Cyclic deformation and phase transformation of 6Mo superaustenitic stainless steel

Abstract

A fatigue behavior analysis was performed on superaustenitic stainless steel UNS S31254 (Avesta Sheffield 254 SMO), which contains about 6 wt.% molybdenum, to examine the cyclic hardening/softening trend, hysteresis loops, the degree of hardening, and fatigue life during cyclic straining in the total strain amplitude range from 0.2 to 1.5 %. Independent of strain rate, hardening occurs first, followed by softening. The degree of hardening is dependent on the magnitude of strain amplitude. The cyclic stress-strain curve shows material softening. The lower slope of the degree of hardening versus the strain amplitude curve at a high strain rate is attributed to the fast development of dislocation structures and quick saturation. The H martensite formation, either in band or sheath form, depending on the strain rate, leads to secondary hardening at the high strain amplitude of 1.5 %.

Precipitation sequences in cold deformed superaustenitic stainless steels

“…Metallographic examination also indicated the formation of sigma phase s precipitates following isothermal aging within the temperature range of 650-950uC for time up to 120 h. A second species of precipitates also nucleates and grows within the same temperature range and is believed to be chi phase x. Both species of precipitation have been reported to form following aging in undeformed superaustenitic steels 1-6 but were also observed in cold deformed condition following heat treatment, [11][12][13][14][15]19,20 however, nucleating at shorter aging times, in agreement with results of the present study.…”

Constitutive equation and dynamic recrystallization behavior of as-cast 254SMO super-austenitic stainless steel

“…Recently, super-austenitic stainless steel (SASS) has been received great attentions due to the favorable combination of high strength and toughness, good weldability and excellent resistance to pitting and crevice corrosion, all which enable its use in chemical, petrochemical, oceanic, nuclear, military and other demanding fields [1][2][3]. It can be said that, the development of SASS successfully provides a bridge between expensive nickel-based alloys and relatively cheap austenitic stainless steels [4].…”

A viscoplastic constitutive model for cyclic hardening in the dynamic strain aging regime

“…Engineering materials subjected to cyclic inelastic deformation generally exhibit cyclic hardening and/or softening, which depends both on the applied strain amplitude and the strain rate under strain control [9][10][11][12]29]. Cyclic preloading also influences the subsequent rate-dependent deformation such as creep and stress relaxation, which is attributed to the change of the dislocation density and the dislocation cell structure, even though the flow stresses immediately before the subsequent tests are the same [13,14].…”