Abstract: A machine structure steel superior in chip disposability and mechanical properties which contains sulfide-type inclusions such that those particles of sulfide-type inclusions with major axes not shorter than 5 &mgr;m have an average aspect ratio not larger than 5.2 and which also contains coarse particles of sulfide-type inclusions such that the relation a/b≦0.25 is satisfied, where a denotes the number of particles of sulfide-type inclusions with major axes not shorter than 20 &mgr;m, and b denotes the number of particles of sulfide-type inclusions with major axes not shorter than 5 &mgr;m. The machine structure steel exhibits good chip disposability and mechanical properties despite its freedom from lead.

Abstract: The invention relates to a process for the desulphurization treatment of a pig iron melt in a container. The characterizing feature of the invention is that the treatment is performed in three phases:In the initial phase such solids are injected that deoxidize the initial slag and increase its basicity and also produce a circulatory movement of the melt and form a basic deoxidized cover slag. In the middle phase the desulphurizing agent is injected for the main desulphurization and in the final phase such solids are injected that purify the melt and produce a final desulphurization and also so influence the desulphurization slag formed that its content of iron granules is low.

Abstract: The efficiency of the use of desulfurizing agents, particularly calcium carbide- and calcium oxide-based desulfurizing agents, to decrease the sulfur content of molten iron is improved by adding a pulse of magnesium, aluminum or calcium metal at a critical concentration of sulfur and oxygen in the molten metal. The improved efficiency enables less desulfurization agent to be employed for the same residual sulfur concentration, with consequently decreased reaction time and costs.