FR2731713A1 - PROCESS FOR MANUFACTURING AN ELECTRIC GRAIN ORIENTED STEEL SHEET, PARTICULARLY FOR CARRYING OUT MAGNETIC CIRCUITS OF TRANSFORMERS - Google Patents

Abstract

Electrical steel sheet is made by concasting steel of composition in wt. %:- 0.02-0.09 C; 2.5-4 Si; 0.027-0.17 Mn; 0.007-0.02 S; 0.01-0.03 Al; 0.004-0.012 N; 0.06-5 Cu; balance Fe and impurities. The concast slab or strip is reheated to 1200-1300 deg. C before being hot rolled to a thickness of 1-5 mm and then coiled at 500-700 deg. C. The strip is then cold rolled to below 0.5 mm, annealed to produce a primary recrystallisation and a decarburisation in a moist atmosphere and then coated with MgO. Finally it is annealed to produce a secondary recrystallisation and coated with an insulation layer which is fired.

Description

PROCESS FOR PRODUCING AN ELECTRIC STEEL SHEET

  GRAINS ORIENTES FOR CARRYING OUT CIRCUITS IN PARTICULAR

MAGNETIC TRANSFORMERS.

  The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet for the realization in particular of magnetic circuits of transformers comprising, successively: a casting of a continuous steel in the form of slab or strip of steel containing, in particular, less than 0.1% carbon, 2.5 to 4% silicon and at least the elements aluminum, nitrogen, manganese, sulfur, copper, intended to form normal growth inhibiting compounds, heating of the slab or strip, - hot rolling of the slab or strip to obtain a sheet of thickness between 1 and 5 mm - hot winding of the hot-rolled sheet - annealing of the hot-rolled sheet - cold rolling to a final thickness of less than 0.5 mm - annealing of primary recrystallization and decarburization in a humid atmosphere - application to at least one face of the decarburized sheet e, magnesia MgO - a final annealing of secondary recrystallization and purification - an application of an insulating coating and a final annealing baking coating, The texture of a grain oriented electrical steel sheet is a so-called texture of Goss symbolized by the MILLER indices, {1 10} <001>, according to which the axis <001>, which is an axis of easy magnetization, is parallel to the rolling direction and the plane {1 10} is a plane parallel to the surface of the sheet. This texture gives the grain oriented electrical steel sheet good magnetic properties. The B800 induction acquired under a magnetic field of 800 A / m and the energy losses W (1.7 / 50) of the steel sheet for a working induction of 1.7 Tesla (T) at a frequency of 50 Hertz are used in practice to evaluate the quality

magnetic.

  Two types of grain oriented steel sheet are marketed.

  - The so-called conventional sheets are characterized by a B800 induction less than 1.86 Tesla; they are obtained by a process which comprises in particular two cold rolling operations separated by an intermediate annealing, the reduction rate of the second rolling being generally

less than 70%.

  The so-called high permeability sheets are characterized by a B800 induction greater than 1.88 Tesla; they are obtained by a process which includes in particular a single cold rolling operation or two cold rolling operations with intermediate annealing, the reduction rate of cold rolling in one operation or the second rolling to

  cold being generally above 80%.

  The steel of conventional sheets contains, before hot rolling, manganese, sulfur and copper. High permeability sheet steel contains, before hot rolling, aluminum, manganese,

copper, sulfur and nitrogen.

  It is known a method for producing a grain-oriented steel sheet having the texture {1 10} <001> with high permeability wherein the steel contains aluminum, manganese, copper sulfur and nitrogen. Aluminum combines with nitrogen to form aluminum nitride AIN, and manganese and copper combine with sulfur to form MnS manganese sulfide and copper sulphide CuS. The precipitates of aluminum nitride, manganese sulphide and copper sulphide inhibit the normal growth of primary grains during static annealing of texturing while allowing the development of

  secondary recrystallization having the desired Goss texture.

  In known manner, the heating of the steel slab before hot rolling is operated at a temperature greater than 1300 C, of the order of 1350 to 1400 C to completely bring into solution the AlN, MnS and CuS precipitates. Their size in the raw state of casting, generally greater than 1 micrometer, is too coarse to allow the development of secondary recrystallization. The compounds AIN, MnS and CuS reprecipitate in the form of fine particles, of average size less than 150 nanometers (nm) during hot rolling and annealing before

  cold rolling performed in a single operation.

  The main disadvantage of reheating the grain-oriented steel slab or strip at a temperature greater than 1300 C is the formation of liquid oxides which necessitates the periodic shutdown of the furnace.

  specially adapted for this production with a view to its removal.

  To obtain a magnetic quality equivalent to that of the products

  from slab reheating in the temperature range 1350-

  1400 C, several metallurgical processes using slab reheating at a temperature lower than 1300 C have been proposed: For example, after cold rolling and decarburization, a nitriding is used which aims at the formation of fine precipitates of silicon nitride and aluminum (Si, Al) N before the beginning of the secondary recrystallization. The nitriding is carried out by additional heat treatment in a gaseous atmosphere containing ammonia NH 3, or by addition of a nitrogen-containing compound, such as manganese nitrides MnN, ferro-manganese FeMnN, chromium CrN, annealing separator consisting mainly of magnesia MgO. The slabs generally contain aluminum, and optionally titanium Ti, chromium Cr, boron B, elements known for their ability to form nitrides TiN, CrN, BN. Since this process involves the precipitation of fine particles (Si, Al) N at the secondary recrystallization annealing stage, the presence of fine precipitates MnS and AlN is not necessary. Consequently, the resetting of the coarse MnS and AlN particles is incomplete during the reheating of the slabs, preceding the hot rolling. In addition, an incomplete solution of the aluminum solution is

  indispensable for the precipitation of silicon nitride.

  German Patent DE 43 1 11 51 and European EP 0 619 376 describe a process which comprises: -A reheating of the slabs to a temperature which is lower than the solubility temperature of the manganese sulphide and which is greater than

  the solubility temperature of copper sulphide.

  Under these conditions, the copper sulphide precipitates are dissolved. On the other hand, the manganese sulphide precipitates are not put back in solution and, being in the form of coarse particles, no longer play

the role of inhibitor.

  -The precipitation, during hot rolling, of more than 60% of the nitrogen in the form of coarse particles AIN which do not play either

the role of inhibitor.

  In the process described in these documents, copper sulphide fine particles CuS, which precipitate during the annealing of the rolled sheet

  hot are the essential inhibitor.

  The subject of the present invention is a process for manufacturing grain-oriented electrical sheet for the realization, in particular, of magnetic circuits of transformers, characterized in that the steel of the following weight composition: from 0.02 to 0.09% of carbon, from 2.5 to 4% of silicon, from 0.027 to 0.17% of manganese, from 0.007 to 0.018% of sulfur, from 0.010 to 0.030% of aluminum, from 0.004 to 0.012% of nitrogen, 0.06 to 0.50% of copper, the remainder being iron and impurities, is subjected after the slab or the strip has been produced by continuous casting at - a heating at a temperature above 1200 C and lower or equal to 1300 C followed by hot rolling, then, after obtaining the hot-rolled sheet, a winding of the sheet

  hot rolled between 500 and 700 C.

  The other characteristics of the invention are: the composition additionally contains up to 0.10% tin, the product resulting from the multiplication of the sulfur content by the manganese content is less than or equal to 120 × 10- 5 - the product resulting from the multiplication of the nitrogen content by the aluminum content is less than or equal to 240 × 10 -6, the steel is hot-rolled so as to precipitate the nitrogen in the form of fine particles containing nitrogen and aluminum with a diameter of less than 100 nanometers, the percentage of nitrogen precipitated being less than 40%, the hot rolled steel is annealed so as to precipitate the nitrogen in the form of fine particles containing nitrogen and aluminum with a diameter of less than 100 nanometers, the percentage of nitrogen precipitated being greater than 60%, the steel is hot rolled so as to precipitate the sulfur in the form of particles of which the number and diameter allow a contribution to the inhibition of normal growth and to the development of secondary recrystallization, after annealing of the hot-rolled sheet at a temperature of between 850 and 1150 ° C. for 1 to 10 minutes and cooling at a speed greater than 10 C per second, the cold rolling to a final thickness of less than 0.5 mm is carried out, in a single operation, with a reduction ratio greater than 70%, the sheet temperature being between and 300 C during minus one rolling pass, - the cold rolling, at a final thickness of less than 0.5 mm, is carried out in two operations with an intermediate annealing, at a temperature of between 850 and 1150 ° C. for 1 to 10 minutes, followed by cooling at a rate greater than 10 C per second, the reduction rate of the second cold rolling being greater than 40%, the temperature of the sheet being between 100 and 300 C penda at least one cold rolling pass when the reduction rate of the second cold rolling is greater than 70%, - prior to the cold rolling in two operations, the sheet is annealed at a temperature between 850 and 1150. C, especially if the final thickness of the sheet is less than 0.27 mrm, - magnesia contains, in addition to optional additions of titanium dioxide, boron or a borated compound, at least one sulfur compound and / or a sulfur and nitrogen compound and / or an antimony compound taken alone or

in combination.

  magnesia contains, in addition to optional additions of titanium dioxide, boron or a compound containing boron, sulfur or one or more sulfur compounds selected from magnesium sulphate, sulphate

of manganese.

  magnesia contains, in addition to the optional additions of titanium dioxide, boron or a borated compound, at least one sulfur and nitrogen compound selected from ammonium sulfate, amidosulphuric acid (

sulphamic acid).

  - magnesia contains, in addition to optional additions of titanium dioxide, boron or a borated compound, an antimony compound, antimony chloride,

  The description which follows and the attached figures, all given as

  non-limiting example, will make clear the invention.

  FIG. 1 is a graph showing mass loss as a function of the reheating temperature of the slab and illustrating the formation

  of fusible oxides above 1300 C.

  Figure 2 shows, after hot rolling, the relationship between the average diameter of the precipitates and the sulfur percentage of the steel. FIG. 3 shows, after decarburization, the precipitate densities as a function of the stopping temperature of the secondary recrystallization annealing. The present invention relates to the use of a steel with the following weight composition: carbon of between 0.02 and 0.09%, silicon of between 2.5 and 4%, and a selection of manganese of between 0.027 and 0, 17%, sulfur between 0.007 and 0.018%, aluminum between 0.010 and 0.030%, nitrogen between 0.004 and 0.012%, copper between 0.06 and 0.50%, the rest being of iron and impurities, composition subject, after the development by continuous casting of the slab or the strip to a core heating at a temperature equal to or lower than 1300 C. Indeed, according to the present invention, there is More fusible surface oxides are formed below this temperature as shown in Fig. 1 for a total slab heating cycle of 4 hours 30 minutes, the dwell time at the intended reheat temperature being one hour. The reheating temperature of the slab is greater than 1200 C according to the invention so that the AlN, MnS and CuS precipitates can be put back in solution during heating of the slab. According to the present invention, the contents of manganese, sulfur, aluminum and nitrogen are chosen in very narrow ranges, which allows the quenching of the AlN, MnS and CuS precipitates in almost complete solution during the heating of the slabs, before hot rolling. , at a temperature equal to or lower than 1300 C which avoids training

surface of fusible oxides.

  According to the present invention, the sulfur-containing and / or nitrogen-containing precipitates are mostly dissolved in the reheating of the slabs as a result of the chemical composition being adapted to the lower reheating temperature. The main inhibitor is aluminum nitride, which precipitates a little during hot rolling and essentially during the annealing of the hot-rolled sheet in the form of fine particles with a mean diameter of less than 100 nm. Manganese sulphide is a complementary inhibitor. Copper has a refining effect on the size of these AlN and MnS precipitates to which it can be associated. The addition of one or more sulfur and / or nitrogen compounds to the magnesia of which the sheet is coated after decarburization reinforces the inhibition

by AIN and MnS.

  Oriented grain steel sheets according to the invention are manufactured from the following successive stages: continuous casting of the steel in the form of slabs with a thickness between 150 and 300 mm, reheating of the core slabs to a thickness of temperature between 1200 and 1300 C, hot rolling to a thickness between 1 and 5 mm, - winding between 500 and 700 C of the hot rolled sheet, - annealing of the hot rolled sheet at a temperature of between 850 and 1150 C for 1 to 10 minutes followed by a very rapid cooling, - cold rolling to a final thickness of less than 0.5 mm in one operation with a reduction ratio greater than 70%, the sheet temperature being between 100 and 300 ° C. for at least one cold rolling pass or - cold rolling at a final thickness of less than 0.5 mm in two operations with intermediate annealing, carried out at a temperature of between 850 and 1150 ° C. 1 to 10 minutes followed by a very rapid cooling, the reduction rate of the second cold rolling being greater than 40%, the temperature of the sheet being between 100 and 300 C for at least one pass when the reduction rate this second cold rolling is greater than 70%, (In the case of two cold rolling operations with intermediate annealing, an optional annealing before the first cold rolling is likely to stabilize the secondary recrystallization; the cooling rate may be slower.) - primary recrystallization annealing and decarburization in a humid atmosphere containing hydrogen and nitrogen at the final thickness, - application on at least one face of the sheet of a anti-sticking agent consisting mainly of magnesia, - final annealing of secondary recrystallization and purification of the metal, - application of an insulating coating and final annealing of the coating. The oriented grain steel according to the invention, having undergone the manufacturing steps previously described, contains from 0.02 to 0.09% of carbon, from 2.5 to 4% of silicon, from 0.027 to 0.17% of manganese, 0.007 to 0.018% sulfur, 0.010 to 0.030% aluminum, 0.004 to 0.012% nitrogen, 0.06 to 0.50% copper, and optionally

  up to 0.10% tin, the balance being iron and impurities.

  The product resulting from the multiplication of the sulfur content by the manganese content is less than or equal to 120.10-5: (% S) x (% Mn) <120.10-5 The product resulting from the multiplication of the nitrogen content by the aluminum content is less than or equal to 240.10-6 (% N) x (% AI) <240.10-6 The percentage of nitrogen precipitated after hot rolling, in the form of fine particles with a diameter of less than 100 nm, is less than at 40% The percentage of precipitated nitrogen, after hot rolling and annealing, in the form of fine particles with a diameter of less than 100 nanometers, is

greater than 60%.

  Magnesia used as a separator during the secondary recrystallization annealing and high temperature purification may contain, alone or as a mixture, sulfur or one or more sulfur compounds selected from magnesium sulphate and / or manganese sulphate, one or more sulfur and nitrogen compounds selected from amidosulfuric acid (sulphamic acid) and / or ammonium sulphate, an antimony compound, boron antimony chloride or a boron and titanium dioxide compound. FIG. 2 shows, after hot rolling, the relationship existing between the average diameter of the precipitates and the sulfur percentage of the steel, in the case of a nearly complete solution of all the precipitates during heating. of the slab. In order to obtain a fine precipitation after hot rolling, the sulfur content according to the present invention is

limited to 0.018%.

  The MnS precipitated ends playing an active role of inhibitor during secondary recrystallization annealing, the sulfur content must be at least equal to

  0.007% to obtain a sufficient amount of these precipitates.

  The manganese content according to the present invention must be greater than 0.027% to obtain the precipitation of a sufficient quantity of fine MnS precipitates exerting an inhibiting effect and to have a free manganese availability in the case of sulfur supply via the magnesia in order to reinforce the inhibitory power of MnS precipitates. It is limited to 0.17% to avoid the presence of a coarse precipitation of MnS in the slabs and an incomplete solution remelting during the

  reheating between 1200 and 1300 C before hot rolling.

  According to the present invention, the respect of the condition [% S] x [% Mn] <120.10-5 favors the presence of fine MnS precipitates in the slabs and

  their redissolving between 1200 and 1300 C before hot rolling.

  In the process according to the present invention, the nitrogen content must be greater than 0.004% in order to obtain sufficient precipitation of fine AlN precipitates during annealing of the hot-rolled sheet. The nitrogen content is limited to 0.012% to avoid the formation of blistering on the surface of the steel. The condition (% N) x (% AI) <240.10-6 makes it possible to obtain the almost complete dissolution of the AIN precipitates during

  heating the slabs between 1200 and 1300 C before hot rolling.

  According to the present invention, the aluminum content must be equal to or greater than 0.010% so that the amount of the AlN precipitates formed during annealing of the hot-rolled sheet is sufficient, AIN being the main inhibitor and to have an availability of free aluminum, in the case of nitrogen supply through the magnesia channel in order to reinforce the inhibitory power of the AlN precipitates. The aluminum content is less than or equal to 0.030% to prevent precipitation of particles

  coarse AIN during the final phase of hot rolling.

  In addition to the elements mentioned above, the steel may contain up to 0.10% tin which is likely to have a beneficial effect on the inhibition. In the process according to the present invention which uses lower sulfur and aluminum contents than in the process for heating slabs at higher temperatures, the density of the inhibiting precipitates containing either sulfur and manganese or nitrogen and aluminum, may be insufficient to obtain a complete secondary recrystallization and homogeneity of the magnetic quality. In order to increase the stability of the secondary recrystallization and thus avoid a dispersion of the values of the magnetic characteristics, it is preferably added to the magnesia one or more compounds containing sulfur, nitrogen or antimony which allow the formation of a complement of inhibitory precipitates, on the one hand, based on sulfur and manganese, and on the other hand based on nitrogen and aluminum, during the rise in temperature preceding the start of recrystallization

secondary.

  The present invention is illustrated from the following observations and examples, with Table 1 giving the chemical composition of the steels tested. Steels 2 to 5 are steels described by the present invention. The phosphorus content, residual element, according to the present

  invention is less than 0.015%.

  Steel No. 1 is a reference steel containing 0.021% sulfur and 0.030% aluminum (Steel No. 1, Table 1) whose slabs were heated to 1400 C before hot rolling, so as to dissolve the majority of AlN, MnS, CuS precipitates of coarse size. The cold rolling was carried out in a single operation after annealing the hot-rolled sheet at 1120 C. The magnetic properties obtained at the final thickness of 0.285 mm are: W (1.7 / 50) = 1.03 Watt / kg; B800 = 1.91 T In the context of the examples presented below describing the present invention, the steel sheets were manufactured in the following manner - continuous casting of steel slabs 210 mm thick, - slab reheating at heart at a temperature between 1200 and 1300 C, with a rise in temperature in 3 hours 30 minutes and a maintenance at the target temperature of 1 hour, - preliminary hot rolling to the thickness of 45 mm in 5 passes 7-pass finishing hot rolling to a thickness of 2.3 mm, the starting temperature of the hot-rolling finishing being between 1070 and 1000 ° C., the final hot rolling temperature being between 965 and 915 C, winding of the hot-rolled sheet at a temperature of 530 C or

640 C,

  - annealing of the hot rolled sheet with a rise in temperature of about 60 seconds, maintaining at 950 C for 160 seconds, very fast cooling of the hot rolled sheet with a passage time between 700 and 300 C less than 15 seconds - cold rolling to the final thickness in six passes corresponding to successive cold reduction rates of about 30%, the rolling temperature reaching the maximum temperature of 230 C in the third pass, (for the examples 2-7) - recrystallization and decarburization in a moist N2 / H2 atmosphere between 800 and 850 ° C., the duration of the heat treatment being less than 500 seconds, - magnesia coating, - slow annealing of secondary recrystallization with a temperature rise of 15 ° C. / h under atmosphere 25% N2-75% H2 between 650 and 1200 C and purification of the metal at 1200 C under hydrogen, ll

  final insulation and baking of the coating.

Example 1

  After reheating of the slab to 1280 C, hot rolling and winding of the sheet at 530 C, the steel n 2 was cold rolled to the intermediate thickness of 0.74 mm, annealed 90 seconds at 1050 C followed by a very fast cooling with a passage time between 700 and 300 C less than 15 seconds, and was then rolled to the final thickness of 0.285 mm which corresponds to a cold reduction rate 61%. After continuing the treatment as indicated above, the magnetic characteristics obtained are the following Losses (1.7 / 50) = 1.27 W / kg

B 800 = 1.85 T

Example 2

  After reheating the slab to 1280 C, hot rolling and winding at 530 C, annealing the hot rolled sheet at 950 C for 160 seconds, very fast cooling, cold rolling to the final thickness of 0.285 mm, which corresponds to a cold reduction rate of 87%, and continuation of the treatment as indicated above, the magnetic characteristics obtained for the steel n 3 are the following Losses (1.7 / 50) = 1.03 W / kg

B 800 = 1.93 T

  From these two examples, it appears that the reduction rate of the final cold rolling must be greater than 70% to obtain the best results.

magnetic properties.

  In Examples 1 and 2, the annealing separator consisted of

  magnesia containing 2% TiO2 and 0.080% boron.

  The percentage of additive is the quotient of the mass of the additive per

the mass of magnesia x 100.

Example 3

  Under the conditions of Example 2, 10% of sulfur in the form of ammonium sulphate is added to the magnesia. The following magnetic characteristics are obtained for steel n 2 Without addition of With 10% addition

(NH4) 2SO4 (NH4) 2SO4

| B800 1.89 T 1.94 T

  The percentage of sulfur is equal to the quotient of the mass of sulfur

by the mass of magnesia x 100.

Example 4

  Under the conditions of Example 2, 3% by weight of sulfur in the magnesium sulphate state are added to the magnesia. The magnetic characteristics obtained for steel No. 2 are the following Losses (1.7 / 50) = 1.02 W / kg

B 800 = 1.94 T

  The percentage of sulfur is equal to the quotient of the mass of sulfur

by the mass of magnesia x 100.

Example 5

  Under the conditions of Example 2, 1% sulfur in the form of amidosulphuric acid is added to the magnesia. The magnetic characteristics obtained for steel n 2 are as follows: Losses (1.7 / 50) = 1.01 W / kg

B 800 = 1.94 T

Example 6

  Under the conditions of Example 2, 0.05% of antimony chloride is added to the magnesia. The magnetic characteristics obtained for steel n 2 are as follows: Losses (1.7 / 50) = 1.03 W / kg

B 800 = 1.92 T

  The mass percentage of antimony chloride is equal to the quotient of the mass of antimony chloride by the mass of magnesia x 100. The addition of sulfur to magnesia makes it possible to reinforce the inhibition by precipitates containing manganese and sulfur during secondary recrystallization annealing. The addition to magnesia of amidosulfuric acid which contains both 33% sulfur and 14% nitrogen makes it possible to introduce into the steel both sulfur and nitrogen to enhance the inhibition by the precipitates containing, on the one hand, manganese and sulfur and, on the other hand, nitrogen and aluminum. The sulfur and the nitrogen diffusing in the steel, it results a complementary precipitation of very fine inhibiting particles before the beginning of the

secondary crystallization.

  The beneficial effect of nitrogen associated with sulfur is illustrated by the fact that the sulfur percentage used in Example 5 is lower than that used.

in example 4.

  The addition to magnesia of ammonium sulphate also allows a simultaneous supply of sulfur and nitrogen. The addition to magnesia of antimony chloride allows the introduction into the steel of antimony, which segregates at the grain boundaries, plays the role of inhibitor. The addition of a soluble sulfur compound is preferred over the possible addition of insoluble elemental sulfur because the dispersion in the milk of magnesia is more homogeneous. Magnesia addition of sulfur, nitrogen and antimony compounds promotes magnetic quality

homogeneous along a coil.

  Table 2 shows that according to the invention, the percentage of nitrogen precipitated in the hot-rolled sheet is less than 40%. Lowering the winding temperature substantially reduces the percentage of nitrogen precipitated, up to less than 5% in the case of steel

n 3, wound at 530 C.

  In general, lowering the winding temperature to less than 600 ° C avoids the precipitation of particles

  coarse substances which do not have an inhibitory effect.

  The amount of nitrogen combined with aluminum was determined from the measurement of precipitated aluminum. By heating the slabs between 1200 and 1300 C according to the present invention, it is possible to obtain, thanks to the strict control of the Mn, S, Al and N contents, a percentage of precipitated nitrogen which is much lower than that characterizing the known process. of

  reheating of slabs at temperatures above 1350 C.

  Table 3 shows that, according to the invention, the percentage of precipitated nitrogen is greater than 60% after annealing of the hot-rolled sheet with

950 C.

  Table 4 shows that, according to the invention, the mean diameter of the precipitates containing nitrogen and aluminum, obtained by annealing the hot-rolled sheet of steel No. 2, wound at 530 ° C. is less than 50 nanometers in a wide annealing temperature range. The precipitates containing nitrogen and aluminum can therefore

play an active role of inhibitor.

  The effect of copper has been analyzed in the context of the present invention. Table 5 gives the average diameter and the density of the precipitates after reheating at 1280 ° C. of steel slab n 2 at 0.15% copper.

  hot rolling to the thickness of 2.3 mm and winding at 640 C.

  By way of comparison, the characteristics of the precipitates of the hot rolled sheet at the thickness of 2.3 mm and wound at 640 ° C. of the reference steel No. 1 at 0.09% copper are presented. It appears from Table 5 that the increase in copper content results in an increase in the density of CuS and INACuS precipitates and a decrease in

of their average diameter.

  In non-rolled hot-rolled sheet steel No. 2, small diameter CuS and INACU particles are predominant, while those containing manganese are minor. The addition of copper and the trapping of sulfur by copper make it possible to avoid, during hot rolling, the formation of coarse particles containing manganese, which is too large to act as an inhibitor. Examination of Table No. 4 shows a decrease in the copper-containing particles as the annealing temperature of the hot-rolled sheet increases, demonstrating the partial dissolution of the particles containing Al, N. Cu, S. FIG. evolution of the density of CuS and MnCuS precipitates after decarburization and during the secondary recrystallization annealing of non-aluminum-containing steel No. 6, a composition chosen to facilitate the counting of precipitates by transmission electron microscopy. This steel, whose slabs were heated to 1400 C, underwent two cold rolling operations with intermediate annealing at 950 C, the reduction rate of the second rolling at

cold being 60%.

  The fine CuS precipitates gradually dissolve before the secondary recrystallization, the release of sulfur accompanied by a fine precipitation of MnCuS particles. According to the present invention, the fine particles CuS do not play a decisive inhibitory role for the

  development of secondary recrystallization.

  In steel No. 2, the percentage of CuS precipitates with an average diameter of less than 100 nm is less than 3% of the total population, after annealing of the hot-rolled sheet. These are MnCuS precipitates formed after decarburization and before secondary recrystallization which reinforce

  inhibition by precipitates containing nitrogen and aluminum.

  According to the present invention, the copper content must be greater than 0.06% to obtain fine precipitation in the hot rolled and hot rolled and annealed stages. The increase in the copper content favors the refinement of the precipitation. The copper content is limited to 0.50% to avoid stripping problems. As has been demonstrated by embodiments 1 to 6, it is possible to manufacture, by heating slabs at a temperature greater than 1200 C and equal to or less than 1300 C, grain-oriented electrical steel sheets which have, the magnetic properties of conventional sheets (B 800 <1.86 T) thanks to cold rolling in two operations separated by an intermediate annealing and a reduction rate at the second cold rolling of between 40 and 70%, ie the properties of high permeability sheets (B 800> 1.88 T) by a single cold rolling operation preceded by annealing, or cold rolling in two operations separated by an intermediate annealing, the rate of

  reduction of the final cold rolling operation being greater than 70%.

  Lowering the reheating temperature compared to the process

  known avoids the formation of liquid oxides fouling the oven.

  The process of the present invention described for continuous casting slabs of between 150 and 300 mm in thickness can be applied to thinner slabs of thickness between 15 and 100

mm approx.

  The process of the present invention can also be applied to thin strips obtained by pouring liquid steel between two rolls, with a thickness greater than 2 mm, the strips being heated between 1200 and

  1300 C before undergoing hot rolling.

  The number of passes of the preliminary hot rolling and finishing hot rolling is a function of the thickness of the continuously cast product and the target thickness in the hot rolled state. If the thickness of the continuously cast product is sufficiently low, hot rolling

preliminary report may be deleted.

  The total duration of the heating cycle of the continuously cast product is a function of its thickness. The lower this thickness, the lower the

  reheating temperature is quickly reached to heart.

Benchmark Si C Mn S AI N Cu Steel

  1 3,16 0.060 0.081 0.021 0.030 0.0074 0.09

  2 3.15 0.044 0.080 0.011 0.025 0.0086 0.151

  3 3.18 0.057 0.081 0.015 0.021 0.0072 0.154

  4 3.16 0.059 0.079 0.014 0.026 0.0073 0.150

  3.15 0.058 0.079 0.012 0.021 0.0093 0.151

  6 3.21 0.042 0.058 0.020 0.001 0.0042 0.205

  Table 1 Chemical analysis (mass percentage) of the slabs Mark Temperature Temperature of% N precipitated Steel heating coil slats

(C) (C)

1 1400 640 40

2 1280 530 21

3 1280 640 24

530 3

4 1280 640 37

530 12

1245 640 34

  Table n 2: Percentage of nitrogen precipitated after hot rolling Mark Temperature Temperature of% N precipitated Steel heating coil slats

(C) (C)

2 1280 530 75

3 1280 640 74

____ _530 75

4 1280 640 77

530 82

  Table 3: Percentage of nitrogen precipitated after annealing of hot-rolled sheet Temperature Diameter Standard deviation Density Nature of average annealing precipitates (C) (nm) (nm) (number / pm2) 900 C 27.05 14.59 13.

2 AINCuS Steel n 2 950 C 29.02 17.18 9.0 AIN and INAC 1000 C 32.49 20.49 7.3 AIN for the most part Steel 1 1120 C 38.8 25.1 7.5 AIN and INAC Table 4: Influence of annealing temperature of hot-rolled sheet on average diameter and density of precipitates containing aluminum CuS MnCuS MnS INACIN AINMnCuS AINMnS Total Average diameter 87.3 141.5 64.7 102.4 - 104.3 Steel (nm) n 1 Density (number / 0.178 0.474 0 0.346 0.272 0 1.269 pUm2) Average diameter 69.4 143.1 85.8 45.9 77.0 70.9 62.3 Steel (nm) n0 2 Density (number / 0.355 0.079 0. 015 0.686 0.138 0.010 1.288 Pm2) Table 5: Characteristics of raw rolled precipitates (before annealing)

Claims (14)

  1. A method of manufacturing a grain oriented electrical steel sheet for the realization in particular of magnetic circuits of transformers comprising successively: a casting of a continuous steel in the form of slab or steel strip containing in particular in its weight composition less than 0.1% of carbon, of 2.5 to 4% of silicon and at least the elements aluminum, nitrogen, manganese, sulfur, copper, intended to form growth inhibitory precipitates normal, - a reheating of slab or strip, - hot rolling of the slab or strip to obtain a sheet thickness between 1 and 5 mm, a hot winding of the hot-rolled sheet, - a annealing of the hot-rolled sheet, cold rolling to a final thickness of less than 0.5 mm, annealing of primary recrystallization and decarburization in a humid atmosphere, application on at least one face of the decarburized sheet , magnesia MgO, a final annealing of secondary recrystallization and purification, an application of an insulating coating and the final annealing of the coating, characterized in that the steel of the following composition by weight: from 0.02 to 0 , 09% carbon, - 2.5 to 4% silicon - from 0.027 to 0.17% manganese - from 0.007 to 0.018% sulfur - from 0.010 to 0.030% aluminum - from 0.004 to 0.012% d nitrogen, from 0.06 to 0.50% of copper, the remainder being iron and impurities, is subjected after elaboration of the slab or strip by continuous casting at a temperature above 1200 C and less than or equal to 1300 C, then after obtaining the hot-rolled sheet, a winding of the hot rolled sheet between 500 and 700 C 2. Method according to claim 1 characterized in that the   The composition further contains up to 0.10% tin.   3. Method according to claim 1 characterized in that the product resulting from the multiplication of the sulfur content by the manganese content is less than or equal to 120.10-5.   4. Method according to claims 1 and 3 characterized in that the   product resulting from the multiplication of the nitrogen content by the   aluminum is less than or equal to 240.10-6.   5. Method according to claims 1, 3 and 4 characterized in that   the steel is hot rolled to precipitate nitrogen in the form of fine particles containing nitrogen and aluminum of smaller diameter   at 100 nanometers, the percentage of precipitated nitrogen being less than 40%.   6. Process according to claims 1, 3 to 5 characterized in that   the hot-rolled steel is annealed so as to precipitate the nitrogen in the form of fine particles containing nitrogen and aluminum with a diameter of less than 100 nanometers, the percentage of precipitated nitrogen being greater than 60%   7. Method according to claims 1, 3 to 6 characterized in that   The steel is hot-rolled so as to precipitate sulfur in the form of particles whose number and diameter allow a contribution to the inhibition of normal growth and to the development of secondary recrystallization.   8. Process according to claims 1, 3 to 7 characterized in that   after annealing of the hot-rolled sheet at a temperature between 850 and 1150 ° C for 1 to 10 minutes and cooling at a rate greater than 10 ° C per second, the cold rolling at a final thickness of less than 0.5 mm is carried out, in a single operation, with a reduction rate greater than 70%, the temperature of the sheet being   between 100 and 300 ° C for at least one rolling pass.   9. Process according to claims 1, 3 to 8 characterized in that   Cold rolling, at a final thickness of less than 0.5 mm, is carried out in two operations with intermediate annealing, at a temperature between 850 and 1150 C for 1 to 10 minutes, followed by cooling at a speed greater than 10 C per second, the reduction rate of the second cold rolling being greater than 40%, the temperature of the sheet being between 100 and 300 C during at least one cold rolling pass when the reduction rate of the   second cold rolling is greater than 70%.   10. The method of claim 9 characterized in that prior to cold rolling in two operations, the sheet is subjected to annealing at a temperature between 850 and 11 50 C, especially if   the thickness of the sheet is less than 0.27 mm.   11. Process according to claims 1, 3 to 10 characterized in that   the magnesia contains, in addition to the optional additions of titanium dioxide, boron or a borated compound, at least one sulfur compound and / or a sulfur and nitrogen compound and / or an antimony compound taken alone or in combination.   12. Process according to claims 1, 3 to 10 characterized in that the   Magnesia contains, in addition to optional additions of titanium dioxide, boron or a compound containing boron, sulfur or one or more sulfur compounds selected from magnesium sulfate, manganese sulfate.   13. Process according to claims 1, 3 to 10 characterized in that   magnesia contains, in addition to optional additions of titanium dioxide, boron or a boron compound, at least one sulfur compound and   nitrogen selected from ammonium sulfate, amidosulfuric acid.   14. Process according to claims 1, 3 to 10 characterized in that   magnesia contains, in addition to optional additions of titanium dioxide, boron or a boron compound, and an antimony compound, the antimony chloride.