RH Vacuum Refining Furnace Process and Equipment Overview

RH Vacuum Refining Furnace Process and Equipment Overview

Refining is the process of transferring the steel molten metal, which has been initially processed in a converter or electric arc furnace, to another reactor for further treatment, also known as secondary refining. The main goal is to divide the traditional steelmaking process into two steps: primary refining and secondary refining. In primary refining, the steel is melted, dephosphorized, decarburized, and alloyed under an oxidizing atmosphere. In secondary refining, the steel undergoes deep decarburization, degassing, deoxidation, removal of inclusions, and modification of inclusions under a vacuum or inert gas/controlled atmosphere. The composition is adjusted, and the temperature of the molten steel is controlled to optimize the process, improve the product structure, develop high-value-added products, and achieve energy savings, reduced consumption, lower production costs, and increased economic benefits.

History of RH Vacuum Refining Technology

The RH vacuum refining technology originated in the 1950s. In 1957, the Albrecht company applied for a patent for the steel vacuum refining degassing method, marking the beginning of the development of vacuum degassing technology. In 1958, Germany's Rhein Company, in cooperation with Heraeus Vacuum Pump Factory, successfully conducted industrial production experiments, achieving significant results. In 1959, the German Metallurgical Association officially named it the RH process. Japan has been the leader in developing this technology, with Nippon Steel inventing the RH-OB process in 1972, which effectively improved aluminum operations. In the 1980s and 1990s, Kawasaki in Japan invented the RH-KTB process, realizing secondary combustion and oxygen blowing decarburization, and combined it with the KPB (MFB) top lance technology for desulfurization, which allowed the production of ultra-low carbon steel with a carbon content of 20 ppm or lower. In China, the development of RH technology began in the 1990s, and now most medium and large steel plants are equipped with RH furnaces.

RH Vacuum Refining Process Overview

1. Steel Water Transfer: The steel ladle to be processed is transported by a crane to the RH ladle car, which then moves to the treatment position below the vacuum chamber. Operators determine the steel liquid level, and the ladle car is then raised to the preset height.

2. Temperature Measurement and Sampling: The steel water is subjected to temperature measurement, sampling, and oxygen analysis by the operators.

3. Vacuum Treatment: The ladle car is raised again by a hydraulic cylinder to insert the immersion pipe of the vacuum chamber into the steel water to the required depth. At the same time, argon gas is blown into the immersion pipe at the preset flow rate, and the vacuum pump is started. The vacuum pumps operate according to the preset evacuation curve, and the steel water begins to undergo treatment in the vacuum environment.

4. Degassing and Decarburization: During the specified time and low-pressure conditions, vacuum degassing is continuously carried out to reach the desired degassing target. In the decarburization process, carbon in the steel reacts with oxygen to form carbon monoxide, which is then evacuated by the vacuum pump. If the oxygen content in the steel is insufficient, oxygen can be provided through the top lance to accelerate decarburization. When decarburization is complete, aluminum is added to deoxidize the steel.

5. Addition of Alloying Materials: After deoxidation, alloying materials are added to the vacuum chamber through the vacuum feeder. At this stage, the steel's temperature, oxygen content, and chemical composition are measured and adjusted.

6. Completion of Treatment: After processing, the vacuum pump system is shut down in sequence, and the vacuum chamber is restored to atmospheric pressure. The ladle car is lowered to the track.

7. Post-Treatment: The ladle car moves to the slagging station where argon gas is blown, and slagging agent is added. Finally, the ladle car is moved to the lifting position, and the ladle is lifted by a crane to the continuous casting ladle turntable.

Main Equipment in RH Vacuum Refining

1. Vacuum Chamber: The metallurgical reaction of steel occurs in a vacuum chamber lined with refractory materials. The lower part of the vacuum chamber contains two immersion pipes with refractory linings: one for upward gas injection (argon) and the other for downward gas flow. The upward pipe constantly blows argon into the molten steel, creating a higher static pressure difference compared to the downward pipe, which allows the steel to flow from the upward pipe to the downward pipe, continuously circulating inside the vacuum chamber.

2. Ladle Lifting System: The ladle lifting system consists of the ladle car, ladle lifting device, and hydraulic station. The hydraulic cylinder drives the lifting frame, allowing the ladle car and steel ladle to be raised, so the immersion pipes in the vacuum chamber can be inserted into the ladle for treatment.

3. Vacuum Pump System: The vacuum pump system primarily uses steam jet pumps, which are composed of working nozzles, diffusers, and mixing chambers. In this special pipeline, steam flows at high speed from the nozzle exit to the diffuser inlet, creating a negative pressure zone in the mixing chamber. At this point, the gas to be evacuated is sucked into the chamber, where the steam and the gas exchange energy. The vacuum pump system consists of multi-stage pumps connected in series for progressive compression.

4. Feeding System: Alloying materials are added to the vacuum chamber through the vacuum feeder to adjust the composition of the steel.

5. Top Lance and Pre-Heating Lance: The top lance plays a critical role in RH refining, including cooling steel, baking the vacuum chamber, aluminum heating, and oxygen blowing decarburization. The pre-heating lance is primarily used for preheating and baking the vacuum chamber.

By using the above processes and equipment, the RH vacuum refining technology effectively improves the quality of molten steel, ensures precise control of its composition, and thus enhances the performance and added value of steel products.