In-situ quench and tempering for microstructure control and enhanced mechanical properties of laser cladded AISI 420 stainless steel powder on 300M steel substrates

Laser cladding offers a very promising path to restore the geometry and structural integrity of ultra-high strength steel components that have suffered from fatigue cracking and wear damage. However, the overall tensile properties of the clad part often result in very poor ductility and low toughness due to untempered martensite formed in the clad layer and Heat-Affected Zone (HAZ). The fatigue properties are also adversely affected as a result of the poor ductility. To overcome this issue, this paper explores controlling the microstructure to achieve enhanced tensile properties. A laser idle time between each clad track was introduced to control the in-situ quench and tempering sequence. The microstructure, tensile, and wear properties of a geometrically repaired ultra-high strength martensitic 300M steel were evaluated. It was found that incorporating a long idle time between each laser clad track produced a mostly tempered martensitic structure in the clad layer resulting in ductility of 17.4% when compared to a deposit without in-situ quench and tempering control of 2.7%. Furthermore, the tensile and wear properties with the deposited layer with idle time were similar to that of the 300M steel baseline. The in-situ control of tempered martensite (through the longer idle time between clad tracks) is a critical process step in the laser cladding repair of aerospace steel components.