Improved mechanical properties of laser-repaired 15-5PH stainless steel by in-situ heat treatment and grain refinement

Abstract

Mechanical properties of repaired part by laser melting deposition (LMD) mainly depend on microstructure of clad layer and heat affected zone (HAZ). For precipitation-hardened steel, the properties of as-deposited materials are usually not satisfactory. Post heat treatment is an effective way to improve mechanical properties but sometimes become infeasible or restricted due to various reasons. In this paper, by deliberately reducing the scanning speed to provide more energy than needed to melt the powder, heat accumulation in the deposited area is enhanced and an in-situ heat treatment is provoked. The strength of as-deposited clad layer is greatly enhanced (1290Mpa for ultimate tensile strength) by precipitation strengthening while maintaining good ductility. The possible influences of excessive heat on the HAZ are also evaluated. Experimental results show all the HAZ samples have a slightly lower strength compared to heat treated substrate. Excessive heat input does not deteriorate the strength of HAZ. On the contrary, the ductility of the material in HAZ is enhanced due to the effect of grain refinement and overage. In this way, the as-repaired parts can achieve a higher strength without heat treatment, which provides a new method for the repair of parts that cannot be subjected to post heat treatment.