Properties assessment of the first industrial coils of low-density duplex δ-TRIP steel

Abstract

A novel low-density steel with high aluminium content was, for the first time, manufactured as coils by the conventional industry process consisting of continuous casting followed by hot-rolling and cold-rolling. The duplex δ-TRIP microstructure, comprising a mixture of blocky retained austenite and both δ- and α-ferrite, was then produced by laboratory-scale heat treatments. The microstructure generation was achieved by an intercritical annealing followed by direct quenching, which was the same process as that for producing conventional dual-phase steels. The alloy exhibits quite interesting mechanical properties with a combination of 930 MPa tensile strength and of 21% total elongation, both in rolling and transverse directions. The formability of this novel alloy was assessed and discussed.

Challenges in the formability of the next generation of automotive steel sheets

“…The δ-TRIP alloys perform UTS × TEL exceeding 30 GPa %. In addition, they have a density approximately 5% lower than conventional automotive steels [30][31][32][33][34][35]. The tensile curves exhibit potential for good formability (Figure 1) [32,34,35].…”

“…The first industrial coils of δ-duplex TRIP alloy were manufactured in 2014 [17]. The δ-duplex TRIP achieve 900 MPa strength combined with approximate 20% of total elongation, similar to DP780 steels [30]. However, the very low R -value lower than 0.4 and severe δ-ferrite texture lead to very poor formability compared to DP780 [17].…”

Regulating tensile properties through bainitic transformation temperature in a hot-rolled δ-TRIP steel

“…This can further stabilise retained austenite. In addition, Al can similarly accelerate the formation of bainite [1,16,17] and facilitate formation of δ-TRIP steels [18,19]. δ-TRIP steels have been recently proposed as a new group of advanced high strength steels for automotive industries [20].…”

Effects of Al content on the high-temperature mechanical properties of Al-TRIP steel

“…It is expected that δ-TRIP steel will become a useful material for automotive structural parts because of its low density, moderate product of ultimate tensile strength (UTS) and total elongation (TE), and excellent welding properties [2,3]. Many studies on the mechanical properties [4][5][6] and microstructure [6][7][8][9] have been reported. At present, the Al content of industrial aluminiumalloyed TRIP steel is generally 0.5-2 wt-%.…”