Effect of Heat Treatment Processes on Microstructure and Mechanical Properties of 1 000 MPa High Strength Steel for Construction Machinery

Different quenching and tempering processes were carried out for 1 000 MPa high strengthen steel for construction machinery, the effects of heat treatment processes on microstructure and mechanical properties were studied, and better quenching temperature and tempering temperature were obtained. The results show that with the increase of quenching temperature, the strength of tested steel increased up to the maximum at 900 ℃ and then decreased. After quenching below 830 ℃, undissolved ferrite exited in microstructure and the microstructure was ferrite and plate martensite. After quenching above 900 ℃, the microstructure was plate martensite. With the increase of tempering temperature, the strength of tested steel reduced, and the toughness and ductility showed a increasing tendency. When tempering temperature was above 450 ℃, the microstructure transformed into tempered sorbite, and impact ductility sharply increased. The optimized heat treatment process was quenching at 900 ℃ and tempering at 500 ℃.