Importance

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Abstract

A melt is produced composed of iron, manganese and carbon in known ratios for free-cutting carbon steel with sulfur being included at roughly 0.15%. Aluminum and silicon are added to kill the steel fully and silica and alumina are added to the slag as conditioners in the ladle in sufficient amounts to provide a low ladle slag V-ratio (ratio of weight percent CaO to weight percent SiO.sub.2) of approximately two to one to retard desulfurization during a subsequent ladle treatment process wherein sulfur modifying powders such as calcium carbide, calcium silicon or, alternatively, magnesium-bearing materials are injected into the meld in an argon stream at a rate of about two pounds of contained calcium (or one pound of contained magnesium) per ton of liquid steel over a period of six to seven minutes. The low V-ratio slag holds desulfurization to about 30% while permitting effective calcium treatment of the molten steel. The resultant inclusions in the plate product are favorable to machinability and consist of a fine, nearly uniform distribution of sulfide inclusions throughout the plate thickness with a minimum of oxide inclusions such as silicates and alumina. An example of a steel chemistry according to the invention is carbon 0.16 to 0.23 weight percent, manganese 1.0 to 1.4 weight percent, sulfur 0.07 to 0.15 weight percent, silicon 0.35 weight percent maximum, aluminum 0.030 weight percent maximum and iron for the balance.

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First Claim