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1、铁素体不锈钢在中国推广应用的若干问题不锈通览一!毽中国特钢企业协会不锈钢分会康喜范如f1引言中国不锈钢表现消费量已连续多年处于世界第一消费大国的位置,2004年12005年分别为447万tH522万t,约占世界消费量的25%.在所消费的钢种结构方面,铁素体不锈钢所占比重偏低,2004年仅占10%.与世界铁素体不锈钢平均消费水平(25%)及某些发达国家(40%)相比,相差甚远.不合理的消费结构致使镍资源大量浪费,这不仅是一经济问题,在达到基本自给的情况下还将危及不锈钢产业链的安全和完整.造成这种不合理的消费,除消费理念外,不具备生产高性能铁素体不锈钢先进生产线是重要原因.我国现已建立两条较先进的
2、不锈钢板带生产线,已具备生产各种类型铁素体不锈钢的能力,因此推广应用铁素体不锈钢的时机已趋成熟.铁素体锈钢的应用,当达到一个较合理的比例后,不仅会具有巨大的经济效益,而且可节约大量镍资源,对国民经济的持续良性发展将具有重大的战略意义.2铁素体不锈钢的特性2.1铁素体不锈钢的化学成分和分类化学成分特点:铁素体不锈钢是一类含铬lO.5%3O%,含碳小于0.l2%,在使用状态下其组织是以铁素体为主的一系列铁铬合金.为了扩大应用范围和解决在使用过程中暴露出的问题,常常通过降低碳,氮和加入MO,Si,Al,Ti,Nb,S和Se等元素赋予其不同的特性.分类:依据钢中的铬含量可将铁素体不锈钢分为低铬(11%
3、15%Cr),中铬(16%一22%Cr)和高铬(23%一32%Cr)三类,其典型钢号见表1和表2.表1低铬和中铬铁素体不锈钢的化学成分/%Table1ChemicalcompositionofLowCrandmidCrferritlcstainlesssteels制号TypeSteelGradeCSiMnPScrMoNNb啊低OcrllIIl(409)O.o81.0o1.0oO.040,04lQ予叫】6XC铬o0Crllm(4o9L)O-031.0o1.0oO.04O.041Q5】6XC型LowO0cfl2(410L)0.o31.O01.00no4no4l1驴吨王oCrO0Cr15Nb(R42
4、9EX)0,031.0o1.0oO.04O.0413O叫印O.3叮1017(430)O,12O.8O.8O.035,O,o3】6O叫8o中00Crl7Ti(43oLX)no3n8n8O.035n0316D叫9=on1qo铬0oD19(:um(43oJ】L)O.0251.001.0oO.04O.O3】6伽O.o258X(C+IO型00CrlSMol(434)O.121.O01.0o0.04O.o3】6O叫8oO.75哇25MidOOer18Mol砸(436I.,)O.0251.O01.00O.04O.03l6O叫90O.75Jj.O-021lX(c+N)-1175Cro0Q18Mo2(444)O
5、.o251舶1舯0.04O.O31加瑚1.75O.o28x(C+N),-OO00Q2O.o251舶1加0.04O.O32】401.5咖0.025铁在不锈通览ATIONOFFERR1CSTAISS砸INCHINAKangXffanSteelCouncilofChinaSpecialSteelEnterprisesAssociation1n1trOdUCtiOnChinahasbeentheworldNo.1intheapparentconsumptionofstainlesssteelformanyyears,respectively4.47milliontonsin2004and5.22mil
6、liontonsin2005,accountsforabout25%intheworldconsumption.Amongthetotalconsumption,ferriticstainlesssteelhasasmallshare,only10%in2004.Comparedwithworldaverageshareof25%,andsameofdevelopmentcountrysshareof40%.thisconsumptionst.ructurecausesthewasteofnickelresource.Besidesthecost,thisstructtirewillinflu
7、encethestainlesssteelindustriaLchain.Theconsumptionconceptisoneofthereasons,butthekeyimportanceisthattherewasnoadvancedproductionlineforhighperformanceferriticstainlessstee1.TwoproductionlineshavenowbeenbuiltinChinaforferriticstainlesssteelstripofdifferentsteelgrades.whichwillexpandtheapplicationoff
8、erriticstainlessstee1.TheproperapplicationratioofferriticstainlesssteelwillincreasetheeconomicbenefitsgreatlyandsavemassivenickelresourceasweL1.Itwillhavestrategicsignificanceforsustaineddevelopmentofnationa1economy.2Characteristicsofferriticstainlesssteel2.1Chemicalcompositionandcategoryofferritics
9、tainlesssteelChemicalproperty:ferriticstainlesssteelisaseriesofferritechromealloyswith10.5%30%chrome,lessthan0.12%carbon,andmainlyinferriticstructureintheapplication.Inordertoextenditsapplicationandsolvetheproblemsoccurredintheapplication.differentpropertiesareachievedbyreducingcarbonandnitrogencont
10、ents,andadditionofMo,Si,AlNb,SandSeelements.Category:FerriticstainlesssteelcanbeclassifiedaccordingtoCrcontentintolowCrfl1%15%),midCr(16%22%)andI1ighCr(23%32%)steel,thetypicalsteelgradeisshownintablelandtable2.2.2Structureofferriticstainlesssteel?Structure:basicstructureisferritic,grainstructureisBC
11、C.?Martensite:undercertainheattreatmentcondition,someferriticstainlesssteelgradesmayhavemartensiticstructure,dependingonsteelcontentandheattreatment.?Effectofmartensiticstructureonferriticstainlesssteelperformance:Forl7%Crferriticstainlesssteel,thetensilestrengthwillbeincreasedwiththeincreaseofmarte
12、nsiticstructure,seeFig.1.TherelationbetweenyieldstrengthandmartensiticstructureisshowninFig.2.Thereisacriticalpoint(approx.15%2O%),whenthemartensiticstructureislowerthanthisvalue,theyieldstrengthwilldecreasewiththeincreaseofmartensiticstructure.Whenthemartensiticstructureishigherthanthiscriticalvalu
13、e,theyieldstrengthwillincreasewiththehighermartensiticcontent.Buttheincreaseofyieldstrengthwillinfluencenegativelyonductility,toughnessand一2一不锈通览表2高铬铁素体不锈钢典型钢号的化学成分/%Table2ChemicalCompositionofhigh-CrferriticStainlesssteels钢号CNSiMnPS0/doNiSteel(1lade0ocr25Ni4MO4rnO.0250.0350.751.O0O.04oO.o3o24.526.0
14、3.54.53.54.5髓时(S44635254_4)O.2044X(C+N)Q800Cr26Mo10.0100.0150.400.400.020O.02o25.O一27.5o-751.5OO.30CuO.20(S44629)00Q26哳3M0Ij0.030.04o1.001.00O.04oO.o3o25.O一28.O3.O一4.01.0-3.5Ti+ICo=6x(C+N)(S4466026.3.3)qmOOCr29Mo40.010O.020O.020O.030O.025O.02028.030.03.54.2O.15C+No-c($447O029.4)cIl0.15髓0(ICr29Mo40-c
15、BOO.o451.O01.O00.040O.03o28.O一3nO3.64.21.006(c哪lm(S4473529.412)ooCr29Mo4Ni20.010O.02oO.3OO.20O.o25O.02528.030.03.54.22.Off-2.50cll0.15(S448O029.4.2)C0.0250(1Cr3OMO20.0100.0150.40O.柏0.030O.02028.532.O1.502.500.50Nb适量(44711)Ql0.202,2铁素体不锈钢的组织结构-组织结构:钢的基体为铁素体,为体心立方(bcc).量增加屈服强度增加.伴随强度增加塑,韧性下晶体结构降,耐蚀性变坏
16、.?马氏体:在定的热处理条件下,某些铁素体不锈钢可能存在马氏体.这取决于钏的J足分和热处理条件.?马氏体对铁素钢性能的影响:对于l7C1铁素体不锈钢,随钢中乌氏体量的增加,拉fll度增加,见图l.钢的屈服强度与钢中马氏体含量之间的关系见图2,显然存在一个临界点(约l5%20%),当其含量低于此点时,随马氏体含量增加屈服强度下降,当高于此临界值后,随马氏体含maenfite马氏体/t钢中马氏体的存在,具有0【+M双相结构的组织特征,有助于钢晶粒细化,从而使脆性转变温度向温度低的方向移动,见图3和图4.martensite马氏体/%图3马氏体(固溶处理温图l马氏体含量对度的奥氏体量)对17%Cr铁
17、17%Cr铁素体锈钢素体不锈钢晶粒尺寸的影毒室温断裂强度的影响响F3EffectofmartensiteFlEffectofmar(austeniteatsolutiontensiteontensiletreatmenttemperature)onstrengthofl7%CrfCrritCgrainsizCstainlesssteel(17%Cr)图2马氏体含量对l7%cr铁索体不锈钢室温屈服强度的影响Fia2Effectofmartensiteonproofstressofl7%Crstainlesssteels一3一不锈通览corrosionresistance.Thesteelwith
18、martensitewillhaveO【+Mduplexstructure,whichhelpstohavefinegrain,andlowertheembrittlementtransitiontemperature,showninFig.3and4.-475embrittlement:ferriticstainlesssteelwithCrcontent>15%issubjecttomuchlowerembrittlementafterlongtimeholdingat370?540Candslowcoolingdownthroughthistemperaturerange.Thes
19、teelembrittleatthefastestspeedat475,whichiscalled475Eembfittlement.TMsisaninherentdisadvantageofferriticstainlessstee1.Thenatureofembrittlementisthatferriticstainlesssteel,underacertaintemperature,willseparateintotwophasesbasedonSpinadalmechanismandformsubmicroatomiccongregationareawithrichCrandrich
20、Fe,thatisthereactionofO【一O【+O【.Crcontentin旺phaseisuDto61%一83%,1020mminsize,bbcandnonmagnetic.?475embrittlementisrelatedtoCrcontentinferriticstainlesssteel,thehighertheCrcontent,themoresensitivetheembrittlementis,showninFig.5+-Sensitivetemperatureof475embrittlementForCrferriticstainlesssteelof475embr
21、ittlement,thesensitivetemperatureisabout475,independentofCrcontentbutrelatedtoagingtimeembrittlementoccurrence,itisdecreasingwithlowerCrcontent.475embrittlementbehaviorsofsometypicalsteelgradesareshowninFig.6toFig.8.-Effectof475embrittlementoncorrosionresistanceofferriticstainlesssteel,O【phaseisharm
22、fultomechanicalpropertvandcorrosionresistanceaswel1.2.3PhysicalpropertiesofferriticstainlesssteelComparedwithaustenitestainlessstee1.physicalpropertiesofferriticstainlesssteelareasfollows:?Magneticascommonsteel-Highthermalconductivity,approx1.31.5timesofaustenitestainlesssteel?LowHnearexpansioncoeff
23、icient,about60%70%lowerthanaustenitestainlessstee1.DatafortypicalsteelgradesisshowninTable3.2.4MechanlcalpropertiesofferriticstainlesssteelatroomtemperatureMechanicalpropertiesoftypicalferriticstainlessgradesatroomtemperatureareshowninTab1e4.?StrengthoflowandmidCrferriticstainlesssteelisequivalentto
24、0Crl8Ni9.butelongationislower.-YieldstrengthofmidCrferriticstainlesssteelcontainingMoisobviouslyhigherthan0Crl8Ni9.?StrengthofhighCrferriticstainlesssteelishigherthan0Crl8Ni9.andYieldstrengthiSnearlydoubleof0Crl8Ni9.Itselongationislowerbutqualifiedwithcustomersneeds.2.5Embrittlementtransitiontempera
25、tureofferriticstainlesssteelFerriticstainlesssteelwithCrcontentmorethan16%hasductilitymbrittlementtransitionproblem,butitwillnothaveanynegativeeffecttotheenduserofthinproducts,especiallyunderthemodernmetallurgicaltechnology,carbonandnitrogencanbecontrolledunderalowerlever,ductility-embrittlementtran
26、sitiontemperatureismuchlowerthanthatatroomtemperature,whichcancompensatetheinferiorityofthisproperty一4一转第8页.喜曩羹喀墓不锈通览-_00I20tllecl1arpyimpacttransitiontemperature夏比冲击转变温度/图4晶粒度对17%Cr铁素体不锈钢冲击转变温度的影响Fig4EffectofferriticgrainsizeontheCharpyimpacttransitiontemperatureofcommercial17%Crsteel?475脆性:含铬大干l5%
27、的铁素体不锈钢在370540长时间保温或缓慢冷却通过此温度区间会产生塑韧性强烈下降的脆性倾向,以475脆化速度最快,这一现象称475脆性.这是铁素体不锈钢的固有缺点.其脆性本质是在一定的温度条件下,铁素体按Spinada1分解机制发生两相分离,形成富铬和富铁的亚微观尺度的原子偏聚区即:o【一o【+o【的反应结果.o【相含铬可高达61%一83%,尺寸为l02Ohm,bcc,无磁性.?475脆性与钢中的铬含量相关,随钢中铬含量增加,其脆性敏感性增加,见图5.W,Q.1101001000482Utime482停留时I4822time48ZC停留时I埘/h图5钢中铬含量对铁素体不锈钢475脆性的影响F
28、ig5EffectofCrContenton475Embrittlementofferriticstainlesssteels?475脆性的敏感温度对于产生475脖I生的含铬量的铁素体不锈钢,其出现脆性的最敏感温度均为475左右,不受钢中铬含量的影响,但出现脆性的时效时间随钢中的铬含量增加而减少.一些典型钢号的475脆性行为见图6一图8.?475脆性对铁素体不锈钢耐蚀性的影响:仅析出不仅有害于力学性能,也损害钢的耐蚀性,见图9.图6时效温度和时间对l8%Cr和Cr26Mol铁素体不锈钢脆性行为的影响Fig6EffectofagingtemperetureandtimeonEmbritfleme
29、ntbehaviorofl8%CrandCr26Molferriticstainlesssteelstime停留时问/h图7时效温度和时间对l8%Cr和Cr26Mo1钢断口形貌转变温度的影响Fig7EffectofagingtemperatureandtimeonFA1v_rofl8%CrandCr26Molferriticstainlesssteelstime停一时闻图8时效温度和时间对00Cr29Ni4Mo2钢的伸长率和断口形貌转变温度的影响Fig8EffectofangtemeperatureandtimeonelogationandFATTof00Cr29Ni4Mo2(2942)fer
30、riticfftahesssteel图9【I相对17%CrW30%Cr铁素体不锈钢耐蚀性的影响(5%沸腾盐酸,时效时间为l小时)Fig9Effectof0【oncorrosionresistanceOf17%Crand30%Crferriticstainlesssteels(5%HCl,boiling,agingtimelh)一5一不锈通览2.3铁素体不锈钢的物理性能特点与奥氏体不锈钢相比,铁素体不锈钢的物理性能有如I特点:-热导率高,约为奥氏锈铡的1.3一1.5倍.?线膨胀系数较奥氏体不锈钢低,约低60%70%.-有磁性,类似普通钢.典型代表牌号的数据见表3.表3铁素体不锈钢的典型物理性能T
31、able3TypicalphysicalpropertiesofferritieStainlesssteelsintheannealedconditionMeanCIEforOCto热导率ThermalConductivity透磁率牌号船100315538100500Magnetic11nYm?w,m?k皿cabil毋409(0(l1砸)l1.711.924I928.5430(OC17)10.4l1.011.426.126_360oll00444(OC1孙知n)10.010.6l1.426.8S635(00C5Njm)l1.023.0$44800(00Cr29Ni21vlo4)94l6-2俐1
32、(00CY30Mo2)9.717.8304(0CrlSNiS)17.2l7.818.416.221.51.022.4铁素体不锈钢的室温力学性能?些代表性的铁索体不锈钢的室温力学性能见表4.表4一些铁索体不锈钢的室温力学性能Table4Mechanicalpropertiesofferritiestainlesssteels(P.Sh.St)川号船Rm/MPa.2/MPaA/_%OCrll1t(409)380>l205200Crl5Nb(R429EX)450205221Cr17(430)/>45020522a00CrlSMo2(444)4152752000Cr25Ni4Mo4Ti(S
33、44635)6205152000Cr29Mo4Ni1($44735,29-4-1)550415l800Cr29Mo4Ni2(S44800,2942)55041520OOCr3OMo2b(44711)529392320crl孙i93o45152054o注:am1.3ram板材sheet;b一3.0ram板材sheet.退火态annealed?低铬,中铬铁素体不锈钢的强度水平与0Crl8Ni9(304)相当,但伸长率较低.?含钳中铬铁素体不锈钢的屈服强度明显高于0Crl8Ni9.?高铬铁素体不锈钢的强度高于0Crl8Ni9,其屈服强度约是0Crl8Ni9的2倍.伸长率较低,但可满足终端用户需求.2
34、.5铁素体不锈铡的脆性转变温度一6一大干l6%Cr的铁素体不锈钢存在着塑一脆性转变的弊病,但对于薄截面尺寸的终端用户不构成危险,尤其是当肓订的冶金技术水平可将钢中的碳,氮控制在较低水平的条件下,其迥一瞻眭转变温度已明显低于室温,极大地减轻了这种特性所构成的危害.2.6铁素体不锈钢的耐蚀性耐蚀性的范围很广,本文仅重点介绍它在大气中的耐锈蚀性能.?在大气中钢的耐锈蚀性与钢中的铬,钼含点蚀指数PitiilghxI一;FerrRicgra(虹%Cr+3.3/1o(铁素体钢)Auslilcgrades%Cr+3.30/do+lff/oN(呶氏体钠)侄35%NaCI溶液巾(35)点蚀电位I硼=lIlXnE
35、al:VonhnVvISCE_旺】曩叫壹图10点蚀指数与点蚀电位之间的关系Figl0Relationbetweenpittingindexandpittingpotentialofstainle88steels不锈通览量相关,通常以钢的耐点蚀指数PRE来表征,即PREu-Cr%+3.3Mo%,PRE与点蚀电位与耐锈蚀性之间的关系见图10和图ll.PRE(a)Okinawa(冲绳岛)南部海岸最严苛的腐蚀环境PRE(b)Shionomisaki(潮岬)海岸严苛的腐蚀环境PRE(C)Igauei3tl岛【J等瞒蚀王1境【a)Themostseverecorrosiveenvironment【b)Se
36、verecorrosiveenvironment(c)ModeratecorrosiveenvironmentS0utlleITlseacoastinOKnawaSeacoastatSIfionomisakiInlandatIgauenuSARN;【1本不锈钢协会制定的测.擘锈蚀点数的方法SARN:Rangntmlt幽咖血谢byJartreeStahas刚船SARN:9一无锈蚀I6一轻微锈蚀3-红锈l0-严重锈蚀SAILN:9:Nonm,6:SizhtstainTni心血,3:Redn碰唱.0;Severerus0n图l1在不同的大气环境中不锈钢的耐锈蚀性能与PRE之间的关系F11Relati
37、onbetweenpittingindexandFL1Sti/gevaluationofSARNafteroneyearexposLlreinvariousenvironment?与奥氏体锈钢比较,铁素体锈钢的耐应力腐蚀性能更加优异,适用易产生应力腐蚀的水处理环境.3铁素体不锈钢的应用范围铁素体不锈钢的可应用范围见表5.表5铁素体不锈钢的主要应用领域Tabre5Majorfieldofapplicationofferriticstainlessstee麻用代表钢号估计用量历tApplieationTypicalGradesConsumption日常用品厨房器具Dailv.articlesand
38、kitchenutensils0Crl7,OCr17砸,0Crl8Mo2洗衣机,消毒柜,热水器Washingmachine,disinfector,water0Crl7,0Cr17Ti,0Crl8Mo2太阳能热水器heater.solarenergywaterheater.0Crl7,0Crl7Ti,OCr18MO25060建筑,装饰管,防盗门,护栏decorationpipe,theflproofdoozO(17,OC17.n,01r18:Mo2屋面板,水槽,电梯handrail,pane1.sinkandelevatorooCr19Mol,00Cr22Mo撕,Oocr30MO2水处理设备W
39、atertreatmentequipmentO(18Mo2,0oCr18Mo2Ti轿车净化排气系统CarexhausterOCr11Ti,0oCIrl1Nbn,0Crl5Nb,O(17n,0oCr190lNb1520轿车装饰Cardecoration0Crl7,OCr17发电厂海水,淡水,盐水冷凝器o0Cr25Mo4Nn,oo06MO3N谄Ti,Powerplantcondcnselofseaater,fleshwaterandsaltwateroCCr29M04,ooCr29MOri,510OOCr29Mo4Ni24推广使用铁素体不锈钢面临的难题(1)大力扭转以有无磁性判断是否具有不锈性的消
40、费误.(2)钢种系列化和产品多样化?0Crl7,0Crl7Ti,0Crl8Mol,0Crl8MO2等通用型.?加速开发高铬铁素体锈钢,00Cr25Mo4一Ni4Ti,00Cr29Mo4Ni2等.?满足轿车生产对排气净化系统用铁素体不锈钢,包括深tO;耐蚀,耐热兼备的牌号.(3)确保通用型l7%Cr型铁素体不锈钢适宜f值和耐皱折性能的生产技术.?冶炼:极低碳,氮和高洁净度技术.?连铸:提高铸坯等轴晶比技术.?热轧:提高f值和改善抗皱折技术.一7不锈通览?冷轧:低成本冷轧工艺.(4)适用于铁素体不锈钢最终产品的制造_【=艺技术.5应用铁素体不锈钢值得注意的几个问题(1)长期运行温度不宜大于3O0,
41、以免引起接豢4页475脆性.(2)在低于一40C要慎重,最好不用.(3)根据使用条件和最终产品的制造工艺,恰当选择不同特性的铁素体不锈钢,如深冲,耐蚀,焊接,抗皱折性能等.(4)胀形成型制品不宜使用铁素体不锈钢.2.6CorrosionresistanceofferriticstainlesssteelAmongitswjderangeofcorrosionresistances,thepaperisonlyfocusedonitsenvironmentalcorrosionresistance.?Intheenvironment,corrosionresistanceisrelatedtot
42、hecontentofCrandMoinsteel,usuallybymeansofPRE-pittingresistanceequivalent,thatisPRETMCr%+3.3Mo%,therelationbetweenPREandpittingpotentialandcorrosionresistanceisshowninFig.10andFig.11.?Comparedwithausteniticstainlesssteel,stresscorrosionresistanceofferriticstainlesssteelismuchhigherandsuitableforstre
43、sscorrosivewatertreatment.3ApplicationfieldofferriticstainlesssteelApplicationfieldofferriticstainlesssteelisshowninTable5.4Difficultiesforfurtherapplicationofferriticstainlesssteel(1)Misunderstandingofnonmagnetism,whichisnottheonlycriteriontojudgethecorrosionresistance.(2)Aseriesofsteelgradesandvar
44、ietyofproducts-GeneraltypeofOCrl7,0Crl7Ti,0Crl8MO1,0Crl8M02?FasterdevelopmentofhighCrferriticstainlesssteel,suchas00Cr25Mo4Ni4Ti,00Cr29M04Ni2.?Steelgradesforcarexhaustingsystem,includingthepropertiesofdeepdrawing,corrosionresistanceandheatresistance.(3)Technologyofgeneraltypeof17%Crferriticstainless
45、steelsuitableforvalueandcorrugationresistant?Smelting:superlowC,Nandhighlypurifiedsteel?Continuouscasting:improvementofequalaxialgrainratio-Hotrolling:improvementoffvalueandcorrugationresistance?Coldroiling:lowcostrolUngprocess(4)Processandtechnologyforfinalproducts.5Issuesontheapplicationofferriticstainlesssteel(1)Thelongtimeoperationtemperatureshouldbelowerthan300Ctoavoid475embrittlement.(2)Carefuluseoravoidanceattemperaturelowerthan一40.(3)Properselectionofferriticstainlesssteelwithdifferentpropertiessuchasdeepdrawing.corrosionresistance,wel
