Low temperature embrittlement of stainless steel pipe

In low temperature environment, deformation energy is small. In low temperature environment, the phenomenon that elongation and reduction of area decrease is called low-temperature embrittlement. It is mainly produced on the body centered cubic structure of ferrite series.

Low temperature processing of stainless steel pipe

The martensite series stainless steel is quenched from the austenitizing temperature and then cooled to a very low temperature to promote the quenching method of producing martensite. Suitable for stainless steels that are easy to produce residual austenite.

At low temperature, the resistance, linear expansion coefficient, thermal conductivity, mass melting and magnetism of stainless steel pipe will change greatly. Resistance and linear expansion coefficient decrease at low temperature; Thermal conductivity and mass heat capacity decrease sharply at low temperature; The modulus (longitudinal elastic modulus) increases at the same time as the temperature decreases.

Because austenitic series stainless steel tubes have Ms point (martensite transformation starting temperature or martensite formation temperature) at low temperature (Subzreo temperature), martensite can be generated when it is kept below Ms point. The formation of martensite at low temperature makes SUS304 (18Cr-8Ni), the representative steel of austenitic stainless steels, nonmagnetic at room temperature and magnetic at low temperature.

As for the low temperature brittleness of ferritic stainless steel pipe, like that of carbon steel, does not exist in austenitic steel. Therefore, ferritic or martensitic stainless steels produce low-temperature embrittlement while austenitic stainless steels or nickel based alloys do not show low-temperature embrittlement. SUS410 (13Cr), SUS430 (18Cr), etc. of ferritic stainless steel pipe show a sharp drop in impact value at low temperature. Therefore, it is necessary to pay special attention when using at low temperature. As a method to improve the impact toughness of ferritic stainless steels, high purification process can be considered. With the help of controlling the level of C and N, when the embrittlement temperature is improved within the range of - 50 ℃ to - 100 ℃, it is possible to use it in freezing related projects. In recent years, SUS430LX (18Cr Ti, Nb LC) and SUS436L (18Cr Mo TiNb LC) have been applied to the shells of refrigeration appliances. Ferritic stainless steel is a body centered cubic structure. When the material performance becomes weak, sharp cracks will rapidly expand and cause brittle failure. Austenitic series stainless steel will not produce brittle failure because of its face centered cubic structure.