Improvement of Cleanness in Melt of Tool Steel by Control of Gas Bubbles And Electromagnetic stirring in the ladle during vacuum treatment

The first part of the project is mainly about changing of slag compositions and see it affect on the inclusions in the ladle furnace. The second part of the project is to study the influence of stirring (EMGAS) on the large inclusions in the steel by changing stirring conditions. The project has done at Uddeholm AB, Hagfors. First, the scrap is melted in ARC furnace then moved to the ladle de-slagging station here removing the slag. After de-slagging, a synthetics slag is added to the melt. During that time, the melt reheating and alloying until getting required compositions and temperature. Slag mainly consists of CaOSiO2-Al2O3-MgO (quaternary system). The project has divided into four periods; The first period was to evaluate the current slag compositions that used in Uddeholm AB for both types of steel, steel A and steel B. The samples of slag and steel were taken before and after vacuum degassing treatment. In this period we can see also the effect of EMGAS on the inclusion removal and Sulfur refining. During vacuum, the melt exposes to two kinds of stirring, electromagnetic stirring and argon as stirring (EMGAS). Electromagnetic stirring applies with very high-intensity stirring reach to 900 A, the direction of stirring is upward. High flow rate of gas argon applies at the same time from two plugs at the bottom of the ladle. Strong stirring aims to remove the sulphur, hydrogen and nitrogen during 50 minutes for steel A and 30 minutes for steel B of vacuum. After vacuum, the cover has been opened and apply only induction stirring with soft stirring, 650A for 20 minutes for both steel A and B, without gas stirring, to remove the large inclusion. The second period is to add l-granules manually after synthetic slag addition stage to kill the slag. Both slag and steel samples have been taken before adding Al, before and after vacuum. The third period is to change slag amount and add pure alumina Al2O3 (260 kg) to ensure the slug was wholly melted at the process temperature. Both slag and steel samples were taken before adding Al2O3, after adding Al2O3 (before vacuum) and after vacuum. The fourth period is related about how the changing of the stirring condition during vacuum and soft stirring after vacuum affects the large inclusions removal in steel melt. The samples for the steel and slag have taken before and after vacuum and after 20 min of soft stirring (before casting).