Effect of tempering temperature on microstructure and mechanical properties of 300M steel

The microstructure and mechanical properties of 300M steel tempered twice at different tempering temperatures were studied by Rockwell hardness tester, scanning microscope and transmission electron microscope. The results show that the strength first increases and then decreases with the increase of tempering temperature in the range of 200 °C to 400 °C; the area reduction, total elongation and impact energy also first increase and then decrease. However, it is most stable for the hardness trend. The yield strength and tensile strength of steel subjected to tempered twice at 300 °C can reach 1828.5±17.7 MPa, 1920.0±11.0MPa, the impact energy can reach 58.2±2.2 J, and the impact toughness is the best.