Abstract
Laser transformation hardening (LTH) is a selective surface heat treatment technique widely employed to improve the surface properties of engineering components through microstructural phase transformation. EN36A steel is typically used in high-precision transmission gears and automotive components, where dimensional stability is crucial. Despite its low-carbon content, EN36A responds well to case-hardening techniques due to its favorable alloying composition, making it a suitable candidate for improving surface hardness without compromising core toughness. In this study, EN36A steel was subjected to LTH using a line beam of geometry dimensions of 15 × 1 mm2 under three different surface conditions: as-received, carbon-coated, and sandblasted. The influence of surface pre-conditioning on the hardened depth of the laser hardening process was systematically evaluated. Among the investigated surface conditions, the sandblasted specimens exhibited the most favorable response to LTH. These specimens developed a deeper hardened layer (∼1.0 mm), higher surface hardness (∼550 HV0.5), and stronger compressive residual stresses (∼−190 ± 10 MPa) compared to the other surface conditions. The results indicate that sandblasting represents the most compatible and effective surface preparation technique for enhancing the efficiency, consistency, and overall performance of laser hardening in EN36A steel. Microstructural analysis of the hardened zones confirmed a predominance of martensite, with hardness profiles showing a gradual decrease with depth, consistent with the reduction in martensitic content. An X-ray diffraction (XRD) analysis revealed noticeable peak broadening due to increased dislocation density and lattice strain after LTH. These microstructural changes, as confirmed by XRD, are responsible for the improvement in hardness across the case depth and the overall strengthening behavior of EN36A steel.
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