Theoretical and experimental investigation into laser surface melting of 321 austenitic stainless steel

Stainless steels are prone to intergranular corrosion and intergranular stress-corrosion cracking when they are subjected to sensitizing heat treatments. However, the use of laser beam with short pulses may homogenize the surface of the workpiece; in this case, intergranular corrosion and intergranular stress-corrosion may be eliminated. In the present study, the laser surface melting of austenitic 321-type stainless steel is conducted experimentally. The resulting surfaces are, then, subjected to the standard electrochemical tests. The study is extended to include the theoretical modelling of laser heating process using an electron kinetic theory approach. The phase change processes are also introduced in the analysis through the classical formulation. The resulting equation of heat transfer is in the form of integro-differential equation and an analytical solution is not possible. A numerical solution using an explicit scheme is employed to solve the governing heat transfer equation. It is found that the rapid decrease in temperature occurs in the vicinity of the surface and a cooling rate of well in excess of 10⁶ °C/s is obtained. On the experimental side, microcracks are observed between the solid and melt boundary. No specific pattern or differentiation on the pit geometry is seen after electrochemical tests.