INFLUENCE OF THE CHEMICAL COMPOSITION OF CAST STEEL ON HOT-TEARING TENDENCY (I)

Abstract

Two different shapes of test casting were used for determining hot-tearing tendency of cast steels. The first one comprised a 40mm diameter vertical cylinder and four horizontal, radial branches, each joined to the cylinder by a special design. The hot-tearing tendency of a steel was determined by fracturing these joints at room temperature. The test casting of the second type was a kind of plate casting, the thickness of its main part being 20mm. Length of hot-tear in this plate was taken as an index to hot-tearing tendency of the cast steel.
Several spoonfuls of molten steel sample were taken from each heat of ordinary cast steel manufactured in a 5-ton basic arc furnace, and then each spoonful was tested after addition of various elements into the spoon. Again, the correlations between the analysis of each element and the resistance of steel to hot-tearing was studied by use of many heats of steel without any addition in the spoon.
From results of studying on the influences of C, Si, Mn, P and S followng conclusions were obtained:
(1) Hot-tearing tendency increased with increase in the carbon content within the range of 0.16-0.6%C.
(2) Silicon did not seem to affect the hot-tearing tendency in a simple way, but a study on the correlation showed that steels containing 0.4-0.5% silicon had the maximum resistance to hottearing.
(3) Hot-tearing tendency decreased as the manganese content increased until the latter reached at least 0.75%, but it seemed to have a minimum point before the manganese content reaches 1%.
(4) Even small additions of phosphorus were so detrimental that increase of the phosphorus from 0.02% to 0.04% had nearly the same effect as increase of the sulphur from 0.01% to 0.02%.
(5) The wellknown fact that sulphur was the most deleterious element was accertained here again.