Calculation of solidification-related thermophysical properties for steels
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I.
INTRODUCTION
IN recent years, numerous advanced models applying finite difference and finite element methods have been developed to simulate the solidification process of metallic alloys. Their accuracy, however, depends not only on the mathematical treatments of the models but also on the thermophysical data used as input data for the calculations. Such data, for example, are the enthalpy-related data (proper enthalpy data or specific and latent heat data), density, and thermal conductivity. Usually, the data of literature, however, cannot be applied directly due to the phase transformation processes causing discontinuities to the properties, depending on the steel analysis and the cooling of the casting. Hence, a reliable simulation of phase transformations would be necessary for the prediction of these properties. Recently, an interdendritic solidification model (IDS)[1] has been developed to simulate the phase transformations during solidification of low-alloyed and stainless steels, and an austenite decomposition model (ADC)[2] has been coupled to the IDS model so that the phase transformation calculations can be reached from 1600 7C down to the room temperature. This model package has now been developed further, to calculate important thermophysical properties (enthalpy-related data, density, and thermal conductivity) as a function of temperature, taking into account the discontinuities of properties caused by the phase transformations. In the present study, a detailed description of this evaluation process with the proper algorithms for calculating the thermophysical properties will be given. These algorithms are based, to some extent, on an earlier study,[3] but while the earlier algorithms were applied only to low-alloyed steels, the present algorithms are applicable to both low-alloyed and stainless steels. In addition, the present density and thermal conductivity data are based on more experiments than earlier, covering a wider composition range of steels extending to the region of AISI 400 series JYRKI MIETTINEN, Research Engineer, is with the Laboratory of Metallurgy, Helsinki University of Technology, 02150 Espoo, Finland. Manuscript submitted April 4, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
stainless steels. First, however, a brief description of the present IDS version will be given, particularly as it has undergone certain changes since the development of the first version.*[1] II.
IDS MODEL
The IDS model was originally developed to simulate the interdendritic solidification of low-alloyed steels and stainless steels containing 16 to 20 pct Cr and 8 to 14 pct Ni.[1] In the model, interfacial material balance equations and Fick’s diffusion laws were combined with a thermodynamic solution model, which links the temperature, the interfacial compositions, and the phase stabilities. In the first version, the thermodynamic properties of solution phases were described with the Wagner–Lupis–Elliott model (WLE).[4,5,6] Later, however, it was found that in stainless steels, in the final stag
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