Effects of Annealing on Carbide Size Distribution and Mechanical Properties of 1.0C-1.5Cr Bearing Steel Prepared by Continuous Casting with 510 mm × 390 mm × 250 mm Dimensions

As the cross-sectional size of bearing steel increases, maintaining a uniform microstructure becomes more difficult. To address this issue in large-section 1.0C-1.5Cr bearing steel, the behavior of carbides during isothermal spheroidization annealing at different positions within the steel was investigated. Quantitative metallography was used to measure the mean diameter of carbides (D), the number of carbides per area (n), and the carbide particle size distribution at both the 1/2 position and the center position of the steel. The results of the study showed good spheroidization of carbides in all the specimens except for the presence of lamellar pearlite organization in the specimens with austenitizing temperatures of 760 °C and 880 °C. As the austenitizing and second annealing temperatures and times increased, the mean diameter of carbides (D) became larger, while the number of carbides per area (n) decreased. It is worth noting that the carbides in the center position are smaller than in the 1/2 position, although the center position had a higher density of carbides. Based on the measured values of D and n, a model was developed to describe the relationship between them. In addition, the mechanical properties were influenced by this uneven carbide distribution: as the carbide size increased, tensile strength decreased, while elongation followed a similar trend. Additionally, tensile strength was higher at the center position than at the 1/2 position, whereas elongation was greater at the 1/2 position.