Controlling intermetallics formation at V-4Cr-4Ti/316SS laser-welded joint

Abstract

In a fusion reactor, the connection between the blanket and peripheral components is closely related to heat transfer. Therefore, the sound joining of the structural materials of the blanket and peripheral components, V-4Cr-4Ti and 316 stainless steel (316SS), is of great importance. However, the properties of these joints are restricted by brittle intermetallics. The effect of a Cu interlayer on the formation of brittle intermetallics was studied. After welding, no significant defects (e.g., pores, macrocracks or microcracks) were observed in the welded joints, which showed good weldability. According to the microstructural analysis, it was verified that there were a large number of Cu-rich phases, Fe-rich phases, and a small amount of the σ phase which comprised Fe and Cr in the weld. In the hardness test, the welded joint was divided into hardened and softened zones. The average hardness of the softened zone was approximately 160 HV, while the average hardness of the hardened zone was approximately 292 HV, which was due to the hardening effect caused by a small amount of the σ phase. According to the tensile test results, the introduction of the Cu interlayer improved the strength and elongation of the weld. The ultimate tensile strength and maximum elongation of the weld were 469 ± 3 Mpa and 9.5 ± 0.2%, respectively. The tensile fracture morphology showed that the welded joint was ductile. The correlation between the microstructure and mechanical properties is discussed.

Keywords

• V-4Cr-4Ti
• Interlayer
• Intermetallic
• Strength