A complex thermomechanical model for simulating the transient fields of the temperature, microstructure, stress, strain, and displacement during quenching of steel profiles is introduced. The thermoplastic material model is formulated on the basis of J2-plasticity theory with a temperature- and phase fraction-dependent yield limit. Coupling effects such as dissipation, phase transformation enthalpy, and transformation-induced plasticity are considered. The validity of the model is verified by comparing the simulation results with available experimental measurements. The introduced model serves as a basis for optimizing the cooling conditions for reducing residual stresses and distortions. The simulation results for T and L profiles of two different types of steel are described.
A complex thermomechanical model is introduced for the simulation of the transient fields of temperature and stresses during the quenching of steel products. The material behaviour is an extension of the classical J 2-plasticity theory with the extension of temperature and phase fraction dependent yield criteria. The coupling effects, i.e., dissipation of mechanical energy, transformation induced plasticity (TRIP), and phase transformation enthalpy, are considered. The model is used for the determination of the optimal cooling or quenching for reducing the distortion in the long steel profiles. The simulation results are presented in order to investigate the effects of material properties, boundary conditions, profile size and geometry. In the simulations, L-, T-and U-profiles made of steel C45 and steel CaD are considered. It is demonstrated that with a higher cooling rate in the mass lumped regions of the profiles, the distortion can be reduced. Basic Equationswhere k is the heat conduction coefficient, q is heat flux vector, and T is the temperature. The heat treatment process is a transient heat conduction problem where the tempera-sufficient to estimate the behaviour of the prismatic profile under such conditions with much fiever degrees of freedom. In addition, the dimensional reduction of the problem from three-dimension to two-dimension substantially simplifies not only the visualisation of the field variables but also the determination of optimal cooling strategy.Temperature field. The microstructure and mechanical properties are strongly temperature dependent. Hence the temperature field must be determined correctly for an accurate simulation. The latent heat of the phase transformation has to be taken into account. The heat conduction is governed by the Fourier law, after which the heat flux vector is parallel to the temperature gradient,The mathematical model of the heat treatment is described by a thermoelastoplastic theory which also covers the phase transformation effects. The temperature field has a great influence on the microstructure and mechanical properties. Hence the temperature field must be simulated accurately. The latent heat of phase transformation is considered as an additional heat source or heat sink. The microstructural evolution is obtained by using the isothermal time-temperature-transformation (TTT-) diagrams charts. The diffusion controlled phase transformations are computed according to the Johnson-Mehl-Avrami equation and the displacive phase transformation is calculated from the Koistinen-Marburger equation [2]. For the determination of stress/strain field, a constitutive relation is established, which depends on temperature and phase fraction. The total strain tensor is additively decomposed into several parts, as usual. The introduced model is applicable to 2D-and 3Dproblems. steel research int. 76 (2005) No.5
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