高品质GCr15轴承钢二次精炼过程中夹杂物的演变规律

采用FE-SEM/EDS研究了转炉流程生产的GCr15轴承钢LF、RH精炼过程中夹杂物的演变规律,分析了其演变机理。结果表明:钢中复合夹杂物的演变规律可归纳为:Al2O3→MgO·Al2O3→(CaO-MgO-Al2O3-(CaS))复合氧化物夹杂和Al2O3→(Al2O3-MnS)→(Al2O3-MnS-Ti(C,N))复合氧硫碳氮物夹杂2种方式。LF精炼过程脱硫作用明显,钢中的硫化物夹杂数量大幅减少。LF精炼初期钢中主要是MnS、Al2O3、TiN的单相夹杂物。LF精炼结束后钢中的夹杂物演变为Al2O3为核心外包氧化物及MnS、TiN、Ti(C,N)、CaS的复合夹杂物。精炼渣中的CaO和耐火材料中的MgO经还原后与钢中溶解氧反应导致LF精炼结束时D类夹杂物增加。RH及软吹处理进一步强化了去除钢中的硫化物,但D类及其与A、T类复合的夹杂物含量增加。在LF阶段,夹杂物尺寸主要集中在1~3μm范围内,到RH阶段,夹杂物尺寸则主要集中分布在小于1μm的粒度范围。最大夹杂物尺寸由10.79μm降到5.68μm,单位面积夹杂个数由372个/mm2降到258个/mm2。RH及软吹处理有效地降低了钢中大于3μm的夹杂物。

The evolution of inclusions in high quality GCr15 bearing steels during secondary refining process

Based on the productive process of BOF-LF-RH-CC for GCr1 5 bearing steels and using FE-SEM/EDS,evolution rule and mechanism of the inclusions in LF and RH refining process have been studied.Results show that two types of evolution manners of the complex inclusions for the steel during refining process are summarized.The complex inclusions originate from Al2 O3 and then change to MgO· Al2 O3 → (CaO-MgO-Al2 O3-(CaS )) and (Al2 O3-MnS )→ (Al2 O3-MnS- Ti (C,N )) respectively. Desulfurization effect is obvious in LF refining process, and sulfide inclusions in steel decrease significantly.The main inclusions at the beginning of LF refining process are some simple inclusions such as MnS,Al2 O3 ,TiN,etc.At the end of LF refining process,the inclusions are compounds which Al2 O3 is covered with MnS,TiN,Ti(C,N)or CaS on the surface.CaO in refining slag and MgO in refractories are easily reduced by aluminum and carbon in the steel and then Ca and Mg will react with the dissolved oxygen in steel,which leads to the number of D-type inclusions increasing at the end of LF refining.After RH and soft blowing process,sulfide inclusions are removed further,the number of D-type inclusions and complex D-type inclusions covered with A-type and T-type inclusions increase.During the LF refining,the size of inclusions mainly concentrates in the range of 1-3μm.During the RH refining,the size of inclusions mainly concentrates less than 1μm.The maximum size of the inclusion changes from 10.79μm to 5.68μm,and the number of inclusions in per square microns decreases from 372/mm2 to 258/mm2 .RH and soft blowing process have removed the inclusions larger than 3μm in steel effectively.