Study On Heat Treatment Process Of 30CrMo Steel By CSP Process

The alloy steel 30CrMo has been widely used in the field of petroleum chemical industry,machinery manufacturing,tool and mould industry because of its excellent mechanical properties.Previous studies showed that,30CrMo steel strip produced by CSP technology has obvious advantages in terms of surface decarburization,composition segregation,microstructure and properties of stability compared with the traditional hot rolling process.However,its final properties often depend on the heat treatment process for 30CrMo steel.In this paper,hot rolled strip steel of 30CrMo produced by CSP process is studied.The change of microstructure and properties under different heat treatment processes are studied systematically,which provides the theoretical basis for the formulation of heat treatment process.Study on the quenching process of CSP hot rolled steel strip of 30CrMo showed that,the initial microstructure of the test steel is composed of fine and uniform pearlite and ferrite.During the reheating process,the initial microstructure transforms into austenite.The increase of the temperature and the prolonging of holding time in the quenching process promotes the grain growth.The austenite growth kinetics model is D=392189.3exp(-1.02×105/RT)t0.031;The martensite structure was obtained after both water quenching and oil quenching.But the types,sizes and mechanical properties of martensite are different under different process conditions.The lamellar martensite and the strip martensite gradually transform into the martensite structure.Coarse grain size increases the size of martensite.The strength and hardness decrease,the elongation increases after quenching.The yield strength under different heating processes can be expressed asσs=-4050.4+16272.2d-1/2;Study on the decarbonization behavior of quenching soaking stage of 30CrMo steel showed that,the decarburized layer thickness increases gradually with the increase of quenching temperature and the prolonging of holding time.But the decarburization thickness decreases firstly and then increases between 1100℃ and1200℃.Decarbonization layer thickness is fitted by the mathematic model.Study on the tempering process of CSP hot rolled steel strip of 30CrMoshowed that,Martensite starts to recover and the carburizing body begins to precipitate with the increase of temperature and time in temper condition.Cementite separates out from the interface.The compressive strength and hardness decreased,the elongation increases.Secondary hardening appears after 5 hours.In summary,The best quenching process of the test steel is 860-900℃,holding times of 15 min,oil quenching.The optimum tempering temperature is 400-500℃,and the optimum tempering time is 5 hours.