Abstract:
The bearings are subjected to complex alternating stress state for a long time, which require excellent service properties such as high hardness, high wear resistance, high elastic limit and high contact fatigue strength. Therefore, in the production of bearing steel, it is necessary to strictly control the process, improve the purity of steel, and ensure the high precision, long service life and high reliability of bearing. At present, the production technology of high-quality bearing steel in China has made great progress. The quality of bearing steel in some enterprises is at the world advanced level, but the stability of the world's leading level still exists a big gap. Now, aluminum deoxidation process is mainly used to produce bearing steel at home and abroad. Through aluminum deoxidation and making high alkalinity slag, the oxygen content in liquid steel can be quickly reduced. The total oxygen content in high-quality bearing steel can be controlled below 5 ppm, but there is still the problem of fatigue failure caused by occasional Ds inclusions. At the same time, there are also other problems, such as blockage of small billet continuous casting nozzle, difficulty in stable control of ultra-low total oxygen and titanium content. In order to solve the above problems, this study proposes a non-aluminum deoxidation process to produce bearing steel, that is, adding silicon-manganese alloy for pre-deoxidation during converter tapping, adding silicon deoxidizer to LF slag surface for diffusion deoxidation, and RH vacuum deep deoxidation to ensure that the total oxygen content of the molten steel is about 8 ppm. While ensuring the low aluminum and low titanium content of liquid steel, the low alkalinity slag is used to change the type of inclusions and control the plasticity of inclusions, so as to effectively solve the problem of liquid steel fluidity. The fatigue life of two kinds of process bearing steel was measured by ultrasonic fatigue testing machine, and the effects of different types of inclusions on fatigue performance were clarified, the fatigue fracture mechanism of different process bearing steel was analyzed, and the critical size of inclusions causing fatigue cracks was predicted. The application of the above key technologies finally plays a guiding role in the large-scale production of non-aluminum deoxidized high-quality bearing steel. However, its quality still lags behind the most advanced production level of bearing steel in the world, including the poor desulfurization effect caused by the use of low basicity slag in the refining process, which needs to be further studied.