IN‐REACTOR LOW‐CYCLE FATIGUE OF TYPE 0Kh16N15M3B STAINLESS STEEL

Abstract

An investigation has been carried out on austenitic stainless steel OKh16N15M3B under normal conditions and also to neutron irradiation of 6.8 x 10I6 nm-2 s-' ( E 0. I MeV) intensity. Thin-walled torsion cylindrical specimens were tested in straincontrolled fully reversed loading mode at 923 K. Various ranges of strain, pre-loading fluences and half-cycle hold times (1, 5 and 30min) were applied. Neutron irradiation was found to result in hardening of the steel, stimulating cyclic stress relaxation and a reduction in cyclic life. When acting together, neutron irradiation and static loads cause a more significant reduction in the number of cycles to failure than if summed up as independent factors. Application of a kinetic failure criterion based on a damage parameter enables an estimation to be made of the limiting state of the steel under high-temperature cyclic loading with hold periods. NOMENCLATUREFr = failure fluence Fa = pre-loading fluence FN = F1 -Fa = loading fluence (fluence accumulated under loading) N / = number of cycles to failure n = cycle number T = temperature t = time t , = cycle period to = cycle period in no-hold-time tests t H = hold time td = t,/tO = dimensionless cycle period v = loading frequency y = shear strain y, = creep strain y p = plastic strain y , = total strain Ay = strain range Af = corrected strain range cr,, = yield stress cru = ultimate strength T = shear stress T,, = maximum stress in a cycle r^ = stress measured from the point of unloading AT = stress range AT" = stress decrease during hold time 6 =tensile elongation to fracture o = damage o, = static damage w f = fatigue damage I// = reduction of area; in tension A T~/ T~ = the degree of stress relaxation A,