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

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 microstructures 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.