轴承钢二次精炼过程夹杂物演变规律

 研究了轴承钢LF精炼和RH真空处理过程各类夹杂物的成分、种类和数量变化,并结合热力学模拟计算了夹杂物与钢液的界面参数,并对试验结果进行分析讨论。夹杂物分析结果表明,精炼25 min后,脱氧产物Al₂O₃消失,钢中夹杂物以纯尖晶石、含少量CaO的尖晶石、CaO·2Al₂O₃和CaO·Al₂O₃为主。继续精炼65 min至LF精炼结束,钢中夹杂物仍以纯尖晶石、含少量CaO的尖晶石、CaO·2Al₂O₃和CaO·Al₂O₃为主。RH真空处理25 min后,钢中夹杂物总数量较LF精炼结束降低75%,其中,纯尖晶石和含少量CaO的尖晶石去除率分别为99.5%和93.2%,CaO·2Al₂O₃去除率为67%。RH破空后钢中夹杂物以液态钙铝酸盐CaO·Al₂O₃和12CaO·7Al₂O₃为主。精炼过程尖晶石类夹杂物尺寸集中在10 μm以下,尺寸大于20 μm夹杂物主要为处于液相区的钙铝酸盐,这些钙铝酸盐在LF精炼前期就已经存在。与钢水接触角大于90°的固态夹杂物纯尖晶石、含少量CaO的尖晶石和CaO·2Al₂O₃在RH真空处理过程容易去除,与钢水接触角小于90°的液态夹杂物CaO·Al₂O₃和12CaO·7Al₂O₃不易去除。因此,将LF精炼结束的夹杂物控制为固态夹杂物有利于RH真空处理过程夹杂物的高效去除。热力学计算结果表明,当钢中w(TO])为0.001 0%、w(Mg])大于0.000 18%时,脱氧产物Al₂O₃热力学上就不能稳定存在。铝脱氧、高碱度渣精炼条件下很难稳定地获得固态Al₂O₃夹杂物。为获得完全固态尖晶石或高熔点钙铝酸盐夹杂物,钢中w(Ca])需控制在0.000 1%以内。钢中w(Ca])大于0.000 2%,就具备生成液态夹杂物的热力学条件。

Investigation on evolution of inclusions in bearing steel during secondary refining

Composition, type and quantity of inclusions in bearing steel during LF refining and RH vacuum treatment were studied. The experimental results were analyzed and discussed in combination with thermodynamic calculation and interface parameters between inclusions and liquid steel. The inclusion analysis results showed that the deoxidization product Al₂O₃ disappeared after 25 min refining, and the inclusions in steel were mainly pure spinel, spinel containing small amount of CaO, CaO·2Al₂O₃ and CaO·Al₂O₃. Pure spinel, spinel containing small amount of CaO, CaO·2Al₂O₃ and CaO·Al₂O₃ were still the main inclusions in steel after 65 min refining to the end of LF refining. After RH vacuum treatment for 25 min, the total number of inclusions in steel was reduced by 75% compared with that after LF refining. The removal efficiency of pure spinel and spinel containing small amount of CaO inclusions was 99.5% and 93.2%, respectively, and that of CaO·2Al₂O₃ inclusion was 67%. The inclusions after RH treatment were mainly liquid calcium aluminate CaO·Al₂O₃ and 12CaO·7Al₂O₃. The size of spinel inclusions in the refining process was concentrated below 10 μm, and the inclusions above 20 μm were mainly calcium aluminates in the liquid phase, which had appeared in the early stage of LF refining. Solid inclusions pure spinel, spinel containing small amount of CaO and CaO·2Al₂O₃ whose contact angle with molten steel was greater than 90° were easy to remove in RH vacuum treatment, while liquid inclusions CaO·Al₂O₃ and 12CaO·7Al₂O₃ whose contact angle with molten steel was less than 90° were not easy to remove. Therefore, controlling the inclusions into solid inclusions after LF refining was beneficial to the high efficient removal of inclusions in RH vacuum treatment. The thermodynamic calculation results show that when the w(TO])is 0.001 0% and w(Mg]) in steel exceeds 0.000 18%, the deoxidization product Al₂O₃ cannot be stable in thermodynamics. It is difficult to obtain solid Al₂O₃ inclusions under the condition of Al deoxidation and high basicity slag refining. To obtain fully solid spinel or high melting point calcium aluminate inclusions, w(Ca]) in steel should be controlled below 0.000 1%。When w(Ca]) in steel exceeds 0.000 2%, it will achieve the thermodynamic conditions for formation of liquid inclusions.