Weldability of a New Ni-Cu Welding Consumable for Joining Austenitic Stainless Steels

Abstract

A new welding consumable, based on the Ni-Cu metallurgical system, was developed to reduce hexavalent Cr (Cr6+) emissions during welding of austenitic stainless steels. However, dissimilar metal welds between Ni-Cu alloys and stainless steels have not been thoroughly evaluated for susceptibility to elevated temperature cracking during welding. This study was performed to determine susceptibility of Ni-Cu/304L dissimilar weld deposits to solidification, liquation, and ductility-dip cracking using the Transvarestraint and cast pin tear tests, the hot ductility test, and the strain-to-fracture test, respectively. Solidification experiments were performed using a button melting apparatus in conjunction with the single sensor differential thermal analysis (SS DTA™) technique to determine phase transformations during solidification. Transvarestraint testing revealed the Ni-Cu weld deposits had a higher solidification cracking susceptibility than conventional stainless steel weld deposits (such as E308L). This was attributed to fully austenitic solidification and stabilization of the TiC eutectic reaction at the end of solidification. Button melts and thermodynamic-based Scheil predictions showed a widening solidification range as weld metal dilution by 304L increased. Solidification cracking susceptibility increased at higher dilutions of 304L due to the increase in solidification temperature range. Hot ductility testing of multipass weld deposits revealed a narrow liquation cracking susceptible region (33–54°C) indicating good resistance to weld metal liquation cracking, although a ductility dip was observed in the temperature range of 800–1,100°C. This ductility trough is likely related to the solid-state weld cracking phenomenon known as ductility-dip cracking. Strain-to-fracture testing revealed that the ductility-dip cracking threshold strain was approximately 2–3% in weld deposits, indicating a moderate to high susceptibility. Weld deposits were considered to have similar weldability to other Ni-base and fully austenitic stainless steel alloys based on the current evaluation.