Influence of Tempering Temperature on the Microstructure and Properties of 25SiMnNi2CrMo Steel

In order to improve the mechanical properties and quality of drill products,the influence of different tempering temperatures on the microstructure and mechanical properties of 25SiMnNi2CrMo steel are studied by using of OM,TEM,impact test and tensile test.The results show that,with tempering temperature increasing after normalizing at 920 ℃,the tensile strength and hardness of the tested material reduce gradually,that the toughness falls after rising,then rises again,and reaches mximum value after tempering at 300 ℃,and that the temper brittleness appears after tempering at 450 ℃.The experimental material has better matching of strength and toughness after tempering at 300 ℃.The mechanical properties are as follows:tensile strength σb 1391MPa,hardness HRC 40 and impact strength AKV 72.5 J.The microstructure of 25SiMnNi2CrMo steel consists of tempering martensite,bainite and retained austenite after tempering at below 300 ℃.When the tempering temperature exceeds 350 ℃,the retained austenite is decomposed and carbide precipitated,the precipitated carbide has the tendency of gathering and glomeration with the tempering temperature increasing.The best tempering process of 25SiMnNi2CrMo steel is put forward.