780 MPa级微合金钢的激光相变硬化工艺及组织性能

利用4 k W光纤激光器对一种780 MPa级Nb-Ti-Mo微合金化的低碳钢进行了激光相变强化处理,研究了激光功率和扫描速度对激光相变区宏观形貌和显微硬度的影响,讨论了激光相变区显微组织的演变规律.结果表明:随着激光功率的增加或扫描速度的降低,激光相变区宽度和深度逐渐增加.激光相变区包含三个区域:微熔区、硬化区和过渡区.微熔区显微组织为铁素体、粒状贝氏体和马氏体;硬化区显微组织为全马氏体;过渡区为相对细小的全马氏体或与铁素体的混合组织.在所研究的参数中,硬化区的硬度可超过母材30%左右,平均硬度达到320 HV.实验钢表面耐磨性能提高30%左右.

Laser Transformation Hardening Process and Microstructure and Properties of 780 MPa Grade Micro-alloy Steel

A Nb-Ti-Mo micro-alloyed ultra-high strength hot-rolled low carbon steel was treated by laser induced phase transformation hardening process， using IPG 4kW fiber laser. The effects of laser power and scanning speed on macroscopic morphology and mirco-hardness were investigated. The microstructure evolution in laser transformation zone was also discussed. The results showed that when the laser power increased or the scanning speed decreased， the width and depth of the laser transformation zone increased. Laser transformation zone can be characterized into three smaller zones in general: micro-melting zone (MZ)， hardening zone (HZ) and transition zone (TZ). In this study， the microstructure in the MZ was ferrite， granular bainite and martensite， whereas the microstructure in the HZ was fully martensite， compared to the microstructure in the TZ which consisted of the relatively finer individual martensite and the structure mixed with ferrite and martensite. The average hardness of the HZ reached 320HV， which was 30% higher than that of the matrix. The wear resistance of the steel was significantly improved by 30% after the laser treatment.