洁净钢精炼钙处理技术探析

Discussion on calcium treatment technology for clean steel refining

结合国内外的研究成果和作者的研究实践,介绍了钙的物理化学性质、钙处理变性原理和相关热力学数据以及存在的问题,探讨了洁净钢钙处理实施的新策略,并推荐了钙处理的控制标准。由于精炼过程钢中的夹杂物发生了演变,钙处理的实际对象从最初的铝脱氧产物(Al_(2)O_(3)夹杂物)变为其演变产物(包括MgO·Al_(2)O_(3)夹杂物和CaO-Al_(2)O_(3)-MgO系夹杂物等);虽然钙处理技术可以控制钢中夹杂物的形态,改善钢液的可浇性,但易影响夹杂物的去除效率,增加大型夹杂物出现的频率,还会使钢液发生二次氧化,加剧耐火材料侵蚀,因此钙处理多数是会污染钢液的;如果没有夹杂物变性的特殊要求且不存在可浇性问题,建议不对钢液进行钙处理,如确实需要也应尽量少添加钙,且宜在精炼结束之后再进行;钢中溶解钙的精确测量仍是难题,钙相关热力学数据也有较大的偏差,而且钙收得率不稳定,因而钙处理目前很难做到精准控制,而w(T[Ca])/w(T[O])控制标准避免了溶解钙的测量,也不涉及热力学数据,可参照w(T[Ca])/w(T[O])=0.91~1.25来控制钙含量,以改善低氧低硫钢液可浇性。同时,为提升钢液的洁净度,仍然推荐尝试获得最低的钙添加量。钢液的可浇性影响因素众多,钙处理技术并不能解决所有可浇性问题。

Aiming at a better understanding on calcium treatment technology,the physical and chemical properties of metal calcium were summarized,the modification mechanisms of calcium treatment and the related thermodynamic data based on the study results in literature.According to the studies and industrial practice of the present authors,the problems of calcium treatment were discussed,and the principle and control standard for calcium treatment were recommended.Due to the evolution of inclusions in steel during refining process,the object inclusions for calcium treatment change from Al deoxidation products(Al_(2)O_(3)inclusions)to their evolution products(including MgO·Al_(2)O_(3)inclusions and CaO-Al_(2)O_(3)-MgO system inclusions,etc.).Although calcium treatment technology can modify the inclusions in steel and improve the castability of steels,it generally declines the removal efficiency of inclusions,enlarges the frequency of macro-inclusions,and leads to reoxidation of liquid steel and corrosion of refractories.Therefore,calcium treatment pollutes liquid steel in most cases.If there are no special requirement on inclusion modification,and no problem with castability of steels,calcium treatment is not recommended to perform.If in need,Ca should be added as little as possible for calcium treatment,and it should be carried out after refining.Accurate measurement of dissolved[Ca]in steel is still a challenge,and large deviations are existed in the thermodynamic data of Ca.In addition,the yield of Ca is unstable as well,so it is difficult to achieve precise control of calcium treatment.Since the measurement of dissolved[Ca]is avoided,and thermodynamic data are not needed,the standard of w(T[Ca])/w(T[O])can be practical in industry.In order to improve the castability of low-oxygen and low-sulfur steels,the Ca content can be controlled referring to the recommended value(0.91-1.25)of w(T[Ca])/w(T[O]).Nevertheless,the lowest Ca addition is still suggested for higher steel cleanliness.Also,calcium treatment cannot solve all the castability problems due to the various influential factors.