【摘要】 采用6 kW多模光纤激光对激光选区熔化（SLM）工艺制备的GH3536(SLMed GH3536)与304不锈钢（SLMed 304）进行了对接焊接试验，在氩气氛围中对接头进行了多次815℃热处理。利用光学显微镜（OM）、扫描电子显微镜（SEM）、能谱分析仪（EDS）、X射线衍射（XRD）、显微硬度仪、拉伸试验机及冲击测试机对不同热处理参数下的接头微观组织和力学性能进行了表征与分析。研究结果表明：在815℃热处理温度下，随着热处理时间的增加，焊缝组织未发生明显变化，但沿着凝固晶界析出颗粒状MoC，颗粒数量与热处理时间呈正相关；随着热处理时间的增加，SLMed GH3536/SLMed 304焊缝组织中大量凝固的亚晶界逐渐消熔，但在凝固亚晶界处会析出少量颗粒状MoC；热处理后接头的显微硬度略有增加，拉伸强度略有降低，但各热处理参数下的接头拉伸强度均大于304母材，热处理后的断后伸长率增大了约10%，且热处理次数对拉伸强度基本无影响；随着热处理时间的增加，接头的冲击吸收能略有下降；在拉伸断口及冲击断口处均观察到大量韧窝，断裂方式均为韧性断裂。更多还原

【Abstract】 Objective GH3536 exhibits outstanding resistance to thermal corrosion, oxidation resistance, high-temperature stability, and microstructural stability. 304 stainless steel has high strength, excellent mechanical properties, strong corrosion resistance, low density, and low cost. At present, the selective laser melting(SLM) preparation process of these two materials is close to maturity. Laser welding has the advantages of high energy density, precise energy control, small heat-affected zone, small post-welding deformation, flexible and controllable beam focusing, and the ability to be implemented in an atmospheric environment. By effectively combining the SLM technology with the welding technology and leveraging the respective advantages of each technology, a better manufacturing strategy can be formed in the manufacturing of hot-service components in aerospace fields. Components such as combustion chambers and engine air intakes in aerospace fields undergo complex thermal environments during service, which may have certain effects on the microstructure and properties of the welded joints. It is necessary to study the microstructure and properties of the welded joints of SLMed GH3536/SLMed 304 after post-weld heat treatment(PWHT).Methods During the welding process, the laser beam is incident perpendicularly on the surface of the plate, with the focus located on the upper surface of the plate. High-purity Ar gas is adopted as the protective gas and the gas flow rate is 15 L/min. The angle between the axis of the protective gas nozzle and the upper surface of the plate is 45°, and the welding test is carried out by drag welding. During the welding process, special fixtures are used to ensure seamless butting of the sample plates. The welding process parameters are as follows: laser power of 2500 W, welding speed of 2 m/min, and defocus amount of 0 mm. The welding direction is perpendicular to the forming direction of the SLM process. This paper stipulates that the forming direction of SLM is the Z-axis direction, the XOY surface is perpendicular to the forming direction, and the XOZ surface is parallel to the forming direction. Heat treatment is carried out on the welded joints. Among them, the samples for the mechanical property test of the joints are divided into 4 batches(4 pieces in each batch). One batch is not subjected to heat treatment, and the other three batches are respectively subjected to high-temperature heat treatment for 1000, 2000, and 3000 s in argon environment at 815 ℃. To clarify the evolution law of the microstructure of the weld seam under different heat treatment conditions, the same sample is used as the microstructure observation sample to analyze the microstructural change law at the same position of the same joint after different post-weld heat treatment time. The microhardness distribution of the weld seam is tested using a hardness tester. The load of the hardness tester indenter is 200 g and the loading time is 15 s. Room temperature tensile tests and impact toughness tests are conducted on the joints under different heat treatment time.Results and Discussions With the increase of the high-temperature heat treatment time after welding, the width of the unmixed zone does not change significantly. The heat treatment time has important influence on element diffusion within the unmixed zone and on its width. In this experiment, the heat treatment time is relatively short, and the width change of the unmixed zone is not significant(Fig. 4). After heat treatment, solidified grain boundaries appear in the weld microstructure(Figs. 5-7), and granular white precipitates MoC are distributed along the solidified grain boundaries. Moreover, the amount of precipitates increases with heat treatment time(Fig. 8). After the heat treatment of the GH3536 base material, a large number of precipitates also appear in the grain boundaries(Fig. 9). Combined with X-ray diffraction(XRD), it can be known that the precipitates in the grain boundaries are MoC(Fig. 10). After heat treatment, the microhardness of the joints increases(Fig. 11). The tensile strength at room temperature of the SLMed GH3536/SLMed 304 joints under different heat treatment time is greater than that of the SLMed 304 base material, and the specimens all break on the side of the SLMed 304 base material(Fig. 12). With the increase of heat treatment time, the impact absorption energy of the joints slightly decreases(Fig. 13).Conclusions Before heat treatment, there are lots of solidified sub-grain boundaries in the weld microstructure. After heat treatment, solidified grain boundaries appear in the weld microstructure, and granular white precipitates MoC are distributed along the solidified grain boundaries and solidified sub-grain boundaries. With the increase of heat treatment time, the solidified sub-grain boundaries gradually melt. After heat treatment, the microhardness of the joints slightly increases and the tensile strength slightly decreases. However, the tensile strength of the joint under each heat treatment parameter is greater than that of the 304 base material. With the increase of heat treatment time, the impact absorption energy of the joints slightly decreases. Lots of dimples are observed at both the tensile fracture surface and the impact fracture surface, and the fracture mode is ductile fracture.更多还原