Temperature Gradient-Induced Microstructural Evolution and Wear Resistance Enhancement in High-Manganese Steels by Laser Transformation Hardening

Despite its excellent impact toughness and work-hardening capacity, high-manganese steel (HMS) suffers from low initial hardness, limiting its wear resistance under low-stress conditions. Conventional surface hardening methods for HMS involve high cost and intensive energy consumption and produce only shallow hardened layers; moreover, the understanding of laser transformation hardening in HMS remains insufficient. To address these gaps, this study employs a high-energy-density laser for rapid and precise surface modification of Mn13 HMS. The studied Mn13 steel contains 1.98 wt.% Cr, which contributes to solid-solution strengthening and influences the phase transformation behavior during laser transformation hardening. By optimizing the laser power, a well-defined laser-quenched layer with a gradient microstructure along the thickness direction is obtained. Microhardness at the surface treated by laser transformation hardening at 1.5 kW improved significantly, primarily due to grain refinement and a dense dislocation network. The small fraction of martensite contributes indirectly by generating geometrically necessary dislocations and acting as local barriers to dislocation glide. Along the depth direction, the microhardness varies with the gradient microstructure: coarse columnar grains at intermediate depths cause a slight decrease in microhardness, while the substrate restores it. Correspondingly, the laser-quenched surface exhibits improved wear resistance, as indicated by reduced friction coefficient, wear depth, and wear volume, and the dominant wear mechanism shifts from adhesive to abrasive wear. Importantly, this gradient configuration maintains a mechanically compatible transition between the quenched layer and the substrate, preserving impact toughness comparable to that of the untreated material.