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Aiming to better understand the effects of heat treatment parameters on Ferrite-Austenite phase transformation in a 2304 duplex stainless steel different thermal cycles were applied to this steel in a quenching dilatometer. The obtained microstructures were characterized by optical microscopy, transmission electron microscopy and electron backscatter diffraction. It was noticed that the austenite formation mechanism is strongly dependent on initial ferritized state. If the initial structure is completely ferritized, the nitrogen supersaturated solid solution leads to chromium nitrides precipitation and the rate of austenite nucleation decreases. For higher cooling rates, the ferrite grain boundaries control the austenite nucleation rate. The higher the ferrite grain size, the lower the final austenite fraction. If the steel is cooled from a partial ferritized state, the ferrite-austenite phase boundaries work as austenite nucleation site and the austenite growth rate is favored due to the high interfacial energy and the austenitic structures becomes coarser.

Vastly used due to their functional properties, NiTi shape memory alloys have mechanical properties and fatigue resistance known to be strongly affected by their thermomechanical state. In this work, the goal was to evaluate the fatigue resistance of near equiatomic Ni-rich NiTi heat treated wires in different tests temperature. In this manner, it was possible to evaluate the phase constitution effect on the fatigue resistance with a fixed thermomechanical condition. For that, a heat treatment at 500 °C for 30 min was performed in initially superelastic wires in an argon atmosphere. DSC tests were performed in order to obtain the transformation temperatures and there different fatigue test temperatures were chosen according to the phase stability ranges. Rotating-bending fatigue tests took place in proper equipment at 4% maximum strain, evaluating the properties of structures constituted by the R-phase, austenite and R-phase + austenite, in each selected test temperature. The results showed that the R-phase presents higher low-cycle fatigue resistance than austenite and a fatigue mechanism was proposed.

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