1967 Volume 53 Issue 1 Pages 11-27
Macroscopic inclusions were intentionally produced by promoting air-oxidation of steel. Relation of macroscopic inclusions to cast structure and effect of the condition of solidification of steel on the occurrence tendency of macroscopic inclusions were studied. Consequently the following results were obtained.
1) Macroscopic inclusions produced by air-oxidation of steel were disposed preferentially inside interdendritic spaces, andthe occurrence tendency ofthem was influenced by the condition of solidification of steel. Therefore, macroscopic inclusions produced by air-oxidation of steel were nothing but secondary deoxidation products of oxygen (oxide) dissolved by air-oxidation having been precipitated during solidification of steel.
2) The growth mechanism of macroscopic inclusions which are very large in comparison with microscopic inclusions is thought to be as follows; When the segregation of oxygen which occurred in melt not by phase change of liquid steel to solid and the enrichment of oxygen to interdendritic spaces by phase change happened together overlapping, a great amount of oxygen capable of growing to macroscopic inclusions is enriched and precipitated in the form of macroscopic inclusion. In order to show that the foregoing presumption is probable interpretation for the growth mechanism of macroscopic inclusions, the phenomena in which oxygen or tin had already segregated in melt not by cell formation were shown.
3) It was shown that macroscopic inclusions produced by air-oxidation contained calcium. From the result, it is concluded that some calcium can dissolve in molten steel, and that exogenous oxide particles may be floatedout by simple mechanism according to Stokes' law qualitatively, and thatthere are, accordingly, only rare macroscopic inclusions in melt, and that exogenous oxide particles develop seldom into macroscopic inclusions.