无钴马氏体时效钢电子束焊接缺陷的微观研究

Microstructure of Co-free maraging steel and defect analysis of electron beam weld joints

为研究18Ni无钴马氏体时效钢电子束焊接缺陷的形成原因,对比分析了同一成分不同批次的两种无钴马氏体时效钢的基体及焊接接头,采用金相显微镜和扫描电镜观察了微观组织结构.研究表明:两种材料的晶粒大小差别较大,但基体组织均为细小板条马氏体组织,晶界分布有片状的奥氏体组织,晶体内部也有少量的奥氏体颗粒;焊缝组织为粗大柱状晶,熔合线附近热影响区组织发生了再结晶,晶粒已明显合并长大.晶粒大小和奥氏体含量的不同,是导致两试样导热性能不同的主要原因,对于导热性能差的材料,焊接时应尽量降低能量输入,减少熔池金属量,以防止焊接缺陷的出现.

To explore the formation of electron beam weld defects of 18 Ni Co-free maraging steel, both base materials and weld joints of two different batches of the steel were studied comparatively, and their microstruetures were examined by optical microscopy and SEM. Results show that the grain sizes of two batches of specimens are quite different; however, the microstructures of both steels are lath martensite. Most of austenites distribute in plate form along grain and lath boundaries, while some of them distributes as fine particles within the matrix. The welding microstructure exhibits a typical cellular-dendritic morphology. In the heat-affected zone, the grains are recrystallized and grow because of high temperatures of electron beam welding. The weldablity of examined materials is related to the grain size and the content of austenites that markedly affect the thermal conduction performance. To reduce the energy input can prevent the appearance of weld defects for the materials with poor thermal conduction performance.