Development of a Novel Welding Technique With Reduced Heat-Input by Employing Double-Pulsed Gas Metal Arc Welding for Aerospace Grade 18% Ni Maraging Steel

Abstract

Eighteen percent Ni maraging steels are high performance Fe–Ni martensite-based alloys with ultra-high strength and good toughness. They find applications in strategic sectors, joining of thick sections often coming into picture. Welding of thick section involves a longer processing time, more passes, and a higher heat-input. Double-pulsed gas metal arc welding (DP-GMAW) is an emerging welding technique, well suited for joining thick sections. DP-GMAW is capable of controlling the solidification parameters, weld pool geometry, and cooling rate at a reduced heat-input. The major concern regarding the welding of maraging steel is the formation of the reverted austenite (RA) phase in the fusion zone (FZ). The formation of RA deteriorates the mechanical performance of welded joints. The presence of RA can be supressed by the usage of suitable welding techniques and proper post-weld heat treatments (PWHTs). DP-GMAW process was employed to carry out the welding; studies on the joints produced are reported in this research paper. The studies also included the effect of various PWHTs on the metallurgical and mechanical properties of the maraging steel weldments. The research used three distinct PWHTs: direct aging (DA), solutionizing + aging (SA), and homogenizing + solutionizing + aging (HSA). The FZ microstructures under DA and SA conditions show that there is RA at the cell boundaries. However, there was no evidence of RA in FZ following HSA. The energy dispersive spectra (EDS) analysis of the as-welded FZ showed segregation along the grain boundaries (GBs). This led to the premature formation of RA upon subsequent aging. The SA treatments proved inadequate to totally eliminate RA in the microstructure. On the other hand, the HSA treatments were effective in evening out concentration differences and preventing formation of RA. This study demonstrates that DP-GMAW combined with HSA treatment has the best mechanical properties.