Characterization of Low Cycle Fatigue of Ferritic–Martensitic P92 Steel: Effect of Temperature

Abstract

Isothermal, strain-controlled low cycle fatigue (LCF) tests of P92 steel are conducted in air at different temperatures ranging from 20 to 650 8C and various strain ranges to clarify the influence of temperature on its LCF behavior. A symmetrical triangular wave form and a constant 1.0 Â 10 À3 s À1 strain rate are employed for all the tests. Cyclic softening behavior is expressed in two ways: peak tensile stress in terms of cycle numbers and in terms of accumulated inelastic strain. Based on the definition of "inelastic ratio," correlation between the value of accumulated inelastic strain ( e in;II ) at the beginning of the second softening stage and the inelastic ratio can be distinctively divided into three regions. The modified cyclic plasticity model, in which a linear term is added into the isotropic hardening variable, is developed to simulate the stress-strain hysteresis loop and the cyclic softening curve. Additionally, parameters in the modified isotropic hardening variable at different temperatures are correlated to the cyclic softening phenomenon. Performances of the modified model are assessed by comparing predictions with experimental results. Good predictive capability of the modified constitutive model is obtained.[ Ã ] X.

Low Cycle Fatigue and Relaxation Performance of Ferritic–Martensitic Grade P92 Steel

“…• 100 (8) σmax is the overall maximum stress of the complete test, whereas σmax,50%Nf is the maximum stress of the stabilized cycle at half-lifetime. The equation was adapted from References [15,23], which used the maximum stress of the first cycle (see chapter 4. Discussion).…”

“…A triangular wave form with a mechanical strain ratio of R ε = −1 was employed ( Figure 3a). The failure criterion was a 10% drop in the peak tensile stress, following the procedure discussed in Reference [15]. LCF-tests were conducted at three temperature levels: 300 • C, 500 • C, and 620 • C. In a second step, hold periods t h under strain control (at the maximum and minimum strain) were included in the LCF-test procedure ( Figure 3b).…”

“…Due to its enhanced creep resistance, compared to earlier grades, P92 can be used up to maximum operation temperatures of 620 • C [14]. A number of studies on the fatigue behavior of P92 have been published recently [15][16][17][18]. It was found that P92 exhibits a considerable cyclic softening, as it is known from P91.…”

Experimental and numerical characterization of low cycle fatigue and creep fatigue behaviour of P92 steel welded joint

“…37 Thirdly, to determine the viscoplastic parameters, stress relaxation behaviour during holding period is used, and details can be referred to Tong et al 38 To get these parameters of different regions in welded joint, the heat treatment homogeneous simulated material of CGHAZ and FGHAZ introduced in Section 2.2 was used, and required CFI tests were performed. Firstly, elastic parameters can be determined by using the first stressstrain hysteresis loop.…”

“…Secondly, isotropic parameters in the modified model (Equation 10) can be determined through the method introduced in our previous study, and the method of deciding back stress parameters also has been discussed. 37 Thirdly, to determine the viscoplastic parameters, stress relaxation behaviour during holding period is used, and details can be referred to Tong et al 38 To get these parameters of different regions in welded joint, the heat treatment homogeneous simulated material of CGHAZ and FGHAZ introduced in Section 2.2 was used, and required CFI tests were performed. Subsequently, the 3 steps parameter determination method is used to determine these parameters step by step.…”