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Physical Properties of Stainless Steel Tube at Low Temperature

Date:2017-11-21    keywords:stainless steel tube
1. Low temperature embrittlement --- in low temperature environment, the deformation energy is small. In the low temperature environment, the reduction of elongation and reduction of area is called low temperature embrittlement. More in the ferritic body of the body to generate cubic tissue.

2. Low temperature processing --- martensitic stainless steel from the austenitizing temperature quenching and then cooled to a very low temperature, to promote the martensite quenching method. Suitable for easy production of retained austenite stainless steel. Stainless steel tube at low temperatures, resistance, linear expansion coefficient, thermal conductivity, quality hot melt and magnetic will change greatly. Resistance and linear expansion coefficient become smaller at low temperature; thermal conductivity and mass heat capacity decrease sharply at low temperature; Young's modulus (longitudinal elastic modulus) increases at the same time when the temperature decreases. Because austenitic stainless steel pipes have a Ms point of low temperature (martensitic transformation start temperature or martensite formation temperature), martensite can be formed while keeping the temperature below the Ms point. The formation of martensite at low temperatures renders SUS304 (18Cr-8Ni), a representative grade of austenitic stainless steel, non-magnetic at ordinary temperatures and magnetic at low temperatures. Regarding the low-temperature state, the ferritic stainless steel tube has low-temperature brittleness like carbon steel, but the austenitic steel does not exist. Ferritic or martensitic stainless steels therefore give low temperature embrittlement whereas austenitic stainless steels or nickel based alloys do not show low temperature brittleness. Ferritic stainless steel pipe SUS410 (13Cr), SUS430 (18Cr) and other low temperature conditions, the impact value showed a sharp decline. Therefore, it is necessary to pay special attention when using it at a low temperature. As a way to improve the impact toughness of ferritic stainless steels, a high-purity process can be considered. With control of C, N levels and improvement of embrittlement temperatures in the range of -50 to -100 °C, it is possible to use them in projects related to freezing. In recent years, SUS430LX (18Cr-Ti, Nb-LC) and SUS436L (18Cr-Mo-Ti, Nb-LC) have been applied to the housing of the freezing apparatus. Because ferritic stainless steel is a body-centered cubic structure, when material properties appear weakened, sharp cracks rapidly expand and cause brittle failure. Austenitic stainless steel does not produce brittle fracture because of its face-centered cubic structure. Arcane investment stainless steel SUS304L (18Cr-9Ni-LC) and SUS316L (18Cr-12Ni-2Mo-LC) showed excellent impact properties even at low temperatures. However, attention should be given to the precipitation of ferrite or the precipitation of martensite due to processing, and the tendency of embrittlement due to precipitation of heterogeneous precipitates due to sensitization caused by carbides or σ.

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