On the formation of austenitic boundary layers by short laser-pulse reaction with steel

Laser pulse hardening of a 0.6 C-steel and a 100 Cr6 ball bearing steel has been used to produce thin austenitic boundary layers. A 10.6-micron TEA CO2 laser with a 20-J pulse energy was used and two conditions were evaluated: in the air and in vacuum. The reaction time in the air is in the 40-80 ns range and the surface selective melting of carbides occurs. The thermal reaction only influences a thin outer skin layer and pure austenitic skin layers are obtained. Higher energy absorption is obtained in vacuum and the thermal effect penetrates deeper. Homogeneous austenitization is found in the presence of a molten phase. Pearlitic structures cannot be transformed in the solid state because carbon has a limited diffusion rate in iron. However, martensitic steel may be rehardened since the process does not require carbon redistribution.