Exhaustemissionregulationsoftheautomotiveareenforcedineachcountrytopreventairpollutionandglobalwarming,andtherestrictionstandardtendstobecomeseverer.Varioustechniquessuchasthecombustionimprovementofgasoline,upgradesofthecatalyst,andthethermalcapacitydecreasesintheexhaustlinesareadoptedtosuittheregulations,andtheseleadtoanincreaseofthemaximumtemperatureoftheexhaustgas.Recently,ferriticstainlesssteelsaremainlyusedtopartsofexhaustlines,astheirthermalexpansioncoefficientissmall,andthecyclicoxidationresistanceandthethermalfatiguepropertyarebetterthanausteniticstainlesssteels.Thispaperpresentsnewlydevelopedheat-resistantstainlesssteelsfromNisshinSteelforexhaustlinesusage,anddescribesthecurrentsofthesteeldevelopmentthatcouldbeenvisagedinthefuture.Withregardtoimprovingthehigh-temperaturestrengthofferriticstainlesssteels,theadditionofNb,MoandCuiseffectiveinsolutionhardeningandprecipitationhardeningat700℃,whiletheadditionofNb,MoandWiseffectiveinmainlysolutionhardeningat900℃.TheadditionofCr,SiandMnsuppressthebreakawayoxidationinairat950℃upto200hofferriticstainlesssteelscontaining14%Cr.Especially,theadditionof0.8%orhigherMnwouldeffectivelyimprovetheadherenceofoxidescale.Itisconfirmedthatferriticstainlesssteels,NSSHR-1(14Cr-lMn-0.9Si-Nb)andNSSHR-2(10Cr-0.9Si-Nb-Ti),ishavingasuperiorheatresistance,formabilityandcostperformancecomparedtoconventionalType441andType439respectively.
