| For practical application of cryogenic engineering, development and characterization of structural materials for use at low temperatures are essential. For these purposes, a system for mechanical testing at liquid helium temperature was developed and it was shown that the precision and accuracy of the system met the requirements of standards for materials testing machines. Using this system, tensile deformation behavior of AISI 304, 316 and 310S austenitic stainless steels at cryogenic temperatures was investigated. Tests were conducted on round, tensile specimens having a 6.25㎜ diameter at 4, 77, and 295 K and loading rate was 0.5㎜/min. Serrations were observed in all alloys at 4 K. The stress-displacement curves at 77 and 4 K showed different tendency from those at 298 K. As the testing temperature decreased, ultimate strengths of 304 and 316 were largely increased compared to the increase of yield strengths, but the increase of ultimate strength of 310S was almost the same to that of yield strength. Type 310S had the highest yield strength and the lowest tensile strength at all temperatures. These tensile characteristics were considered to be strongly affected by austenite stability. |
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