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Low alloy high strength structural steel refers to the steel that adds certain alloy elements on the basis of ordinary carbon structural steel to improve its mechanical properties. Alloy high strength structural steel is a kind of steel with high strength and toughness. Generally, the impact toughness of structural steel is poor and the welding performance is not good. Alloy steel can be used to improve the impact toughness and welding performance of structural steel.
Low alloy high strength structural steel is generally referred to as carbon steel with an alloy element content of 12-18%. Such steel is also called low alloy or medium alloy steel. To determine the alloy content, it is generally calculated according to the mass fraction, not the volume fraction. The microstructure of low-alloy, high-strength structural steel includes ferrite and pearlite, tempered sorbite, bainite and martensite.
Due to the presence of certain alloy elements, the mechanical properties of low-alloy, high-strength structural steels are improved, and the mechanical properties of welds are also improved. Low-alloy high-strength structural steel usually has a yield strength of more than 345 MPa and an elongation of not less than 21%.
Low alloy high strength structural steel usually has four types of features.
High strength: The yield strength of common low alloy high strength structural steel ranges from 315 MPa to 655 MPa.
Good toughness: Alloyed elements such as manganese, nitrogen and chromium can improve the toughness of low alloy high strength structural steel so that it can possess lower temperature toughness equivalent to that of medium carbon manganese steel.
Good weldability: Low alloy high strength structural steel has good weldability due to its low carbon equivalent, and can be welded by general welding methods;
Good resistance to atmospheric aging: Low alloy high strength structural steel has a higher resistance to atmospheric aging than carbon structural steel.
Common low alloy high strength structural steel grades and corresponding chemical composition:
Q420C: C 0.15-0.20, Si 0.50-0.70, Mn 1.00-1.30, P 0.030 Max, S 0.015 Max, Ni 0.25 Max, Cr 0.20-0.40, Cu 0.30 Max, Mo 0.12-0.20;
Q390C: C 0.10-0.18, Si 0.40-0.55, Mn 0.80-1.10, P 0.030 Max, S 0.020 Max, Ni 0.25 Max, Cr 0.20-0.35, Cu 0.30 Max;
Q420D: C 0.15-0.20, Si 0.50-0.70, Mn 1.00-1.30, P 0.030 Max, S 0.015 Max, Ni 0.25 Max, Cr 0.30-0.50, Cu 0.25 Max;
Q460B: C 0.12-0.20, Si 0.30-0.50, Mn 1.20-1.50, P 0.025 Max, S 0.015 Max, Ni 0.15 Max, Cr 0.30-0.50, Cu 0.25 Max.
Low alloy high strength structural steel is widely used in engineering structures such as bridges, ships, vehicles, etc., and has become the preferred material for large-scale engineering structures. Therefore, it is necessary to further understand the properties and application of low alloy high strength structural steel, so as to better apply it.
