The order of adding ferroalloys is to add the weak deoxidizing ability first, and then add the stronger deoxidizing ability. Generally, after the slag removal is completed, the carburization operation is completed, and the alloy is added after adding part of the slag to make the reduced slag. The addition requirements of different alloys are as follows:
When smelting silicon steel or spring steel and heat-resistant steel, a large amount of ferrosilicon must be added for alloying, and the added ferrosilicon must be roasted red for a long time. The main reason is that ferrosilicon contains a lot of hydrogen, which can be removed after roasting red, and the melting of ferrosilicon can also be accelerated by preheating; in addition, because ferrosilicon is relatively light when a large amount of ferrosilicon is added to the furnace, a part of silicon and slag must be deoxidized The effect is to generate the acidic product silica, which reduces the basicity of the local slag, which is detrimental to the quality of the steel. In order to prevent this situation, a proper amount of lime should be added before and after adding ferrosilicon to maintain the alkalinity of the slag and a high voltage is applied for a few minutes to make the slag melt and react well and become uniform white slag. The recovery rate of ferrosilicon is between 90% and 98%. In refining, when the chemical composition is adjusted, the temperature is appropriate, and the slag is good, then ferrosilicon can be added. Tapping within 10-25min after joining. If the time is too short, the ferrosilicon will not have time to completely melt, and the distribution of silicon in the steel will not be uniform. If the time is too long, it is easy to make the molten steel absorb gas and affect the quality of the steel.
Ferromanganese can be added at the same time as the reduction slag is made, and the manganese is generally controlled at the lower limit of the composition for the first time. The recovery rate of ferromanganese is over 95%.
Ferrochromium is generally added at the beginning of the reduction period. The affinity between chromium and oxygen is greater than that between iron and oxygen, that is, chromium is easier to oxidize than iron. If it is added during the melting period and oxidation period, chromium will be oxidized, which not only causes the loss of alloy elements but also thickens the slag, which affects dephosphorization and smelting operations, so ferrochrome should be added during the reduction period. If the slag turns green after addition, it means that the slag is not well deoxidized, and the reduction must be strengthened to reduce the chromium oxide in the slag. After the reduction is good, the slag will turn white. The recovery rate of ferrochrome is greater than 95% under the condition of white slag in the reduction period.