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Author:Nurmi, Sonja
Title:Korkeahiilisten ja jousiterästen kuonapuhtauden parantaminen
Improvement of inclusion cleanliness of high carbon and spring steels
Publication type:Master's thesis
Publication year:2004
Pages:71+43      Language:   fin
Department/School:Materiaali- ja kalliotekniikan osasto
Main subject:Metallurgia   (Mak-37)
Supervisor:Holappa, Lauri
Instructor:Antola, Tuomas
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark V80     | Archive
Keywords:clean steel
Si-killed steel
deformable inclusions
kuonapuhtaus
piitiivistys
sulkeumien muokkautuvuus
senkkakuona
Abstract (eng): Inclusions have a negative impact on many steel properties.
Cleaner steel is therefore needed for more demanding applications, and a great deal of effort has been put into achieving better inclusion cleanliness.
In the case of high carbon and spring steels, clean steel is defined as steel with as few and minor inclusions as possible, and those inclusions that are inevitably left in the steel should be deformable in rolling conditions.

The literary section of this thesis examines the formation and removal of inclusions from the steel bath, as well as factors affecting the deformability of inclusions.
The single most important factor is the chemical composition of the inclusions, which should in the Si02-CaO-AI20 3 system be near the eutectic composition between pseudowollastonite and anorthite.
It is possible to modify the chemical composition of the inclusions by controlling the deoxidation process and composition of steel and ladle slag.

Trial heats were produced at the Koverhar steel plant using Si-deoxidation and modified slag practice to achieve a suitable inclusion composition.
Samples were taken from rolled wire and analysed with a scanning electron microscope (SEM).
Most of the detected inclusions were deformed in the desired rolling direction, which indicates that the chosen method offers a viable means of producing cleaner steel.
The composition of the inclusions was predicted by thermodynamic calculations made with the FactSage TM program.
The calculations show which phases are stable at any given circumstances and the composition of the phases as well.
Abstract (fin): Teräksessä olevat sulkeumat vaikuttavat negatiivisesti useisiin teräksen ominaisuuksiin, minkä vuoksi vaativiin sovelluksiin tarvitaan entistä puhtaampaa terästä.
Koska sulkeumista ei voi päästä kokonaan eroon, pyritään niistä tekemään mahdollisimman pieniä ja valssattaessa muokkautuvia, jolloin ne eivät ole niin haitallisia.

Työn kirjallisessa osassa tutustuttiin sulkeumien muodostukseen ja poistumiseen terässulasta sekä ennen kaikkea niiden muokkautuvuuteen liittyviin tekijöihin.
Sulkeumien kemiallinen koostumus on tärkeimpiä niiden muokkautuvuuteen vaikuttavia tekijöitä ja siihen voidaan vaikuttaa muun muassa teräksen koostumusta, tiivistystä ja senkkakuonan koostumusta säätämällä.

Työn kokeellisessa osassa suoritettiin koesulatuksia Koverharin terästehtaalla tehostetulla piitiivistyksellä ja muunnellulla pintakuonalla sopivan sulkeumarakenteen saavuttamiseksi.
Valssatusta langasta tehtiin pitkittäissuuntaiset hieet, joista tutkittiin sulkeumien muotoa ja koostumusta pyyhkäisyelektronimikroskoopilla (SEM).
Suurin osa löydetyistä sulkeumista oli muokkautuneita valssaussuuntaan, minkä perusteella voidaan todeta kuonapuhtaamman teräksen valmistamisen olevan mahdollista valitulla menetelmällä.

Työssä tutkittiin myös termodynaamisen laskennan avulla syntyvien sulkeumien koostumusta, sekä tulenkestävien materiaalien kestoa.
Tähän käytettiin FactSage TM -ohjelman Equilib-tasapainomoduulia, jonka avulla pystyttiin laskemaan, mitkä faasit olivat stabiileja, sekä mikä niiden koostumus oli annetuissa olosuhteissa.
ED:2004-11-04
INSSI record number: 26448
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