Strain rate effects on tensile deformation behavior of Fe‐3.5Mn‐0.3C‐5Al ferritic based lightweight steel

Tensile deformation behavior of Fe‐3.5Mn‐0.3C‐5Al ferritic based lightweight steel was studied in a large range of strain rate (0.001 s−1–1200 s−1). Microstructures of the steel before and after tension were observed. The results show that Fe‐3.5Mn‐0.3C‐5Al lightweight steel has a good strength (820 MPa) and plasticity (40 %) and exhibits excellent combinations of specific strength and ductility (>32000 MPa %) at the strain‐rate of 0.001 s−1 after annealing at 850 °C for 5 minutes then directly quenching into water. The austenite in the steel tested was transformed into α′‐martensite during the tensile deformation process. With an increase in strain rate from 0.001 s−1 to 1200 s−1, tensile strength of the steel investigated increased from 820 MPa to 932 MPa, while its elongation first decreased from 40 % to 15 %, and then increased from 15 % to 29 %. At the strain rate of 1200 s−1, adiabatic heating resulted in temperature rising in matrix, suppressed the transformation of austenite to α′‐martensite. Comparing with transformation induced plasticity steel, the austenite in 3.5Mn lightweight steel is obviously unstable and cannot provide progressive phase transition. With an increase in strain rate 0.001 s−1 –1200 s−1, tensile strength of the steel investigated increased 820–932 MPa, while its elongation first decreased 40 %–15 %, and then increased 15 %–29 %. Value n increases from small to large. When the deformation is near the end, the strain hardening value increase rapidly, and then breakage occurs. The strain hardening exponent n of transformation induced plasticity steel is almost in a constant state.