硅脱氧55SiCr钢中镁硅橄榄石夹杂的一种潜在来源

A potential source of forsterite inclusion in Si-killed spring steel 55SiCr

国内某钢厂55SiCr钢由铝脱氧工艺调整为硅脱氧工艺后,镁硅橄榄石成为旋转弯曲疲劳断口夹杂物的主要类型。借助Explorer 4自动扫描电镜、FactSage等方法,探究了不同钢厂硅脱氧弹簧钢夹杂物控制差异,并计算了典型夹杂物平衡凝固过程的析出相。结果表明,日本神户制钢9254-M钢中只有少量夹杂物发生结晶且结晶尺寸小,夹杂物中MgO含量控制极低;日本制铁公司9254V钢中夹杂物均发生了玻璃态结晶转变,结晶尺寸较小,夹杂物中MgO质量分数平均值为14.5%。国内某钢厂55SiCr钢只有部分夹杂物发生结晶,但析出较大尺寸镁硅橄榄石,且夹杂物中MgO含量波动范围较大。随着CaO-SiO_(2)-Al_(2)O_(3)-MgO系夹杂物中MgO含量升高,夹杂物在铸坯凝固及加热过程中更易结晶出镁硅橄榄石相。这种结晶析出的镁硅橄榄石与MgO质耐材侵蚀剥落形成的镁硅橄榄石,均成为旋转弯曲疲劳断口镁硅橄榄石夹杂的潜在来源。

After the deoxidation process of spring steel 55SiCr was adjusted from Al-killed to Si-killed in a domestic steel plant,forsterite inclusions became the main type of inclusions in the rotating bending fatigue fracture.By using methods such as Explorer 4 automatic scanning electron microscopy and FactSage,the differences in inclusion control of Si-killed spring steels from different steel mills were investigated,and the precipitation phases of typical inclusion equilibrium solidification processes were calculated.The results show that only a small amount of inclusions crystallize and the crystal size is small in the 9254-M steel made in Kobe Steel,Japan,and the MgO content in the inclusions is controlled very low.The inclusions in the 9254V steel produced by Nippon Steel underwent a glass state crystallization transformation,with a smaller crystal size and an average MgO mass fraction of 14.5 mass%in the inclusions.Only some inclusions crystallize in a 55SiCr steel produced by a domestic steel plant,but larger sized forsterite precipitates,and the MgO content in the inclusions fluctuates widely.As the MgO content in CaO-SiO_(2)-Al_(2)O_(3)-MgO system inclusions increases,the inclusions are more likely to crystallize forsterite phase during the solidification and heating process of the casting bloom.The crystallized forsterite and the forsterite formed by erosion and peeling of MgO based refractory materials both become potential sources of forsterite inclusions in rotational bending fatigue fractures.