KR20010013319A - Amorphous or Glassy Alloy Surfaced Rolls for the Continuous Casting of Metal Stip - Google Patents

Abstract

Twin roll casting has been applied with some success to non-ferrous metals, which solidify rapidly on cooling. The same, however, is not true for ferrous metals, as it has not been possible to achieve sufficiently rapid and even cooling of metal over the casting surfaces of the rolls. This problem has been overcome by utilising a metallic surface for the rolls, which has a high affinity for the molten steel of the casting pool and a melting temperature greater than the temperature of the casting surface. The molten steel produces extremely good wetting of the casting surface of the roll, resulting in a wetting angle of the molten steel on the casting surface of less than 40°. Preferably, this wetting angle is less than 20° and the casting surface has an Arithmetic Mean Roughness Value (Ra) of less than 10 microns. These desirable properties on the roll surface are achieved by selecting an at least partially amorphous alloy of two constituents. Preferably, the alloy is a fully amorphous alloy of the nickel-phosphorus systemcontaining about 10 % phosphorus and the balance nickel, which may be applied by eletroless coating. This roll surface prevents the build-up of iron oxide on the casting surfaces of the rolls, which build-up interferes with the uniform conduction of heat away from the molten steel, resulting in simultaneous solidification of the delta and gamma iron phases (0.01-0.18 %C), which causes a surface defect, known as "crocodile-skin". The net effect of utilising this amorphous alloy for the surface of the casting roll is a superior and uniform conduction of heat away from the molten steel, rapid transformation of the steel's microstructure into the wholly austenitic (gamma) region, exhibited by fine prior austenite grain boundaries conforming to dendritic grain boundaries and absence of "crocodile-skin" surface defects on the cast strip.

Description

Amorphous or Glassy Alloy Surfaced Rolls for the Continuous Casting of Metal Stip}

It is known to cast metal strips by continuous casting in a twin roll casting machine. In this technique, the molten metal is introduced into a semi-rotating horizontal casting roll where it is cooled, so that the metal shell solidifies at the moving roll surface and flows together into the nip between them and fed downward from the nip between the rolls. Make The term "nip" as used herein refers to the general area where the roll is nearest. Molten metal is fed from the ladle into a small one or a series of vessels and flows through the metal feed nozzle located above the nip to flow molten metal directly from the vessel into the nip between the rolls, extending along the nip length and directly into the nip length. A casting pool of molten metal is formed which is supported on the above roll casting surface. This casting pool is generally defined between side plates or dams which are supported to slide in contact with the end face of the roll to prevent the two ends of the casting pool against outward flow. However, other alternative means such as electromagnetic barriers may also be proposed.

Although two-win roll casting has been successfully applied to non-ferrous metals which achieve rapid solidification upon cooling, there are problems in applying this technique to casting of ferrous metals. One particular problem is whether to achieve rapid cooling of the metal over the casting surface of the roll,

U.S. Patent No. 5,520,243 (PCT / AU / 00593) describes the casting surface of a roll by taking steps to ensure that the roll surface has some flatness in relation to the relative vibrational movement between the molten metal of the casting pool and the casting surface of the roll. There is known a technique in which the cooling of the metal in the furnace is significantly improved. In particular, this patent significantly improves the heat transfer from the solidified molten metal by applying vibrational movements of selected frequencies and amplitudes, thereby enabling the achievement of a whole new effect in the metal solidification process, thus casting The thickness of the metal is greatly increased or the casting speed is greatly increased at a particular strip thickness. Improved heat transfer is associated with the very fine surface structure of the cast metal.

U.S. Patent No. 5,584,338 discloses that the efficient relative vibration between the molten metal and the casting surface of the casting pool is due to the application of sound waves to the casting pool, and the increased heat transfer and solidification structure fineness is applied to the application of sound waves in a very low sound range. It is known that the technique is achieved by.

U.S. Patent No. 5,720,336 describes the study of heat transfer mechanisms occurring at the interface between the casting surface and the molten metal of the casting pool, and the casting surface is covered with a layer of material that is at least partially liquid at the solidification temperature of the metal, thus casting pool and rollers. It is known that the heat flux of the solidification process is controlled and improved by ensuring that improved heat transfer can be achieved without the occurrence of relative vibrations between them.

In this description it is necessary to refer to the quantitative measurement of the flatness of the casting surface. One particular method used in the experiments and helpful in understanding the present invention is a standard measurement known as the Arithmetic Mean Roughness Value, generally indicated by the sign R _a . This value is defined as the mathematical mean value for all absolute distances of the rafness profile from the profile's centerline within the measurement distance l _m . The centerline of the profile is the line from which the surrounding roughness values are measured, and within the limits of the roughness-width cut-off, become a line parallel to the general direction of the profile, and the sum of the areas contained between them. The parts of the profile lying on the side are identical. The algebraic average roughness value is defined as

x = l _m

R _a = 1 / l _m ∫ │ y │ dx

x = 0

Although the above studies enable the achievement of high solidification rates for the casting of ferrous metal strips, it is difficult to produce strips that do not exhibit surface defects known as "crocodile-skin". This defect occurs when the gamma phase and the δ iron phase solidify simultaneously in the shell on the casting surface of the roll in a twin roll casting machine under the condition of deformation of the heat flux through the solidification shell. The γ phase and the δ iron phase have different thermal strength properties and thus the heat flux deformation creates local deformations in the solidification shell that come together in the nip between the casting rolls, resulting in crocodyl-skin defects on the surface of the resulting strip. Conventionally, this problem has been addressed by efforts to maintain the accumulation of oxides on casting rolls within stringent limits by complicated roll cleaning apparatus.

Light oxidation deposits are beneficial to ensure a controlled uniform flow rate during metal solidification on the cast roll face. Oxidized electrodeposits melt when the roll surface enters the molten metal casting pool and establish a thin liquid interface between the casting surface and the molten metal of the casting pool to promote good heat flux. However, too much oxide accumulation causes the melting of the oxide to produce a high initial heat flux, but the oxide then resolidifies, resulting in a sharp decrease in heat flux. Deformation of the reaction heat flux in the solidification shell creates local deformations that lead to crocodyl-skin surface defects.

If the cast surface of the roll is made of a material with high affinity for the molten metal of the casting pool in order to make very good wettability to the cast surface by molten metal, the detrimental effect of the metal oxide can be prevented and achieve high solidification rate can do. With sufficient wettability by the molten metal, solidification can proceed quickly, leaving no time for a significant amount of oxide to be produced. In the case of steel, the steel melt can quickly solidify into a solid phase of a single phase to prevent any potential crocodile-skin defects.

The present invention relates to the casting of metal strips. In particular, it relates to a non-proprietary implementation of the casting of ferrous metal strips.

1 is a diagram of an experimental apparatus for determining a metal solidification rate under imaginary conditions of a double roll casting machine;

FIG. 2 shows an impregnation paddle incorporated in the experimental apparatus of FIG. 1; FIG.

3 is a diagram showing a heat resistance value obtained during solidification of a typical steel specimen in an experimental apparatus;

4 shows the relationship between the wettability of the interface layer and the measured heat flux and interface resistance;

5 shows the effect of wetting on resistance to nucleation;

6 shows shell surface temperatures occurring in a steel shell electrodeposited on a chromium substrate;

7 is a graph of the results of heat flux measurements on steel shells deposited on nickel-phosphorus substrates and chromium substrates;

FIG. 8 is a graph showing the K-value measurement on a steel shell electrodeposited during dip testing using nickel-phosphorus alloy and chromium substrate.

9 and 10 are optical microscope graphs of steel shells electrodeposited in a dip test with reference to FIG. 8;

11 is a graph showing K-value measurements on steel shells deposited during different dip tests using various substrates and steel mixtures.

12-16 are optical microscope graphs of the steel shell electrodeposited during the dip test with reference to FIG.

17 is a plan view of a continuous strip casting machine operated according to the present invention;

18 is a side sectional view of the strip casting machine shown in FIG. 17;

FIG. 19 is a vertical sectional view along line 19-19 of FIG. 17;

20 is a vertical cross sectional view along line 20-20 of FIG. 17;

FIG. 21 is a vertical cross sectional view along line 21-21 of FIG.

According to the present invention, a casting pool of molten metal is in contact with a moving casting surface so that the metal solidifies from the pool onto the moving casting surface, the casting surface is provided by a solid coating on a thermally conductive body, and the coating of molten metal on the casting surface Provided is a continuous casting method of a metal strip made of a material having a wetting angle of less than 40 ° and having a melting point higher than the casting surface temperature during metal solidification.

Also preferably, the coating is made of a material whose wet angle of the molten metal on the cast surface is less than 20 °.

Preferably, the coated surface has an algebraic average roughness value (R _a ) of less than 10 microns.

The coating material should be chosen so that it does not melt or dissolve at the temperature of the casting surface during solidification.

Preferably, the coating material is at least partially amorphous. For example, it includes an amorphous alloy of two metals. One of these metals is phosphorus.

In particular, the coating material comprises an amorphous nickel-phosphorus alloy containing 10% phosphorus.

The thermally conductive body can be copper or a copper alloy.

The molten metal may be iron.

In particular, the molten metal may be molten steel. In this case, the choice of coating material in which the molten steel has a low wetting angle allows solidification of the steel into a single phase solid structure on the coating side.

Accordingly, the present invention provides that the casting pool of molten metal contacts the moving casting surface so that the metal solidifies from the pool onto the moving casting surface, the casting surface is provided by a solid coating on the thermally conductive body, and the coating is performed on the molten metal on the casting surface. Of steel strips with a wetting angle of less than 40 ° and made of a material having a melting point higher than the casting surface temperature during metal solidification and of a single-phase solid structure on the casting surface where the phase does not deform before the strip leaves the casting surface. Provides a continuous casting method.

The invention is carried out by a twin roll casting machine.

Accordingly, the present invention provides that molten metal is introduced into a nip between a pair of parallel casting rolls through a metal feed nozzle located on top of the nip to create a casting pool of molten metal supported on the casting surface of the roll just above the nip. The casting surface of the roll is provided by a solid coating on the thermally conductive body, and the coating is made of a material having a melting angle of molten metal on the casting surface of less than 40 ° and having a melting point higher than the temperature of the casting surface during metal solidification. Provided is a continuous casting method of a metal strip to be produced.

1 and 2 show a metal solidification test rig that advances into a molten metal bath at a rate such that a chilled block of 40 mm x 40 mm closely simulates the conditions at the casting surface of a twin roll casting machine. Illustrated. As the steel moves through the molten bath, it solidifies into chilled blocks, forming a solidified steel layer on the surface of the blocks. The thickness of the solidification layer can be measured in terms of its entire area to indicate the strain in the solidification rate and thus the effective rate of heat transfer at various locations. Therefore, not only the measured value of the total heat flow but also the total coagulation rate can be calculated. It is also possible to investigate the microstructure of the strip surface in order to correlate the change in the solidification microstructure with the observed change in solidification rate and heat transfer value.

The experimental rig shown in FIGS. 1 and 2 is provided with an induction furnace 2 comprising a melt of molten metal in an inert atmosphere, for example provided by argon or nitrogen gas. The impregnation paddle, generally designated 3, is mounted on the slider 4, which can be advanced into the melt 2 at a selected speed and then retractable by the action of the computer controlled motor 5.

The impregnation paddle 3 comprises a steel body 6 having a substrate 7 in the form of a chromium-plated copper disk of diameter 46 mm and thickness 18 mm. The impregnation paddle is equipped with a thermocouple to monitor the temperature rise of the substrate, which provides a measure of heat flux.

Tests performed on the experimental rigs shown in FIGS. 1 and 2 show that the observed solidification rate and heat flux values, as well as the microstructure of the solidification shell, are greatly affected by the conditions at the shell / substrate interface during the solidification process. Giving. The test shows that high heat flux and solidification rate are achieved on the substrate, which produces fine grain structure of solidified metal.

The total resistance to heat flux (heat sink) from the melt to the substrate during solidification is governed by the thermal resistance of the shell and the shell / substrate interface to solidify. In the case of a typical continuous casting part (slab, block or billet) in which solidification is completed in about 30 minutes, the heat transfer resistance is governed by the solidifying shell resistance. However, this experiment shows that under thin strip casting conditions where solidification is completed within seconds, the heat transfer resistance is dominated by the interface thermal resistance at the surface of the substrate.

The heat transfer resistance is defined as

R _(t) = ΔT _(t) / ΔQ _(t)

Here, Q, ΔT and t represent the heat flux, the temperature difference and the time between the melt and the substrate, respectively.

Figure 3 shows the heat resistance values obtained during the solidification of a typical magnesium-killed low carbon steel sample in the test rig. This shows that the shell thermal resistance contributes only a small fraction of the total thermal resistance governed by the boundary thermal resistance. Moreover, it is shown that the boundary thermal resistance does not change significantly over time, indicating that the initial melt / substrate contact is governed by the melt / substrate thermal resistance.

For two component systems (melts and substrates), the melt / substrate boundary resistance and heat flux are determined by the wettability of the melt on the particular substrate. This is shown in Fig. 4, which shows how the boundary resistance increases and how the heat flux decreases with increasing wetting angle consistent with the wettability with decreasing heat flux.

The importance of substrate wetting by melt is shown by the development work described in the above-mentioned US Pat. No. 5,520,243 (PCT / AU93 / 00593) describing the application of vibrational movement. The application of vibrational movement aims to promote wetting of the substrate and increase the nucleation density of the melt coagulation. The mathematical model described on page 10 in that case is based on the required wettability and takes into account the vibrational energy required to achieve this. In experiments confirming this analysis, it is shown that sufficient improvement in heat flux cannot be achieved unless the substrate is flat. In particular, this applies even if the vibration energy, in order to obtain sufficient wetting of the substrate board show that there is need to have a D'algebraic average fitness value of less than 5 microns (R _a). These results are appropriate for chromium substrates in which the steel melt has adequately good wettability. However, according to the present invention, the cast surface of the roll can be made of a material having high wettability with respect to the steel melt, thereby achieving better wetting than can be achieved with the chromium surface. In this case, the casting surface having an algebraic average D'fitness value of less than 10 microns (R _a) In order to produce a strip with a reasonable surface finish and a fine structure is preferable, the flatness of the substrate is not particularly critical. For metal coagulation on a flat substrate, it can be simulated that coagulation proceeds at heterogeneous nucleation sites through the substrate. The effect of the wetting angle on the free energy of the nucleation according to the classical heterogeneous nucleation theory is shown in Fig. 5, where the free energy element increases with the increase of the wetting angle, i. Is showing. Wetting angles below 40 ° show good wetting efficiency with negligible energy barrier to solidification. Wetting angles above 75 ° indicate poor wetting, an energy barrier sufficient for metal solidification. Twin roll strip casting machines for ferrous metal casting generally use casting rolls having a grommet or nickel casting surface made by plating. Such face is rough and can withstand the thermal stress associated with strip casting. Moreover, steel melts have adequately good wettability on the chromium and nickel surfaces to obtain efficient heat flux values. In addition, the metal oxide electrodeposited from the general steel melt used in the strip casting has a high affinity for chromium and nickel and thus shows good wettability, ie low wetting angle, for such casting surfaces. This means that there is a strong tendency for the oxide coating to diffuse on the casting surface and accumulate as the casting proceeds.

FIG. 6 shows measurements of shell surface temperature occurring in a steel shell electrodeposited on the chromium surface in the dip test shown in FIGS. 1 and 2 for a clean substrate surface and many oxide electrodeposition layers. In this figure, for a flat substrate surface, it can be seen that the surface of the solidification shell is slowly reduced in temperature as the solidification proceeds. Where the substrate has a thick oxide layer covering the shell, the reaction proceeds to an under-cooling temperature of up to 1200 ° C. with an abrupt inversion step initially and the shell temperature increases. Under-cooling is thought that the oxide proceeds in liquid form, but as the temperature reaches 1200 ° C., the oxide provides nucleation sites for metal coagulation. However, solid oxides provide a barrier to heat flux that results in a loss of cooling efficiency and increases shell surface temperature. In the past, it was thought that this effect could be overcome by the deep cleanliness of the rolls during casting in order to maintain oxide levels within a very tight range, however, an optional material that causes very wet wetting by steel melt. It is believed that by forming a casting surface from the steel melt the steel melt can solidify without significant under-cooling below the liquid temperature. Such cooling proceeds so rapidly that there is no time for the oxide to form on the casting surface so that solidification can occur without significant interference with the electrodeposited oxide. In particular, these results were proved by the dip test in the field shown in FIGS. 1 and 2 using a cooling substrate of a nickel-phosphorus alloy containing 10% phosphorus. These alloys are coated on a chill roll by a non-deposition process and promote good wettability by steel melt. For most steel melts, the wetting angle on this coating is less than 25 °.

Fig. 7 shows heat flux measurements obtained during the solidification process of carbon steel on a nickel-phosphorus alloy substrate as compared to the heat flux measurements during the solidification process on a chromium substrate of a carbon steel shell. Carbon steel in these tests has the following composition, referred to as MO6 steel. Carbon: 0.06 wt%

Magnesium: 0.6 wt%

Silicone: 0.28 wt%

Aluminum: ≤0.002 weight%

Melt free oxygen 60-100 parts / million

FIG. 8 provides measurement results of K-values (indication of heat flux) of multiple dip tests using carbon steel melts of this composition with nickel-phosphorus alloy and chromium substrates. The results shown in FIGS. 7 and 8 show that the nickel-phosphorus alloy substrate results in a higher heat flux than the general chromium substrate. In the case of nickel-phosphorus alloy substrates, there is a variation in the heat flux over different tests, especially in the results shown in FIG. 8, with a decreasing K value through the continuous dip test. These variations are due to the oil on the surface of the nickel-phosphorus alloy substrate as the test proceeds. Therefore, in order to achieve a long lifetime coating in commercial strip casting for steel strip casting at high melting temperatures, it is desirable to modify the composition of this special alloy to increase the melting temperature. However, this test shows that dramatically improved results achievable with low wetting angles, and that the nickel-phosphorus alloys tested are fully suitable for casting other metals such as copper.

9 and 10 are optical microscope graphs magnified 100 times of the MO6 steel shell electrodeposited on a nickel-phosphorus alloy substrate in FIG. 9 and a chromium substrate in FIG. 10. The shell electrodeposited on the nickel-phosphorus alloy substrate is almost twice the thickness of the shell electrodeposited on the chromium substrate, and in the case of the nickel-phosphorus alloy substrate, it has a higher heat flux and rapid solidification. This shows that very high solidification rates are achievable and thus the present invention enables strip casting at much higher production rates than has been possible so far. In addition, the microstructure of the shell electrodeposited on the nickel-phosphorus alloy substrate is much finer than that deposited on traditional chromium substrates and shows prominence throughout the entire shell. This microstructure shows conventional austenite grains that accurately follow the dendrite grains, which show that the liquid carbon steel solidifies directly into austenite. There is no potential for the generation of crocodile skin defects through this solidification process, since these defects occur only when there are γ and δ phases in the solidified steel shell.

The enhanced wettability of nickel-phosphorus alloys is due to its amorphous structure. It has been found that liquids generally have a high surface affinity for other liquids because they have no preferred orientation, and similar effects occur when we wet amorphous solids. The wettability of the liquid metal on the coating side can thus be increased dramatically if the coating material is entirely amorphous. The nickel-phosphorus alloy having a 10% amorphous phosphorus content used in the test referred to in Figs. 8 and 9 can be easily electrodeposited by a non-precipitation process to have a process composition and to efficiently have an overall amorphous structure. When the amorphous content changes to deviate significantly from the process composition, the electrodeposited two metal alloy coatings show a partial crystal structure rather than the overall amorphous structure. Moreover, the crystal structure is also obtained by annealing the coating at high temperature after electrodeposition, a phenomenon used to increase hardness in certain coating applications.

To demonstrate the effect of amorphous coatings on enhancing wettability and the heat flux according to the present invention, steel melts were used on nickel-phosphorus alloy substrates of varying phosphorus composition, on nickel-phosphorus alloy substrates annealed at high temperature prior to testing and Another series of tests was performed to solidify on a flat nickel substrate to provide standard data or to control the data. Moreover, another test to show the direct solidification of the steel according to the invention into austenite dendrites is a peritectic grade which creates a total distortion during the solidification process through simultaneous solidification into the γ and δ phases. Including electrodeposition of shells from steel. The results of this test are shown in Figures 11-16.

11 provides measurement results for K-values of multiple dip tests. Dip tests (1-27) all used a steel melt having the MO6 composition described above. Steel shell in the test (1-9) is nickel having a flat substrate and the nickel, the nickel content of 10% with a R _a value of 5.6 has a R _a value of 8.7 is deposited on the alloy substrate.

The nickel-phosphorus substrate used in the test (1-9) is electrodeposited by the non-precipitation process and is not annealed. Very high K-values are obtained through these substrates compared to the flat nickel substrates used as controls. These results are similar to the results shown in FIG.

8 shows test results 10-15 in a nickel substrate where the nickel substrate is held as a control comparison for the result of solidification on a nickel-phosphorus alloy substrate having _a phosphorus content of 5% and a R _a value of 6.6. Doing. The K-value of the 5% phosphorus alloy is low compared to that of the 10% phosphorus alloy of Test 1-9, even if a flat substrate is used, which indicates that the partial crystal structure, which is inevitable in the 5% phosphorus alloy, results in wetting and overall heat flux. It is showing a decrease.

11 also shows that all MO6 substrates have a phosphorus content of 10%, one of which is annealed for 1.5 hours at a temperature of 400 ° C. after non-precipitation electrodeposition, and the other substrate is on a flat nickel-phosphorus alloy without any annealing. The results of the electrodeposited test 16-23 are shown. Unannealed substrates produce high K-values as experienced in tests (1-9), but annealed substrates produce very low K-values compared to those achieved with planar nickel substrates. FIG. 12 is a photomicrograph of a shell electrodeposited on a nickel substrate in test 11, FIG. 13 is an optical microscope graph of a shell electrodeposited on an anneal substrate in dip test 18, and FIG. 14 shows the same dip test ( 18 is an optical micrograph of a shell electrodeposited on a nickel phosphorus alloy substrate that was not annealed. The microstructures shown in the shell electrodeposited on the nickel substrate of test 11 and the annealing substrate in test 18 are similar. In both cases the shells are relatively thin and have a coarse microstructure showing initial solidification to ferrite. The shell of FIG. 14 as electrodeposited on an annealed alloy substrate is very thick and shows a finer structure incorporating the high coagulation rate achievable according to the invention that solidifies directly into austenite.

FIG. 8 shows that the shell is electrodeposited on a nickel-phosphorus alloy substrate that has a phosphorus content of 10% compared to the control substrate of nickel as previously used in the test (1-15) but partially annealed at 400 ° C. for 45 minutes. Provide the results of the test (24-27). The partially annealed substrate exhibits a k-value between the k-values of the annealed and unannealed substrates of the test (16-23), and also shows the effect of amorphous coatings, and the k-value ratings and crystal structure It shows a decrease in heat flux depending on the degree present in the coating.

FIG. 11 shows the results obtained from tests 29-31 in which the shell was electrodeposited on a 10% phosphorus nickel-phosphorus alloy substrate from a ferritic steel composition having a carbon content of 0.13%. In general, steels of such compositions cannot be cast with good surface quality by direct thin strip casting techniques because the steel solidifies simultaneously into the γ phase and the δ ferrite phase to create large deformations in the solidification shell. However, in the present test, the ferritic steel composition made from the shell shows the same microwater bath and the same K-value obtained with MO6 steel on the nickel-phosphorus alloy substrate and shows similar heat flux during solidification.

The solidification structure of the shell of ferritic steel produced in the test 30 is shown in FIG. 15, and the solidification structure of the shell of the same steel electrodeposited onto a textured chromium substrate is shown in FIG. The structure of Fig. 15 is very similar to that shown in Figs. 9 and 14, and shows the austenitic grain boundary immediately before the liquid carbon steel shows direct solidification with austenite. Moreover, there is no indication of any ferrite growth even after the coagulation has proceeded to the stage where the cooling rate decreases.

This means that when austenite solidification is initiated in accordance with the invention in a strip casting process, even if there is a subsequent deformation at low temperature after the strip has left the casting surface or casting surfaces, it does not return to ferrite growth, but rather complete deformation into austenite. I can do it.

In the present invention, the material of the cast side of the roll must have a melting temperature higher than the temperature of the cast side during the metal solidification period. The temperature of the casting surface may vary depending on the wetting angle of the molten metal on the casting surface. In more detail, the temperature in the cast surface coating experiment may increase as the wet angle decreases. The coating material can therefore be chosen to maintain a balance between high heat flux and fast solidification and to maintain the coating temperature safely below the melting temperature of the coating.

The results shown in FIGS. 8 and 11 for unannealed nickel-phosphorus substrates indicate an increase in loss of performance due to corrosion of the coating. For high temperature steel casting, two other metal amorphous coatings can be used according to the invention. For the selection of the complete coating, it is necessary to consider the melting temperature of the coating, the interface temperature during the casting period and the annealing temperature of the coating. Table 1 shows the relative standards for the various alloy coatings that can be used according to the invention in the casting of thin steel strips.

coating T interface (C) T melting point (C) T crystal (C) Electrodeposition method Ni-P 750 870 200 Non-precipitation Ni-B 750 1065 (1018) - Non Precipitation / Thermal Spray Mo-P 730 1650 431 Non-precipitation Mo-B 730 2180 - PVD / CVD Cr-B 780 1630 - PVD / Thermal Spray / CVD Ti-P 1082 1495 882 - Ti-B 1082 1540 884 PVD / CVD Ta-B 882 2390 2050? PVD / CVD W-B 707 1970 - PVD / CVD Co-P 843 1023 - - Co-B 843 1110 - - Zr-B 1680 863 PVD / Thermal Spray / CVD Fe-P 983 1048 735 - Fe-B 983 1174 912 CVD V-B 980 1735 - CVD

In Table 1, the interface temperature is calculated assuming complete contact of the steel at 25 ° C. with the coating at 1650 ° C.

Figures 17-21 illustrate a twin roll continuous strip casting machine operating according to the present invention. This casting machine comprises the main frame 11 of the machine erected from the bottom 12. The frame 11 supports a casting roll carriage 13 which is horizontally movable between the assembly table 14 and the casting table 15. The carrier 13 conveys a pair of parallel casting rolls 16, from which molten metal from the ladle 17 through the tundish 18 and the feed nozzle 19 during the casting operation. This is supplied to form a casting pool. The casting roll 16 causes the shell to solidify on the roll surface 16a, which is water cooled and moves, and the solidified strip product 20 is produced in the nip between them to exit the roll outlet. This product can be supplied to a standard coiler 21 and subsequently transported to a second coiler 22. The vessel 23 is mounted on a machine frame adjacent to the foundry, where molten metal flows over the tundish through the overflow spout 24 into the vessel, or during a casting operation during a serious failure or product If there is a serious mass production of defective goods, the flow is diverted to this vessel by the operation of an emergency plug (25) on one side of the tundish.

The roll carriage 13 comprises a carriage frame 31 installed by the wheels 32 on a rail 33 extending along a part of the main machine frame 11, whereby the roll carriage 13 is generally a rail 33. It is installed to move along. The carriage frame 31 carries a pair of roll cradles 34 on which the rolls 16 are rotatably installed. The roll cradle 34 is mounted on the carriage frame 31 by interconnecting the auxiliary slide members 35, 36, and allows the cradle to move above the carriage under the influence of the hydraulic cylinder units 37, 38, which will be described below. However, when required to form a weak transverse line along the strip, it adjusts the nip between the casting rolls 16 and also allows these rolls to move correctly with short time intervals.

By the operation of moving the hydraulic piston and the cylinder unit 39 connected between the drive bracket 40 and the main machine frame on the roll carriage, the carriage can be moved along the rail 33 as a whole, so that the assembly table 14 And the cast bar 15 to allow the roll carriage to move with each other.

The casting roll 16 is rotated reversely through the drive shaft 41 from the transmission installed on the drive motor and the carriage frame 31. The rolls 16 are formed to extend in the longitudinal direction in a row and have copper peripheral walls provided with cooling water passages at regular intervals along the perimeter. The cooling water passage is supplied with cooling water from the cooling water supply duct through the roll end portion in the roll drive shaft 41 connected to the cooling water supply hose 42 via the rotary glands 43. The rolls are typically about 300 mm in diameter and have a length of at least 2000 mm to produce a 2000 mm wide strip product.

The ladle 17 has a conventional configuration as a whole and can be fixed on the overhead crane by the yoke 45 to allow a certain distance from the hot metal housing. These ladles are adapted to be operable by the servo cylinders with the stopper rods 46, allowing molten metal to flow from the ladles to the tundish 18 through discharge nozzles 47 and refractory shrouds of refractory. .

The tundish 18 is also of conventional construction. It is made of refractory material such as magnesium oxide (MgO) in the form of a wide plate. One side of this tundish receives molten metal from the ladle and also has the overflow 24 and emergency plug 25 described above. The other side of the tundish is provided with a series of metal outlets 52 arranged longitudinally with a series of predetermined intervals. The lower part of the tundish bears a mounting bracket 53 for mounting the turn dish on the roll carriage frame, and a hole is provided to receive the indexing pegs (54) on the carriage frame to position the tundish correctly. do.

The delivery nozzle 19 is formed of an elongated body made of a refractory material such as alumina graphite. The lower portion is tapered to converge inward and downward, so as to project into the nip between the casting rolls 16. A mounting bracket 53 is provided to support it on the roll carriage frame, on top of which a side flange is formed which is located above the mounting bracket and protrudes outward.

The nozzles 19 are arranged in a series of horizontally spaced intervals, and may have flow passages generally extending in the vertical direction, so as to appropriately lower the discharge rate of the metal throughout the width of the roll, and the initial solidification roll The molten metal is fed into the nip between the rolls without direct penetration into the surface. Alternatively, the nozzle may have a single continuous slotted outlet so that a slow curtain of molten metal can be fed directly into the nip between the rolls and / or submerged in the molten metal pool.

This pool is bounded at the end of the roll by a pair of side closure plates 56 fixed to the stepped end 57 of the roll when the roll carriage is at the casting table. The side closure plate 56 is made of a strong refractory material, such as boron nitride, and has a scalloped scalloped side edge 81 to fit the curve of the stepped end 57 of the roll. This side closure plate is installed in a plate holder 82 movable from the casting table by the operation of a pair of hydraulic cylinder units 83, such that the side closure plate is engaged with the stepped end of the casting roll so that the casting roll during the casting operation A closure is made for the molten pool of metal formed above.

During the casting operation, a ladle stopper rod 46 is activated to allow molten metal to be fed from the ladle to the tundish through the metal supply nozzle, through which the molten metal flows into the casting roll. The clean head end of the strip product 20 is guided to the jaw of the coiler 21 by the operation of the apron table. The apron table 96 hangs on the pivot mounting 97 above the main frame and is shaken toward the coiler by the operation of the hydraulic cylinder after the end of the cleaning head is formed. The table 96 can operate on an upper strip guide flap 99 operated by a piston and cylinder arrangement, the strip product 20 being defined between a pair of vertical side rollers 102. Can be. After this head tip is guided into the jaw of the coiler, the coiler rotates and winds up the strip product, and the apron table returns to its inactive position, where the machine of the product hangs directly on the coiler 21. It simply hangs on the frame clear. The resulting strip product 20 is subsequently transferred to the coiler 22 to produce the final coil, which is then moved from the casting machine to another place.

The lower part is tapered to converge inward and downward, so as to project into the nip between the casting rolls 16. A mounting bracket is provided to support it on the roll carriage frame, and on its upper side there is formed a side flange which is located above the mounting bracket and protrudes outward.

The nozzles 19 are arranged in a series of horizontally spaced intervals, and may have flow passages generally extending in the vertical direction, so as to appropriately lower the discharge rate of the metal throughout the width of the roll, and the initial solidification roll The molten metal is fed into the nip between the rolls without direct penetration into the surface. Alternatively, the nozzle may have a single continuous slotted outlet so that a slow curtain of molten metal can be fed directly into the nip between the rolls and / or submerged in the molten metal pool.

All parts of all types of twin roll casting machines shown in FIGS. 11-15 are described in more detail in US Pat. No. 5,284,681, US Pat. No. 52,772,43, and PCT Application PCT / AU93 / 00593. Check it.

Claims (34)

A continuous casting method of a metal strip in which a casting pool of molten metal is in contact with a moving casting surface and the metal solidifies from the pool onto the moving casting surface, The casting surface is provided by a solid coating on the thermally conductive body, and the coating is made of a material having a wetting angle of molten metal on the casting surface of less than 40 ° and having a melting point higher than the temperature of the casting surface during metal solidification. Continuous casting method. The method of claim 1, And the coating is made of a material having a wet angle of molten metal on the cast surface of less than 20 °. The method according to claim 1 or 2, A continuous casting method, characterized in that the coated surface has an algebraic average roughness value (R _a ) of less than 10 microns. The method according to any one of the preceding claims, Continuous casting method, characterized in that the molten metal is molten steel. The method of claim 4, wherein A continuous casting method, wherein steel solidifies into a single-phase solid structure on a casting surface. The method according to any one of the preceding claims, A continuous lead method, characterized in that the coating material is at least partially amorphous. The method of claim 6, Continuous casting method, characterized in that the coating material is entirely amorphous. The method according to any one of the preceding claims, A continuous casting method, characterized in that the coating material consists of an alloy of two metals. The method of claim 8, Continuous casting method, characterized in that one of the two metals is amorphous. The method of claim 9, Continuous casting method, characterized in that the other one of the two metals is nickel. The method according to any one of claims 8 to 10, Continuous casting method, characterized in that the alloy is a process alloy. The method according to any one of the preceding claims, Continuous casting method characterized in that the molten metal has a process composition. The method according to any one of the preceding claims, A continuous casting method, characterized in that the thermally conductive body is a copper or copper alloy body. The casting pool of molten metal contacts the moving casting surface so that the metal solidifies from the pool onto the moving casting surface, the casting surface is provided by a solid coating on the thermally conductive body, and the coating has a wetting angle of 40 ° on the casting surface. In the continuous casting method of a steel strip made of a material having a melting point less than and higher than the temperature of the casting surface during metal solidification, A method of continuous casting, characterized in that the steel solidifies into a single-phase solid structure on the casting surface which does not deform before the strip leaves the casting surface. The method of claim 14, A steel casting method, characterized in that the steel has a carbon content of 0.53% by weight or less, and the single phase structure comprises a solid austenite dendrite. The method of claim 15, Continuous casting method, characterized in that the steel has a peripheral composition. The method of claim 16, Continuous casting method, characterized in that the steel has a carbon content of 0.13% by weight. The method according to any one of claims 14 to 17, A continuous casting method, wherein the coating material is made of an amorphous alloy of two metals. The method of claim 18, Continuous casting method, characterized in that one of the two metals is phosphorus. The method of claim 19, Continuous casting method, characterized in that the coating is a nickel-phosphorus alloy containing 10% phosphorus. The method according to any one of claims 14 to 20, Continuous casting method, characterized in that the thermally conductive body is a copper or copper alloy body. The method according to any one of claims 14 to 21, And wherein the moving casting surface is one of the surfaces of the pair of casting rolls forming the nip and the casting pool is supported on the casting roll above the nip and the strip is fed from the nip downward from the solid phase of the single phase. The casting pool of molten metal is brought into contact with the moving casting surface such that the metal solidifies from the pool onto the moving casting surface, the metal is peritic in composition, the casting surface is provided by a solid coating on the thermally conductive body, and the coating is on the casting surface. In the continuous casting method of steel strip made of a material having a melting point of molten metal of less than 40 ° and having a melting point higher than the temperature of the casting surface during metal solidification, A method of continuous casting, characterized in that the metal solidifies into a single-phase solid structure on the casting surface which does not deform before the strip leaves the casting surface. A continuous casting apparatus for metal strips comprising a casting roll having a casting surface in contact with a casting pool of molten metal and means for cooling the casting roll to solidify the metal therein, And the roll surface is formed of a solid coating composed of an amorphous alloy of two metals on a thermally conductive body of the roll. The method of claim 24, Continuous casting apparatus, characterized in that one of the two metals is phosphorus. The method of claim 25, Continuous casting apparatus, characterized in that the coating alloy is a nickel-phosphorus alloy. The method of claim 26, Continuous casting apparatus, characterized in that the coating alloy comprises 10% phosphorus. A casting roll comprising a thermally conductive cylindrical roll body covered by a solid coating forming a cylindrical metal casting surface, A casting roll, wherein the coating consists of an amorphous alloy of two metals. The method of claim 28, A casting roll, wherein one of the two metals is phosphorus. The method of claim 29, A casting roll, wherein the casting alloy is a nickel-phosphorus alloy. The method of claim 30, A casting roll, wherein the coating alloy comprises 10% phosphorus. Cast steel strip produced by continuous casting from a steel having a carbon content of 0.53% by weight or less and having a microstructure derived from direct solidification from molten metal to austenite prior to low temperature deformation. 33. The method of claim 32, A cast steel strip, characterized in that the steel has a peripheral composition. The method of claim 33, wherein Cast steel strip, characterized in that the steel has a carbon content of 0.13% by weight.