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采用V形缺口试样,通过上限温度为500~900℃的热疲劳试验研究了QT400球墨铸铁的热疲劳行为,并对不同上限温度下材料热疲劳裂纹的萌生与扩展以及试样的显微组织与硬度等进行了分析。结果表明,热疲劳裂纹主要从试样的V形缺口底部萌生,上限温度越高,裂纹萌生越早,萌生后扩展速率也越快,其热疲劳寿命越低;随着上限温度的升高,试验后试样基体的硬度逐渐增加,上限温度由700℃上升到800℃时,试样硬度快速上升;热疲劳试验过程中的氧化腐蚀、球墨形态以及组织变化等为球墨铸铁QT400的热疲劳破坏的主要影响因素。
The thermal fatigue behavior of QT400 ductile iron was investigated by thermal fatigue test with V-notch at 500 ~ 900 ℃. The thermal fatigue crack initiation and propagation and the microstructure of QT400 ductile iron under different temperatures were investigated. And hardness were analyzed. The results show that the thermal fatigue crack initiation mainly occurs from the bottom of the V-shaped notch of the sample. The higher the maximum temperature, the earlier the crack initiation and the faster the expansion rate after initiation, and the lower the thermal fatigue life. With the increase of the maximum temperature, After the test, the hardness of the sample matrix gradually increases, and the hardness of the sample rapidly increases when the upper limit temperature rises from 700 ℃ to 800 ℃. The thermal fatigue failure of the ductile iron QT400 is caused by the oxidation corrosion, the morphology of the nodules and the microstructure during the thermal fatigue test The main factors.