Laser surface treatments represent some of the most advanced and versatile processes for enhanced materials applications. Laser hardening is a technique to generate a hard wear-resistant surface microstructure in metals due to the rapid heating and cooling cycles imposed by a laser beam. This work intends to understand the influence of the laser variables on hardness after laser hardening of an AISI D6 steel. A fiber laser, which is a new source available for industrial applications, has been used. The overall absorptivity measured was ∼37 % and the laser treatment produced two different zones: Remelted and heat-affected. The surface layer was remelted and composed of martensite and retained austenite. The region next to the free surface is composed of primary austenite dendrites with martensite plates with hardness between 400 and 500 HV. The region called the heat-affect zone is composed of martensite, retained austenite, and carbides and has a hardness up to 800 HV. The case depth in laser treated samples was between 1 and 2 mm.
An automotive shaft was surface-remelted and hardened using a 2 kW fiber laser and an adapted linear axis whose rotating axis produced helical tracks at 120 RPM. The process variable was the laser power, ranging from 300 to 1100 W, which produced two regions in the material: a martensitic region (MR) and a partially transformed region (PTR). The MR is formed after rapid solidification or austenitization followed by rapid cooling (10(7) K.s-1). The PTR is composed of martensite, unchanged pearlite and proeutectoid ferrite. The maximum case depth was about 0.3 mm. The microhardness inside the martensitic regions are at least double that of the base material, i.e. between 800 than 600 HV compared to 300 HV. Thermal simulations using a modified Rosenthal formalism help elucidate the phase transformation inside the material and show good agreement with experimental results. The experimental laser-steel absorptivities were measured; they ranged between 38 and 59% depending on the laser power and the amount of liquid at the surface
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