Partitioning of C into κ-carbides by Si addition and its effect on the initial deformation mechanism of Fe-Mn-Al-C lightweight steels

The effect of Si addition on the initial deformation mechanism of Fe-30Mn-9Al-0.9C-0.5Mo cast lightweight steel has been investigated. Atomic-scale analysis by three-dimensional atom-probe tomography confirmed that Si addition accelerates the formation kinetics of the kappa-carbide, and increases remarkably the partitioning coefficient of carbon by more than 2 times. Promotion of C partitioning into kappa-carbides by Si addition leads to deformation localization in an aged state. This is attributed not only to the increase of the kappa-carbide size associated with higher coherency strain, but also to higher frequency of Al-C bonding formation. First-principles calculations indicated that the energy required for a/2<110> shearing of K-carbide in the aged 1%-Si steel is higher (561 mJ/m(2)) than that in the aged Si-free steel (494 mJ/m(2)). Therefore, Si addition leads to a significant energy difference for shearing and results in different shear bands formation. The operative deformation mechanism can be calculated for this alloy system as a function of precipitates volume fraction and size. It was determined that deformation proceeds primarily by kappa-carbide shearing as long as the radius of kappa-carbides is smaller than 13.4 nm. (C) 2018 Elsevier B.V. All rights reserved.