Effect of Tempering Process on Secondary Hardening of HJ Low Alloy High Speed Steel

The mechanical properties and microstructure of HJ low alloy high speed steel under different kinds of tempering process were studied.The results show that by increasing the tempering temperature,the hardness of the steel increases with the retained austenite decreasing gradually.The peak of hardness reaches when the steel is tempered at 540 ℃.The carbide gathers and grows can result in the decreasing of the hardness by increasing the tempering temperature ulteriorly.But the hardness increases when the steel is tempered at 540 ℃ for 4 h with the retained austenite decreasing ulteriorly.