Classification of low alloy steels
1.Classification by main quality grades
A. Ordinary quality low alloy steel. Refers to low-alloy steel for general use (WS≥0.045%, WP≥0.045%) that does not require special quality control requirements in the production process. This type of steel mainly includes general-purpose low-alloy steel, low-alloy reinforced steel, and general low-alloy steel for railways.
B. High-quality low alloy steel. Refers to low-alloy steels other than ordinary-quality low-alloy steels and special-quality low-alloy steels. The production process requires special quality control (WS and WP are lower than ordinary quality low-alloy steels, control grain size, improve surface quality, etc.). This type of steel mainly includes weldable low-alloy high-strength structural steel, low-alloy steel for boilers and pressure vessels, low-alloy steel for shipbuilding, low-alloy steel for automobiles, and low-alloy steel for bridges, free-cutting structural steel, and low-alloy steel for railways. Alloy steel etc.
C. Special quality low alloy steel. Refers to low-alloy steel (WS<0.020%, WP≤0.020%) that requires special control of quality and performance in the production process. This type of steel mainly includes low-alloy steel for low temperature, low-alloy steel for nuclear energy, special low-alloy steel for ships, and so on.
2.Classification by main performance and use characteristics
It is divided into weldable low-alloy high-strength structural steel, low-alloy weathering steel, low-alloy reinforced steel, low-alloy steel for railways, low-alloy steel for mining, and other low-alloy steels.
Low alloy steel-grades
1.Low alloy high strength structural steel
The designation of this steel is the same as that of carbon structural steel. For example, Q345 means low-alloy high-strength structural steel with ơS≥345MPa.
2.Free-cutting structural steel
The grade of this kind of steel starts with the Chinese pinyin prefix “Y” of the word “Yi”, and the following numbers represent ten thousand percent of the average carbon content. If the manganese content in the steel is high, “Mn” is marked. For example, Y40Mn represents free-cutting structural steel with an average WC=0.4% and higher manganese content.
Classification of alloy steel
1.Classification by main quality class
A. High-quality alloy steel. Refers to alloy steels that require special control of quality and performance during production. This type of steel mainly includes alloy steel for general engineering structures, alloy reinforced steel, alloy steel for railways, wear-resistant steel with sulfur and phosphorus content greater than 0.035%, and silicon-manganese spring steel, etc.
B. Special quality alloy steel. Refers to alloy steels that require special strict control of quality and performance in the production process. All other alloy steels except high-quality alloy steels are special-quality alloy steels. This type of steel mainly includes alloy steel for pressure vessels, alloy structural steel, alloy spring steel, stainless steel, heat-resistant steel, alloy tool steel, high-speed tool steel, bearing steel, etc.
2.Classification by main performance and usage characteristics
It is divided into alloy steel for engineering structure, alloy steel for mechanical structure, bearing steel, tool steel, stainless, corrosion-resistant and heat-resistant steel, special physical property steel, etc.
Alloy steel-grades
1.Alloy steel for mechanical structure and alloy steel for engineering structure
A. Quenched and tempered alloy structural steel, case hardened alloy structural steel, alloy spring structural steel. The grades of these steels are represented by “two digits + element symbol + number”. The first two digits indicate the percentage of carbon content in ten thousand, the element symbol after it indicates the alloying elements contained in the steel, and the following number indicates the percentage of the alloying element content (if WMe<1.5%, no number is indicated thereafter; If 1.5%≤WMe<2.49%, then mark 2; if 2.5%≤WMe<3.49%, then mark 3; …). If “A’ is added at the end of the grade, it means that the content of sulfur and phosphorus in the steel is low, and the quality of the steel is high. For example, 18Cr2Ni4WA means WC=0.18%, WCr=2%, WNi=4%, Ww<1.5%, sulfur, Alloy carburized steel with low phosphorus content.
B. High manganese wear-resistant steel. The grade of this steel is represented by “ZG+Mn+number”. In the formula, “ZG” is the Chinese pinyin prefix of “cast steel”, and the number indicates the percentage of average manganese content. For example, ZGMn13-1 means high manganese wear-resistant steel with WMn=13% and serial number 1.
2.Bearing steel
The grade of this steel is represented by “G+Cr+number+(other elements+number)”. In the formula, “G” is the Chinese pinyin prefix of “roll”, and the number after the inscription indicates the thousandth of the average chromium content. If it contains other elements, the expression method is the same as that of alloy spring steel. For example, GCr15SiMn means WCr=1.5%wsi<1.5%, WMn<1.5% bearing steel.
3.Alloy tool steel
This type of steel mainly includes steel for measuring and cutting tools, cold work dies steel, and hot work dies steel. Its grade representation method is similar to that of alloy spring steel. The difference is: that when the wC in the steel is less than 1%, the number before the grade represents the average A few thousandths of carbon content: If the wC in the steel is ≥ 1%, the carbon content is not marked before the grade. For example, 9Mn2V means WC=0.9%, WMn=2%, WV<1.5% alloy tool steel: CrWMn means WC≥1%, WCr<1.5%, Ww<1.5%, WMn<1.5% alloy tool steel.
4.High-speed tool steel
The designation method of this kind of steel is similar to that of alloy tool steel, the main difference is that no matter how much carbon content is in the steel, the number is not marked before the designation. For example, W18Cr4V means high-speed tool steel with WW<=18%, WCr=4%, WV<1.5% and its WC=0.7~0.8% is not marked.
5.Stainless steel and heat-resistant steel
The representation of this type of steel is similar to that of alloy tool steel, except that when WC≤0.03% or WC≤0.08%, the numbers before the grades are replaced by “00” or “0” respectively. For example, 3Cr13 means average WC=0.3%WCr=13%, stainless steel: 00Cr17Ni14 Mo2 means average WC≤0.03%WCr=17%WNi=14%WMo=2% stainless steel.
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