Effect of κ Carbides on Deformation Behavior of Fe-27Mn-10Al-1C Low Density Steel

Abstract

Fe-Mn-Al-C steel, which is a potential lightweight material for automobiles, has a variety of microstructures and good mechanical properties. The effect of κ carbides on the mechanical properties and strain hardening rate of Fe-27Mn-10Al-1C (wt.%) low density steel was studied by short-time heat treatment to control the precipitation behavior of κ carbides. Quenched specimens have an excellent combination of strength and plasticity and continuous high strain hardening rate, which is due to the uniform distribution of κ carbides with an average size of 1.6 nm in an austenite matrix. The fracture mode of the sample changed from ductile fracture to cleavage fracture, which was because the aging treatment promoted the precipitation of B2 phases and κ carbides at grain boundaries. The size and volume fraction of nanoscale κ carbides in austenite grains increase with the increase of aging temperature, and the yield strength increases but the density of slip bands decreases, resulting in the gradual decrease of strain hardening rate.

The effect of nano-sized κ-carbides on the mechanical properties of an Fe-Mn-Al-C alloy

“…As it appears, the SRO is not clearly visible in the part of the carbide annotated with the yellow dashed line, which is caused by the glide planar softening effect that has been described in [19,27]. Also, a small step can be observed, which indicates that the specific carbide has been sheared by dislocations.…”

“…In Figure 10, the same area of a single grain of the 550_8 sample after tensile deformation with a strain of 2% was studied via STEM (Figure 10a), DF TEM (Figure 10b), and TKD (Figure 10c-e). From the STEM image, the formation of micro-bands can be observed between the dislocation walls [27]. Inside the bands, gliding dislocations also appear.…”

“…This means that the intermediate distance or the size of the austenite channels between the carbides is larger in the 600_1 sample. The dislocations glide [26] during deformation and interact with the κcarbides by shearing them [23,27]. The shearing occurs as the carbides are coherent with the austenite matrix.…”

Microstructure evolution and mechanical behavior of Fe–Mn–Al–C low-density steel upon aging

“…Hence, this sample exhibits higher UTS and YS but decreased work-hardening. This decrease is attributed to the decrease of the slip band density and the softening effect caused by the shear of the κ-carbides [76]. The softening effect takes place as the leading dislocation gliding through the lattice meets the κ-carbide and destroys the SRO while shearing the carbide, and therefore, the following dislocations glide more easily, thus explaining the change in the slope of the tensile curves.…”