What Will Happen to Seamless Steel Pipes in Low Temperature Environments?
1. Low temperature embrittlement of seamless steel pipes: In low temperature environment, deformation energy is small. In a low temperature environment, the phenomenon that the elongation and shorteni...
1. Low temperature embrittlement of seamless steel pipes: In low temperature environment, deformation energy is small. In a low temperature environment, the phenomenon that the elongation and shortening rate of the section decrease is called low temperature embrittlement. It mostly occurs on the body-centered cubic structure of the ferrite series.
2. Low-temperature processing of stainless steel pipes: The martensitic stainless steel is quenched from austenitizing temperature and then cooled to a very low temperature to promote the quenching method of martensite. It is suitable for producing stainless steel with retained austenite.
At low temperatures, the resistance, linear expansion coefficient, thermal conductivity, mass melting and magnetism of seamless pipes will change greatly. Electrical resistance and linear expansion coefficient decrease at low temperature; thermal conductivity and mass heat capacity decrease sharply at low temperature; Young's modulus (longitudinal elastic modulus) increases when the temperature drops. Because the austenitic stainless steel pipe has a low temperature (Subzreo temperature) Ms point (martensite anomaly start temperature or martensite formation temperature), martensite can be formed when it is kept below the Ms point. The formation of martensite at low temperature makes SUS304 (18Cr-8Ni), the representative steel of the austenitic series of stainless steels, have right and wrong magnetic properties at room temperature, but become magnetic in low temperature environments.
Regarding the low-temperature brittleness of ferritic stainless steel pipes like carbon steel at low temperature, austenitic steel does not exist. Therefore, ferritic or martensitic stainless steel develops low-temperature embrittlement, while austenitic stainless steel or nickel-based alloy does not exhibit low-temperature embrittlement. The impact value of ferritic stainless steel pipes such as SUS410 (13Cr) and SUS430 (18Cr) flashed sharply at low temperatures. Therefore, it is necessary to pay special attention when using it at low temperature. As a way to improve the impact toughness of ferritic stainless steels, a high-purification process can be considered. With the help of controlling C and N grade levels, when the embrittlement temperature is improved in the range of -50°C to -100°C, it is possible to use it in freezing-related engineering. In recent years, SUS430LX (18Cr-Ti, Nb-LC) and SUS436L (18Cr-Mo-Ti, Nb-LC) have been applied to the shell of freezing appliances. Ferritic stainless steel has a body-centered cubic structure. When the function of the material becomes weak, the sharp cracks will rapidly expand to form brittle damage. The austenitic series stainless steel has a face-centered cubic structure without brittle damage. Aoshu's investment in stainless steel SUS304L (18Cr-9Ni-LC) and SUS316L (18Cr-12Ni-2Mo-LC) showed excellent impact characteristics at low temperatures. However, attention should be paid to the separation of ferrite or the separation of martensite due to processing, and the tendency of embrittlement caused by separation of carbides or σ phases due to sensitization.
Tips: In case ASTM A53 Grade B in ERW (electric resistance welded) pipe, the weld seam shall be done the heat treatment with a minimum 1000°F [540°C]. In this way the no untempered martensite remains.
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