Abstract
The effects of oxide and sulphide inclusions on the bending property and the surface defects of cold rolledsheet of 18-8 and 18 Cr stainless steels were investigated. The results are summarized as follows:
(1) The bending property of the sheet containing chromium-oxide as a main constituent of oxide inclusionsis far superior to that of the sheet containing silicate.
(2) An increase in the sulphide quantity in the range of this experiment causes a decline in the bendingproperty, but hardly affects other mechanical properties, with the exception of a slight deterioration of theErichsen value on 18-8 stainless steel sheet.
(3) When the sulphide quantity is equal, chromium-oxide coexisting with sulphide inclusion improves thebending property far more than the other-oxide. This is due to the fact that the particles of chromium-oxideincluded in sulphides prevent the sulphides from the string-like elongation.Consequently, in order to improve the bending property both in 18-8 and 18 Cr stainless steels, it isessential to reduce the amount of sulphide inclusion by lowering the sulphur content in metal and toprovide oxide Inclusions which are reluctant to take a stringer shape such as chromium-oxide formedby lowering the silicon content and increasing the manganese content in metal within the limit of specifications.
(4) Independent of the main constituent of oxide inclusions, chromium-oxide or silicate, surfacedefects and sand marks are formed whenever the oxide inclusions crowd locally, however, the defectsoccurring due to chromium-oxide can be removed not more easily than those due to silicate by mechanicalsurface conditionings.
Thus, while chromium-oxide formed by lowering the silicon content in metal considerably improvesthe bending property, it affects deterioratively on the removal of the surface defects.
