Effect of heat treatment process on microstructure and properties of PH13-8Mo steel

Microstructure and mechanical properties of PH13-8Mo steel treated at different quenching and tempering temperatures were studied by means of optical microscopy,transmission electron microscopy and mechanical property test. The results show that the high strength and toughness is obtained due to the formation of fine lath martensite with high density dislocations after quenching. When tempering at about 500 ℃,the fine and dispersive precipitated NiAl phase,which retains coherent lattice relationship with matrix is responsible for the strength peak of the steel. The coherent precipitation of NiAl phase occurs at about 450 ℃,and gradually falls out of coherent lattice relationship with matrix when the tempering temperature is higher than 510 ℃. While the tempering temperature is higher than 700 ℃,precipitated NiAl phase is dissolved. The optimum comprehensive properties can be obtained for PH13-8Mo steel after quenching at 925 ℃ and then tempering at 510 ℃.