1. Definition of carbon steel and five elements in steel

Iron-carbon alloys containing less than 2% carbon are called steel. The five elements in carbon steel refer to the main components in the chemical composition, namely C, Si, Mn, S, P (carbon, silicon, manganese, sulfur, phosphorus). Secondly, gas will inevitably be mixed in the steelmaking process, including O, H, N (oxygen, hydrogen, nitrogen). In addition, in the aluminum-silicon deoxidation-killing process, Al must be contained in molten steel, and when Als (acid-soluble aluminum) ≥ 0.020%, it also has the effect of refining grains

2. How is steel tempered?

The main task of steelmaking is to adjust the content of carbon and alloy elements in the steel to the specified range according to the quality requirements of the steel being made, and to reduce the content of P, S, H, O, N and other impurities below the allowable limit . The steelmaking process is essentially an oxidation process. The excess carbon in the charge is oxidized and burned into CO gas to escape, and other Si, P, Mn, etc. are oxidized and enter the slag. Part of S enters the slag, and part of it generates SO2 to be discharged. When the composition and temperature of molten steel meet the process requirements, the steel can be tapped. In order to remove excess oxygen in the steel and adjust the chemical composition, deoxidizers and iron alloys or alloying elements can be added.

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3. Converter steelmaking

The molten iron transported from the torpedo car can be poured into the converter after desulfurization, slag blocking and other treatments as the main charge, plus less than 10% scrap steel. Then, oxygen is blown into the converter for combustion, and the excess carbon in the molten iron is oxidized and a large amount of heat is released. When the probe detects that the predetermined low carbon content is reached, the oxygen blowing is stopped and the steel is tapped. Generally, deoxidation and composition adjustment operations are required in the ladle; then carbonized rice husk is thrown on the surface of the molten steel to prevent the molten steel from being oxidized, and then it can be sent to the continuous casting or mold casting work area. Bottom blowing argon, RH vacuum treatment, and powder spraying treatment can be added to the steel with high requirements, which can effectively reduce the gas and inclusions in the steel, and further reduce carbon and sulfur. After these out-of-furnace refining measures, the composition can be finally fine-tuned to meet the needs of high-quality steel.

4. Initial rolling

The die-cast steel ingot adopts the new technology of hot charging and hot delivery, enters the soaking furnace for heating, and then rolls it into slabs, tube billets, billets and other rough products through the blooming mill and billet continuous rolling mill. Surface cleaning, (flame cleaning, grinding) high-quality products also need to be peeled and flaw detected on the rough rolling, and put into storage after passing the inspection. At present, the products of the blooming mill include blooming slabs, rolling billets, steel billets for oxygen cylinders, round tube billets for gears, axle billets for railway vehicles, and steel for plastic molds. Blooming slabs are mainly supplied to hot rolling mills as raw materials; rolled billets are mainly sent to high-speed wire rod mills as raw materials, except for some external supplies. Due to the advanced nature of continuous casting slabs, the demand for blooming slabs has been greatly reduced, so it has turned to other products mentioned above.

4. Hot continuous rolling

Continuous casting slabs or rough rolling slabs are used as raw materials, heated by a walking heating furnace, descaled by high-pressure water, and then enter the rough rolling mill. After the final rolling, it goes through laminar cooling (computer controlled cooling rate) and coiler coils to become straight hair coils. The head and tail of straight hair curlers are often tongue-shaped and fish-tail-shaped, with poor thickness and width precision, and the edges often have defects such as wavy, hemmed, and tower-shaped. The coil weight is relatively heavy, and the inner diameter of the steel coil is 760mm. (Generally, the pipe industry likes to use it.) After the straight hair coil is processed by cutting head, tail, edge and multi-pass straightening, leveling and other finishing lines, it is then cut or recoiled to become: hot-rolled Steel plates, flat hot-rolled steel coils, slitting strips and other products.

5. Continuous cold rolling

The hot-rolled steel coil is used as the raw material, and the scale is removed by pickling, followed by continuous cold rolling. The finished product is hard rolled coil. Due to the cold hardening caused by continuous cold deformation, the strength and hardness of the hard rolled coil increase, and the ductility and plastic index decrease. , so the stamping performance will deteriorate and can only be used for parts with simple deformation. Hard-rolled coils can be used as raw materials for hot-dip galvanizing plants, because hot-dip galvanizing units are equipped with annealing lines. The weight of hard rolled coils is generally 6~13.5 tons, and the inner diameter of steel coils is 610mm. Generally, cold continuous rolling plates and coils should undergo continuous annealing (CAPL unit) or bell furnace annealing to eliminate cold work hardening and rolling stress, and reach the mechanical performance indicators specified in the corresponding standards. The surface quality, appearance, and dimensional accuracy of cold-rolled steel sheets are superior to those of hot-rolled sheets, and the thickness of the products is as thin as about 0.18mm, so they are favored by the majority of users. The cold-rolled steel coil is used as the substrate for deep processing of the product and becomes a high value-added product. Such as electro-galvanized, hot-dip galvanized, anti-fingerprint electro-galvanized, color-coated steel coils, vibration-damping composite steel sheets, PVC-coated steel sheets, etc. These products have excellent qualities such as aesthetics and high corrosion resistance, and have been widely used. Cold-rolled steel coils must be finished after annealing, including cutting the head, cutting the tail, trimming, leveling, flattening, recoiling, or longitudinally shearing the plate, etc. Cold-rolled products are widely used in automobile manufacturing, home appliances, products, instrument switches, construction, office furniture and other industries. The weight of each package after the steel plate is bundled is 3 to 5 tons. The weight of flattened rolls is generally 3~10 tons/roll. The inner diameter of steel coil is 610mm.