高氮钢复合焊接接头微观组织及力学性能

Microstructure and mechanical properties of composite welded joints of high nitrogen steel

为了研究和掌握高氮钢复合焊接接头的微观组织和力学性能,以8mm厚的高氮钢板为试验材料,采用额定功率为4kW的Nd∶YAG固体激光器对其进行了激光-电弧复合焊接,利用金相显微镜和扫描电子显微镜对焊接接头的微观组织和断口形貌进行拍照和分析,并利用能谱分析仪和X射线衍射仪,从微区成分元素的种类、含量及物相组成方面进一步分析母材、热影响区、焊缝区的微观组织。结果表明,焊缝区的组织为典型的树枝晶和少量的等轴晶形貌,母材、热影响区都是奥氏体组织,焊缝区除了奥氏体组织外还伴有少量的δ铁素体组织;焊缝中的第二相粒子主要是通过冶金反应产生,以TiO_2、尖晶石(MnAl_2O_4)以及硅酸盐等形式存在,对晶粒有明显的细化作用,可增加焊缝强度;拉伸断裂出现在焊缝区,断口组织形貌为典型的韧窝断裂,并在断裂处可发现有空洞和第二相粒子的形貌特征,说明焊缝缺陷可能导致力学性能薄弱。此研究为激光-电弧复合焊接在高氮钢焊接领域的应用奠定了一定基础。

In order to study the microstructure and mechanical properties of welded joints of high nitrogen steel,high nitrogen steel plate with 8 mm thickness was used as test material and Nd∶ YAG solid state laser with the rated power of 4 kW was used to do laser-arc composite welding. The microstructure and fracture morphology of the welded joint were photographed and analyzed by a metallographic microscope and a scanning electron microscope. The microstructures of the base material,the heat affected zone and the welded zone were further analyzed in terms of element composition,content and phase composition by energy a spectrum analyzer and a X-ray diffractometer. The results show that the microstructure of the welded zone is typical dendrite and a small amount of equiaxial morphology. Both the base material and the heat affected zone are austenitic tissues. The welded zone is accompanied by a small amount of delta ferrite in addition to austenite tissues. The second phase particles in weld seam are mainly produced by metallurgical reaction in the form of TiO2,spinel（ MnAl2O4） and silicate. It has obvious refinement to the grain and can increase the strength of weld seam. Tensile fracture occurs in the welded zone. Fracture morphology is typical of dimple fracture. The morphology of the cavity and the second phase particles can be found at the fracture. It is indicated that weld defects may lead to weak mechanical properties. The study lays a foundation for the application of laser-arc composite welding in the field of high nitrogen steel welding.