Effects Of Different Temperature Control Caliber Rolling And Heat Treatment On The Microstructure And Properties Of 42CrMo

Medium-carbon low-alloy steel is widely used in the shipbuilding industry,mechanical parts manufacturing industry,and construction industry due to its excellent comprehensive mechanical properties,However,its poor weldability and low-temperature toughness limit its application.To solve the problem of using medium carbon low alloy steel in extreme environments,the 42CrMo steel is used as raw material in this paper,through caliber rolling,heat treatment,Tempforming process to control the microstructure,grain orientation,carbide distribution analysis and performance testing,etc.,the mechanism of strengthening and toughening of caliber rolling is studied.The research results show that:after the normalized 42CrMo steel is direct caliber rolled at different temperatures,the microstructure of the experimental material is composed of nano-scale carbides and ultra-fine grains with strong texture,and the tensile strength of the 42CrMo steel can reach 1200MPa,the impact toughness is higher than 100 J even at temperatures as low as-80?,which is an order of magnitude higher than the tempered state.After sub-temperature quenching of 42CrMo steel,the microstructure of caliber rolling at different temperatures is composed of ferrite and tempered sorbite.There are slender fiber grains,<101>//RD texture is strong,nano-scale spherical or granular carbonization,which relatively distributed in the matrix,and alternately in layers along the rolling direction.After sub-temperature quenching,the tensile strength of 42CrMo steel rolled at different temperatures is above 1400MPa,the sample after temperaturecontrolled caliber rolling has a lower ductile-brittle transition temperature,at the impact temperature of-80?,the impact toughness is as high as 107J,the experimental material has a good combination of strength and toughness,and the comprehensive mechanical properties are higher than that of quenched and tempered 42CrMo steel.The 42CrMo steel is fully austenitized(y)and then water quenched,and then caliber rolled at different temperatures,the structure is tempered sorbite,and the microstructure is composed of spherical nano-scale carbides,slender fiber grains and slender ferrite grains along the rolling direction of strong texture;The 42CrMo steel subjected to caliber rolling after complete quenching has relatively good strength and toughness,and the tensile strength is above 1500MPa.After complete austenitization at 850?,the samples subjected to caliber rolling at 650? have obvious inversion temperature ductile-brittle transition phenomenon.Which impact toughness is as high as 183J at-80?,and its comprehensive mechanical properties are much higher than those of modulated 42CrMo steel.There are uniformly distributed and high-density dimples in the tensile fracture,and the size and depth of the dimples are basically the same.The mechanism of strengthening and toughening of 42CrMo steel after caliber rolling is mainly due to ultra-fine grain refinement,nano-particle dispersion,and strong texture are obtained in the material structure after caliber rolling.Under the comprehensive action of these three factors the body-centered cubic steel can obtain high toughness,and have high toughness and plasticity at a lower temperature.The 42CrMo steel after caliber rolling has a large number of delamination cracks and crack bifurcations in the tensile and impact specimens.A large number of delamination cracks and crack bifurcations appeared on the tensile and impact specimens of 42CrMo steel after caliber rolling.Crack bifurcation and delamination can effectively reduce the stress concentration at the crack tip.This is also one of the main reasons for the improvement of tensile and impact properties of the material.