ABSTRACT

The element sulphur is usually added to form MnS inclusions and improve the machinability of micro-alloyed steel. However, the MnS inclusions tend to elongate in rolling direction during hot working process and deteriorate the mechanical properties of steels. In this work, the effect of heat treatment on the morphological changes of elongated MnS inclusions was investigated. The research results show that the as-cast type II MnS inclusions tend to flattened and elongated morphology after rolled. The shape changes of the MnS inclusions during the heat treatment process is flat →cylinderization→ovulation→spheroidization. The morphological changes leading to cylinderization, ovulation and spheroidization of the MnS inclusions are controlled by the potential gradient induced by the inherent curvature difference. The transformation modes of ovulation and spheroidization depend on the initial aspect ratio (Length to width, L/W). The transport mechanisms for cylinderization, ovulation and spheroidization of the MnS inclusions are all controlled by surface diffusion.

摘要

通常添加元素硫以形成MnS夹杂物，并改善微合金钢的可切削性。但是，MnS夹杂物在热加工过程中倾向于在轧制方向上伸长并且使钢的机械性能劣化。在这项工作中，研究了热处理对伸长的MnS夹杂物形态变化的影响。研究结果表明，铸态II型MnS夹杂物在轧制后趋于扁平化和拉长。热处理过程中MnS夹杂物的形状变化是平坦→圆柱化→排卵→球化。MnS夹杂物导致圆柱化，排卵和球化的形貌变化是由固有曲率差引起的电势梯度控制的。排卵和球化的转换模式取决于初始长宽比（长度与宽度，L / W）。MnS夹杂物的圆柱化，排卵和球化的传输机制均受表面扩散控制。