Stainless steel tube performance at low temperature

1. Low temperature embrittlement --- In low temperature environment, the deformation energy is small. In a low temperature environment, the phenomenon that the elongation and the reduction of the area are reduced is called low temperature embrittlement. It is mostly produced on the body-centered cubic structure of the ferrite series.

2. Low-temperature processing --- The martensite series stainless steel is quenched from the austenitizing temperature and then cooled to a very low temperature to promote the quenching method for producing martensite. Suitable for stainless steel that is easy to produce retained austenite.

Stainless steel tubes undergo large changes in resistance, coefficient of linear expansion, thermal conductivity, mass hot melt, and magnetic properties at low temperatures. Resistance, linear expansion coefficient becomes smaller at low temperature; thermal conductivity and mass heat capacity decrease sharply at low temperature; Young's modulus (longitudinal elastic modulus) increases simultaneously when temperature drops. Since the austenitic series Stainless steel tube has a low temperature (Subzreo temperature) Ms point (martensitic transformation start temperature or martensite formation temperature), martensite can be formed while remaining below the Ms point. The formation of martensite at low temperatures makes SUS304 (18Cr-8Ni), a representative steel of austenitic stainless steel, non-magnetic at normal temperature and magnetic in low temperature environments.

Regarding the low-temperature state, the ferritic Stainless steel tube has low-temperature brittleness like carbon steel, while the austenitic steel does not. Therefore, ferrite or martensitic stainless steel produces low temperature embrittlement while austenitic stainless steel or nickel based alloy does not exhibit low temperature brittleness. In the ferritic Stainless steel tube, SUS410 (13Cr) and SUS430 (18Cr) showed a sharp drop in impact value at a low temperature. Therefore, it is necessary to pay special attention when using it in a low temperature state. As a method of improving the impact toughness of the ferritic series stainless steel, a high purification process can be considered. By controlling the C, N level and the embrittlement temperature is improved from -50 ° C to -100 ° C, it is possible to use it for freezing related engineering. In recent years, SUS430LX (18Cr-Ti, Nb-LC) and SUS436L (18Cr-Mo-Ti, Nb-LC) have been used.

And the like is applied to the casing of the refrigeration appliance. Since ferritic stainless steel is a body-centered cubic structure, when the material properties are weakened, sharp cracks rapidly expand to cause brittle failure. Austenitic stainless steels do not cause brittle failure because they are face-centered cubic structures. Arcane injection stainless steel SUS304L (18Cr-9Ni-LC) and SUS316L (18Cr-12Ni-2Mo-LC) and the like exhibit superior impact characteristics at low temperatures. However, it is necessary to pay attention to precipitation of ferrite or precipitation of martensite due to processing, and there is a tendency for embrittlement to cause embrittlement due to precipitation of carbides or σ equivalent heterophase.