added. or) CF-?A, CF-3MA. and CF-8A have the same composition rangesCF-3, CF-3hl. and CF-8. respectively. but habe balanc ed compositions so that ferrite contents are at Ie\els that permit hi gher mechanica l property specifications than those forlatedgrades.Theyareco~ered by ASTM A 351. [f) Nb. 8 x %,C min (l.O%, maxi: or Nb+Ta x QC t I. Iq, max). (g) For CN-7hlS. silicon ranges from 2.50 to 3.50%,


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788 / Heat Treaters Guide

Summary of Applications for Various Corrosion-Resistant Cast SteelsAllO) Characteristicsc4-I5CA-40CA-6NhlCA-6NCB-30CB-7Cu- ICB-7Cu-2cc-soCD-4hlCuCE-30CF-3. CF-8. CF-0.CF.3hl. CF-BM.CF-YC.CF-I6FCG-YhlCH-20CK-20CFu-7hl

Hidrly used in mildI corrosilr en\ ironmrnts: hardcnahlc: good eroston resistanceS~milartoCA-15at higher strength Ic\ellmproied proper&> o\er CA IS. especialI) impro\rd resistance rocaitxionOurjtanding combinations ofa=ngth. ~oughnesi. and #eldahiltv u ith moderateI good corrosion resistanceImproved performance m oxidizing eni ironmentb compared to CA- 15: excellent resistance to corrosion b nitri c acid. alkaline solutions. and many organicchemicalsHardrnahls H ith good corrorion resistanceSuprnor combination of strength. toughness. and ucldabili~ 1%th moderateI good cormston re+anceUsed in highl) owbring medtaihor HNO,. astd nunc \raterstSimilar to CF.8 in corrosion resistawe. but higher svrngth. hardness . and stress-comosion cracking resistance: txrl lent resistance to en\ ironments

rn\ol\ ing abmston orerojion-coTToj1on: usefully employed in handling hoth oxidizing and reductng cormdentsSimilmtoCC-50. but Ni imparts higher strength and roughness level>. Agmde a\ilahlc with controlled ferrireCF types: most wtdrly wed corroston-reststant alloys at ambient an d cr)ogemc temperatureshl anations: enhanced resistance to halogen ion and redwing acidsC and F \ xiations: wed \t here application does not pemtit posnrcld heat treat.Agradessvailsble M ith controll ed femteGreater resistance to pitting and corrosion in reducing media than CF-8hl: not suitahlr for nitric acids orothrrstrongl) ovidring environmentsSuperior to CF.8 in specialized chemical and papsrnpplication~ in resistance IO hot HJSOI. org.+ acids. and dilure H+SO,. rhe high nickel an d chromium

contents also make thus alloy less susceptthle to tntergranular conosion after exposure to carhtde-precipitstng trmpcraruresimproved corroston wsistance com pared to CH-20HighI) resistant to H,SO,. H xPO,. H&GO,. salts. and seawater. Good resistance to hot chloride -11 solutions . mtric acid. and many reducing chemicals

Welding Conditions for Corrosion-Resistant Steel CastingsACIdesignation Pw ofelectrodes used(a) T Preheat OF Poshreld heat treatmentCA-6Nhl Same compositionCA-15 410CA-40 -I IO or 120CB-7Cu Same compoiition or 308CB-30 442cc-so 446CD-4hlCu Sdmc conipo>tllonCE-30 312CF.3 308LCF.8 308CF.YC 347CF-3hl 316LCF-8hl 316CF-I2hl 316CF-IhF 308 or 308LCF-20 308CG-YM 317CH-20 309CK-20 310CN-7hl 320

100-150XX-3152(x)-3 I5315-42s20@7OO

700

Not requtred

Nor requtredNot rrqwredNot requiredNot requtredNot requiredNot requiredNot requiredNot requiredNot requiredNot requiredNot requiredNot requiredNot required

590-620 C I I 100. I I .50 n610-760CtII2S-IXX)~F1.lurc~~~l610.760C I II25-lUWFj,iurcoolSO-590 T I YOW I IOU Fj. air cool790 T ( I-150 FI. nu n. atr cool900C I I6iOFt. arc001Heat to 1120C tIO5OF). cool to ItUOC ( IYOO F). quenQuench from I OW I I20 C i2OOO-20.50 F)Llsuall~ unneccssagQuench from I t2-0 I I20 C I I YOO-2050 F)llsudl~unnrsrssqhIidl) uM+XSSLUJ

-UN

Quench from 1070-I 150C t lYS@1100F~Quench from 1070-I ISOT (IYSO-2100F)Quench from IOYO- I I.50 C (2000-2 100F)Quench from IOYO- I I50 C t X00-2 IO0 FJQuench from IWO-I 110C t IYW20SOFtQuench from IOYO- I ISWC (XXI-2lOOF)Quench from I @X1- I I80 C (X00-2 I SO F)Quench Tom I 120 T t2050 F)

Note: hletal arc. inert-gas arc. and electroslng \t elding methods can be used. Sugared electrical ssrttngs and electrode rircj for \ arious wctton thicknesses arc:Section thickness,mm (in.) Electrodediameter, mm (in.) Current.A hbximum mvoltage, V3.2-6.4 t +,i) 2.1t3h:l 45-70 2-l3.2-6.-l ( i-,il 3 2lb) 70. I05 253.1-6.4 I &,) 1.01j.3~1 100-140 156.4-I 3 Is,-,;) -

-1.8 13.,(4 I 30- 180 6?13t. ) 6.4 I I., I 110-290 7t;11 Lime-


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Cast Stainless Steels / 78

Compositions of ACI Heat-Resistant Casting AlloysAC1 designation UNSnumber ASTM specfications(a) C

Composition, S(b)Cr Ni Si (max)HAHCHDHEHFHHHIHKHKSOHKU)HLHNHPHP-SOHZ(s)HTHI-30HlIHHHX

A217 0.20 max 8-10 I .Oo19605 A197.A608 0.50 mab 26-30 4 ma\ 2.00193005 A 97. .A608 0.50 max 26-30 4-7 l?.caJY 3403 A297.A608 0.10-0.50 26-30 Y-II 2.00JY2603 A2Y7.A608 O.O-0.40 IY-23 Y-12 1.00593.503 4 297. ,460x. AU7 0.~0-0 so 21-28 II-11 1.00JY4003 AY7.AS67.A608 0.20-0.90 26-30 14-18 2.00JY127-I A 397.435 I. AS67. A608 0.70-0.60 2-l-28 18-22 2.00

A351 0.25-0.3s 23.0.17.0 19.0-22.0 I .7sA351 0 35-0.4s 23.0>27 0 lY.0.110 I .7s

J946O-t A297.A608 0.10-0.60 28-32 18-22 XKIJ942 I.3 A:Y7,A608 0.~0-0.50 19-23 23-27 2.00

A 197 Cl 35-0.7s 24-28 33-37 2.ocl0 -Is-o.ss 24-28 33-37 2.50

194605 A297.A3Sl.AS67.A608 0.35-0.75 13-17 33.37 7.SfJA3SI 0.2%0.35 13.0.17.0 33 O-37.0 ?.S(JA297.A608 0 354.75 17-21 37-41 2.50A 297. A608 0.50.75 10-l-t 58-62 SOA297.A608 0.35-O 7s IS-19 M-68 2.50

(a) ASTM deslgnatlons are the same as ACI desipattonl. th t Rem Fe in dl compositions. hlanpanesc content: O.R., to 0.65 5 for HA. 15 fo r HC. I .Sq for HD. and 2% for the oalloys. Phosphorusandsulfurcontents: 0.04% tmax) forall hut HP-SOkVZ. hlolvhdenum is tntentionally addcdonl) to HA. u hish hat0.90 to I 70% hlo: maximum forotheralloysissrtatO.S% MO. HHalsocontai nsO.2rL Ntmaxt tcjAIsocontains1to65 W:O.I to I.OQ~Zr.andOO35% Slma~land Ptmax,

General Corrosion Characteristics of Heat-Resistant Cast Steels and Typical Limiting Creep Stress Values atIndicated Temperatures

Alloj Corrosion characteriskzsCreep testtemperature

T OFLimiting creep stress(0.ooo1 a/h)MPa hi

HAHC

HDHEHFHH(a)HIHK

HLHNHPHP-SOWZHT

HUHU

HX

Good oxidation resistance to 650 C ( 1200 F): w idrIb used in oil refining indus tqGood sul fur and oxidation resistance up to IOYS C I 2OUO F); minimal mechanica l propertws:

used in applications where stwngh is not a consideranon or for moderate load lwanng up to6S0 C t I200 F,

650 I200 21.5 3.1870 1600 S.15 0.75

Ebcellrnt oxidation and sulfur resistance plus \\sldahili~ 981) 1800Higher temperature and sulfur resistant capabilities than HD 980 I 80Excellent general corrosion resistance to 8 IS C i IS00 FI H ith modcrate mechanical propcntes 870 16(x)High suengh: oxidation resistant to I090 C (2000 F,: most \5 idcly used 980 IS00lmprotrd owiation resistance compared to HHBecause of itzi high temperature strength. uldely used for strw.ed parts in sbuctural spphsatton>up to I IS0 C (2 I(x) F): offers good res lstance to sorrosion h) hot ga.w>. mcludmg wlfur-

bearing gases. in hoth oxtdizing and reducing conditions (although HC. HE. and HI are moreresistant in oxidizing gasej): used in illr, ammonia. hydrogen. and molten neutral salt\: m Idellused for tubes and furnace parts

9x0IWO

I800I900

Improved sulfur resistance compared to HK: cspeciall useful \\ here ewrssi\e ,caline must bra\ aided Y8tIVery high strength at high temperatures. resibtant tooxtdizing and reducing flue g&e\Resistant to both oxidizing and carhuririnp atmospheres at high temperatureslmpro~edcrecpmpturcstrrngthat lO9CCt~000F1andaho\ecomparcdtoHPHidely used in thermal shocb applications: corrosion resistant in atr. okidizing and redwing

flue gases. carburizing gases. salts. and molten metals: performs satisfactorily up to I I SO CtZIOOF, in ohidiling atmospheres and up to IO% C (2000 FI in reduang atmosphere>.provided that limiting creep stress \alurs are not exceeded

Higher hot strength than HTand ohen selected for its superior corroston resIstaweHigh hot strength and clectrkal resisti\ Ity: performs satisfactotil) to I I70 C I 20.50 FI in

strongl y oud izing atmospheres and up to IWO C I 1900 FI inoxidizing or reducmg produc t,ofcombustion that do not contain sulfur: resistant to some 4ts and molten metal 2.54 mm/yr. or 100 mils/yr). (b) Ctained 2gofsul fur/mr(S grinsS/ICO ftj. (c)Contamed 120gS/mJ(300g rainsS/IO0ftt td~Contained-10gISlnt~ilOO~~insS/lOO~~

cast stainless steels

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