This disclosure describes methods for improving the performance and consistency of steels by closely controlling the initial homogenization of steel compositions prior to hot working. Experimental data is provided illustrating that the traditional austenitization techniques do not take into account diffusion of the various components within a steel composition and, as such, may not completely homogenize the steel composition. In the methods described in this disclosure, the initial step of austenitizing the steel ingot is altered to achieve a more homogenous distribution of the different components throughout the ingot. The improved method includes heating the steel composition to a temperature within the upper half of the pure austenitic phase temperature range and maintaining the steel composition at that temperature for a period of time determined based on the diffusivity in the austenitic phase of the steel composition of at least one constituent of the steel.

A molten pig iron manufacturing method using a fixed-type DC electric furnace, wherein an auxiliary raw material is supplied to the fixed-type DC electric furnace and molten pig iron having a C concentration of 2 to 4 mass % at a temperature of 1400 C. to 1550 C. is tapped from a tap hole in a state in which a solid iron source is present in the furnace inner peripheral wall space and in a state in which the solid iron source is not present in the upper electrode facing space.

There is proposed a method for preliminary treatment of molten iron wherein heat source for dissolving scrap is ensured sufficiently to improve iron yield while decreasing phosphorus concentration efficiently by suppressing the amount of flux solvent used in the process of desiliconization, dephosphorization and decarburization. In the method for preliminary treatment of molten iron by conducting desiliconization and dephosphorization of molten iron with a converter type container, molten iron is first charged into the converter type container to conduct desiliconization and then intermediate slag removal is conducted, and subsequently a lime-based flux solvent is added to the container while blowing oxygen to conduct dephosphorization of the molten iron, and thereafter newly untreated molten iron is charged into the container to conduct desiliconization, and subsequently the above treatments are repeatedly conducted with the same container.

A method for preparing low-cost clean steel includes steps of: preliminarily desulfurizing iron melt: preliminarily desulfurizing in an iron melt channel during blast furnace tapping and during iron folding in an iron folding room, adding a desulfurizing ball into the iron melt during the blast furnace tapping or the iron folding; dephosphorizing and controlling sulfur: dephosphorizing and controlling sulfur during converter steelmaking, in such a manner that P0.014% and S0.004% during tapping; rapidly dephosphorizing by slag-forming: rapidly dephosphorizing by slag-forming during converter tapping, at a converter end point, controlling a C content at 0.020.10%, adding a dephosphorizing ball through an alloy chute during the converter tapping, blowing argon and stirring at the same time; purifying steel melt during RH refining: adding a purifying ball at a late stage of the RH refining when a vacuum degree is at 66.7500 Pa; and continuously casting with whole-process protection.

An argon oxygen decarburization (AOD) refining method for molten austenitic stainless steel includes, preparing molten austenitic stainless steel in an electric arc furnace, pouring the molten austenitic stainless steel into an AOD refining furnace by adjusting a carbon concentration of the molten austenitic stainless steel to 2.0 wt % to 2.5 wt %, decarburizing the poured molten austenitic stainless steel by blowing oxygen (O.sub.2) and argon (Ar) thereinto, and reduction-decarburizing the decarburized molten austenitic stainless steel by blowing argon (Ar) thereinto.

A molten steel denitrification method, wherein an extremely low nitrogen concentration range is stably reached in a short time without use of a top-blown gas, is a denitrification process wherein CaOandAl.sub.2O.sub.3-containing slag formed by a combination of an Al addition step of adding a metalAl-containing substance to molten steel to deoxidize and turn the molten steel into Al-containing molten steel and a CaO addition step of adding a CaO-containing substance to the molten steel is brought into contact with the Al-containing molten steel to remove nitrogen in the molten steel, in which the molten steel is stirred at a stirring power density of 60 W/t or higher. In the denitrification process, a surface of the molten steel or the slag is subjected to an atmosphere of 1.010.sup.5 Pa or lower. In a steel production method, the obtained molten steel is cast after the components are adjusted.

A method for producing spheroidal graphite cast iron having a specific final composition includes: subjecting a molten iron to a spheroidization treatment using a spheroidizing agent of an FeSiMgCa-based alloy containing no rare earth element; conducting an inoculation treatment using a first FeSi-based inoculant; and conducting a pouring inoculation treatment with a given amount of a second FeSi-based inoculant containing 45-75% of Si, 1-3% of Ca, and 15 ppm or less of Ba.

A method for producing a molten steel may provide: solid-state direct reduced iron containing 3.0% by mass or more of SiO.sub.2 and Al.sub.2O.sub.3 in total and 1.0% by mass or more of carbon, a ratio of a metallic iron to a total iron content contained in the solid-state direct reduced iron being 90% by mass or more, and an excess carbon content Cx to the carbon contained in the solid-state direct reduced iron being 0.2% by mass or more. Such methods may include: a slag separation including heating the solid-state direct reduced iron and melting it in an electric furnace without introducing oxygen to separate into a molten steel and a slag, and continuously discharging the slag, and a decarburization including blowing, in the electric furnace, a total amount of oxygen introduced into the electric furnace to the molten steel to decarburize the molten steel after the slag separation.

In an electric arc furnace system for making steel, a method and structure (1) for eliminating teeming hang-ups and ensuring temperature homogeneity in a ladle which teems into an ingot mold by gas purging at all possible steps under both atmospheric and vacuum conditions, and (2) for preventing non-metallic inclusions from appearing in the final product by deflecting the granular material in the teeming ladle well block away from the ingot mold by a heat resistant but combustible deflector just prior to entry of the teeming stream into the ingot mold.

Additive for the thermochemical treatment of molten iron in order to separate, distribute, agglomerate, precipitate, spheroidize and/or crystallize combined, solvated and/or colloidal carbon present in molten iron in the liquid state into graphite in its hexagonal diamond or Lonsdaleite form, in order to produce ductile, nodular, spheroidal, vermicular, coral, spheroidized or grey iron with superior mechanical properties, iron with high metal yield and zero contraction during casting; the additive comprises two or more elements in the metallic state selected from the S-block of periods 2 to 7 of the periodic table of elements; and two or more elements in the metallic state selected from F-block of periods 6 to 7 of the periodic table of elements. The additive makes it possible to produce cast iron parts with Type I and II spheroidal graphite in hexagonal diamond or Lonsdaleite form as per the ASTM-A247 standard.