Abstract The characteristics and transformation of M2C and MC, the most common primary carbides in Cr4Mo4V bearing steel, have been investigated via scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction at high austenitization temperatures. It was first found that the transformation of rod-like M2C and spherical MC primary carbides during heating occurs at approximately 1180 and 1200 °C, respectively. In the transformation process of M2C, the periphery first transforms into an MC-type carbide, and then the internal untransformed M2C and newly-formed MC-type melt, and re-solidify in a M2C” eutectic carbide structure with a composition change and a finer lamellar spacing. In contrast, MC carbides melt directly with the re-solidified product also being constituted of finer M2C” eutectic carbides. The transformation process is controlled by the diffusion of alloying elements Mo and V, while the matrix provides Fe for the formation of M2C”. In addition to elucidate the transformation mechanisms, this study also highlights the essential effect of the melting matrix on the modification of primary M2C and MC carbides in Cr4Mo4V steel.

中文翻译：

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Cr4Mo4V轴承钢奥氏体化过程中初生碳化物的特征及转变

摘要 通过扫描电子显微镜、能谱仪和 X 射线衍射在高奥氏体化温度下研究了 M2C 和 MC 是 Cr4Mo4V 轴承钢中最常见的一次碳化物的特征和转变。首次发现棒状 M2C 和球形 MC 初生碳化物在加热过程中的转变分别发生在大约 1180 和 1200°C。在 M2C 的转变过程中，外围首先转变为 MC 型碳化物，然后内部未转变的 M2C 和新形成的 MC 型熔体，重新凝固为 M2C”共晶碳化物组织，成分发生变化，更细的层状间距。相比之下，MC 碳化物直接熔化，再凝固的产品也由更细的 M2C”共晶碳化物构成。转变过程受合金元素 Mo 和 V 的扩散控制，而基体为 M2C 的形成提供 Fe”。除了阐明转变机制外，本研究还强调了熔炼基体对 Cr4Mo4V 钢中原生 M2C 和 MC 碳化物变质的重要影响。