EFFECT OF ROLLING RATIO ON DISTRIBUTION OF SAND MARKS OF BEARING STEEL

The study of non-metallic inclusions-I

Abstract

Generally, the origin of sand marks is considered as the ingot defects, such as non-metallic inclusions, blow holes, pin holes, cavities and segregations.
In the present investigation, the authers are convinced that the origin of sand mark is (mostly) non-metallic inclusions in the ingot.
The statistics of the number of sand marks on the high-carbon low-chromium bearing steel rod shown in this first report.
The results are summarized as follows:
(1) The number of the smaller sand marks, 0.1mm to 0.4mm long, shows no change by the position of the ingot.
(2) As for the larger sand marks, about 0.5mm long, the number of them at the top of ingot is higher than the bottom of ingots, and there is the same tendency among the number of sand marks to the ingot position when ingot is rolled as the same rolling ratio at the top of ingots and the bottom of ingots.
(3) The number of the larger sand marks is proportional to the rolling ratio of steel rods.
(4) With increase of the rolling ratio, there is a tendency that the number of the smaller sand marks is decreased and the number of the larger sand marks is increased and finally, sand marks disappeared when the rolling ratio is much larger (such as 250 rolling ratio).