Research On Reversed Austenite Control And Performance Of Low Carbon Martensitic Stainless Steel

ZG0Cr13Ni4Mo has a wide application prospect due to its excellent corrosion resistance and high strength and toughness.Its plasticity and toughness are mainly affected by the content and morphology of reversed austenite,so it is of great significance to control the reversed austenite in ZG0Cr13Ni4 Mo.In order to systematically analyze the influence of reversed austenite content and morphology on mechanical properties,this thesis,taking ZG0Cr13Ni4 Mo low-carbon martensitic stainless steel as the research object,studies the influence of tempering treatment,original directional solidification microstructure and original as-cast microstructure on the formation of reversed austenite and mechanical properties during tempering.It provides experimental basis for the preparation and engineering application of large low-carbon martensitic stainless steel components.The microstructure of 0Cr13Ni4 Mo steel is characterized by XRD,SEM and EBSD.It is found that the secondary tempering of 0Cr13Ni4 Mo steel at different temperatures from530℃ to 630℃ results in the nucleation of reversed austenite in the original austenite grain boundary,martensite lath boundary,martensite lath bundle boundary and martensite lath.When tempering at a lower temperature of 550℃,the reversed austenite nucleates mainly in the form of shear;when the tempering temperature exceeds 570℃,the reversed austenite mainly nucleates in the form of diffusion.With the increase of the secondary tempering temperature,the content of reversed austenite,tensile strength,elongation and product of tensile strength and elongation all increase first and then decrease.When the secondary tempering temperature is 590℃,the content of reversed austenite(16.3%)in 0Cr13Ni4 Mo steel is the most,and its tensile strength,elongation and product of tensile strength and elongation are the highest,respectively 1090 MPa,22.79% and 24.8GPa· %.The 0Cr13Ni4 Mo steel ingots with directional solidification microstructure are prepared with the pull-down speeds of 1μm/s,5μm/s and 50μm/s,which is found that with the increase of the pull-down speed,the directional growth of austenite dendrites gradually refines,the content of reversed austenite in the heat-treated microstructure gradually increases,and its tensile strength and product of tensile strength and elongation gradually increase.When the pull-down speed is 50μm/s,the content of reversed austenite in steel(8.61%)is the largest,and its tensile strength and product of tensile strength and elongation are the highest,respectively 975 MPa and 21.1GPa· %.Through the original as-cast microstructure with different solidification speeds obtained by pouring step castings with thicknesses of 40 mm,60mm and 80 mm,it is found that the grain size of the casting increases and the content of reversed austenite in heat treated microstructure decreases with the increase of casting thickness.After heat treatment,the content of austenite in the casting with thickness of 40 mm is the highest(10.04%),and the tensile strength,elongation and product of tensile strength and elongation are the highest,which are 935 MPa,20.8% and 19.4GPa·%.The TRIP effect of reversed austenite improves the comprehensive mechanical properties of 0Cr13Ni4 Mo steel.