High-throughput compositional mapping of phase transformation kinetics in low-alloy steel

Abstract

Knowledge of phase transformation kinetics is a key point in designing steel grades, in particular modern high-performance grades, highly sought-after in energy and transportation applications.The design space for these grades is highly multi-dimensional given the numerous potential alloying elements. The characterization techniques that are usually relied on to assess transformation kinetics, such as metallography or dilatometry, are highly time consuming, due to their limitation to either a single transformation time or a single composition per experiment. The high-throughput approach showcased here overcomes those limitations by combining compositionally graded samples with time-and space-resolved in situ X-ray diffraction, yielding full kinetic records over a range of compositions in a single run. Its application to low-alloy steel required addressing specific challenges related to the reactivity and thermodynamics of the material. The transformation of austenite into ferrite was chosen to illustrate its benefits. Using the rich resulting database, the transformation mechanism was examined quasi-continuously

Ferrite precipitation in quaternary Fe–C–X1–X2 systems using high-throughput approaches

“…The graded samples Fe-C-X 1 -X 2 were created from homogeneous ternary samples Fe-C-X 1 and Fe-C-X 2 (listed in table 1), where X 1 and X 2 are substitutional elements (Ni, Mo or Cr). The methodology used to fabricate the diffusion couples was already detailed in a previous study [13] and only a summary is given below.…”

“…However, it is now well documented that these two models are not suitable to describe ferrite growth kinetics in alloyed steels [9,10,11,12]. Some of the experimental results showed that the measured kinetics can be slower than the predicted ones using PE and LE [9,13]. This additional dissipation of the driving force was explained by two main factors, the intrinsic interface mobility [14,15] and solute drag (SD).…”

“…Odqvist et al [17], Zurob et al [18] and Chen et al [19] proposed different numerical models to describe ferrite growth kinetics based on the SD effect. Recently, the authors [12] modified the original 'three-jump' solute drag model put forth by Zurob et al [18] and tested its validity on different ternary Fe-C-X systems (X: Ni, Mn, Si, Cr and Mo) at different temperatures and on a large set of compositions [13,20]. The results of the experiment, which involved measuring the growth kinetics of ferrite as a function of composition and temperature, showed a good match with the predictions of the solute drag model.…”

“…This last version of the SD model was validated experimentally on a large dataset of kinetics obtained on variable compositions in different Fe-C-X ternary systems and at different temperatures [20]. This was made possible using a newly developed high-throughput methodology combining compositionally graded materials and high-energy X-ray diffraction [13]. The methodology involves conducting in situ, space-resolved synchrotron X-ray diffraction measurements on samples with varying compositions.…”

“…The objective of the present study is to use the same combinatorial approach [13] to study the effect of composition on ferrite growth kinetics in different quaternary Fe-C-X 1 -X 2 systems (where X 1 and X 2 are Ni, Cr and Mo). Further, the obtained results will be compared with the new version of the solute drag model to validate it using this unprecedented dataset of ferrite 4 precipitation kinetics across a wide range of alloy compositions.…”