It was obvious that NH
3 partial pressure, H
2 partial pressure, carbon activity, and atmospheric imbalance of NH
3 partial pressure in a furnace is essential for carbonitriding process, thus, quantum shift of nitrogen concentration in the steel will be achieved in the factory. The scratched contact life is very important performance for rolling bearings, however, there is no research about relationship between nitrogen concentration and the scratched contact life. Keeping this situation in mind, the scratched contact life of SUJ2 (SAE52100 equivalent) of which nitrogen concentration accurately controlled is investigated in this research. To avoid uncertain accidents occurred by additive contamination to lubrication oil, ball bearing's inner rings added the artificial dent by Rockwell indenter (196 N) were used for the scratched contact life test. Weibull slope of the test results by this operation condition became shaper than that of test result by general test method (
i.e., bearing's rolling contact fatigue life test under contaminated lubrication condition). Therefore, it is thought that the test method in this research is suitable to get quantitative data. Significance test of the results appeared that when the surface nitrogen concentration is over 0.05 mass%, the scratched contact life is superior to that of normal SUJ2 with a reliability of 99%. Besides, experimental results revealed that, when the surface nitrogen concentration is 0.4 mass%, the life can be longer than that of 0.1 mass% nitrogen concentration. The sample whose surface nitrogen concentration is 0.4 mass% demonstrated L50 life that was 4 times as long as normal SUJ2.
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