Deoxidation of Steel Sep03

Deoxidation of Steel

Deoxidation of Steel  Steel making process consists of refining of hot metal to steel which is done under oxidizing atmosphere. During refining process oxygen get dissolve in steel. The following are the main sources of oxygen in steel. Oxygen blowing Use of oxidizing slags and iron ore during the steel making processes Picking of atmospheric oxygen by the liquid steel during the teeming operation Oxidizing refractories of the lining Rusted and wet scrap. Deoxidation is the last stage in steelmaking. During making of steel, the steel bath at the time of tapping contains 400 to 800 ppm activity of oxygen. Deoxidation is carried out during tapping by adding into the teeming ladle appropriate amounts of ferro alloys or other special deoxidizers. If at the end of the blow the carbon content of the steel is below specifications, the liquid steel is also recarburized in the teeming ladle. However, large additions in the teeming ladle have the adverse effect on the temperature of the liquid steel. Solubility of oxygen in steel is negligibly small. During solidification of molten steel, excess oxygen is rejected by the solidifying steel. Solubility of oxygen in liquid steel is 0.23 % at 1700 deg C. It decreases during cooling down process and then drops sharply during the solidification of liquid steel reaching 0.003 % in solid steel. The excess oxygen liberated from the solid solution oxidizes the components of steel such as C, Fe, and alloying elements resulting into blowholes and non metallic inclusions entrapped within the cast steel structure. Both blowholes and inclusions have considerable effect on the mechanical properties and impact adversely the steel quality. In order to prevent oxidizing of steel components during solidification the oxygen content of liquid steel need to be reduced. This is done by deoxidation of steel which...