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Numerical modeling and simulation of case hardening of steel

Carburizing is commercially important variant of case hardening, which is using to obtain a surface resistant to the external stresses and an adequate ductility in the core of the part. The feasibility of this process lies in the occurring solid-solid phase transformations during the heat treatment which provided a proper amount of carbon in the steel. The mathematical model and computer simulation for the prediction of mechanical properties macrostructure of case hardened steel specimen as function of carbon content was developed. The computer simulation of case hardening of steel is consist of two main parts: computer simulation of the diffusion of carbon in surface layer of specimen and computer simulation of quenching with low-temperature tempering. The solution for these two phenomena was performed using a two-dimensional analysis. In this way the computer program is prepared for simulation case hardening of axisymmetric workpieces. The mathematical model of heat and mass transfer in transient state of workpieces of low carbon steel subjected to carburizing process is established. The governing equations for diffusion of carbon were presented by Fick’s law, but the Fourier’s law of heat conduction was applied for definition transient temperature field during the quenching. Because of wide range of applicability and ease of use of finite volume method (FVM), integrated computer program for simulation of both, diffusion of carbon and transient temperature field in case hardening process was created by using of FVM numerical method. In this way the cooling time from 800 °C to 500 °C was calculated by using the computer program for simulation of transient temperature field. Material parameters are taken from the data tables, but finite values of material data are adjusted by inversion method. The distribution of hardness in specimen points has been calculated by conversion of calculated time of cooling from 800 °C to 500 °C to the hardness. Conversion of time of cooling from 800 °C to 500 °C to the hardness have done using the Jominy test properties of applied steel. Hardness distribution in surface layer of specimen has been based on calculated distribution of carbon content. The distribution of other mechanical properties and microstructure distribution specimen of case hardened steel was predicted using empirical relations that exist between hardness and other mechanical properties of steel. The established procedure was applied in computer simulation of case hardening steel shaft.

Computer simulation, case hardening, mechanical properties

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