Laser Welding of 422 Stainless Steel with Inconel 625 Filler Metal

Abstract

Laser welding of Type 422 stainless steel (SS) with Inconel 625 filler metal additions was investigated. Tensile, impact, and fatigue crack growth tests were performed on laser welds and 422 SS base plates as well. The soft zone, consisting of ferrite with extensive M 23 C 6 carbides at grain boundaries, was observed in the heat-affected zone (HAZ) adjacent to the weld interface of 700°C/2 h tempered welds. The existence of soft zone in the weld was detrimental to impact toughness and caused brittle fracture at room temperature. Nevertheless, such a deteriorated effect was less severe at elevated temperatures. Either the soft zone or the weld metal (Inconel 625) did not affect the strength of welds in tensile tests. Consequently, the fracture location of laser-welded specimens was in the base metal at both 25 and 540°C. The fatigue crack growth rates (da/dN) in the weld metal and HAZ of the weld after tempering were less than those of the 422 SS base material for similar AK ranges. The retardation in da/dN was obvious at low ΔKs for the weld tempered at 700°C/2 h. Such retardation became very significant and an accelerated da/dN in the HAZ was resulted if the tempering treatment was not performed on the weld.