On the Factors Governing Austenite Stability: Intrinsic versus Extrinsic

Abstract

In this review, we separate the different governing factors on austenite stability into intrinsic and extrinsic factors, depending on the domain defined by austenite grain boundaries. The different measuring techniques on the effectiveness of the governing factors in affecting the austenite stability are discussed. On the basis of the austenite stability, a new alloy design strategy that involves the competition between the intrinsic and extrinsic factors to control the transformation-induced plasticity (TRIP) effect to realize the stronger the more ductile steel is proposed. The present review may provide new insights into the development of novel thermal-mechanical processing to advance the mechanical properties of steels for industrial applications.

The Effect of Adding V and Nb Microalloy Elements on the Bake Hardening Properties of ULC Steel before and after Annealing

“…In annealed samples, factors such as the surrounding structure, the composition of the alloying elements, morphology, and size affect the stability of residual austenite [ 32 ]. Primary banded austenite and other austenites with low stability experience phase transformation at lower strains.…”

Investigation of the Microstructural Evolution during Hot Stamping of a Carburized Complex Phase Steel by Laser-Ultrasonics

“…While the beginning of the phase transformation is nearly identical for all three semi-finished parts and both quenching rates, the transformation curve is shifted to lower temperatures. Due to the additional carburization process and the increased carbon content, the austenitic phase is thermally stabilized [ 39 ]. In the case of a quenching rate of 30 K/s, there were only minor differences between the material conditions regarding T end .…”

The relative contributions of TWIP and TRIP to strength in fine grained medium-Mn steels

“…In TRIP-assisted steels, it is well known that a decreasing grain size has a strong mechanical stabilisation effect on austenite, inhibiting the formation of 𝛼 ′ -martensite [26,48,63]. Additionally, blocky or equiaxed austenite is generally less stable than film or lamellar austenite in medium Mn steels [64,65]. Therefore, it should follow that the WQ samples would form less 𝛼 ′ -martensite than the FC samples at a similar strain since the lamellar width of the WQ samples was much finer than the grain size in the FC samples.…”

“…In Figs. 7d-f, the fine austenite lamella in Area 1 and a wide lamellar austenite grain in Area 4 had different surface area to volume ratios yet both remained largely untransformed, suggesting that other effects such as texture, Schmid factors and stress shielding were possibly also involved [33,[64][65][66]. Nevertheless, in this alloy with a very high austenite stability where the formation of 𝛼 ′ -martensite was nucleation-limited, grain boundary area to volume ratio would have certainly played a significant role among the other factors known to contribute to 𝛼 ′ -martensite transformation.…”