Steel is the carbon content between 0.04% -2.3% of the iron-carbon alloy. In order to ensure its toughness and ductility, carbon content of not more than 1.7%. The main elements of steel, iron, carbon, there are silicon, manganese, sulfur and phosphorus. Classification of steel variety, the main method has the following seven: 1, according to the 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., classified according to chemical composition (1) Carbon steel: a. low-carbon steel (C ≤ 0.25%); b. in 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. in steel (total content of alloying elements> 5 ~ 10%); c. high-alloy steel (total content of alloying elements> 10 %). 3, according to the forming method of classification: (1) forged steel; (2) steel; (3) hot-rolled steel; (4) cold-drawn steel. 4, according to the classification of microstructure (a) annealed state: a. sub-eutectoid steel (ferrite + pearlite); b. eutectoid steel (pearlite); c. eutectoid steel (pearlite + permeability carbon body); d. ledeburite steel (pearlite + cementite). (2) normalizing the status of: a. pearlite steel; b. bainitic steel; c. martensitic steel; d. austenitic steel. Steel (3) no phase change or phase transition part 5, the end-use category (1) construction and engineering steel: a. ordinary carbon structural steel; b. low-alloy structural steel; c. reinforced steel. (2) a. machinery manufacturing steel structural steel: (a) quenched and tempered structural steel; (b) hardened steel: including case-hardened steel, ammonia permeability steel, surface hardened steel; (c) easy to cut structural steel; (d) cold plastic deformation of steel: steel, including cold forming, cold heading steel. b. c. spring steel bearing steel (3) tool steel: a. carbon tool steel; b. alloy tool steel; c. high-speed tool steel. (4) Special Performance Steel: a. acid-resistant stainless steel; b. heat-resistant steel: including anti-oxidation of steel, refractory steel, valve steel; c. electric steel; d. wear-resistant steel; e. low-temperature steel ; f. electrical steel. (5) professional steel - such as bridge steel, shipbuilding steel, boiler steel, pressure vessel steel, steel and other agricultural machinery. 6, Classification (1) Ordinary steel a. carbon steel: (a) Q195; (b) Q215 (A, B); (c) Q235 (A, B, C); (d) Q255 (A, B); (e) Q275. b. c. low-alloy structural steel structural steel for a particular purpose an ordinary steel (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) cutting steel; (e) bearing steel; (f) for a particular 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 acid; (b) heat-resistant steel; (c) electric steel; (d) electrical steel; (e) high wear-resistant manganese steel. 7, according to the smelting method of classification (1) the open-hearth steel furnace a. Seed: (a) acid open-hearth steel; (b) basic open-hearth steel. b. converter steel: (a) acid converter steel; (b) basic converter steel. Or (a) bottom-blowing converter steel; (b) side-blown converter steel; (c) BOF steel. c. EAF steel: (a) electric arc furnace steel; (b) steel electroslag furnace; (c) induction furnace steel; (d) vacuum consumable furnace steel; (e) electron beam furnace steel. (2) by oxygen level and pouring boiling points a. system of steel (F); b. semi-killed steel (b); c. killed steel (Z); d. special killed steel (TZ).