1. A gas that dissolves in metals, primarily hydrogen and oxygen. In the smelting process, the main sources of gas are: 

(1) furnace gas: non-vacuum smelting, furnace gas is the main source of gas in the metal. In addition to oxygen and nitrogen in the furnace gas, but also contains water vapor, hydrogen, carbon monoxide, carbon dioxide, sulfur dioxide and hydrocarbons. The composition of furnace gas varies with the fuel used and the conditions of combustion; for example, a reverberatory or crucible furnace fueled with heavy oil or gas often contains 5-10% water vapor and more hydrogen and carbon monoxide. 

(2) charge: Most of the electrolytic metal surface have residual electrolyte, processing workshop return materials mostly contain oil, water, emulsion and so on. Foreign waste mostly have water corrosion, corrosion and so on. In particular, open stacking and wet season, charge surface adsorption of moisture. These allow the metal to absorb more hydrogen during the smelting process.

 (3) Refractory: the Moisture in the Refractory also causes the metal to inhale, especially when the new furnace starts production.

 (4) FLUXES: Many fluxes contain water. Some (such as charcoal, Rice Bran, etc.) contain adsorbed water. Some fluxes (such as Borax) contain crystal water. In order to reduce the source of gases in the smelting process, the flux should be dried or dehydrated. 

(5) operating tools: operating tools that are not preheated thoroughly can also increase the gas content of the metal.

2. Gas dissolution process and solubility solubility of gas in metal: Metal in solid, the solubility of the gas is very small, with the rise of the temperature solubility slowly increases, to the melting point temperature solubility increases sharply, continue to improve the temperature of molten metal, gas solubility continues to increase, to a maximum point began to decline, to the boiling point temperature of the metal, the solubility of the gas is almost zero. Different alloying elements have different effects on the solubility of gas in the alloy. Some elements, such as nickel, have greater binding force with gas, which increases the solubility of gas in the alloy. Other elements such as aluminum and tin can reduce the solubility of gas in the alloy. The effect of alloying elements on hydrogen solubility in copper alloys is as follows: Cu Ni & Gt; Cu Pb > Cu Ag > Cu Au > Cu Sn > Cu Al

3. Degassing method 

(1) gas degassing method: One is an inert gas (such as N2, etc.) , the other is an active gas (such as CL2, etc.) the smaller the number of bubbles, the degassing is beneficial. However, due to the high speed of bubble floating, the short time to pass through the melt, and the fact that the bubble can not be evenly distributed in the whole melt, it is not easy to completely degassing by this method, and the degassing effect decreases significantly with the decrease of hydrogen content in the melt. 

(2) flux degassing: The flux degassing is the use of molten salt thermal decomposition or replacement reaction with the metal, resulting in insoluble in the melt of volatile bubbles and hydrogen removal. Such as aluminum bronze commonly used cryolite flux degassing, copper and nickel alloys commonly used fluorite, Borax, calcium carbonate and other flux degassing. When the flux is refined, the dry flux is generally pressed into the molten pool with a perforated cover. In order to improve the removal effect, dry nitrogen can also be used to blow the powder flux into the bath. The flux can remove slag as well as degassing. 

(3) boiling degassing: a common method of smelting zinc-rich brass in a frequency furnace. But there are two conditions: one is that the boiling temperature of high zinc brass is lower, and the other is that the melt temperature of channel part is higher. The boiling temperature of cu-zn alloy decreases with the increase of zn content. Due to the highest temperature of the melt in the channel part of the power frequency furnace, the steam bubbles that first form zinc float up immediately. With the increase of the bath temperature, the steam pressure in the furnace increases gradually, and even the surface of the bath bubbles when the bath temperature reaches the boiling point of zinc. When the vapor pressure above the Molten Pool Rises Above Atmospheric Pressure, Zinc vapor is ejected to the furnace mouth and is oxidized and burned, forming a boiling flame phenomenon. The more times, degassing effect is better, generally 2-3 times can be. Brass containing less than 20% zinc can not be degassed by boiling. The disadvantage is that low boiling point metal elements (such as ZINC, etc.) more loss. 

(4) other degassing methods: 1) condensation degassing; 2) Oscillation Degassing; 3) direct current electrolysis degassing

4. The process of oxygen removal by reducing oxides in molten metal is called deoxidation. The process of Deoxidation in Molten Metals and alloys is a displacement reaction, where under operating conditions any substance from which oxygen can be obtained from Molten metals, that is, an element whose decomposition pressure is lower than that of the deoxidized metal oxides, it’s usually used as a deoxidizer.

 5. Deoxidizer Deoxidizer is divided into surface deoxidizer and metal-soluble Deoxidizer. The surface deoxidizer is basically insoluble in the metal, the deoxidization only takes place on the surface in contact with the metal, and the deoxidization speed is slow. It has the advantage of being insoluble in metal, and the Deoxidizer does not affect the quality of metal. Common Surface Deoxidizers are: Calcium Carbide, magnesium boride, charcoal, Boron (B2O3) and so on. The Deoxidizer dissolved in the metal can interact with the oxide in the molten metal in the whole Molten Pool, and the deoxidization effect is much better. The disadvantage is that the residual deoxidizer will remain in the metal and affect its properties. Commonly used deoxidizers are: Phosphorus, silicon, manganese, aluminum, magnesium, calcium, titanium, lithium and so on. These elements can be added in the form of a master alloy. The small solid oxide produced by deoxidation increases the viscosity of the metal or becomes an inhomogeneous inclusion in the metal, so the addition amount should be controlled. Requirements for DEOXIDIZERS: 1. Harmless to the properties of metals or alloys. 2. The deoxidation product is preferably insoluble in molten metal and is easily removed. 3. The Deoxidizer should be sufficiently active, that is, the deoxidization product should be quite different from the molten metal in specific gravity and melting point. Copper-phosphorus master alloy can not only deoxidize, but also improve the fluidity of the alloy, so it is widely used in copper alloy production.

 Source: Hot Working Forum