Hybrid fiber laser-arc welding of 10-mm thick CA6NM stainless steel

Single pass butt welds were successfully manufactured using a 5.2 kW fiber laser in tandem with arc welding to join 10-mm thick plates of CA6NM, a low carbon martensitic stainless steel in cast form that is widely used for hydroelectric turbines. The joint integrity was evaluated in terms of the weld geometry, discontinuities, microstructure and mechanical properties (tensile and Charpy impact) in both the as-welded and post-weld tempered conditions. Though visible cracks were absent, some defects such as porosity and underfill were observed. The as-welded fusion zone consisted mainly of lath martensite and residual delta ferrite; the latter transformed to tempered lath martensite after post-weld tempering. Four distinct heat affected zones were identifiable through characterization of the microstructure and hardness evolution. Evaluation of the mechanical properties indicated acceptable tensile strength in both the as-welded and post-weld tempered conditions, though the latter was critical for attaining acceptable Charpy impact energy values.