Study of creep – fatigue interaction in ferritic steels

Abstract

The creep-fatigue interaction phenomenon occurs when the material is subjected to sufficiently high temperatures and stress cycles that not only produce creep deformations, but also fatigue deformations. This combination of effects seriously reduces the life of the components, which is why it is of industrial interest. Under these requests, 1Cr 0.5Mo low alloy steel was studied under these requests by conducting short tests at 600 °C, 168 MPa, 131 MPa and 30 minutes of hold periods at peaks, which led the research to tests that simulate industrial conditions. Subsequently, the behavior of steel was analyzed when subjected to the interaction of creep-fatigue, with cyclic loads between 20 and 131 MPa without permanence with durations of 10 and 1342 cycles at equal frequency, followed by a stationary regimen of creep at stress-counting stress and design temperature (70 MPa and 540°C). The results were compared in all cases with those obtained by studying the material only subject to the creep condition. This type of thermo-mechanical request is presented in isolated overloads in continuous process plants of the oil and
gas industry, petrochemical and power generation, which can lead to early material failures.
Since tested specimens at fatigue stresses with a positive mean stress value, the material presented the ratcheting effect and as a result of it, an accumulation of plastic deformations that cause the degradation of steel and the decrease of its resistance to creep.