Laser hardening of metallic materials

The surface microstructure of metallic materials formed under the effect of laser radiation is characterized by high degree of nonequilibrium, has layered structure consisting of the main three zones formed from the fused material, the heat-affected zone and the tempering zone. As the laser radiation energy increases, the size of the modified layer increases, and the coverage width of the melting zone and heat-affected zone is determined by the maximum penetration depth of the melting and polymorphic transformation isotherms. The distribution of microhardness over the depth depending on the laser radiation energy is exponential or extreme, and the microhardness is usually maximum in the heat-affected zone. As the laser energy increases, the microhardness of the hardened surfaces changes with extreme dependence. Laser hardening of metallic materials is the result of two competing hardening and softening processes. As result of mathematical processing of experimental results, empirical equations for the distribution of microhardness over the depth of laser-hardened surface layers of various steels and ARMCO-iron are obtained. Empirical equations consist of two terms, the first of which describes the processes of hardening, and the second — softening. The obtained equations allow optimizing the laser hardening modes and predicting the hardened layer depth.