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Formation and Evolution of Non-Metallic Inclusions in the Ladle Treatment - Ingot Casting - Electroslag Remelting Process Chain
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2025 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The need for high-quality tool steel is ever rising in many applications. One factor which impacts the quality of tool steel is the cleanliness of the steel, which can be defined as the number, sizes, and types of nonmetallic inclusions present in the steel. Electroslag remelting is a process that is good at improving the cleanliness of steel. The final quality of the remelted ingot is influenced by a range of different factors, one being the quality of the electrode used for the remelting. In this study, the characteristics of the nonmetallic inclusions found in the ladle treatment and casting process were analyzed and compared to help map out the evolution of the non-metallic inclusions during these two steps in the process chain. The characteristics investigated were the size, morphology, and composition of the non-metallic inclusions, which were done using electrolytic extraction on several steel samples to gather the non-metallic inclusions and using a scanning electron microscope to investigate them. The results showed that the nonmetallic inclusions found in the electrode ingot were MgO – Al2O3 spinels and Al2O3. The inclusions found in the ladle were Al2O3 and inclusions composed of Al2O3 – MgO – CaO with S and SiO2. Additionally, the size of the inclusions was not affected by their location within the electrode ingot, but there were signs that clusters formed in higher numbers towards the center of the ingot, as well in the bottom part of the ingot.

Abstract [sv]

Behovet av högre kvalitets verktygsstål ökar i många applikationer. En faktor som påverkar kvaliteten hos stålet är stålets renhet, vilket kan definieras som antalen, storleken and typen av ickemetalliska inneslutningar som finns i stålet. Elektroslagg omsmältnings-processen är en process som ofta används för att göra stålet renare. Den slutliga kvaliteten hos gjutet beror på många faktorer, en av dem är kvaliteten hos elektroden som används i omsmältningen. I denna studie analyserades och gemfördes egenskaperna hos ickemetalliska inneslutningar som hittades i skänkugnen och gjutprocessen för att kunna kartlägga hur de utvecklas mellan de här två stegen i processkedjan. Egenskaperna som analyserades var storleken, morfologin och kompositionen hos de ickemetalliska inneslutningarna. Inneslutningarna var samlade med elektrolytisk extraktion och ett svepelektronmikroskop användes för att undersöka dem. Resultaten visar att de ickemetalliska inneslutningarna som hittades i gjutet var MgO – Al2O3 spineller och Al2O3. I skänkugnen så hittades Al2O3 och inneslutningar som bestod av Al2O3 – MgO – CaO med S and SiO2. Storleken hos inneslutningarna var samma oavsett vart i gjutet de hittades, men det verkade som att mera kluster formades i mitten och botten av gjutet.

Place, publisher, year, edition, pages
2025. , p. 31
Series
TRITA-ITM-EX ; 2024:578
Keywords [en]
Tool Steel, Non-Metallic Inclusions/NMI, MgO – Al2O3 Spinel, Electrolytic Extraction, Ladle Treatment, Ingot Casting, Electro-Slag Remelting/ESR
Keywords [sv]
Vertygstål, Ickemetalliska Inneslutningar, MgO – Al2O3 Spinell, Elektrolytisk Extraktion, Skänkbehandling, Gutning, Elektroslagg Omsmältnings-Process
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-362345OAI: oai:DiVA.org:kth-362345DiVA, id: diva2:1951792
Subject / course
Materials Design and Engineering
Educational program
Degree of Master
Presentation
2025-03-24, 00:00
Supervisors
Examiners
Available from: 2025-04-14 Created: 2025-04-14 Last updated: 2025-04-14Bibliographically approved

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