Numerical-experimental analysis of the effect of surface oxidation on the laser transformation hardening of Cr-Mo steels

Laser surface hardening is a technology that enables important advantages to be obtained in comparison with conventional techniques in terms of accuracy of the heat affected zone and productivity. Nevertheless, the development of realistic and flexible models has to be fulfilled in order to control the effects of every set of process conditions. Despite many different models having been developed, very few of them deal with the increment of absorption related with the instantaneous value of the layer of oxide growth during the process in a non-protective atmosphere. This work analyzes the problem of oxide formation at the external surface using kinetic relations, whose parameters have been related with the process variables, considering non-equilibrium conditions. Then, the oxide thickness was associated with a value of absorption through an innovative formula that considers the path of the laser radiation in the interface oxide-base material. The thermal calculations obtained by this method have allowed phase changes to be predicted using Avrami law. Both thermal and metallurgical results for different process conditions have been compared with experimental data showing an excellent agreement. (C) 2015 Elsevier B.V. All rights reserved.