Technological improvement of refractory materials for 120t converter slag retaining system
Description：On the 120t converter, by optimizing the size and taper of the tapping hole, and adding replaceable bowl bricks, the tapping time is shortened and the service life of the tapping hole is increased. In addition, reducing the aperture of the sliding plate, using a slag stopper at the front stop, and optimizing the material of the sliding plate can also increase the service life of the slag stop sliding plate.
Keyword：Technological improvement, refractory materials
Realed product：Mgo-C brick,
- The slag blocking process of the converter slide plate
The key technology for smelting clean steel is slag-free tapping, that is, using the converter tapping nozzle sliding nozzle slag blocking technology. Because the sliding plate opens and closes very quickly, it can effectively block the early and late slag during the tapping process, and it can be combined with infrared slag detection technology and -PLC control technology to realize automatic slag judgment and slag blocking. It is the current converter. A production technology with the best steel slag retaining effect. The sliding plate slag retaining technology is adopted to achieve rapid slag retaining, the success rate of slag retaining is improved, the average slag thickness is reduced, the yield of alloys and deoxidizers is improved, the amount of phosphorus returned to molten steel is reduced, and the refining slagging agent and various Consumption of deoxidizer.
Hebei Yongyang Special Steel New District has one 120t converter, and since it was put into production, it has used sliding plate to stop slag tapping, achieving a very good smelting effect. The smelted steel grades include 60Si2Mn, Q335B, 9SiCr, 33MnCrTiB, 50CrV, 55CrMn, U71Mn, etc. The main products are light rail, heavy rail, crane rail, mining steel, elevator steel, spring flat steel, etc.
- Damage to the refractory material of the slag retaining system
The refractory material of the converter slag retaining system includes a slag retaining slide plate and a tapping port. The slide plate system is installed at the end of the converter tapping port. The skateboard system consists of an inner nozzle, an outer nozzle, an inner slide, and an outer slide (Figure 1). The improvement of the service life of refractory materials of the converter slag retaining system can save labor intensity, reduce production costs, and improve production efficiency and safety.
2.1 Damage to the tap hole
When molten steel flows through the inner hole of the tap hole at high speed, the high-temperature steel flow and the inner hole of the tap hole produce strong erosion, causing mechanical damage to the tap hole.
Oxygen in the molten steel or slag oxidizes the magnesium-carbon steel taphole, which makes the refractory structure loose and causes a decrease in life.
2.2 Damage to the converter skateboard
In the process of tapping steel, the converter slide plate has to withstand the erosion of high temperature molten steel and steel slag; during multiple slag blocking operations, the slide plate and slideway have to withstand the erosion, wear, oxidation and erosion of high temperature molten steel and steel slag. Therefore, the converter slide plate is mostly made of aluminum-zirconium-carbon material with excellent corrosion resistance and thermal shock resistance.
- improvement measures
Refractory materials for Yongyang converter slag blocking are provided by Pu Nai Company. Initially, the life of the tap hole is about 200 furnaces, and the life of the slide plate is about 14 furnaces. The consumption of refractory materials is relatively large, the cost is high, and the production efficiency is low. After several technical improvements, the refractory material for converter slag blocking has achieved very good results.
3.1 Optimization of the design of the inner hole of the tap hole
The taphole adopts a split type. Compared with the integral taphole, its density, high temperature strength, corrosion resistance are improved, and the service life is longer (Figure 2).
The inner hole diameter of the original tapping port is 160mm, and the tapping time is 6~8min. The long tapping time causes the following adverse effects:
(1) Long tapping time increases the corrosion loss of the side lining of the converter steel;
(2) Long tapping time leads to a greater loss of steel temperature, so the requirements for tapping temperature are higher, which also prolongs the cycle period of the converter and reduces production efficiency;
(3) The contact time between the molten steel flowing through the tap hole and the air becomes longer, and this contact between the molten steel and the nitrogen and oxygen in the air increases the nitrogen and oxidation of the molten steel.
After demonstration, the inner hole diameter of the tap hole was changed to 180mm, and the taper of the inner hole was increased. Practice has proved that changing the hole diameter and taper of the tapping brick can shorten the tapping time from 6 to 8 minutes to 3.5 to 5 minutes. The shortened tapping time improves the production efficiency of the converter and reduces the temperature loss during the tapping process.
The test results meet the production requirements, so it is finally determined to adopt a steel port with an inner diameter of 150/180mm. The wall thickness of the front end of the tapping port remains unchanged, but the shortening of tapping time reduces the erosion and erosion of the inner hole of the tapping port, and the average service life of the tapping port can be increased from the original 200 furnaces to more than 300 furnaces. As a result, the time for replacing the tapping port is reduced, and the consumption of gunning material for the tapping port is reduced.
3.2 The use of tapping bowl bricks
The joint between the tap hole and the inner nozzle used at present is easily eroded by molten steel, which limits the life of the tap hole. Therefore, a replaceable bowl brick is installed at this position (Figure 3). When the bowl brick is severely damaged by erosion and melting, the bowl brick can be replaced at the same time as the inner nozzle is replaced. This method is expected to increase the overall life of the tap hole by more than 400 furnaces.
3.3 Improvement of slag stop slide
The raw material zirconium mullite used in the traditional aluminum-zirconium-carbon slide plate is easy to decompose during use, resulting in a loose structure and a decrease in the corrosion resistance of the slide plate, which affects the further improvement of the service life of the slide plate (1). Substituting zirconium corundum and zirconium oxide for zirconium mullite and increasing the content of zirconium oxide can improve the corrosion resistance of the material. Optimize the firing system and firing atmosphere to promote the growth of SiC whiskers in the slide (Figure 4). The generation of a large number of SiC whiskers in the matrix is beneficial to improve the strength of the material and at the same time help to improve the thermal shock resistance of the material.
After the shape of the tap hole inner hole is changed, the tapping speed increases, the interference between the molten steel and the tap hole is weakened, the steel flow is relatively stable, and the turbulence at the end of the tap hole is reduced, and slag entrapment in the later stage is avoided. The erosion is reduced. The tapping time is shortened, which reduces the scouring time of the slag blocking slide plate and the inner and outer nozzles, and reduces the reaming rate of the slide plate and the inner and outer nozzles. After adopting the new tapping port, the service life of the slide plate can be increased from about 14 furnaces to about 18 furnaces. Later in the experiment, the nozzle diameter was changed from 150mm to 140mm, and the tapping time did not increase significantly, and the service life of the slide plate could be increased to more than 20 furnaces, up to 23 furnaces.
3.4 Front and rear double slag retaining technology
The slag stopper is used to block the slag in the early stage before the steel, and then the sliding plate is used to block the slag in the later stage when the steel is about to end. The combined use of these two slag-retaining methods significantly improves the slag-retaining effect. After the tapping is completed, the slag stopper is inserted into the tapping hole of the slag stop slide with a device, and the impact of the early slag is prevented by a relatively large friction force, so as to achieve the purpose of blocking the early slag. The front gear does not use a sliding plate to block the slag because the cost of the slag plug is lower and the use effect is better.
- in conclusion
On the 120t converter, by optimizing the size and taper of the tapping hole, and adding replaceable bowl bricks, the tapping time is shortened and the service life of the tapping hole is increased. In addition, reducing the aperture of the sliding plate, using a slag stopper at the front stop, and optimizing the material of the sliding plate can also increase the service life of the slag stop sliding plate. By taking the above measures, the average life of the 120t converter slide plate has been increased from 14 furnaces to more than 20 furnaces, and the service life of the tap hole has been increased to more than 300 furnaces. After using the tap hole with bowl bricks, it is expected that the life will be increased to 400 furnaces.