Study On The Strength And Toughness Of 35CrMoA Steel By Intercritical Hardening

The experiment scheme was designed by using orthogonal regression to analyze the influence of original structure,quenching temperature and tempering temperature on the strength and toughness of 35CrMoA steel and discuss these problems,which were content and shape of martensite and ferrolites,austenite crystal grain, transition character of non-homogeneous after intercritical hardening .The experimental result proved that: (1)Original structure had certain influence on the mechanical property of intercritical hardening. Comprehensive mechanical properties of quenched and tempered 35CrMoA steel after prequenching was higher than hot rolled,normalized,quenched 35CrMoA steel.(2)Intercritical hardening was proceeded from 780℃to 810℃, along with power-up of heating-up temperature, the ferrolites decreased and martensite increased. 35CrMoA steel had the highest strength,hardness and toughness which ferrite content and morphology to achieve the best at 800℃.(3)The result of analyzing quenching microscopic structure indicated that ferrite phases were the uniform distribution of granular and a few needle-like and the organizations are more coarse, when original structure was hot rolled,normalized. When original structure was quenched and quenched and tempered, ferrite phases were the uniform distribution of needle-like and a few granular and the organizations were small, quenched and tempered 35CrMoA steel have a larger number of needle-like ferrite and distributed more evenly.This was why mechanical property of quenched and tempered is higher than that of hot rolled,normalized,quenched. (4)The result of crystal analysis indicated: non-dissolved ferrolites inhibited austenite's growth. Low heating-up temperature of intercritical hardening reduced the velocity of atomic diffusion. So the grain of 35CrMoA steel after intercritical hardening was thinner than convential quenching. (5) The result of fractography analysis indicated: 35CrMoA steel after conventional quenching and tempering treatment, fracture surface are a small number of dimples and quasi-cleavage, the fracture is more flat. when the intercritical hardening temperature is 800℃, fracture has obvious dimples,showing a typical ductile fracture,which effectively improved the toughness of the material.(6) Under the conditions of the intercritical hardening, martensite shape has a relationship with the quenching temperature.Quenching temperature have an impact on the ferrite content and shape of an impact,enabling intercritical hardening temperature is not the same time, martensite shape had changed.(7) Hot rolled 35CrMoA steel's strength and hardness is slightly lower than that of conventional fully quenched after 800℃quenching and 550℃tempering,but the toughness to be improved significantly. Quenched and tempered 35CrMoA steel's strength and hardness is not only slightly higher than that of conventional fully quenched after 800℃quenching and 550℃tempering, but also the toughness to be improved significantly. Hot rolled and quenched and tempered 35CrMoA steel's mechanical properties are better than 850℃convential quenching after 800℃quenching.