Soft free-cutting steel contg. large sulphide inclusions - where controlled deoxidation of molten steel in ladle ensures good surface finish during machining

摘要

The inclusions have the shape of a lens, but the semi-finished prods. machined from the steel have a good surface finish obtd. by measuring the oxygen content of the molten steel in the ladle and then injecting a deoxidant to reduce the oxygen to teh deisred percentage. The oxygen content of the molten steel is pref. measured via electromotive force; and the dissolved oxygen in the melt is pref. reduced to 30-130 ppm, esp. 40-60 ppm, prior to casting. The pref. deoxidant is Al or its alloys; and deoxidn. is pref. controlled via the equation log(O) = -20600/T + A; where (O) is the dissolved O2 in ppm before casting: T is the steel temp. in degree K; and A is a function of the initial O2 content and the type and amt. of deoxidant used plus the injection time. A good surface finish can be obtd. despite the presence of numerous large sulphide inclusions in the steel.