Effect of Single-Pass and Overlapping Laser Surface Melting Process on Microstructure and Microhardness of AISI 431 Duplex Steel

Laser surface melting of AISI 431 duplex stainless steel was performed using an Nd:YAG pulsed laser. The single-pass laser melting stage was performed to select the optimal sample; and then, 10%, 30%, and 50% overlapping were applied on it. The results of microstructural studies showed that the single-pass laser melting process created a columnar structure due to epitaxial growth and a fully ferritic structure was formed in the molten zone. Also, the hardness of this region decreased from 440 to 130 HV. Moreover, with 50% and 30% overlapping, the reheating of the area adjacent to the molten zone provided the conditions for the formation of austenite from ferrite. Also, austenite transformed to martensite during the high-rate cooling and the final structure was martensite. With 50% overlapping, the hardness of the MZ increased compared with that of the single-pass sample from 130 to 320 HV.