engleski

Prediction of unavoidabledistortions in transformation-free cooling by a newly developed dimensionless model

Former investigations in transformation-free cooling processes of long cylindrical workpieces in a gas nozzle field showed a typical behaviour of the dimensional changes, which correlated to only few dimensionless numbers. These numbers are created by the following parameters: shape and dimensions of component, its initial temperature, temperature of the quenching media, heat transfer coefficient, heat conductivity, heat capacity, density, thermal expansion coefficient, Young’s modulus, Poisson’s ratio, yield strength and strain hardening behaviour. The representative group of 28 austenitic stainless steels was selected from literature. Their properties were statistically analyzed in order to carry out a systematic investigation of the most significant material properties and process parameters of dimension and shape changes during transformation-free cooling. The characteristic values of statistically significant interval of considered austenitic steel properties – average and standard deviation - as well as the range of usual process parameters for their heat treatment are used for simulations execution by the commercial FEM program SYSWELD. The relative changes of the component dimensions obtained from numerical simulations, have been analyzed in dependence of six autonomous dimensionless numbers with their interactions in order to find the proper equations for prediction of unavoidable distortion in a transformation-free cooling. To define these equations, the method of nonlinear regression analysis was used.

unavoidable distortion; thermal strain; dimensionless numbers; austenitic steel

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