ひびわれに及ぼす加熱雰囲気中のSおよびSulphide処理の影響

抄録

Making further investigation of the results of the authors’ previous studies on surface fissures caused by the enrichment of tramp elements while heating, the influence of sulphur on surface fissures was examined minutely, and a new preventive method was established thereby. The chief results obtained are as follows: (1) The surface fissures of steel are prevented by the following procedure: Powders of fused mixture of iron sulphide and iron oxide or of sodium sulphide are scattered uniformly upon the steel surface from which the scales has been removed mechanically and let it lying there for a while till sulphide melts and reacts upon the nonferrous alloys on the surface layer, and then the steel is hot-worked, or else the steel is immersed in molten iron sulphide and then hot-working follows: (a) The reason why such an effect attained is considered due to the reaction of iron or sodium sulphide upon the enriched, copper because of higher affinity of copper to sulphur, and the copper sulphide produced is removed from steel surface by dissolving into the molten iron sulphide, and this also reacts upon the enriched tin. (b) This preventive method is most effective when the composition of the sulphide is eutectic in FeO-FeS system, and the effect of sodium sulphide is comparatively lower than that of iron-sulphide, (c) This method is completely effective for steels containing Cu and Sn, except steel containing As. For any commercial steel containing small quantities of Cu, Sn and As, however, it is available most effectively. (2) When the steel is heated in atmosphere containing sulphur, (a) The enrichment of copper does not occur in the atmosphere containing 0.06∼0.20%SO₂. (b) As the SO₂ content in the atmosphere increases, the depth of cracks tends to decrease, but penetration of scale consisting of FeS-FeO-silicate ternary eutectic is intensified and brings about cracks in hot-working. (c) The scaling loss of steel is proportionally increased as the SO₂ content in the atmosphere is increased and the removal of scale becomes difficult.