Materials Science Forum Vols. 473-474

Abstract: The application of the FEM based phase elements is very useful for evaluation of the effects of TTT phase transformations diagrams. The comparison of the different TTT diagrams of the same type of the 50 CrV 4 steels shows that fine differences are possible to be evaluated and approximated by this simulation. Examples are presented for the use of the multiple regression calculation applying the data of the suitable TTT diagrams.

Abstract: Two computer programs were used for simulation of continuous steel casting processes in frame of this work. In the same time industrial experiments by isotope technics were carried out for observation of solidification and shell thickness. The comparison of calculations and experimental results mutually verified the applicability of methods for more sophisticated control of continuous casting procedure.

Abstract: The CA method provides an excellent possibility for a lifelike simulation of transformation processes. Using CA method the processes can be displayed on the screen of the computer as a film. CA method is widely used to simulate the transformations controlled by short-range diffusion such as recrystallisation and grain growth. At the simulation of transformations based on long-range diffusion a well-known problem is that the results of simulation depend strongly on the selected nucleus geometry and the neighbourhood of cells. In this paper the influence of neighbourhood will be analysed in the case of simulated precipitation processes. On the one hand, it is verified that an anisotropic (dendritic) structure is formed if there is no strict restriction for the computational algorithm. On the other hand, it is demonstrated that an isotropic phase growth can be obtained by using a special simulation technique based on the joint application of finite difference (FD) and of CA methods.

Abstract: The paper focuses on the microstructural investigation of Al-Si binary alloys solidified under steady- and non-steady state conditions using a unidirectional heat removal. A brief description of the developed solidification simulation software and its validation by computer aided image analysis are also given.

Abstract: The lifetime management of different engineering appliances, structures and structure elements is one of the important technical-economic problems of nowadays. The problem is basically appeared in technical, economic and political dimensions and the solution can be imagined according to many approaches: microstructural approach, application of new design conceptions and operational approaches (conventional methods, fitness for purpose, structural integrity, integrity management, risk management). The methods, applied in the different approaches have basically two types: engineering and fracture mechanical methods. The time of operation, the frequency data of fractures and the fracture causing failure statistics of the engineering structures having great importance shows, that the significance of cyclic loadings, fatigue and fatigue crack propagation is emphasized in general. The sketched possibilities are shown by two examples in this paper. One of them is the system of lifetime management for cyclic loaded structures having cracks or crack like defects; the other is the building-up and purport of the integrated management system for hydrocarbon transporting pipelines.

Abstract: Technologies applied in machining metals are often characterised by highly localised shear strain, which can be regarded nearly as adiabatic, and which might lead to thermoplastic instability in certain cases. In cutting, similar incidents can be observed in the shear zone, in which γ=2–50, dγ/dt≈104 s-1, dT/dt=106 K/s, and under such extreme conditions chaotic phenomena may occur occasionally. Chip formation can be described by a two-dimensional model, where the variation of shear stress τ and temperature T in time are given by autonomous differential equations, while the material characteristics are determined by exponential constitutive functions. The solutions of equations can be classified by the coefficients of the characteristic equation of the Jacobian matrix. Two types of stable focuses and Hopf bifurcation can possibly occur, which corresponds to the two types of chips; continuous chip and segmental chip. The model should be broadened to describe the typical chaotic phenomena.

Abstract: The inner structure of the continuously cast semis has a great importance from the point of view of further processing and application. The main reason for this is the very direct effect of the inner structure’s features (ie. porosity, macrosegregations, geometry of primary dendrites) on the technological characteristic features of the semis during further processing (ie. crack sensitivity, formability, etc.). The paper deals with the possible ways of macrostructure determination on the basis of the results of mathematical modeling of continuous casting process. We pay a special attention to the columnar-equiaxed transition as a function of heat parameters of the casting process and to the macrosegregation formation caused by the motion of solute enriched interdendritic liquid in the mushy zone.