With the development of science and technology and industry, higher requirements are placed on materials, such as higher strength, high temperature resistance, high pressure, low temperature, corrosion resistance, wear and other special physical and chemical properties. Carbon steel is no longer complete. fulfil requirements.
Insufficient carbon steel:
(1) Low hardenability. In general, the maximum hardenable diameter of carbon steel water quenching is only 10mm-20mm.
(2) The strength and yield are relatively low. For example, the σs of ordinary carbon steel Q235 steel is 235 MPa, while the σs of low alloy structural steel 16Mn is 360 MPa or more. The σs /σb of 40 steel is only 0.43, which is much lower than that of alloy steel.
(3) Poor tempering stability. Due to poor tempering stability, carbon steel is subjected to quenching and tempering, in order to ensure higher strength, lower tempering temperature is required, so that the toughness of steel is lower; in order to ensure better toughness, high tempering is adopted. The strength at the time of temperature is low, so the comprehensive mechanical performance level of carbon steel is not high.
(4) The requirements for special performance cannot be met. Carbon steel is often poor in terms of oxidation resistance, corrosion resistance, heat resistance, low temperature resistance, wear resistance, and special electromagnetic properties, and cannot meet the needs of special performance.