Extraordinary ductility in Al-bearing δ-TRIP steel

Abstract

An iron-based alloy system has been developed that exhibits impressive combinations of tensile strength and elongation that are not available with current steels used in the manufacture of automobiles. Furthermore, the heat treatments required to achieve these properties are consistent with practical production processes. The alloys rely on significant concentrations of ferrite-stabilizing solutes so that d-ferrite which forms during solidification is retained in the microstructure.

Thermal stability of retained austenite in bainitic steel: an in situ study

“…Applications range from the formable alloys for the automobile industry (Matsumura et al 1987a,b), ductile cast irons (Rundman & Klug 1982), railway lines (Yates 1996;Bhadeshia 2007) and armour Bhadeshia 2005). There also exist many variants of the basic concept, which are the subject of intense research from both a fundamental and an applied perspective (Saha Podder et al 2007;Stone et al 2008;Menapace et al 2009;Sugimoto 2009;Caballero et al 2010;Yi et al 2010). Structures of this kind, but on a scale finer than carbon nanotubes, can now be produced on a commercial scale, as reviewed recently (Bhadeshia 2010).…”

Retention of δ-ferrite in aluminium-alloyed TRIP-assisted steels

“…The allotriomorphic ferrite is generated either by transformation from austenite or by inter-critical annealing (Bhadeshia 2001). There may be an advantage in replacing such ferrite with stable d-ferrite that is retained from the solidification process (Chatterjee et al 2007;Yi et al 2011a). This is because the steel cannot ever be made fully austenitic.…”

“…This means that it is not possible during resistance spot-welding to create a fully martensitic heat-affected zone, which, because of the high carbon concentration, embrittles the joint. The new class of steel that relies on the permanent presence of d-ferrite is known by the name d-TRIP steel and seems to show extraordinary combinations of mechanical properties (Yi et al 2011a).…”

Overview of Lightweight Ferrous Materials: Strategies and Promises

“…33,34 In these steels, a large amount of dferrite is retained in the microstructure from the solidification process at all temperatures. The remainder of the microstructure in d-TRIP steels consists of bainitic ferrite and retained austenite.…”

“…The pure high Al-containing ferritic steels can be interstitial free (IF) 20 and bake hardenable; 28 some of the low-density steels containing austenite are precipitation hardenable (by j-carbides). 21,[29][30][31] Others could involve transformation-induced plasticity (TRIP; including d-TRIP), [32][33][34] twinning-induced plasticity (TWIP), 18,22,35,36 shear band induced plasticity (SIP), 19 or micro band induced plasticity (MBIP), 37,38 depending on the alloy composition and processing parameters. Furthermore, the duplex steels can sometimes contain certain amounts of F m3m -type D0 3 or CsCl-type B2 phase formed due to decomposition of L'12 j-carbides during an ordering heat treatment.…”