Basic knowledge of steel

Basic knowledge of steel

2019-07-27 10:57:21 253

Steel is an iron-carbon alloy containing between 0.04% and 2.3% carbon. We usually refer to it as iron and steel, with a melting point of 1515 degrees. In order to ensure its toughness and plasticity, the carbon content generally does not exceed 1.7%. In addition to iron and carbon, the main elements of steel include silicon, manganese, sulfur, phosphorus, etc., which refer to iron-carbon alloys containing less than 2% carbon. According to different ingredients, it can be divided into carbon steel and alloy steel. According to performance and use, it can be divided into structural steel, tool steel and special performance steel.

Steel classification methods are various, and the main methods are as follows:

1, by quality classification (1) ordinary steel (P ≤ 0.045%, S ≤ 0.050%) (2) high-quality steel (P, S are ≤ 0.035%) (3) high-quality steel (P ≤ 0.035%, S ≤ 0.030 %)

2. Classification by chemical composition (1) Carbon steel: a. Low carbon steel (C ≤ 0.25%); b. Medium carbon steel (C ≤ 0.25 ~ 0.60%); c. High carbon steel (C ≤ 0.60%) ). (2) Alloy steel: a. Low alloy steel (total content of alloying elements ≤ 5%) b. Medium alloy steel (total content of alloying elements > 5~10%) c. High alloy steel (total content of alloying elements >10%) .

3. Classification according to forming method: (1) forged steel; (2) cast steel; (3) hot rolled steel; (4) cold drawn steel.

 4. Classification according to metallographic structure (1) Annealed state a. Hypoeutectoid steel (ferrite + pearlite) b. Eutectoid steel (pearlite) c. Hypereutectoid steel (pearlite + cementite) d. Leysite steel (pearlite + infiltration). (2) Normalized state: a. pearlitic steel; b. bainitic steel; c. martensitic steel; d. austenitic steel. (3) No phase change or partial phase change

5. Classification by use (1) Steel for construction and engineering: a. Ordinary carbon structural steel; b. Low alloy structural steel; c. (2) Structural steel a. Steel for machine building: (a) tempered structural steel; (b) Surface hardened structural steel: including carburized steel, ammonia steel, surface quenching steel; (c) easy-cut structural steel; d) Steel for cold plastic forming: including steel for cold stamping and steel for cold heading. b. Spring steel c. Bearing steel (3) Tool steel: a. Carbon tool steel; b. Alloy tool steel; c. High speed tool steel. (4) Special performance steel: a. Stainless acid-resistant steel b. Heat-resistant steel including anti-oxidation steel, heat-strength steel, gas valve steel c. electro-thermal alloy steel; d. wear-resistant steel; e. low-temperature steel; f. Electrical steel (5) Professional steel - such as steel for bridges, steel for ships, steel for boilers, steel for pressure vessels, steel for agricultural machinery, etc.

6. Comprehensive classification (1) Ordinary steel a. Carbon structural steel: (a) Q195; (b) Q215 (A, B); (c) Q235 (A, B, C); (d) Q255 (A, B); (e) Q275. b. Low-alloy structural steel c. Ordinary structural steel for specific use (2) High-quality steel (including high-quality steel) a. Structural steel: (a) high-quality carbon structural steel; (b) alloy structural steel; (c) spring Steel; (d) easy-cut steel; (e) bearing steel; (f) high-quality structural steel for specific purposes. b. Tool steel: (a) carbon tool steel; (b) alloy tool steel; (c) high speed tool steel. c. Special properties steel: (a) stainless acid-resistant steel; (b) heat-resistant steel; (c) electrothermal alloy steel; (d) electrical steel; (e) high-manganese wear-resistant steel.

 7. Classification according to smelting method (1) According to furnace type a. Flat furnace steel: (a) acid open hearth steel; (b) alkaline open hearth steel. b. Converter steel: (a) acid converter steel; (b) alkaline converter steel. Or (a) bottom-blown converter steel; (b) side-blown converter steel; (c) top-blown converter steel. c. Electric furnace steel: (a) electric arc furnace steel; (b) electroslag furnace steel; (c) induction furnace steel; (d) vacuum consumable furnace steel; (e) electron beam furnace steel. (2) According to the degree of deoxidation and the pouring system, a. boiling steel; b. semi-killed steel; killed steel; d. special killed steel.

 8. Comparison of steelmaking process and properties: HeatTreatment - is a method of using heating and cooling to change the physical properties of metals. Heat treatment can improve the microstructure of the steel to achieve the desired physical requirements. Toughness, hardness and wear resistance are several of the properties obtained by heat treatment. In order to obtain these characteristics, it is necessary to use quenching (also known as quenching), tempering, annealingand surface hardening in heat treatment.

Hardening (also known as quenching) - the metal is uniformly heated to a suitable temperature, then rapidly immersed in water or oil to quench, or cooled in the air or in the freezing zone to obtain the desired hardness of the metal. Tempering - Steel parts become brittle after hardening, and the stress caused by quenching and quenching can cause the steel parts to be broken by light tapping. To eliminate brittleness, tempering can be used. Tempering is the reheating of the steel to the appropriate temperature or color and then quenching. Although tempering slightly reduces the hardness of the steel, it increases the toughness of the steel and reduces its brittleness. Annealing-annealing is a method of eliminating the intrinsic stress of steel and refining steel. The annealing method is to heat the steel to a temperature higher than the critical temperature, and then put it into dry ash, lime, asbestos or enclose it in the furnace, and let it cool slowly.

Hardness - is the ability of a material to resist the penetration of foreign objects. The most common method of testing the hardness of steel is to use a trowel to rub on the edge of the workpiece, and the depth of the scratches on the surface is used to determine the hardness. This method is called a test method. This method is not scientific. It is extremely accurate to test with a hardness tester and is a commonly used method for modern test hardness. The most commonly used test method is the Rockwell hardness test. The Rockwell hardness tester uses the depth of the diamond to penetrate the metal to determine the hardness of the metal. The greater the penetration depth, the smaller the hardness. The depth at which the diamond rushes into the metal can be pointed out by the pointer to the correct number, which is called the Rockwell hardness number. Forging - is a method of hammering a metal into a certain shape. When the steel is heated to the forging temperature, it can be subjected to forging, bending, drawing, forming, and the like. Most steels are easy to forge when heated to bright cherry.

Brittleness - indicates the property of metal to be easily broken. The brittleness of cast iron is large, and it may even break when it falls. Brittleness is closely related to hardness, and materials with high hardness are usually brittle. Ductility - (also known as softness) is the property of the metal being permanently deformed by external forces without breaking, and the ductile metal can be drawn into a thin line. Elasticity - is a property in which a metal is deformed by an external force and returns to its original shape when the external force is removed. Spring steel is a very flexible material. Hardness - is the metal that resists penetration or cutting of foreign objects. A common method of increasing the hardness of steel is quenching. Extensibility - also known as forgeability - is another representation of metal ductility or softness. Extensibility is a property in which a metal is subjected to hammer forging or rolling and is not broken when deformed. Toughness - the ability of a metal to withstand shock or shock. Toughness and brittleness are just the opposite.