Non-Equilibrium Simulations

Chapter 4

Alloys

Abstract

1. Introduction

103

Bobyr Sergiy Volodimyrovych

Using the Principles of

for the Analysis of Phase

Nonequilibrium Thermodynamics

Transformations in Iron-Carbon

Using the principles of nonequilibrium thermodynamics, a technique has been developed for calculating diffusion flows during phase transformations in ironcarbon alloys. Expressions for the calculation of cross coefficients, driving forces, and flows in Onsager equations for the model thermodynamic system are given; examples of the use of the developed technique are given for the processes of graphitization and the formation of carbides in chromium steel during tempering. The nonequilibrium thermodynamics analysis of the eutectoid transformation is executed into carbon steel. Onsager's equations of motion are built for the model thermodynamics system describing eutectoid transformation. The basic kinetic parameters of process are growth rate of perlite and between inter-plates distance for the stationary process of eutectoid transformation. We founded dependencies of basic kinetic parameters of process from the size of supercooling. A nonequilibrium thermodynamic model of the austenite nondiffusion transformation in iron and alloys based on it is developed, taking into account internal stresses in the system. Onsager motion equations are found for a model thermodynamic system describing a nondiffusion transformation and kinetic equations for changing deformations and growth rates of the α-phase. A scheme of austenitic nondiffusion transformations is constructed, including normal and martensitic transformations, as limiting cases.

Keywords: nonequilibrium thermodynamics, the iron-based alloys, transformation

The study of phase transformations is one of the most important problems in the

physics of metals [1–3]. Phase transformations are divided into diffusion and nondiffusion [1]. If the kinetics of phase transformation in steels and cast irons is determined by the diffusion of carbon, this allows them to be attributed to conversions controlled by diffusion [1–4]. Such transformations in iron-carbon alloys include pearlitic transformation of austenite, and transformations occurring during

of austenite, diffusion, equations of motion, nondiffusion transformation
