Refractories and Industrial Ceramics
Vol. 42, Nos. 5 – 6, 2001
UDC 666.762.8:621.746.328.3
SUBMERSIBLE LADLE NOZZLES FOR CONTINUOUS CASTING MACHINES: STATE OF THE ART AND PROSPECTS OF DEVELOPMENT V. V. Kolomeitsev, E. F. Kolomeitseva, and S. A. Suvorov Translated from Ogneupory i Tekhnicheskaya Keramika, No. 6, pp. 49 – 58, June, 2001. The state of the art in the technology, properties, and uses of submersible quartz and corundum-graphite nozzles for continuum steel casting is considered. Corundum-graphite nozzles display a low heat resistance, increased air permeability and, moreover, are environmentally hazardous. The existing methods for updating corundum-graphite nozzles fail to settle the question of channel clogging in casting rimmed steel and other types of steel. Quartz nozzles fabricated by conventional technologies are devoid of these shortcomings; however, they have a shorter life because of the chemical interaction of alloying steel components and their oxides with SiO2. Comparative tests on submersible quartz nozzles differing in structure and chemical and phase composition showed the emerging potential for new technologies and approaches in the production and uses of updated quartz glass-based nozzles for casting common and low-alloy steels. For casting common steels, updated submersible quartz nozzles are developed with a warranty endurance, under slab CCM operating conditions, of 720 tons (in terms of steel cast) against the rated life of 1200 tons. For low-alloy steels, modified submersible quartz nozzles are recommended with a warranty endurance of 360 tons (in terms of steel cast) against the rated life of 540 tons.
The properties and uses of refractory materials for continuous casting machines (CCM) have been studied in a number of works [1 – 7]. The updating of casting technology remains inseparable from improvements in the operational properties of refractory materials and refractory engineering components, which in full measure is relevant to submersible ladle nozzles. Conventionally, in CCM-assisted steel pouring technology, submersible nozzles made of composite materials (corundum-graphite and other carbon-containing composites) or from quartz are used. The advantages of quartz or corundum-graphite nozzles for casting low-alloy, killed, semikilled, or rimmed steels are still a controversial issue [1, 4, 8, 9]. Therefore, the efficiency of their use should be considered with allowance made for their properties and service conditions, and taking into account social, ecological, and economic expedience that would allow the appropriate choice of material and structure in order to attain the optimum result. The submersible nozzle is an engineering component intended for protection of the molten metal from oxidation and for controlled delivery of the metal to the CCM mould to provide the required conditions for crystallization and properties of the continuous casting. Viewed in this light, all requirements placed on the submersible nozzle as a multifunctional engineering component
should be formulated allowing for specific conditions of its service and with observance of all specifications of its operational reliability. Generally, the specifications on submersible nozzles contain just data on chemical composition, open porosity, shape, and dimensions [10]. Specifications from foreign manufacturers contain also characteristics of the warrantable service life for CCM submersible nozzles exploited under normal (rated) operating conditions. In practice, domestic metallurgical manufacturers set the rated service life for submersible nozzles depending on the characteristics of the steel cast. The CCM productivity and characteristics of continuous castings (surface condition, concentration of nonmetallic inclusions) are determined by the properties of refractory materials and the casting technology used. Any departure from the normative requirements of casting technology leads to a degradation of the cast product. Such departures most likely occur at the beginning and end of the casting process, or during replacement of the casting ladle, intermediate ladle, or submersible nozzle. Under these conditions, each 1 – 1.5 min needed, for example, for replacement of the nozzle in a slab CCM, entail the loss of 4 – 8 tons of continuously cast product and the rejection of 5 – 10 tons of substandard product because of the “cold shut” fault [11]. Shortening the replacement time improves the CCM economic indicators; still, it does not preclude losses in the form of substandard metal 251
1083-4877/01/0506-0251$25.00 © 2001 Plenum Publishing Corporation
252 sent back for reprocessing. Minimization of losses from the above factors can be attained with allowance for the endurance properties of CCN refractory materials under operating conditions. Thus, endurance as the total estimator of the nozzle’s qualities and operating conditions serves also as an indicator of operational reliability. The concept of “endurance,” because of its wide (and frequently inadequate) use in the literature, requires definition in more precise terms. Therefore, it would appear appropriate to suggest terms for defining the operational reliability of submersible ladle nozzles. Service life, or simply life (endurance) is the operating time which, once exceeded, gives grounds for the given component to be taken out of service because of its actual wear (which is determined by the component’s properties only) on condition of the strict observance of all requirements placed on the technological use of the component (in this case, the CCM submersible nozzle). The typical features attesting to the nozzle wear are: (i) cracks; (ii) crusting and narrowing of the running channel and steel-tapping holes; (iii) wall burn-out in the slag zone; (iv) fracture of the submersible section; (v) distortion of the channel, bottom section, splitter, and steel-tapping holes from true geometry, which causes turbulization of molten metal poured in the mould. Warranty endurance (rated life) is the operating time which, once exceeded, gives grounds for the given component to be taken out of service because of its reaching the rated wear (which is determined by the component’s properties only) on condition of the strict observance of all requirements placed on the technological use of the component (in this special case, the CCM submersible nozzle). The typical features attesting to the rated wear of the components used in slab CCMs are: – residual wall thickness not less than 14 mm for the quartz nozzle and not less than 20 mm for the corundumgraphite nozzle; – narrowing of the cross-sectional area of the running channel and steel-tapping holes not exceeding 30% for the quartz nozzle and 20% for the corundum-graphite nozzle.1 In certain cases [12], the specific wear rate is assigned starting from the mean residual wall thickness of the nozzle. However, the objection against this approach is that nozzles are frequently taken out of service because of local wear, for example, the wall burn-out in the slag zone, which in fact determines the nozzle’s service life. Operational endurance is the operating time which, once exceeded, gives grounds for the given component (the nozzle) to be taken out of service for reasons determined both by the component’s properties and the processing factors including nonobservance of the CCM casting technology or violation of the operating instruction. 1
We note here that in bloom CCMs exploited at the Oskolskii Electrometallurgical Works Joint-Stock Co., the residual wall thickness of corundum-graphite nozzle is 5 – 7 mm, which formally equates the operating endurance to the rated life.
V. V. Kolomeitsev et al. Each of the above indices of operational reliability in a given set of nozzles is brought in correspondence with the arithmetic mean of a representative sample, which is the amount of steel cast using a single nozzle. It is recommended to determine the operational reliability indices (service life, warranty endurance, and operational endurance) for each type of steel. Practical experience shows that these parameters differ from one metallurgical manufacturer to another. In this paper, we are concerned with discussing the operational reliability indices of nozzles used for casting of two groups of steels differing in Mn concentration. The first group includes killed (ks), semi-killed (ss), and rimmed (rs) carbon steels and other types of steel containing up to 0.85% Mn; the second group includes low-alloy steels containing up to 1.8% Mn. This classification is conventional [4, 6, 13] and is based on the property of manganese and its oxides to enter into chemical reaction with refractory components of the nozzle material to yield low-melting compounds that degrade the performance characteristics of the nozzle. With Mn contained in molten steel at levels below 0.85%, its effect on the nozzle endurance is less significant. One can learn about the properties of submersible nozzles from a variety of sources (advertising materials, specifications, published documents concerned with composition, structure, and service characteristics, etc.). It may happen that data extracted from those sources are far from reality; therefore the actual indices of operational reliability should be determined under realistic conditions of exploitation of a given nozzle fabricated by a given technology. So, for a rated open porosity not exceeding 20% (TU 14–8-231–77 Specifications), the best operational endurance was observed in nozzles with an open porosity of 13 – 16% [14]. According to data from [5], the best operational endurance was displayed by nozzles with an actual open porosity of 10 – 14% as compared to the rated value not in excess of 16%. In [4], a relation between nozzle characteristics and operational reliability indices was considered and main factors were established that determine service life; based on the data obtained, requirements placed on nozzle parameters were formulated. It was established [4, 5] that the service life of quartz nozzles depends on porosity and faults that arise in the nozzle material during casting and heating operations, and it increases substantially in nozzles with a material porosity 10 – 14%. It can be further extended if the difference in density is minimized and a high-purity quartz glass and an advanced technology (in particular, preventing in-process contamination) are used. With open porosity decreasing to £ 13%, the heat resistance of nozzles decreases despite the low amount of crystalline phase in the nozzle material [14]. The method of [15] predicts the disruptive temperature gradient DTd for quartz material to be 1700°C, whereas the experimental value of DTd lies in the range of 1000 –
Submersible Ladle Nozzles for Continuous Casting Machines 1300°C. Allowing for the fact that the actual temperature gradient for a nozzle immersed in the mould is 1220 – 1250°C, the probability of nozzle fracture is rather high, which was indeed observed in operating nozzles [14]. It is well known that nozzles with an open porosity of the nozzle material of 16 – 18% may have a poor heat resistance and undergo degradation when mounted in the mould if the percentage of crystalline phase in the nozzle material reaches a critical value. According to [14], the submersible nozzles fabricated by the technology of [1] are prone to degradation in the initial casting phase with a material porosity of £ 13%. The service life of quartz nozzles is affected substantially by their structural bulk inhomogeneity [4, 9]. Thus, the chemical composition, phase composition, and structure are factors — all other things being the same — which determine the service life of submersible quartz nozzles. During service, the phase composition and structure of the quartz-nozzle material undergo change depending on the operating conditions and material properties. A variation in porosity within 14 – 16% leaves the nozzle resistance to low-manganese steels virtually unaffected; however, the resistance of nozzle material in contact with the molten slagforming heat-insulating mixture (SHM) decreases by a factor of 1.5 – 2. Consequently, the nozzle life of casting steels containing £ 0.85% Mn is chiefly determined by the wear rate of the nozzle material in the slag zone and to a lesser extent by erosion of the running channel, bottom section (splitter), and steel-tapping holes. In casting high-manganese and other reactive steels, the wear of quartz nozzles in contact with molten steel is determined by the resistance of nozzle material to erosion and chemical corrosion. Chemical corrosion results in the formation of low-melting eutectics of silicon dioxide and oxides of alloying elements and causes erosion of the running channel, steel-tapping holes, and bottom section. The nozzle life in this case is mainly determined by the wear rate of the material in contact with molten steel and, to a lesser extent, in contact with the SHM melt. The wear rate of quartz nozzles used for casting low-alloy steels depends on the concentration of alloying components. With these steels, the wear rate is higher than that with steels of standard range, and for this reason quartz nozzles employed for casting steels with more than 0.85% Mn have a shorter life [4]. Because of the stringent requirements placed on the endurance of nozzles for casting alloy steels, carbon-containing materials and nozzles different in composition and in design were developed [2, 6, 7, 11, 16]. In casting high-manganese steels, the service life of these nozzles is longer than that of quartz nozzles [3] fabricated by the traditional technology. However, the corundum-graphite nozzles available from both domestic and foreign manufacturers suffer from a number of shortcomings such as low thermal stability and rather moderate slag resistance. Furthermore, the running channels and steel-tapping holes in these nozzles show a tendency to
253 clogging, which reduces sharply their efficiency when used to cast steels of standard assortment. Corundum-graphite nozzles, apart from their modest economic efficiency (high costs incurred in their production and use), run into social and environmental problems [17]. Installation of nozzles — engineering components weighing more than 25 kg and maintained at a temperature higher than 1000°C — is a manual operation that requires considerable physical exertion and careful execution; moreover, the personnel is occupationally exposed to carcinogenic compounds emitted by the corundum-graphite material. Another disadvantage of this material is the high air permeability under operating conditions, which facilitates penetration of atmospheric oxygen into the running channel of the nozzle with ensuing undesirable effects such as the oxidation of alloying components and the increased concentration of nonmetallic inclusions in the cast product. Techniques have been proposed to reduce oxidation of the bond and graphite in corundum-graphite nozzles by introducing antioxidants, by creating multiple-layer structures, or by cladding the outer surface with low-melting materials; purging the running channel with a stream of argon was also considered. While improving the nozzle performance, these techniques failed to resolve the problem of clogged channel arising from handling rimmed steel and other types of steel. Quartz nozzles are devoid of these shortcomings owing to the ability of quartz material to sinter and thus to reduce air permeability to a minimum. The service life of submersible nozzles is determined by a variety of technological factors of which the most important are: (i) chemical composition of steels and SHM; (ii) casting rate; (iii) temperature of steel in the intermediate ladle; (iv) construction of refractory components of the intermediate ladle; (v) mating of the nonswirl nozzle and submersible nozzle; (vi) other factors collectively termed metallurgical. Processing and production factors, along with quality indices, determine the operational endurance of a nozzle. The service life depends on a range of properties and processing factors. As assessed from various data, the overall effect due to production factors may account for 20 to 70% of total life. A quantitative analysis of the effect of processing and production factors on the operational reliability of submersible nozzles, despite its evident importance, has never been conducted. The results of tests from [2, 5, 8, 12, 14] show that the departure of operating parameters of the CCM casting process from the norm and the spread in nozzle characteristics reduce the service life (in terms of metal cast) of the given nozzle, which leads to an increase in the cost of steel. Technological uses of submersible nozzles fabricated from different materials have been considered in [1 – 9, 11, 12, 19 – 26]. The quartz-nozzle technologies proposed in a range of variants [1, 3, 9, 20 – 26] differ mainly in the methods for preparation of suspensions and in molding and heat-treat-
254 ment techniques; here preference should be given to the so-called wet technology. Depending on the processing parameters, the equipment used and the quality of raw materials, the operational endurance of nozzles may vary in a wide range. The operational endurance of quartz nozzles during the running-in period was 107 and 160 tons for the casting of low-alloy and common steels, respectively. The average specific wear rate of the nozzle wall was 0.075 mm for 3sp-grade steel and 0.2 mm for 17G2SF-grade steel per ton cast metal. Improvements in technology allowed the operational endurance of quartz nozzles to be increased to 141 and 250 tons, and the wall wear to be decreased to 0.112 and 0.056 mm for low-alloy and killed carbon steels, respectively [21]. A vibrational-casting method for fabrication of submersible quartz nozzles using a coarse-grained material for that purpose was considered [22]. The service life and operational endurance of nozzles made using this technology were 496 and 308 tons for 2ps-grade steel and 279 and 233 tons for 17G1S-grade steel. The maximum wall wear did not exceed 6.5 mm, which corresponds to a specific wear rate of 0.046 – 0.07 mm per ton cast metal. Still, this technology has not gained industrial acceptance due to occupational-safety considerations, the high level of manual labor, and low productivity. The technology [3] for submersible quartz nozzles was improved in [24] with a view to obtaining nonfired components. The semi-finished product was prepared by centrifugal casting from high-concentration suspensions and subjected to hydrothermal treatment. The nozzles thus prepared were reported to have passed tests successfully; however, no detailed data on their endurance were available. Further progress in the quartz-nozzle technology was achieved by use of a plasmatron-produced opaque quartz glass, a centrifugal flooded-bottom mold casting technique, and heating at 1000 – 1100°C [12]. Tests showed that nozzles fabricated by this technology were not inferior in endurance to corundum-graphite nozzles (Vesuvius, Germany), with the advantage of lower cost. Issues concerning technological and constructional implications of the endurance of submersible nozzles and the quality of continuous castings have always been the focus of interest over the entire period of development and updating of the steel casting technology. Despite the wealth of patents granted, only three types of nozzle construction have gained wide acceptance in industry. They differ in the manner of mating between the submersible nozzle and the intermediate ladle (a suspended unit or a monoblock unit), in the design of the bottom section lowered into the mold, as well as in the outlet of the flow of steel from the tapping holes at a given angle (acute, direct, or obtuse). The geometry of the submersible nozzle is an issue of special concern. A properly designed nozzle must ensure a nearly laminar flow of molten metal into the cavity of a
V. V. Kolomeitsev et al. mold, considering that the casting regime is essential for the surface cleanliness, the amount (as small as possible) of nonmetallic inclusions, and the structure of the continuous casting. Establishing optimum, standard dimensions for the CCM submersible nozzle is at present an industrially vital problem awaiting solution. Some metallurgists believe that strips (partly composed of SiO2 ) that occur on the surface of slabs arise because of the use of quartz nozzles. In reality, they arise from peripheral nonmetallic inclusions that are found at all steps of the steelmaking process and then, driven by the temperature gradient, spread over the inner perimeter of the mould. The appearance of strips is governed by a variety of factors such as construction and material of the mould, properties and construction of the submersible nozzle, CCM refractory materials, and steel casting conditions. At present, standard submersible nozzles for slab CCMs designed in 1972 – 1978 [1] are used at practically all metallurgical plant of the former Soviet Union. The submersible nozzle described in [12] has a channel of smaller diameter and a flooded bottom section. Corundum-graphite nozzles have been considered in [2, 6, 7]. An updated modification of submersible nozzle was developed in [25]. Nozzles of this design, fabricated by technologies of [5, 26], were tested at leading metallurgical plants of Russia and showed performance characteristics not inferior to those of foreign analogs. COMPOSITION, STRUCTURE, AND PROPERTIES OF SUBMERSIBLE NOZZLES RELATED TO OPERATIONAL RELIABILITY Data on operational reliability of submersible quartz nozzles available from the literature are exceptionally controversial. To resolve the issue at least in part, tests were conducted on slab CCM nozzles differing in material composition, structure, and properties. The tests were carried out at metallurgical plants conventionally labeled M, C, and A. Results of these tests conducted in 1995 – 1999 were in part published in [5]. Four sets of submersible quartz nozzles of materials differing in porosity, structure, and chemical and phase composition were studied. Test data on quartz and corundum-graphite nozzles from [12 – 16] were also used. Test results for slab CCM quartz nozzles (sets 1 and 2 ) used for casting 08yu, 3ps, 2sp, and 3sp-grade steels at plant M are presented in Table 1 and Fig. 1 and 2. A comparison of these data shows that the operational reliability of set 1 nozzles is appreciably inferior to that of set 2 nozzles. The average wear of set 1 nozzles at the slag zone level is 1.9 times that of set 2 nozzles; correspondingly, the service life and warranty endurance in set 2 are smaller by a factor of 2 and 1.7 (see Figs. 1 and 2 and Table 1).
Submersible Ladle Nozzles for Continuous Casting Machines 293
60 50
255
a
353
60
a
50 40 30 20
40 30 20 10
10
268 324
60
307
b
50
Frequency, %
Frequency, %
660
40 30 20 10
300
50
366
b
60 50 40 30 20 10
484
c
c
50 40 30
40 30 20
20 10
10 230
330
430
530
630
Amount of metal cast, tons
230
730
Fig. 1. Operational reliability histograms for set 3 nozzles (solid lines) and set 1 nozzles (dashed lines) for common steels cast at plant M. (Arrowed numbers indicate the average value): a) service life; b) operational endurance; c) warranty endurance.
In tests carried out using common steels, 50% of the total number of set 1 nozzles with an average endurance of 300 tons were excluded from consideration because of their service life exhaustion. Only 9% of set 2 nozzles with an average endurance of 400 tons (which accounts for 60% of their service life) were used. The main reasons for replacement of set 1 nozzles were: (i) wear (50%); (ii) wear of the wall to a rated thickness of 14 mm (15%); (iii) fracture of the
330
430
530
630
730
Amount of metal cast, tons
830
Fig. 2. Operational reliability histograms for set 2 nozzles for common steels cast at plant M. For notations, see Fig. 1.
bottom section of the nozzle (15%); (iv) technological factors (20%). The large spread in property indices and the structural inhomogeneity of material are related to the rather low service life of set 1 nozzles; this is clearly seen in a histogram for specific wear rate in the slag zone (Fig. 3). The high wear of the bottom section of set 1 nozzles causes the flow of metal from steel-tapping holes to be disturbed, which degrades the quality of the continuous casting. It is to be in-
TABLE 1. Operational Reliability Indices for Submersible Quartz Nozzles Tested at Metallurgical Plants Wear rate per ton metal cast, mm
Metallurgical plant
Nozzle set number
Number of nozzles tested
Operational endurance, tons
Warranty endurance, tons
Service life, tons
Number of nozzles replaced because of wear (% of the total)
Endurance of nozzles replaced because of wear, tons
minimum
maximum
M M M C C A A
1 3 2 2 4 2 4
26 13 22 18 16 16 14
268 324 307 447 280 229 188
300 366 484 506 306 260 160
293 353 660 561 350 296 194
50 67 9 12 84 43 67
300 353 409 575 336 228 156
0.033 0.016 0.06 0.02 0.036 – –
0.11 0.086 0.06 0.06 0.12 – –
256
V. V. Kolomeitsev et al. 350
60
561
50
40
30
30
20
20
10
10
447
280
Frequency, %
30 20 10
506
306
30 20 10
160
c
50 40
30
30
20
20
10
10 330
430
530
630
260
60
40
Amount of metal cast, tons
730
a
b
229
40
50
230
188
50
b
40
60
296
50
40
50
Frequency, %
194
a
100
150
200
250
c
300
Amount of metal cast, tons
350
Fig. 3. Operational reliability histograms for set 2 nozzles (solid lines) and set 4 nozzles (dashed lines) for common steels cast at plant C. For notations, see Fig. 1.
Fig. 4. Operational reliability histograms for set 2 nozzles (solid lines) and set 4 nozzles (dashed lines) for low-alloy steels cast at plant A. For notations, see Fig. 1.
ferred therefore that the submersible quartz nozzles of set 1 are less suited for casting low-alloy steels. Test results for quartz nozzles of set 2 at plant M (Table 1; Figs. 2 and 3) show that the main reasons for replacement of nozzles in the casting of common steels were: (i) wear (9%) and (ii) technological factor (91%). Set 2 nozzles featured a high homogeneity of properties and, as a consequence, a low spread in specific wear rate in the slag zone (Fig. 3). The operational reliability indices of set 3 nozzles (Table 1; Figs. 1 and 3) show that the service life of these nozzles is only slightly higher than that of set 1 nozzles. Because of the wear, 67% of the total of set 3 nozzles with an average endurance of 353 tons were replaced in casting 2sp and 3spgrade steels. The operational endurance of set 3 nozzles was 17% higher than that of set 1 nozzles. A statistical life analysis for sets 1 and 3 nozzles shows that, for a confidence probability of 95%, the deviation of mean values of the two samples is significant. The average life for set 1 nozzles was 293 ± 38 tons (standard deviation 150 tons) and for set 3 nozzles, it was 353 ± 39 tons (standard deviation 110 tons); as is seen, the gain in service life in the latter is insignificant.
Comparative results of the tests carried out on set 2 and 4 nozzles for 08ps, 08yu, SAE 1006, ST12, RST1203, 3sp, and 20sp-grade steels using slab CCMs at plant C are given in Table 1 and Figs. 3 and 4. The operational reliability of set 2 nozzles (Fig. 4) was 1.6 times that of set 4 nozzles, which is in nice agreement with the ratio of the specific wear rate of the two sets (see Fig. 3). For reasons of wear, 84% of the total of set 4 nozzles with an average operational endurance of 336 tons (in conformance with the rated life) and only 12 % of set 2 nozzles with an average endurance of 575 tons (likewise in conformance with the rated life) were left out of consideration for common steels. The reduced life of set 2 nozzles at plant C in comparison to that at plant M (561 tons against 660 tons) can be explained by the high proportion of low-silicon SAE 1006grade steels used for casting tests at plant C. The service life of set 2 nozzles for the least corrosive 10KhSND-grade steel at plant A was 660 tons against 345 tons for set 4 nozzles. Undoubtedly, of interest are comparative results for set 2 and 4 submersible quartz nozzles (Fig. 5) obtained in casting
Submersible Ladle Nozzles for Continuous Casting Machines
257
Frequency, %
0.038 a b tests for low-alloy steels of grades A572-50, ST 44.2, 43A, 70 and 50B. 0.061 The operational reliability indices (Table 1; Fig. 5) of set 50 2 nozzles are 1.21 – 1.6 times. By reason of wear, 67% of the total of set 4 nozzles (service life 194 tons) and 43% of 30 set 2 nozzles (service life 296 tons) were set apart from cast10 ing tests. The operational endurance of set 4 nozzles was 188 tons, in conformance with their service life of 194 tons. 0.041 d c 0.072 50 A comparison of operational reliability indices of corundum-graphite nozzles [11] and quartz nozzles fabricated by 30 technologies of [5, 25, 26] used for casting steels with 10 £ 0.85% Mn revealed no sizable advantages of the former; on the other hand, an environmental and economic analysis 0.04 0.06 0.08 0.10 0.12 0.04 0.06 0.08 0.10 0.12 showed the latter to be less suited for casting common Specific wear rate, mm/ton steels. Comparative tests of corundum-graphite and modified Fig. 5. Wear rate histograms (mm per ton metal cast) for the nozzle wall quartz nozzles for low-alloy steels revealed the advantages at the slag-zone level for common steels: a, b, c, and d refer to set 2, 4, 3, of the latter. These, with virtually the same endurance and and 1 nozzles. Arrowed numbers indicate the average wear rate. cost, are easier to use, do not emit carcinogenic compounds, and do not require heating to high temperatures before placing in the mould; they also do not form nonmetallic incluteraction between alloying components (or their oxides, sions (carbides or oxycarbides) that might impair the mainly Mn) and silicon dioxide. strength and performance characteristics of certain specialModified quartz nozzles, owing to their low reactivity tograde steels. wards alloying components, exhibit an endurance comparaThus, the tests conducted made it possible to obtain reble to that of corundum-graphite nozzles and have an advanfined wear parameters of ladle nozzles that can be used for tage over the latter in economic, social, and ecological asintroduction into the corresponding normative documents pects. concerned with the casting of steel on slab continuous castComparative tests on submersible quartz nozzles differing machines. ing in structure and chemical and phase composition showed the emerging potential for new technologies [5, 25, 26] and CONCLUSIONS approaches in the production and uses of updated quartz glass-based nozzles for casting common and low-alloy steels. The state of the art in the technology, properties, and For casting common steels, updated submersible quartz uses of submersible quartz and corundum-graphite nozzles nozzles are recommended whose warranty endurance, under for continuous casting of steel has been considered. slab CCM operating conditions, is 720 tons (in terms of steel Corundum-graphite nozzles display a number of serious cast) against the rated life of 1200 tons. shortcomings such as low heat resistance and rather high air For casting low-alloy steels, modified submersible permeability and, like many carbon-containing materials, quartz nozzles are recommended whose warranty endurance, they are ecologically hazardous [10]. Because of the high air under slab CCM operating conditions, is 360 tons (in terms permeability, the alloying components of steel, under operatof steel cast) against the rated life of 540 tons. ing conditions in the running channel of the nozzle, undergo oxidation, which results in the increase of nonmetallic incluREFERENCES sions (oxide, oxycarbide and carbide compounds) in the continuous casting. Techniques for improving corundum-graph1. D. I. Gavrish, V. I. Gromov, V. V. Kolomeitsev, et al., “Nozzles ite nozzles were developed. These techniques — building up of opaque quartz glass for use in continuous-casting machines,” multilayer structures, protecting the surface with low-meltOgneupory, No. 9, 6 – 9 (1978). 2. A. A. Kortel’, L. M. Aksel’rod, B. K. Vasil’ev, et al., “Submersiing coatings, introducing antioxidants, injecting argon into ble corundum-graphie nozzles for slab continuous-casting mathe nozzle channel — indeed improve the operational propchines,” Ogneupory, No. 6, 37 – 40 (1990). erties but fail to provide conditions that would prevent the 3. V. V. Kolomeitsev, “Optimized technology for fabrication of equipment from clogging during the casting of rimmed steels quartz nozzles for continuous-casting machines,” Ogneupory, and other types of steels. No. 8, 33 – 37 (1990). The quartz nozzles fabricated by conventional technolo4. V. V. Kolomeitsev, “Physical mechanical properties and operagies are devoid of those shortcomings; however, their life for tional reliability of quartz nozzles for continuous-casting macasting low-alloy steels is lower because of the chemical inchines,” Ogneupory, No. 1, 13 – 16 (1988).
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