Vpliv magnetnega staranja na lastnosti neorientirane elektropločevine : diplomsko delo

Zupančič, Matej (author), Markoli, Boštjan (mentor)

Namen diplomske naloge je preučiti vpliv magnetnega staranja na izbrane lastnosti vzorcev neorientiranih elektropločevin. Te so hladno valjani polizdelki iz zlitin Fe – Si in Fe – Si – Al, pogosto uporabljeni v električnih rotirajočih strojih, generatorjih in elektromotorjih. Vzorci treh različnih kvalitet elektropločevine, izdelani v podjetju SIJ Acroni, d. o. o, so vsebovali različne koncentracije ogljika in bili starani pri atmosferskem tlaku in štirih različnih pogojih 12 oziroma 24 ur. Vzorci so bili metalografsko pripravljeni in pregledani s svetlobnim in vrstičnim elektronskim mikroskopom. Vpliv magnetnega staranja na vzorce je bil opazovan s pomočjo meritev trdote po Vickersu in z merjenjem specifičnih magnetnih izgub pri 50\ Hz in 1,5\ T z Epsteinovim aparatom. Ugotovljeno je bilo, da so se vrednosti trdot vzorcev znižale z daljšanjem časa staranja, specifične izgube pa z omenjenim časom naraščale. V vseh mikrostrukturah vzorcev je bil opažen cementit po kristalnih mejah, ki se je izločil že med rekristalizacijskim žarjenjem. Ta cementit je opazno spremenil rezultate specifičnih izgub po staranju, saj zaradi izločanja ogljika na njem ni prišlo do velikih razlik v spreminjanju magnetnih izgub med staranjem pri različnih temperaturah staranja. To odkritje ima lahko veliko praktično vrednost, saj je mogoče s staranjem pri nižjih temperaturah dobro oceniti spreminjanje magnetnih izgub tudi pri višjih temperaturah, kar bi nižalo stroške staranj industrijskih vzorcev v primerjavi z zahtevanim staranjem po standardu SIST EN 10106:2016. Odkrito je bilo tudi, da se v primeru vmesne prekinitve staranja v skladu z omenjenim standardom končne lastnosti elektropločevine ne spremenijo znotraj eksperimentalnih napak. Pri eni od skupin vzorcev je bilo med staranjem odkrito izjemno veliko povečanje specifičnih izgub, za katerega je bilo dokazano, da je posledica izločanja z bakrom bogatih izločkov. Za točno določitev izločenih faz pa bodo potrebne še dodatne preiskave.

• Language: Slovenian
• Keywords: Elektropločevina, magnetno staranje, magnetne izgube, trdota, mikrostruktura.
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: M. Zupančič
• Year: 2024
• Number of pages: XIV, 139 f.
• PID: 20.500.12556/RUL-162797
• UDC: 669
• COBISS.SI-ID: 212623107
• Publication date in RUL: 27.09.2024

Secondary language

• Language: English
• Title: Influence of magnetic ageing on non-oriented electrical steel sheet properties : diploma thesis

Abstract

The purpose of this diploma thesis was to study the influence of magnetic aging on selected properties of samples of non-oriented electrical sheets. These are cold-rolled semi-finished products of Fe–Si and Fe–Si–Al alloys, often used in electric rotating machines, generators and electric motors. Samples of three different qualities of non-oriented electrical steel, produced by the company SIJ Acroni, d. o. o, contained different concentrations of carbon; they were aged at atmospheric pressure in four different conditions for 12 and 24 hours, respectively. The samples were metallographically prepared and examined with a light and scanning electron microscope. The effect of magnetic aging on the samples was observed by means of Vickers hardness measurements and by measuring core loss at 50 Hz and 1.5 T with an Epstein frame. It was found that the hardness values of the samples decreased with longer aging time, while the core loss increased with said time. In all the microstructures of the samples, cementite was observed along the crystal boundaries, which was already precipitated during the recrystallization annealing. This cementite significantly changed the values of core loss after aging, as there were no large differences in the change of said loss during aging at different aging temperatures due to precipitation of carbon on it. This discovery can be of great practical importance, as aging at lower temperatures allows for a good assessment of changes in magnetic loss even at higher temperatures, which would lower the cost of aging industrial samples compared to the aging required by the SIST EN 10106:2016 standard. It was also discovered that in the case of an intermediate interruption of aging according to the mentioned standard, the final properties of electrical steel do not change within the experimental errors. In one group of samples, an extremely large increase in core loss was detected during aging, which was shown to be due to the precipitation of a copper-rich phase. Additional investigations will be required to determine the exact phase precipitated.

• Keywords: Non-oriented Electrical Steel, Magnetic Ageing, Core Loss, Hardness, Microstructure.