<p> The dominant slag-metal reaction site in AC electro-slag remelting (ESR) has been directly determined by estimating the rate of sulphur transfer at the electrode tip/slag and metal pool/slag interfaces. In this investigation, negligible sulphur transfer has been assumed at the droplet/slag interface, and the basis for such assumption is discussed. Using a 5.825" diameter mould and CaF2-CaO slags, it has been established that the electrode tip/slag interface is the dominant reaction site. Calculations indicate that the pool sulphur is close to equilibrium with the slag. The importance of all six reaction sites in AC ESR are discussed. The results indicate the importance of the slag/atmosphere interface, especially when using slags of low lime content. Conventonal overall sulphur balances have been carried out and the results are in agreement with the rates obtained at the different interfaces, thus indicating internal consistency of the results. </p> / Thesis / Master of Engineering (MEngr)

Nitrogen-alloyed tool steel is made at Uddeholms AB by adding high-nitrogen ferroalloy after vacuum degassing where introduced impurities are hard to remove. In this thesis two types of high-nitrogen ferrochromium are compared, a solid version and a powder cored wire. They are examined in crossection and 16 samples from four charges are examined with Pulse Distribution Analysis as well as systematic microscopy of polished cross sections. The PDA results missed smaller spinel inclusions shown in previous research to be detrimental. The wire form shows promise but more charges need to be evaluated before a conclusion is drawn. / Kvävelegerat verktygsstål tillverkas hos Uddeholms AB genom tillsats av kväverika ferrolegeringar efter vakumavgasning, och orenheter som introduceras i detta steg är svåra att avskilja. I den har uppsatsen jämförs två typer av kväverikt ferrokrom varav en i form av stycken och en i form av tråd med pulverkärna. De undersöks i tvärsnitt och totalt 16 prov från fyra charger undersöks med PDA (pulsfördelningsanalys) och systematisk mikroskopering i tvärsnitt. Resultaten från PDA missade mindre inneslutningar av spinell vilka tidigare har visat sig problematiska. Trådformen verkar lovande men fler charger behöver undersökas för att kunna dra en definitiv slutsats.