The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermodynamic calculation (TC). It was shown that the ferrite-based lightweight steels with 5 wt.% or 8 wt.% Al were basically composed of ferrite, austenite and κ-carbide. As the annealing temperature increased, the content of the austenite in the steel gradually increased, while the κ-carbide gradually decomposed and finally disappeared. The mechanical properties of the steel with 5 wt.% Al and 2 wt.% Cr, composed of ferrite and Cr7C3 carbide at different annealing temperatures, were significantly inferior to those of others. The steel containing 5 wt.% Al, annealed at 820°C for 50 s then rapidly cooled to 400°C and held for 180 s, can obtain the best product of strength and elongation (PSE) of 31242 MPa·%. The austenite stability of the steel is better, and its PSE is higher. In addition, the steel with higher PSE has a more stable instantaneous strain hardening exponent (n value), which is mainly caused by the effect of transformation induced plasticity (TRIP). When the κ-carbide or Cr7C3 carbide existed in the microstructure of the steel, there was an obvious yield plateau in the tensile curve, while its PSE decreased significantly.
Key words
ferrite-based lightweight steel；microstructure；mechanical properties；TRIP effect；κ-carbide
{{custom_keyword}} /
{{custom_sec.title}}
{{custom_sec.title}}
{{custom_sec.content}}
References
[1].Frommeyer G，Brüx U． Microstructures and mechanical properties of high-strength Fe-Mn-Al-C light-weight TRIPLEX steels[J]． Steel Research International，2006，77 ( 7 ) : 627-633．
[2].Sohn S S, Lee B J, Lee S, et al. Effect of annealing temperature on microstructural modification and tensile properties in 0.35 C–3.5 Mn–5.8 Al lightweight steel[J]. Acta Materialia, 2013, 61(13): 5050-5066.
[3].Yuji SUTOU. High strength and low density alloy based on Fe-20Mn-Al-C [J]. Modern Metallurgy, 2014, 01:37-43.
[4].Central Iron and Steel Research Institute Edited. Physical chemistry phase analysis of steel and iron-nickel base alloys, first ed., Shanghai Science and Technology Press, Shanghai, 1981, pp. 205-209.
[5].GAO Xu-tao, SUN Ji-quan, ZHAO Ai-min, et al. Effect of austempering isothermal-time at bainite field on retained austenite and mechanical properties in TRIP steel [J]. Material Science and Technology, 2011, 19(6): 123-128.
[6].AD Chiro, JH Root, S Yue, The effect of microstructure on the strain-induced transformation of a Si-Mn bainitic steel[C]. //Proc. 37th MWSP conf, Hamilton, Canada: ISS, 1995.
[7].Wei Xi-cheng, Li Lin, Fu Ren-yu. Review on the relation between microstructure and properties of TRIP steel [J]. Journal of Iron and Steel Research, 2001, 13(5): 71-76.
[8].Chan-Young Lee, Junyeong Jeong, Jeongho Han, et al. Coupled strengthening in a medium manganese lightweight steel with an inhomogeneously grained structure of austenite [J]. Acta Materialia, 2015, 84: 1-8.
{{custom_fnGroup.title_en}}
Footnotes
{{custom_fn.content}}
Funding
Shanghai Municipal Science and Technology Commission
{{custom_fund}}
PDF(1994 KB)
({{custom_author.role_en}}), {{javascript:window.custom_author_en_index++;}}
