不锈钢激光-MAG复合焊接头微区性能研究

激光复合焊可用于不锈钢焊接，但激光复合焊接头热影响区小，组织变化梯度大.研究接头微区性能可以确定接头薄弱环节，为焊接接头的工艺评定和断裂分析提供理论依据.为此，本文对4 mm厚SUS301L-HT不锈钢进行激光-MAG复合焊接，采用维氏硬度、微型剪切和微拉伸等试验，研究了焊接接头焊缝、热影响区及母材的微区力学性能，并结合金相、断口扫描等分析了各微区力学性能的差异.结果表明：焊缝区域组织主要为柱状奥氏体树枝晶+少量的δ铁素体；母材的剪切强度和抗拉强度最高，分别为560和1 066 MPa，其次为复合焊接头热影响区，焊缝区域最差，接头硬度分布规律与各微区强度变化趋势一致；运用数学方法，得出了接头微拉伸强度与微型剪切强度、硬度之间关系的经验公式.接头各微区剪切断口和拉伸断口SEM分析呈现典型的韧性断裂特征.
The laser hybrid welding can be used for stainless steel welding, but the laser hybrid welded joint has a small heat affected zone and a large microstructural change gradient. The study of joint micro-area performance can determine the weak link of the joint, provide a theoretical basis for the process assessment and fracture analysis of welded joints. The laser-MAG hybrid welding was applied to weld the stainless steel with 4 mm thickness. The properties of the welded metal, heat affect zone and base metal were researched by hardness test, micro- tensile test and micro-shear test. The differences of micro-zone properties were analyzed using metallography and SEM. The results indicate that the microstructure of the welded metal is columnar austenite dendrites and small amount of δ-ferrite. The base metal had the highest shear strength of 560 MPa and tensile strength of 1 066 MPa, followed by heat-affected zone and welded metal. The hardness distribution of welded joint was consistent with the trend of micro-intensity. By mathematical method, the experienced formula of micro-tensile strength and micro-shear strength as well as micro-tensile strength and hardness were obtained respectively. It was found by analyzing shear and tensile fracture of joint, fracture morphology of the micro-zone was a dimple pattern with feature of ductile fracture.