Corrosion Resistance Comparison of Two Maraging Stainless Steels for Aerospace Application

Martensitic stainless steels owe their high strength to ageing heat treatments, inducing hardening phases precipitation. The temperature of these treatments is around 450-550°C and the nature of the precipitates varies according to the steel’s chemical composition.

This specific microstructure induces structural hardening and thus properties that meet the requirements of sometimes critical aeronautical structural parts. Thanks to a beneficial compromise between a mechanical strength (UTS) from 1,500 to 1,800 MPa and a fracture toughness (K_IC) from 70 to 100 MPa√m, these steels are suitable for severe conditions in service.

In this context, Aubert&Duval produces MLX^®465 (AMS5936) and MLX^®17 (AMS5937) grades, which are high strength steels with similar mechanical properties completed with good corrosion resistance thanks to a content of chromium (> 11 wt.%) associated with molybdenum.

However, the higher amount of molybdenum for MLX^®17 leads to a different corrosion behavior. This study focuses on the impact of this difference on the pitting corrosion resistance as well as stress corrosion cracking sensibility.

The advantage of MLX^®17 compared to MLX^®465 lies in its better passive layer stability, as demonstrated with the pitting corrosion tests. Globally, the results showed that MLX^®17 presents the best balance between mechanical properties and corrosion resistance.