抄録
Investigations were made on the character and mechanism of the occurrence of fine (extra small) sand marks which appeared in bearing-steel SUJ 3 molten by an acid furnace.
Further comparative tests of acid and basic furnace products were carried out.
1) The fine sand marks appeared only in acid furnace products and the appearance of fine sand marks depended on cutting conditions. When the cutting speed was fast and the edge angle of bite small, the fine sand marks can be distinguished well.
2) In the comparative tests, it was found that normal sand marks in basic furnace products were more numerous than in an acid furnace but A and B-type inclusions in the former were much less than in the latter and A-type inclusions were chiefly sulphide system and B-type alumina.
3) The fine sand marks are caused by numerous A and B-type inclusions and partly by the fiber structure, and not the same as normal sand marks.
