Análisis del comportamiento cíclico a temperaturas intermedias de aceros dúplex basado en las tensiones de retroceso y fricción

S. HEREÑÚ,; I. ALVAREZ-ARMAS; S. DEGALLAIX; A. CONDÓ; F. LOVEY; A. F. ARMAS

Rosario,Argentina

Conferencia; 4ª CONFERENCIA SOBRE USOS DEL ACERO DEL IAS; 2008

Instituto Argentino de Siderurgia

Low cycle fatigue (LCF) behaviour at different temperatures of duplex stainless steel (DSS) SAF 2507 samples with two thermal treatment conditions: as-received (unaged) and aged (100 hours at 475ºC) has been studied. Cyclic tests were carried out on an electromechanical testing machine under plastic strain control using a fully reversed triangular form signal. The specimens were tested in air in the temperature range between 20 and 500ºC. The average total strain rate of the tests was maintained at 2 x 10-3 s-1.  In order to have a complete understanding of the cyclic response, the corresponding cyclic flow stress components, the friction and the back stresses have been analyzed in relation with the microstructure observed. The friction stress attains higher levels at room temperature than at intermediate temperatures in both thermal conditions due to the lattice friction stress experienced by screw dislocations in the ferrite phase. The cyclic softening observed in aged samples at all temperatures is caused by the decrease of the back stress. The demodulation of the initial spinodal decomposition could be responsible for such behaviour. On the other hand, the increase of back stress in unaged samples at 300°C is consistent with the high dislocation density observed in the ferrite phase ascribed as a typical manifestation of DSA.