RU2469815C2 - Method of heating metallic ingot, method of continuous or semi continuous casting with direct cooling, and method of ingot rolling - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method comprises stage (a) of ingot preheating to temperature of crystallisation center formation lower than hot processing temperature, step (b) of additional ingot heating to temperature of the growth of isolated phase, and step (c). In step (c), given ingot temperature after step (b) does not equal hot processing preset temperature, additional ingot heating is performed to preset hot processing temperature.

EFFECT: ingots that may be rolled without hot treatment or additional homogenisation.

18 cl, 46 dwg, 11 ex

Description

FIELD OF THE INVENTION

The present invention relates to methods for casting metals, in particular metal alloys, as well as methods for processing metal ingots, providing for their two-stage heating.

State of the art

Metal alloys, and in particular aluminum alloys, are often cast from a liquid state in order to obtain ingots or ingots, which are subsequently rolled, hot worked and similar operations to produce sheet and plate products, which are used for the manufacture of numerous types of products. Ingots are often obtained by direct cooling (continuous casting) casting, however, there are equivalent casting methods, such as electromagnetic casting (discussed, for example, in US patents 3985179 and 4004631), which also find application. Further consideration relates mainly to continuous casting, but exactly the same principles apply to all foundry processes in which the same or equivalent properties of the cast metal microstructure are created.

Direct cooling cooling of metals (for example, aluminum and aluminum alloys, which are hereinafter generally referred to as "aluminum") in order to obtain ingots is usually performed in shallow forms (molds) with a vertically arranged axis and open ends. Moreover, in the initial position, the lower end of the mold is closed by a moving down platform (which is often called the bottom). The mold is surrounded by a cooling jacket in which coolant such as water is constantly circulating, creating external cooling of the mold wall. The molten aluminum (or other metal) is introduced into the upper end of the cooled mold, and as the molten metal solidifies in a region adjacent to the inner peripheral surface of the mold, the platform is lowered. With continuous movement of the platform and the corresponding continuous supply of molten aluminum into the mold, you can get an ingot of any desired length, which is limited only by the available free space under the mold. Further detailed information on continuous casting can be obtained from US Pat. No. 2,301,027 (the contents of which are incorporated herein by reference) and from other patents.

With some equipment modifications, continuous casting can also be performed horizontally, i.e. with an orientation of the mold different from vertical, and in these cases, the casting process can be essentially continuous. In the following discussion, vertical continuous casting is considered, but the same principles apply to horizontal continuous casting.

In vertical continuous casting, the ingot emerging from the lower (output) end of the mold is solid outside, but its core is still in a molten state. In other words, the hole of molten metal inside the mold is pulled down into the core of the downward moving ingot, some distance below the mold in the form of a reservoir of molten metal. In the downward direction, the indicated reservoir has a gradually narrowing cross-section, as the ingot metal crystallizes inward from the outer surface, until the core becomes completely solid. The section of the product made of cast metal, the outer shell (crust) of which is solid and the core is molten, is hereinafter referred to as the "nucleus" of the ingot, which after complete solidification becomes a finished ingot.

An important feature of the continuous casting process is the continuous supply of cooling fluid, for example water, and bringing it into direct contact with the outer surface of the growing ingot nucleus directly below the mold, and thereby direct cooling of the metal surface. This direct cooling of the surface of the ingot maintains the peripheral part of the ingot in the solid state and at the same time promotes internal cooling and crystallization of the ingot metal.

Traditionally, under the mold create one cooling zone. Typically, a cooling effect in said zone is obtained by directing a substantially continuous stream of water uniformly to the peripheral surface of the ingot directly below the mold, with water being released, for example, from the lower end of the mold cooling jacket. In the process, water at a large angle and with a significant force (impulse) hits the surface of the ingot and flows down along its surface. At the same time, the water continues to cool the ingot, but its cooling effect decreases until the surface temperature of the ingot is approximately equal to the temperature of the water.

Usually, when cooling water comes into contact with hot metal, two boiling phenomena occur. In the area of slowing down the movement of a stream of water and immediately adjacent to this area (directly below and above the stream) a film is formed under the liquid, mainly consisting of water vapor - a classic bubble boiling occurs. As the ingot cools and the effects of vaporization and bubble mixing weaken, the flow conditions of the liquid and the boundary thermal layer change and undergo forced convection in the bulk of the ingot material until, finally, the hydrodynamic state in the lowest extreme zone of the ingot turns into a simple free falling of the film from the entire surface of the ingot.

Ingots obtained by continuous casting are usually subjected to hot and cold rolling operations or other hot processing processes to obtain products in the form of sheet and plate products of various thicknesses and widths. However, in most cases, before rolling or other hot processing operations, a homogenization process is required to transform the metal into a more usable form and / or to improve the final properties of the rolled products. Homogenization is performed to even out concentration gradients at the microscopic level. The homogenization step involves heating the ingot to an elevated temperature (in general, to a temperature above the phase transition temperature, for example, the dissolution temperature of the alloying element, often above 450 ° C, and usually (for several alloying elements) in the range of 500-630 ° C ) for a significant time interval, for example several hours, and in the general case, up to 30 hours.

The need for such a homogenization operation arises due to microstructure defects that can be detected in the molded product and which arise in the early stages or final stages of crystallization. At the microscopic level, the crystallization of alloys obtained by continuous casting is characterized by five phenomena: (1) the formation of crystallization centers of the primary phase (the frequency of which may or may not be associated with the presence of an additive grinding the grain of the alloy); (2) the formation of mesh, dendritic or combined mesh and dendritic microstructures that define the grain; (3) displacement of the solution from the network / dendritic structure due to the prevalence of nonequilibrium crystallization conditions; (4) the movement of the displaced solution, which is enhanced by changing the volume of the crystallizing primary phase; and (5) the concentration of the displaced solution and its crystallization at the final reaction temperature (for example, eutectic temperature).

Therefore, the final metal structure is very complex and is characterized by a variation in composition not only within the grain, but also in areas adjacent to intermetallic phases, where relatively soft and hard areas coexist in the structure, which, if not modified or transformed, will create final variations in design properties that are unacceptable for the final product.

The concept of homogenization is of a general nature and is generally used to describe heat treatment designed to correct microscopic defects in the distribution of dissolved elements and to (simultaneously) modify intermetallic structures present at interfaces. It is generally accepted that as a result of the homogenization process, the following occurs:

1. The distribution of elements within the grain becomes more uniform.

2. Any constituent particles with a low melting point (for example, eutectics) that formed during the molding process at the grain boundaries and junctions of three grains are dissolved back into the grains.

3. Certain intermetallic particles (for example, peritectics) undergo chemical and structural transformations.

4. Large intermetallic particles (such as peritectics) that are formed during casting can be destroyed and rounded during heating.

5. There is a separation of phases (for example, those that can be further used to harden the material), which dissolve when heated, and then (after dissolution and redistribution) are evenly distributed over the grain, when the ingot is again subjected to cooling below the dissolution temperature, and, either kept at a constant temperature, allowing the formation of centers of crystallization and grain growth, or cooled to room temperature and preheated to high operating temperatures.

In some cases, it is necessary to apply heat treatment of the ingots in fact during the continuous casting process in order to correct the differential stress fields arising during casting. Specialists in the art divide alloys into alloys in which, in response to these stresses, post-crystallization cracks form, and into alloys in which precrystallization cracks form.

Post-crystallization cracks are caused by macroscopic stresses that develop during the casting process and which, upon completion of crystallization, lead to the formation of transcrystalline cracks. This phenomenon is usually eliminated by maintaining the surface temperature of the ingot during the casting process at an elevated level (thus reducing the temperature gradient in the ingot - and hence the stress) and transferring the ingots obtained in the traditional way to the stress relieving furnace immediately after casting.

Pre-crystallization cracks are also caused by macroscopic stresses that develop during the casting process. However, in this case, macroscopic stresses arising during crystallization are attenuated due to intergranular fracture and shear structure along the eutectic network with a low melting point (associated with the release of the dissolved component during crystallization). It has been found that by smoothing the linear temperature gradient from the center to the surface (i.e., the derivative of the temperature from the surface to the center of the growing ingot), such cracking can be successfully reduced.

Such defects make the ingot unsuitable for many applications. Numerous attempts have been made to overcome this problem by controlling the cooling rate of the surface of the ingot during casting. For example, for alloys prone to post-crystallization cracking, US Pat. No. 2,705,353 uses a cleaner to remove refrigerant from the surface of the ingot at a distance below the mold so that the internal heat of the ingot can heat the surface to be cooled. The idea was to keep the surface temperature at a level above 300 ° F (149 ° C), and preferably within a typical annealing temperature range, from about 400 ° F to 650 ° F (from 204 ° C to 344 ° FROM).

US Pat. No. 4,237,961 discloses another direct cooling casting system in which the refrigerant purifier is in the form of an inflatable elastomer collar. The main purpose of this cleaner is the same as in the aforementioned patent - maintaining the surface temperature of the ingot at a level sufficient to reduce internal stresses. In this patent, the surface temperature of the ingot is maintained at approximately 500 ° F (260 ° C), which also corresponds to the annealing temperature range. The purpose of this process was the possibility of producing ingots of very large cross section. In this case, the development of excess temperature stresses inside the ingot was prevented.

For alloys prone to precrystallization cracking, US Pat. the overall increase in casting speed, implemented in this process.

Another design of a direct cooling casting apparatus and a purifier for removing cooling water is presented in Canadian Patent 2095085. The main and auxiliary jets of cooling water are used in this design, followed by a cleaner to remove water, followed by a third jet of cooling water.

Disclosure of invention

Embodiments or aspects of the present invention are based on the observation that metallurgical properties equivalent or identical to those obtained during the standard homogenization of metal ingots (a procedure requiring several hours of heating at elevated temperature) can be imparted to such an ingot if the temperature of the cooled crust is allowed to approach with the temperature of the still molten core of the ingot nucleus at a value equal to or higher than the temperature of the phase transformations of the metal, at In-situ homogenization of the metal takes place (i.e., homogenization directly at the place of casting), and which for most aluminum alloys is usually at least 425 ° C, and it is also desirable to leave the ingot at this or close to it temperature at the appropriate time so that the required transformations occur, at least in part.

Interestingly, the necessary metallurgical changes in this way can often be created in a relatively short time (for example, 10-30 minutes), and the procedure for obtaining such a result can be integrated into the foundry operation itself, thereby eliminating the need for an inconvenient and costly homogenization operation. Without being attached to any particular theory, it can be assumed that this is possible because the desired metallurgical changes are created or maintained when the alloy is in the process of casting, due to the significant effect of back diffusion (in any of the states: solid, liquid, as well as their mixed "porridge" form) for a short period of time, in contrast to the alloy, which has undesirable metallurgical properties formed during standard cooling, which then require itelnogo time to correct them in the process of standard homogenization procedure.

Even in cases where homogenization of a standardly obtained ingot by the technology is not provided, it is possible to obtain a gain in properties that will facilitate the processing of the ingot or give the product improved properties.

The casting method, including in-situ homogenization, as described above, can then be optionally supplemented with a quick cooling operation before the ingot is removed from the casting machine, for example, by immersing the front of the growing ingot in a bath of coolant. This is done after removal of the cooling liquid that was supplied to the surface of the ingot nucleus and after sufficient time has passed for all the proper metallurgical transformations to take place.

The term “in situ homogenization” was introduced to describe this phenomenon, in which microstructural changes are obtained during the casting process itself, the changes being mentioned being equivalent to those obtained by traditional homogenization performed after casting and cooling. Similarly, the term “in-situ rapid cooling” is introduced to describe the quick-cooling operation performed during the casting process itself after in-situ homogenization.

It should be noted that embodiments of the present invention can be applied to the casting of composite ingots (ingots with filled inserts) consisting of two or more metals (or from the same metal from two different sources), for example, as described in the patent publication US 2005-0011630, published January 20, 2005, or in US patent 6705384, issued March 16, 2004. Composite ingots of this kind are cast in much the same way as monolithic ingots made of one metal, but a casting mold or similar device has two or more inlets separated by an inner wall of the mold or by a continuously supplied strip of solid metal that is embedded in the resulting ingot. After leaving the crystallizer through one or more outlet openings, the composite ingot is subjected to liquid cooling, while the cooling liquid can be removed in the same way as for a monolithic ingot, with the same or equivalent effect.

In a first aspect of the invention, there is provided a method of heating a metal ingot to prepare the ingot for hot processing at a predetermined temperature, in which at step (a) the said ingot is preheated to the temperature of formation of crystallization nuclei lower than the specified temperature of hot processing at which the metal Secondary phase precipitation nucleates to provide nucleation of crystallization centers; in step (b), the ingot is additionally heated to the growth temperature of the precipitated phases, at which the specified growth occurs, to ensure the growth of the precipitated phases in the metal; and in step (c), if after step (b) the temperature of the ingot is still not equal to a predetermined hot working temperature, the ingot is additionally heated to a predetermined hot processing temperature, namely, to the state of readiness for hot processing.

The term “hot working” may include, for example, processes such as hot rolling, extrusion and stamping.

In accordance with this method, the dispersed phases, usually formed during homogenization and hot rolling, are obtained in such a way that upon preliminary two-stage heating of the ingot to the hot rolling temperature and holding for some time, the degree of filling of the dispersed phases and their distribution in the ingot become similar to those which are usually found after the complete homogenization process or more successful, but these properties are achieved for a significantly shorter industrial a little time.

In a preferred embodiment of the method, in step (a), the temperature of the ingot is gradually increased within the temperature range of the nucleation of crystallization centers. The temperature of the ingot may increase at a rate of less than 25 ° C per hour.

The metal in the General case is an aluminum alloy, which has the characteristics suitable for deep drawing. This alloy can be selected from the group consisting of alloys AA3003 and AA3104.

The temperature at which the formation of crystallization nuclei begins is preferably in the range of 380-450 ° C, and the ingot is kept at this temperature for 2-4 hours.

The temperature at which the growth of precipitation of the secondary phases begins may also be in the range of 480-550 ° C. In this case, the ingot is maintained at the indicated temperature for at least 10 hours.

The ingot is preferably obtained by a casting method in which, in step (a), molten metal is supplied from at least one source to the peripheral region of the molten metal, thereby creating a peripheral region for the molten metal; in step (b), the peripheral portion of the metal is cooled, thereby forming an ingot nucleus having an outer hard crust and an inner molten core; in step (c), the ingot nucleus is advanced in the growth direction, outward from the peripheral region of the molten metal, and at the same time, molten metal is additionally supplied to said region, thereby extending the molten core contained within the hard crust beyond said region; and in step (d), the outer surface of the ingot nucleus emerging from the peripheral region of the molten metal is cooled by directing coolant to said outer surface, while an effective amount of coolant is removed from the outer surface of the ingot nucleus in the region of the outer surface of the ingot, where the cross section an ingot perpendicular to the direction of growth crosses the area of the molten core, so that after the removal of the specified effective amount of coolant On the other hand, the internal heat of the molten core reheats the hard crust adjacent to the molten core, thereby causing the core and crust temperatures to approach a combination temperature of 425 ° C or higher.

In a second aspect of the invention, there is provided a process for continuous or semi-continuous casting with direct cooling of cast metal ingots, wherein in step (a) a direct cooling casting mold is provided, comprising one or more inlets and one or more outlets; in step (b), molten metal is fed into at least one inlet of the casting mold; in step (c), the mold is cooled to crystallize the peripheral portion of the metal, thereby forming an ingot nucleus having an outer hard crust and an inner molten core; in step (a), the ingot nucleus is continuously advanced beyond the boundaries of the at least one outlet of the mold, thereby extending the molten core inside the solid crust beyond the specified at least one outlet of the mold; in step (e), the ingot nucleus emerging from the crystallizer is cooled in order to continue its crystallization by directing coolant to the outer surface of the ingot nucleus; in step (f), coolant is removed from the surface of the ingot nucleus until the ingot transitions to a completely solid state, so that the internal heat from the molten core again heats the hard crust adjacent to the core, thereby balancing the temperature of the core and the crust at the combination temperature, at this coolant is removed from the surface at such a distance from the specified at least one outlet of the mold that the temperature of combination is greater the temperature of phase transformations at which the metal undergoes in-situ homogenization; in step (g) the ingot is cooled or the ingot is allowed to cool; in step (h), the ingot is preheated to a temperature effective for hot rolling without disrupting the homogenization process; and in step (i), said ingot is hot rolled; characterized in that the preheating step (h) is carried out in two stages, the ingot being heated in the first stage to the temperature of formation of crystallization centers below the temperature effective for hot rolling, and the ingot is held at the temperature of formation of crystallization centers for a time interval effective for formation of crystallization nuclei in the ingot, and in the second stage, the ingot is heated from the temperature of formation of crystallization centers to a temperature effective for hot rolling, and I withstand ingot at a temperature effective for hot rolling for a time interval sufficient to allow crystal growth before performing step (i) hot rolling.

The phase transformation temperature is usually 425 ° C. or more.

In a third aspect of the invention, there is provided a method for hot rolling an ingot obtained by direct cooling casting, in which, in step (a), the ingot obtained by direct cooling is rapidly cooled from an elevated temperature of the casting; in step (b), the ingot is preheated to a temperature effective for hot rolling; and in step (c), the ingot is hot rolled at a specified temperature effective for hot rolling, characterized in that the preheating step (b) is performed in two stages, and in the first stage, the ingot is heated to the temperature of formation of crystallization centers, below the temperature effective for hot rolling, and the ingot is held at the temperature of formation of crystallization centers for a time interval effective for the formation of crystallization nuclei in the ingot, and in the second stage the ingot is heated from perature nucleating to a temperature effective for hot rolling, and the ingot is maintained at a temperature effective for hot rolling for a time interval sufficient to allow crystal growth before performing step (c) hot rolling.

In this first stage, the ingot is preferably heated to a temperature in the range of 380-450 ° C, and the temperature is maintained for 2-4 hours.

The ingot can be heated to the temperature of formation of crystallization centers at an average rate of about 50 ° C per hour.

In this second stage, the ingot is preferably heated to a temperature in the range of 480-550 ° C, and the temperature is maintained for a time interval selected from the condition of increasing the length of the entire pre-heating stage to 10-24 hours.

The ingot can be heated from the temperature of formation of crystallization centers to a temperature effective for hot rolling at a rate of about 50 ° C per hour.

Brief Description of the Drawings

Figure 1 is a vertical cross section of a mold for direct cooling, which corresponds to a preferred embodiment of the process, and illustrates the case when the ingot remains hot during the entire casting process.

Figure 2 is a cross-section similar to Figure 1, and showing a modified preferred embodiment, in which the position of the cleaner during the casting process can be changed.

Figure 3 is a cross-section similar to Figure 1, and illustrating the case in which the ingot is additionally cooled (quick cooling) from the bottom side during casting.

4 is a top view of a J-shaped casting mold illustrating a preferred embodiment of the invention.

FIG. 5 is a graph of the distance X of FIG. 1 for the mold of FIG. 4, wherein X values corresponding to the points of the mold perimeter are measured clockwise from point S in FIG. 4.

FIG. 6 is a perspective view of a cleaner for the mold of FIG. 4.

7 is a graph illustrating a casting process that corresponds to an embodiment of the present invention, and shows the surface temperature and core temperature of the ingot versus time for an Al-1.5% Mn-0.6% Cu alloy, the ingot being obtained by casting with direct cooling, subjected to water cooling, followed by removal of cooling water. The thermal background in the region where crystallization and reheating of the Al-1.5% Mn-0.6% Cu alloy takes place is similar to the background given in US Pat. No. 6,019,939 for the case where the ingot was not forcedly cooled in its volume (lower the graph represents the surface temperature, and the upper graph (dashed line) represents the temperature in the center of the ingot).

Fig. 8 is a graph illustrating the same casting process as in Fig. 7, but continued in time, and in particular showing a cooling period, after reaching a combination temperature or a reduction temperature.

Fig.9 is a graph similar to Fig.7, but showing the temperature measurement data of the same casting taken in three slightly different time intervals (data for three different values of the length of the ingot). In the three plots, solid lines show surface temperatures, while dashed lines show core temperatures. From each curve, you can determine the time intervals during which surface temperatures remain above 400 ° C and 500 ° C, and in each case they exceed 15 minutes. For each case, the recovery temperatures of 563, 581 and 604 ° C are shown.

Fig. 10a shows electron micrographs in transmitted light of an Al-1.5% Mn-0.6% Cu alloy similar to that shown in US Pat. corresponding to sample A of the above example. The microphotographs show a typical distribution of precipitated phases in a 6 mm thick sample taken in an area of 25 mm from the surface and from the center of the ingot.

Figure 10b is a micrograph of the same region as Figure 10a, but made in polarized light to show the size of the recrystallized grains.

In FIG. 11a shows electron micrographs in transmitted light of an Al-1.5% Mn-0.6% Cu alloy similar to that shown in US Pat. No. 6,019,939 with crystallization and a cooling history corresponding to a commercial direct cooling foundry process and heat and mechanical treatment corresponding to the sample In the given example. The microphotographs show a typical distribution of precipitated phases in a 6 mm thick sample taken in an area of 25 mm from the surface and from the center of the ingot.

Fig. 11b is a micrograph of the same region as Fig. 11a, but made in polarized light to show the size of the recrystallized grains.

On figa presents electron micrographs in transmitted light alloy Al-1.5% Mn-0.6% Cu, similar to that shown in US patent 6019939 with crystallization and a cooling history corresponding to Fig.7 and Fig.8, and thermal and mechanical processing corresponding to sample C of the example. The microphotographs show a typical distribution of precipitated phases in a 6 mm thick sample taken in an area of 25 mm from the surface and from the center of the ingot.

Fig. 12b shows a micrograph of the same region as Fig. 12a, but made in polarized light to show the size of the recrystallized grains.

On figa presents electron micrographs in transmitted light alloy Al-1.5% Mn-0.6% Cu, similar to that shown in US patent 6019939 with crystallization and a cooling history corresponding to Fig.9, and thermal and mechanical processing corresponding to the sample D of the given example. The microphotographs show a typical distribution of precipitated phases in a 6 mm thick sample taken in an area of 25 mm from the surface and from the center of the ingot.

On fig.13b shows a micrograph of the same area as figa, but made in polarized light to show the size of the recrystallized grains.

On figa presents electron micrographs in transmitted light alloy Al-1.5% Mn-0.6% Cu, similar to that shown in US patent 6019939 with crystallization and a history of cooling, corresponding to a commercial casting process with direct cooling, and heat and machining corresponding to sample E of the above example. The microphotographs show a typical distribution of precipitated phases in a 6 mm thick sample taken in an area of 25 mm from the surface and from the center of the ingot.

Fig.14b is a micrograph of the same region as Fig.14a, but made in polarized light to show the size of the recrystallized grains.

On figa presents electron micrographs in transmitted light alloy Al-1.5% Mn-0.6% Cu, similar to that shown in US patent 6019939 with crystallization and a history of cooling, corresponding to a commercial casting process with direct cooling, and heat and mechanical processing corresponding to sample F of the given example. The microphotographs show a typical distribution of precipitated phases in a 6 mm thick sample taken in an area of 25 mm from the surface and from the center of the ingot.

Fig. 15b is a micrograph of the same region as Fig. 15a, but made in polarized light to show the size of the recrystallized grains.

On Fig presents a raster electron micrograph (SEM) of an Al-4,5% Cu alloy with a linear scan curve of copper (Cu) through the center of the structure of crystallized grains, which shows a typical microliquation typical of a traditional direct cooling casting process.

On Fig presents SEM alloy Al-4,5% Cu with a linear curve of the scan of copper (Cu) for the case of using a cleaner and temperature (300 ° C) recovery / combination according to the recommendations of patents 2705353 or 4237961.

On Fig presents SEM of the Al-4,5% Cu alloy with a linear scan curve of copper (Cu), corresponding to a variant implementation of the present invention, when the ingot in its volume is not subjected to forced cooling (see Fig.19).

Fig. 19 is a graph illustrating the thermal history of the Al-4.5% Cu alloy for the region where crystallization and reheating take place when the ingot in its volume is not subjected to forced cooling (see Fig. 18).

On Fig presents SEM of an Al-4,5% Cu alloy with a linear scan curve of copper (Cu), corresponding to a variant implementation of the present invention, for the case when the ingot is subjected to forced cooling in its volume after a deliberate delay (see Fig.21) .

On Fig is a graph illustrating the thermal history of the Al-4,5% Cu alloy for the region where crystallization and reheating take place, in the case when the ingot is subjected to forced cooling in its volume after an intentional delay (see Fig. 20) .

On Fig graphically presents a representative fraction of the area of the intermetallic phases during casting, in comparison with three different technological schemes.

Fig. 23 is a graph illustrating the thermal background of the alloy (AA6063) Al-0.5% Mg-0.45% Si for the region where crystallization and reheating take place, when the ingot is not subjected to forced cooling in its volume .

24 is a graph illustrating the thermal history of the alloy (AA6063) Al-0.5% Mg-0.45% Si for the region where crystallization and reheating takes place when the ingot is forcedly cooled in its volume after deliberate delay.

On figa, 25b and 25C presents x-ray alloys processed according to Fig.23 and Fig.24, revealing the phase composition of the alloy.

Figures 26a, 26b, and 26c graphically depict FDC techniques performed on ingots obtained by the traditional casting method and on ingots processed according to the procedures of Figures 23 and 24.

27a and 27b are optical micrographs of intermetallic structures in an Al-1.3% Mn alloy casting (AA3003) processed in accordance with an embodiment of the present invention; intermetallic structures show kinks.

28 is an optical micrograph of modified intermetallic structures in an Al-1.3% Mn alloy casting processed in accordance with an embodiment of the present invention.

Fig. 29 is a transmitted electron micrograph of an intermetallic phase in a casting obtained according to an embodiment of the present invention; the intermetallic phase is modified by diffusion of silicon into a particle; visible depleted area.

On Fig is a graph illustrating the thermal background of the alloy Al-7% Mg, processed in the traditional way.

On Fig is a graph illustrating the thermal history of the Al-7% Mg alloy for the region where crystallization and reheating take place, in the case when the ingot in its volume is not subjected to forced cooling with a reduction temperature below the dissolution temperature of beta (β) - phase.

Fig. 32 is a graph illustrating the thermal history of the Al-7% Mg alloy for the region where crystallization and reheating take place when the ingot in its bulk is not subjected to forced cooling with a reduction temperature above the dissolution temperature of beta (β) - phase.

On Fig presents a curve obtained on a differential scanning calorimeter (DSC), and showing the presence of beta (β) -phase in the range of 451-453 ° C in the alloy, which is obtained by traditional casting with direct cooling (Fig.30).

On Fig presents a curve obtained on a differential scanning calorimeter (DSC) and showing the absence of beta (β) -phase (Fig.31).

On Fig presents a curve obtained on a differential scanning calorimeter (DSC) and showing the absence of beta (β) -phase (Fig.32).

The implementation of the invention

The following description relates to casting aluminum alloys with direct cooling (continuous casting), but only as an example. This embodiment of the invention is applicable to various methods of casting metal ingots, to casting most alloys, in particular alloys of light metals, and in particular those alloys whose phase transformation temperature exceeds 450 ° C, and which require homogenization after casting and before hot working, for example by rolling. In addition to aluminum-based alloys, examples of other metals that can be cast are alloys based on magnesium, copper, zinc, lead, tin and iron. This embodiment can also be applied to casting pure aluminum and other metals, in which one of the five results of the homogenization procedure can be obtained (see the description above).

1 is a simplified cross-sectional view of a vertical continuous casting machine 10 that can be used to implement at least part of a process in accordance with one embodiment of the present invention. For specialists in this field of technology it should be clear that such a foundry machine can be part of a larger group of foundry machines that work simultaneously and in a similar way, for example, part of a casting table in several forms.

The molten metal 12 enters the vertically located mold 14 with water cooling through the mold inlet 15 and exits the outlet 17 in the form of an ingot nucleus 16. The nucleus of the ingot has a liquid metal core 24 inside the solid outer crust 26, which thickens as the ingot cools (as shown by line 19) until a completely solid ingot is obtained. It should be understood that the mold 14 externally restricts and cools the molten metal so that the formation of hard crust 26 begins, while the cooling metal exits the mold, moving outward in the direction indicated by arrow A in FIG. 1. When an ingot appears at the exit of the mold, the coolant jets 18 are directed to the outer surface of the ingot to intensify cooling and support the crystallization process. The coolant is usually water, but for special alloys, such as aluminum-lithium alloys, another liquid, such as ethylene glycol, can also be used. A typical supply of cooling fluid for direct cooling castings is, for example, from 1.04 l / min / cm (liters per minute per centimeter of the circumference of the ingot) to 1.78 l / min / cm.

An annular cleaner 20 is provided, which is in contact with the outer surface of the ingot and is located at a distance X below the outlet 17 of the mold in order to remove coolant (shown in the form of jets 22) from the surface of the ingot, so that the surface of the part of the ingot below the cleaner remains free of coolant when further lowering of the ingot occurs. It is shown that the coolant jets 22 flow down from the cleaner 20, but are separated from the surface of the ingot 16 at a certain distance and do not create a cooling effect.

The distance X is chosen so that the coolant is removed from the ingot while the ingot is still in its germinal state (i.e., while it still has a liquid core 24 inside the solid crust 26). In other words, the purifier 20 is positioned where the cross section of the ingot, taken perpendicular to the direction of motion A, intersects a portion of the liquid metal core 24 of the ingot nucleus. In places located below the upper surface of the cleaner 20, continued cooling and crystallization of the molten metal of the core of the ingot release latent heat of crystallization and direct physical heat to the hard crust 26. This conversion of latent heat into physical heat, in the absence of continued forced (liquid) cooling, leads to that the temperature of the hard crust 26 (below the point where the cleaner 20 removes the coolant) increases (compared with the temperature immediately above the clean Lemma) and approaches (combined) with the temperature of the molten core; moreover, this occurs at a value which is chosen above the phase transformation temperature at which the metal undergoes in-situ homogenization. At least for aluminum alloys, the "convergence temperature" is usually chosen to be 425 ° C or more, and it is better to choose it equal to 450 ° C or more. For practical reasons of temperature measurement, the “matching temperature" (the total temperature that the molten core and the hard crust acquire for the first time) is taken to be the "rebound temperature", which is the maximum temperature that the hard crust acquires in the process under consideration, after the coolant is removed.

It is permissible to raise the reduction temperature above 425 ° C as much as possible, and, in general, the higher the indicated temperature, the better the in-situ homogenization result, however, naturally, the reduction temperature cannot be raised to the point at which the metal melts, since the cooled and crystallized outer crust 26 absorbs heat from the core and sets a ceiling for the recovery temperature. In passing, it is worth mentioning that the reduction temperature, usually equal to at least 425 ° C, will be higher than the annealing temperature of the metal in question (the annealing temperatures of aluminum alloys are usually in the range 343-415 ° C).

The temperature of 425 ° C is a critical temperature for most alloys, since at lower temperatures the diffusion rates of metal elements inside the crystallized structure are too low to normalize or equalize the chemical composition of the alloy with grain. At the indicated or higher temperature, and in particular at a temperature of 450 ° C. or more, diffusion rates are suitable to obtain the desired alignment in order to achieve the desired in situ homogenization effect of the metal.

In fact, it is often required to ensure that the combination temperature reaches a certain minimum temperature above 425 ° C. For any particular alloy, usually there is some transition temperature between 425 ° C and the melting point of the alloy, for example, the dissolution temperature of the excess phase or the phase transformation temperature, above which microstructural changes of the alloy take place, for example, the transition from β-phase to α-phase or intermetallic structure . If the combination temperature is chosen above the temperatures of such phase transformations, then necessary changes can be introduced into the alloy structure.

The recovery temperature and the combination temperature are determined by the parameters of the casting process, and, in particular, by installing a cleaner 20 under the mold (i.e., distance X in FIG. 1). It is desirable to choose the distance X in such a way that: (a) after removal of the cooling liquid, sufficient liquid metal remains in the core, the core has a sufficient superheat temperature, and the latent heat of the molten metal is sufficient to allow the temperature of the core and core of the ingot to reach the desired combination temperature referred to above; (b) after removal of the coolant, the metal was exposed to a temperature above 425 ° C for a time sufficient to allow the necessary microstructural changes to occur at normal cooling rates in air and at normal casting speeds; and (c) the ingot has been exposed to coolant (i.e. until the coolant has been removed) for a time sufficient to crystallize the crust to the extent that the ingot is stabilized and the crust will prevent molten metal from breaking inside the ingot and its outflow .

It is usually difficult to position the cleaner 20 below the mold outlet 17 at a distance closer than 50 mm and provide sufficient space for liquid cooling and crystallization of the crust, so this value is usually a practical lower limit for distance X (minimum distance). It has been found that in order to obtain the required reduction temperatures, the upper practical limit (maximum distance) is approximately 150 mm, irrespective of the size of the ingot, and the interval of preferred distances X is usually from 50 mm to 100 mm. The optimal position of the cleaner can vary from alloy to alloy and from one casting machine to another (since casting ingots of different sizes can occur at different casting speeds), but this position is always above the place where the core of the ingot completely hardens. A suitable position (or range of positions) can be determined for each case by calculation (from the equations of heat generation and heat loss), or by measuring surface temperatures (for example, using standard thermocouples embedded in the surface, or contact or non-contact temperature sensors), or through experimental tests. In molds with direct cooling of normal productivity, forming ingots with a diameter of 10 cm to 60 cm, a casting speed of at least 40 mm / min is usually used; more preferred are speeds of 50-75 mm / min (or 9.0 × 10 ⁻⁴ −4.0 × 10 ⁻³ m / s).

In some cases, it is desirable to set the distance X different at different points in time during the casting process, for example, either by moving the cleaner 20 closer to the mold 14, or by moving further away from the mold. This is necessary to take into account the various thermal conditions that occur in transition phases, at the beginning and at the end of the casting process.

At the beginning of the casting process, the lower block closes the outlet of the mold and gradually lowers to start the formation of the ingot. Heat is removed from the ingot to the lower block (which is usually made of heat-conducting metal), and the heat of the ingot leaves the outer surface of the growing ingot. However, as the casting process continues, and the newly appearing portion of the ingot moves farther away from the lower block, the heat is lost to the ingot only from its outer surface. At the end of the casting process, just before it is terminated, it may be desirable to make the outer crust colder compared to its normal state. This may be necessary because the last portion of the ingot that is to exit the mold is usually gripped by a lifting mechanism so that the entire ingot can be lifted. If the crust is colder and thicker, there is less likelihood that the lifting mechanism will cause the ingot to deform or rupture, which could create a hazard during the lifting operation. To achieve this, it is possible to increase the feed rate of the coolant in the final phase of the casting process.

In the initial phase, more heat is taken from the ingot than in the phase of the normal casting process, due to heat extraction in the lower block. In this case, the cleaner can be temporarily moved closer to the mold in order to shorten the period of time during which the surface of the ingot is exposed to cooling water, and thereby reduce heat removal. After a certain time, the cleaner can be rearranged to the normal position for the period of the phase of the normal foundry process. In practice, it was found that in the final phase of the casting process no movement of the cleaner may be required, however, if necessary, the cleaner can be raised to compensate for additional heat, which is removed by increasing the flow rate of the coolant.

The distance over which the cleaner should be moved (change X, i.e., ΔX), and the times at which these movements should be performed, can be calculated from the heat loss equations, estimated based on experimental data, or (more preferably) they can be determine, based on the values of the surface temperature of the ingot above (or, if possible, below) the cleaner, determined by the corresponding sensor. In the latter case, an abnormally low surface temperature may indicate the need to reduce the distance X (in order to cool the ingot to a lesser extent), and an unusually high surface temperature may indicate the need to increase the distance X (in order to cool the ingot to a greater extent). A sensor suitable for such a purpose is described in US Pat. No. 6,012,507, issued January 11, 2000, and the contents of which are incorporated herein by reference.

At the beginning of the casting process, on the first 50-60 centimeters of the length of the ingot, adjustment of the position of the cleaner is usually required. The change of position can be made in several stages in small steps, for example, 25 mm in each case. For an ingot with a thickness of 68.5 cm, the first change in position can be made in the range of 150-300 mm from the beginning of the ingot, and then similar changes can be made with an ingot length of 30 cm and 50-60 cm. For an ingot 50 cm thick, position adjustment can be done at lengths of 15 cm, 30 cm, 50 cm and 80 cm. The final position of the cleaner is the position that is required for the normal casting process, so the cleaner starts its work at the point closest to the mold and then moves downward as the casting continues . This procedure approximates the reduction in heat loss as the newly emerging portion of the ingot moves more and more away from the lower block during the casting process. And the distance X, thus, begins with a shorter than required for the phase of the normal foundry process, and gradually increases to the value necessary for the phase of the normal foundry process.

At the end of the casting process, if at least some adjustment of the position of the cleaner is required, this adjustment can be made within the last 25 cm of the casting, and usually only one adjustment per one or two centimeters is required.

The position of the cleaner can be adjusted manually (for example, if the cleaner is supported by chains that have links or eyes that include protrusions (for example, hooks) mounted on the cleaner, it is possible to support and raise the cleaner so that these protrusions can be inserted to various links or eyes). On the other hand (and this is more preferred), the cleaner can be supported and moved by electric, pneumatic or hydraulic lifts, which (as an option) can be connected via a computer (or similar device) to a temperature-sensitive device of the aforementioned type, so that the cleaner can be moved with the participation of the feedback loop with integrated logic. A device of this type is shown in a simplified form in figure 2.

The apparatus shown in FIG. 2 is similar to that of FIG. 1, except that the cleaner 20 can be adjusted in height, for example, from an upper position shown by solid lines to a lower position shown by dashed lines. Thus, the distance X from the outlet of the mold 14 can be changed by ΔX (either up or down). This adjustment is possible due to the fact that the cleaner 20 is supported on adjustable supports 21, which are hydraulic cylinders with pistons, which are driven by a hydraulic machine 23. The hydraulic machine 23 is controlled by a computer 25 depending on the temperature information provided by the temperature sensor 27, which controls the surface temperature of the ingot 16 immediately below the outlet 17 of the mold 14. As noted above, if the temperature detected by the sensor 27 is lower in advance of the set value, the cleaner 20 can be raised, and if the indicated temperature is higher than a predetermined value, the cleaner can be omitted.

In all forms of embodiments of the invention, it is desirable that the alignment temperature for the ingot at a point below the purifier 20 remains above the phase transformation temperature for in-situ homogenization (generally above 425 ° C) for a sufficient time so that the required microstructural changes can occur. The exact time will depend on the alloy, but it is desirable that it be in the range from 10 minutes to 4 hours, depending on the diffusion rates of the elements and the value to which the reduction temperature rises above 425 ° C. Usually, the desired changes do not occur more slowly than in 30 minutes, and often in the range of 10 to 15 minutes. This differs sharply from the time required for traditional alloy homogenization, which usually takes from 46 to 48 hours at a temperature above the temperature of phase transformations (for example, the temperature of dissolution of the excess phase) of the metal (often 550-625 ° С). Despite the significant reduction in process time in the embodiments of the invention compared to traditional homogenization, the final microstructure of the metal is essentially the same in both cases, i.e. cast products, in accordance with embodiments of the invention, have a microstructure of a homogenized metal, and there is no need to subject the products to traditional homogenization. They can be rolled and hot worked without additional homogenization. Therefore, the process in the present embodiments is referred to as “in situ homogenization”, i.e. homogenization carried out during the casting process, and not after.

As a result of applying the coolant and its subsequent removal, the newly appearing surface of the ingot is first subjected to rapid cooling, which is typical for the film boiling and bubble boiling modes of the film, which ensures a rapid decrease in the surface temperature to a low level (for example, to 150 ° С-300 ° C), but then the coolant is removed, and thus the excess temperature and latent heat of the molten core of the ingot (as well as the physical heat of the solid metal) are possible secondly heat the surface of the hard crust. This ensures that the temperatures necessary for the desired microstructural changes are obtained.

It should be noted that, if the coolant is allowed to come into contact with the ingot for longer than it is required (or not removed at all) before it is removed from the surface of the ingot, then it will not be possible to use overheating of the molten core and latent heat of crystallization to reheat the ingot crust, sufficient to obtain the required metallurgical changes. Although this will result in some temperature alignment of the ingot, and even possibly this will lead to a beneficial reduction in stress and cracking, the required metallurgical changes will not be obtained, and a standard additional homogenization process will be required before rolling the ingots to a calibrated or required thickness. The same problem can occur if the coolant is removed from the surface of the ingot in the required manner, and then the coolant is additionally brought into contact with the ingot before the temperature is equalized to the volume of the ingot and the necessary microstructural changes in the metal occur.

In some cases, the cooling liquid (in particular, water-based cooling liquid) may temporarily or at least partially leave the surface of the ingot due to the natural bubble boiling of the film, since the vapor that forms on the surface of the metal discharges the liquid refrigerant with ingot. However, usually the liquid returns to the surface when further cooling occurs. If such a temporary discharge of coolant occurs in front of the cleaner used in this embodiment, a double dip in the temperature profile may occur on the surface of the ingot. The cooling liquid cools the surface until it is discarded for some time due to bubble boiling of the film, after which the temperature rises to some extent; then the surface of the ingot passes through a layer of coolant trapped on the upper surface of the cleaner (the surface of the cleaner may tilt inward to the side of the ingot to form a layer of coolant), and the surface temperature of the ingot will drop again to rise again when the cleaner removes all coolant from surface of the ingot. Due to this, the cooling curve of the surface of the ingot acquires a W-shaped profile (as can be seen in Figs. 23 and 24).

The cleaner 20 of FIG. 1 can be made in the form of a ring of soft, heat-resistant elastomeric material 30 (for example, heat-resistant silicone rubber) held inside the surrounding rigid support body 32 (made, for example, of metal).

Although figure 1 shows the cleaner 20, which directly physically stops the access of the coolant, if necessary, you can use other means of removing coolant. Indeed, it can often be beneficial to provide a non-contact method for removing coolant. For example, to stop the flow of coolant along an ingot, jets of gas or other liquid can be directed to the desired location. On the other hand, bubble boiling of the film mentioned above can be used, i.e. it is possible to prevent the return of coolant to the surface of the ingot after the liquid has left the surface due to bubble boiling of the film. Examples of non-contact methods for removing coolant are given, for example, in US Pat. No. 2,705,353, German Patent DE1289957, as well as in US Pat. The bubbling boiling of the film can be facilitated by the addition of dissolved or compressed gas, for example carbon dioxide or air, to the coolant, as described in US Pat. No. 4,474,225, as well as US Pat.

On the other hand, the feed rate of the coolant in the jets 18 can be controlled up to the point where all the coolant evaporates from the surface of the ingot before the ingot reaches a critical point (distance X) under the mold, or before the surface of the ingot cools to a temperature lower critical surface temperature. This can be done by using a coolant supply as described in US Pat. No. 5,582,230, issued December 10, 1996, and the contents of which are incorporated herein by reference. In this design, the coolant is supplied through two rows of nozzles connected to different sources of coolant, which allows a simple way to change the amount of coolant supplied to the surface of the ingot, and to provide evaporation of the fluid at the desired point (at a distance of X). Alternatively or additionally, it is possible to perform thermal calculations by methods similar to those described in US Pat. No. 6,546,995, which are based on taking into account successive annular sections of the mold and supply such a volume of water that will evaporate as required.

Aluminum alloys that can be cast in accordance with the considered embodiments of the invention include thermally untreated alloys (for example, AA 1000, 3000, 4000 and 5000 series) and heat-treated alloys (for example AA 2000, 6000 and 7000 series). In the case of heat-treated alloys, the casting of which is carried out in a known manner, according to patent publication PCT / JP02 / 02900, the homogenization step is followed by rapid cooling to a temperature below 300 ° C (preferably to room temperature) before performing heating and hot rolling, followed by homogenization and curing, give extremely high rates of material (indentation resistance, improved rates of moldable workpieces, as well as high hardness) compared with materials subjected to washed by traditional processing. The unexpected fact is that, if necessary, these characteristics can be repeated in the considered embodiments of the invention during the manufacture of the ingot, if the ingot (i.e., the portion of the ingot that has just undergone in-situ homogenization) is subjected to rapid cooling ( quenching) after a sufficient period of time has passed (for example, 10-15 minutes) after cleaning the coolant to allow homogenization of the alloy, but before additional deep cooling is performed ingot. This final rapid cooling (rapid in-situ cooling) is shown in FIG. 3, where a direct cooling casting operation is performed (essentially the same as in FIG. 1), but the ingot is immersed in a water bath 34 (which may be otherwise called water well) at an appropriate distance Y from the bottom of the point at which the coolant is removed from the ingot. As already mentioned, the distance Y must be sufficient so that the necessary in-situ homogenization can take place over an effective period of time, but not enough to allow further substantial cooling of the ingot. For example, it is desirable that the temperature of the outer surface of the ingot immediately before immersion in the bath 34 be higher than 425 ° C, and it is better to be in the range from 450 ° C to 500 ° C. Subsequent immersion leads to rapid cooling of the ingot in water and its temperature drops to a value (for example, 350 ° C), below which the transformations in the solid structure do not occur at a noticeable rate. Further, the ingot may be cut in order to obtain a standard cut used for rolling or further processing.

By the way, in order for the ingot to be subjected to rapid water cooling along its entire length, the foundry well (the well into which the ingot is lowered after it leaves the mold) must be deeper than the length of the ingot, so that when further molten metal is added to the mold; the ingot could continue to sink into the well and into the bath 34 until it is completely submerged. On the other hand, the ingot can be partially immersed to the maximum depth of the bath 34, and then additionally supply water to the casting well and raise the level of its surface in the bath until the ingot is completely submerged.

It should be noted that the considered embodiments of the invention are not limited to casting cylindrical ingots and can be applied to obtain ingots of a different shape, for example, ingots with a rectangular cross section or a cross section, which is obtained by direct cooling in a mold, and is shown in FIG. 9 or FIG. .10 of U.S. Patent 6,546,995, issued April 15, 2003, and the contents of which are incorporated herein by reference. Figure 10 of this patent is duplicated in this application as figure 4, which is a top view of the mold of a casting machine. It is seen that the mold has an approximately J-shape and is intended to produce ingots having a cross section of the corresponding shape. At the nucleus of an ingot obtained from such a crystallizer, the molten core at different points of the perimeter of the cross section would be at different distances from the outer surface, and thus, while cooling the ingot at the same distance X for all points of the perimeter, different sections of the ingot crust were obtained would have different amounts of heat from overheating and latent heat of crystallization.

In fact, it is desirable that all sections of the crust along the perimeter of the ingot have the same temperature combination. In US Pat. No. 6,546,995, uniformity of casting characteristics around the mold perimeter is provided by adjusting the geometry of the mold surfaces of the mold to the shape of the cast ingot. In the considered embodiments of the present invention, it is possible that each portion of the crust of the ingot embryo (after cessation of cooling) is subjected to the same amount of heat from the side of the molten core and has the same temperature of combination due to the division of the perimeter of the ingot into conditional segments in accordance with the shape of the ingot and removing coolant in different segments at different distances from the outlet of the mold. For some segments (those that will be subjected to more intense thermal effects from the core), the coolant will be exposed for a longer period of time than other segments (those that are less exposed to heat). Therefore, after removal of the coolant, some segments of the crust will have a temperature lower than other segments, and this lower temperature will compensate for the more intensive heat input to these segments from the core, so that the temperature of alignment will be aligned around the perimeter of the ingot.

This can be achieved, for example, if the cleaner is designed so that (a) it has a shape that fits snugly against the shaped ingot along the perimeter of the ingot, and (b) there are different planes on the side of the cleaner facing the mold, or the shaped circuit, and these various planes or sections of the circuit were separated from the outlet of the mold at various distances. Fig. 5 is a graph illustrating the change in distance X along the perimeter of the mold of Fig. 4, the design of which is designed to obtain the same alignment temperatures along the perimeter of the ingot (the graph starts at point S of Fig. 4 and follows in a clockwise direction). Then, to obtain the required equality of the temperature of registration along the perimeter of the ingot, a cleaner having a corresponding shape along its perimeter is used.

Figure 6 shows a cleaner 20 'that would be suitable for the manufacture of an ingot having a shape similar to that shown in figure 4. It can be seen that the cleaner 20 'has a complex shape, with areas that are raised relative to other areas, which ensures the removal of coolant from the outer surface of the ingot appearing in these places, and that, according to the calculation, it is necessary to ensure equal temperatures of coincidence along the perimeter of the ingot in the areas below purifier 20 '.

The points at which coolant must be removed from different segments and the width of the segments themselves can be determined by computer simulation of the heat flux inside the cast ingot or by simple experimental testing for each ingot of a different shape. And again, the task is to achieve the same or high similarity of the temperatures of the combination along the perimeter of the ingot crust.

As already discussed in detail, embodiments of the invention, at least in their preferred embodiments, provide an ingot having a microcrystalline structure resembling or identical to the structure of a casting of the same metal obtained in the traditional way (without removing coolant) and subsequently subjected to standard homogenization. Therefore, the ingots obtained in accordance with the considered variants of the invention, can be subjected to rolling or hot processing, without resorting to additional homogenization. Typically, the ingots are first subjected to hot rolling, and this requires that they be preheated to the proper temperature, typically at least 500 ° C, and more preferably at least 520 ° C. After hot rolling, the resulting sheets of intermediate thickness are usually cold rolled to the final calibrated thickness.

As regards another aspect of the considered embodiments, it has been found that at least some metals and alloys benefit from the use of a two-stage preheating process after forming the ingot and before hot rolling. For the manufacture of such ingots, the above-described process with “in-situ homogenization” is ideally suited, but as an option they can also be obtained through a traditional casting process, in which case all useful properties will still be obtained. Such a two-stage preheating process is particularly suitable for alloys with characteristics suitable for deep drawing, for example aluminum alloys containing Mn and Cu (for example, aluminum alloy AA3003 containing 1.5% by weight. Mn and 0.6% by weight. Cu). Such alloys are based on dispersion hardening. In the two-stage preheating process, the surface layer is usually removed from the ingots obtained by direct cooling casting, after which they are placed in the preheating furnace to carry out the two-stage heating process, which includes: (1) slow heating to an intermediate temperature of formation of crystallization centers, less than the standard hot rolling temperature for the alloy in question, and (2) continued slow heating of the ingot to normal preheating temperature for oryachey rolling or to a lower temperature and maintaining the alloy at this temperature for a certain number of hours. The intermediate temperature creates the opportunity for the nucleation of crystallization centers of the metal and for the reverse absorption or destruction of unstable centers and their replacement with stable crystallization centers, which form centers for more stable growth of the precipitated phase. The holding period at elevated temperature gives time for the evolution of the precipitated phase from stable crystallization centers before rolling begins.

The heating step (1) may include maintaining the temperature at the temperature of the formation of crystallization centers (the lowest temperature at which the formation of centers begins) or, more preferably, includes gradually increasing the temperature to a higher value corresponding to step (2) . At this stage, the temperature can be 380-450 ° C, and preferably 400-420 ° C, and this temperature can be maintained constant or slowly increased within the specified range. It is desirable that the rate of increase in temperature be less than 25 ° C / h, and preferably less than 20 ° C / h, and that the increase process lasts for 2-4 hours. The rate of heating to the temperature of formation of crystallization centers can be higher, for example , on average, approximately 50 ° C / h (although the rate of temperature rise in the first half hour may be higher, for example, 100-120 ° C / h, and then it should decrease as it approaches the temperature of formation of crystallization centers).

After step (1), the temperature of the ingot continues to increase (if necessary) either to the temperature of hot rolling, or to a lower temperature at which the evolution of the precipitated phase can occur, usually in the range of 480-550 ° C, and preferably 500-520 ° C . Then this temperature is kept constant or it is slowly raised (for example, to the temperature of hot rolling) for a certain period of time, preferably not less than 10 hours and not more than 24 hours as a whole for the entire two-stage heating process.

Although heating the ingot directly to hot rolling temperature (for example, 520 ° C) creates a high population of secondary crystals or a precipitated phase, crystals of the final precipitated phase are usually small in size. Preheating with an intermediate temperature leads to the formation of crystallization centers, and continued heating to a rolling temperature (for example, 520 ° C) or lower temperature leads to an increase in the size of crystals of the secondary precipitating phase, for example, a larger amount of Mn and Cu leaves the solution and continues to grow crystals of the precipitated phase.

After heating to a hot rolling temperature, a standard hot rolling process is usually carried out without delay.

The above process, including in situ homogenization, can also be applied to composite ingots (with filled inserts), as described in US patent application 10/875978, filed June 23, 2004 and published January 20, 2005 under the number 2005- 0011630, as well as as described in US Pat. No. 6,705,384, issued March 16, 2004, the contents of which are incorporated herein by reference.

The present invention will now be described in more detail by way of examples and comparative examples, which serve only the purposes of illustration and which should not be construed as limiting the idea of the invention.

Example 1

Three ingots were obtained by direct cooling casting in a mold for continuous casting of flat billets for sheet rolling with dimensions of 530 mm and 1500 mm, with a final length of more than 3 m. The ingots had the identical composition Al-1.5% Mn-6% Cu in accordance with US patent 6019939 (the contents of which are incorporated into the present invention by reference). The first ingot was obtained by direct cooling casting in accordance with traditional technology, the second ingot was obtained by direct cooling and in situ homogenization in accordance with the procedure shown in Figs. 7 and 8, in which the cooling liquid was removed and the ingot was provided the ability to cool to room temperature after removing it from the casting well, and the third ingot was obtained by direct cooling and homogenization casting and rapid in-situ cooling in accordance with the procedure of Fig. 9, with which removed the coolant from the surface of the ingot, and the ingot was given the opportunity to reheat, and then quickly cool in a water well, located about one meter below the mold.

Figure 7 shows in more detail the change in time between the surface temperature and the core temperature of an Al-Mn-Cu alloy ingot during casting, subsequent water cooling, and the removal of coolant. The surface temperature graph shows a deep temperature drop immediately after casting, when the ingot comes into contact with the coolant, but the temperature in the core does not change much. The surface temperature drops to a low value, approximately 255 ° C immediately before removal of the coolant. Then, the surface temperature rises and approaches the core temperature at a temperature of combination or reduction of 576 ° C. After combining temperatures (when the ingot is completely solid), the temperature slowly drops and corresponds to cooling in air.

On Fig shows the same casting operation as in Fig 7, but for a longer period of time, and in particular, the figure shows the cooling interval following the moment of combining temperatures or the moment the start of recovery. The graph shows that the temperature of the crystallized ingot remains above 425 ° C for more than 1.5 hours, which is enough in excess to obtain the required in situ homogenization of the ingot.

Fig.9 is similar to Fig.7, but depicts the temperature measurements of the same foundry process, but taken at three slightly different points in time (at different lengths of the ingot, as shown in the graph). In three graphs, solid lines show surface temperatures, and dashed lines show temperatures at the center of the ingot thickness. The time intervals during which surface temperatures remain above 400 ° C and 500 ° C can be determined from each graph, and in each case they exceed 15 minutes. Reduction temperatures of 563, 581 and 604 ° C are shown for each case.

Samples of these ingots were then rolled, either with standard preheating to hot rolling temperature, or with different preheating to demonstrate the nature of the embodiments of the invention.

Casting processes were carried out under typical industrial cooling conditions, and, for example, at a speed of 60 mm / min, a coolant flow rate of 1.5 l / min / cm, and a metal temperature of 705 ° C.

Each ingot was cut along the axial line (in the middle section), and two parts of 250 mm wide were obtained from each ingot, then, while maintaining the thermal background (data of the sample temperature over time) in the center and on the surface, each piece was 250 mm wide was cut into several ingots for rolling with a thickness of 75 mm and a width of 250 mm (half the thickness of the original ingot) and a length of 150 mm (in the casting direction).

Then the ingots for rolling were processed in the following ways.

Sample A (obtained by direct cooling casting with standard thermal history and homogenization, modified compared to the standard one) was placed in a 615 ° С furnace, where after about two and a half (2.5) hours the metal temperature stabilized and the sample was kept at a temperature 615 ° C for an additional 8 hours. The sample was cooled in a furnace for three hours to 480 ° C and then kept in a furnace at 480 ° C for 15 hours, after which it was removed and subjected to hot rolling to a thickness of 6 mm. A part of this control sample with a thickness of 6 mm was then cold rolled to a thickness of 1 mm, heated to an annealing temperature of 400 ° C at a rate of 50 ° C / h, aged for two hours, after which the furnace was cooled.

Electron micrographs in transmitted light, showing the distribution of the secreted secondary phase, were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of a 6 mm sample (Fig. 10a). Images of the structures of recrystallized grains were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of a 1 mm sample (Fig. 10b).

This sample represents casting and homogenization in the traditional way, except that the homogenization operation was reduced to a total of 26 hours, while standard homogenization was carried out in 48 hours.

Sample B (obtained by direct cooling casting with standard thermal history and a modified two-stage preheating) was placed in a furnace with a temperature of 440 ° C, where after about two (2) hours the metal temperature stabilized and the sample was kept at 440 ° C for an additional 2 h. The temperature of the furnace was raised to allow the metal to heat up to 520 ° C in two (2) hours, then the sample was kept for 20 hours, after which it was removed and subjected to hot rolling to a thickness of 6 mm. A part of this control sample with a thickness of 6 mm was then cold rolled to a thickness of 1 mm, heated to an annealing temperature of 400 ° C at a rate of 50 ° C / h, aged for two hours, after which the furnace was cooled.

Electron micrographs in transmitted light, showing the distribution of the secondary precipitating phase, were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of a 6 mm sample (Fig. 11a). Images of the structures of recrystallized grains were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of a 1 mm sample (Fig. 11b).

Sample C (obtained by direct cooling casting with in-situ homogenization (with thermal history according to Figs. 7 and 8) and a modified two-stage preheating) was placed in a furnace with a temperature of 440 ° C, where after about two (2) hours the metal temperature stabilized and the sample was kept at 440 ° С for an additional 2 hours. The furnace temperature was raised to allow the metal to heat up to 520 ° С in two (2) hours, then the sample was kept for 20 hours, after which it was removed and subjected to hot rolling up thickness 6 mm. A part of this control sample with a thickness of 6 mm was then cold rolled to a thickness of 1 mm, heated to an annealing temperature of 400 ° C at a rate of 50 ° C / h, aged for two hours, after which the furnace was cooled.

Electron micrographs in transmitted light, showing the distribution of the secreted secondary phase, were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of a 6 mm sample (Fig. 12a). Images of the structures of recrystallized grains were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of a 1 mm sample (Fig. 12b).

Sample D (obtained by direct cooling casting with in-situ homogenization and rapid cooling (Fig. 9) with two-stage preliminary heating) was placed in a furnace with a temperature of 440 ° C, where after two (2) hours the metal temperature was stabilized and the sample was kept at a temperature of 440 ° C for an additional 2 hours. The furnace temperature was raised to allow the metal to heat up to 520 ° C in two (2) hours, then the sample was aged for 20 hours, after which it was removed and subjected to hot rolling to a thickness of 6 mm . A part of this control sample with a thickness of 6 mm was then cold rolled to a thickness of 1 mm, heated to an annealing temperature of 400 ° C at a rate of 50 ° C / h, aged for two hours, after which the furnace was cooled.

Electron micrographs in transmitted light, showing the distribution of the secondary precipitating phase, were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of a 6 mm sample (Fig. 13a). Images of the structures of recrystallized grains were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of 1 mm of the sample (Fig.13b).

Sample F (obtained by direct cooling casting with standard thermal history and homogenization, modified compared to the standard one) was placed in a 615 ° С furnace, where after about two and a half (2.5) hours the metal temperature stabilized and the sample was kept at a temperature 615 ° C for an additional 8 hours. The sample was cooled in a furnace for three hours to 480 ° C and then kept in a furnace at 480 ° C for 38 hours, after which it was removed and subjected to hot rolling to a thickness of 6 mm. A part of this control sample with a thickness of 6 mm was then cold rolled to a thickness of 1 mm, heated to an annealing temperature of 400 ° C at a rate of 50 ° C / h, aged for two hours, after which the furnace was cooled.

Electron micrographs in transmitted light, showing the distribution of the secondary precipitating phase, were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of a 6 mm sample (Fig. 14a). Images of the structures of recrystallized grains were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of 1 mm of the sample (Fig.14b). This sample represents casting and homogenization in the traditional way, although standard homogenization takes 48 hours.

Sample G (obtained by direct cooling casting and modified one-stage preheating) was placed in a furnace with a temperature of 520 ° C, where after about two (2) hours the metal temperature stabilized and the sample was kept at 520 ° C for 20 hours, after which was removed and hot rolled to a thickness of 6 mm. A part of this control sample with a thickness of 6 mm was then cold rolled to a thickness of 1 mm, heated to an annealing temperature of 400 ° C at a rate of 50 ° C / h, aged for two hours, after which the furnace was cooled.

Electron micrographs in transmitted light, showing the distribution of the secreted secondary phase, were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of a 6 mm sample (Fig. 15a). Images of the structures of recrystallized grains were obtained in longitudinal sections taken within 25 mm from each edge (edge of the surface and center) of a 1 mm sample (Fig. 15b).

Comparative Example 1

To illustrate the difference between the embodiments of the present invention and the known casting processes, Al-4.5 weight% Cu alloy ingots were cast in accordance with conventional direct cooling casting technology, according to the method described in US Pat. Nos. 2,705,353 and 4,237,961, and the method proposed in the embodiments of the present invention. According to the aforementioned patents, a cleaner was used during casting, which was positioned so as to obtain a reduction / combination temperature of only 300 ° C. In a casting process according to embodiments of the present invention, a cleaner is used that is positioned so as to obtain a reduction temperature of 453 ° C. Using a scanning electron microscope, micrographs (raster electron micrographs, SEM) of three final products were obtained and are presented, respectively, in FIGS. 16, 17 and 18. FIG. 19 shows graphs of temperature changes for the core and surface of the ingot obtained by the method corresponding to the variants of implementation of the present invention, without the operation of rapid cooling (see Fig. 18).

The presented SEMs show how the concentration of copper varies within the grain in the product obtained by foundry methods other than those proposed in the embodiments of the present invention (FIGS. 16 and 17 — the curve rises in the graphs between the peaks are noteworthy). However, for the product obtained according to the variants of implementation of the present invention, SEM show a significantly smaller variation in the Cu content within the grain (Fig. 18). Such a microstructure is typical of a metal subjected to standard homogenization.

Example 2

An Al-4.5% Cu alloy ingot was obtained in accordance with the present invention and was subjected to (quick) cooling at the end of the casting process. On Fig shows the SEM with the results of scanning the line of copper (Cu) for the obtained ingot. It should be noted the absence of any intracrystalline segregation of copper within a single grain. Although the considered grains are slightly larger than those shown in Fig. 16, a reduced number of intermetallic phases occurs at the intersection of single grains, and the particles themselves are rounded.

On Fig presents a thermal background of the casting process of the ingot, which shows the operation of rapid cooling at the end of the casting process. The temperature (452 ° С) of the combination in this case lies below the solubility line for the selected composition, but the desired properties are obtained.

Comparative Example 2

On Fig shows a representative fraction of the area of the intermetallic phases during casting, in comparison with the three different technological schemes discussed above: standard continuous casting with direct cooling (denoted by "DC"), casting with direct cooling, but without final quick cooling according to an embodiment of the invention (designated as "In-situ Sample ID") and direct cooling castings and final rapid cooling according to an embodiment of the invention (designated as In-situ Quench "). It is believed that a smaller area is more favorable for the mechanical properties of the finished alloy. The comparison shows a decrease in the area fraction of intermetallic phases during casting by various methods taken in this order. The largest area of intermetallic phases is obtained with a conventional direct-cooling casting process, and the smallest using an embodiment of the present invention with final rapid cooling.

Example 3

An Al-0.5% Mg-0.45% Si (6063) alloy ingot was obtained in accordance with the process illustrated by the graph of FIG. 23. The graph shows the thermal background for the region in which crystallization and reheating occurs when the bulk of the ingot is not subjected to forced cooling.

Casting of the same alloy was carried out under the conditions shown in FIG. 24 (including rapid cooling). This graph shows the evolution of the temperature of the ingot when the surface and core temperatures converged at a value of 570 ° C, and then the ingot was forcibly cooled to room temperature. This can be compared with the procedure shown in Fig. 8, which included a high reduction temperature and slow cooling, which is desirable when a faster correction of intracrystalline segregation is required, or when the alloy contains slowly diffusing elements. Using a high reduction temperature (significantly higher than the dissolution temperature of the excess alloy phase) and keeping it for a long period of time allows elements located near grain boundaries to diffuse very quickly into intermetallic phases and, thus, allow modification or a more complete transformation into more useful or advantageous intermetallic phases, and the formation of zones around the intermetallic phases that are free of precipitated phases. It should be noted that Fig. 24 contains a W-shaped cooling curve of the crust characterizing the bubble boiling of the film before the cleaner.

Comparative Example 3

On figa, 25b and 25C presents x-ray alloy 6063, revealing the differences in the quantities of α - and β-phases, while comparing traditional casting with direct cooling with two in-situ processes corresponding to Fig and 18.

The upper curve in each figure represents the alloy obtained by the traditional direct cooling casting method, the middle curve corresponds to a reduction temperature lower than the temperature of phase transformations of the alloy, and the lower curve corresponds to the reduction temperature higher than the temperature of phase transformations of the alloy.

Comparative Example 4

FIGS. 26a, 26b, and 26c graphically represent the FDC technique, wherein FIG. 26a corresponds to an ingot obtained by conventional direct cooling casting, FIG. 26b corresponds to the alloy of FIG. 23, and FIG. 26c corresponds to the alloy of FIG. 24. From the figures, an increase in the presence of the desired α-phase is seen when the reduction temperature passes through the temperature of the phase transformations.

By the way, more detailed information on both the FDC method and the SiBut / XRD method, as well as their application to the study of phase transformations, is contained in the publication by N. Cama, J. Worth, PVEvans, F.Bosland, JMBrown "Intermetallic Phase Selection and Transformation in Aluminum Zxxx Alloys "(Solidification Processing, Proceedings of the 4 th Decennial International Conference on Solidification Processing, University of Sheffield, July 1997, eds J.Beech, H. Jones, p.555 (the contents of this publication are incorporated into the present invention by reference).

Example 4

27a and 27b show two optical micrographs of intermetallic structures in an Al-1.3% Mn (AA3003) alloy casting obtained in accordance with the present invention. It is seen that intermetallic structures (dark areas in the figure) contain cracks or kinks.

Fig. 28 is an optical micrograph similar to that of Figs. 27a and 27b, which also shows that the intermetallic structure contains cracks or fractures. A large region of the particle has the composition of MnAl ₆ . The ribbed relief shows the diffusion of silicon into the intermetallic structure with the formation of AlMnSi.

Example 5

On Fig presents an electron micrograph in transmitted light of the intermetallic phase of the alloy AA3104 in the molten state without final rapid cooling, it is shown in Fig.31. The intermetallic phase is modified by diffusion of Si into the particle, and the depletion zone is shown. The sample was taken from a surface where the initial exposure to a cooling liquid forms a nucleus of particles. However, the reduction temperature modifies the particle and modifies the structure.

Comparative Example 5

On Fig presents the thermal background of the alloy Al-7% Mg obtained in the traditional way. It can be seen that there is no restoration of the temperature of the crust due to the prolonged presence of coolant.

On Fig and 32 presents the thermal background of the alloy Al-7% Mg for the case when the ingot was not subjected to cooling during the pouring process. This alloy is the basis of Fig. 30.

Comparative Example 6

On Fig presents a curve obtained on a differential scanning calorimeter (DSC), which shows the presence of beta (β) -phase in the range of 450 ° C in the alloy, which is obtained by traditional casting with direct cooling and which is the basis of Fig.30. Said β phase is a problem during rolling. The presence of the β phase is seen from a small dip in the curve immediately after 450 ° C, when heat is absorbed so that the β phase transforms into the α phase. A large dip ending at 620 ° C represents the melting of the alloy.

On Fig presents a curve similar to the curve of Fig, which shows the absence of beta (β) -phase in the material cast in accordance with the present invention, when the ingot remains hot during casting (without final rapid cooling) (see Fig. .31).

On Fig again presents a curve similar to the curve of Fig for a material cast in accordance with the present invention, when the ingot remains hot during the casting process (without final rapid cooling) (see Fig. 32). Again, the curve shows that the beta (β) phase is absent.

Claims (18)

1. A method of heating a metal ingot to prepare the ingot for hot processing at a predetermined temperature, in which, at step (a), the specified ingot is preheated to the temperature of formation of crystallization centers lower than the specified temperature of the hot processing at which precipitation originates in the metal secondary phases, in order to ensure the nucleation of crystallization centers, in addition, at step (b), the ingot is additionally heated to the growth temperature of the precipitated phases at which this growth occurs, To ensure the growth of the precipitates in the metal, and in step (c) if after step (b) the ingot temperature is still not equal to the predetermined temperature of the hot working is further heated ingot to a predetermined hot working temperature is up to a state of readiness to hot processing. 2. The method according to claim 1, characterized in that in step (a) the temperature of the ingot is gradually increased within the temperature range of the nucleation of crystallization centers. 3. The method according to claim 1, characterized in that the indicated temperature of the ingot is increased at a rate of less than 25 ° C / h. 4. The method according to claim 1, characterized in that the metal is an aluminum alloy. 5. The method according to claim 4, characterized in that the aluminum alloy has characteristics suitable for deep drawing. 6. The method according to claim 4, characterized in that said alloy is selected from the group consisting of alloys AA3003 and AA3104. 7. The method according to claim 4, characterized in that the temperature at which the formation of crystallization centers begins is in the range of 380-450 ° C, and the ingot is kept at this temperature for 2-4 hours 8. The method according to claim 4, characterized in that the temperature at which the growth of secondary phase precipitates begins is in the range of 480-550 ° C, and the ingot is kept at this temperature for at least 10 hours 9. The method according to any one of claims 1 to 8, characterized in that said ingot is obtained by a casting method, in which, at step (a), molten metal is supplied from at least one source to the peripheral region of the molten metal, thereby creating the peripheral portion for molten metal, in step (b), cool the peripheral portion of metal, thereby forming an ingot having an outer hard crust and an inner molten core, in step (c) the ingot is advanced in the direction of growth, outward from the peripheral region limiting the molten metal, and at the same time additionally supplying molten metal to the specified region, thereby extending the molten core contained within the hard crust beyond the specified region, and in step (d) cool the outer surface of the ingot emerging from the peripheral region of the molten metal, by the direction of the coolant to the specified outer surface, while removing the effective amount of coolant from the outer surface of the ingot in the outer the surface of the ingot, where the cross section of the ingot, perpendicular to the growth direction, intersects the area of the molten core, so that after removing the indicated effective amount of coolant, the internal heat of the molten core again heats the hard crust adjacent to the molten core, thereby causing the core and crust temperatures to approach combination temperature 425 ° C or higher temperature. 10. A method of continuous or semi-continuous casting with direct cooling of cast metal ingots, in which, in step (a), a direct cooling casting mold is provided, comprising one or more inlets and one or more outlets, in step (b), molten metal is fed in at least one inlet of the casting mold, in step (c), the mold is cooled to crystallize the peripheral portion of the metal, thereby forming an ingot having an outer hard crust and an inner shell an augmented core, in step (d), the ingot is continuously advanced outside the at least one outlet of the mold to extend the molten core inside the hard crust beyond the specified at least one outlet of the mold in step (e) cool the ingot emerging from the crystallizer, to continue its crystallization, by directing the coolant to the outer surface of the ingot; in step (f), coolant is removed from the surface of the ingot until the ingot going to a completely solid state, so that the internal heat from the molten core again heats the hard crust adjacent to the core, thereby balancing the temperature of the core and the crust at the combination temperature, while the coolant is removed from the surface at such a distance from the indicated at least one outlet of the mold, so that the combination temperature is higher than the phase transformation temperature at which the metal undergoes in-situ homogenization, in step (g) the ingot is cooled or the ingot is allowed to cool, in step (h) the ingot is preheated to a temperature effective for hot rolling without disrupting the homogenization process, and in step (i) the ingot is hot rolled, characterized in that the preheating step (h) is carried out in two stages, and in the first stage, the ingot is heated to the temperature of formation of crystallization centers, below the temperature effective for hot rolling, and the ingot is held at the formation temperature crystallization centers during the time interval effective for the formation of crystallization centers in the ingot, and in the second stage, the ingot is heated from the temperature of the formation of crystallization centers to a temperature effective for hot rolling, and the ingot is kept at a temperature effective for hot rolling for a time interval, sufficient to allow crystal growth, prior to performing step (i) of hot rolling. 11. The method according to claim 10, characterized in that the temperature of the phase transformations is 425 ° C or more. 12. A method of hot rolling an ingot obtained by direct cooling casting, in which in step (a) the ingot obtained by direct cooling is rapidly cooled from the elevated temperature of the casting, in step (b), the ingot is preheated to a temperature effective for hot rolling and in step (c), the ingot is hot rolled at a specified temperature effective for hot rolling, characterized in that the preheating step (b) is performed in two stages, and in the first stage, the ingot is heated to a temperature of crystallization centers are lower than the temperature effective for hot rolling, and the ingot is held at the temperature of formation of crystallization centers for a time interval effective for the formation of crystallization centers in the ingot, and in the second stage the ingot is heated from the temperature of formation of crystallization centers to a temperature effective for hot rolling, and the ingot is held at a temperature effective for hot rolling, for a period of time sufficient to ensure crystal growth, until stage (c) of hot rolling. 13. The method according to p. 12, characterized in that at the specified first stage, the ingot is heated to a temperature in the range of 380-450 ° C. 14. The method according to p. 12, characterized in that at the specified first stage, the temperature is maintained for 2-4 hours 15. The method according to p. 12, characterized in that the ingot is heated to a temperature of formation of crystallization centers with an average speed of about 50 ° C / h 16. The method according to any one of paragraphs.12-15, characterized in that in the specified second stage, the ingot is heated to a temperature in the range of 480-550 ° C. 17. The method according to p. 16, characterized in that at the specified second stage, the temperature is maintained for a time interval selected from the condition of increasing the length of the entire pre-heating stage to 10-24 hours 18. The method according to p. 16, characterized in that the ingot is heated from the temperature of formation of crystallization centers to a temperature effective for hot rolling, at a speed of about 50 ° C / h

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