Rotary friction welding of additively manufactured 17-4PH stainless steel

Abstract

• Rotary friction welding (RFW) was employed to weld additively manufactured 17-4PH stainless steel. • Dynamic recrystallization caused grain refinement in FZ, TMAZ, and HAZ. • The formation of Cr-rich carbides and Cu-clustering resulted in sensitization in FZ and HAZ. The aim of the present study is to investigate the effect of rotary friction welding (RFW) on the microstructure, tensile properties, hardness, wear resistance and corrosion properties of the weld joint of an additively manufactured solid cylinder made of 17-4PH stainless steel. Significant grain refinement was observed in the welding zone (WZ) due to the plastic deformation and dynamic recrystallization. The morphology of the grains changed from columnar in the as-printed condition to equiaxed in the welding zone. The microhardness of the WZ is ≈10 % higher than the heat affected zone (HAZ) due to the grain refinement but still lower (≈27 %) than the as-printed microstructure which contains nano-sized carbides and less retained austenite (γ fcc ) due to the rapid solidification. The precipitation of Cr-rich carbides was observed in the WZ and HAZ leading to sensitization and decrease of corrosion resistance (up to ≈90 %). Cu-rich clusters were formed at the interface of Cr-rich carbides/matrix in the WZ and HAZ due to the cube-cube orientation relationship. The depletion of matrix from Cr and Cu in the welding zone decreased the stability of martensite after friction welding leading to the formation of 7–10 % retained austenite. At low load (2 N), the wear resistance of as-printed microstructure (base metal, BM) was found to be superior to WZ and HAZ. However, at intermediate and high loads (5 N and 10 N), the wear resistance of WZ was either better or comparable to the as-printed microstructure. Adhesion and Oxidative wear were the main wear mechanisms at all loads during the reciprocating action. Oxide films grow until they reach a critical thickness prior to becoming unstable and spalling off to form wear debris.