Analysis of the interaction between moving α/γ interfaces and interphase precipitated carbides during cyclic phase transformations in a Nb-containing Fe-C-Mn alloy

Abstract

The interaction between moving a/g interfaces and interphase precipitated (IPd) carbides during the austenite (g) to ferrite (a) and the ferrite (a) to austenite (g) transformation has been systematically investigated through cyclic phase transformation experiments for a 0.1C-1.5Mn alloy containing 0.1 wt% Niobium (Nb) and its Nb-free counterpart. Shifts in the critical reaction temperatures during continuous heating and cooling are observed, which are attributed to the pinning force (PF) originating from the IPd carbides present. By applying the Gibbs energy balance (GEB) model to analyze experimental results, the PF was derived to be about 15 J/mol for the a/g transformation and about 5 J/mol for the g/a transformation, respectively, both of which are quite small compared to chemical driving force of phase transformations. Moreover, various modified Zener pinning equations have also been used to predict the PF, and it was found that these values are comparable with those obtained from experiments, which suggests that the classical Zener theory still has promising potential for carbide-interface interaction analysis.

A Non-steady State Model for the Austenite-to-ferrite Transformation Kinetics under the Non-partition Condition in Fe–C–Mn Alloys

“…The expression for the width of the spike, D/v can be derived from Eq. (12). Figure 12 indicates that the width of the spike can be well described by D/v.…”

“…The potential well is transformed to the activity coefficient distribution using Eq. (12). Figure 1(a) is an example of such interaction potential, which is for γ stabilizer.…”

“…Then the value of f α is one using Eq. (12). The effective potential depth E 0 and half of the potential difference between α and γ phase ΔE are introduced.…”

“…The developed model is a non-steady state (time-dependent) one, which is an extension of the quasi-steady state model used for describing the solute drag effect in the γ to α transformation of Fe-C-X alloys by many authors. [5][6][7][8][9][10][11][12] A non-steady state (time-dependent) solute drag model was proposed by Murakami et al 13) to calculate the development of interface segregation during ferrite transformation. In their model the austenite/ferrite interface moving velocity is calculated from the growth rate of ferrite.…”

Detailed In Situ Hot Stage Transmission Electron Microscope Observations of the Localized Pinning of a Mobile Ferrite-Austenite Interface in a Fe-C-Mn Alloy by a Single Oxidic Particle

“…However, in such a case where different phases exist on either side of the interface the driving force for interface motion generally is much higher than for recrystallization conditions and the effect may be less notable. [13] Previous experimental studies of the d-ferrite-to-austenite and a-ferrite-to-austenite transformations indicate that the transformation interfaces interact with particles in the parent phase [14,15] and transformation kinetics were found to be retarded in a similar fashion to Zener pinning during grain growth. [4,14] The interaction of oxide particles with grain boundaries can also reduce austenite grain growth at high temperatures (1200°C) in Fe-0.15C-1.0Mn-1.0N steels deoxidized with Ti and Zr [16] and improve stability of the microstructure in austenitic stainless steel heat treated at 1150 to 1250°C for 100 to 1000 hours.…”