Introduction
External refining is a metallurgical process used to produce high-quality steel ingots and billets by removing impurities from the molten steel. This is done by controlling the chemical compositions of the steel, by using a process of decarburization and oxidation through the addition of reactive agents. The external refining process is usually done in a furnace, and can be done in a number of different ways, depending on the desired quality of the product.
History
The history of external refining goes back more than two thousand years. The earliest use of this process is believed to have occurred in China during the Han Dynasty (206 BC-220 AD), when charcoal was first used to decarburize pig iron and cast iron in the production of low-grade steel. In Europe, the first use of external refining is thought to have occurred during the Middle Ages, when the furnace was used to remove impurities from molten iron and steel. This process was improved on during the Industrial Revolution, when new materials and techniques were developed to refine steel and other metals to meet higher quality standards.
Objectives of External Refining
External refining is used to increase the quality of the steel or other metal being processed. This is done by removing impurities that can lower the quality of the steel and decrease its strength and wear resistance. By improving the quality of the steel, the process can also increase the performance and life of the product. The removal of impurities can also improve the texture, colour, and overall appearance of the steel or other metal products.
Methods of External Refining
There are several different methods of external refining that can be used to refine iron, steel and other metals.
Vacuum De-Carburization
This method is used to remove carbon from steel and other metals. In this process, a vacuum is created within the furnace, and reactants such as oxygen, nitrogen, or hydrogen are introduced. The reactants chemically react with the carbon in the steel, reducing its concentration, and are then exhausted from the furnace. This method can be used to reduce the carbon content in steel from more than four percent to levels as low as one percent.
Oxidation
This method is also used to reduce the carbon content of steel and other metals. In this process, oxygen is introduced into the furnace and reacts with the carbon in the steel, forming carbon monoxide and other gaseous products. The carbon monoxide is then exhausted from the furnace and the oxygen is used to oxidize other impurities in the steel. This process can be used to reduce the carbon content of steel to levels as low as 0.03%.
Vacuum Degassing
Vacuum degassing is a process used to remove impurities from steel and other metals such as nickel, zinc, and copper. In this process, a vacuum is created within the furnace, and a vacuum pump is used to create a partial vacuum. This creates an area low in pressure and high in temperature, which allows for the release of volatile impurities from the liquid metal. These impurities are then removed from the furnace and exhausted from the system.
Conclusion
External refining is a metallurgical process used to improve the quality of steel and other metals. The process involves controlling the chemical composition of the molten metal to remove impurities that can reduce the quality of the product. There are a number of different methods of external refining that can be used, such as vacuum de-carburization, oxidation, and vacuum degassing. Each process has its own advantages and disadvantages, and must be used properly in order to achieve desired results.
