A typical high-sulfur microalloyed steel was investigated by a sub-rapid solidification process for grain refinement of the as-cast microstructure. The size and distribution characteristics of the MnS precipitates were analyzed. The variations in the dendrite morphology and secondary dendrite arm spacing (SDAS) under different cooling rates have been studied, which strongly influence the precipitation behavior of MnS. The 3D-morphology of MnS precipitates was revealed by a novel saturated picric acid deep-etching method. Most MnS precipitates with a length smaller than 5 μ m were columnar or equiaxed in the corresponding dendrite zones under sub-rapid solidification conditions at cooling rates of 261 to 2484 K/s. Furthermore, an area scan analysis of the precipitates showed the number of small MnS per square millimeter with lengths lower than 3 μ m decrease from 200,537 to 110,067. The percentage of large MnS with a length over 5 μ m increased from 2.6 to 6.2 pct as the solidification condition changed from sub-rapid to air cooling. In addition, the size of MnS precipitate was found to depend linearly on the SDAS.

中文翻译：

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亚快速凝固过程中高硫微合金钢的MnS析出行为

通过亚快速凝固工艺研究了一种典型的高硫微合金钢，以细化铸态组织的晶粒。分析了MnS沉淀物的尺寸和分布特征。研究了不同冷却速率下枝晶形貌和二次枝晶臂间距 (SDAS) 的变化，这对 MnS 的析出行为有很大影响。MnS 沉淀物的 3D 形态通过一种新的饱和苦味酸深度蚀刻方法揭示。在亚快速凝固条件下，冷却速率为 261 至 2484 K/s，大多数长度小于 5 μm 的 MnS 析出物在相应的枝晶区呈柱状或等轴状。此外，沉淀物的面积扫描分析显示，每平方毫米长度小于 3 μm 的小 MnS 数量从 200,537 减少到 110,067。随着凝固条件从亚快速冷却变为空冷，长度超过 5 μ m 的大 MnS 的百分比从 2.6 pct 增加到 6.2 pct。此外，发现 MnS 沉淀物的大小与 SDAS 呈线性关系。