Observation of Nonmetallic Inclusions in Aluminumdeoxidized Iron Alloy

研究了铝脱氧铁合金中的夹杂物。铝脱氧铁水采用首席研究员搭建的超快速冷却装置进行凝固，或在铜模或水中淬火。通过首席研究员开发的 TEM 样品制备新方法，通过 TEM 观察铁合金中的夹杂物。在这些铁样品中观察到非晶态SiO_2夹杂物。球形夹杂物的最小尺寸达到几纳米量级，为FeO·Al_2O_3。随着冷却速度的降低，这些夹杂物的尺寸变得更大。因此，这些夹杂物被视为二次脱氧产物。奥斯特瓦尔德的阶梯法则和均相成核理论得出这样的结果：这些夹杂物在冷却过程中很可能经历了液态氧化铝的状态，最终凝固为γ、δ、κ、Rheta-氧化铝。无定形二氧化硅夹杂物被认为是该过程的一个证据。另一方面，在该实验中观察到树枝状和枫树状的初级脱氧产物，它们的尺寸没有根据冷却速度而改变。 Al扩散前沿附近形成的细小FeO·Al_2O_3夹杂物对这些初级脱氧产物的形成起着重要作用。

The inclusions in iron alloy deoxidized with aluminum were investigated. The Al-deoxidized liquid iron were solidified using ultra-rapid cooling device, which was constructed by the head investigator, or quenched in copper mold or in water. The inclusions in iron alloy were observed by TEM through the new method of preperation of the specimen for TEM which was developped also by the head investigator. The spherical inclusions of Al_2O_3, FeO・Al_2O_3, FeO and amorphous SiO_2 inclusions in these iron specimens were observed. The smallest size of the spherical inclusions reaches to the order of a few nm and they are FeO・Al_2O_3. The size of these inclusions became larger as the cooling speed decreased. Therefore, these inclusions were regarded as the secondary deoxidation product. Further, the alumina inclusions were not the alpha-alumina, but the gamma, delta, kappa, rheta-alumina.A consideration based on the Ostwald's step rule and homogeneous nucleation theory lead the result that these inclusions have probably experienced the state of liquid alumina in the cource of the cooling and finally solidified as the gamma, delta, kappa, rheta-alumina. The amorphous silica inclusions are considered to be one evidence of this process.On the other hand, the dendritic and maple-like primary deoxidation products were observed in this experiment which did not change their size according to the cooling speed. The fine FeO・Al_2O_3 inclusions formed near the diffusing front of Al would play an important role on the formation of these primary deoxidation products.