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用旋转弯曲疲劳试验机研究了不同稀土含量对工厂冶炼的40MnB、25MnTiB、20钢过载疲劳寿命和疲劳极限的影响。稀土含量0.02%时,过载疲劳寿命可成倍增加,含量再多,疲劳寿命改善不明显。含稀土0.02%时,疲劳极限无甚变化,含量再多,稍有降低,变化趋势与疲劳寿命相似。扫描电镜对疲劳断口的检验表明,疲劳裂纹源在夹杂处形成,裂纹扩展与夹杂物的数量有关,含稀土0.02%时,疲劳断口上夹杂物较少。定量金相显微镜检验表明,含稀土0.02%时夹杂物最少。稀土对钢的净化作用是提高过载疲劳寿命的主要原因。
The effects of different rare earth contents on overload fatigue life and fatigue limit of 40MnB, 25MnTiB and 20 steel smelted in the factory were studied by rotating bending fatigue tester. Rare earth content of 0.02%, the overload fatigue life can be doubled, the content of more fatigue life improvement is not obvious. Containing rare earth 0.02%, the fatigue limit of little change, more content, slightly lower, the trend of change and fatigue life similar. Scanning electron microscopy examination of the fatigue fracture shows that the source of fatigue cracks is formed at the inclusions, and the crack propagation is related to the amount of inclusions. When the content of rare earth is 0.02%, there are fewer inclusions on the fatigue fracture. Quantitative metallographic examination showed that inclusions with 0.02% RE were the least. The purification of rare earth steel is to improve the fatigue life of overload the main reason.