High-strength two-phase steel plate with high rigidity and suitability for welding

 

(57) Abstract:

The invention relates to high-strength steel used in construction and for the manufacture of pipes, and to the production of this steel. The technical result is the provision of essentially uniform thickness sheet of microstructure in sheets with a thickness of at least 10 mm and the increase in ordinary share banit/martensite to about 75% and above. High strength steel composition containing a ferrite phase and martensite/bainite phase in which the ferrite phase has an initial allocation of carbides or carbonitrides of vanadium, niobium, is obtained by first rolling at a temperature higher than the temperature of recrystallization of austenite, the second rolling at a temperature below the temperature of recrystallization of austenite; cooling to a temperature between the point of turning Ar3500oC and cooling water to a temperature below approximately 400oC. 11 C.p. f-crystals, 4 Il., 5 table.

The invention relates to high-strength steel used in construction and for the manufacture of pipes, and to the production of this steel. In particular, the invention relates to the production of two-phase high-strength steel sheet containing ferrite and martensite/beinin the data toughness and weldability. In addition, the invention relates to the production of two-phase high-strength steel, which is a high-tech due to its structure, operational flexibility and the ease with which the microstructure can be changed in practice.

Art

Two-phase steel containing ferrite as a relatively soft and martensite-banit as a relatively solid phase, is obtained by annealing at a temperature in the range between temperatures of turning Ar3and Ar1and subsequent cooling to room temperature, at speeds in the range from speed air cooling up to speed quenching in water. The choice of annealing temperature depends on the chemical composition of steel and the desired volume ratio of ferrite and martensite/bainite phase.

The status of the production of low-carbon and low-alloy two-phase steels are well described and is the subject of intense research metallurgists (see, for example: proceedings of the conference "Fundamentals of Dual-Phase Steels, "Formable HSLA and Dual Phase Steels", U.S. patent 4067756 and 5061325). However, two-phase steel are mainly used in the automotive industry, where high working strength characteristics lead to the forming press is th less than 10 (usually 2-3) mm and fluidity and strength, respectively, within 344,7-to 413.6 MPa (50-60 ksi) and 482,6-620,5 MPa (70 to 90 ksi). In the volume of the microstructure of martensite/bainite phase is typically about 10-40%, the rest is soft ferritic phase. Moreover, one of the factors limiting the widespread use of such steels is their high sensitivity to processing conditions, often requiring to achieve the desired properties of the exact exposure temperature in a narrow range and (compliance) other conditions. Beyond these rather narrow range for most structural steels leads to a very dramatic and drastic deterioration of properties. Because of this sensitivity were almost impossible to obtain with the use of a constant technology, and therefore their production is concentrated on a small group of world famous steel mills.

For example, SU 1158602 A, 1985 a method of obtaining a two-phase steel comprising heating a steel ingot to a temperature sufficient to dissolve carbonitrides of vanadium, niobium, rolling ingot and the formation of the sheet in one or more passes to first reduce the volume at the temperature of recrystallization of austenite, the rolled sheet in one or more passes before the second reduction at a temperature below its recrystallization temperature and which has the possibility of obtaining a steel sheet for manufacturing a pipe with a uniform microstructure in large sheets thickness with a high proportion of martensite/bainite, high yield strength, toughness and good weldability in the absence of softening in the heat impact zone (HAZ).

In connection with this object of the invention is the use of high working strength characteristics of two-phase steel for improved forming properties, and to obtain such a steel sheet for manufacturing pipes for main pipelines, which after 1-3% strain compression ratio would be high, i.e. 690 MPa (100 ksi), preferably 827,3 MPa (120 ksi) yield strength. Thus, the sheet dual phase steel with the described characteristics would serve as a half-pipe pipelines.

The objective of the invention is to provide essentially uniform thickness sheet of microstructure in sheets with a thickness of at least 10 mm. Goal is to increase the volume fraction beynite/martensite to about 75% and above in fine distribution of the constituent phases in the microstructure and thereby obtaining a high-strength two-phase steel with excellent toughness. The goal is to obtain a high-strength two-phase steel with excellent weldability and resistance to loss of strength in the zone of heat includes heating a steel ingot to a temperature sufficient for dissolution of carbonitrides of vanadium, niobium, rolling ingot and the formation of the sheet in one or more passes to first reduce the volume at the temperature of recrystallization of austenite, the rolling of the sheet in one or more passes before the second reduction at a temperature below the temperature of recrystallization of austenite, but higher than the temperature of the point of turning Ar3and cooling, heating of the ingot lead to a temperature sufficient to dissolve substantially all of the carbonitrides of vanadium, niobium, cooling sheet lead first to a temperature between the point of turning Ar3approximately 500oC, and then finally cooled in water to a temperature of 400oC obtaining ferrite and martensite/bainite phase, and having a yield strength of at least 690 MPa after 1 to 3% strain.

Heating a steel ingot for dissolution of carbonitrides of vanadium and niobium can lead to 1150-1250oC.

Rolling steel ingot prior to the first reduction can be performed with the degree of deformation of about 30-70%, and rolling the sheet to the second volume decrease with deformation rate of 30-70%.

Cooling of the laminated sheet to a temperature between the point of turning Agry between the point of turning Ar3approximately 500oC can be performed before the transformation began in the ferritic phase of 20-60% by volume.

The final cooling in water laminated sheet can be performed with a cooling rate of at least 25oC/s

The sheet can be molded in an annular workpiece or pipe for the pipeline.

An annular workpiece or pipe for the pipeline can be extended to 1-3%.

Steel may have the following chemical composition, wt.%:

Carbon - 0,05 - 0,12

Silicon - 0,01 - 0,50

Manganese - 0,40 - 2,0

Niobium - 0,03 - 0,12

Vanadium 0.05 to 0.15

Molybdenum - 0,2 - 0,8

Titanium - 0,015 - 0,03

Aluminum - 0,01 - 0,03

Iron - Rest

Pcm0,024, where Pcmis a parameter of proclaimeth that represents the following value:

< / BR>
where C, Si, Mn, Cu, Ni, Cr, Mo and V contents of the respective elements in the steel, wt.%. Pcman indicator, which determine the strength and weldability of steel. This is known in the art and industry (see, for example, "Introduction to the Physical Metallurgy of Welding", Kenneth Easterling, 1983, p. 224).

The sum of the concentrations of vanadium and niobium in the steel may be 0.1 wt. %.

The concentration of vanadium Yves quantity wt.% - 0.3 to 1.0%.

In conventional two-phase steels values of the volume fractions of the constituent phases is sensitive to small variations of the initial temperature of the cooling.

However, according to the invention the chemical composition of the steel and the regulation of thermo-mechanical modes of rolling allows you to get the suitable as material for pipes pipelines high strength (yield strength of more than 690 MPa (100 ksi), and after 1 to 3% strain of at least 827,3 MPa (120 ksi) two-phase steel microstructure containing ferrite matrix 40-80%, preferably 50-80%) by volume of martensite/bainite phase, with the proportion of bainite in the martensite/bainite phase is less than about 50%.

In a preferred variant embodiment of the ferritic matrix further strengthen with high dislocation density (> 1010cm/cm3and by dispersing microscopic discharge at least one, and preferably all carbides and carbonitrides of vanadium, niobium and molybdenum carbide, i.e., (V, Nb)(C, N) and Mo2C. Fine (diameter of 50 angstroms) particles of carbides or carbonitrides of vanadium, niobium and molybdenum are formed in the ferrite phase at the interfacial reactions allocation, which flow is adout carbides of vanadium and niobium (V, Nb)(C,N). Thus, by adjusting the chemical composition and thermo-mechanical modes of rolling, it is possible to obtain a two-phase steel of a thickness of at least about 15 mm, preferably at least about 20 mm ultra-high strength.

The strength of the steel depends on the presence of martensite/bainite phase, the increase of which leads to an increase in strength. However, there must be a balance between strength and toughness (ductility), which is ferritic phase. For example, after 2% strain yield stress is achieved at the level of at least about 689,4 MPa (100 ksi), if the volume fraction of martensite/bainite phase is at least about 40%, at least about 827,3 MPa (120 ksi), if this share is about 60%.

The preferred steel with a high density of dislocations and precipitates of vanadium and niobium in the ferritic phase produced by finishing compression rolling at temperatures above the temperature of transformation of Ar3, cooling in air to a temperature between the temperatures of point transformations of Ar3500oC, followed by quenching at room temperature. Therefore, this method is the opposite of the method for producing a two-phase steels for the, the which should be free from allocation to ensure appropriate forming properties. Allocations are formed discretely on a movable boundary between ferrite and austenite, but only when there is an appropriate amount of vanadium, or niobium, or both, and conditions of rolling and heat treatment are monitored closely. In other words, vanadium and niobium are the key elements of the chemical composition of steel.

Description of drawings

In Fig. 1 shows a plot of the fraction V (% by volume) of the formed ferrite (ordinate) from the initial temperature hardeningoC (abscissa) for the known steels (dashed line) and for the steel according to the invention (solid line).

In Fig. 2A and 2B shows a scanned electron micrograph of a two-phase microstructure, obtained by the method in mode A1. In Fig. 2A shows the plot near the surface, and Fig. 2B - in the middle (thickness) part. These figures are grey areas - ferritic phase, and the highlights - martensitic phase.

In Fig. 3 shows an electron micrograph of precipitates in ferritic phase particles of niobium and vanadium carbonitride with a diameter of less than about 50, preferably about 10-50 EN

In Fig. 4 shows graphs of the dependence of Vickers hardness in the HAZ (ordinate) for steel, manufactured according to the invention in the mode A1 (solid line), and a similar graph for commercial X100 steel pipes pipelines (dashed line). The steel according to the invention shows a slight decrease in strength in the HAZ supplying heat 3 kJ/mm, while for X100 steel strength (grade Vickers hardness in the HAZ is significantly (about 15%) is reduced.

The steel according to the invention has a high strength at very high weldability and toughness at low temperatures and contains (by weight):

0,05 - 0,12% C, preferably 0,06 - 0,12%

more preferably 0.08 to -0,11;

from 0.01 to 0.50% Si

of 0.40 to 2.0% Mn, preferably 1,2 - 2,0;

more preferably 1,7 - 2,0;

0,03 - 0,12% Nb, preferably 0.05 to 0.1;

0.05 TO 0.15% V;

0.2 to 0.8% Mo;

0.3 to 1.0% Cr, preferably for use in a hydrogen environment;

0,015 - 0,03% Ti,

0,01 - 0,03% Al,

Pcm0,24,

the rest is Fe and incidental impurities.

The sum of the mass fractions of vanadium and niobium is 0.1%, but more preferably the content of each of them is 0.04%. The concentration of well known contaminants N, P, S minimization titanium nitride. The preferred concentration N of about 0.001 to 0.01%, the concentration of S is not more than 0.01% and the concentration of P is not more than 0.01 mass%. The steel of this chemical composition is free of boron, in the sense that it is not added, its concentration is 5 million-1(5 ppm), preferably < 1 million-1(1 ppm).

In General, the method of producing the material according to the invention includes:

conventional forming an ingot of the above composition;

heating the ingot to a temperature preferably in the range from 1150 to 1250oC, sufficient to dissolve substantially all of the carbonitrides of vanadium, niobium and, therefore, to translate into the solution essentially all of the niobium, vanadium and molybdenum;

hot rolling of the ingot (first reduction) in one or more passes with a compression of about 30-70% on the first temperature level, when recrystallized austenite;

hot rolling of compressed ingot for one or more passages (the second volume reduction of 30-70%) at a slightly lower temperature level, when the austenite is not recrystallized, but when the temperature above the point of becoming Ar3;

air cooling to a temperature in the range between the temperature of point Ar3greater least 25oC/s, preferably at least about 35oC/s (hardening of the ingot) to a temperature not higher than 400oC, when excluded further transformation; and, if desired

air cooling to room temperature with getting rolled high strength steel sheet for pipes pipelines. In the end, the beans get almost the same size - 10 μm, preferably 5 μm.

High-strength steel should have diverse properties that provide a combination of the elemental composition of the alloy and machining. Role of alloying elements in the alloy and the preferred limits of their concentrations according to the invention are described below.

The carbon matrix provides the hardening of all steels and welds at any microstructure, and this hardening is caused by the release sufficiently small and numerous particles NbC and VC. In addition, the allocation NbC during hot rolling helps to slow recrystallization and suppression of grain growth by getting crushed grains of austenite. This leads to increased and strength, and viscosity at low temperatures. Carbon also improves the ability to hardening, i.e. to the formation of a hard and durable mikros is. If the carbon content is greater than 0,12%, the steel is jednolinkowy in place of welding, and its viscosity will decrease as in the steel sheet, and in the HAZ of the weld.

Manganese strengthens the matrix in steels and welds, as well as increases the ability to solidification. To achieve the necessary high strength minimum amount of Mn should be 0.4 percent. Like the carbon excess Mn harmful effect on the viscosity of the sheets and welded joints and causes jednoralski welded joints (in the field); therefore, the quantity limit of 2.0%. This restriction is necessary to prevent appreciable axial segregation in steels during continuous casting of pipes, pipelines, contributing to cracking due to hydrogen absorption (TOV).

Silicon is always added to the steel in the amount of at least 0.01 percent for deoxidation. A greater number of Si harmful effect in the HAZ on the viscosity, which decreases to an unacceptable level when more than 0.5% Si.

Niobium improves the grain microstructure of rolled steel, which improves both strength and ductility. The selection of carbide of niobium during hot rolling slow recrystallization and inhibits the growth of grains that provides what about the excess niobium harm weldability and toughness in the HAZ, therefore a maximum of 0.12%.

Titanium is effective when added in a small amount for the formation of small particles of TiN, which reduce the grain size as in the rolled structure, and in the HAZ, thereby improving the viscosity. Titanium is added in an amount such that the ratio Ti/N was in the range of 2.0 to 3.4. Excess titanium due to the formation of large particles of TiN or TiC will worsen the viscosity of steel and welds. The content of Ti < 0,002% cannot provide sufficient fine grain, and > 0,04% causes a reduction in viscosity.

Aluminum is added for deoxidation. This requires at least 0,002% Al. If the aluminum content is too high (> 0,05%), there is a tendency to the formation of inclusions of type Al2O3that reduce the viscosity of steel in the matrix and in the HAZ.

Vanadium added for increased strength due to the formation in steel fine particles VC annealing, and HAZ - during cooling after welding. In the solution of the vanadium is a potent tool contributing to the hardening of steel. So it will be effective to maintain the strength of high-strength steel in the HAZ. The maximum vanadium is 0.15%, and the excess will cause jednoralski in the welding area (field) value allocation of particles of vanadium carbonitride diameter 50, preferably 10-50 angstroms.

Molybdenum increases the hardness of steel after quenching, as a strong microstructural matrix; it also provides the hardening due to selection when re-heating of the particles Mo2C and NbMo. Excess Mo causes jednoralski in the weld zones (in the field) and deteriorates the toughness of the steel itself and in the HAZ, so its maximum is 0.8%.

Chromium increases the hardness of steel after quenching. It improves the corrosion resistance and resistance to cracking when navodorozhivanii. In particular, it is preferable to prevent the penetration of hydrogen through the formation on the surface of the steel foil enriched Cr2O3. As for molybdenum, the excess Cr causes jednoralski in the weld zones (in the field) and deteriorates the toughness of the steel itself and in the HAZ, so its maximum is set at 1.0%.

The nitrogen penetrates into the steel during its production and remains in it. A small amount of nitrogen is useful for the formation of small particles of TiN, which prevent grain growth during hot rolling and this increases the fine grain rolled steel as such and in the HAZ. Required measures at the spine of steel in the HAZ, therefore, a maximum of 0.01%.

Thermomechanical treatment has two objectives: obtain a fine homogeneous austenite grain and high density of dislocations and shear zones in two phases.

The first target is to reach a heavy rolling at temperatures above and below the recrystallization temperature of austenite, but always above the temperature of point Ar3. Rolling at a temperature above the recrystallization temperature continuously grinds grain of austenite and rolling below this temperature aligns the grain size of austenite. Therefore, cooling below the temperature of Ar3when the austenite begins to transform to ferrite, leads to the formation of a fine-grained mixture of austenite and ferrite, and with the rapid cooling below the temperature of Ar1to a finely divided mixture of ferrite and martensite/bainite.

The second goal is achieved by a third compression of aligned grains of austenite during rolling at temperatures between Ar1and Ar3when 20% to 60% of the austenite is transformed into ferrite.

Thermomechanical processes according to the invention is important to ensure the desired distribution of the constituent phases.

The temperature that defines the boundary between levels, Kogel carbon the concentration of niobium and the magnitude of compression during rolling. This temperature can easily be determined for each steel composition or experimentally, or mathematical modeling.

Line pipe is formed from a sheet known has been operating a UOE-way, U-shape by bending the sheet, and then shaping the O-shaped workpiece and ruzveltova it at 1-3%. The formation and expansion, providing a concomitant effect on increasing hardness, provide very high strength pipe.

The following examples illustrate the described invention.

£ 500 received in one melting alloy with the chemical composition given in table. 1 was melted in a vacuum induction furnace, poured into ingots, odouli the slab thickness of 4 inches, procomil them at 1240oC for 2 hours and subjected to hot rolling with a compliance regime under the table. 2.

Alloy and thermo-mechanical process designed to obtain the following ratios strong carbidopa additives, in particular niobium and vanadium:

- about one third of these compounds is highlighted in the austenite prior to quenching; the allocation inhibit recrystallization, contributing to the compression of the grains of austenite, causing it to become article is Nita ferrite, passing through intergranular and subcriterion region; these allocations contribute to the hardening of the ferritic phase;

- about one third of these compounds is retained in solid solution to highlight in the HAZ, which eliminates the usual softening observed in other steels.

Thermomechanical rolling process square (100 mm x 100 mm) forged slab shown below (see tab. 2).

To determine the number of ferrite and other transformation products of austenite were quenched after heating to different final temperatures (see table. 3).

The surrounding air was cooled to these temperatures after finish rolling.

The total amount of ferrite phase and includes proeutectoid ("residual ferrite"), and eutectoid ("transformed ferrite") fractions of ferrite.

Quantitative metallographic analysis was performed to investigate the dependence of the number of transformed austenite from the quenching temperature after finish rolling: these data are shown graphically in Fig. 1 and summarised in table. 3.

The speed of hardening at a temperature of finish rolling should be about 20-100oC/s, more preferably 30-40oC/s to get geleia initial temperature quenching from 660oC to 560oC the transformation of austenite occurs within 35-50%. If the initial hardening temperature of not lower, the steel does not undergo any additional transformations; the number (austenite) is about 50%.

If steel with high volume fractions of secondary or martensite/bainite phase is usually characterized by low plasticity and toughness, the steel according to the invention is excellently retain sufficient plasticity that provides shaping and beading in has been operating a UOE process. Plasticity keep by maintaining effective size of the particles in the microstructure, for example in a batch martensite in General below 10 μm, particles less than 1 micron. On Micrography with scanning electron microscope (SEM) in Fig. 2 shows a two-phase microstructure comprising ferrite and martensite obtained in mode A1. There has been a surprising uniformity of the microstructure through the thickness of the sheet in all two-phase steels.

In Fig. 3 shows the electronic Micrography showing fine interfacial selection in the ferritic region was obtained in mode A1. Eutectoid ferrite is usually observed near the boundary in the second phase and is equal to

The basis of the invention is the discovery that the austenitic phase has shown remarkable resistance to further transformations after approximately 50% conversion. This results from the combination of stabilization mechanisms and effects of aging austenite.

(A) Stabilization of austenite. There are at least three mechanisms of stabilization of austenite in steels according to the invention, which allow to explain the termination of its further transformation in the ferritic phase.

(1) Thermal stabilization. A large driving force for carbon emissions from the transformed ferrite in neprevyshenie austenite during its transformation leads to several effects, usually called thermal stabilization. This mechanism can lead to some General enrichment of the austenite carbon; more specifically, the peak concentration of carbon strengthens the boundary of the austenite/ferrite, locally preventing further turning. Moreover, the carbon can also rapidly be allocated in a dislocation at the front turning, braking it and stopping the transformation.

(2) the Peak concentration. Carbon and other such strong austenite stabilizers, as Mn, when the conversion is transferred into the residual austenite. However, because IU the t to the local peaks of the concentration of carbon and magnesium on the front of transformation of austenite. This locally increases the ability of steel to hardening, leading to stabilization. The total reduction transformation contributes to this process, eliminating the possibility of homogenization.

(3) Chemical stabilization. Due to the considerable amount of Mn in the steel and the presence of bound Mn, zone of residual austenite are also areas of high Mn content, which increases their ability to hardening significantly more than in the entire volume of the alloy. When applied cooling rates and thermomechanical processing, this can lead to stabilization of the transformation of austenite into ferrite.

(B) aging of the austenite. This is considered the main factor for steels according to the invention. If the phase austenite contains a lot of Nb and V in supersaturated solid solution, as in the case of the steels according to the invention, and if the temperature of austenite transformation is sufficiently low, then the excess of Nb and V may lead to the phenomenon of separation or predvidevanja fine grains. Preguidelines may include dislocation of the atmosphere in the austenite in General and, in particular, when the transformation that can stop him front and stabilize the austenite from further turning.

In table. 4ASS="ptx2">

The yield strength after 2% elongation in forming the tube will correspond to the minimum desired strength equal to at least 689,5 MPa (100 ksi), preferably at least 896,2 MPa (130 ksi) due to the excellent performance of the solidification of samples with such microstructures.

In table. 5 shows the performance impact strength of specimens with a V-shaped incision in Sharpie (Techn. conditions E-23 ASTM) at -40oC obtained on the longitudinal (L-T) and transverse (T) samples of the alloys processed according to the modes A1 and A2.

The indices of the table. 5 indicate the excellent ductility of the steels according to the invention.

A key aspect of the present invention is a high strength steel with good weldability, as well as exceptional resistance to loss of strength in the HAZ. To study jednoralski and softening in the HAZ were conducted laboratory tests on a single weld. In Fig. 4 shows a graph for the steel according to the invention. This graph shows that in contrast to the known steels, such as commercial steel X100 for pipes, two-phase steel according to the invention is not observable (measurable) softening in the HAZ. In patiyala. For steel according to the invention the metal in the HAZ retains at least 95% of the strength of the base metal. These data about the strength obtained for calorific welding level 1-5 kJ/mm.

1. A method of obtaining a two-phase steel comprising heating a steel ingot to a temperature sufficient to dissolve carbonitrides of vanadium, niobium, rolling ingot and the formation of the sheet in one or more passes to first reduce the volume at the temperature of recrystallization of austenite, the rolling of the sheet in one or more passes before the second reduction at a temperature below the temperature of recrystallization of austenite, but higher than the temperature of the point of turning Ar3and cooling, characterized in that the heating of the ingot lead to a temperature sufficient to dissolve substantially all of the carbonitrides of vanadium, niobium, cooling sheet lead first to a temperature between the point of turning Ar3approximately 500oC, and then finally cooled in water to a temperature of 400oC obtaining ferrite and martensite/bainite phase, having a yield strength of at least 690 MPa after 1 to 3% strain.

2. The method according to p. 1, characterized in that the heating of the steel ingot for the dissolution of CTCU steel ingot to first reduce the amount of carry out with the degree of deformation of about 30 - 70%, and rolling the sheet to the second volume decrease with the degree of deformation of 30 - 70%.

4. The method according to p. 1, characterized in that the cooling of the laminated sheet to a temperature between the point of turning Ar3approximately 500oC spend on the air.

5. The method according to p. 1, characterized in that the cooling of the laminated sheet to a temperature between the point of turning Ar3approximately 500oC is carried out before the transformation began in the ferritic phase of 20 to 60% by volume.

6. The method according to p. 1, wherein the final cooling in the form of a laminated sheet carried out with a cooling rate of at least 25oC/s

7. The method according to p. 1, wherein the sheet is formed into an annular material or pipe for the pipeline.

8. The method according to p. 1, characterized in that the annular material or pipe for pipelines extend to 1 - 3%.

9. The method according to p. 1, characterized in that the steel has the following chemical composition, wt.%:

Carbon - 0,05 - 0,12

Silicon - 0,01 - 0,50

Manganese - 0,40 - 2,0

Niobium - 0,03 - 0,12

Vanadium 0.05 to 0.15

Molybdenum - 0,2 - 0,8

Titanium - 0,015 - 0,03

Aluminum - 0,01 - 0,03

Iron - Rest

Particle0,24, where Particleis parameterstable 0.1 wt.%.

11. The method according to p. 9, characterized in that the concentration of vanadium and niobium in steel individually comprise of 0.04 wt.%.

12. The method according to p. 9, characterized in that the steel further comprises chromium in an amount of 0.3 to 1.0 wt.%.

 

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FIELD: aggregate of particles of magnesia.

SUBSTANCE: the invention presents an aggregate of particles of magnesia, that has a controlled structure of particles and may be used in the capacity of covers for annealing forming a forsterite film. The aggregate of particles of magnesia has a diameter of pores corresponding to the first inflection point on the curve of a total volume of pores of the aggregate, makes no more than 0.3.10-6.m. Volume of inter-particle pores is from 1.40.10-3 up to 2.20.10-3 m3 / kg. The volume of pores inside the particles is from 0.55.10-3 up to 0.80-10.10-3 m3 /kg. There is a description of a cover for annealing of a sheet made out of the anisotropic electrical steel, that contains the aggregate of particles of magnesia and an annealed sheet. The technical result is an increase of insulating and magnetic properties of anisotropic electrical steel.

EFFECT: the invention ensures an increase of insulating and magnetic properties of anisotropic electrical steel.

3 cl, 4dwg, 4 tbl,6 ex

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