Density functional theory study of the influence of Ti and V partitioning to cementite in ferritic steels

Abstract

We perform density functional theory calculations to investigate the partitioning behavior of Ti and V between cementite and ferrite. The energetics show that Ti and V partition to cementite. The chemical bonds in Ti-and V-substituted cementite are stronger than that of cementite, and these alloyed cementite are more stable than cementite. Furthermore, the elastic properties of alloyed cementite are investigated.Ferromagnetic Ti-and V-substituted cementite are mechanically stable, but non-magnetic Ti-and V-substituted cementite are mechanically unstable. Ti and V partitioning can enhance the resistance to shear strain, the stiffness and the stability against shear of ferromagnetic cementite. Finally, we present the electronic structures to understand the bonding properties of the alloyed cementite.

Site preference of manganese in Mn-alloyed cementite

“…After optimization of geometric structure, the lattice constants and equilibrium cell volume of (alloyed) cementite are shown in Table . The calculated lattice constants and equilibrium cell volume of cementite agreed with the reported experimental and theoretical results. Table shows that cementite exhibits small lattice distortion after Mn atoms replaced Fe atoms at varying contents and occupancies, but the orthorhombic crystal structure of cementite does not change.…”

“…By comparison the DOS of Fe 2 MnC at different sites, it is found that the DOS at the Fermi level of Fe 2 MnC with Mn substitutions at the 8d sites is smaller than those at the 4c and 4c + 8d sites. The stability of compounds usually can be reflected by the DOSs of the Fermi level: the smaller the DOSs at the Fermi level, the more stable the crystal structure . Therefore, from the DOS results of alloyed cementite Fe 2 MnC, Fe 2 Mn(8d)C is more stable than Fe 2 Mn(4c)C and Fe 2 Mn(4c + 8d)C, which is consistent with the energetic results as mentioned in the Section 3.2.…”

“…Cementite was modeled by using a 16‐atom cell (Fe 12 C 4 ), which exhibited a complex orthorhombic structure and a space group of Pnma (62) with 8 symmetry operations (Fig. ) . Alloyed cementite Fe 23 MnC 8 (Mn at.% = 3.125 at.%) was modeled by replacing one of the Fe atoms at 4c or 8d sites of a 1 × 1 × 2 supercell.…”

“…Many researchers have found that heavily cold‐drawn deformation causes partially decomposition and structural transition of cementite, which plays an extremely important role in the strengthening mechanism of pearlitic steel wires . Recently, pearlitic steels with microalloying elements, such as Mn, Cr, V, and Si, have attracted more attention . It has been consistently found that the carbide‐forming elements, such as Mn, Cr, and V , partition to the cementite phase, while the noncarbide‐forming elements, such as Si, Al, Ni, and Co , have a higher concentration in the bcc α‐Fe phase.…”

“…It has been consistently found that the carbide‐forming elements, such as Mn, Cr, and V , partition to the cementite phase, while the noncarbide‐forming elements, such as Si, Al, Ni, and Co , have a higher concentration in the bcc α‐Fe phase. Also, the effects of alloy elements (such as Mn , Cr , Co , Ni , V , and Ti ) on the structural, magnetic, electronic, and other properties of bulk cementite have been theoretically studied. Thus far, researchers have investigated the site preference of alloying element atoms in cementite via theoretical calculations, but most of them lack supporting experimental data.…”