Effect of Mn and C on Age Hardening of Fe–Mn–Al–C Lightweight Steels
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The effects of Mn and C content on the age hardening of Fe–Mn–Al–C lightweight steels, which have austenitic or duplex (austenite and ferrite) microstructures, were investigated. An increase in Mn content induced a delay of the age hardening that is caused by the formation of intra-granular κ-carbides. In order to interpret the effect of Mn content, first-principles calculations were conducted using the supercells of Fe24Al8C8, Fe24Al8C7, Fe24(Al7Mn)C8, and Fe24(Al7Mn)C7. The calculations showed that an increase in Mn content could be the source of the delay of the intra-granular κ-carbide formation by suppressing C atom’ occupation of the vacancy at the body-centered site of L12. An increase in C content accelerated the formation of intra-granular κ-carbides, which induced the intense age hardening, and coarse inter-granular κ-carbides, which resulted in significant decrease in impact absorbed energy due to inter-granular fracture.
KeywordsLightweight steel Age hardening κ-carbide First-principles calculations Manganese Carbon
This work was funded by the Fundamental R&D Program (Development of technologies for commercial manufacturing of light-weight steels for power plant components, Grant No.: PNK5690) of Korea Institute of Materials Science (KIMS) and by the Materials and Components Technology Development Program (10048157) funded by the Ministry of Trade, Industry and Energy (MOTIE, Korea).
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