Study On China Low Activation Martensitic Steel In Laser Weld

Fusion reactor structural material is one of the keys whether commercial application of fusion energy can be achieved. Reduced activation ferritic/martensitic steels (RAFM) are commonly considered as the primary structural materials for the DEMO fusion plant and the first fusion power reactors because of their excellent thermophysical properties, mechanical properties and their relative mature technical foundation, for example, the low irradiation swelling and thermal expansion coefficient, high thermal conductivity etc. China Low Activation Martensitic steel (CLAM) is the RAFM which have independent intellectual property rights with Chinese and optimized chemical composition and properties. CLAM is considered as the primary structural materials for the China designed ITER test blanket module.The solution of CLAM steel welding technology will lay the foundation for engineering applications. The laser welding is widely used because of its high quality, high-precision, high efficiency etc. In this paper, 5mm and 6mm of CLAM steel were welded using different welding parameters (output power, welding speed, defocus amount) by Nd: YAG laser, And some specimens were tempered. Microstructure and carbide distribution of welded joints were observed by metalloscope and SEM. Mechanical properties were detected respectively in hardness test, tensile test and impact test experiments.Welding parameters were optimized by comparing the quality of the samples with different welding parameters. Analysing the influence of different welding process parameters on the weld and heat affected zone (HAZ), that was, the greater the energy of welding wire, width of weld and HAZ; larger of the organizations. According to the analysis of organization, we knowed that the weld area before heat treatment was mainly grain coarsening lath martensite; the HAZ was martensite and a small amount of residual austenite. After tempering treatment, welded joints are tempered martensite. Irregular shape, short rod-like carbides were precipitated in grain boundaries of martensitic or austenite, which were mainly distributed defects, such as dense dislocation lines and the cell walls. Fewer intragranular carbides distribution. Pre and Post tempering treatment, the analysis of hardness of the welded joints showed: before tempering,the hardness of the weld slightly lower than the base material, the hardness of HAZ showed up first, then decreased, which mainly dued to the formation of small microstructure in fine-grained region, so the hardness increased; After tempering, the strength of joints overall reduced, the hardness of the weld and HAZ were greater than the base metal, HAZ wasn't intenerated. After tempering, the tensile strength of welded joints reached an average of 688MPa at room temperature, the specimens were fractured in the base material, the joints showed good strength; the minimum impact energy of 1/2 standard impact specimens reached 88J, gray fiber zone accounted for the vast majority of the impact fracture, micro-morphology was apparent dimple , the weld showed good toughness.