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The depth homogeneity of laser-treated zones is one possible factor to define the quality and efficacy of altered mechanical properties in materials. For instance, half-rounded cross-sectional shapes of laser hardened zones using Gaussian beams provide dissimilar hardened depth in the edges and center of the treated area. This means that the in-depth distribution of compressive residual stress varies between the edges and the center of the hardened area. Nonhomogeneity of compressive residual stress distributions can inhibit fatigue properties and can lead to product failure. The utilization of oscillated laser beams has been proven to improve the welding efficiency and energy input distribution to the material, which promises achieving a homogeneous depth of laser-treated zones in hardening applications. Therefore, this work examines the influence of triangular, square, and circular beam oscillation strategies on the energy input distribution during the process and the geometry of the laser-treated zones on microalloyed steel. Laser beam pathways were assembled using a vector graphic editor to visualize the energy distribution from each oscillation strategy. Cross section images of the hardened tracks were taken and related to the thermal energy input profiles. It was revealed that each oscillation strategy demonstrates characteristic temporal and spatial thermal energy input distribution, influencing the geometry of the hardened zone. The circular oscillation strategy produced a widely constant depth in contrary to the triangular and square beam oscillation due to its characteristic energy distribution that allows homogeneous heat dissemination in the material. This confirms that the laser beam oscillation strategy can tailor the energy input distribution to optimize the processing outcome.

Laser surface hardening provides for many advantages in terms of flexible production due to very localized and controlled energy input into the material. Laser processing offers the possibility to treat surfaces in order to locally strengthen the areas that are prone to fatigue cracking. It is well known that laser energy absorption depends on many parameters, e.g., the surface structure and the surface orientation. The incident angle of the laser beam plays a key role in this regard. When complex geometries like crankshaft fillets are treated, the surface cannot be considered a series of flat surfaces. Obviously, this leads to locally varying degrees of energy absorption. In the present work, curved surface structures were chosen in order to analyze the impact of the geometrical characteristics on surface and subsurface material properties after laser treatment. Microstructure evolution generally was found to be similar for flat and curved geometries. However, even if higher absorption in the groove due to the illumination at larger incident angles was expected, the outer parts of the curved geometry were not fully hardened. Thus, the increased effective length of the complex geometry-treated and the larger heat-affected volume are expected to have a more dominant influence on the final appearance of the subsurface microstructure. Eventually, for austenitization of the complete illuminated surface volume, the energy density needs to be increased.

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