With the development of science, technology and industry, higher requirements, such as higher strength, resistance to high temperature, high pressure, low temperature resistance, corrosion, wear and other special physical and chemical properties of the requirements placed on the materials, carbon steel can not fully meet the requirements. Carbon steel in the performance of the following deficiencies: profiles (1) under the hardenability low general carbon steel water quenching maximum quenching diameter of only 10mm-20mm. (2) strength and yield is relatively low, such as ordinary carbon steel Q235 steel σs 235MPa, low-alloy structural steel 16Mn the σs compared to 360MPa or more. 40 steel σs / σb is only 0.43, much lower than the alloy steel. (3) Poor tempering stability due to differential tempering stability, carbon steel during quenching and tempering treatment, in order to ensure the high strength requires the use of a lower tempering temperature, so that the toughness of steel is low; in order to ensure better toughness, strength and high tempering temperature is low, not high level of mechanical properties of carbon steel. (4) can not meet the requirements of the special properties of carbon steel in anti-oxidation, corrosion resistance, heat resistance, low temperature resistance, wear-resistant and special electromagnetic often poor, can not meet the performance requirements of the special use.