LF软吹时间对硅脱氧弹簧钢氧化物夹杂控制影响

 对于一些采用硅锰脱氧冶炼工艺的特殊钢,为保证钢水洁净度,常会选择较长时间的LF软吹处理,导致过程能耗增加。通过工业试验,借助FEI Explorer 4自动扫描电镜检测,研究不同LF精炼软吹时间对硅脱氧弹簧钢55SiCr铸坯氧化物夹杂成分、数量的影响;并采用夹杂物极值统计法,对比评价不同LF精炼软吹时间对应成品盘条横截面最大夹杂物尺寸控制情况。结果表明,在LF软吹10 min与软吹40 min 两种工艺条件下,铸坯中尺寸大于5 μm的氧化物夹杂成分接近,均在CaO-SiO₂-Al₂O₃相图中假硅灰石、钙长石和钙铝黄长石共晶低熔点区,其中软吹10 min工艺铸坯氧化物夹杂组成落入低熔点区的数量所占比例更大。LF软吹10 min与软吹40 min铸坯中尺寸大于5 μm的氧化物夹杂数量密度分别为11.70个/100 mm2和14.59个/100 mm2,尺寸大于15 μm 的氧化物夹杂数量密度分别为0.53个/100 mm2和1.65个/100 mm2,LF软吹10 min工艺铸坯大尺寸氧化物夹杂数量密度略低于LF软吹40 min工艺。当预测面积为30 000 mm2时,两种LF软吹时间对应成品盘条横截面最大夹杂物尺寸分别为27.1 μm和28.1 μm,盘条最大夹杂物尺寸控制无显著差别。结合硅锰脱氧钢中大尺寸低熔点CaO-SiO₂-Al₂O₃系夹杂物主要源自钢包渣乳化卷入,具有与钢水和氩气泡界面接触角很小、难以通过吹氩上浮去除的特点,建议硅锰脱氧钢LF软吹过程按短时间快节奏进行控制。

Effect of LF soft bubbling time on oxide inclusions in Si-killed spring steel

In order to ensure the cleanliness of molten steel, the long-time soft bubbling during LF refining process is often chosen for some Si-Mn deoxidized special steels, resulting in increased energy consumption in the process. Based on the industrial tests, the effects of LF soft bubbling time on the composition and number density of inclusions in Si-killed spring steel bloom were investigated through a scanning electron microscope (FEI Explorer 4), and the maximum size of inclusions in the crossing section of wire rods collected from the LF process with different soft-bubbling times was compared and evaluated by the extreme-value statistical method. The results showed that for the LF processes with two soft-bubbling time, 10 min and 40 min, the compositions of oxide inclusions larger than 5 μm in the blooms were close, and both in the low-melting point region at the eutectic zone of pseudo-wollastonite, anorthite, and gehlenite of CaO-SiO₂-Al₂O₃ phase diagram. The proportion of oxide inclusions falling into the low-melting point region in the 10 min soft-blowing process was higher than that in the 40 min soft-blowing process. The number densities of oxide inclusions with size larger than 5 μm were 11.70 /100 mm2 and 14.59 /100 mm2 respectively in the blooms adopted 10 min and 40 min soft-bubbling processes. Meanwhile, the number densities of oxide inclusions with size above 15 μm were 0.53 /100 mm2 and 1.65 /100 mm2, respectively. The number density of large oxide inclusions in the bloom of 10 min soft-bubbling process was slightly lower than that of 40 min soft-bubbling process. When the predicted area was 30 000 mm2, the maximum sizes of oxide inclusion in the cross sections of wire rods were 27.1 μm and 28.1 μm respectively, and there was no significant difference of them. The low-melting point CaO-SiO₂-Al₂O₃ inclusions with large size in Si-Mn killed steel mainly come from the emulsification of ladle slag, which had a small interface-contact angle with molten steel and argon bubble and was difficult to be removed by argon floating. It is suggested that the soft-bubbling time during LF refining should be controlled in a short time for Si-Mn deoxidized steel.