1, the concept of steel: steel is made into ingots, billets or steel products with various shapes, sizes and properties that we need through pressure processing.
Steel is an indispensable and important material for national construction and the realization of the four modernizations. Wide application range and many varieties. According to the different cross-sectional shapes, steel products are generally divided into four categories: profiles, plates, pipes and metal products. In order to facilitate the organization of steel production, order supply and good management, it is also divided into heavy rail, light rail, large steel, medium steel, small steel, cold-formed steel, high-quality steel, wire rod, medium-thick steel and thin steel.
2, the production method of steel
Most steel products are processed by pressure, and the pressure will cause plastic deformation of the processed steel products (billets, ingots, etc.). According to the processing temperature of steel, steel can be divided into cold working and hot working. The main processing methods of steel are:
Rolling: a pressure processing method in which the steel and metal blank passes through the gap (various shapes) between a pair of rotating rollers, and the cross section of the material is reduced and the length is increased due to the compression of the rollers. This is the most commonly used production method for producing steel, mainly used for producing steel profiles, plates and pipes. Cold rolling and hot rolling.
Forged steel: a pressure processing method that uses the reciprocating impact of forging hammer or the pressure of press to change the blank into the shape and size we need. Generally divided into free forging and die forging, it is often used to produce large cross-section materials such as profiles and cogging.
Drawn steel: a processing method of drawing and rolling metal blanks (molds, pipes, products, etc.). ) reducing the cross section and increasing the length through the die hole is mostly used for cold working.
Extrusion: It is a processing method that steel is put into a closed extrusion box, and one end is pressed, so that the metal is extruded from the specified die hole to get the finished product with the same shape and size, which is mostly used to produce non-ferrous steel.
First, ferrous metals, steel and non-ferrous metals Before introducing the classification of steel, briefly introduce the basic concepts of ferrous metals, steel and non-ferrous metals.
1, ferrous metals refer to iron and ferroalloys. Such as steel, pig iron, ferroalloy, cast iron, etc. Both steel and pig iron are alloys based on steel and with carbon as the main additive element, which are collectively called iron-carbon alloys.
Pig iron refers to the products made of iron ore smelted by blast furnace, which is mainly used for steelmaking and casting steel. Cast pig iron is smelted in a smelting furnace to obtain cast iron (liquid), and the liquid cast iron is cast into cast steel, which 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, which is used as deoxidizer and alloying element additive for steel.
2. Put pig iron for steelmaking into a steelmaking furnace and smelt it according to a certain process to obtain steel. Iron and steel products include steel ingots, continuous casting billets and direct casting steel parts. Generally speaking, steel refers to steel rolled into various kinds of steel. Steel belongs to ferrous metal, but steel is not completely equal to ferrous metal.
3. Iron and steel nonferrous metals, also known as nonferrous metals, refer to metals and alloys other than ferrous metals, such as copper, tin, lead, zinc, aluminum, brass, bronze, aluminum alloy and bearing alloy. In addition, chromium, nickel, manganese, molybdenum, cobalt steel, vanadium, tungsten and titanium are also used in industry. These metals are mainly used as alloy additives to improve the properties of metals, among which tungsten, steel, titanium and molybdenum are mostly used to produce cemented carbide for cutting tools. These nonferrous metals are called industrial metals, and steel products also include precious metals: platinum, gold, silver and rare metals, including radioactive steel products such as uranium and radium.
Second, the classification of steel materials
Steel is an iron-carbon alloy, and its carbon content is between 0.04% and 2.3%. In order to ensure its toughness and plasticity, the carbon content generally does not exceed 1.7%. Besides iron and carbon, the main elements of steel are silicon, manganese, sulfur and phosphorus. There are various classification methods for steel products, and the main methods are as follows:
1, steel classified by quality
(1) Ordinary steel (P≤0.045%, S≤0.050%)
(2) High quality steel (both P and S are ≤0.035%)
(3) High quality steel (P≤0.035%, S≤0.030%)
2. Classification by chemical composition
(1) 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%).
(2) Alloy steel: a. Low alloy steel (total content of alloy elements ≤ 5%); B medium alloy steel (total content of alloying elements > 5 ~10%); C. high alloy steel (total content of alloying elements > 10%).
3. Steel products are classified according to forming methods: (1) forged steel; (2) cast steel; (3) hot rolled steel; (4) cold-drawn steel bars.
4, steel according to the metallographic organization classification
(1) Annealing: A. Submerged arc welding steel (ferrite+pearlite); B.*** steel precipitation (pearlite); C. steel precipitates through steel (pearlite+cementite); D ledeburite steel (pearlite+cementite).
(2) normalizing: a. pearlite steel; B. bainite steel; C. martensitic steel; Austenite steel.
(3) The steel has no phase change or partial phase change; 5. Classification by purpose.
(1) steel for building and engineering: a. ordinary carbon structural steel; B. low alloy structural steel; C. steel bars.
(2) Steel structure
A steel for machine building: (a) quenched and tempered structural steel; (b) Case-hardened structural steel: including carburized steel, ammoniated steel and case-hardened steel; (c) free-cutting 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 and acid-resistant steel; B. Heat-resistant steel: including oxidation-resistant steel, heat-resistant steel and valve steel; C. electrothermal alloy steel; D. wear-resistant steel; E. low temperature steel; Electrical steel.
(5) Professional steel-such as steel for bridges, ships, boilers, pressure vessels and agricultural machinery.
6. Comprehensive classification
(1) ordinary steel
A. carbon structural steel: (a) q195; (b) Q2 15(A、B)； (c) Q235(A、B、C)； Q255(A、B)； Question 275.
B. Low alloy structural steel
C. General structural steel for special purposes
(2) High-quality steel (including advanced high-quality steel)
A. steel structure steel: (a) high-quality carbon structural steel; (b) alloy structural steel; Spring steel; Free cutting steel; Bearing steel; (f) Special-purpose high-quality structural steel.
B. Tool steel: (a) carbon tool steel; (b) alloy tool steel; (c) high-speed tool steel.
C. Special performance steel: (a) stainless steel and acid-resistant steel; Heat-resistant steel; Electrothermal alloy steel; (d) electrical steel; (e) High manganese wear-resistant steel.
7. Classification of smelting methods
(1) by furnace type
A. open hearth steel: (a) acidic open hearth steel; Alkaline open hearth steel.
B converter steel: (a) acidic converter steel; 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 furnace steel; Electroslag furnace steel; Induction furnace steel; (d) Vacuum consumable furnace steel; (e) electron beam furnace steel.
(2) Steel is divided according to deoxidation degree and gating system.
A. boiling steel; B. semi-killed steel; C. killed steel; Special killed steel.
Four kinds of steel
Grade I HPB235(Q235) rebar with standard strength of 235 N/mm2.
Secondary HRB335(20MnSi) 335
Three-level HRB 400(20 mnsy)400
ⅳrrb 400(20 mnsi)400
Comprehensive classification of steel materials: (1) Ordinary steel A. Carbon structural steel: (a) Q195; (b) Q2 15(A、B)； (c) Q235(A、B、C)； Q255(A、B)； Question 275 .b B. Low-alloy structural steel C. General structural steel for special purposes
(2) High-quality steel (including advanced high-quality steel)
A. structural steel: (a) high-quality carbon structural steel; (b) alloy structural steel; Spring steel; Free cutting steel; Bearing steel;
(f) Special-purpose high-quality structural steel.
B. Tool steel: (a) carbon tool steel; (b) alloy tool steel; (c) high-speed tool steel. C. Special performance steel: (a) stainless steel and acid-resistant steel; Heat-resistant steel;
Electrothermal alloy steel; (d) electrical steel; (e) high manganese wear-resistant steel
* Rails need to bear the pressure, friction and impact load of locomotives, and have sufficient strength, hardness and toughness, with high quality requirements. Its mechanical properties must be tested, and macroscopic inspection and drop weight test must be carried out.
The major scientific and technological projects undertaken by Baotou Steel, such as high-strength and high-toughness bainitic rail and rare-earth high-strength weathering steel, have passed the expert appraisal. Experts agree that bainite rail is a major breakthrough in the history of research and development of railway rail materials, which fills the gap of high-speed and heavy-duty rails in China and reaches the international advanced level.
At present, the rails used abroad are basically pearlite steel. Although the strength of rail can be improved by alloying or heat treatment technology, it is close to the limit, which can not fundamentally solve the problem of maintaining good toughness while improving strength, and can not meet the increasingly high technical requirements for rail and turnout rail under high speed and heavy load. Bainite steel is an invention patent of Professor Fang Hongsheng of Tsinghua University. In 2005, coordinated by Baotou Science and Technology Bureau, the cooperation between Baotou Steel and Tsinghua University was promoted, and it was listed as the key cooperation project of Industry-University-Research in Baotou City. Bainite rail solves the technical problem that strength, toughness, plasticity and machinability meet the requirements at the same time. The operation tests of Shenyang Railway Bureau, Shijiazhuang-Taiyuan Railway, beijing-baotou railway Railway and Daqin Railway in recent two years have proved that the strength, toughness and service life of bainite turnout rails can be increased by more than 2 times, 4 times and 3 times respectively. On June+10, 2008, Baotou Steel won the bid with absolute advantage at the bidding project meeting organized by the Ministry of Railways. The next step will be extended to curved track, combined turnout track and other varieties, and the economic and social benefits will be more significant.