采用4 kW光纤激光器对厚度为4.5 mm的热轧700 MPa级纳米析出强化钢进行激光相变硬化处理, 主要研究激光功率、扫描速度对相变区组织、硬度及耐磨性的影响。结果表明, 激光相变区呈“月牙形”, 主要由三个部分组成, 由外至内依次是表面微熔区、相变硬化区和过渡区, 三个区域的组织依次分别为马氏体＋粒状贝氏体、马氏体和细小马氏体＋铁素体。激光相变硬化处理后相变硬化区和过渡区(统称“硬化层”)硬度得到提高, 平均硬度比基体提高了40～80 HV0.3。随着激光功率的增加或扫描速度的减小, 硬化层深度逐渐增加, 功率为3.5 kW时硬化层深度达到1.1 mm。当扫描速度为20 mm/s, 激光功率在2.0～3.5 kW之间时, 激光相变硬化后试样的耐磨性较基体提高了29%～44%。研究结果表明激光相变硬化可显著提高实验钢的表面硬度和耐磨性能。

In this paper, hot-rolled nano-scale precipitate strengthened steel was used for laser transformation hardening with a thickness of 4.5 mm by 4 kW fiber laser. The effects of laser power and scanning speed on microstructure, hardness and wear resistance were investigated. Results showed that laser transformation zone was “crescent”, mainly consisted of three parts, surface micro-melting zone followed by phase transformation hardening zone and transition zone from the outside to the inside. The microstructure were martensite＋granular bainite, martensite, and fine martensite＋ferrite, respectively. The hardness of phase transformation hardening zone and transition zone (called “hardened layer”) were improved. Compared with matrix, average hardness of hardened layer was improved by 40～80 HV.0.3 With increasing laser power and decreasing scanning speed, the depth of the hardened layer increased gradually; when laser power is 3.5 kW, the depth of the hardened layer was 1.1 mm. When scanning speed is 20 mm/s, the laser power is between 2.0～3.5 kW, compared with matrix, the wear resistance of sample after laser transformation hardening was improved by 29%～44%. The results showed that laser transformation hardening can significantly improve the surface hardness and wear resistance of experimental steel.