Development of model-based laser irradiation customization strategies for optimized material phase transformations in the laser hardening of Cr-Mo steels

An inverse approach for the Laser Surface Hardening Process is proposed. It departs from specific austenization requirements in terms of a desired size for the austenized region at any cross section of the treated sample, aiming at calculating suitable process parameters to obtain it. This approach contrasts with conventional direct procedures, from process parameters to thermal cycles and austenite distribution, where stochastic design strategies, falling on the dynamics of successive approximations, are performed. A thermo-metallurgical numerical model is used to determine the irradiance distribution capable of meeting the prescribed austenization requirements. This theoretical irradiance distribution is implemented by means of an adaptative high-frequency scanning of the treated surface. The minimum scanning frequency to guarantee the equivalence between the pursued theoretical irradiance distribution and the scanning is established attending to the evolution of temperature and its influence on the austenization rate by means of Avrami Law. A value of 100 Hz grants a continuous heating of the material. Considering this threshold, equations to calculate the parameters of the scanning to achieve the desired irradiance distribution are built. These equations are used to approach a design case where real hardened cross sections are achieved, confirming the utility of the proposed systematic methodology.