Aluminum-alloyed lightweight stainless steels strengthened by B2-(Ni, Fe)Al precipitates

The age hardenability of Al-alloyed lightweight stainless steels with the base chemical composition Fe- 10.5Cr-3Al (wt.%) and Ni concentrations in the range 3-15 wt.% was studied. Alloys containing 3% and 6% Ni exhibited almost fully ferritic matrix microstructures and a weak age hardening response. Alloys containing 9%, 12%, and 15% Ni, on the other hand, developed primarily martensitic microstructures. Differential scanning calorimetry measurements indicated the occurrence of an exothermic reaction in the approximate temperature range 375-625 degrees C. Dilatometry measurements indicated that the exothermic reaction was accompanied by a net contraction. Hardness measurements after aging for 5 min indicated significant hardening of alloys already at 350 degrees C due to the formation of B2-(Ni,Fe)Al intermetallic precipitates. The age hardening response was significantly superior to that of conventional precipitationhardenable martensitic stainless steels. Tensile elongation in the aged condition was negatively influenced by the presence of soft ferrite regions. Processing conditions associated with a fully martensitic microstructure prior to aging are required to render a uniform age hardening response. Guidelines for the development of a new family of lightweight precipitation-hardenable steels with lower raw material costs and a higher corrosion resistance compared to the standard 18Ni maraging steels are provided. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

The age hardenability of Al-alloyed lightweight stainless steels with different Ni concentrations was studied, showing significant impact on microstructures and hardening response. Hardness measurements indicated significant hardening at 350 degrees Celsius, while tensile elongation in the aged condition was negatively influenced by soft ferrite regions. Guidelines for the development of a new family of lightweight precipitation-hardenable steels were provided.