Effect of Simulated Braking Heat on the Microstructure and Properties of CL65 Wheel Steel

To investigate the effect of braking temperature rise on the service performance of CL65 wheel steel in plateau mountain areas, finished CL65 wheel steel was selected as the research object, heat-treated using a Gleeble-3500 thermal simulation system, and examined via room-temperature tensile tests, hardness tests, and multi-scale characterization techniques to study the regulation of braking temperature rise on the microstructure, mechanical properties, and fracture behavior of the material. The results indicate that 500 ℃ is identified as the critical temperature for the microstructural and property transformation of CL65 wheel steel. Below this temperature, the microstructure remains a stable lamellar pearlite structure (with an interlamellar spacing of approximately 100 nm), and no significant fluctuations in mechanical properties are observed. Above 500 ℃, cementite is progressively spheroidized, leading to a notable decrease in strength and hardness, while the elongation is significantly increased. At 700 ℃, the microstructure is completely spheroidized (with cementite particles sized between 150 and 300 nm). Compared to the base metal, the yield strength and tensile strength are reduced from 696 MPa and 1 104 MPa to 472 MPa and 819 MPa (approximately 67% and 74% of the base metal, respectively), hardness is decreased from 327 HV to 243 HV, and elongation is continuously increased from 15% to 20%. Concurrently, the fracture mechanism progressively evolves from cleavage-dominated brittle fracture to dimple-dominated ductile fracture, exhibiting a significant temperature dependence. In this study, the evolution mechanism and degradation threshold of the microstructure and properties of CL65 wheel steel during braking temperature rise are clarified, which can provide a theoretical basis for the service safety assessment and material optimization of heavy-duty wheels in plateau mountain areas.