Microscopic Failure Mechanism of Graphite in Ferrite Ductile Iron
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摘要: 采用原位显微观察方法对拉伸及冲击截荷下的铁素体球墨铸铁中石墨损伤破坏机制进行研究，分析石墨球的形态、分布对裂纹萌生和扩展等微观机理的影响。结果表明：在拉伸载荷下当石墨球均匀分布且间距大于石墨平均尺寸时，石墨球与基体界面脱离，且石墨球内部产生径向裂纹或贯穿整个石墨的裂纹；当石墨球聚集分布且间距小于石墨平均尺寸时，石墨球与基体之间裂纹连接形成尺寸较大的裂纹。在冲击载荷下，石墨球存在“洋葱状”开裂及内部径向开裂等补充破坏机制。在拉伸和冲击载荷下不规则石墨球均存在明显层状撕裂现象；快速封闭的奥氏体壳可保持石墨球圆整且周围铁素体晶粒均匀分布；慢封闭的奥氏体壳导致石墨畸变，周围铁素体晶粒分布不均匀。Abstract: The failure mechanism of graphite in ferrite ductile iron under tensile and impact action was studied by in-situ microscopic observation. The influence of morphology and distribution of graphite nodules on the micro-mechanism of crack initiation and propagation was analyzed. The results show that the graphite nodules separated from the matrix when the graphite nodules uniformly distributed and the spacing was larger than the average graphite size under tensile action, and there were radial cracks in the graphite nodule or cracks throughout the whole graphite. When graphite nodules showed aggregative distribution and spacing was smaller than the average size of graphite, the cracks between the graphite nodules and the matrix connected to form larger cracks. Under impact loads, there were complementary failure mechanisms such as "onion-like" cracking and internal radial cracking in graphite nodules. Lamellar tearing was observed in irregular graphite nodules under tensile and impact loads. The rapidly closed austenite shell could keep the graphite nodule rounded and the surrounding ferrite grains evenly distributed; slow closed austenite shell resulted in graphite distortion and uneven distribution of ferrite grains.
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Keywords:
- ferrite ductile iron /
- graphite nodule /
- failure mechanism /
- ferrite /
- crack
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