钙处理对硅脱氧弹簧钢55SiCr氧化物夹杂的影响

Influence of calcium treatment on oxide inclusions in Si-killed spring steel 55SiCr

为了将硅脱氧弹簧钢中SiO2类高熔点硬质夹杂改性成低熔点夹杂物,在炼钢生产中进行了钙处理试验。利用FEI Explorer 4自动扫描电镜对硅脱氧弹簧钢55SiCr在正常工艺与钙处理工艺处理后的铸坯、盘条中氧化物夹杂的成分、尺寸、数量、形貌进行检测,统计分析2种工艺下夹杂物尺寸、夹杂物轧制变形性的差异,并通过弹簧钢丝Nakamura旋转弯曲疲劳测试对比2种工艺下夹杂物控制水平。分析结果表明:硅脱氧弹簧钢55SiCr钙处理工艺后氧化物夹杂主要为CaO-SiO2-(CaS)类,尺寸较大,且此类夹杂物在盘条轧制过程中不易变形细化,最终恶化弹簧钢疲劳性能;正常工艺处理后氧化物夹杂尺寸随着夹杂物中Ca含量升高有增大倾向,CaO-SiO2-Al2O3系相图中方石英、磷石英与莫来石交界区的夹杂物轧制变形性优于假硅灰石和钙长石共熔区的夹杂物。

In order to modify the SiO2 hard inclusions with high melting point in Si-killed spring steel into low melting point ones,calcium treatment was adopted in steelmaking process.The composition,size,morphology and amount of oxide inclusions in bloom and wire rod of Si-killed spring steel 55 SiCr with and without calcium treatment were examined using an FEI Explorer 4 automated scanning electron microscope,and the difference of size and rolling deformability of oxide inclusions subjected to the two processes were statistically analyzed,while Nakamura rotating bending test of inductively tempered spring wire was also conducted to compare the inclusion control levels of the two processes.The results show that the oxide inclusions in bloom of spring steel 55 SiCr with calcium treatment process are mainly CaO-SiO2-(CaS)type,whose size is larger than that without calcium treatment process,and these inclusions are not easy to deform during the rolling process,which deteriorate the fatigue properties of spring steel wire eventually.The oxide inclusion size increases with the increase of Ca content in the inclusions after conventional processing,and the rolling deformability of inclusions in the boundary zone of cristobalite,phosphatite and mullite in the phase diagram of CaO-SiO2-Al2O3 system is better than that in the eutectic zone of pseudo-wollastonite and anorthite.