Study of stainless steels modified by additions of boron and nitrogen in order to obtain wear resistant materials with low friction coefficient

Abstract

The oil industry is technologically and economically very important and it has gained a continuously growing interest in Brazil. From the components and materials point of view, there are many challenges on this demanding field, especially considering the severe wear and corrosion environments found offshore. A critical case corresponds to the pipelines used for oil exploitation and drilling, also known as risers. Normally hot rolled stainless steels that show suitable corrosion resistance are used for this type of application. However, depending on the circumstances, their tribological properties might be rather poor. Recently, Prof. Bolfarini, DEMa/UFSCar in a joint effort with Petrobras coordinated a project for the development of modified wear resistant stainless steels prepared by spray forming. Boron additions were conducted in order to precipitate hard boride particles, which were responsible for the improved wear resistance. As a natural follow up for this successful project, another very important tribological property, the friction coefficient, will be investigated in this study. In this context, a metallurgical solution for the simultaneous improvement of wear resistance and to achieve a low friction coefficient was elaborated by adding or precipitating hard and lubricant particles. Among the high performance lubricant materials, hexagonal boron nitride shows outstanding properties due to its structure that is very similar to graphite. Consequently, this proposal is focused on the study of stainless steels modified with nitrogen and boron, prepared via spray forming to obtain in situ precipitation of iron/chromium borides and hexagonal boron nitride. The starting point will be a super duplex stainless steel with 0.3%N (wt.%) and progressive additions of boron according to calculations/simulations to be performed with Thermocalc software. The resistance to corrosion and wear will be evaluated and the results compared with the materials developed to date by the research group, as well as with commercially available materials. (AU)