Investigation On The Micro-structure And Property Of A New Duplex Stainless Steel Obtained By Nitriding Treament On The Surface Of SUS430 Stainless Steel

SUS430 ferritic stainless steel own good thermal conductivity, low coefficient of expansion, fatigue, low price and so on, but the poor strength and low hardness etc.of this type of steel strength limits its application.Recent research show that the hardness of the nitriding low carbon stainless steel after high temperature tempering rise up to 1000 HV.To explore the possibility of industrial application of ferrite-austenitic duplex phase or austenite- martensite duplex stainless steel by nitriding treatment.The paper take the SUS430 stainless steel that widely used as the base material. The steel sheet sample of SUS430 ferritic stainless was pickled to remove the surface of the sample of scale,corrosion and other debris etc.Then sandblasting sand for the experiment of the sample after etch cleaning,to get a sandblasting effect.Once again do etch cleaning to the sample after sandblasting.Do nitriding processing for the sample aften a series of processing in the type LD50 TZ glow ion nitriding furnace.Characterization to the microstructure of low carbon alloy steel would been done after nitriding treatment using microscope(OM), X-ray diffraction(XRD), scanning electron microscope(SEM),transmission electron microscopy(TEM) and other instruments. Doing hardness and tensile mechanical properties test to the experimental steel using microhardness(HV-1000) and a hydraulic servo system(MTS-810).Ther rearch show that the core microstructure of SUS430 after low temperature nitriding(570℃,36h) is uniform ferrite grain size and the surface layer is nitride layer with small grains, and the hardness rises to 1197.7 HV from the origin 297.7HV,and the tensile strength rises up to 420 MPa,and the tensile fracture morphology of nitriding is brittle fracture and the core is of ductile fracture;The core microstructure after high temperature diffusion(1050℃,4h) is martensite and the surface layer is the mixture of surface being austenite with nitrogen and core being for the ferrite,and the hardness being for 694.8after high temperature diffusion.The tensile strength rises up to 1100 MPa after high temperature diffusion,and the tensile fracture morphology is of ductile fracture.The original organization being for SUS430 stainless steel after high temperature nitriding(1100℃,24h) acquires surface nitriding layer with fine grains.The microstructure of nitriding layer contains austenite-ferrite duplex stainless steel and decomposition nitrides and the core contains ferrite and a small amount of martensite.The tensile strength of experiment steel has greatly improved,from original 450 MPa to 800 MPa.The hardness of experiment steel increased from original 297.7 HV to 297.7HV.The tensile fracture morphology of surface layer of experiment steel after high temperature nitriding consistsof a large number of shallow nest toughness of small,being for a typical ductile fracture and the tensile fracture morphology of core of experiment steel after high temperature nitriding is part of a brittle cleavage fracture characteristics and is part for brittle fracture with tiny toughening nest.