An Introduction to Stainless Steels

It is undeniable that despite the technological progress of the past 250 years, steel still plays a key role in modern technology, and in the public imagination it continues to be the benchmark material to be compared with the latest that have been developed. For a long time, steel has been considered the universal material, and research in the past has led to the development of countless types of this material. As happens quite often in research and development, almost by accident it was noticed that the addition of chromium to steel improved its corrosion resistance properties. This was the incipit for the birth of stainless steels, a family of alloys characterized by an interesting combination of corrosion resistance and the possibility of tailoring mechanical and technological properties. Since that time, major families of stainless steels have been developed, and the continuing need to meet new challenges in applications has led to the formulation of increasingly complex compositions to give rise to new, higher-performance materials. With regard to stainless steels, the main driving force for development is often the corrosion resistance improvement with the goal of approaching, if not exceeding, the performance of a family of alloys that are in some ways close relatives to some stainless steels, but more expansive and based on another metal: nickel alloys. This race for improvement led to the development of high-performance stainless steels, among which the most similar group to nickel alloys stands out: superaustenitic stainless steels. In order to fully understand the characteristics of this group of alloys, a necessary step lays in the analysis of the other types. This turns out to be a key aspect for understanding the differences, superiority and critical issues of these alloys, as well as the possibilities for their use.