管线钢铸坯中硫化物特征及形成机理

 对管线钢铸坯中的硫化物特征进行了分析，并对其形成机理进行了讨论。发现从中间包钢液到铸坯，管线钢中夹杂物由低熔点的CaO Al2O3向CaS Al2O3类型转变，且夹杂物尺寸越小，在冷却过程中的转变越充分。根据形貌特征，含硫化物夹杂可分为以下几类，即硫化物在氧化物表面部分析出、硫化物半包裹氧化物、硫化物完全包裹氧化物、纯硫化物和在TiN上析出的硫化物。采用FactSage软件对冷却过程管线钢中的夹杂物转变进行了计算，发现随着温度的降低，液态钙铝酸盐夹杂物逐渐经历CaO·Al2O3→CaO·2Al2O3→CaO·6Al2O3→Al2O3的转变过程，同时CaS和MnS相也在冷却过程中析出，且MnS的析出温度低于CaS，这解释了铸坯中硫化物的特征和形成。

Characteristics and formation mechanism of #br# sulfide in the slab of pipeline steel

The characteristics of sulfide in the slab of pipeline steel was analyzed and the formation mechanism was discussed in the current work. It was found that from the molten steel in tundish to the slab, inclusions transformed from liquid CaO Al2O3 to CaS Al2O3 type, and the smaller the size of inclusions, the more complete the transformation in the cooling process. According to the morphology, sulfide containing inclusions could be classfied into partial precipitation of sulfide on oxide surface, semi encapsulation of oxides by sulfide, complete encapsulation of oxides by sulfide, pure sulfide, and sulfide precipitated on TiN. The transformation of inclusion phases during the cooling of pipeline steel was calculated employing FactSage software. It was indicated that with the decrease of temperature, liquid calcium aluminates transform along the path of CaO·Al2O3→CaO·2Al2O3→CaO·6Al2O3→Al2O3. Phases of CaS and MnS will also precipitate during the cooling process, and the precipitation temperature of MnS was lower than that of CaS, which could explain the characteristic and formation of sulfide in the slab.