Three-dimensional Investigations of Non-metallic Inclusions in Stainless Steels before and after Machining

Abstract

The focus of this study is to investigate non-metallic inclusions (NMIs) in stainless steels before (in steel samples) and after machining (in steel chips). In this study, the electrolytic extraction (EE) technique was used to extract non-metallic inclusions from steel samples. This makes it possible to investigate NMIs on film filters as three-dimensional objects by using SEM. The characteristics of NMIs in steel and chips have been systematically investigated and compared. Based on the results, it was found that the morphology of NMIs was significantly changed after machining. Overall, three different main shapes of NMIs were found: 1) a similar shape, 2) a stretched shape, and 3) a brittlely fractured shape. Furthermore, the degree of deformation of MnS and soft oxide NMIs in different zones of the chips depends on the distances from the contact zone of the tool and the chip. The total areas of MnS and soft oxides in the secondary deformation zone were increased by up to 2-3 times compared to that of the reference steel sample. This study also shows the advantages of the EE method in investigating NMIs in chips compared to using the conventional two-dimensional investigations of NMIs on the polished metal surface.

Evaluation of Sulfide Inclusions before and after Deformation of Steel by Using the Electrolytic Extraction Method

“…According to results obtained by Inoue et al [16], this electrolyte can be recommended for the extraction of different nonmetallic inclusions (including MnS) from metal samples without dissolving the inclusions. Moreover, an application of this electrolyte for extraction of thin plate-like or film-like MnS inclusions in deformed steels and in chips after machining did not show any dissolution of these inclusions during electrolytic extraction experiments [7,17]. These results have shown that a 10%AA electrolyte is suitable for safe extractions of MnS inclusions.…”