GCr15轴承钢连铸过程MgO·Al_(2)O_(3)夹杂物形成机理

Formation mechanism of MgO·Al_(2)O_(3)inclusions in GCr15 steel in continuous casting

为了研究GCr15轴承钢浇铸过程MgO·Al_(2)O_(3)夹杂物形成原因,以改善钢的可浇性,对LF结束、RH结束、中间包冲击区、中间包浇铸区进行夹杂物全流程分析。LF结束夹杂物主要为镁铝尖晶石,并含有少量钙铝酸盐夹杂物。RH真空处理后镁铝尖晶石夹杂物被高效化去除,钢液中仅剩少量低熔点和高熔点钙铝酸盐夹杂物,中间包浇铸时可以在钢液中检测到许多MgO·Al_(2)O_(3)夹杂物。采用不含氧化镁的中间包覆盖剂和铝质中间包内衬,在不改变连铸其他工艺参数条件下,中间包MgO·Al_(2)O_(3)夹杂物数量并没有得到显著降低,中间包钢液中仍然可以检测到许多MgO·Al_(2)O_(3)夹杂物,这说明中间包钢-渣-耐火材料间的反应并不是MgO·Al_(2)O_(3)夹杂物的生成原因。向铁质提桶取样器中加入成分以SiO_(2)、Cr_(2)O_(3)、Fe_(2)O_(3)为主的铬质引流砂,并利用该铁质提桶取样器对RH破空后钢水进行取样,尽管钢水总氧质量分数增加0.0001%,但可以在所取的钢样中检测到许多MgO·Al_(2)O_(3)夹杂物,说明钢液的轻微氧化对MgO·Al_(2)O_(3)夹杂物形成具有重要的影响。通过分析中间包覆盖剂成分,发现浇铸过程覆盖剂碱度偏低,Cr_(2)O_(3)和FeO含量偏高,且同一炉钢水浇铸后期覆盖剂中Cr_(2)O_(3)、FeO含量较浇铸前期有所降低,说明浇铸过程覆盖剂会向钢水传氧,由此造成对钢液的氧化,因此,覆盖剂成分的稳定控制对于轴承钢MgO·Al_(2)O_(3)夹杂物的形成具有重要影响。

The compositions of inclusions were analyzed in GCr15 steel in LF refining,RH degassing and continuous casting.The inclusions were composed of MgO·Al_(2)O_(3)with a small amount of calcium aluminate after LF refining.Many MgO·Al_(2)O_(3)inclusions were detected in the continuous casting although the inclusions were calcium aluminate after RH degassing.Using Al_(2)O_(3)-based tundish working lining and low content of MgO covering flux,and unchanging other parameters of continuous casting,MgO·Al_(2)O_(3)inclusions were also be detected in large numbers in the tundish,indicating the reaction of steel-slag-refractory in the tundish was not the mainly reason for the formation of MgO·Al_(2)O_(3)inclusions.However,many MgO·Al_(2)O_(3)inclusions could be detected when the molten steel without MgO·Al_(2)O_(3)inclusions reacted with the packing sand with high contents of SiO_(2),Cr_(2)O_(3)and Fe_(2)O_(3),which means the slight oxidation of molten steel could lead to the formation of MgO·Al_(2)O_(3)inclusions.High contents of FeO and Cr_(2)O_(3)were found in the tundish flux and decreased with the casting goes on,indicating the existence of the reactions between Al in the molten steel and FeO,Cr_(2)O_(3)in the tundish flux,which leads to the oxidation of molten steel.Therefore,the composition control of tundish flux was important to the formation of MgO·Al_(2)O_(3)inclusions.