Abstract
Creep and stress relaxation behavior at room temperature has been investigated for 17-4 PH martensitic stainless steel (SUS630: 17Cr-4Ni-3Cu-Nb) in comparison with a high-strength carbon steel for F10T high-tension bolts. Both steels showed creep strain at stresses around the 0.2% proof stress, and the creep curves followed a logarithmic creep law. Though the 0.2% proof stresses were almost the same, the creep strain of SUS630, which was precipitation hardened, was lower than that of F10T carbon steel. From the stress relaxation tests, it was confirmed that the stress relaxation property of SUS630 was superior because of the lower stress relaxation values at the same initial stress. The observed stress relaxation curves were compared with the ones predicted from the creep data by the time hardening theory and strain hardening theory. Though the calculated values of the stress relaxation from the creep data was consistent with the measured values at lower stresses below 800 MPa, the calculated values became larger at higher stresses. Since the deviation mainly occured at an early stage of the stress relaxation test, it was atributable to the difference in the velocity of loading before the tests.
