(Received 9 February 1990; accepted 9 January 1991)
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Experiments show that some austenitic steels at extreme cryogenic temperatures are toughened by warm prestress. We demonstrate this for Fe-17Cr-3Ni-13Mn-0.33N steel specimens that were warm precracked at 295 K and then fractured in liquid helium at 4 K where failure occurs by slip-plane cracking. On the other hand, Fe-13Cr-5Ni-22Mn-0.21N steel with higher toughness and a ductile fracture mechanism at 4 K was not affected by similar warm precracking. Austenitic and ferritic steel behaviors are compared, and precracking procedures for 4-K fracture tests are discussed.
National Institute of Standards and Technology, Boulder,
Superconducting and Cryogenic Technology Center, Kobe Steel, Ltd., Kobe,
Stock #: JTE12575J