Aging effects on the cyclic deformation mechanisms of a duplex stainless steel

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

“…So observation of these bundles is a common feature. Llanes et al [36] observed a dominant structure evolution in the ferritic grain of AISI 329 grade of DSS at ε pl /2 > 1.0 × 10 −3 with the development of vein into wall structure. Kruml et al [75] observed two characteristic types of dislocation structure in the ferritic phase of DIN X2CrNiMoN22-5 grade of DSS at ε pl /2 = 4.5 × 10 −3 .…”

“…Some of the above-mentioned factors also are known to have pronounced effect on the change in cyclic stress-strain behaviour and fatigue life of DSS due to aging treatment at 475 • C. So a discussion on the change in fatigue behaviour of DSS due to aging treatment at 475 • C must be done in conjunction with the above-mentioned factors. For example, Llanes et al [36] observed ferrite like deformation mechanism and fatigue softening at ε pl /2 = 1.2 × 10 −3 for the AISI 329 grade of DSS in the aged condition (0.074 wt.% nitrogen, 38%␥62%␣, wrought), while Vogt et al [42] for their alloy BöA920 grade of DSS (0.4 wt.% nitrogen, 70%␥30%␣, wrought) observed no change in fatigue resistance even at ε pl /2 = 5.3 × 10 −3 after aging treatment at 475 • C. This difference may be attributed to several factors such as nitrogen content, ferrite volume fraction.…”

“…9. Cyclic hardening/softening curves for DSS grades (a) SAF 2507 at different plastic strain ranges [70]; (b) (f) AISI 329 unaged (UA) and aged (A25, A200) condition [36]; (c) UR52N+ in the annealed and aged condition [42]; (d) BöA920 in the annealed and aged condition [42]. Fig.…”

“…The curve changes from one of a high strain-hardening rate in the first regime, to a low strain-hardening rate in the second regime. 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.…”

“…However, this grade of steel embrittles when exposed in the temperature range of 280-500 • C limiting its application to temperatures below 280 • C. This phenomenon is termed 475 • C embrittlement as the rate of embrittlement is highest at 475 • C [13][14][15]. The embrittlement changes the tensile [16][17][18][19][20][21][22], fracture [23][24][25][26][27][28][29][30][31][32] and fatigue [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]23,48,49] behaviour of this steel.…”