轧制过程界面反应形成细微夹杂物机理及氧化物冶金作用

In order to develop a new technical method and process for controlling the physicochemical characteristics of compound inclusions in steel and improving steel cleanliness, based on high temperature equilibrium system between CaO-SiO2-Al2O3-MgO-MnO compound inclusions and molten steel deoxidized by Mn and Si, effect of cooling process on the interfacial chemical reaction between them was investigated. By heat treatment and rolling experiments, influence mechanism of comprehensive "solid-solid" or "liquid-solid" interface interaction between them on the physicochemical characteristics of compound inclusions in steel was studied and revealed. Heat treatment and rolling process parameters were continuously adjusted, optimized, associated and matched in experiments, to derive and establish quantitative relationship between various parameters and physicochemical characteristics of compound inclusions. Related indexes were also proposed to evaluate the optimization of physicochemical characteristics of compound inclusions. Fine and uniformly distributed inclusions were obtained. Effect of oxide metallurgy was enhanced for improving the tissue and mechanical properties of steel. Then well-matched optimization system of rolling process with heat treatment process was constructed. According to above experimental results, theoretical thermodynamic and dynamic models were built and verified. Successful implementation of this study has important academic significance and practical application value for greatly improving the quality of steel products such as tire cord steel, thread steel and so on.

为开辟一条控制钢中复合夹杂物物化特性和进一步改善钢基体洁净度的新技术方法和工艺途径，本项目旨在基于“钢液-夹杂物”高温平衡体系以及冷却制度对二者界面化学反应的影响规律，研究和揭示不同轧制工艺下CaO-SiO2-Al2O3-MgO-MnO类复合夹杂物与锰硅系脱氧钢之间“固-固”或“液-固”界面物化综合作用和机理，并结合成熟热处理和轧制工业实验，不断调整、优化、关联、匹配热处理和轧制工艺参数，推导和建立各类参数与夹杂物物化特性之间的定量关系和相关评价指标，实现复合夹杂物的细微化和弥散化，增强氧化物冶金作用效果和改善钢基体组织、性能，最终构建和形成与不同热处理工艺良好匹配的轧制工艺优化体系以及相应的热力学和动力学理论模型。该项目的成功实施，对于进一步提高钢产品的机械性能以及有效改善甚至大幅度提高帘线钢、螺纹钢等线、棒材的产品质量具有十分重要的理论意义和实际应用价值。

“钢液-夹杂物”高温平衡体系中所形成的夹杂物，其物化特性在后续轧制过程中会由于夹杂物与钢基体之间的界面反应而发生改变。本研究以锰硅脱氧钢及其内部夹杂物为研究载体，构建了“钢液-夹杂物”高温平衡体系，探索了轧制工艺包括温度和时间等对夹杂物与钢基体之间界面物化作用的影响机理，开发和构建了定量预测和控制夹杂物物化特性的热力学和动力学理论模型，从而揭示了在不同热加工体系中钢基体和夹杂物特性的变化行为。.研究结果表明：（1）为实现夹杂物的塑性化，锰硅脱氧钢（U71Mnk重轨钢）LF精炼渣成分的优化范围如下：CaO，SiO2，Al2O3，MgO的成分范围分别为44.2-51.7 wt pct，41.4-47.0 wt pct，0-4.7 wt pct，5.0-7.0 wt pct，而渣碱度和钙铝比应该分别为1.00-1.25和>9.0的范围。（2）LF精炼后，钢液中全氧含量，[Al]和[S]含量分别逐渐稳定在0.0008-0.0012 wt pct，0.002-0.0028 wt pct和0.0026-0.0037 wt pct的范围内。三种典型非金属夹杂物，CaO-SiO2-Al2O3-MgO，MnS和CaO-SiO2-Al2O3-MgO-MnS等的数量密度逐渐降低至0.25/mm2，且基本上无大于6.0 μm的夹杂物生成。（3）1473 K轧制温度下加热过程中，CaO-SiO2-Al2O3-MgO-MnO类复合夹杂物与锰硅系脱氧钢之间会发生“液-固”界面化学反应，同时造成钢基体与氧化物中的各类元素发生相互扩散作用。氧化物中MnO的含量和金属中Si的含量是金属与氧化物“固-液”化学反应以及元素扩散的主要驱动力；（4）不同轧制温度进行保温后，界面附近钢基体中析出氧化物颗粒和Mn含量降低，分别形成了PPZ（颗粒析出区）和MDZ（Mn损耗区）。二者均随轧制温度和轧制时间的增大而增大；（5）较低温度下（<1173 K），锰硅脱氧钢与MnO-SiO2-FeO氧化物之间的固相反应可以被忽略，而较高温度下（>1573 K），大量Mn2+和Si4+由氧化物扩散至钢基体中，导致界面附近钢基体中Mn和Si含量明显升高和氧化物成分由2MnO•SiO2为逐渐转变为MnO•SiO2。（6）轧制温度、时间等参数对PPZ和MDZ宽度的影响实验结果与动力学理论模型预测结果吻合较好，验证了模型预测的可靠性。