Analysis and Formulation of Evolution of Hot Deformation Microstructure in Ultra-Low Carbon Steels

预测钢热变形过程中显微组织变化的计算机模型已经开发出来，但它还不能应用于含碳量不超过0.05%的低碳钢。本文研究了碳含量在0.0008 ~ 0.495mass %范围内的三种Fe-Ni-C和四种Fe-Mn-C合金的扭转热变形。热扭转过程中的原位X射线衍射研究证实，在合金的γ→α相变起始温度附近，变形过程中发生了γ→α相变。变形应力虽然随着相变而降低，但在不发生相变的情况下，变形应力几乎不随碳含量而变化，因此，即使碳含量在0.05%（质量）以下的低碳钢，也可以使用上述计算机程序。初步确定了上述转变的温度范围，并对转变的原因进行了讨论。有人指出，需要做更多的工作来制定转变的动力。

A computer model which predicts microstructural changes during hot deformation of steels has been already developed, but it has not been able to be applied to low carbon steels containing carbon no more than 0.05 mass%. Recently, such low carbon steels MC being produced more and more in quantity, so the extension of the above model to them has become a very urgent problem.Hot deformation of three Fe-Ni-C and four Fe-Mn-C alloys whose carbon content range between 0.0008 and 0.495 mass% were studied in torsion. An in-situ X-ray diffraction study during hot torsion proved that γ→α transformation occurred during deformation around their thermodynamical γ→α transformation start temperatures. Although deformation stress decreased corresponding to the transformation, it was shown that it scarcely changed according to the carbon content when the transformation did not occur.These results indicate that the above computer program can be used even in low carbon steels whose carbon contents are no more than 0.05 mass%. The temperature range of the above transformation was roughly determined and the cause of the transformation was discussed. It was pointed out that much more work is needed to formulate the kine6cs of the transformation.