Studium svařitelnosti a vlastností svarových spojů oceli T24

Abstract

Production of electric and thermal energy belongs to important branches of industrial production in the Czech Republic and also in the world. Thermal power plants can be considered as main source, even when nuclear power plants and other alternative sources exist. The development in the last years has been directed to enhance the affectivity of coal power plants by increasing the working parameters of steam; those parameters put higher demands on the used material and on welded joints of the power plant pressure units. The dissertation deals with problems of weldability and properties of low-alloyed heat-resistant steel T24, and also with analysis of metallurgical and mechanical properties of welded joints. The theoretical part of the dissertation deals with analysis of the present state of knowledge regarding the heat-resistant steel T24 used in power industry. Emphasis is placed on its heat-resistance and weldability. In conclusions of the theoretical part the problems of secondary hardening of steel T24 are analysed. Based on the theoretical analysis the aims and methods for experimental work have been determined. The experimental part of the dissertation is focused on real welded joints of steel T24 and their evaluation. In the first part the parameters of welding of test welded joints and their heat treatment have been proposed. Samples were tested by weldability tests - Tekken, RD and simulation tests to determine the appropriate preheating temperature and for verification of consumables for welding of steel T24. In the second part of the experiment testing welds of the T24 steel have been welded. These welds were subjected to metallographic tests, hardness tests and impact tests. A part of the test samples has been put to long-term thermal exposition for the purpose of study the influence of the thermal processing on secondary hardening of welded joints of T24 steel. The aim to evaluate the results is to confirm or to disprove the necessity of pre-heating and especially of post weld heat treatment on T24 steel welds. In conclusions of the dissertation the discussion and summary of the achieved results have been performed. The set of the results at this work is contribution to practical applications and acceptation of the welding technology of T24 steel.