Electron-Microscopic Observation of A-Type Nonmetallic Inclusions in Ball-Bearing Steel.

Abstract

A-type nonmetallic inclusions in ball-bearing steel were examined by an optical microscope, acid test and extraction method, however it was not easy to identify each inclusion by these methods. Therefore, the inclusions microscopically observed were extracted on carbon films and observed by an electron microscope, and then each inclusion was respectively identified by electron diffraction.
Moreover, to confirm the results obtained, the materials similar to these inclusions identified were composed experimentally and examined by an optical microscope, X-ray and electron diffraction.
In consequence, the following conclusions were obtained:
A-type nonmetallic inclusions in ball-bearing steel were classified into two groups. That is, the one belonged to such substance as α-cristobalite (α-SiO₂)+rhodonite (MnO·SiO₂) and the other as manganese sulfide (MnS)+iron sulfide (FeS) or manganese sulfide only. Therefore, it was supposed that the combositions of many silicate type inclusions in this steel were in coexisted range of SiO₂ and MnO·SiO₂ in MnO-SiO₂ system, and those of sulfide type inclusions in coexisted range bf MnS and FeS or MnS range in MnS-FeS system.
Besides the nonmetallic inclusions above mentioned, there were a few inclusions which were composed from other components and could not be identified by electron diffraction.