Observation of Nonmetallic Inclusions in Aluminumdeoxidized Iron Alloy

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_2inclusions 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_3inclusions formed near the diffusing front of Al would play an important role on the formation of these primary deoxidation products.

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.