低氧特殊钢中大尺寸DS类夹杂物生成机理

为了探讨低氧特殊钢中大尺寸DS类夹杂物的生成机理,通过ASPEX PSEM explorer自动扫描电镜对比分析国内外低氧特殊钢试样中夹杂物特征(国内、外试样各两个),发现国内试样中夹杂物平均尺寸大于国外试样,夹杂物的最大尺寸则数倍于国外试样：国内试样中夹杂物的最大尺寸分别为24.9和13.1μm,国外试样分别为7.6和7.5μm.对比国内外特钢试样中大尺寸与小尺寸夹杂物可发现二者成分基本相同,推断大尺寸DS类夹杂物可能是细小夹杂物碰撞长大而形成.通过分析大尺寸夹杂物的可能来源,在实验室通过高温共聚焦激光扫描显微镜观察夹杂物在钢中固/液相界面处的行为.结果发现,总氧降低至7×10-6时,尺寸5μm以下的微细夹杂物可被固/液相界面所捕捉,并在固/液相界面处发生碰撞、聚集、长大而生成大尺寸(>12μm) DS类夹杂物.

Formation mechanism of oversized DS-type inclusions in low oxygen special steel

To investigate the generation mechanism of oversized DS-type inclusions in low oxygen special steel, a comparative analysis of inclusions was performed on overseas and domestic special steel samples by the automatic secondary electron microscopy ASPEX PSEM explorer. Both the average size and maximum size of inclusions are larger in domestic samples than overseas samples. Particularly, the maximum size of inclusions in domestic samples is several times that in overseas steel samples:24. 9 and 13. 1μm in domestic samples and 7. 6 and 7. 5μm in overseas samples, respectively. Based on the chemical composition analysis of inclusions in domestic samples, it is found that the oversized inclusions and smaller inclusions have similar compositions. Therefore, the detected DS-type inclusions are endogenous but not exogenous, which can be produced by collisions among inclusion particles. To further study the possible origins of the oversized DS-type inclusions, in-situ observation on the behaviors of inclusions at the solid/liquid interface in low oxygen special steel show that tiny inclusions less than 5μm can be easily and stably captured by the solid/liquid interface with a total oxygen content of 7í10 -6 . Moreover, collisions, agglomeration/coalescence and growth of inclusions captured by the solid/liquid interface result in the formation of much larger size DS-type inclusions over 12μm.