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对球墨铸铁在真空下加热时球状石墨的变化过程进行了高温金相观察,发现在球状石墨周围基体熔化之前,圆整度较好的致密石墨球沿晶界或其周围的显微缺陷有少量线型生长,周围形成明显的黑环,而其外形基本保持不变。圆整度较差的松散石墨球则具有较大的线型生长,而且在1000℃左右体积也有较大的增长。当石墨球周边的基体出现液相后,碳原子向熔体的扩散速度激增,石墨立即在熔体中开花、解体,过程进行甚快,在我们的观察条件下仅约三十秒钟。对试样随炉冷却时石墨的再结晶过程也进行了观察和常温金相分析。结果表明解体的石墨具有多种形态,且大多起因于其周围基体的熔化,由于直接观察到了奥氏体熔化而使金相磨面产生褶皱,从而可以推断:大断面球铁件中心部份出现畸变石墨的主要原因是由于奥氏体外壳在共晶主平台温度回升时发生重熔而引起的。
The ductile iron under vacuum heating of spherical graphite was observed during the high-temperature metallographic changes and found that before the spherical graphite around the matrix melting, the roundness better compact graphite ball along the grain boundaries or the surrounding micro-defects have a small amount Linear growth, the formation of a clear black ring around, and its basic shape remained unchanged. Loose graphite balls with poor roundness have a larger linear growth, but also have a greater increase in volume at about 1000 ° C. When the matrix around the graphite ball appeared in the liquid phase, the diffusion rate of carbon atoms into the melt increased sharply. The graphite immediately began to flow and melt in the melt, and the process proceeded very fast. In our observation condition, it took only about thirty seconds. The recrystallization of graphite during the furnace cooling was also observed and analyzed at room temperature. The results show that the disassembled graphite has many morphologies and mostly results from the melting of the surrounding matrix. Due to the direct observation of the austenite melting, the metallographic surface is wrinkled, which leads to the conclusion that the central part of the large-section ductile iron appears The main reason for distorted graphite is due to remelting of the austenitic shell when the eutectic main platform temperature rises.