Research On Vacuum Diffusion Bonding Of CLF-1Low Activation Martensite Steel

Test blanket module (TBM) is planned to be used by the international cooperation to simulate and test the device that is related to the fusion reactor technology during the operation of International Thermonuclear Experimental Reactor (ITER). Because of the harsh service environment, the structural materials used need to have very good resistance to radiation performance and good second processing performance except for the good mechanical properties, especially the welding performance. Reduced activation ferritic/martensitic steels (RAFM) are commonly considered as the primary structural materials for TBM. They have higher alloy element content, and ordinary melting welding methods are difficult to get high quality weld joints. Besides, many of the components in TBM module are made by sealed-welding. Hence the study of this kind of material in vacuum diffusion welding is of great significance.CLF-1low activation martensite steel was welded by vacuum diffusion welding process in this paper based on TBM module. In order to optimize the vacuum diffusion welding process parameters of CLF-1low activation martensite steel, research had been done from the deformation conditions, microstructure, combining rate in the interface, distribution of micro hardness, the mechanical properties, the fracture morphology and many other aspects of the welding joints, exploring different welding parameters’influence on the performance of the joint. And this provided the basis.data for TBM module. The results showed that:Within the scope of welding temperature between1010～1100℃, welding pressure of10-20MPa, holding time for80～180min, welding deformation and combining rate in the interface had a very good corresponding relationship with welding temperature, welding pressure and holding time. They generally rose with the increase of the welding parameters. Weld defects in the interface gradually eliminated with the increase of welding temperature and welding pressure. Welding pressure also had obvious inhibiting effect to the growth of the grain. Extending holding time was good for atomic diffusion to fill up holes on the interface. The microstructures of base materials were mostly lath martensite and a few ferrite. After the welding heat cycle, microstructures of the joints were still martensite and a few austenite. But the content of austenite increased. After the solid solution treatment of980℃/45min and drawing tempering treatment of740℃/90min, Only martensite phase could be found in the welding seam while austenitic phase disappeared. The welding seam’s micro hardness distributed evenly, with an average of242.7-254.9HV. And no tempering softening and carbide separation phenomena were found in that area. Elements around the weld in general distributed uniformly.The various welding process parameters of the welding joints’ tensile properties are close to or higher than the base materials, but elongation and area reduction are obviously different. When using the parameters of welding temperature of1010℃, welding stress for10MPa, holding time for80min and welding temperature of1010℃, the welding stress for20MPa, holding time for150min, tensile specimens were broken in the interface of the joints, and the fracture morphology typically presented brittle fracture, and the elongation and section shrinkage rate was very low. While using the parameters of welding temperature of1050～1100℃, welding stress for15-20MPa, holding time for80～150min, tensile specimens were broken in the base material, and the fracture morphology typically presented ductile fracture, and the elongation and area reduction was better than the base material. The impact absorbing energy with roughly140.7J of base material after heat treatment were far higher than the primitive base material impact toughness (13.3J). However, the impact toughness of welding joints was significantly lower than that of the base materials after heat treatment, but amplified with the increase of deformation. When using the parameters of welding temperature of1010～1050℃, the welding stress for10-20MPa, holding time for80-150min, impact specimens were broken along the interface, and the fracture morphology typically presented brittle fracture. While using the parameters of welding temperature of1050～1100℃, welding stress for15-20MPa, holding time for80-150min, as welding temperature and holding time increased, welding deformation increased, and the same time the welding joints’ average impact absorbing power also increased. The highest impact absorbing power was up to68J, reached62%of the minimum measurement value of base materials. The fracture morphology showed that the fracture surface included the base material and the interface of the joints. Besides, the greater the impact absorbing power of the welding joints, the larger the proportion of the base material occupied. Acidification treatment to the welding surface could improve the welding joints’impact toughness. Test results showed that high combining rate in the interface (94.3%) and excellent microstructure and mechanical properties of CLF-1low activation martensite steel welding joint could be obtained when using the welding parameters of welding temperature of1100℃, welding stress for15Mpa and holding time for150min.