Deformation and microstructure evolution of a duplex stainless steel under out-of-phase thermo-mechanical fatigue

Application of a Modified Stress−Strain Approach for the Fatigue‐Life Prediction of a Ferritic, an Austenitic and a Ferritic–Austenitic Duplex Steel under Isothermal and Thermo‐Mechanical Fatigue

“…Thus, the fatigue behavior can be improved by the two‐phase structure only within a particular range of strain amplitude and temperature. However, the cyclic strength of the fatigue tests of the duplex steel was significantly higher than that of the austenitic steel . Thus, with a change of the test conditions from strain‐ to stress‐controlled fatigue tests, the fatigue lives of the duplex steel were expected to be longer than for the austenitic steel.…”

“…It gives a lifetime prediction within the scatter band of a factor of three for all cases where the maximum temperature was 800 °C, although a ductile‐to‐brittle transition occurred in the investigated temperature range (400–800 °C) at approximately 750 °C . Since the duplex steel shows a roughly comparable behavior with embrittlement at 475 °C, the damage parameter P SWT is applied to describe the fatigue lives . Therefore, the damage parameter P SWT is shown for the duplex, ferritic and austenitic steels in Figure .…”

“…In order to ensure a constant cooling rate down to temperatures of 100 °C during thermo‐mechanical loading, three in‐line air nozzles were placed at an angle of 120° around the specimens. A more detailed description of both servo‐hydraulic systems is given in previous works of the authors' group …”

“…The isothermal fatigue behavior of duplex steels is investigated by Alvarez‐Armas et al, Llanes et al, Gironés et al, Sahu et al Furthermore, Siegmund et al investigate a duplex steel under thermal cycling, and use a model to describe the thermal stresses and strains induced in both the ferritic and austentic phases. In earlier studies of this authors' research associates, the thermo‐mechanical fatigue behaviors of both the duplex stainless steel and the two single‐phase reference steels were investigated. A special feature for the duplex steel is the embrittlement in the temperature range of 280–600 °C, which is caused by spinodal decomposition of the ferritic phase .…”

“…On the basis of the investigations of Kolmorgen et al and additional isothermal fatigue tests on the austenitic and ferritic reference stainless steels, the fatigue‐life results of thermo‐mechanical and isothermal low‐cycle fatigue tests at elevated temperature were re‐evaluated. To this end, the steels with the ferritic (AISI 430), austenitic (AISI 316L), and ferritic–austenitic (SAF 2205) structures were characterized.…”