淬火和回火工艺对3.5Ni钢组织和力学性能的影响

Effect of quenching and tempering process on microstructure and mechanical properties of 3. 5Ni steel

通过拉伸和冲击试验以及SEM、TEM和EBSD组织观察,研究了不同热处理工艺参数对3.5Ni钢显微组织和力学性能的影响。结果表明:3.5Ni钢在860℃保温1 h水淬后得到细小的板条马氏体(LM)加粒状贝氏体(GB)组织;570℃回火后,LM的板条变粗,GB中的M/A岛也溶解消失,基体上有大量渗碳体析出。随着回火温度的升高,板条继续合并长大,并且开始出现多边形铁素体,渗碳体也不断长大。回火温度为570~600℃时,低温韧性随回火温度的升高而增加,但是继续升高回火温度会使得低温韧性下降。研究表明:3.5Ni低温钢经860℃水淬+600℃回火的热处理可以获得最佳的力学性能。

Influence of heat treatment processes on microstructure and mechanical properties of 3. 5Ni steel were investigated by means of tensile test,impact test,SEM,TEM and EBSD. The results show that the microstructure of fine lath martensite and granular bainite is obtained for the steel by water quenching at 860 ℃ for 1 h. After tempering at 570 ℃ for 1 h,martensite laths start to merge and broaden,M / A island in the granular bainite is dissolved and some fine cementite is precipitated dispersively in ferritic matrix. With the increase of tempering temperature,the martensite lath width increases,polygonal ferrite appears and cementite size also increases.Cryogenic toughness is improved by increasing the tempering temperature from 570 to 600 ℃,but decreased by the further increase of tempering temperature. The best combination of mechanical properties of the 3. 5Ni steel occurs by quenching at 860 ℃ in water and then tempering at 600 ℃.