Low cycle fatigue behaviour of duplex stainless steel: influence of isothermal aging treatment

Abstract

A B S T R A C TThe low-cycle fatigue behaviour of a duplex stainless steel was comparatively studied in standard heat-treated and isothermally aged (at 475 • C for 100 h) conditions by mechanical testing, scanning and transmission electron microscopy. It was established that fatigue life is longer in the aged condition as compared to the annealed condition at lower values of total strain amplitude ε/2 ( ε/2 = 4.0 × 10 −3 and 6.0 × 10 −3 ) and becomes similar in annealed and aged conditions at ε/2 = 8.0 × 10 −3 . Fatigue resistance of the material converges with increase in ε/2 values as a result of rapid cyclic softening of the ferritic phase in the aged condition.Keywords cyclic softening; duplex stainless steel; 475 • C embrittlement; low-cycle fatigue. N O M E N C L A T U RE c [−] = fatigue ductility exponent K [MPa] = cyclic strength coefficient n [−] = cyclic strain hardening exponent R [−] = load ratio ε [−] = strain ε f [−] = fracture strain ε f [−] = fatigue ductility coefficient ε/2 [−] = total strain amplitude ε el /2 [−] = elastic strain amplitude ε pl /2 [−] = plastic strain amplitude σ [MPa] = stress σ ys(0.2%) [MPa] = 0.2% offset yield strength σ uts [MPa] = ultimate tensile strength σ [MPa] = stress range σ mean [MPa] = mean stress σ /2 [MPa] = stress amplitude ( σ /2) max [MPa] = maximum stress amplitude I N T R O D U C T I O NDuplex stainless steels (DSS) are increasingly used as structural material in oil, power and petrochemical industries. However, the use of these grades of steel is limited to temperatures below 280 • C as they experience embrittlement in the temperature range of 280-500 • C. The iron-chromium binary system has a miscibility gap in this temperature range, and the ferritic phase decomposes into Correspondence: J. K. Sahu.

High‐temperature low‐cycle fatigue behaviour of a cast Al–12Si–CuNiMg alloy

“…The cyclic softening behaviour of the alloy presents a strong dependence on total strain amplitude and temperature. It is consistent with the previous reports …”

Fatigue crack initiation behavior in embrittled austenitic–ferritic stainless steel

“…In many applications DSSs are subjected to cyclic loading and sometimes to severe environment conditions. The low cycle and high cycle fatigue behavior of DSSs in ambient air, corrosive environment and at high temperature were studied extensively [1][2][3]. In recent years progress was made in understanding the fatigue crack initiation behavior in low cycle fatigue (LCF) and high cycle fatigue (HCF) regimes in DSSs [4][5][6][7][8][9][10].…”

Cyclic deformation behaviour, microstructural evolution and fatigue life of duplex steel AISI 329 LN

“…For total strain controlled fatigue tests, cyclic deformation curves for the investigated material are shown in [26]. For lifetimes >10 5 cycles, the change in temperature decreases due to heat transfer saturation effects while the electrical resistance shows the cumulative fatigue damage with continuously increasing values.…”