Effects of Temperatures of Rolling and Annealing on Microstructures and Tensile Properties of Low Carbon Ferritic Low Density Steels

The microstructural modification and the effect of cold/warm rolling and annealing on tensile properties of ferritic low density steels containing different amounts of carbon (0.0035 mass%, Steel 1 and 0.04 mass%, Steel 2) and aluminium (6.8 mass%, Steel 1 and 9.7 mass%, Steel 2) were investigated with respect to amount of ferrite, grain size and formation of Fe3Al intermetallic. The Steel 1 was deformed by cold rolling at room temperature and Steel 2 was deformed through warm rolling at 250 degrees C to avoid prior cracks formation. After rolling, samples of Steels 1 and 2 were annealed at 900 degrees C for 5 minutes. The yield strength, ultimate tensile strength and ductility increase while yield ratio decreases with annealing. This is due to formation of Fe3Al intermetallic and reduction of ferrite grain size. Due to high interstitial Carbon in Steel 2, yield point phenomenon was observed which may reduce the formability of the steel. The cracks started during tensile test at the ferrite grains and ferrite grain boundaries and the fracture took place in the quasi cleavage mode in Steels 1 and 2. The grain refinement and the microstructural features due to rolling and annealing are accountable for the good combination of strength and ductility of the both steels.

Automated summary

This study investigated the microstructural modification and the effects of cold/warm rolling and annealing on the tensile properties of ferritic low density steels with different carbon (0.0035 mass%, Steel 1 and 0.04 mass%, Steel 2) and aluminium (6.8 mass%, Steel 1 and 9.7 mass%, Steel 2) contents, focusing on the amount of ferrite, grain size, and formation of Fe3Al intermetallic. Steel 1 was deformed by cold rolling at room temperature, while Steel 2 was deformed through warm rolling at 250 degrees C to prevent crack formation. After rolling, samples of Steels 1 and 2 were annealed at 900 degrees C for 5 minutes. The annealing process resulted in an increase in yield strength, ultimate tensile strength, and ductility, as well as a decrease in the yield ratio. This was attributed to the formation of Fe3Al intermetallic and reduction in ferrite grain size. The presence of high interstitial carbon in Steel 2 led to a yield point phenomenon, which may negatively impact the steel's formability. Cracks initiated at the ferrite grains and grain boundaries, and fracture occurred in a quasi cleavage mode in both Steels 1 and 2. The grain refinement and microstructural changes due to rolling and annealing contributed to the good combination of strength and ductility in both steels.