Effect of Laser Traverse Speed during Laser Hardening on Hardness Distribution and Microstructure of Hot Work Tool Steel H11

The paper describes the effect of laser traverse speed during laser hardening on hardness and microstructure. The experimental material is hot work tool steel AISI H11 with samples sized 100x100x35 mm. The initial state of the material before laser hardening is quenched and tempered. The laser hardening temperature is constant at 1100 degrees C, selected laser traverse speed was 1, 2, 4, and 6 mm/s. A numerical simulation performed in DEFORM-3D software before the experiment showed tendencies of temperature displacement and expected course of hardness. Increasing traverse speed leads to decreased laser-hardened depth and decreased hardness drop in the heat-affected zone (HAZ). The experimental program confirmed the results of the numerical model. The differences in the microstructure were investigated by light (LM) and scanning electron microscopes (SEM), which revealed an evident difference between the surface area and the locality with the lowest hardness. Local differences from the perspective of presence of carbides were analysed by energy dispersive spectroscopy (EDS). This investigation was performed to optimize laser traverse speed to improve the subsurface hardness profile, which is essential for the lifetime and reliability of forging dies.