In situ control of tempered martensite during laser cladding repair of aero-grade 300M steel using AISI 420 stainless steel powder

The aim of this paper was to investigate the effect of delay time between the clad tracks on the microstructure hardness evolution. AISI 420 stainless steel was deposited onto 300M steel substrate using a fiber delivered disk laser and a powder blown coaxial nozzle. The delay between the clad tracks was aimed at controlling the in situ quench and tempering sequence during the cladding process. Four different delay times were investigated (continuous build, t = 2 s, t = 5 s, and t = 60 s). No micro-cracking and very little porosity were observed for all variables. The microstructure changed from untempered martensite structure at a continuous build to a fully tempered martensite structure at t = 60 s. The delay time between the clad tracks is the most influential parameter to control the in situ tempering and is crucial to restore the tensile and fatigue properties of aero-grade high strength steel for repair applications.