Avaliação da formação da austenita no revenimento do aço inoxidável supermartensítico e seu efeito nas propriedades mecânicas e resistência à corrosão localizada

Abstract

Encouraged by the oil and gas industry, supermartensitic stainless steels were developed as an evolution of martensitic stainless steel. They are characterized as an intermediate alternative between martensitic and duplex stainless steels in terms of corrosion resistance and manufacturing cost. In this work, the influence of the austenite formation during tempering in the mechanical properties and resistance to localized corrosion was evaluated by performing heat treatment in different tempering conditions, varying its temperature, its soaking time at 650°C and the number of tempering cycles (single and double tempering). Microstructural analyses were performed by scanning electron microscopy (SEM) and X ray diffraction (XRD). The mechanical properties were evaluated by microhardness and tensile tests. The tensile fracture surfaces were also evaluated. The localized corrosion resistance was investigated by cyclic potentiodynamic anodic polarization. The results showed that the increase of the tempering temperature in the range of 615 to 700°C causes the rise and reduction of retained austenite fraction according to tempering temperature, even the austenite formation is always increasing. In the other hand, increasing the soaking time from 15 min to 24 h at 650°C also enlarges the austenite formation, but lower difference in terms of retained austenite fraction was observed, mainly between 2 h and 24 h. Furthermore, with the double tempering, the retained austenite fraction has a significant growth. No influence of austenite formation during tempering on localized corrosion was observed, considering the technique and conditions used in this work