The diploma thesis studies the constitutional characteristics of steel for electrical industry. The electrical industry is a rapidly growing and evolving industry involved in the generation, transport, distribution and sale of electricity. In this thesis, we concentrated on three types of steel from SIJ Acroni d.o.o., which are key in each of these areas of electrical industry.
We focused on the non-oriented electrical steel sheet type EV22Al10, the austenitic stainless steel type 316 L and the high-strength low-alloyed steel type S690QL. Specifically, the characteristics of each steel, which most distinguish them from the other types and are the reason why we choose them for specific applications. Particular emphasis was placed on the microstructure, how it influences the development of properties and how it changes during different heat treatments. Knowing the microstructure and its influence is key to achieving the desired properties and quality of the product and to planning its further processing or use.
During the experimental work, metallographic samples of the steels in question were prepared and taken from different stages of the production of each steel. They were then observed under a light microscope and compared with each other. The microstructures of continuously cast slabs, hot-rolled and heat-treated plates and strips were observed. By observing the microstructural changes during each stage, changes in other mechanical properties such as strength, hardness, ductility, toughness, formability, etc. can be predicted.
In the case of non-oriented electrical sheet, we monitored the formation of ferrite grains, deformation during rolling and lastly annealing for recrystallization. In the case of stainless steel, initially, we had large dendritic branches in the microstructure, and then rolling and solution annealing resulted in a steel with a homogeneous austenitic microstructure. The initial microstructure of the high - strength low - alloyed improved structural steel was martensite. The steel was then rolled, quenched and tempered until the last stage sample contained a bainitic-martensitic microstructure.
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