关键词: S55C钢, 激光淬火, 工件厚度, 显微组织, 硬度, 耐磨性

Abstract: S55C steel workpieces with different thicknesses (h=2.5-15.0 mm) were subjected to laser surface quenching treatment with constant laser parameters (power of 750 W, scanning speed of 7.5 mm/s). And combining with numerical simulation, the effect of workpiece thickness on the microstructure, hardness, and wear resistance of the steel was investigated. The results show that the hardened layer of all the specimens consistes of martensite and retained austenite. When h<7.5 mm, there is still troostite in the microstructure. While, when h≥7.5 mm, the martensite becomes finer and the content of retained austenite is lower. In the thickness range of 2.5-7.5 mm, the microhardness increases rapidly with increasing thickness, reaching a maximum value of approximately 780 HV0.5 at 7.5 mm. Subsequently, as the thickness further increases, the hardness remains basically unchanged. The hardened depth (defined as the region with hardness >600 HV0.5) also increases with thickness until h≥7.5 mm, beyond which it stabilizes at about 0.5 mm. The simulation and analysis indicate that a cooling rate ≥2.1×10³℃/s is required to form a fine martensitic structure with high hardness (≥600 HV0.5), meeting the hardening requirements for guide rails. The friction and wear tests reveal that both the average friction coefficient and wear mass loss generally decrease with increasing thickness. The dominant wear mechanism transforms from a combination of abrasive, adhesive, fatigue, and oxidative wear to predominantly abrasive and oxidative wear.

Key words: S55C steel, laser quenching, workpiece thickness, microstructure, hardness, wear resistance