Abstract: Through the spheroidization experiment of a novel kind of carbide-free bainitic bearing steel-GCr15SiAlMo, a new cyclic spheroidization annealing process, suitable for bearing steel, is optimized. The microstructures of the steels spheroidized are observed by the scanning electron microscopy (SEM) and the X-ray diffraction (XRD). The results show that the GCr15SiAlMo bearing steels with the microstructures of carbide free bainite has satisfactory properties on the carbide spheroidization. After 4 cycles, the microstructure mostly contains spheroidized carbide, but there are a lot of lamellar carbides in the microstructures spheroidized at 700 ℃ for 10 h. Consequently, compared with the conventional spheroidization process, the cyclic spheroidization process is more rapid and fully. By the spheroidization annealing, the average diameter of the carbides is less than 0.55 μm. The diameter of the carbides less than 1 μm is more than 93%, and some even reach 99%. Meanwhile, these results show that Al can enhance the A1 point of the bearing steels and suppress the precipitation of the network carbides. Besides, adding moderate Aluminium will improve the annealing process and restrain the carbide growth in the steels.

Key words: bainite, bearing steel, carbide, spheroidizing annealing