Phase Tranformation Modeling of Medium-carbon
نویسندگان
چکیده
The kinetics of phase transformations in medium-carbon forging steels (MCFS) have been modeled based on CALPHAD multicomponent thermodynamics and the classical nucleation-growth theory. New treatments include the time dependency of parabolic growth rate of proeutectoid ferrite (α) , which account for the soft impingement effect by carbon enrichment in austenite (γ). And a potential transition of γ/α interface equilibrium has also been considered depending on temperatures and velocity of the moving interface. To make a realistic prediction of the onset of pearlite (P) transformation, a normal distribution of γ grain size has been assumed and successive α→P transformation kinetics in each grain size have been summated. The developed program coupled with thermodynamic solver, 'ThermoCalc', calculated the isothermal kinetics of MCFS and has been found to predict well the effect of minor difference of chemical composition / holding temperatures. INTRODUCTION Medium carbon steels containing 0.2~0.5 mass percent carbon are used in a large quantity as materials for hot forging parts. A prediction of the microstructure consisting of proeutectoid ferrite (α), pearlite (P), and bainite (B) has long been a desired technology, which would be the basis for balancing mechanical properties and good machinability of final products. The α/P/B fraction after forging is mainly affected by both carbon and manganese content, austenite (γ) grain size (AGS), and cooling schedules. Thermodynamics in Fe-Mn-C ternary system have been well discussed in terms of partitioning of Mn, and the parameters describing diffusion-controlled transformation can now be calculated by CALPHAD method for the ternary and even higher-order system. However, there is still discussion on the type of equilibrium operating at the real interface between α and γ. On the other hand, AGS and cooling rate are strongly related to hot working conditions and have been evaluated in the course of thermal-mechanically coupled FEM analysis. Senuma et al.[1] reported experimental equations for AGS for low carbon steel based on the relationship between rolling conditions and fractions of dynamic/static recrystallized γ grain, and Yogo[2] et al. recently modified the equation to be applicable to forging process. A lot of work has been devoted to understand the kinetics of α, P and B transformations in the framework of the classical nucleation-growth theory, and there are some integrated models[3-6] reported to be able to predict the evolution of complex α+P+B structure. These models so far have been developed for low-carbon steel strips, and therefore, focused on the prediction of α grain size as Materials Science Forum Vols. 539-543 (2007) pp. 2443-2448 online at http://www.scientific.net © (2007) Trans Tech Publications, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 161.111.90.248-27/02/07,11:19:16) well as the fraction of widmanstätten α or B. In view of the circumstances, we have firstly constructed an integrated physical model of the successive α→P transformation for medium-carbon forging steel (MCFS). And a trial program empowered by CALPHAD method has been developed to evaluate the usefulness of such computerized predictions. This article presents the newly introduced features of treating the above diffusion-controlled phenomena in the model, together with the current status in predicting α→P transformation behaviors of MCFS by the program. The possible B transformation from the remaining γ are also to be considered and will be included in a separate paper.
منابع مشابه
Modeling Investigation of Dielectric Constant Effect on NMR and IR Properties of C48 as a Single Walled Carbon Nanotube
A cluster model for active site of nanotube (C48) was presented and investigated the geometricstructure and thermochemical parameters. Quantum-mechanical calculations were performed at theHF / 510-30, 6-310, 6-3 IG• and 6-310" levels of theory in the gas phase and three solvents atfour temperatures. Also, nuclear shielding parameters of the active site of nanotube have been takeninto account us...
متن کاملSeparation of methacrylic acid from aqueous phase using quaternary amine
The feasibility of extractive reaction of methacrylic acid from aqueous solution using a quaternary amine, tri–octyl methyl ammonium chloride (TOMAC) as an extractant, was studied. The diluents chosen in the present work belong to different chemical classes, n–butyl acetate, carbon tetrachloride, isoamyl alcohol, methyl isobutyl ketone, and toluene. The effect of initial acid concentration in t...
متن کاملInvestigation of Vacancy Defects on the Young’s Modulus of Carbon Nanotube Reinforced Composites in Axial Direction via a Multiscale Modeling Approach
In this article, the influence of various vacancy defects on the Young’s modulus of carbon nanotube (CNT) - reinforcement polymer composite in the axial direction is investigated via a structural model in ANSYS software. Their high strength can be affected by the presence of defects in the nanotubes used as reinforcements in practical nanocomposites. Molecular structural mechanics (MSM)/finite ...
متن کاملDetection and Modeling of Medium-Scale Travelling Ionospheric Disturbances in Iran Region
Ionosphere layer variations are divided into regular and irregular. Regular changes can be considered as daily changes, changes depending on latitude and changes due to solar activity. Travelling Ionospheric Disturbances (TID) is one of the irregular changes of ionosphere which categorized in small, medium and large scales. Medium-scale Travelling Ionospheric Disturbance (MSTID) which are propa...
متن کاملMathematical Modeling of Adsorption Process of Ethyl Acetate Impurity of Supercritical CO2 on Activated Carbon
A mathematical model is described and applied for adsorption process of ethyl acetate from supercritical CO2 stream on activated carbon particles. This model has the ability of illustrating variation of effluent concentration towards different parameters such as flow rate, temperature and pressure. In this research, a vast area of operational conditions is experienced. Mass transfer resistance ...
متن کاملVelocity Modeling in a Vertical Transversely Isotropic Medium Using Zelt Method
In the present paper, the Zelt algorithm has been extended for ray tracing through an anisotropic model. In anisotropic media, the direction of the propagated energy generally differs from that of the plane-wave propagation. This makes velocity values to be varied in different directions. Therefore, velocity modeling in such media is completely different from that in an isotropic media. The vel...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2006