P20模具钢的双层回火激光熔覆修复技术

Dual-layer Temper Technique for Laser Cladding Repair of P20 Mold Steel

传统的焊接方法修复失效模具,易造成较大的热输入,导致热影响区性能恶化,需要进行后续高温回火热处理。利用双层回火激光熔覆修复技术,通过充分利用后道熔覆层对前道熔覆层的回火作用,可免去后续回火热处理步骤。采用3.5kW半导体激光器对P20模具钢进行了双层回火熔覆,基于修正后的Higu-chi模型确定了最优层间能量密度组合,利用光学显微镜和显微硬度仪表征了修复部位热影响区的微观组织和硬度分布。结果表明,P20模具钢最优的双层回火激光熔覆层间能量密度组合为5&10kJ/cm2;采用该能量密度组合的双层回火激光熔覆修复工艺,可获得组织为均匀回火索氏体、平均硬度约400HV的修复热影响区,其修复效果优于需要进行后续回火热处理的传统单层模具修复工艺。

Mold repair using conventional welding methods is likely to cause a large heat input, resulting in the deterioration of performance of the heat affected zone （HAZ） and the need for subsequent high-tempera- ture heat treatment. This paper presents a dual-layer temper laser cladding repair technique, which can avoid subsequent high-temperature heat treatment by taking full advantage of the temper effect of the second layer against the first layer. Dual-layer temper cladding repair was carried out on P20 steel plates using a diode la- ser of 3.5 kW. Interlayer power density combinations were determined by the modified Higuchi model. Opti- cal microscope and micro-hardness tester were used to characterize the morphology, microstructure and hard- ness profile of the HAZ of the repair area. The results show that the optimal power density combination for dual-layer temper laser cladding repair of P20 mold steel is 5＆10 kJ/cm^2. The dual-layer temper laser clad- ding repair technique using this optimal power density combination can obtain a better repair effect than the traditional single-layer repair technique that need subsequent heat treatment, and the microstructure of its re- pair HAZ is tempered sorbite and its hardness is approximately 400 HV.