Abstract
It is well known that the reliability concerning ductility of low alloy steel castings is poor compared to homogeneous steel because of segregation of alloying elements, microshrinkage and nonmetallic inclusions contained in steel castings. Many studies have been carried out to elucidate the cause and solve the problem of decrease in toughness of low alloy steel castings. As a result, it became clear that the toughness of low alloy steel castings was not equal to that of homogeneous steels, however much the microporosities and nonmetalic inclusions were reduced. Therefore, this study was made to find a method of improving the toughness of low alloy steel casting by eliminating carbon segregation in the segregation region, because carbon is the most improtant element that has an influence on the metallurgical properties of steels. Although carbon is segregated simultaneously in chromium, manganese and molybdenum segregation regions, it seemed that carbon segregation in steel castings could be eliminated by the addition of silicon that increase the activity of carbon in the segregation region.
The toughness of low alloy steel castings decreased with an increase in carbon segregation under quenched and tempered conditions. The addition of silicon was effective for vanishing carbon segregation and increased the toughness of low alloy steel castings. The impact values of steel castings approached those of rolled steel, when the carbide segregation completely vanished.
Suitable chemical composition of steel casting without carbide segregation were determined from the interaction coefficients which indicate the influence of alloying elements on carbon activity in austenite structure and the segregation ratios of alloying elements.
