Teoretické a experimentální studium teplot fázových transformací ocelí

Abstract

The key parameters, in the area of parameters optimization of metallurgical processes, in particular the technology of casting and subsequent solidification of steel, are the transformation temperatures in high temperature region: liquidus temperature (TL), peritectic transformation temperature (TP) and solidus temperature (TS). Due to the technological, and consequently economical, importance of the knowledge of correct phase transformation temperatures, significant attention is still paid to the methods of its determination. There are two main approaches, traditional experimental methods, most often represented by thermal analysis methods and theoretical methods using ICT. The dissertation thesis deals with study of TL, TP and TS. A research was performed with focus on the topic of thermal analysis, with regard to the acquisition. Original experimental data (TL, TP and TS) of 18 samples of steel were obtained by Differential Thermal Analysis and Direct Thermal Analysis methods. The obtained experimental data were evaluated and a basic statistical analysis was performed. Based on the obtained data, it was found that the differential and direct thermal analysis methods are set correctly and the results are reproducible and comparable. Thermal analysis results shows high level of consistency and low variability. The TL, TP, and TS calculations were performed using existing empirical models, obtained by research and were calculated with Thermo-Calc by CALPHAD method and with InterDendritic Solidification by Phase Field method. The calculated data has been verified, confronted and discussed with data published in literature, and its compliance with empirical models and software calculations has been verified. Based on the analysis of the empirical equations results and software and its consistency with the experimental results, the new empirical model (NEM) for the calculation of TL, TP and TS was created. Basically, it is a calculator, where selected empirical equations are implemented, all suited in the EXCEL editor. The mean value of the results is then the final temperature TL, TP or TS. The results of the empirical models are further analysed statistically and the standard deviation, variation coefficient and variation range are evaluated. Based on statistical analysis, the equations that yielded results significantly deviated and thus adversely affecting the outcome of the model, were excluded. In case of peritectic transformation temperature, only one equation was used. NEM results were compared and verified with experimental results, empirical and software calculations. The created application is a simple, low-cost and reliable mean for calculating TL, TP, and TS. The main contribution of the thesis is the acquisition of original data and the extension of the thermo-physical and thermodynamic properties of steels. The data can be used to optimize casting conditions in the steel casting industry. Furthermore, the data can be used as input data for modelling software that allows modelling of casting processes of steels and following solidification (Magmasoft, Procast) or to modify thermodynamic software databases. Acquired new knowledge can contribute to the development of metallurgy, foundry and material engineering, thermal analysis methods and physical-numerical modelling. As a result, it will enable the optimization of steel casting and solidification processes where the goal is to obtain a better and less expensive product.