MODELLING AND NUMERICAL ANALYSIS OF HARDENING PHENOMENA OF TOOLS STEEL ELEMENTS

摘要

This research the complex model of hardening of tool steel was shown. Thermal phenomena, phase transformations and mechanical phenomena were taken into considerations. In the modelling of thermal phenomena the heat transfer equations has been solved by Finite Elements Method by Petrov-Galerkin formulations. The possibility of thermal phenomena analysing of feed hardening has been obtained in this way. The diagrams of continuous heating (CHT) and continuous cooling (CCT) of considered steel are used in the model of phase transformations. Phase altered fractions during the continuous heating (austenite) are obtained in the model by formula Johnson-Mehl and Avrami and modified equation Koistinen and Marburger. The fractions ferrite, pearlite or bainite, in the process of cooling, are marked in the model by formula Johnson-Mehl and Avrami. The forming fraction of martensite is identified by Koistinen and Marburger equation and modified Koistinen and Marburger equation. The stresses and strains fields are obtained from solutions by FEM equilibrium equations in rate form. Thermophysical values in the constitutive relations are depended upon both the temperature and the phase content. The Huber-Misses condition with the isotropic strengthening for the creation of plastic strains is used. However the Leblond model to determine transformations plasticity was applied. The numerical analysis of thermal fields, phase fractions, stresses and strain associated deep hardening and superficial hardening of elements made of tool steel were done.