FEMNAL – A NEW LIGHTWEIGHT STEEL FOR MILITARY VEHICLES

Paper #:
  • 2017-01-1703

Published:
  • 2017-03-28
Abstract:
FeMnAl is in a class of steels called Hadfield steel. This paper will present details, including ballistic performance, Johnson Cook coefficients, and other previously published and unpublished data for the specific alloy: Fe-30Mn-9Al-1Si-.9C-.5Mo. This particular alloy exhibits improved performance over Rolled Homogenous Armor (RHA) at equivalent aerial density. It has tunable ductility (>40% ductility) and corrosion resistance similar to 340 stainless steel. Because it has the equivalent volumetric ballistic properties to RHA at a reduced density, it can be introduced into current vehicles for any RHA component without changing part thickness or geometry. This allows current interfaces with other components to be maintained and achieve a 10% weight reduction without any change in ballistic performance. This makes introduction of this material as a weight reduction technology less costly than using a material that requires a different thickness to meet ballistic requirements. FeMnAl is a fully austenitic steel with increased strength and hardness from homogeneous and consistent precipitation of κ-carbide. But, because of its high aluminum content and relatively low iron content, it is barely a steel. Ballistically it behaves like a steel. From a corrosion and a work hardening perspective, it behaves more like an aluminum. The alloy was specifically designed to be relatively low cost to produce. It is age hardened at a relatively low temperature of 550°C to avoid grain boundary precipitation. FeMnAl appears to be relatively robust to impurities and therefore does not require hipping. And it is remarkable that the cast product has superior ballistic performance to RHA. However, FeMnAl high manganese and aluminum content mean that work hardening prevents cold rolling to create wrought product. The wrought product would be created from a cast ingot that is hot rolled. To date only the cast product has been evaluated. Future work will evaluate the wrought properties.
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