氧含量、温度与铋对易切削钢中MnS形貌的影响

Influence of temperature,oxygen,and Bi on the morphology of MnS in free-cutting steel

运用热态实验、化学分析、扫描电镜分析、热力学计算等方法研究了全氧、温度和Bi元素对MnS夹杂物形貌的影响.结果表明,钢中较高的氧含量、高温加热和Bi均可有效降低钢中夹杂物的长宽比,并可以提高大粒径夹杂物的比例.统计分析发现,MnS夹杂物的长宽比随全氧含量升高而降低.无论在铸态钢或轧材中,夹杂物的长宽比随着单个夹杂物的面积增大而增大.随热处理温度的升高,钢中出现大粒径的夹杂物,同时夹杂物的外围轮廓变得清晰. 900℃和1200℃热处理后钢中面积0～5μm2夹杂物长宽比低于2. 0,比加热前夹杂物长宽比降低了43%.热态实验发现T. O=2. 2×10-5、0. 0010%Bi的易切削钢中,面积0～5μm2夹杂物长宽比低于1. 6,比900℃和1200℃热处理后的夹杂物的长宽比降低了20%以上.

The influence of oxygen,temperature,and Bi on the morphology of MnS inclusions in free-cutting steel was studied using thermal experiments,chemical analysis,scanning electron microscopy ( SEM) research,and thermodynamic calculations. The results show that high oxygen content,high temperature heating,and Bi can effectively reduce the aspect ratio of inclusions in steel and improve the proportion of large particle size inclusion. Statistical analysis reveals that the aspect ratio of MnS inclusions reduce when the total oxygen content becomes higher. The aspect ratio of inclusions increases as the area of a single inclusion in as-cast steel or rolled wire increases. With the increase of the heat treatment temperature,large particle inclusions were found in samples,and the contour of inclusions became clearer. The aspect ratio of inclusions with an area of 0--5 μm2 became less than 2. 0 after 900 ℃ and 1200℃ heating,which was lower than the aspect ratio before heat treatment by 43%. Thermal experiments reveal that in S--Bi freecutting steel with total oxygen ( TO) content of 2. 2 × 10 - 5 and Bi content of 0. 0010%,the aspect ratio of inclusions with area of 0--5 μm2 is less than 1. 6,which is 20% lower than that after 900℃ and 1200℃ heat treatment.