LMM GROUP One Stop Solution for Steel Industry: Types of converter steelmaking and analysis of damage mechanism of refractory lining used

Converter steelmaking is currently one of the most widely used steelmaking methods in the world. It has become the mainstream steelmaking method due to its high efficiency, short smelting cycle, low steel production cost, and suitability for the smelting of multiple steel grades. According to statistics, converter steelmaking accounts for more than 70% of the world’s total crude steel output. my country’s converter steelmaking accounts for more than 90% of crude steel output, as shown in Figure 1. According to statistics from the China Iron and Steel Association, as of 2017, my country had 547 steelmaking converters with a total production capacity of 688.91 million tons. In terms of quantity, there are 14 converters with a capacity of 300t and above, and the number of converters with a capacity of 100t and above has exceeded 60%. As the country continues to increase efforts to eliminate backward production capacity, my country’s converters will further develop in the direction of large-scale converters.

Main types and smelting processes of steelmaking converters

Converters can be divided into acid converters and alkaline converters according to the nature of the refractory materials of the lining; according to the part where the gas is blown into the furnace, the converters are divided into bottom blowing, top blowing, side blowing and top and bottom combined blowing converters; according to gas types It is divided into air converter and oxygen converter. Basic oxygen top blowing and top and bottom combined blowing converters have become the most commonly used steelmaking equipment due to their fast production speed, large output, high single furnace output, low cost and low investment. The converter is mainly used to produce carbon steel, alloy steel, etc.

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Converter steelmaking uses molten iron, scrap steel, and ferroalloys as the main raw materials, adding a small amount of quicklime, blowing in air or oxygen to oxidize impurities such as silicon, manganese, phosphorus, sulfur, and carbon, and release a large amount of heat (including 1%(w) of silicon can increase the temperature of pig iron by 200℃), which can make the furnace reach a high enough temperature (without external energy), relying on the physical heat of the molten iron itself and the chemical reaction between the components of the molten iron Generate heat to complete the steelmaking process in the converter.

Refractory materials for steelmaking converter and its damage mechanism

The refractory materials used in the lining of steel-making converters are mainly MgO-C bricks, and a small amount of high-purity magnesia bricks and magnesia dolomite fired bricks are also used. The unshaped refractories used are MgO-SiO2, MgO-C, and MgO-CaO. Quality, high purity MgO quality, etc.

Refractory material type for converter

material type	China	Japan
Shaped products	Magnesia carbon brick	Magnesia carbon brick
Unshaped repair material	MgO-siO、MgO-C、MgO-CaO	MgO-SiO、MgO-C、MgO-CaO、High MgO
Breathable element	Dispersed MgO-C breathable bricks, ring-slit MgO-C breathable bricks, through-hole breathable bricks	Dispersed MgO-C air-permeable brick, ring-slit MgO-C air-permeable brick, porous plug type air supply element (MHP)
Slag stop slide / nozzle	Magnesium-carbon slides, aluminum-carbon slides, aluminum-carbon slides, aluminum-carbon-inlaid slides; non-burning aluminum and carbon nozzles, non-burning aluminum and carbon nozzles, non-burning magnesia-carbon outer nozzles	Magnesium-carbon slides, aluminum-carbon slides, aluminum-carbon slides, aluminum-carbon mosaic slides; non-burning aluminum and carbon nozzles, non-burning aluminum and carbon nozzles

The lining of the converter steel is corroded by a series of strong mechanical, physical and chemical effects during the smelting process. The converter combined blowing process is to install breathable bricks at the bottom of the converter, and blow oxygen, carbon dioxide, argon or nitrogen into the furnace through the breathable bricks to strengthen the stirring of the molten pool and improve the smelting reaction, thus shortening the steelmaking time and increasing The quality of molten steel reduces the cost of steelmaking. However, combined blowing also accelerates the corrosion of refractory materials in the furnace lining, and various parts of the converter are corroded under different conditions.

1）Scour or mechanical shock. The operations such as adding scrap steel and adding molten iron directly face the large-surface furnace lining of the converter, which has a strong impact, abrasion, and erosion on the large-surface furnace lining, which are the main factors of corrosion of the refractory lining. During the smelting process, the airflow in the furnace scoured the furnace wall, furnace cap and other refractory materials, the molten steel and slag melted and washed the furnace lining, and the high temperature reaction during the smelting process caused physical erosion of the furnace lining.

2）Oxidation and chemical attack. Oxidation is a major cause of corrosion of magnesia-carbon bricks in the converter lining. In this process, the carbon components in the magnesia-carbon bricks are oxidized by oxygen-containing components (such as high-temperature oxidizing gas, iron oxide, oxygen, and magnesium oxide) to cause the material The structure is loose and brittle.

FeO+C(s)=Fe+CO(g)， (1)

O2(g)+2C(s)=2CO(g)， (2)

MgO(s)+C(s)=Mg(g)+CO(g)。(3)

The iron oxide in the slag reacts with the graphite or tar/resin on the hot surface of the brick lining, or oxygen erodes the graphite or the binder on the cold surface of the brick lining. In both cases, the strength of the brick is reduced. The fluid is eroded down and lost.

The chemical reaction between iron oxide (FeO) or acidic components in slag, such as SiO2, CaO and MgO, is shown in the following formula:

FeO+MgO=FeO·MgO， (4)

SiO2+2MgO=2MgO·SiO2，(5)

CaO+SiO2+MgO=CaO·MgO·SiO2。(6)

All of the above reactions can turn the furnace lining into slag and cause refractory damage.

3) Thermal shock peeling. The working environment of the air supply element is high pressure and large flow (pressure greater than 1MPa, flow rate 0.15~0.2m3·min-1·t-1), and its damage mechanism is spalling and scouring wear caused by thermal stress concentration [8].

4) Abrasion, melting loss and peeling. Sliding nozzles and sliding plates have to withstand the erosion of high temperature molten steel and steel slag during the tapping process of the converter; the erosion and penetration of strong alkaline slag; and the strong thermal shock of intermittent high temperature (~1600℃). In addition, during the slag blocking operation, the sliding plate must bear the abrasion of steel slag.

Therefore, the erosion and erosion of high-temperature molten steel and steel slag, high-temperature oxidation, roughening and abrasion of sliding surfaces, and thermal shock damage are the main damage methods. The future technical direction of refractory optimization for steelmaking converter is:

Develop high-performance, wear-resistant, thermal shock-resistant low-carbon magnesia-carbon bricks;
Develop fast sintering, pollution-free hot repair materials and long-life gunning materials;
Develop long-life combined blowing gas supply components, optimize furnace bottom tuyere structure and layout, and adapt to advanced steelmaking technical requirements such as top and bottom combined blowing, low-oxygen tapping, bottom blowing powder injection, bottom oxygen supply, and bottom blowing CO2;
Improve the performance and structure of the slag stop slide, prolong the service life and reduce the number of daily replacements.

New technology of refractory materials for steelmaking converter

Development and application of high performance lining brick

Magnesia carbon bricks are widely used as converter lining bricks due to their excellent slag erosion resistance, thermal shock resistance, spalling resistance and abrasion resistance, and good stability at high temperatures. Because magnesia-carbon bricks are prone to oxidation, the thermal shock resistance and erosion resistance are deteriorated. Researchers have conducted extensive research. Its key technical hot spots are reflected in: 1) Application of anti-oxidation and self-repairing new composite antioxidant: using metal Al, Si powder, or Al-Si composite powder as the antioxidant for magnesia carbon bricks, in situ after heat treatment or high temperature service The reaction produces high corrosion resistance phases such as SiC and AlN, which significantly improves the performance of low-carbon magnesium-carbon materials. 2) Preparation and application of low-dimensional graphitized carbon: the addition and application of various pre-synthesized nano-carbons such as nano-carbon black, nano-graphite-oxide composite powder, etc.; low-dimensional graphitized carbon is synthesized in situ, and a suitable transition is selected Inorganic or organic compounds of elements (Fe, Co, Ni) are used as catalysts. Phenolic resins are cracked to produce CO, C2H2, CH4 and other gases. Under the catalysis of transition metals, low-dimensional graphitized carbon such as carbon nanotubes and carbon nanofibers are formed. Through the development and application of these new technologies, MgO-C bricks maintain good corrosion resistance and thermal shock resistance.

MgO-C bricks used in different parts of the converter have different performance requirements. In order to meet the demand, Shinagawa Refractories of Japan has developed a series of MgO-C bricks that meet the performance requirements of different parts. The basic performance and typical characteristics are shown in Table 2. The analysis of the microstructure of the MgO-C brick after use shows that the damage of the MgO-C brick is mainly reflected in the erosion and damage of the molten slag. Researchers in Japan investigated the damage factors of MgO-C bricks and found that limiting the diffusion rate of Mg(g) in MgO-C bricks at high temperatures can reduce the rate of brick damage. The results of the anti-slag erosion test showed that with the increase of the apparent porosity of MgO-C bricks (heat treated at 1500°C), the erosion index of the bricks rose linearly (see Figure 4). Based on this, the dense structure MgO-C brick (B, see Table 2) was prepared by adjusting the amount of antioxidants, the gradation of raw material particles and the production process.

Table 2 Performance of MgO-C brick

project	HS	MR	CB	A	B	C	D	E
MgO	77	79	79	78	78	76	67	84
C	15	13	14	17	17	15	30	10
Apparent porosity /%	3.0	3.8	1.0
Bulk density/(gcm-3)	2.99	2.97	2.92	2.95	3.06	2.98	2.71	3.08
Flexural strength at room temperature /MPa				36	31	49	38	53
Typical characteristics	Wearable	Impact resistance	Impact resistance	Universal	Anti-erosion	Wearable	Impact resistance	anti-oxidation

The MgO-C bricks in the converter charging area are often subjected to mechanical impact from scrap steel materials, which are prone to cracks and expansion, resulting in damage to the lining. The creep resistance of different types of MgO-C bricks is very different, as shown in Figure 5 [3], which causes differences in the thermal shock resistance and mechanical impact resistance of MgO-C bricks. Researchers from Shinagawa Refractories Corporation in Japan found that MgO-C bricks (HS) with higher high temperature flexural strength cannot alleviate the occurrence of damage, while MgO-C bricks with higher fracture energy (fracture toughness) can effectively inhibit cracks Extension. Therefore, two new types of MgO-C bricks, namely matrix-enhanced MgO-C brick (MR) and carbon-bonding-enhanced MgO-C brick (CB), have been developed. The properties are shown in Table 2. The two new types of MgO-C bricks have higher fracture energy (MR0.40kJ and CB0.49kJ, HS only 0.26kJ), crack propagation is suppressed after mechanical impact, and both have better corrosion resistance than HS bricks. Among them, carbon Combined with reinforced MgO-C bricks, the corrosion resistance is better. Figure 2 (Load-displacement curve of several MgO-C bricks after firing at 1200℃)

Magnesium carbon bricks at the taphole of the converter often affect their service life due to carbon oxidation, thermal shock spalling and flow steel wear. Therefore, it is an inevitable trend to develop low-carbon magnesia-carbon bricks with good wear resistance and thermal shock resistance. Researchers at the Second Steel Plant of Taiyuan Iron and Steel used fused magnesia with m(CaO): m(SiO2) ≥ 2 and high-purity flake graphite (C mass fraction ≥ 98%) as the main raw materials, with Al, Mg-Al , Si, B4C, CaB6 are antioxidants, and thermosetting phenolic resin is used as the binder to prepare high-quality low-carbon MgO-C bricks. The properties are shown in Table 3. The newly developed low-carbon magnesia-carbon bricks are used in steel-making converters, and the life of a furnace is stable at 500-700 times, which is significantly higher than the 300-400 times imported low-carbon magnesia-carbon bricks.

Performance of low carbon MgO-C brick

project	C	MgO	Compressive strength at room temperature / MPa	Bulk density / (gcm3)	Apparent porosity /%
Newly developed bricks	5.98	89.70	64.7	3.10	4.6
Imported bricks	5.07	88.99	40.2	3.05	5.5
	6.18	89.07	43.5	3.08	5.2
	5.57	88.52	41.6	3.10	5.5

Development and Application of Unshaped Refractories

Due to the increase in the amount of scrap used in steelmaking and the application of new top and bottom blowing technologies, the working conditions of the converter are more demanding, and the damage of refractory materials is accelerated. The development of monolithic refractories and the application of repair technology have been greatly developed, which can greatly increase the overall service life of the furnace lining without affecting normal production, so that the life of the furnace lining can reach more than 8,000 times, or even more than 20,000 times. At present, large-surface hot repair materials are generally used to maintain the feeding side, furnace bottom and tapping side of the converter, gunning materials are used to maintain the molten pool, fillets and trunnions of the converter, and grout is used for the converter tapping. The caulking and the maintenance of the tapping area when changing the mouth. Among them, large fabrics mainly include MgO-SiO2 (also called water-based large fabrics), MgO-C, MgO-CaO, etc., and gunning materials mainly include MgO, MgO-CaO, and MgO-Cr2O3. These unshaped refractory materials are divided into anhydrous repair materials (mainly asphalt, coal tar and asphalt powder, phenolic resin combination) and water-based repair materials (MgO-SiO2-H2O combination and phosphate combination) according to the different bonding agents. The repair materials of the system have their own advantages and disadvantages, as shown in Table 4. In view of the shortcomings and application requirements of existing repair materials, researchers have conducted a lot of research and developed larger fabrics or gunning materials with better performance.

Types and performance characteristics of high temperature repair materials

classification	Phenolic resin series	Asphalt		Water system
classification	Phenolic resin series	Liquid	Powder	Water system
fluidity	excellent	excellent	excellent	excellent
Adhesion	general	excellent	excellent	general
Hardening time	fine	fine	fine	excellent
Durability	general	fine	fine	General/Bad
other	high cost	Not easy to store, generally more popular Refractory Encyclopedia

At present, the large-surface repair materials for converters used for on-site repair mainly use organic substances such as coal tar, asphalt (about 8%~15%(w)), and resin as binders, which inevitably have some problems, such as: sintering time Too long, after the organic matter is burned out, the material will have many pores and poor compactness, which will result in intolerance to slag erosion, low strength, short service life, and serious pollution of the on-site workshop environment. Qin Yan et al. [16] selected high-purity magnesia powder (w(MgO)=97.02%) and mid-range magnesia particles (w(MgO)=94.80%) as the main raw materials, using ultrafine silica powder (w(SiO2)=96.0%) ) Used as a binder to develop a new type of long-life carbon-free environmentally friendly large-surface repair material for converters.

Environment-friendly water-based converter large-surface repair material does not produce harmful gases during the sintering process, which is safe and environmentally friendly. The product adopts wet self-flow pouring method, which has good high-temperature spreading performance. After high-temperature sintering, it forms a ceramic bond, with compact structure, oxidation resistance, erosion resistance, and bulk density up to 2.83g·cm-3. After being applied by many converter steelmaking users, the on-site use is smoke-free, shortening the sintering time by more than 50% compared with conventional large carbon-based fabrics, and extending the service life by 2 to 3 times.

Table 5 Converter large surface repair material particle ratio w/%

project	Mid-range magnesia		High purity magnesia	other	DispersantE8	Add water	Flow value /mm
project	5~3 mm	3~1 mm	1~0 mm	≤0.074 mm
	23	12	30	35	0.5	5	270

Due to the continuous mechanical impact and the erosion of slag, the refractory materials of the bottom, trunnion and two major surfaces of the oxygen top-blowing converter are easily damaged, and it is necessary to regularly repair the trunnion and slag line by gunning. At present, the converter gunning material commonly used in China is magnesium gunning material. In order to improve its shortcomings of corrosion resistance, erosion resistance, and low service life, Yao Yashuang et al. [22] developed a new type of converter magnesium carbon gunning material. . The raw materials used for gunning materials are mainly 3～0mm magnesia (w(MgO)=95.2%), 3～0mm carbon (w(C)=94.2%), asphalt A (fixed C46.2%, softening point 140～160 ℃), asphalt B (fixed C43.5%, softening point 100～120℃), additives, etc. The carbon and pitch B are combined in different proportions as the carbon source of gunning material, and the fixed carbon mass fraction is about 5% to 7%. It can be known from the test that due to the large particle size of asphalt B, its heating and carbonization speed is slower, and the carbonization degree is higher, which is more beneficial to the adhesion of gunning materials. Among them, the gunning material with a carbon to asphalt mass ratio of 7:2 has the best performance, greater strength after burning, and better corrosion resistance. The application results show that the new converter magnesium-carbon gunning material has low rebound rate, good adhesion and high sintering strength; the original magnesium gunning material has a service life of 7 to 8 furnaces, and the use of the new magnesium-carbon gunning material The service life is 10-13 furnaces, which is increased by more than 30%, greatly reducing the number of converter repairs.

In order to solve the problem of sticking slag on the slag sticking surface of the converter furnace mouth and furnace cap, Zhu Shanhe et al. [23] developed a converter anti-sticking slag gunning material using recycled magnesia carbon bricks as the main raw material. The application results show that the developed anti-sticking slag gunning material has good construction performance. Through semi-dry gunning construction, a complete and uniform sticky slag isolation spray layer can be formed on the surface of the converter mouth. The thickness of the spray layer can reach 35-50mm. The spray adhesion rate is more than 80%, and only one gunning per shift can meet the needs of sticky slag isolation; the thick gunning layer itself and the bonding strength of the gunning surface are low, which reduces the peeling and cleaning of sticky slag Difficulty, reducing the number and time of cleaning sticky slag, effectively improving the cleaning efficiency of sticking slag at the converter mouth, and shortening the non-production operation time; without changing the production process, the converter production capacity can be improved.

Japan’s Shinagawa Refractories Co., Ltd. has developed a quick-hardening MgO-C converter hot repair material. The performance is shown in Table 6 [24]. The developed carbon-bonded MgO-C gunning material has good adhesion even if it is sprayed to the surface of bricks above 1300℃ after slagging. It can significantly improve the hot repair efficiency of the converter, can be constructed at ultra-high temperature, and the hardening time is greatly reduced , Which helps shorten the repair time.

Table 6 The characteristics of Shinagawa’s fast-hardening MgO-C gunning compound

Numbering	FRX-M90-D104	FRX-M90-D110	D110FRX-M90-D58
MgO	77	75	77
CaO	0.8	0.7	0.8
C	7.6	7.2	7.6
Apparent porosity /%	25.5	25.3	25.7
Bulk density / (gcm3)	2.46	2.47	2.42
Adhesion strength /MPa	2.6	2.3	2.5
Heat flow index /%	100	98	100
Hardening time index /%	88	70	100

Top and bottom combined blowing technology

The converter composite blowing process uses bottom blowing gas to stir the molten pool to make the steel slag reaction close to equilibrium, avoiding molten steel over-oxidation and improving the metal recovery rate and molten steel quality. The air supply elements at the bottom of the converter are divided into two categories: nozzle type and brick type. Among them, brick-type air supply elements have become the mainstream direction of development due to their stable performance. Brick-type air supply elements are mainly divided into three types: dispersion type, circular seam type and through-hole type. Dispersion type ventilating bricks have the disadvantages of large gas bypass resistance and low life; ring-seam ventilating bricks are relatively dense and have a longer life than dispersive bricks. They are widely used and are well received, but their stability is far less than that of through-hole vents. brick. Therefore, through-hole ventilation bricks are the new mainstream of future development and application of air supply components. Optimizing its position at the bottom of the molten pool is essential for obtaining a good metallurgical effect for bottom blowing. At present, the most widely used straight hole type gas supply element (MutipleHolePlug, MHP) was first developed by Japan Steel Pipe Company. Its advantages are small gas supply resistance, large gas flow adjustment range, good air tightness, and not easy to leak; metal The reinforcement of the pipe to the refractory brick makes the brick not easy to peel and crack.

In order to optimize the performance of the gas supply element, through the adjustment of the refractory material ratio of the gas supply element and the special treatment of the internal stainless steel tube, the service life of the gas element is greatly improved, and the matching degree with the converter age can be increased. Zhang Yueming uses high-purity fused magnesia (w(MgO)≥97%) and natural flake graphite (w(C)≥98%) as the main raw materials, adding Al, Si powder and B4C (total <6%) as Antioxidant, thermosetting, asphalt modified resin is selected as the binder, and an appropriate amount of asphalt powder is added, and the high-performance MgO-C gas supply element is prepared by the isostatic molding method. The prepared MgO-C gas supply element has significantly improved oxidation resistance, fracture toughness and thermal shock performance, good air tightness, erosion rate of 0.28mm/heat, and maximum life of 2113 heats. In order to reduce the carburizing speed of the stainless steel pipe and increase its service life, the surface coating method of α-Al2O3/ALCH slurry is adopted, and the ratio of α-Al2O3/ALCH is controlled to be greater than 3/7, and the coating thickness is greater than 1mm , To form a dense protective isolation layer with stable thermal performance and resistance to carbon reduction on the surface of the stainless steel tube.

Refractory bricks for converter gas supply components have a large temperature difference between inside and outside, which increases the temperature gradient difference within the refractory bricks; in addition, the temperature drops sharply after tapping, and the ventilated bricks suffer extremely large thermal shocks. Due to the existence of these thermal stresses, cracks are generated and propagated inside the ventilating brick, causing intermittent peeling of the refractory brick. Researchers from Shinagawa Refractories found that the cracks generated in the ventilated bricks are mainly parallel to the hot surface. The damage caused by thermal spalling is far more serious than the damage caused by molten steel corrosion and wear. On the basis of fully investigating the damage mechanism of air-permeable bricks, high-performance air-permeable bricks with high fracture toughness and excellent thermal shock resistance have been developed. The specific properties are shown in Table 7. First, by improving the toughness of the material, the occurrence and propagation of cracks are suppressed, and the peeling damage is greatly reduced. Secondly, by increasing the size of the breathable brick to extend the distance from the crack to the peeling surface, it also effectively reduces the occurrence of peeling. When used in a 220t converter, the loss rate is reduced by about 40% compared with the traditional breathable brick. The spalling damage has been improved, and the converter has operated more than 4000 furnaces without replacing the ventilating bricks.

Performance of refractory bricks for converter gas supply elements

project	MHP Breathable brick	MHP brick	Traditional breathable brick
Mgo	80	75.5	70
C	15	20	27
Apparent porosity /%	2.6	4.6	1.0
Bulk density / (g*cm3)	2.87	2.80	2.72
Compressive strength at room temperature /MPa	35	33

Skateboard slag retaining technology

The converter sliding plate slag blocking technology is an emerging technology that has developed rapidly in recent years. The technology is mainly composed of three parts: the sliding plate slag blocking system, the infrared slag detection system and the hydraulic drive system. The infrared slag detection technology is combined with the PLC control technology. , To realize automatic slag judgment and slag blocking, is currently the best and latest production technology and equipment for converter tapping and slag blocking. Sliding nozzle slag retaining technology has outstanding advantages in reducing molten steel back to phosphorus, improving alloy yield, reducing inclusions in steel, improving molten steel cleanliness, reducing ladle sticking slag, and extending ladle service life.

The inner nozzle of the tapping hole of the converter is connected to the end of the tapping brick, and the upper sliding plate of the outlet is connected below, and the outer nozzle is connected to the lower sliding plate of the outlet. Therefore, the inner/outer nozzle and slide plate not only have to withstand the erosion of high-temperature molten steel and slag, but also withstand the erosion and penetration of strong alkaline slag during the tapping process of the converter, and also withstand the high temperature (~1600℃) during discontinuous tapping. The strong thermal shock. In addition, during frequent slag blocking operations, the casting holes and slideways of the slide plate have to withstand the abrasion and melting loss of high temperature molten steel and steel slag. Therefore, it is required that the material selection of the inner/outer nozzle and the slide plate should pay attention to better slag corrosion resistance, high temperature oxidation resistance and excellent thermal shock resistance. The slide material should also have excellent wear resistance.

At present, there are three main materials for the outer nozzle of the converter tapping nozzle on the market: non-burned magnesia carbon, non-burned aluminum-zirconium carbon and zirconia (inlaid core). Among them, the magnesia-carbon nozzle occupies the mainstream of the market due to its cost advantage. The performance of the carbon nozzle is slightly better than that of the magnesium carbon. The nozzle with an inlaid zirconia core is in the research and development stage, and its service life can reach more than 120 times, and can even be synchronized with the life of the tapping nozzle. Most of the non-burning nozzles are treated with bitumen soaking to close the pores, improve density and corrosion resistance, and their service life ranges from 30 to 90 heats.

Physical and chemical indexes and service life of different material outer nozzles

Material	chemical components（w)/%				Bulk density/(gem-3)	Apparent porosity /%	Service life/time
	A1,O3	MgO	C	ZrO2
Magnesium Carbon		≥80	≥9		≥2.90	≤10	30~80
Aluminum Zirconium Carbon	275		≥6	≥3	≥3.00	≤10	50~90
Zirconia(Inner core)				≥90	≥4.5	≤15	90~120

The slag retaining slide is one of the most critical components in the application of sliding nozzle slag retaining technology. At present, the material of the domestic slag stop slide is mostly aluminum-zirconium carbon. As the material of the flow control slide, it has high strength, good thermal shock resistance, excellent erosion resistance and corrosion resistance; but for the slag stop technology, the service life of the slide is partial. Low, only stable at about 10 to 14 furnaces. Therefore, the researchers improved the performance of the slag stop slide through a variety of ways. Studies have shown that the introduction of expanded graphite and Si powder can promote the formation of SiC whiskers in aluminum-carbon refractory materials to a certain extent, improve the toughness of the slide plate, enhance the ability to resist crack growth, and make the slide plate’s thermal shock resistance and service life improve.

In order to meet the high life requirements of 18-20 heats or even more than 25 heats proposed by steel companies, the material of the skateboard has been transformed from conventional refired aluminum-zirconium-carbon to a composite structure with aluminum-zirconium-carbon for the body and zirconium-based inlay layer. . At present, there are mainly the following three categories:

①The upper slide plate inlaid with zirconium ring is matched with the lower slide plate inlaid with zirconium plate;

②The upper slide plate inlaid with zirconium plate is matched with the lower slide plate inlaid with zirconium plate;

③The upper slide plate inlaid with zirconium ring is matched with the slideway anti-slip area Lower slide plate inlaid with zirconium plate. The service life of the inlaid sliding plate on the 120-300t converter (front and late slag blocking) can be stabilized at least 15-18 times. If other slag blocking methods are used for the slag blocking at the early stage, the sliding plate life can be reached only in the later stage. 20-25 heats.

Physical and chemical indicators and service life of different material skateboards

Material	Al2O3	MgO	C	ZrO2	Bulk density /(gcm3)	Apparent porosity /%	Service life/heats
Magnesium Carbon	≥4	≥75	≥2.5		≥2.85	≤10	6-8
Aluminum carbon	≥85		≥6		≥2.95	≤8	6-10
Spinel Carbon	≥75	≥6	≥6		≥2.95	≤8	6-10
Aluminum Zirconium Carbon	≥70		≥6	≥6	≥3.10	≤8	10-15
Aluminum zirconium carbon inlaid zirconium ring/plate							23-25

The disadvantage of sliding nozzle slag blocking technology is that the life of refractory components is relatively low. To this end, Interstop and RHI cooperated to improve the traditional steel pouring system and developed a new type of sliding nozzle of CG120 for the taphole of the steelmaking converter. The CG120 sliding nozzle system adopts a brand-new structure, and the entire sliding nozzle device can be removed from the steel shell when replacing the inner slide plate. The system improves the use effect of refractory materials and significantly shortens the converter shutdown time. The life of the upper connecting element of the CG new sliding nozzle is 24.8 furnaces, and the life of the refractory element is 24.8 times.

Sinosteel Luo Nai Institute summarized the damage reasons of the converter slag stop slide and found that the upper slide of the slag stop was in contact with molten steel, mainly due to erosion and reaming damage, and the lower slide was in contact with the outside air, mainly due to thermal shock crack propagation damage. Therefore, through the process of inlaying zirconium rings on the upper slide plate and zirconium plates on the lower slide plate, and through measures such as phase composition control and microstructure control, the thermal shock resistance of the zirconium ring and zirconium plate is improved, and the life of the slag stop slide is stable. At about 20 heats, the cost-effectiveness of sliding slag blocking is significantly improved. The three series of products developed can meet the needs of different working conditions. The specific performance is shown in Table 10.

The physical and chemical indexes and performance of the zirconium ring and zirconium plate of the converter sliding plate

performance	GH/GB-A	GH/GB-B	GH/GB-C
w(ZrO+HfO,)/%	≥95.0	≥95.0	≥95.0
Apparent porosity /%	≤8.0	≤12.0	≤18.0
Bulk density ( gcm3)	≥5.2	≥5.0	≥4.8
Compressive strength /MPa	≥180	≥150	≥120
Thermal shock resistance (1 100 ℃, water cooling)/time	No cracking 2 times	No cracking 3 times	No cracking 3 times

By continuously improving and optimizing the shape and structure design of the sliding plate and the design of the inlay structure, increasing the locking force of the sliding plate under high temperature expansion and deformation, preventing the occurrence and expansion of abnormal cracks, preventing the Compressive strength formation of abnormal seepage steel channels; increasing infrared slag detection The accuracy of the system and the stability of the operating speed of the cylinder of the hydraulic drive unit focus on solving the deficiencies found in the application, which greatly improves the safety and reliability of the sliding slag retaining technology.

The progress of steelmaking technology promotes the development of new technology of refractory materials for steelmaking converters. The refractory materials involved in the new technology not only have the characteristics of stable high temperature structure, resistance to peeling, abrasion resistance, and good slag resistance, but also reflect the development concept of energy saving, long life, low carbon and environmental protection. The future development trends of refractory materials for steelmaking converters are:

1) Develop and promote high-performance magnesium-carbon refractory materials;

2) Promote and apply new environmentally friendly unshaped refractory materials and high-temperature repair technology;

3) Develop new type of composite structure refractory materials, such as composite gas supply elements, composite slide plates, etc.

4) Research and develop light-weight, energy-saving and high-temperature refractory materials.

One stop service for steel industry - LMM GROUP

LMM GROUP One Stop Solution for Steel Industry

Wednesday, January 6, 2021

Types of converter steelmaking and analysis of damage mechanism of refractory lining used

Main types and smelting processes of steelmaking converters

Refractory materials for steelmaking converter and its damage mechanism

New technology of refractory materials for steelmaking converter

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