Anomalous cyclic behaviour of ferritic stainless steels

A. ARMAS, M. AVALOS, J. MALARRIA, I. ALVAREZ-ARMAS, C. PETERSEN

Garmisch-Partenkirchen

Conferencia; 4th International Conference on Low Cycle Fatigue and Elasto-Plastic Behaviour of Materials; 1998

The strain cyclic behaviour of high-chromium ferrite stainless steels (AISI 430F, AISI 420 and MANET II) has been investigated at temperatures ranging from room temperature to 823 K. Cyclic hardening curves of type AISI 430F steel show a strong temperature dependence. A pronounced cyclic hardening and increase in saturation peak stress is observed between 623 and 773 K where the flow stress for the first tensile stroke at the maximum strain is independent of the temperature. For fully annealed AISI 420 initial hardening followed by saturation is the characteristic feature observed in this steel between 523 and 723 K. Normalized and tempered MANET II (a variant of the German steel DIN Nr. 1.4914) softens during cyclic loading at all temperatures. Negative strain rate sensitivity was observed plotting the peak tensile stress difference between hysteresis loops at different strain rates. It is proposed that dynamic strain ageing mechanism caused by the drag of solution carbon atoms is responsible for the unusual cyclic behaviour observed in these steels.