调质/复合感应淬火对40CrNiMo钢淬硬层组织及硬度的影响

The Influence of Tempering/Composite Induction Hardening on the Microstructure and Hardness of the Hardened Layer of 40CrNiMo Steel

摘要: 为探究调质预处理与感应淬火工艺匹配对40CrNiMo钢淬硬层组织及硬度分布的影响，设计了三种回火温度(550, 600, 650℃)与两种感应工作电流(1.3, 1.5 kA)组合下的复合热处理试验。利用光学显微镜(OM)、扫描电镜(SEM)及维氏硬度计分析了淬硬层的组织演化与硬度梯度特征。结果表明：调质回火温度决定了原始回火索氏体中碳化物的尺寸与分布状态，其中600℃回火可获得碳化物均匀细小的组织，为后续感应加热提供了理想的奥氏体化起点。感应工作电流从1.3 kA增至1.5 kA后，硬化层深增加，硬度梯度减缓，表面硬度的变化受控调质温度的影响显著。当调质回火温度为600℃、工作感应电流为1.5 kA时，复合淬火后表层硬度达60.2 HRC，硬化层深度0.96 mm，硬度梯度32.4 HRC/mm，为组织、硬度及梯度的最优匹配。

Abstract: To investigate the influence of the matching between tempering pretreatment and induction hardening processes on the microstructure and hardness distribution of the hardened layer in 40CrNiMo steel, a composite heat treatment experiment was designed under combinations of three tempering temperatures (550, 600, 650˚C) and two induction working currents (1.3, 1.5 kA). Optical microscopy (OM), scanning electron microscopy (SEM), and a Vickers hardness tester were utilized to analyze the microstructural evolution and hardness gradient characteristics of the hardened layer. The results indicate that the tempering temperature determines the size and distribution state of carbides in the original tempered sorbite. Tempering at 600˚C results in a uniform and fine carbide structure, providing an ideal starting point for subsequent induction heating. When the induction working current is increased from 1.3 kA to 1.5 kA, the depth of the hardened layer increases, the hardness gradient slows down, and the change in surface hardness is significantly influenced by the tempering temperature. When the tempering temperature is 600˚C and the working induction current is 1.5 kA, the surface hardness after composite quenching reaches 60.2 HRC, with a hardened layer depth of 0.96 mm and a hardness gradient of 32.4 HRC/mm, representing the optimal matching of microstructure, hardness, and gradient.