With the development of science and technology and industry, the material has put forward higher requirements, such as higher strength, resistance to high temperature, high pressure, low temperature, corrosion resistance, wear and other special physical and chemical properties of the requirements, carbon steel can not fully meet the requirements, so the emergence of alloy steel plate.

Classification of alloy steel

According to the content of alloying elementsLow alloy steel (the total amount of alloying elements is less than 5%), medium alloy steel (the total amount of alloying elements is 5%-10%), high alloy steel (the total amount of alloying elements is higher than 10%).By alloying element compositionChromium steel (Cr-Fe-C), chromium-nickel steel (Cr-Ni-Fe-C), manganese steel (Mn-Fe-C), silicon-manganese steel (Si-Mn-Fe-C).According to the small specimen normalized or cast organizationPearlite steel, martensitic steel, ferrite steel, austenitic steel, lainitic steel.According to the use ofAlloy structural steel, alloy tool steel, special performance steel.

Carbon steel in the performance of the main deficiencies in the following areas.
(1) low hardenability in general, the maximum quenching diameter of carbon steel water quenching is only 10mm-20mm.
(2) strength and yield strength is relatively low, such as ordinary carbon steel Q235 steel σs for 235MPa, while low-alloy structural steel 16Mn σs is more than 360MPa. 40 steel σs/σb is only 0.43, much lower than the alloy steel.
(3) poor tempering stability due to poor tempering stability, carbon steel in the tempering treatment, in order to ensure higher strength need to use a lower tempering temperature, so the steel toughness is low; in order to ensure better toughness, the use of high tempering temperature strength and low, so the carbon steel comprehensive mechanical properties level is not high.
(4) can not meet the requirements of special performance carbon steel in oxidation resistance, corrosion resistance, heat resistance, low temperature resistance, wear resistance and special electromagnetic properties are often poor, can not meet the needs of special use performance.