蠕化率对蠕墨铸铁组织及热疲劳性能的影响

采用自约束热疲劳试验机,对不同蠕化率下的蠕墨铸铁进行热疲劳性能试验并观察其组织变化。结果表明,试样的抗热疲劳性能随着蠕化率的升高呈现先上升后下降的趋势。当蠕化率为70%~80%时,蠕墨铸铁的热疲劳性能最好。蠕虫状石墨占基体比重有一个最佳值,蠕化率过低时,由于球状石墨数量较多分布较密集,导致热疲劳性能较差;蠕化率过高时,由于蠕虫状石墨过于粗大使裂纹扩展速度加快,导致热疲劳性能较差。在裂纹扩展后期,主裂纹变粗大导致其向前扩展所需驱动力不足以及主裂纹上形成分叉裂纹及二次裂纹,进而导致裂纹扩展呈现先快后慢、阶段性扩展的特点。

Effect of Vermicularity on Thermal Fatigue Property of Compacted Graphite Iron

The thermal fatigue property of compacted graphite iron with different vermicularity was tested on self-restrict thermal fatigue experimental machine. The results showed that the thermal fatigue properties of samples with increasing vermicularity presented a downward trend after the first rise. Compacted graphite iron had the best thermal fatigue property with the vermicularity of 70%-80%. Brittle phase graphite had a best proportion in the matrix. When the vermicularity was excessively low, a larger number of spheroidal graphite with dense distribution led to low thermal fatigue resistance. When the vermicularity was excessively high, the thick compacted graphite iron acce-lerated crack propagation, leading to low thermal fatigue resistance. In the later stage of crack propagation, the insufficient driving force caused thicker main crack and the forming of branch crack and secondary crack, making the propagation of thermal fatigue crack fast at first and then slow down.