Estudo da reversão da austenita em aço inoxidável martensítico-ferrítico para aplicação no setor de óleo e gás

Abstract

The microstructural evolution of dual-phase stainless steel with a martensitic-ferritic structure (AIMF) was investigated using in-situ high temperature X-ray diffraction. The tempering of this alloy is performed for adjustment of properties, and such treatment is accomplished at intercritical temperatures. The stability of austenite formed during this treatment depends on a number of factors, such as the local chemical composition, temperature and soaking time. After cooling, some amount of this reversed austenite may transform into untempered martensite while other part stay retained. To better understand the effect of retained austenite in this new alloy of AIMF and than verify if it is possible to improve this material properties it is essential to know the evolution and the relationship between these microstructures during tempering. In this work, the formation of reversed austenite was analyzed by means of HT-XRD at different temperatures and times. Specimens were also characterized using optical and scanning electron microscopy. Mechanical properties as strength, hardness and toughness were evaluated at different tempering conditions. It was observed that there is a critical tempering temperature in which reverted austenite tends to stabilize and remain untransformed during cooling. Nevertheless, beyond the presence of retained austenite was also detected precipitation of other phases which may have damaged the material toughness.