Abstract
Three steels with carbon content below 0.04 % and sulfur content of 0.03 % having different manganese contents of 0.3, 0.6 and 1.2 %, respectively, were quenched from various temperatures on cooling subsequent to solidification. The number and volume fraction of manganese sulfides in those steels were measured, and also the relation between the sulfide distridution and microsegregation was examined in a 1 % Mo steel. Through these experiments, the precipitation behavior of sulfides in the steels which transformed from δ-ferrite to austenite after the completion of solidification was investigated.
The results were as follows :
(1) Sulfides were grouped into two categories, one crystallized by a eutectic reaction and the other precipitated after solidification. The latter was observed in all steels used in this work, but the former only in the 1.2 % Mn steel.
(2) The crystallized sulfide, which was typical of colony type sulfides, coarsened remarkably in δ-ferrite, but hardly in austenite.
(3) A small number of sulfides were precipitated in δ-ferrite, but after δ-γ transformation the number increased steeply.
(4) The precipitated sulfides were classified into the colony type and non-colony type. The former increased but the latter decreased with increasing cooling rate and decreasing manganese content.
(5) Most of the precipitated colony type sulfides were observed in the finally solidified region. The distribution of fine non-colony type sulfides was roughly uniform, while that of coarse one concentrated in the solute-enriched region, like the colony type sulfides did.
