REFRACTORIES

FOR

CONTINUOUS

A.K. Karklit, Yu.V. and N.M. Frolovskii

STEEL

CASTING

Materikin,

The USSR has developed and, during the p a s t 10 y e a r s , extensively introduced into the industry the method of continuous steel casting for obtaining cast blanks which have a m o r e homogeneous s t r u c t u r e mad c h e m i c a l composition than ingots cast in molds. The continuous steel casting plant p r o d u c e s round, square, r e c t a n g u l a r , and hollow tube blanks, etc. Carbon killed and r i m m e d s t e e l s can be cast, including those with highly ductile p r o p e r t i e s for the production of cold- and h o t - r o l l e d sheet, low- and high-alloyed, e l e c t r i c a l engineering s t e e l s and alloys. The r e l i a b i l i t y of the operation of continuous steel casting plant l a r g e l y depends on the s e r v i c e of the r e f r a c t o r i e s that are employed. The specific f e a t u r e s of continuous casting involve s t r i c t e r r e q u i r e m e n t s being p l a c e d on the r e f r a c t o r i e s in all sections of the p r o c e s s , f r o m the steel casting ladle to feeding the m e t a l into the mold. Lining Steel-Casting Ladles. The t e m p e r a t u r e of the steel tapped during continuous steel casting is 30-60~ higher than during ingot casting. The duration of the casting is 1-2 h, which is 20-30% g r e a t e r than with top casting into ingot molds f r o m ladles of the s a m e capacity. T h e r e f o r e the r e s i s t a n c e of the linings in ladles f o r continuous casting is reduced. In o r d e r to i m p r o v e the life of the linings it is n e c e s s a r y to use ladle r e f r a c t o r i e s of i m p r o v e d quality (KShP-39 and KShP-37). Highly aluminous p r o d u c t s made f r o m n a t u r a l raw m a t e r i a l s , for example, A r k a l y k s k raw m a t e r i a l s , a r e v e r y effective, e s p e c i a l l y in the slag belt; the life of the lining can be i n c r e a s e d to 14-16 heats. It is also planned to make linings f r o m acid r a m m i n g bodies [1]. The working l a y e r of the acid lining is converted into a viscous g l a s s y m a s s , which is densified and consolidated by the p r e s s u r e of the iron. In the p r e s e n c e of a continuous layer, the slag cannot p e n e t r a t e the c r a c k s , and hinders the diffusion of the s l a g - f o r m i n g oxides at the grain boundaries. Volume diffusion, and accordingly solution of the r e f r a c t o r y , occurs slowly, so the life of the lining can be brought to 15-25 or m o r e heats, depending on the thickness and the working conditions, iV[echanization of the filling and tamping of the r a m m i n g bodies however r e q u i r e s the thickening of the lining to 150-250 ram, and also a sufficiently a c c u r a t e shape and rigidity in the housing of the s t e e l casting ladle. Lining the I n t e r m e d i a t e Ladle. The main cause of failure is damage done during the r e m o v a l of the adhering m e t a l r e s i d u e s , which a g g r a v a t e the e r o s i o n in the joints of the s t r u c t u r e , reaching t h i c k n e s s e s of 6-8 m m b e c a u s e of the complex shape of the ladles. E x p e r i e n c e showed that it would be effective to u s e different linings. In the continuous s t e e l casting plant in the open h e a r t h shops of the Donetsk MetaUurgJtcal and other f a c t o r i e s for casting one heat, the m a x i m u m r e s i s t a n c e (up to 28 heats) was achieved by using a rigid b r i c k s t r u c t u r e clamped at the top with a m e t a l band welded to the upper p a r t of the ladle housing. Curved r e f r a c t o r y shapes a r e u s e d in the rounded (small radius of curvature) sections to eliminate cutting of s t a n d a r d p r o d u c t s and to reduce the thickness of the joints. In s o m e c a s e s it is d e s i r a b l e to u s e s e m i acid ladle products, and also k y a n i t e - sillimanite, which expand during heating, thus closing the joints. At the N o v o - L i p e t s k Metallurgical F a c t o r y for casting s e v e r a l heats s u c c e s s f u l use has been made of h i g h - a l u m i n a r a m m i n g bodies (19-40 heats). In i n t e r m e d i a t e ladles t h e r e is v e r y little slag and no s t i c k ing of slag on the lining containing high A1203 concentrations which is usual for steel casting ladies. The c h e m i c a l r e s i s t a n c e of the h i g h - a l u m i n a bodies is higher than that of acid bodies, and so they a r e p r e f e r r e d for i n t e r m e d i a t e ladles, but it is also p o s s i b l e to o p e r a t e with acid bodies.

All-Union Institute of R e f r a c t o r i e s . I.P. Bardin S c i e n t i f i c - R e s e a r c h Institute of F e r r o u s Metallurgy. T r a n s l a t e d f r o m Ogneupory, No.9, pp.4-10, September, 1971. 9 1972 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced [or any purpose whatsoever without permission of the publisher. A copy of this article is available from the publisher for $15.00.

559

TABLE 1. P r o p e r t i e s 9f Stopper Tubes

Content, OZ~ ~

R e f r a e t o ~

~nder lo.d 212

I~l~

Pha~eoompo-

Refractories Plant Chamotte, Semiluks 37"38 ~2 1720 1390 1445 1600[ 0,15 22,7 2,02 111101__[112 High- alumina bonded (witheleetrocorundum) 52--6011,2--1770 1445 1520 1660 0 21,0 2,20-.

.

.

.

.

-

1,7

TABLE

2. Characteristics

I

of Plugs for Intermediate

I

12'

-

i!l]I

Ladies

Content, % Plugs* A1203

tF%03

High-alumina with a Polozhe kaolin bond. . . . . . . . . . . . 51,90 1,15 1790 Electrocorundum and Lamensk 71,70 1,45 1880 clay....... ....... ... High-alumina from the Vnukov and Semiluks Refractories Plants. . . . . . . . . . . . . . . . 72--73 0,70 ~1800

5"-- I < "N t) 1500

21,6

2,18

3--4

1560

19,4

2,62

3--4

1570

19--21 2,45

10--15

* All plugs were thermally shock resistant (in accordance with the requirements of GOST 550O-64). Stopper Tubes. In the steel casting ladles of the continuous steel casting plant the tubes operate in heavier conditions than when the casting is done in steel ingots. The f i r e c l a y tubes stand up s a t i s f a c t o r i l y if the individual routine control is strict, and when each tube is of a high quality. Using e l e c t r o m a g n e t i c waves of superhigh f r e q u e n c y it is possible to evaluate the uniformity of the s t r u c t u r e a c r o s s the section of the tube, in combination with the specified average p o r o s i t y [2]. The bond which in f i r e c l a y products contains a large quantity of glass phase and mullite of less perfect crystallization is less c o r r o s i o n - r e s i s tant. The r e s i s t a n c e of the bond is inereased if it is enriched with alumina by using high-aIumina kaolinite - h y d r a r g i l l i t e ores or adding c o m m e r c i a l aluminas to the clay with e l e c t r i c - f u s e d corundum in the form of a combined-grinding mixture. Table 1 shows the c h a r a c t e r i s t i c s of such products. The wear (reduction in diameter) during the hot time of the tubes with the high-alumina bond is 50~c less than in the chamotte products. The s e r v i c e of the stopper tubes in intermediate ladies is improved with air cooling of the rod (core). During the casting of a large number of heats in s u c c e s s i o n it is possible to use the above improved quality tubes, and also high-alumina tubes. Nozzles and Plugs for Steel Ladies. Magnesite fired and unfired nozzles are sueeessfully used in these ladles. The installation of the nozzles is done outside the ladle which means that nozzles have to be made with a reversible cone, and the ladles fitted with the appropriate devices. The plugs operate with a large number of coverings (up to 60 per cast); repeated changes in the flow conditions of the metal enhance the erosive wear of the plug and the seating of the nozzle. Chamotte plugs serve satisfactorily for casting killed, alloyed, and electricalengineeringsteels. For the corrosive steels (manganese, low-carbon rimmed med) it is possible to use plugs with a higher content of alumina (plugs for special purposes or high-alumina specified by GOST 5500-64).

560

Plugs for Intermediate L a d l e s * With a highly r e s i s t a n t batching device, covering of the jet with the plug in the intermediate ladle is s c a r c e l y e v e r required, but the long casting period makes it n e c e s s a r y in certain c a s e s to use special high-alumina plugs. These plugs were developed by the East Institute of R e f r a c t o r i e s (Table 2) and have been s u c c e s s f u l l y tested for casting up to 10 heats of killed steel at the N o v o - L i p e t s k Metallurgical Factory, and are now being produced by r e f r a c t o r y concerns.

I

3O

22

14 I

lJO0

140G

00 ~

Fig.1. Relationship between the viscosity of synthetic specimens of contact layer and the composition of the slags and temperature: Mix composition for determina-

No.

tion of viscosity, %

of curve

AltOs 20 20 20 20 ~0 10 30

SiO~ FeO-;-Fe~O3 ~'v~nO 50 20 10 40 20 20 35 20 25 35 30 15 30 40 20 20 40 30 10 40 20

Nozzles and Batching Devices for Intermediate Ladles. The batching equipment is a complex and critical section of the continuous steel casting plant. This device should meet the following r e q u i r e m e n t s : the delivery of steel into the mold should be in the f o r m of a compact and stable jet without spattering; there should be r e s i s tance against c o r r o s i o n and tightening, that is, a constant c r o s s section in the channel; it shouldbe possible to r e t a r d the jet, e s p e cially with an automatic cycle, and there should be reliable covering or shut off; another r e q u i r e m e n t is simplicity and at the same time reliable operation over a p e r i o d of s e v e r a l hours during the casting of "heat on heat." The results of the s e r v i c e of batching devices are determined by the p h y s i c o c h e m i c a l p r o c e s s e s at the contact zone between the steel (slag) and the r e f r a c t o r y . The essential p r o c e s s f a c t o r s a r e : chemical reaction between the oxide components of the steel with the components of the r e f r a c t o r y ; the formation of a contact l a y e r between the jets of steel and the r e f r a c t o r y in conditions of continuous diffusion exchange with the medium boundaries; the development of dynamic equilibrium depending on the viscosity of the contact l a y e r and the ratio of the adhesion f o r c e s between the contact layer, the r e f r a c t o r y , and the steel, which is in turn connected with the surface tension f o r c e s .

Investigations of the reaction between aluminosilicate r e f r a c t o r i e s and steel and slag in the s y s t e m s C a O - SiO2- AI203 and AI203- SiO2 - MnO- F e O - Fe203, have shown that the solubility of the refractory diminishes linearly with an increase in the content of alumina, the activity of the slags, and with a reduction in their basicity. The solution of the refractory is accelerated with an increase in the content of iron and manganese oxides in the steel, and a reduction in the content of alumina and silica. The compositions of the contact layer vary in wide limits (Table 3). The viscosity of the melts synthesized from oxides and close in composition to a number of specimens from the contact layer of aluminosilicate refractories are shown in Fig.1. The viscosity depends on the content of silica in the melt, and with an increase in this there is a reduction in the ratio O:Si, which is accompanied by an enlargement of the silicon-oxygen anions and an increase in the viscosity [10]. The effect of the alumina concentration on the viscosity is less important. The predominance of the lower oxides of manganese and iron causes a reduction in the viscosity, which is also explained by the change inthe size of the anions [10]. The adhesion properties of the contact layer depend on the surface tension and the wetting angle on

the boundaries

with the refractory and steel: tV = ~st (1 +cos 0),

where est is the s u r f a c e tension of the contact layer, and 0 is the wetting angle of the r e f r a c t o r y or steel by the contact l a y e r . Wear of the batching devices will o c c u r if the adhesion of the contact l a y e r to the steel is g r e a t e r than to the r e f r a c t o r y . In the oposite ease c o n s t r i c t e d flow may occur. F r o m the viscosity and surface

* Nonstopper casting is not considered in this article.

561

bO

* Indicates the content of Cr20 a.

69 (ZrO0

Killed carbon

29

6--9 2--16

91 (MgO) Killed c.arbon 97 (MRO) Rimmed

M agnesite

Zircon

7~5

67 (MgO) Killed carbon 12 (Cr2Os) Rimmed

70 61

22 20

Magnesite - chromite

63--6750

23~27

Killed carbon Manganese Rimmed Transformer 2--15

62--72 (A12Oa)

High- alumina

3

4,5--31 9--13

279

60--88

26--43 20--22 27--29 51,5

31--54 56--58 42--46 13,5

Killed carbon limmed Manganese Transformer

97 (AI2Oa) Rimmed

34--36 (Al=Oa)

Fireclay

26--4031

Al2Os+TiO~

38~48 I

SiO,

Killed carbon Manganese

Steel

of C o n t a c t L a y e r , ~,

Cornnd ul~n

26--30 (A12Oa)

Co.tent of main oxide

Composition

Semiaeid

Nozzle

T A B L E 3, C h e m i c a l

;,

I

0,5--1

I

3--4

6--23

6

1--31

45,5 1

16--53

0,5--16

4

4

2,5

1,5

2,5--13

1 --

2 4

1

I--5

1,5

4,5--8 2,5 3--5 5--6 1--6

FeO

Fe~Oa

2 2,5

0,5

4,5

1

0,5

1

0,5--4 2 2--3 12

1,0

CaO

48--79 22--49

13 62

0,5--1 0,5

0,4--4,2 2,5--3 2--3 20

MgO

2--3 3--14

3,5--14,5

1--3,5 13 5

2,5--20,5 7--9 13,5--29

9--19 25,5

MnO

9,5*

2,4

R~O

{91

Authors

[8]

[81

[8]

Authors

[81 [81 [8] [81

[5, 6] [8]

[3, 4] [3]

Literature source

p r o p e r t i e s of the melt corresponding in composition to the contact l a y e r it is possible to evaluate the expected r e s i s t a n c e of a p a r t i c u l a r r e f r a c t o r y m a t e r i a l in batching devices. During investigations of the magnesite r e f r a c t o r i e s the effect of the quantity of impurities in the p e r i c l a s e was noted. In magnesite containing 91-92% magnesium oxide the ratio of the impurities is unfavorable, and after firing f o r m s about 10% fusible silicates (monticellite etc.). With an i n c r e a s e in the calcium oxide content (CaO:SiO2 > 2) we observe cracking of the r e f r a c t o r i e s due to the polymorphic i n v e r sions of the dicalcium silicate. In p e r i c l a s e r e f r a c t o r i e s made f r o m sea water magnesia (95-97% MgO) the p r e s e n c e of about 2.5% of uniformly distributed monticellite has no great effect on the r e s i s t a n c e . E x p e r i ments have shown that i n s e r t s fitted to the nozzles p r e p a r e d f r o m s e a water magnesia, have a g r e a t e r r e s i s t a n c e , and can be used for casting low-carbon r i m m e d steels for up to 2-3 heats, one after the other. F r o m investigations of r e f r a c t o r i e s in the s y s t e m s ZrO 2 - SiC 2 - M n O - F e O - F e 2 0 ~ the i n c r e a s e in the viscosity and adhesion of the contact l a y e r to the r e f r a c t o r y with an i n c r e a s e in the content of ZrO 2 and SiC 2 has been well established. This suggests that zirconium-containing r e f r a c t o r i e s are p r o m i s i n g for use in continuous steel casting plant. Until now only zircon products have been widely used. Depending on the p r o p e r t i e s and b e h a v i o r of the contact layer, batching devices can be classified 1into four groups. In the batching devices of the f i r s t group, a highly fluid contact l a y e r is f o r m e d during the p r o c e s s of casting, which is continuously wetted by jets of steel. Inthe batchers of the second group a viscous contact l a y e r is formed, whose adhesion to the steel is g r e a t e r than to the r e f r a c t o r y . The wear of the b a t c h e r s of both types during casting is substantial. In the batchers of the third group a viscous contact l a y e r develops whose adhesion to the r e f r a c t o r y is g r e a t e r than to the steel, and the wear is only moderate. The use of these b a t c h e r s is most effective. Inthe b a t c h e r s o f the fourth group the difference in the values of the adhesion between the contact l a y e r and the r e f r a c t o r y and the steel is v e r y great, which causes construction of the channel. Classifying r e f r a c t o r y m a t e r i a l s of batchers in a p a r t i c u l a r group depends of c o u r s e on the type of steel. On the basis of brief s c i e n t i f i c - e x p e r i m e n t a l data, a s e r i e s of r e f r a c t o r i e s was developed for batching devices, ensuring the casting of steels of different grades. F o r killed steel type St.3, r i m m e d carbon (2 kp-3kp) manganese, and also steels with an i n c r e a s e d content of aluminum the zircon nozzles are r e commended. The t r a n s f o r m e r steel and also small quantities of killed steel (up to 30 ton p e r single batcher) can be s u c c e s s f u l l y cast through f i r e c l a y nozzles. The casting of steels with a v e r y high degree of c o r r o s i v e n e s s (low-carbon rimmed) r e q u i r e s the use of composite batching devices made f r o m high-alumina nozzles (82% A1203) and corundum or p e r i c l a s e i n s e r t - b a t c h e r s . The design of the devices is v e r y important. Composite devices made f r o m different m a t e r i a l s , and in which the m o r e r e s i s t a n t m a t e r i a l is used for the inserts, have proved t h e m s e l v e s . One of the most complicated problems is in the casting of steel deoxidized by a large quantity of aluminum (more than 1 kg p e r ton of steel), since the balance of the diffusion of the oxides into the contact l a y e r causes an i n c r e a s e in its viscosity, and an unfavorable ratio of the adhesion f o r c e s . The best sob~tion at the p r e s e n t time is to use nozzles with a channel having an i n c r e a s e d diameter, whose dimensions are d e t e r m i n e d by the tightening-up kinetics. The n e c e s s a r y velocity of flow is regulated by retarding it with a plug, and the c o m p a c t n e s s of the jet is p r e s e r v e d by using an additional nozzle lowered into the mold and being an extension of the f i r s t (the s o - c a l l e d "head-free" casting). Work is also continuing with the testing of certain types of r e f r a c t o r i e s with reduced adhesion to the contact layer. Nozzles for Incorporating the Jet under the Steel Level in the Mold. Covering the jet improves the quality of the metal. In the casting of e l e c t r i c a l engineering steels through an elongated nozzle the content of oxygen in the metal diminished f r o m 0.0027 to 0.0022%, nitrogen f r o m 0.0113 to 0.0093%, and nonmetallic inclusions f r o m 0.00745 to 0.00042%. The compactness of the jet is not disturbed during retardation, which makes it possible to reduce the danger of constricted flow in the nozzle. Complete coverage of the jet during the route f r o m the steel casting ladle to the mold is prospective for the n e a r future. F o r the int e r m e d i a t e l a d l e - mold section, r e f r a c t o r i e s have been developed on the basis of c l a y - g r a p h i t e mixtures, and also f r o m fused quartz. With lower tapping of the jet the s e r v i c e conditions of the nozzles are made somewhat e a s i e r . With side tapping best results were obtained with nozzles made f r o m fused quartz. The choice of the type of nozzle and the content of alumina in graphite nozzles depends on the type of steel being cast, and the casting conditions.

563

CONCLUSIONS As a r e s u l t of work c a r r i e d out by institutes and e n t e r p r i s e s in the r e f r a c t o r i e s and m e t a l l u r g i c a l industry of the USSR, v a r i o u s types of r e f r a c t o r i e s have been developed for continuous steel casting plant that is widely u s e d in production conditions. The speeding up of the work of continuous casting plant, the extension of the range of steels being cast, and the d e v e l o p m e n t of continuous casting plant of various designs all r e q u i r e decisions to be made in the field of r e f r a c t o r y m a t e r i a l s . It is n e c e s s a r y to continue r e s e a r c h into the m e c h a n i s m r e s p o n s i b l e for the f o r m a t i o n of the contact l a y e r between the steel and the r e f r a c t o r y , the way in which it r e a c t s , and the m o v e m e n t in various boundary conditions; it will also be n e c e s s a r y to develop f u r t h e r scientific e x p e r i m e n t a l t h e o r i e s for the contact layer, and through the accumulation of the n e c e s s a r y data to approach the p r o b l e m s of constructing a m a t h e m a t i c a l model for the process. The main p r o b l e m is to i m p r o v e r e f r a c t o r i e s u s e d in batehing setups in o r d e r to c r e a t e reliable channels for t r a n s p o r t i n g the s t e e l to the mold at a controllable velocity. F o r the important e l e m e n t s of the complex, that is, the unit r e s p o n s i b l e for the flow of m e t a l f r o m the ladle and its control, and also for introdueing the moIten m e t a l u n d e r the m e n i s c u s into the mold it is n e c e s s a r y to develop r e f r a c t o r i e s with the optimum p h y s i c o e h e m i c a l p r o p e r t i e s , ensuring continuous operation of the plant f o r sufficiently long p e r i o d s , m e a s u r e d as a function of the type of s t e e l in t e r m s of 4-12 h or m o r e . LITERATURE

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

564

CITED

V.G. Flyagin et al., Ogneupory, No.3, 27 (1971). R.S. B e r n s h t e i n et al., Ogneupory, No.12, 13 (1970). J.R. Rait, T r a n s . Brit. C e r a m . Soc., 42, No.4, 57 (1943). E.I. Isaev, in: Trudy Dnepropetrov. Metal. In-ta, No.45, 71 (1961). M.S. Kamenichnyi, Ogneupory, No.2, 73 (1948). T . W a h l b e r g , J e r n k o n t o r e t s Annaler, 137., No.l, 1 (1953). V.A. Bron et al., Trudy VostIO, No. 2 83 (1960). T r u d y VIO, No.35, 52 (1963). N.V. Pitak and V.M. Strelets, Ogneupory, No. 1, 15 (1962). Sh.M. Mikiashvili et al., Izv. Akad Nauk SSSR, Otd. Tekh. Nauk, 1, 115 (1957).