对FV520B不锈钢零件的激光熔覆热影响区进行了组织特征分析, 结合过冷奥氏体连续冷却转变(CCT)实验、模拟热影响区拉伸及冲击实验, 研究了热影响区组织及力学性能的演变规律和机理. 结果表明, 热影响区可以按照组织演化特点分为4个特征区域: 半熔区(A区), 析出相溶解区(B区), 完全奥氏体化区(C区)和部分奥氏体化区(D区). 各区域均为马氏体组织, 靠近界面区域的组织较为粗大, 第二相发生溶解, 硬度更高, 固态相变点更低; 距界面稍远区域回火马氏体增多, 第二相未溶解, 但有长大的趋势, 硬度较低, 固态相变点较高, 接近原始材料. 决定激光熔覆热影响区组织及力学性能的最主要因素是热循环的最高温度, 最高温度越高, 强度损失越大, 固态相变点越低, 相应硬度越高, 延伸率及冲击功降低.

FV520B steel is a martensitic stainless steel developed by Firth-Vickers, with good corrosion resistance and weldability, high strength and toughness. It has been widely used in heavy load and corrosion-resistant components such as compressor impeller, valves, fasteners and pump shafts, which are easy to be damaged because of severe service-environments. The production cycle of those expensive components are long. If these components can be repaired and remanufactured, the accessional value of the products can be reserved. At the same time, it can save time, resources and funds, and reduce environmental pollutions. Laser cladding is an attractive green reconstruction technology, which is widely used for the remanufacturing of faulty metal parts. However, the heat-affected zone (HAZ) of remanufactured parts will experience cycles of heating and cooling during the cladding operation, its properties will change and may be extremely different than that of the unaffected area of the base material. Hence, the study of HAZ of FV520B steel is essential. The laser cladding on FV520B stainless steel was conducted to investigate the evolutions of microstructure and mechanical property of HAZ. The microstructure of the HAZ was characterized by means of OM and SEM, and hardness distribution was measured. Thermo-simulation was carried out to analyze the continuous cooling transformation (CCT) diagram, which provides useful instructions to investigate the microstructure evolution of HAZ. Simulated HAZ specimens and its mechanical properties were obtained by Gleeble 3500 thermal/mechanical simulator and MTS 810 material testing system. The results indicate that, HAZ can be divided into four zones: semi-melton zone, precipitation dissolved zone, completely austenization zone and partially austenization zone. The microstructures of the HAZ are martensite, the grain grows and second phase particles dissolve in the areas near the fusion zone. Meanwhile, its martensite transformation start temperature lower, and hardness higher than that of the unaffected area of the base material. The maximum temperature of thermal cycle dominates the evolution of microstructure and property of HAZ. With the decrease of the maximum temperature, the solid-state transformation temperature, elongation and impact energy increase, and the hardness decrease. Thermal cycle have a little influence to the tensile strength of HAZ under the processing parameters in this study. It can be speculated that the reduction in impact toughness and elongation of the HAZ can be controlled by decreasing the scanning speed of cladding.