manufacture of steel grit

- Sep 07, 2017 -

The following is a procedure for the manufacture of steel having the desired composition for use in the preparation of shot. Use may be made of an electric arc furnace in which the initial charge of scrap steel is reduced to a molten state after which ore (iron oxide) is added in amounts to obtain an oxidized state Within the furnace which is maintained throughout the heat. In practice, the iron oxide or ore is added before the bath reaches a temperature of approximately 2500-2600 F.


It is believed that oxygen present under the oxidizing conditions maintained within the furnace combines with silicon to form a silicon oxide which finds its way into the slag. This thereby tends to reduce the silicon content of the bath to about 0.10 percent or less. As 'will hereinafter be pointed out, it is desirable to maintain the silicon content at this low level during the heat because silicon tends to hold such gases as nitrogen and hydrogen which find their way into the shot or pellets formed as blow holes or hollows.


When the temperature of the bath reaches approximately 2700-2750" F., reaction begins to take place between carbon and iron oxide, first forming carbon monoxide and then carbon dioxide. The formation of carbon monoxide and carbon dioxide causes boiling to take place in the bath. During the boil, the entrapped gases and metal oxide inclusions are removed from the melt, producing a fluid metal having high surface tension.


After boiling to remove the entrapped or dissolved gases and the oxide inclusions, the bath is held at the elevated temperature for a refining period during which the composition of the slag is controlled by the addition of ferromanganese, mill scale, burned lime, fiuorspar and the like in the case of a basic furnace. or ferromanganese, mill scale, silica sand, lime and the like in the case of an acid furnace.


When the bath reaches pouring temperature at about 29003200 F., alloying ingredients are added such as by way of ferrosilicon and ferromanganese to adjust the bath to the desired composition. These materials function concurrently to de-oxidize the bath but it is desirable to make use of a strong de-oxidizing agent in addition to these alloying elements for securing the desired results.


For production of shot having rounded shapes and which are free of hollows formed by occluded gases, such as nitrogen and hydrogen, it is desirable, as previously pointed out, to maintain oxidizing conditions within the furnace until the addition of the alloying elements prior to pouring and for this purpose it is desirable also to reduce the silicon content in the bath to below 0.10 percent. The boiling period isintendedto remove the entrapped gases, the entrapped slag and oxide inclusions which may be formed by oxidation of such elements.

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