A revolutionary process of out-of-furnace vacuum arc degassing of liquid steel
MEDICOM GUARANTEES
A revolutionary process of out-of-furnace vacuum arc degassing of liquid steel
Cost efficiency and quality of finished metal are the keys to steelmaking competitiveness. Foreign steelmakers usually enhance steel quality by taking advantage of double-stage out-of-furnace treatment of liquid steel (applying two stations, namely a ladle furnace and a vacuum-treatment degasser). However, this technology requires large initial outlay and operates cumbersome cycling, recirculation, and tank degassers, as well as bulky ladle furnace stations that heat and refine molten steel. Moreover, these units have poor production rates, e.g. it takes up to 40 to 60 minutes to treat liquid steel. This is unsuitable for shops armed with high-performance steelmaking equipment.
Application of ladle furnace stations requires extra overheating of liquid steel in the ladle by some 20-40oC to offset subsequent thermal losses during the vacuum degassing stage. This additional overheating undermines resistance of ladle’s lining, especially in the slag layer area, as well as boosts gas contents in the source metal. This process also requires slag removal from the ladle and application of costly graphite electrodes.
Low pace of metal’s heating in the ladle furnace (less than 2-5oC per minute) and poor heat efficiency (60-70%) prove that the double-stage out-of-furnace treatment has exhausted all the opportunities to accelerate heat transfer and mass transfer processes.
Scientists working with MEDICOM firm have designed, tested, and applied a fundamentally new power-saving, pollution-free, single-unit process of out-of-furnace vacuum arc degassing (VAD) of liquid steel.
The essence of the new VAD process is as follows. When liquid steel is tapped into the casting ladle, the stream of metal passes through an electric arc. Thus, for the first time in the world practice this process combines high-speed stream degassing with electric arc heating of liquid metal. Electrodynamic forces of the arc actively disperse the tapped liquid steel into drops, thus speeding up heat and mass transfer in the ladle. As a result, gases and nonmetallic inclusions are thoroughly refined out of steel. Besides, liquid steel is rapidly heated up to the required temperature and becomes homogeneous.
The process enhances ductility, strength, and impact resistance of finished steel simultaneously lowering the weight and extending the working life of machinery, gearing, and tools twofold to threefold. The new VAD process requires 3 to 4 times as few capital investments as similar foreign methods and excludes the ladle furnace station from the steelmaking process. Since steel treatment is 30-40% less time-consuming and casting temperature can be lowered by 20-40oC, production rate of out-of-furnace steel treatment goes up. Liquid steel needs not to be additionally overheated in the furnace or in the ladle, while the vacuum arc degassing treatment counterbalances thermal losses and ensures the necessary heating.
Scheme of a single VAD treatment unit
Advantages of the new VAD:
The rate of metal’s heating in the ladle increases from 2-3oC per minute to 10-20oC per min;
Heat efficiency is boosted from 60-70% to 75-85%;
Slag needs not to be run off the ladle;
There is no need in preparing a special slag blanket;
Graphite electrodes are not needed to run the process;
It takes 1.5 times as few electric power and 2-3 times as few natural gas.
Introduction of the new vacuum arc degassing to direct-current steelmaking complexes can yield a considerable enhancement of cost efficiency. Therefore, application of the new VAD in steelmaking saves feedstock and energy. The VAD-treated steel can be used in all kinds of industries.
Applications:
car plates for automotive industry;
drill tubes, oil & gas conveyance pipes and tubes;
special steels for the military-industrial complex;
wearable parts for agricultural machines and equipment;
axles, shafts, and pinions of rolling stock, friction bearings, etc. for transportation machinery;
tool steels.
The vacuum arc degassing method has already been introduced to 2-10-ton units in casting and smelting shops. At this point of time, specialists are working on a project of applying the VAD in steel-smelting shop with a 30-ton ladle and in converter shop with a 150-ton ladle. Execution of the project will take up to 18 months, while the payback period comes to 24 months.
The National program for development of Ukraine’s mining and smelting complex provides for restructuring of steelmaking facilities to make continuous-cast steel account for up to 80% of the Ukraine’s total steel output by the year 2010. Phasing in of the new national technical standards will enable manufacturing high-quality competitive steel grades in Ukraine. To meet the requirements of the national program and of the new standards, steelmaking shops will have to equip themselves with out-of-furnace units to treat liquid steel.
Since vacuum arc degassing is truly cost-efficient, causes no pollution, and has weighty advantages over similar foreign treatment methods, it is reasonable to recommend widespread application of the VAD in steelmaking and casting shops of metallurgical mills and machine-building works.
the Metal