Microsegregation in high-molybdenum austenitic stainless steel laser beam and gas tungsten arc welds

Abstract

An austenitic stainless steel with 6 % molybdenum (thickness 6 mm) was welded using laser beam (LB) and gas tungsten arc (GTA) processes at various welding speeds. Depending on the welding speed the primary dendrite spacing ranged from 12 to 17 μm and from 2 to 7 μm for the GTA and LB welds, respectively. Extensive segregation of molybdenum was observed in the GTA welds. The segregation ratio for molybdenum, CID/CD, was found to be 1.9 in the GTA weld, and 1.2 in the LB weld. Distribution of iron, chromium and nickel was found nearly uniform in both welds. A recovered microstructure was observed after a post-weld annealing heat treatment. Annealing had a profound effect on the molybdenum segregation ratio in the laser weld. The critical pitting temperature (CPT) determined by a standard test was 55° C for welds made using both processes, whereas it was 75 °C for the base metal. Upon homoge-hization the CPT of the laser beam weld increased to the base metal value, while that of the gas tungsten arc weld remained at 60° C.An austenitic stainless steel with 6 % molybdenum (thickness 6 mm) was welded using laser beam (LB) and gas tungsten arc (GTA) processes at various welding speeds. Depending on the welding speed the primary dendrite spacing ranged from 12 to 17 μm and from 2 to 7 μm for the GTA and LB welds, respectively. Extensive segregation of molybdenum was observed in the GTA welds. The segregation ratio for molybdenum, CID/CD, was found to be 1.9 in the GTA weld, and 1.2 in the LB weld. Distribution of iron, chromium and nickel was found nearly uniform in both welds. A recovered microstructure was observed after a post-weld annealing heat treatment. Annealing had a profound effect on the molybdenum segregation ratio in the laser weld. The critical pitting temperature (CPT) determined by a standard test was 55° C for welds made using both processes, whereas it was 75 °C for the base metal. Upon homoge-hization the CPT of the laser beam weld increased to the base metal value, while that of the gas tungsten arc weld re...