Steelmaking deoxidizers are used in the process of steel making to remove oxygen from molten metal during the initial stages of reduction. There are various routes available to control oxygen content, inclusion chemistry and the final oxidation level of the steel. The most common elements used for deoxidation are silicon, aluminum and manganese. In addition, barium and calcium are sometimes added.
Aluminum is a very strong deoxidizer, and it is widely used in the steelmaking industry. It is also effective at suppressing blow holes and the formation of carbon monoxide during solidification. This is due to the high density of aluminum. Several steel producers are also beginning to form liquid calcium aluminate inclusions in their liquid steel. Calcium can alleviate the clogging problem associated with alumina in aluminum killed steels.
Generally, silicon, aluminum and manganese are the components used in steel deoxidation. They are added to the molten steel in the proper ratios. Silicon and manganese can be added as a single element or in a mix. If a strong deoxidizer is needed, special deoxidizers are available.
Some of the more complex deoxidizers are: Si-Al-Ba-Ca, Si-Al-Mn and Si-Al-Ti. These compounds are used for improving processing properties, impact toughness and workability.
Other types of deoxidizers include silicon-copper slab, 20 percent magnesium-copper slab and 2 percent lithium copper. Usually, a composite deoxidizer is added at the bottom of the ladle. Depending on the proportion of adding, the amount of composite deoxidizer is adjusted. Another method of deoxidization is diffusion.
The primary use of steelmaking deoxidizers is for ordinary steel, whereas it has some applications for LF furnace and electric furnace. The final product is a briquette. When this deoxidizer is injected into molten steel, it effectively deoxidizes the molten metal in the first stage of reduction. Among these, the most important application is for the casting of steel.
An effective steelmaking deoxidizer can be divided into a primary deoxidizer and an intermediate deoxidizer. Primary deoxidizers are formulated with iron containing powder and are used for the initial reduction stage of smelting. Intermediate deoxidizers are formulated with silicon carbide and are added at the end of the reduction stage.
During the deoxidization process, the carbon content of the steel is reduced. The result is a cleaner ingot skin. A lower carbon content ingot makes it ideal for applications involving heat treatment. Moreover, a clean ingot skin also results in a defect free casting.
In the past, a combination of silicon and manganese was the only basic deoxidation strategy. However, newer techniques and advanced slag conditioning have led to an increase in soluble magnesium in many steels. Residual levels of magnesium below one ppm are very difficult to process, and can cause problems.
Deoxidizing agent technology has undergone rapid change over the last five years. It has become cost effective and free of operation burden. Compared with alkaline products, acid based products can remove scales and oxides faster. While manganese and silicon are the most common deoxidizers, other elements such as zirconium, calcium and titanium are being investigated for complex deoxidation.
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