How is steel classified

1. The concept of steel

Steel is a material ingot, billet or steel that is processed by pressure into various shapes, sizes and properties we need.

Steel is widely used and has a variety of varieties. According to the different cross-sectional shapes, steel is generally divided into four categories: profiles, plates, pipes and metal products. In order to facilitate the organization of steel production, ordering, supply and management work are divided into heavy rail, light rail, large section steel, medium section steel, small section steel, steel cold-formed section steel, high-quality section steel, wire rod, medium and thick steel plate, thin steel plate, electrical silicon steel sheet, strip steel , seamless steel pipe steel, welded steel pipe, metal products and other varieties.

2. Production method of steel

Most of the steel processing is that the steel is processed by pressure, so that the processed steel (billet, ingot, etc.) is plastically deformed. According to the processing temperature of steel and steel, it can be divided into cold working and hot working. The main processing methods of steel are:

Rolling: The steel metal billet is passed through the gap between a pair of rotating rolls (various shapes), and the cross-section of the material is reduced due to the compression of the rolls, and the length is increased. This is the most commonly used production method for steel production. It is mainly used to produce steel profiles, plates, pipes. Divided into cold rolling and hot rolling.

Forging: A pressure processing method that uses the reciprocating impact force of a forging hammer or the pressure of a press to change the blank into the shape and size we need. It is generally divided into free forging and die forging, and is often used to produce materials with large cross-sectional dimensions such as large steel bars and billets.

Drawing: It is a processing method in which the rolled metal blanks (types, pipes, products, etc.) are drawn into a cross section to reduce the length and increase the length.

Extrusion: It is a processing method for steel to place metal in a closed extrusion box and apply pressure at one end to make the metal extrude from the specified die hole to obtain a finished product with the same shape and size. It is mostly used for the production of non-ferrous metal steel .

3.Ferrous metals, steel and non-ferrous metals

Before introducing the classification of steel, briefly introduce the basic concepts of ferrous metals, steel steel and non-ferrous metals.

(1) Ferrous metals refer to iron and iron alloys. Such as steel, pig iron, ferroalloy, cast iron, etc. Both steel and pig iron are alloys based on iron and steel, with carbon as the main additive element, collectively referred to as iron-carbon alloys.

Pig iron refers to the product made by smelting iron ore in a blast furnace. It is mainly used for steelmaking and steel castings. Smelting cast pig iron in an iron melting furnace to obtain cast iron (liquid), and casting liquid cast iron into cast steel, this cast iron is called cast iron.

Ferroalloy is an alloy composed of iron, silicon, manganese, chromium, titanium and other elements. Ferroalloy is one of the raw materials for steelmaking. It is used as a deoxidizer and alloy element additive for steel during steelmaking.

(2) Put the pig iron for steelmaking into the steelmaking furnace and smelt it according to a certain process to obtain steel. Steel products include steel ingots, continuous casting slabs and straight steel products that are directly cast into various steel castings. Generally speaking, steel generally refers to steel rolled into various steel products. Steel Steel is a ferrous metal, but steel is not exactly equal to ferrous metal.

(3)Steel non-ferrous metals, also known as non-ferrous metals, refer to metals and alloys other than ferrous metals, such as copper, tin, lead, zinc, aluminum, brass, bronze, aluminum alloy and bearing alloys. In addition, chromium, nickel, manganese, molybdenum, cobalt steel, vanadium, tungsten, titanium, etc., these metals are mainly used as alloy additions to improve the performance of the metal, including tungsten, steel titanium, molybdenum, etc., for the production of carbide tools. These non-ferrous metals are called industrial metals, steel in addition to precious metals: platinum, gold, silver, and rare metals, including radioactive uranium, radium and other steel.

4.The classification of steel

Steel is an iron-carbon alloy with a carbon content between 0.04% and 2.3% of steel. In order to ensure its toughness and plasticity, the carbon content is generally not more than 1.7%. The main elements of steel in addition to iron, carbon, silicon, manganese, sulfur, phosphorus and so on. Steel classification methods a variety of steel, the main methods are as follows:

(1) Steel is classified according to quality

Ordinary steel (P≤0.045%, S≤0.050%)

High quality steel (P, S ≤0.035%)

High quality steel (P≤0.035%, S≤0.030%)

(2) Sort by chemical composition

Carbon steel: steel a. Low carbon steel (C≤0.25%); b. Medium carbon steel (C≤0.25~0.60%); c. High carbon steel (C≤0.60%).

Alloy steel: a. low alloy steel (total alloying element content ≤5%); b. Medium alloy steel (total alloying element content > 5~10%); c. High alloy steel (total alloying element content > 10%).

(3)Steel is classified by forming method: forged steel; Cast steel; Hot rolled steel; Cold pull

(4) Steel is classified according to metallographic structure

Annealed state: hypoeutectoid steel (ferrite + pearlite); eutectoid steel (pearlite); eutectoid steel (pearlite + cementite); Ledeburitic steel (pearlite + cementite).

Normalized state: pearlitic steel; bainite steel; martensitic steel; austenitic steel.

The steel has no phase transformation or partly undergoes phase transformation

(5)Classified by purpose

Steel for construction and engineering: Ordinary carbon structural steel; Low alloy structural steel; Reinforced steel.

Steel structure steel:

Steel for machinery manufacturing: Quenched and tempered structural steel;Surface hardened structural steel: including carburizing steel, ammoniated steel, and surface hardened steel; Easy-cut structural steel; Cold plasticity Steel for forming: including steel for cold stamping and steel for cold heading.

Spring steel

Bearing steel

Tool steel: carbon tool steel; alloy tool steel; high-speed tool steel.

Special performance steel: Stainless acid-resistant steel; Heat-resistant steel: including anti-oxidation steel, heat-strength steel, valve steel; Electric heating alloy steel; Wear-resistant steel; e. Low-temperature steel; Electrical steel.

Steel for professional use – 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

Carbon structural steel: Q195; Q215 (A, B); Q235 (A, B, C); Q255 (A, B); Q275.

Low alloy structural steel

Ordinary structural steel for specific purposes

(2) High-quality steel (including high-grade high-quality steel)

Steel structural steel: high-quality carbon structural steel; alloy structural steel; spring steel; free-cutting steel; bearing steel; high-quality structural steel for specific purposes.

Tool steel: carbon tool steel; alloy tool steel; high-speed tool steel.

Special performance steel: stainless acid-resistant steel; heat-resistant steel; electric heating alloy steel; electrical steel; high manganese wear-resistant steel

7.Classified by smelting method

(1) According to furnace type

Open hearth steel: acidic open hearth steel; basic open hearth steel.

Converter steel: acidic converter steel; basic converter steel. Or bottom-blown converter steel; side-blown converter steel; top-blown converter steel.

Electric furnace steel: electric arc furnace steel; electroslag furnace steel; induction furnace steel; vacuum consumable furnace steel; electron beam furnace steel.

(2) Steel products are classified according to the degree of deoxidation and pouring system

Boiling steel; Semi-killed steel; Killed steel; Special killed steel.

Comprehensive classification:

(1) Ordinary steel

Carbon structural steel:Q195; Q215 (A, B); Q235 (A, B, C); Q255 (A, B); Q275; Low-alloy structural steel; General structural steel for specific purposes

(2) High-quality steel (including high-grade high-quality steel).

Structural steel: high-quality carbon structural steel; alloy structural steel; spring steel; free-cutting steel; bearing steel; high-quality structural steel for specific purposes.

Tool steel: carbon tool steel; alloy tool steel; high-speed tool steel

Special performance steel: stainless acid-resistant steel; heat-resistant steel; electric heating alloy steel; electrical steel; high manganese wear-resistant steel.