Comparative study of precipitation effects during aging in superaustenitic and superferritic stainless steels

The concept of designing a steel that would match high corrosion resistance coupled with improved mechanical properties when exposed at elevated temperatures has always been a challenge for a metallurgist. The present paper relates the results of microstructural analysis of two commercial superaustenitic stainless steel grades and a novel experimental grade of superferritic stainless steel. A study of the microstructural stability and attendant mechanical property evolution has been carried out, employing a variety of aging experiments. Following prolonged aging up to 1000 h in the temperature range between 650 and 950 degrees C, microstructure evolution was determined, while the mechanical properties were preliminary assessed via hardness testing. The present study helped clarify the effect of high temperature exposure on the precipitation sequences of both superaustenitic and novel superferritic stainless steels. The heat treatments performed indicate a number of precipitation sequences of intermetallic phases taking place, such as sigma phase formation, clearly specifying a time-temperature regime where care must be taken during the fabrication and use of these materials.