<p>This thesis has been performed at Uddeholms AB with the purpose to investigate theparameters affecting the formation of inclusions during the manufacturing of a low carbonmanganese-steel.A follow-up, steel and slag sampling and evaluations in microscope have been done for a totalof five heats.The results for each heat have been evaluated in relation to the theory from the literaturesurvey and suggestions for changes in the process to reduce the amount of inclusions whichhave a negative effect on the steel quality have been given.The project extends over a large process where many parameters affect the formation ofinclusions. However, a tendency that a higher addition of alloys seems to increase the totalamount of inclusions before and after the vacuum degassing is seen.The majority of the studied inclusions seem to approach the composition of the top slag aftervacuum degassing. Ladle glaze may cause the inclusions which had a different compositioncompared to that of the slag.A high or low ladleage together with a high argon flow during vacuum degassing seems todissolve particles from the refractory which later on get trapped inside the inclusions.The floatation for two heats has been studied where a short floatation seems to give a higheramount of inclusions in casted material.In machined material so called stringers were found. The main composition of those stringerswas pure alumina. Inclusions with a composition of pure alumina were not found in the liquidsteel, thus the pure alumina inclusions must be formed during the casting. The reason whythose pure alumina inclusions are formed remains for further investigations.</p>

This thesis has been performed at Uddeholms AB with the purpose to investigate theparameters affecting the formation of inclusions during the manufacturing of a low carbonmanganese-steel.A follow-up, steel and slag sampling and evaluations in microscope have been done for a totalof five heats.The results for each heat have been evaluated in relation to the theory from the literaturesurvey and suggestions for changes in the process to reduce the amount of inclusions whichhave a negative effect on the steel quality have been given.The project extends over a large process where many parameters affect the formation ofinclusions. However, a tendency that a higher addition of alloys seems to increase the totalamount of inclusions before and after the vacuum degassing is seen.The majority of the studied inclusions seem to approach the composition of the top slag aftervacuum degassing. Ladle glaze may cause the inclusions which had a different compositioncompared to that of the slag.A high or low ladleage together with a high argon flow during vacuum degassing seems todissolve particles from the refractory which later on get trapped inside the inclusions.The floatation for two heats has been studied where a short floatation seems to give a higheramount of inclusions in casted material.In machined material so called stringers were found. The main composition of those stringerswas pure alumina. Inclusions with a composition of pure alumina were not found in the liquidsteel, thus the pure alumina inclusions must be formed during the casting. The reason whythose pure alumina inclusions are formed remains for further investigations.

Detta examensarbete har utförts på Uddeholms AB i Hagfors i syfte med att undersöka möjliga orsaker till uppkolning av smältan under tillverkning av ett lågkolhaltigt krom-manganstål i ljusbågsugnen. Totalt följdes sju charger upp vid nedsmältningen i ljusbågsugnen. Provtagning av stål, slagg och skrot utfördes under processen. Dessutom undersöktes effekten av syrgasfärskning samt grafitelektrodernas inverkan på kolhalten. Resultatet för varje undersökt parameter har utvärderats och kopplats till teorin, med syftet att genom möjliga samband erhålla förslag till en processföring där behovet av syrgasfärskning för reducering av kolhalt i ljusbågsugnen kan undvikas. Projektet har behandlat en process där många faktorer kan inverka på uppkolningen av smältan. Dock kan ett samband mellan höga kolhalter och tillsatser av skrotet CrNi-rusor ses. På majoriteten av charger med för hög kolhalt tillsattes detta skrot. Dåliga grafitelektroder uppvisar också en tendens att bidra till uppkolning av stålsmältan. Syrgasfärskning tenderar att oxidera större mängder krom och mangan till slaggen, vilket leder till ökade legeringskostnader per tillverkad charge. Den främsta anledningen till de för höga kolhalterna har med stor sannolikhet berott på en kombination av tillsatt skrot med för hög kolhalt samt användning av dåliga elektroder under nedsmältning. Vidare uppföljning av elektroderna och kontroll av skrotet för att minimera uppkolning kvarstår för framtida arbete.