Q235钢中夹杂物演变规律和生成机理分析

 为了更好地控制Q235钢中非金属夹杂物的种类和数量,提高钢的冲击韧性,采用自动扫描电镜分析了Q235钢中非金属夹杂物在LF精炼、中间包和连铸坯中成分和形貌的演变规律。采用FactSage热力学软件对钢中各类夹杂物的生成机理进行了分析。研究发现,钢中非金属夹杂物的演变规律为均相的SiO₂-MnO夹杂物→均相的SiO₂-Al₂O₃-MnO-TiO_x夹杂物→双相的Al₂O₃-SiO₂-CaO包裹着MgO·Al₂O₃类夹杂物→多相的TiO_x-SiO₂-Al₂O₃-CaO-MnO-MnS夹杂物。样品冷却过程中均相的SiO₂-MnO夹杂物发生相变析出纯SiO₂导致在LF精炼初期钢中出现双相SiO₂-MnO类夹杂物。加入的硅钙钡合金中铝含量较高,导致液态夹杂物在钢液中析出MgO·Al₂O₃,以及在LF出站钢样品中出现双相的Al₂O₃-SiO₂-CaO包裹着MgO·Al₂O₃类夹杂物。含钛的夹杂物在连铸坯凝固冷却过程会析出纯的Ti₃O₅,并且钢中还会析出MnS析出相,因此连铸坯中存在多相的TiO_x-SiO₂-Al₂O₃-CaO-MnO-MnS夹杂物。

Evolution and formation mechanism of inclusions in a Q235 steel

In order to control the amount and type of inclusions in a Q235 steel and improve the impact toughness of the steel, the variation in morphologies and composition of inclusions in the production process of LF→tundish→bloom was analyzed using ASPEX. Thermodynamic analysis of the formation mechanism of different type inclusions was performed using FactSage. It is found that the evolution of non-metallic inclusions in steel was, homogeneous SiO₂-MnO inclusions→homogeneous SiO₂-Al₂O₃-MnO-TiO_x inclusions→two-phase Al₂O₃-SiO₂-CaO enveloping MgO·Al₂O₃ inclusions→multiphase TiO_x-SiO₂-Al₂O₃-CaO-MnO-MnS inclusions. The two-phase SiO₂-MnO inclusions found in the steel at the beginning of LF refining are caused by the phase change of pure SiO₂ in the SiO₂-MnO inclusions during the cooling process. The two-phase Al₂O₃-SiO₂-CaO found in the LF outbound steel sample encloses the MgO·Al₂O₃ inclusions because of the high aluminum content in the added silicon calcium strontium alloy, resulting in liquid inclusions in the molten steel,MgO·Al₂O₃ was precipitated. Titanium-containing inclusions would precipitate pure Ti₃O₅ during solidification and cooling of the continuous casting billet, and the precipitated phase of MnS will precipitate in the steel. Therefore, there were heterogeneous TiO_x-SiO₂-Al₂O₃-CaO-MnO-MnS inclusions in the continuous casting bloom.