Influence of heat input on the microstructure and mechanical properties of CLAM steel multilayer butt-welded joints

Tungsten inert gas (TIG) welding was considered as one of the candidate technologies to achieve the box structure of test blanket module (TBM). In this paper, the effects of heat input on the microstructure and mechanical properties of multilayer TIG butt-welded China Low Activation Martensitic (CLAM) steel were investigated by microstructure observations, Vickers hardness, tensile and Charpy impact tests. The results showed that the microstructure of the weld metal (WM) were coarse quenched martensite and residual delta-ferrite. When the heat input value increased from 1.73 kJ/mm to 2.41 kJ/mm, the width of martensite laths increased slightly and the delta-ferrite content decreased firstly then increased. Moreover, the increasing heat input resulted in remarkable tempering effect on the previous layer of the WM by the following deposited layers. The transverse hardness distribution of the joints showed that softening occurred in the heat-affected zone (HAZ), and the hardness of WM decreased slightly as the heat input increased. The ultimate tensile strength values of the joints with various heat input were all higher than 630 MPa, and the rupture position located at the HAZ. Charpy impact toughness of the as-welded joints met the toughness criteria for the welded joint (≥27 J) of creep resistant 9Cr steel according to the standard of ISO-3580.