Understanding the role of aluminium in low level nitrogen steels via microstructural characterisation

Abstract

The mechanical and microstructural properties of steels can be affected by dopant elements or the presence of impurities. Aluminium has historically been added to steels principally as a de-oxidant but it has also been shown to have a significant effect on the mechanical properties. It is well known that aluminium usually combines with nitrogen to form A1N precipitates at high temperature mostly in austenite (dependent on the relative concentrations of Al and N). Aluminium therefore acts as a grain refining element. A series of low carbon, low nitrogen steels have been prepared with varying additions of aluminium up to 1 wt%. These changes in properties of the steel cannot be attributed to the presence of aluminium nitride and hence it important to understand the specific role and mechanism which the aluminium plays. The location, concentration and chemistry of the aluminium have been investigated using SEM and TEM. The results show clear evidence for segregation of aluminium to the grain boundaries. © 2008 IOP Publishing Ltd.