Deoxidization

This method of deoxidization involves adding specific metals into the steel. These metals will react with the unwanted oxygen, forming a strong oxide that, compared to pure oxygen, will reduce the steel's strength and qualities by a lesser amount.

The chemical equation for deoxidization is represented by:

${\displaystyle nD+mO\longrightarrow D_{n}O_{m}}$

where n and m are coefficients, D is the deoxidizing agent, and O is oxygen.

Thus, the chemical equilibrium equation involved is:

${\displaystyle K_{eq}=a_{ox}/(a_{D}^{n}*a_{O}^{m})}$

where a_ox is the activity, or concentration, of the oxide in the steel, a_D is the activity of the deoxidizing agent, and a_O is the activity of the oxygen.

An increase in the equilibrium constant K_eq will cause an increase in a_ox, and thus more of the oxide product.

K_eq can be manipulated by the steel temperature via the following equation:

${\displaystyle logK_{eq}=A_{D}/T-B_{D}}$

where A_D and B_D are parameters specific to different deoxidizers and T is the temperature in K°. Below are the values for certain deoxidizers at a temperature of 1873 K°.[1][3]

Below is a list of commonly used metallic deoxidizers:

• Ferrosilicon, ferromanganese, calcium silicide - used in steelmaking in production of carbon steels, stainless steels, and other ferrous alloys
• Manganese - used in steelmaking
• Silicon carbide, calcium carbide - used as ladle deoxidizer in steel production
• Aluminum dross - also a ladle deoxidizer, used in secondary steelmaking
• Calcium - used as a deoxidizer, desulfurizer, or decarbonizer for ferrous and non-ferrous alloys
• Titanium - used as a deoxidizer for steels
• Phosphorus, copper(I) phosphide - used in production of oxygen-free copper
• Calcium hexaboride - used in production of oxygen-free copper, yields higher conductivity copper than phosphorus-deoxidized
• Yttrium - used to deoxidize vanadium and other non-ferrous metals
• Zirconium
• Magnesium
• Carbon
• Tungsten

Vacuum deoxidation is a method which involves using a vacuum to remove impurities. A portion of the carbon and oxygen in steel will react, forming carbon monoxide. CO gas will float up to the top of the liquid steel and be removed by a vacuum system.

As the chemical reaction involved in vacuum deoxidation is:

${\displaystyle C+O\longrightarrow CO}$

the reaction between carbon and oxygen is represented by the following chemical equilibrium equation:

${\displaystyle K_{CO}=P_{CO}/(a_{C}*a_{O})}$

where P_CO is the partial pressure of the carbon monoxide formed.

Decreasing the oxygen activity(a_O) will result in a higher equilibrium constant, thus more product, CO. To achieve this, subjecting the pool of steel to vacuum treatment decreases the value of P_CO, allowing for more CO gas to be produced.[1][4]

This method relies on the idea that deoxidation of slag will lead to the deoxidation of steel.

The chemical equilibrium equation used for this process is:

${\displaystyle K_{FeO}=a_{[O]}/a_{(O)}}$

where a_[O] is the activity of the oxygen in the slag, and a_(O) is the activity of oxygen in the steel.

Reducing the activity in the slag (a_[O]) will lower the oxygen levels in the slag. Afterwards, oxygen will diffuse from the steel into the lesser concentrated slag. This method is done by using deoxidizing agents on the slag, such as coke or silicon. As these agents do not come into direct contact with the steel, non-metallic inclusions will not form in the steel itself.[1]