The source of steel is iron ore sand, which is the existing form of iron element (FE) in nature. Pure iron does not exist in nature. Iron ore is mainly divided into magnetite, hematite and limonite, which are iron oxides. The difference lies in their oxidation methods. The higher the iron content in iron ore, the better. Theoretically, the highest iron content in iron ore is about 72%, and iron content above 60% is called rich iron ore. The iron ore is first reduced to iron (milling iron) in the furnace, and then sent to the steelmaking furnace for decarbonization and refining into steel, and the scrap steel can also be smelted and recycled in the steelmaking furnace. General steel according to the use of different properties, shapes of goods, namely the so-called steel products. Generally, iron and steel products are iron ore reduction, melting into milling iron (milling), milling iron refining into steel (steel-making), steel rolling and processing to make a variety of iron and steel products, steel products in the broad sense include cast iron, cast steel, forged steel products and steel processing products.
The process of refining iron ore into iron in a furnace (blast furnace) is called milling. The outside of the furnace is made of steel plate and lined with firebrick inside. A furnace with a height of 20-30m and a furnace diameter of 6-8m is called a blast furnace (a large blast furnace with a daily mill iron output of more than 10000 tons) has a hearth diameter of 13-14m and a furnace height of more than 100m. During milling, iron ore, coke and limestone are alternately put into operation from the top of the furnace. The air heated by the hot blast furnace is blown into the lower tuyere of the blast furnace, and the coke in the furnace is burned to generate 1500. At the high temperature of C, the carbon monoxide (CO) produced in the furnace rises from the furnace, and the carbon monoxide reduces the iron ore; the milled iron from the bottom of the furnace flows out of the milling mouth, and is temporarily stored in the mixing furnace and transported to the steel-making workshop, or injected into the mold with the shape of pig trough by melting and milling in barrels.
The carbon content of milling iron melted from blast furnace is high (C content is more than 3%), and there are many impurities such as silicon (SI), phosphorus (P), sulfur (s), etc. the products are hard and brittle. The reduction of impurities into strong and tough steel products, this process is called steelmaking. In addition to milling iron and scrap steel, there are also fluxes for removing impurities, such as quicklime, fluorite, deoxidizer, alloy iron, etc., which improve the quality of steel. There are three kinds of steelmaking methods: converter, electric furnace and open hearth furnace. The raw materials used vary with the type of steelmaking furnace. Converter is used for melting and milling, EAF is mainly made of scrap steel, and open hearth furnace is made of milling iron and scrap steel. Alloy steel spring
The electric furnace of EAF steelmaking process is like a pot, which is composed of furnace cover, furnace wall and hearth. The outer side is made of thick iron plate, and the inner side is provided with cooling water pipes. The furnace bed is built with refractory bricks and refractory materials. The furnace body can be tilted back and forth, and the electrode is inserted vertically in the center of the furnace cover, which can automatically adjust the rise and fall. The arc light of the electrode dissolves the scrap steel, carries out oxidation and reduction refining into high-quality steel products There are two kinds of Furnaces: direct current (DC) and alternating current (AC). The DC electric furnace uses one electrode and three AC electric furnaces. Therefore, the unit consumption of DC furnace electrode is lower, the heat efficiency of solution is better, and the noise is low.
Converter steelmaking method: the converter is mainly composed of melting and milling raw materials, with short refining time and almost no fuel, which can reduce the cost. After the melting and milling of blast furnace is put into the converter, high-pressure oxygen is blown into the converter to oxidize and burn the carbon and other impurities in the milling iron, and the steel with high purity can be extracted. There are three ways of oxygen blowing: top blowing, bottom blowing and top bottom blowing. Stainless steel spring
Open hearth steelmaking process: open hearth furnace is a reverberatory furnace with flat bottom shape. Milling iron, scrap steel and limestone are added and heated and dissolved with fuel. Carbon (c) and silicon (SI) and phosphorus (P) in the milling iron are oxidized by oxygen or iron oxide. After refining, ferrosilicon, ferromanganese and aluminum are added to remove oxygen and nitrogen in molten steel. The steelmaking time is long. In recent years, this method has gradually disappeared and replaced by converter. Continuous casting: molten steel can not be directly rolled and rolled, but must be made into blocks (almost disappeared now) or semi-finished products such as flat steel blank, outline blank and small steel blank by continuous casting. Continuous casting equipment has vertical, bending and horizontal forms. The equipment includes steel dividing groove, copper mold, cooling device, straightening machine, drawing machine, cutting device, etc. the molten steel flows out of the molten steel from the ladle to the steel dividing groove according to the mold Mold casting products can be cooled and then heated and rolled. After continuous casting, the method of direct rolling and rolling with unequal cooling has been adopted, which can save energy and reduce cost.