Calculation of stress relaxation properties for type 42 stainless steel

摘要

Analytical life prediction methods are being developed for high temperature turbine and valve studs/bolts. In order to validate the approach, the calculated results are compared to the resuls of uniaxial stress relaxation testing, bolt model testing and service experience. Long time creep, creep-rupture and stress relaxation tests were performed by the National Research Institute for Metals of Japan (NRIM) for 12Cr-1Mo-1W-1/4V, Type 422 stainless steel bolting material, at 500C, 550C and 600C. Based on these results and limited tests for a servcie exposed bolt, the creep behavior can be described using a two-parameter material model; is not an element/is not an element_r=1-(1-(t/tr)~(m+1)~delta where is not an element_r is the rupture strain, t_r is the rupture time, m and delta are material constants. For comparison with the measured uniaxial stress relaxation properties. the stress relaxation was calculated using the two-parameter creep equation and a strain hardening flow rule. The rutpture time data was correlated using time-temperature parameter methods. A power law was used for the rupture strain versus rupture time relationship at each temeprature. The calculated stress versus time curves were in good agreement with the measured at all temperatures and for initial strain levels of 0.10