Abstract
In this paper, analytical results are compared for the newly developed steels, Fe-Mn-Al-C (X105) and Fe-Mn-Al-Nb-Ti-C (X98), after being hot-rolled and also after undergoing thermomechanical treatment in a Gleeble simulator. These steels have a relatively low density (~6.68 g/cm3) and a content of approx. 11% aluminum. The multistage compression of axisymmetric samples constituting a simulation of the real technological process and hot-rolling performed on a semi-industrial line were carried out using three cooling variants: in water, in air, and after isothermal heating and cooling in water. The temperature at the end of the thermomechanical treatment for all variants was 850 °C. On the basis of detailed structural studies, it was found that the main mechanism for removing the effects of the strain hardening that occurred during the four-stage compression involved the dynamic recrystallization occurring in the first and second stages, the hot formability and dynamic recovery in successive stages of deformation, and the static and/or metadynamic recrystallization that occurred at intervals between individual deformations, as well as after the last deformation during isothermal heating. Analysis of the phase composition and structure allowed us to conclude that the tested steels have an austenitic-ferritic structure with carbide precipitates. Research using scanning and transmission electron microscopy identified κ-(Fe, Mn)3AlC and M7C3 carbides in both the analyzed steels. In addition, complex carbides based on Nb and Ti were identified in X98 steel; (Ti, Nb)C carbides occurred in the entire volume of the material. Slow cooling after thermomechanical treatment influenced the formation of larger κ-carbides at the border of the austenite and ferrite grains than in the case of rapid cooling. The size and morphology of the carbides found in the examined steels was varied. Back-scattered electron diffraction studies showed that wide-angle boundaries dominated in these steels.
Highlights
IntroductionDue to their excellent mechanical properties, relatively high plasticity, and forecasted relatively low production costs (e.g., no heat treatment), Fe-Mn-Al-C steels, which are the subject of this analysis, can be potentially used for elements of transport infrastructure and vehicles such as cars, buses, or trains, as well as in all kinds of constructions where the weight of the structure is one of the most important criteria for the selection of materials [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]
For X98 steel at a temperature of 1050 ◦ C, the deformation εmax was 0.18 and increased to about 0.25 with a decrease in the compression temperature to 850 ◦ C
In the case of X105 steel, the deformation εmax had a value of 0.16 at 1150 ◦ C and increased with the reduction in the compression temperature to 850 ◦ C to about 0.28, so the plasticizing deformation values increased by about 75%
Summary
Due to their excellent mechanical properties, relatively high plasticity, and forecasted relatively low production costs (e.g., no heat treatment), Fe-Mn-Al-C steels, which are the subject of this analysis, can be potentially used for elements of transport infrastructure and vehicles such as cars, buses, or trains, as well as in all kinds of constructions where the weight of the structure is one of the most important criteria for the selection of materials [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. There has been a development of steels with reduced density, which include Fe-Mn-Al-C steels with a 15% lower density compared to typical structural steels [4,17,18,19,20,21,22,23,24] In their papers, Chen et al presented the division into different structures of Fe-Mn-Al-C steel with reduced density after hot-rolling (Figure 1) [1,2,4]. Chen et al presented the division into different structures of Fe-Mn-Al-C steel with reduced density after hot-rolling (Figure 1) [1,2,4] They described that, depending on the content of alloying elements such as Al, Mn, and C, the structure of these steels. In Fe-Al-Mn-C alloys with a high manganese content (above 10%), Mn atoms take the place of Fe atoms in the above carbide, and the stoichiometry of the Fe3 AlCx carbide is transformed into (Fe, Mn) AlCx [18,25,26]
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