Vacuum degassing is a process under low pressure and high temperature conditions to remove hydroxide, hydrogen and other dissolved gases from molten steel in order to reduce the emission of harmful gases. This process is also known as vacuum dehydration and deoxidation.
The main task of vacuum degassing of molten steel is to reduce the content of dissolved hydrogen, carbon and oxygen in the steel. These substances are dissolved in the steel at high temperatures, causing bubbles to form in the steel, which can make the steel porous. It also causes hot crack, blade crack and other defects in the heat-treated product. Therefore, it is necessary to remove these substances from the molten steel as far as possible.
The process of vacuum degassing includes several steps. Firstly, the furnace is heated to a certain temperature and the molten steel is poured into a degassing tank or a stainless steel consumable electrode arc furnace. Secondly, the molten steel is subjected to an environment with a lower partial pressure of oxygen, and a vacuum is created in the tank. During the process of degassing, argon and nitrogen are used to sparge the atmospheres to help remove dissolved gases. Thirdly, after the steel is degassed to a certain depth, its temperature is raised to improve the effect of degassing and reduce the content of dissolved gases.
The degassed steel is then sent to the furnace to further reduce the oxygen concentration. In the furnace, the steel is heated by an inert gas such as argon to a temperature of around 1500℃. The temperature of the steel is then raised or lowered depending on the steel composition. Finally, the steel is cooled to reach a certain composition and create a homogeneous structure.
The benefits of vacuum degassing include improved cleanliness of the steel and a homogeneous structure, as well as improved surface finish and machinability. Vacuum degassing also helps reduce the occurrence of defects such as undercuts due to dissolved oxygen in the steel during casting.
Vacuum degassing has become a popular method for refining molten steel as it is relatively quick and effective. However, it is important to remember that the process should be regularly monitored to ensure that the steel has the desired properties. Additionally, it is essential to ensure that the vacuum system is set up correctly and maintained regularly in order to get the best results.
