Microstructural Evolution and Mechanical Properties Co-relation of Cold-Rolled Ferritic Lightweight Steel with Increasing Carbon

Abstract

The structure-properties relationship of cold-rolled and annealed Fe-7 wt. % Al lightweight steels for varying carbon contents is explored in this work. Unlike Fe-Mn-Al-C based steels, which experienced processing issues, the hot-worked plates of the present steel were successfully cold-rolled to 2mm thick sheets. Various phases present in the steel for different carbon contents as predicted using the Thermo Calc programme are in line with the experimental findings. The basic alloy with 0.01C contains only a ferrite phase, however, the alloys with higher carbon content have a significant quantity of κ-carbide precipitates. The addition of carbon to Fe-7 wt. % Al steel has improved its tensile strength significantly (438 to 828 MPa). Tensile elongation, on the other hand, has decreased dramatically (26 to 12 per cent) with increasing carbon content The reduction in ductility with increasing carbon is mainly ascribed to the increasing κ-carbide precipitates volume fraction with higher hardness, but not due to the environmental embrittlement as observed in case of higher Al containing steels.


optical micrographs showing the microstructure of cold-rolled and annealed Fe-7Al steel with (a) 0.01, (b) 0.15, (c) 0.35 and (d) 0.5wt.% carbon.
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Scanning electron micrographs showing the microstructure of cold-rolled and annealed Fe-7Al steels with (a) 0.01, (b) 0.15, (c) 0.35 and (d) 0.5wt.% carbon. The volume fraction of carbides increases with increase in carbon content.
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Engineering stress-strain curves for tensile samples of cold-rolled and annealed Fe-7Al steel with different carbon content.
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Scanning electron micrographs showing the room temperature tensile fracture surface of cold-rolled and annealed Fe-7Al steel with: (a) 0.01, (b) 0.15, (c) 0.35 and (d) 0.5wt.% carbon. (Insert in the bottom-left are the fracture surface of the same composition at higher magnification respectively).
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