Effect Of Vanadium And Nickel On Properities Of18Cr-2Mo Ferritic Stainless Steel

With the shortage of nickel resources, developing low nickel ferriticstainless steel is a trend in the world.18Cr-2Mo ferritic stainless steel is themost typical one of the high chromium ferritic stainless steel, while the poorimpact performance, high ductile to brittle transition temperature, poorweldability and some other shortcomings all restrict its development andapplication when using as thick plate. In order to resolve these problems, thisarticle has systematically investigated the influence principle of vanadiumand nickel on the materials’ microstructure, mechanical properties, corrosionresistance and weld abilities with respectively adding them into niobiumstabilizing18Cr-2Mo ferritic stainless steel, through various equipments suchas scanning electron microscope (SEM), transmission electron microscopy(TEM) and X-ray diffraction (XRD). Besides that, the aging precipitationbehavior and impact energy changing rules of niobium-vanadium bistablestainless steel, and the effect of welding heat input on the microstructure andimpact toughness have also been researched. The main conclusions are asfollows.Vanadium significantly improves low temperature and pit resistance ofthick specifications ferritic stainless steel, because carbon and nitrogen insteel would be fixed more effectively by vanadium and niobium together,dispersing in grain in terms of fine precipitations. With adding nickel, yieldstrength of test steels was improved remarkably, due to its solid solutionstrengthens effect. Meanwhile, impact toughness at low temperature has beenmarkedly improved, but steel with the addition of nickel has stress corrosioncracking (SCC) tendency.Impact toughness of ferritic stainless steel bearing vanadium rapidlydescends between750℃and950℃, specially at850℃. With aging time increasing at800℃, tested steel would precipitate sharply, and impacttoughness became poorer, due to amouts of brittleness phases precipitatingand coarsing like (Nb,V)(C,N) and Fe2Nb and so on. With the increase ofheat input, grain size of steel rapidly grew up, while its toughness declinedgently. In order to avoid grain of welding heated affected zone (HAZ)coarsening and measure the toughness, lower heat input than15kJ/cm wassuggested.Vanadium would be harm to the toughness of ferritic stainless steel HAZ,and when the total carbon and nitrogen content was lower than150ppm, allof weld joints would not generate intragranular corrosion. On the contrary,toughness of HAZ significantly could be improved by nickel, but tendency ofSCC becomes more sensitively after welding。...