Heat treatment effects on the weld joint of CLF-1 fabricated by laser welding

Abstract

In this paper, laser weld technology was applied to produce the welded joints of CLF-1 steel, which is the primary material for manufacturing test blanket module (TBM). The microstructures and mechanical properties of the joints were studied at as-welded state, post-weld heat treatment (PWHT) of 710 °C/2 h/air cooling (PWDT), and PWHT of 980 °C/1 h/air cooling (AC) followed by tempering at 710 °C/2 h/AC (PWNT). The results showed that abundant lath martensite phase with width 800 nm and small amount of δ-Fe phase were present in the weld at as-welded state. Its impact toughness was about 40 J. The microstructures of the weld at PWDT state included a large amount of tempered lath martensite with width 650 nm, few δ-Fe, M23C6 carbide (distributed along the boundary of martensite) and MX carbide (precipitated inside the martensite). Its impact toughness was about 237 J (equivalent to the base metal). The microstructures of the weld at PWNT state included a large amount of tempered lath martensite with width 350 nm, M23C6 carbide and MX carbide. Even though the δ-Fe phase disappeared, the impact toughness (about 156 J) was lower than that of the weld at PWDT state due to the aggregated growth of M23C6 and MX carbides.