Fatigue deformation-induced response in a superduplex stainless steel

Abstract

The cyclic deformation behavior of SAF 2507 superduplex stainless steel (SDSS) was studied under constant plastic-strain amplitudes. The cyclic hardening/softening curves show initial hardening, followed by softening and, finally, saturation behavior. Two regimes can be differentiated in the cyclic stress-strain curve (CSSC) of SDSS. The transition point at which the cyclic strain-hardening rate changes is identified to be p /2 ϭ 7 ϫ 10 Ϫ3 . Transmission electron microscopy (TEM) results on dislocation structures suggested that there is a close relationship between the CSSC, hardening/ softening curves, and the dislocation substructure evolution. In the low-plastic-strain-amplitude regime of the CSSC, the dislocation activity in the austenite grains is found to be higher than that in the ferrite grains. At higher plastic strain amplitudes, low-energy dislocation structures are found in the ferrite grains, while clusters and bundles of dislocations can be observed in the austenite grains. Strain localization due to formation of these structures resulted in a decrease in the cyclic strain-hardening rate within the high-plastic-strain-amplitude regime. Dislocation substructure evolution is also used to explain the shape of the hardening/softening curve.

Role of nitrogen in the cyclic deformation behavior of duplex stainless steels

“…The most recent study on the cyclic response of a duplex stainless steel (53 pct ␥-47 pct ␦) was conducted by Goh et al [17] They presented similar results to those of Vogt et al, i.e., two different regimes were identified in the CSSCs. They also found that at a plastic-strain amplitude below 7 ϫ 10 Ϫ3 , austenite mainly controls the cyclic deformation, whereas both phases take part in accommodating plastic strain.…”

“…Magnin et al [5,6] and Goh et al [17] have reported the same tendency to have two regimes in their CSSCs, changing from a high CSHR in the first regime to a low one in the second regime. Transition points were identified at pa values of 1 ϫ 10 Ϫ3 and 7 ϫ 10 Ϫ3 , respectively.…”

Effect of 475°C embrittlement on the mechanical properties of duplex stainless steel

“…Goh and Yip [71] conducted plastic strain controlled fatigue test ( ε pl /2 = 2 × 10 −4 to 8 × 10 −2 ) with SAF 2507 grade of DSS. They observed a common trend of cyclic hardening/softening for all the imposed values of ε pl /2.…”

“…Llanes et al [36] have described the cyclic stress-strain response of DSS in the annealed and aged conditions in three stages in terms of plastic strain amplitudes ( ε pl /2 < 10 −4 , 10 −4 < ε pl /2 < 10 −3 , ε pl /2 > 10 −3 ) each amenable to be characterized by well-defined and distinct cyclic deformation mechanisms. Goh and Yip [71] identified two separate regimes with different strain-hardening rates in the CSSC plotted by them. The first regime, at ε pl /2 < 7.0 × 10 −3 , had a high cyclic strain-hardening rate, while the second regime, at ε pl /2 > 7.0 × 10 −3 , had a strain-hardening rate that is less pronounced than the first.…”

Enigma of dislocation patterning due to slip in fatigued austenite

“…Moreover, the dislocation substructures and their patterns undergo changes during cyclic plastic deformation (Kuhlmann-Wilsdorf and Laird, 1977; Lukas and Kunz, 2002; Ma and Laird, 1988; Mayama et al., 2008; Mughrabi, 1983, 2006, 2009). It has already been investigated by many eminent scientists that cyclic plastic deformation alters the microstructure in different length scales and causes extreme instabilities with different loading amplitudes (Das et al., 2011b, 2011c; Goh and Yip, 2002; Shih et al., 2010; Yaguchi et al., 2001). Plastic deformation usually results in spatially heterogeneous arrangement/patterning of dislocations in the matrix.…”