doktorsko delo
Rok Markežič (Author), Roman Šturm (Mentor), Nikolaj Mole (Co-mentor)

Abstract

Orodja za tlačno litje, izdelana iz orodnih jekel za delo v vročem stanju, so med obratovanjem izpostavljena cikličnim toplotnim in mehanskim obremenitvam. Visoke obratovalne temperature povzročajo mikrostrukturne spremembe, toplotno mehčanje in izgubo trdote materiala orodij ter posledično zmanjšanje odpornosti orodij na obrabo in poškodbe. Poznavanje spreminjanja trdote orodij je ključnega pomena za natančno napovedovanje in podaljšanje njihove obratovalne dobe. V doktorskem delu je bil najprej raziskan vpliv temperature na pojavnost obrabnih in poškodbenih mehanizmov na orodjih z analizo iztrošenega segmenta orodja. Pri tem so bile uporabljene numerične metode izračuna temperaturnih polj, meritve trdote, svetlobna mikroskopija, vrstična elektronska mikroskopija ter rentgenska difrakcija. Rezultati analize so pokazali višjo stopnjo obrabe in poškodb na površinah segmenta z višjo doseženo temperaturo med tlačnim litjem. Z izvedbo visokotemperaturnih testov mehčanja, meritvami trdote ter z analizo mikrostrukture materiala je bilo analizirano toplotno mehčanje tipičnega orodnega jekla za delo v vročem stanju. Na osnovi znanega kinetičnega zakona popuščanja je bil razvit in validiran nov model za napovedovanje spreminjanja trdote materiala pri časovno spremenljivih temperaturnih pogojih. Rezultati validacije so pokazali dobro ujemanje med napovedanim in izmerjenim spreminjanjem trdote. Novorazviti model je bil nato preizkušen na primeru napovedovanja trdote materiala pri cikličnem toplotnem obremenjevanju. Za izvedbo testov cikličnega toplotnega obremenjevanja je bilo razvito namensko preizkuševališče. Dokazano je bilo dobro ujemanje med napovedanim in izmerjenim spreminjanjem trdote materiala med cikličnim toplotnim obremenjevanjem. Uporaba razvitega modela je bila na koncu prikazana še na primeru napovedovanja spreminjanja trdote igle orodja za tlačno litje.

Keywords

orodna jekla za delo v vročem stanju;toplotno mehčanje;kinetični zakoni popuščanja;tlačno litje;trdota;mikrostruktura;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UL FS - Faculty of Mechanical Engineering
Publisher: [R. Markežič]
UDC: 669.14:621.78:620.17(043.3)
COBISS: 32317187 Link will open in a new window
Views: 1131
Downloads: 194
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Other data

Secondary language: English
Secondary title: Prediction of properties of hot work tool steels under cyclic thermal loading conditions
Secondary abstract: High pressure die casting dies, made of hot work tool steels, are during operation exposed to cyclic thermal and mechanical loads. High operational temperatures cause microstructural changes, thermal softening, loss of hardness and consequently reduction in damage and wear resistance. Understanding the loss of hardness of dies during die casting process is crucial for precise die lifetime prediction and prolongation. In this doctoral thesis, first the effect of temperature on the occurrence of damage and wear was researched by examination of a used insert of a die casting die. Numerical methods for temperature fields calculation, hardness measurements, optical microscopy, scanning electron microscopy and x-ray diffraction analysis were used. Results have shown an increase in the occurrence of damage and wear on surfaces with higer temperature during the die casting process. By performing high temperature softening tests, hardness measurements and microstructural analysis, thermal softening of a typical hot work tool steel was analysed. A new model for hardness change predictions during time and temperature dependent conditions was developed on the basis of a known tempering kinetic law and validated. The validation results have shown a good agreement between predicted and measured changes of hardness. The new model was then tested on hardness change predictions during cyclic thermal loading conditions. Cyclic thermal loading tests were performed on a newly developed test equipment. Hardness change predictions with the newly developed model were in good agreement with measured changes of hardness. The use of the new model was additionally demonstrated on hardness change predictions of an insert of a die casting die.
Secondary keywords: hot work tool steels;thermal softening;tempering kinetic laws;high pressure die casting;hardness;microstructure;dissertations;Orodja;Disertacije;Obraba;
Type (COBISS): Doctoral dissertation
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za strojništvo
Pages: XXVIII, 124 str., [1] f. pril.
ID: 12064902