Effect Of Sub-temperature Quenching On Microstructure And Properties Of 22SiMnCrNi2Mo Steel

This paper mainly studies the influence of direct quenching and QLT subcritical quenching on the steel structure and properties of 22SiMnCrNi2Mo,and discusses the influence of different heat treatment parameters on the toughness of the two kinds of heat treatment processes,as well as the contents and morphology of martensite and ferrite.According to the experimental results,the optimal quenching process is determined,which can provide the basis for the engineering application.The experimental results show that:(1)adopt direct quenching,with the increase of quenching temperature,yield strength and tensile strength of 22SiMnCrNi2Mo steel increase with the increase of quenching temperature.The growth rate of Yield strength of tempering is bigger than the tensile strength at 200?,but the growth rate of tensile strength of 500? tempering is big than the yield strength.(2)direct quenching and tempering after 200?,low-temperature impact toughness of 22SiMnCrNi2Mo steel increase with the increasement of the quenching temperature.Direct quenching and tempering after 500 ?,low-temperature impact toughness of 22SiMnCrNi2Mo steel increase with the quenching temperature rise.(3)after direct quenching and 200? tempering,the content of ferrite and retained austenite decrease,the relative contents of martensite increases along with the increase of quenching temperature.As the ferrite is decreasing,the form is continuously refined into a needle,and the tissue becomes thinner and more uniform.Direct quenching after 500?,ferrite always exists in the form of block in organization.The basic form has no change,but the relative content of ferrite decrease just as the rise of quenching temperature.(4)810?840? directly quenching and tempering after 200?,fracture microstructure under 40 ? is composed of lots of toughening nest,and rarely has crystallization field.Shear deformation of the lip of the fracture is more and more big with the increase of quenching temperature.500 ?tempering-there is a small amount of impact fracture surface toughness under 40 ?,and is basically composed of quasi cleavage plane and torn edges.(5)adopt QLT subcritical quenching and 200? tempering,22SiMnCrNi2Mo steel strength improve before the rise of temperature,the growth rate of the tensile strength of tempering is bigger than Yield strength at 200?.And low temperature toughness is just the opposite,it increases first after lower with the increase of quenching temperature,the lowest at 830?.(6)by QLT subcritical quenching and 500? tempering,the strength of 22SiMnGriSNi2Mo steel rises as the temperature,the growth rate of tensile strength and yield strength is same.The low temperature toughness was reduced first and then increased,but the change was smaller.(7)the strength and low temperature toughness of QLT is reduced with the increase of tempering temperature,while the elongation of the fracture increases with the increase of the tempering temperature.(8)the organization after QLT subcritical quenching and 200? tempering is plate strip and needle distribution,and it is the form of the spacing between martensite and ferrite,ferrite ductile phase interval surrounded the strengthening phase fibrous martensite.Steel have been exist in acicular ferrite,morphology and distribution did not significantly change,and ferrite exist in block form after QLT subcritical quenching and 200? tempering.(9)it is toughening fossa fracture after QLT subcritical quenching and 200? tempering,and the distribution of toughening nest has not changed with the change of the quenching temperature.AS QLT subcritical quenching and 500 ? tempering as Direct quenching after 500 ?,there is a high proportion of crystalline fracture area,and the shear lip out fracture tearing trace is not obvious,fracture surface is composed of quasi cleavage plane and torn edges,with a certain amount of toughness.(10)to compare directly the quenching and QLT subcritical quenching process,QLT is found that the quenching process for quenching temperature 830 ?,tempering temperature 200 ?,material tenacity can achieve the optimal.