Effects of dilute substitutional solutes on interstitial carbon inα-Fe: Interactions and associated carbon diffusion from first-principles calculations

Abstract

By means of first-principles calculations coupled with the kinetic Monte Carlo simulations, we have systematically investigated the effects of dilute substitutional solutes on the behaviors of carbon in α-Fe. Our results uncover that: (i) Without the Fe vacancy the interactions between most solutes and carbon are repulsive due to the strain relief, whereas Mn has a weak attractive interaction with its nearest-neighbor carbon due to the local ferromagnetic coupling effect. (ii) The presence of the Fe vacancy results in attractive interactions of all the solutes with carbon. In particular, the Mn-vacancy pair shows an exceptionally large binding energy of -0.81 eV with carbon. (iii) The alloying addition significantly impacts the atomic-scale concentration distributions and chemical potential of carbon in the Fe matrix. Among them, Mn and Cr increase the carbon chemical potential whereas Al and Si reduce it. (iv) Within the dilute scale of the alloying solution, the solute concentration and temperature dependent carbon diffusivities demonstrate that Mn has a little impact on the carbon diffusion whereas Cr (Al or Si) remarkably retards the carbon diffusion. Our results provide certain implication for better understanding the experimental observations related with the carbon solubility limit, carbon micro-segregation and carbide precipitations in the ferritic steels.

The role of silicon, vacancies, and strain in carbon distribution in low temperature bainite

“…From the binding energies calculated for the octahedral and tetrahedral positions for C, the activation energy or energy barrier to diffuse the C atom from one octahedral to another octahedral position through the tetrahedral interstitial in a pure Fe system, was determined to be ∆E =0.87 eV [12,24], which agrees well with experimental results [26,27]. The changes of these energy barriers in the presence of Si lead to the effect that at lower C concentrations, Si diminishes the C diffusivity [25].…”

“…In general, ab initio results indicate a repulsive interaction of C with substitutional Si in ferrite [24,25] , but the excess solution enthalpy for Fe-C and Fe-Si-strongly depends on the interatomic distance. From the binding energies calculated for the octahedral and tetrahedral positions for C, the activation energy or energy barrier to diffuse the C atom from one octahedral to another octahedral position through the tetrahedral interstitial in a pure Fe system, was determined to be ∆E =0.87 eV [12,24], which agrees well with experimental results [26,27].…”

Comparative Effect of Mo and Cr on Microstructure and Mechanical Properties in NbV-Microalloyed Bainitic Steels

“…A higher binding energy means that a higher activation energy is required for C atom to jump into another position. The carbon diffusivity in Fe also changes in the presence of different solutes and it was reported for both Cr and Mo that the activation enthalpy for carbon diffusion in iron increases [70][71][72]. However, the carbon diffusivity in ferrite was decreased more in the presence of Mo than of Cr [73].…”

Effects of Nb and C Addition on Corrosion Resistance of Metal-Injection-Molded 440C Stainless Steel

“…Moreover, the samples with Nb exhibited a lower decarburization rate during sintering. Because Nb can form carbides with carbon and retard the diffusion of carbon, the carbon atoms become more difficult to shift to the surface of the sample for reaction with the atmosphere [8]. The densities of the samples reached much the same level, and densification was almost completed (> 97%), as shown in Table 2; therefore, the effects of density on corrosion resistance may be ignored.…”