Hardened layer microstructure and wear resistance of 7CrSiMnMoV cold work tool steel after laser surface quenching: processes and mechanisms
摘要
This study employs laser surface quenching to enhance the wear resistance of 7CrSiMnMoV cold work tool steel with the underlying mechanisms explored. The microstructures of hardened layers were characterized by SEM and EBSD, while their wear resistance was evaluated under dry sliding conditions, with worn surfaces analyzed by laser scanning confocal microscope and SEM. The results demonstrated that laser surface quenching resulted in gradient microstructures in the depth direction of the hardened layer, which transitions from acicular martensite at the surface to lath martensite, and finally to the original pearlite structure in the substrate. The surface hardness of the hardened layer increased from 260 HV1 to a maximum value of 949.2 HV1, which was attributed to the significant grain refinement induced by the fast heating and cooling nature of laser surface quenching. The friction coefficient and wear loss volume were significantly reduced after laser surface quenching due to the weakening of oxidative wear and adhesive wear. With a laser energy density of 25 J/mm2, the lowest friction coefficient (0.57) and wear loss (8.66 × 10–3 mm3), as well as the smallest average grain size (0.65 μm) was obtained.
Highlights A gradient microstructure with coarse acicular martensite transitioning to lath martensite to original pearlite was formed via laser surface quenching. Laser surface quenching can significantly reduce the friction coefficient and wear loss volume. Laser surface quenching achieves significant grain refinement, with the smallest average surface grain size obtained at a laser energy density of 25 J/mm2. The improvement in wear resistance was attributed to the reduction of oxidative and adhesive wear resulting from grain refinement.