Analysis of the hysteresis loops of a martensitic steel

Microstructural evolutions and cyclic softening of 9%Cr martensitic steels

“…Indeed, the macroscopic stress can be divided between the isotropic stress R, the kinematic stress X (or backstress) and the viscous stress r v as initially proposed by Cottrel [13] (see Fig. 3 viscous materials [4]. The main results of this study are illustrated in Fig.…”

“…Compositions and heat treatments are given elsewhere [4,5]. Pure fatigue (PF), relaxation-fatigue (RF) and true creep-fatigue (CF) tests (during the holding period, the stress is held constant, which differs from usual relaxation-fatigue tests during which the strain is held constant during the hold time) were carried out at 823 K and controlled on the total strain.…”

Creep-Fatigue Interactions in a 9 Pct Cr-1 Pct Mo Martensitic Steel: Part II. Microstructural Evolutions

“…In addition, the work softening effect observed under cyclic loadings on 9 to 12 pct Cr steels has already been qualitatively attributed to the coarsening of their microstructure. [20,[28][29][30][31] This study proposes a quantitative multiscale characterization of the microstructural evolutions taking place on a P91 steel subjected to pure fatigue (PF), relaxationfatigue (RF), and CF tests. Bright-field TEM observations are coupled to electron backscattered diffraction (EBSD) measurements carried out via scanning electron microscopy (SEM).…”

Creep-Fatigue Interactions in a 9 Pct Cr-1 Pct Mo Martensitic Steel: Part I. Mechanical Test Results

“…In the present case, P91 steel, like other 9 to 12 pct Cr steels, experiences a cyclic work softening effect that can be correlated to the decrease of the kinematic stress. [32,33] In addition, the cyclic softening effect was found to be directly correlated to the cumulative plastic strain level. This cyclic softening effect can be explained by the microstructural coarsening and the decrease of the dislocation density.…”

“…These microstructural evolutions are the reason why the 9 to 12 pct Cr steels soften under cyclic loadings. [20,[30][31][32][33] First modeling attempts were recently carried out to predict the cyclic softening effect on the basis of the observed microstructural evolutions. [34,35] The first part of this study presents the results of mechanical tests (CF tests, creep tests, sequential tests, etc.)…”