回火温度对大尺寸锻态35CrMo钢微观组织和力学性能的影响

研究了回火温度对大尺寸锻态35CrMo钢调质处理后组织特性及力学性能的影响,特别针对回火过程中渗碳体的析出动力学及大尺寸试块的组织性能不均匀性展开了分析。结果表明,锻坯热处理前的铁素体、珠光体带状组织经调质处理后完全消除,最终组织为含有大量渗碳体析出的回火马氏体,同时试块心部包含少量分布于原奥氏体晶界的回火贝氏体。回火过程中渗碳体的析出分为C扩散控制的快速长大阶段和Cr扩散控制的尺寸稳定阶段。锻态35CrMo钢经调质处理后仍存在力学性能各向异性,随着回火温度的升高,试验钢横、纵向强度下降,塑性和韧性同步提升。经综合考虑,当回火温度为570 ℃时,其强度、塑性和韧性具有最优匹配。

Influence of tempering temperature on microstructure and mechanical properties of forged 35CrMo steel with large-scale

Influence of tempering temperature on microstructural characteristics and mechanical properties of forged 35CrMo steel with large-scale was investigated after quenching and tempering, especially focusing on the dynamics of cementite precipitation during tempering process and the inhomogeneity of microstructure and mechanical properties. The results show that the banded microstructure of ferrite and pearlite in the forged steel can be completely eliminated after quenching and tempering, the microstructure is mainly composed of tempered martensite with abundant cementite, and some tempered bainite along prior austenite grain boundary is also observed. The kinetics of cementite precipitation can be divided into two stages comprising rapid growth stage controlled by C diffusion and steady size stage controlled by Cr diffusion. The anisotropy of mechanical properties still exists in the forged 35CrMo steel after quenching and tempering. With the increase of tempering temperature, the transverse and longitudinal strengths decrease, while the ductility and toughness are improved concurrently. It is concluded that the optimal combination of strength, ductility and toughness can be obtained when tempered at 570 ℃。