Analysis of temperature and microstructure in the quenching of steel cylinders
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I. INTRODUCTION
QUENCHING is an integral part of industrial heattreatment processes for steels and provides a means by which the mechanical properties of a steel part can be controlled. During quenching, the steel is typically cooled from above the austenizing temperature by means of a liquid spray or by immersion in a liquid bath. Depending on the temperature field developed within the material, different types of phase transformations occur, which result in a variety of microstructures, residual deformations and hardnesses and residual stress distribution.[1] Two important questions in the heat treatment of steels are (1) what are the microstructural, hardness, deformation, and residual stress distributions produced under a given set of quenching conditions, an (2) what are the quenching conditions required to produce a specified microstructure and residual stress pattern? The answers to these closely inter-related questions necessitates the development of efficient computational models which can relate the quenching-process parameters to the mechanical property attributes (e.g., hardness and residual stress) of the quenched steel part. This is the focus of the current study. The modeling of phase transformations that take place during the quenching of steels has received considerable attention.[2–12] These models fall into two types, based on how they consider the enthalpy changes and volumetric strains that occur during the transformations.[13] In one type of model,[2,3] the specific heat and/or the coefficient of thermal expansion are assumed to change significantly over some temperature range to simulate the effect of the enthalpy P.R. WOODARD, Research Staff Member, formerly with the School of Aeronautics, Purdue University, is with the National Research Council, Ontario, Canada. S. CHANDRASEKAR, Professor, is with the School of Industrial Engineering, Purdue University, West Lafayette, IN 47907. H.T.Y. YANG, Professor, is with the Department of Mechanical and Environmental Engineering, University of California at Santa Barbara, Santa Barbara, CA 93106. Manuscript submitted January 9, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
and volume changes which occur during the transformation. In such a model, the stress and temperature analyses are then uncoupled from the evolution of the microstructure. A drawback of this type of model is that it is not generally possible to make a detailed prediction of the microstructure. In the second type of model,[4,5,7–12,14] the phase transformations are described by nucleation and growth equations for each phase. This type of model involves a coupling between the temperature and stress analyses and the microstructural evolution. The second type of model has been applied to calculate microstructures and, to a lesser extent, to calculate the residual stresses in quenched steel cylinders. Agarwal and Brimacombe[4] used such a model to estimate the distribution of pearlite in quenched eutectoid carbon steel rods. Residual stresses associated with the formation of pearlit
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