Optimal beam spot diameter for the laser surface hardening of a medium carbon steel

Abstract

The results of experiments and FEM-simulation on laser surface hardening of a medium carbon steel are described. A 2-dimensional computer program, which can be used generally for the determination of transient temperature distributions in welding and surface heat treatment, was used in the first place to investigate the effects of traverse speed and beam spot diameter on the shape and size of hardened zones. For the confirmation of the accuracy of the numerical analysis a medium carbon steel of 5 mm thickness was heat-treated with a 1 kW CO2 laser. A simulation scheme for the cooling time and the corresponding CCT-diagram showed that the cooling rate is high enough to consider the heated zone above the Acl temperature as the martensitic hardening zone. With proper assumption of the absorptivity the numerical and experimental shape and size of hardened zones were in good agreement. The numerical analysis showed that with increasing beam spot diameter the width and depth of the hardened zone increased for relatively small beam spot diameters, but decreased rapidly after reaching the.maximum value, while with increasing traverse speed the width and depth of the hardened zone decreased monotonously. It could be also observed that for a given traverse speed and laser power input there exists a optimal range of the beam spot diameter, which produces a large width of the hardened zone but no melting on the surface.The results of experiments and FEM-simulation on laser surface hardening of a medium carbon steel are described. A 2-dimensional computer program, which can be used generally for the determination of transient temperature distributions in welding and surface heat treatment, was used in the first place to investigate the effects of traverse speed and beam spot diameter on the shape and size of hardened zones. For the confirmation of the accuracy of the numerical analysis a medium carbon steel of 5 mm thickness was heat-treated with a 1 kW CO2 laser. A simulation scheme for the cooling time and the corresponding CCT-diagram showed that the cooling rate is high enough to consider the heated zone above the Acl temperature as the martensitic hardening zone. With proper assumption of the absorptivity the numerical and experimental shape and size of hardened zones were in good agreement. The numerical analysis showed that with increasing beam spot diameter the width and depth of the hardened zone increased for r...