Steel Production Process

Steel companies, accounting for over 80% of the world's ferrous metallurgical industry capacity, employ the traditional long-process production technology of "sintering – ironmaking – steelmaking – rolling." This technology boasts advantages such as high efficiency and large-scale steel production, far exceeding the output of electric arc furnace steelmaking and direct reduced iron processes. Below, we will examine the production process of a specific factory to understand steel production:

Coking

Coking production process: Coking is the process of mixing and crushing coking coal, then feeding it into a coke oven for dry distillation to produce hot coke and coke oven gas.

Sintering

Sintering Production Process: The sintering process involves mixing and granulating iron ore powder, various fluxes, and fine coke, then feeding the mixture into the sintering machine via a feeding system. The fine coke is ignited by an ignition furnace, and the sintering reaction is completed by ventilation fans. The high-heat sintered ore is then crushed, cooled, and screened before being sent to the blast furnace as the main raw material for smelting iron.

Pelletizing

The pelletizing process of a grate mill-rotary kiln-annular cooler mainly includes the following parts: coal preparation system, raw material system, dry mixing system, pelletizing and roasting system, and grinding system. The pelletizing process can be summarized as follows: prepared raw materials (finely ground concentrate and additives, etc.) are dry-mixed in a certain proportion, then fed into the pelletizing system for pelletizing, and then into a grate mill-rotary kiln-annular cooler for drying, high-temperature roasting, and cooling until finally sent to the finished product system. The high-temperature roasting in the rotary kiln is the most crucial step, determining the performance and yield of the pellets, as shown in the diagram above.

Blast Furnace Ironmaking

Blast furnace production process: Blast furnace operation involves adding iron ore, coke, and flux into the furnace from the top, followed by high-temperature hot blast blown in through tuyeres at the bottom. This generates reducing gases, reducing the iron ore and producing molten iron and slag.

Non-blast furnace ironmaking

The direct reduction ironmaking method involves reducing iron ore in a shaft furnace using high-temperature reducing gas or a solid reducing agent. Invented in 1932 by Martin Wiberg, the first production plant was built in Sweden and is known as the Wiberg Soderfors process. Initially, this method used charcoal to produce reducing gas. Later, due to economic reasons, coke was used instead. In the 1960s, with the development of the oil and natural gas industry, the shaft furnace direct reduction method using natural gas as energy flourished. Over the past 30 years, various shaft furnace direct reduction methods have emerged, including the Armco process, the Purofer process, the Midrex process, the NSC process, and the HYL process. In the early 1970s, the externally heated shaft furnace direct reduction method (KM process) using coal as a reducing agent was put into production.

Rotary hearth furnace direct reduction (RHF) technology involves feeding iron ore powder (or laterite nickel ore, vanadium-titanium magnetite, sulfuric acid slag, metallurgical dust, dust collector ash, steelmaking sludge, etc.) into carbon-containing pellets after batching, mixing, pelletizing, and drying. These pellets are then added to a rotary hearth furnace with an annular furnace and a rotating hearth. At a furnace temperature of approximately 1350 °C, the iron ore is reduced by carbon as the furnace hearth rotates once. When the iron content of the iron ore powder is above 67%, the RHF process produces metallized pellets for use in blast furnaces. When the iron content is below 62%, a rotary hearth furnace-melting furnace molten iron reduction process is used, producing molten iron for steelmaking. Typically, the metallization rate can reach over 80%, and the metallized pellets can be used as feedstock for blast furnaces.

The COREX process is a coke-free molten reduction ironmaking process jointly developed by the former West German company KORF and the Austrian company VOEST-ALPINE. Originally named the KR process, it was developed based on the Midrex shaft furnace direct reduction process owned by KORF Engineering.

Finex is a novel process for directly smelting iron using iron ore powder and non-coking coal powder.

The key technology of the Finex process is the reduction of iron ore powder into powdered DRI (Direct Reduced Iron) within a mainstream fluidized bed reactor. After hot pressing, the DRI hot-pressed iron blocks are melted and reduced back into molten iron using a melting gasifier. Compared to traditional blast furnace ironmaking, the Finex process eliminates the coking and sintering processes, producing molten iron of comparable quality to blast furnace and Corex processes. Currently, the world's only Finex process facility (with an annual production capacity of 1.5 million tons of molten iron) was commissioned in POSCO on April 10, 2007, with a designed capacity of 4300 tons per day.

Converter Steelmaking

Converter steelmaking process: The steel plant first sends the molten steel to the pretreatment station for desulfurization and dephosphorization. After converter blowing, it is then sent to a secondary refining station (RH vacuum degassing station, Ladle Injection tank blowing station, VOD vacuum oxygen blowing decarburization station, STN mixing station, etc.) for various treatments to adjust the steel composition, depending on the characteristics and quality requirements of the ordered steel grade. Finally, it is sent to a continuous casting machine for large and flat steel billets to be cast into red-hot steel billet semi-finished products. After inspection, grinding or burning off surface defects, it can be directly sent downstream for rolling into finished products such as bars, wire rods, plates, coils, and sheets.

Electric arc furnace steelmaking

Electric arc furnace (EAF) steelmaking primarily utilizes the heat of an electric arc, reaching temperatures as high as 4000℃ in the arc zone. The smelting process is generally divided into melting, oxidation, and reduction phases. The furnace creates both oxidizing and reducing atmospheres, resulting in highly efficient dephosphorization and desulfurization.

This is a steelmaking process that uses electricity as its energy source.

Types of electric arc furnaces include electric arc furnaces, induction furnaces, electroslag furnaces, electron beam furnaces, and consumable arc furnaces. Electric arc furnace steel, as commonly referred to, is steel produced in a basic electric arc furnace.

Electric arc furnace steel is often used to produce high-quality carbon structural steel, tool steel, and alloy steel. These steels are of excellent quality and have uniform properties. At the same carbon content, electric arc furnace steel exhibits superior strength and ductility compared to open-hearth steel. Electric arc furnace steel primarily uses scrap steel of similar steel grades as raw material, sometimes replacing some scrap steel with sponge iron. The chemical composition and alloy element content are adjusted by adding ferroalloys.

Electric arc furnace steelmaking, which uses scrap steel as raw material, requires less infrastructure investment than the blast furnace-converter method. At the same time, the development of direct reduction has provided metallized pellets for electric arc furnaces to replace most of the scrap steel, thus greatly promoting electric arc furnace steelmaking.