IT8322974A1 - Process for producing an oriented grain steel electrical tape with a high magnetic flux density - Google Patents

Description

DESCRIPTION of the patent for industrial invention entitled:

"Process for producing an electric steel strip with oriented grain having a high magnetic flux density"

SUMMARY

The present invention relates to a process for the production of an oriented grain steel electrical strip

an aspect of the present invention consists in ensuring in a plate values of: S <.0.007%, Mn = 0.08 0.45%, P = 0.015 0.45%. The present inventive idea abolishes the conventional concept of using MnS as an inhibitor. The present invention avoids incomplete secondary recrystallization via the S content, which is decreased to as low a level as possible. Furthermore, a product with a high magnetic flux density can be successfully produced by adding suitable amounts of Mn and P. Given these advantages it is also possible to use, in the present invention, a high content of Si in the plate, which leads to a reduction of the watt loss. Furthermore, according to the present invention, the heating temperature of the plate , which is carried out before hot rolling, can be drastically reduced and this in comparison with the known technique. It is thus possible to achieve a significant cost reduction given the decrease in thermal energy and given the fact that it is avoided the formation of slag completely. In addition, the loss of watts of a product obtained by heating the plate at low temperature is considerably and lower than that of a product obtained by heating the plate at a high temperature.

DESCRIPTION

The present invention relates to a process for the production of an oriented grain electric steel strip having a high density. of magnetic flux.

The grain-oriented electrical steel tape? a material of good susceptibility? magnetic composed of crystal grain having the so-called Goss structure, expressed as 100 ^ <001> by means of the Killer index, in which the orientation of the crystals of the strip plane? the. plane and the? orientation of the crystals in the direction of lamination? parallel to axis <001>. Oriented Grain Steel Electrical Tape is used for the core of transformers, generators and other electrical equipment and devices.

Directed grain steel electrical tape should exhibit excellent magnetization and watt loss characteristics. The magnetization characteristic is defined by the magnitude of the density? of the magnetic flux induced in the electrical steel strip with grain oriented through a predetermined magnetic field. Here B is used. The material of good susceptibility? magnetic with a high density? of magnetic flux, that is? good characteristics of magnetization, pu? advantageously to reduce the size of the electrical equipment and devices.

The loss of watts is defined as the power lost following transformation into thermal energy in a core, when it is energized through an alternating magnetic field with an intensity? predetermined. Here W is used. . How? known the characteristic of watt loss is influenced by the density? of the magnetic flux, from the thickness of the tape, from the impurities, from the resistivity? and by the size of the grain in the electrical steel strip with oriented grain. Yup ? There has been an increased demand for electrical oriented grain steel strips with a low wattage loss, along with the trend for energy conservation.

The electrical oriented grain steel strip is produced by hot and cold rolling of a plate to the desired final thickness for the strip and by final annealing of the resulting steel strip to cause selective grain growth of the primary recrystallization 110 001, that is? to carry out the so-called secondary recrystallization.

To achieve secondary recrystallization, fine precipitates, such as MnS and A1N, must be finely and uniformly dispersed in phases in the steel, while the steel is subjected to treatments before the final annealing at a high temperature, so? to suppress grain growth of primary recrystallization having orientations other than orientation | ll0j <001>, during final annealing at high temperature (inhibitory effect). By controlling secondary recrystallization, it is possible to increase the proportion of accurately oriented grain 100 <001 > in the grain of the crystal, cos? to increase the density? of magnetic flux of the electrical tape of grain oriented steel and reduce cos? the-period. of watt loss. It is therefore important to develop production techniques that allow the control of secondary recrystallization.

Japanese Examined Patent Publication (Kokoku) No. 40-15644 (Taguchi et al) and Japanese Examined Patent Publication (Kokoku) No. 51-13469 (Imanaka et al) describe the basic techniques for making tape electric steel grain oriented with density? high magnetic flux and decreased watt loss.

The basic techniques described in the Japanese patent publications examined above, however, present some fundamental problems. In the process described in the examined Japanese Patent Publication No. 40-15644, it is difficult to achieve optimal global production conditions and to produce in stable conditions. electrical steel strips with oriented grain with high density of magnetic flux. What are the results, the procedure? unsuitable for the permanent production of products with the best magnetic characteristics.

The process disclosed in Examined Japanese Patent Publication No. 51-13469 involves double cold rolling and the use of an expensive element such as Sb or Se. Therefore this process involves high production costs.

Furthermore, both prior art processes require high plate heating temperatures, which are disadvantageous from an energy point of view. used to heat the plate, decreased yield due to slag generation and increased costs for the maintenance of the plate heating furnaces.

When a plate is heated to make it laminable, it is necessary to raise the heating temperature of the plate to sufficiently high values to dissolve MnS and other inhibitory elements in the solid. The latter precipitate in the form of MnS, A1N and the like when the steel is hot rolled or hot strip annealed. How much greater? the degree of orientation desired, the greater the quantity? of MnS, A1N and other fine precipitates that must be present in the steel and therefore the higher the heating temperature required for the plate. Japanese Examined Patent Publication No. 48-51852 discloses an improvement in the process of Japanese Examined Patent Publication No. 40-15644. According to this procedure, is the Si content of the starting material increased? However, a high silicon content greatly restricts the balancing lamination conditions under which A1N can? be secured in the hot rolled strip. Furthermore, since? the silicon content is high, the temperature range in which A1N precipitates during hot rolling in a manner suitable for secondary recrystallization becomes higher with a consequent request for a higher temperature. high heating temperature of the plate.

The adoption of continuous casting has created additional problems in the production of oriented grain steel electrical strip. In continuous casting, portions with incomplete secondary recrystallization, referred to as veins, are occasionally generated in the steel. There? compromises the magnetic characteristics of steel. The vein problem is greatly aggravated by a high Si content. When the Si content exceeds 3.0% it becomes extremely difficult to safely produce electrical steel strip with oriented grain. The Japanese Patent Publication Not Examined Ito. 48-53919 (M.F. Littman) describes how to overcome the vein problem by subjecting a continuous jet steel bar to a dual stage of hot rolling in the production of hot rolled strip. Japanese Unexamined Patent Publication No. 59-37009 (Akira Sakakura et al.) Discloses a process for producing an electrical oriented grain steel strip in which a hot rolled steel strip is produced by a dual rolling stage 'hot. These two processes, of the known art, however, do not make concrete use of the advantages of the continuous jet, that is to say? the omission of blank lamination. Two further publications, Japanese Patent Publication, Unexamined No. 54-120214 (Fumio Matsumoto et al.) Describes how to use a single hot roll to produce grain-oriented electrical steel strip using a continuous casting bar. However, these proposals require the reconstruction of the casting or lamination installations and do not completely solve the problem of vein generation.

It is an object of the present invention to provide a method for producing an electric steel strip of oriented grain having a density. of magnetic flux of 1.89 Tesla or more, using a single stage of cold rolling, in which one can? obtaining a secondary and stable crystallization under less severe conditions than the known technique, even at a low heating temperature of the plate, with a high content of Si with respect to the known technique and / or using a continuous jet plate.

The essence of the process according to the present invention lies in the steps of: preparing a plate which has a temperature of 1430 ° C or less and which consists of 0.025%? 0.075% of C, 3.0% to 4.5% Si, 0.010% to 0.060% of aluminum soluble in / acid, 0.0030% to 0.0130 of N, not more? 0.007% of S, 0.08% to 0.45% of Mn and 0.015% to 0.045% of P, the remaining percentage being Fe; hot rolling the plate to form a hot rolled web; annealing the hot rolled strip at a temperature in the range of 850 ° C to 1200 ° C for a short period of time; cold roll the annealed strip heavily with a reduction of not less than 80%, so? to obtain the desired final thickness for the sheet; continuously decarbonise-anneal the cold rolled strip cos? obtained in a humid atmosphere of hydrogen and then apply an annealing separator on the strip and allow the final annealing to take place at a high temperature.

One of the aspects according to the present invention consists in the sulfur content equal to 0.007% or less. In the prior art, as disclosed in examined Japanese Patent Publications Nos. 30-3651, 40-15644 and 47-25250, sulfur? considered useful for producing an electric sheet of oriented grain steel, as the sulfur forms MnS, one of the precipitates indispensable to generate secondary recrystallization. According to These publications, the effect of sulfur? pi? important in a certain range of content that is determined by the quantity? of MnS solute brought into the solid solution during the plate heating process.

A1N also forms precipitates believed to be useful for the production of an oriented grain steel electrical sheet. Conventionally, both MnS and A1N precipitates were used as inhibitors.

The inventors of the present invention investigated in detail the precipitation behavior of MnS and A1N. They found that when a plate having the composition of an electrical steel sheet is heated and then hot rolled and when the hot rolled strip is annealed, it first precipitates MnS at a high temperature and then precipitates A1N at a low temperature. Since? MnS? already? present in steel when A1N precipitates, A1N tends to precipitate around MnS. . involving complex precipitation. What? the magnitude and dispersion state of A1N is influenced by the precipitation state of MnS. That is? when ? large the quantity? of precipitated MnS, A1N? large in size and found unevenly dispersed.

As known from Japanese Unexamined Patent Publication No. 48-51852, a fundamental concept in metallurgy for producing a grain oriented electrical steel strip having a high density. of magnetic flux with a single cold rolling process, consists of creating a suitable dispersion state of A1N using the oc-? T transformation that occurs during hot rolling or annealing. When the content of Si? high, the transformation is changed disadvantageously, and so? the dispersion of A1N is compromised. In the case of continuous casting, it is believed that there? involve the generation of veins.

Based on the findings described above and transformation considerations?.? y, the inventors of the present invention have decreased the quantity? of precipitation of MnS. They therefore found that even with a high Si content in the steel, the dispersion state of A1N could be kept uniform and that the A1N precipitates could be kept small in size.

One of the characteristics of the present invention therefore lies in the fact that the sulfur content? lower than the prior art. Even with this, the precipitation of A1N can? be controlled in a suitable way and you can? avoid the generation of veins in the continuous jet, which can occur when? high the Si content.

? Since? the sulfur content? low, the entity? precipitation of MnS according to the present invention? less than in the known art. -Decrease the entity? of the precipitation of Mn and P means that the quantity is decreased? total of inhibitors, there? which tends to diminu? -? re the density? of the magnetic flux. To compensate for the decrease in density? of the magnetic flux, Mn and P are added to the steel in quantities? suitable.

Another characteristic according to the present invention resides in the fact that Mn and P added to the steel do not change the inhibitors but make the structure of the primary recrystallization suitable before the secondary recrystallization. That is? they compensate for the decrease indicated above in the density? of magnetic flux and also increase the density? of the magnetic flux by checking the structure. The grain of the crystal? refined and has a uniform size, with the result of stabilizing the secondary recrystallization.

Another feature according to the present invention is that the Si content in the starting material? equal to at least 3.0%, while secondary recrystallization is stabilized and thus avoided? the generation of veins. There? involves minimal losses of watts and very high densit? of magnetic flux obtainable in the electric steel strip with high grain orientation.

The present invention will come described in more detail with reference to the attached drawing tables, in which:

Figures 1A to, 1D show photographs of the macrostructures of the crystal grain in the products obtained using steels containing 0.004%, 0.007%,

0.015%, and 0.025% of S;

Figures 2A to 2D show photographs of the macrostructures of the crystal grain in the products

obtained using continuous jet bars containing

0.004%, 0.007%, 0.012%, and 0.030% of S;

figure 3? a graph of the influence of Mn and P

on the density? magnetic B ^;

figure 4? a graph showing the influence of

Mn and P su relative to a product obtained using a continuous jet plate containing 0.0090% N;

figure 5? a graph of the magnetic characteristics of the products obtained therein

/ conditions shown in Figure 3, but with plate heating temperatures of 1150 ° C e

1350? C;

figure 6? a graph showing the influence

the heating temperature of the plate on

density magnetic flux of products;

figure 7? a graph showing the relationship

between the density? of magnetic flux (B) of the products

and the speed? of heating in the temperature range ? ? between 700 and 1000 ° C, said heating being carried out

during a final high temperature annealing;

figure 8? a graph showing the relationship between the density? of the magnetic flux, the loss of watts s

and the Cr content; And

figure 9? a graph similar to that of figure 5 relating to steels containing Cr.

Four steels were prepared in the form of small samples with a thickness of 40 mm in which the content of S was respectively equal to 0, 004%, 0.007%, 0.015% and 0.025% and which contained 0.030% of C, 3.45% of Si , 0.030% acid-soluble aluminum and 0.0085% nitrogen.

These were heated to 1200 ° C in an oven and then removed from the oven and allowed to cool in an air environment up to a temperature of 1000 ° C. The four steels were then kept in an oven for 30 seconds at 1000 DEG C. The four steels at a temperature of 1000 ° C were hot rolled in three passes to form hot rolled strips with a thickness of 2.3 mm. Then the following treatments were carried out: continuous annealing at 1100 ° C for 2 minutes; cold rolling to form 0.30mm cold rolled sheet; decarburization-annealing in hydrogen-moist atmosphere; application of MgO; final annealing at elevated temperature at 1200 ° C for 20 hours.

How is it evident from the macrostructures of the grain of the? crystal, of the products shown in Figures 1A to ID no incomplete secondary recrystallization occurs when the content of S /? equal to 0.007% or less. Furthermore, in accordance with the experiments of the inventors of the present invention, no incomplete secondary recrystallization occurs when the content of Si? equal to 4.5% or less and when the S content? equal to 0.007% or less. In accordance with what? the content of S? limited to 0.007% or less according to the present invention. The S content is desirably decreased in the melting stage of the melt steel since the desulfurization treatment during annealing at a high final temperature can? be facilitated. According to current fusion techniques to decrease sulfur, the S content that pu? be easily obtained without incurring cost increases? usually 0, OC1% or more. Four continuous jet plates, in which the S content was 0.004%, 0.007%, 0, C12%, and 0.030%, respectively and which contained 0.055% C, 3.30% Si, 0.25 % Mn, 0.030% acid-soluble aluminum and 0.0080% nitrogen, were heated to 1410 ° C in an oven and were hot rolled to form 2.3 mm thick rolled strips. Then the following treatments were carried out successively: continuous annealing at 1150 ° C for 2 minutes; cold rolling to form a 0.30 mm cold rolled strip; decarburization-annealing in a humid atmosphere of hydrogen; application of MgO as annealing separator and final annealing at elevated temperature at 1200 ° C for 20 hours.

It is still evident from the crystal grain macrostructures shown in Figures 2A to 2D, that veins are generated less easily when the content? low and the veins are not generated in any way when the content of S? equal to 0.007% or less.

In addition, continuous jet plates were prepared in the form of small samples with a thickness of 40 mm in which the content of Mn and P was varied and which contained 0.050% C, 3.40% Si, 0.002% S, 0.030 % acid-soluble aluminum and 0.0080% nitrogen. Were they heated? at 1150 ° C in an oven and were hot rolled by three passes to form hot rolled sheets with a thickness of 2.3 mm. The hot rolling finishing temperature was approximately 820 ° C.

Then the following treatments were carried out in succession: continuous annealing at 1100 ° C for 2 minutes; cold rolling to form 0.30mm cold rolled sheet; decarburization-annealing in a humid atmosphere of hydrogen; application of MgO and final annealing at a high temperature of 1200 ° C for 20 hours.

The. Density of magnetic flux B of the products is shown in Figure 3. In Figure 3 x corresponds to, d and a <1.80 Tesla ,? corresponds to 1.80 <B <1.89 Tesla, or corresponds, to 1.89 <B <1.91 Tesla and? corresponds to 1.91.Tesla <B ^. As is evident from Figure 3, when the content of Mn? low, secondary recrystallization becomes unstable and when the Mn content? high, the density is high? of the magnetic flux However, when Mn is added in addition to a certain content, it is ineffective in improving the density? of magnetic flux B and is also uneconomical as the quantity? of alloy of the additive becomes disadvantageously high.

When the content of P? too low, the density? of magnetic flux B? low and the generation of incomplete secondary recrystallization is increased. When the content of P? too high, the incidence of breakage during cold rolling is increased.

What? the Mn content is limited in a range from 0.08% to 0.45% and the P content is limited in a range from 0.015% to 0.045%, in accordance with the present invention.

In these intervals the density? of magnetic flux B.? is equal to 1.89 Tesla or more ?, the recrystallization? 10

secondary is stable and not? the problem related to breakages is significant.

Continuous jet plates, in which the Mn and P content was varied and which contained 0.060% C, 3.45% Si, 0.004% S, 0.033% acid-soluble aluminum and 0.0090% nitrogen, were heated to 1410 ° C and were then hot rolled to form 2.3mm thick hot rolled strips. The following treatments were then carried out in succession: continuous annealing at 850 ° C for 2 minutes; cold rolling to form cold rolled strips of 0.30 mm; decarburization-annealing in a humid atmosphere of hydrogen; application of MgO as annealing separator and final annealing at elevated temperature at 1200 ° C for 20 hours.

The density of magnetic flux B of the product is shown in Figure 4, where x corresponds to B. {J., 80 Tesla,? corresponds to 1.80 <<1.89 Tesla, or corresponds to 1.89 <B <1, 92 Tesla,? corresponds to 1.92 Tesla <B <1.93 Tesla, and * corresponds to 1.93 <Bicorne is evident from Figure 4, when the content of Mn? too low, secondary recrystallization becomes unstable and when the Mn content? high, the density? of magnetic flux B? high. However, when Mn is added in quantity? higher than a certain content, it is ineffective to improve the density? of magnetic flux B and becomes uneconomical as the quantities become disadvantageously high? of additive alloy.

When the content of P? low, the density? of magnetic flux B.? too low and incomplete secondary recrystallization generation is increased. When the content of P? too high, the incidence of breakages during cold rolling is increased.

What? the Mn content is limited in a range of 0.08% to 0.45% and the P content is limited in a range of 0.015% to 0.045% according to the present invention. In these intervals the density? of magnetic flux B? 1.89 Tesla or more, secondary recrystallization 10

? stable and not? the problem relating to breakages is significant.

As regards the other components, the steel which is subjected to the treatments according to the present invention can? be melted in a converter, in an electric oven, or in a Martin oven, provided? the composition of the steel falls within the previously reported ranges.

The content of C turns out to be cos? equal to at least 0.025%. With a C content of less than 0.025%, secondary recrystallization is unstable. Even if secondary recrystallization occurs, the density? of magnetic flux? low (B? equal to 1.80 Tesla at most). On the other hand the content of C? equal to 0.075% maximum, as the decarburization-annealing time? high and therefore uneconomical when the 'C content exceeds? 0.075%.

The content of Si? equal to 4.5% maximum. With an Si content greater than 4.5%, numerous rotations take place during cold rolling. The content of Si? equal to at least 3.0%, preferably at least 3.2%. With a Si content of less than 3.0%, you can't? to obtain the loss of watts to the degree pi? high, that is? w ^ 7/50 1.05 W / kg with a sheet thickness of 0.30 mm.

Since? in the present invention A1N is used for the precipitates indispensable for the secondary recrystallization, the quantity? minimum of A1N must be ensured in order to provide an acid soluble Ir content and an N content of at least 0.010% and 0.0030% respectively. Is the Al content soluble in acid? equal to 0.060% maximum. With an acid-soluble Al content greater than 0.060%, A1N does not disperse uniformly in the hot rolled strip, thus resulting in poor secondary recrystallization. The content of N? equal to 0.0130% maximum. With an N content of more than 0.0130%, bubbles are formed on the surface of the steel sheet.

When the steel has the composition described above, a high plate heating temperature, higher than 1300 ° C, accepted in conventional practice, is not required. Even more? Surprisingly, when the inventors of the present invention heated two plates to a high temperature and a low temperature respectively and then subjected them to treatments to produce grain-oriented electrical steel strips, they found that the products so? obtained, with an identical density? of the magnetic flux, considerably less watt loss occurred in the case of heating the plate at low temperature than in the case of heating the plate at high temperature. What? the heating of the plate at low temperature not only allows reductions in the cost of production and an easy use of a continuous jet bar as starting material, but also allows a reduction in watt loss.

Figure 5 illustrates the magnetic characteristics of the products obtained under the same conditions as those of Figure 3, but with heating temperatures of the plate at 1150 ° C? 1350? C. From the comparison between the two products (1150? C and 1350? C), it is evident that a lower heating temperature of the plate can? decrease. in a drastic way the loss of watts for the same density? of the magnetic flux.

/ When the heating temperature of the plate? equal to 1280 ° C or less, no slag is formed during the heating of the plate. Also when the heating temperature of the plate? equal to 1280? C or less and when the content of Si? equal to 3.0% or less, you can? get the product to the highest degree? high, that is? a product exhibiting a watt loss ^ of 1.50 w / kg or less with a web thickness of 0.30 min,

The lower heating temperature of the plate is not specifically limited, but what about it? desirably 1050? C, as at temperatures below 1050? C a large driving force is required for hot rolling and quality is compromised. the shape of the steel strip. Therefore a lower plate temperature of 1050 ° C is preferred from the standpoint of industrial steel production.

The plate used can? be any plate produced by rough lamination or continuous casting. A continuous jet plate preferably derives from the continuous jet which has the inherent labor economy and yield improvement characteristics.

Furthermore, the continuous jet ensures a uniform chemical composition in a plate, resulting in uniform magnetic characteristics in the longitudinal direction of the product.

As described in Japanese Unexamined Patent Publication No. 53-19913, if a continuous jet plate is heated to an elevated temperature, such as about 1320 ° C, veins are generated and so on. stable production becomes impossible. However since? the heating temperature of the plate can? be 1280 ° C or less, according to the present invention, incomplete secondary recrystallization does not occur in any way. Therefore, the present invention makes it possible to provide a watt loss to the degree pi? high, using a low temperature heating of the plate, comparable to that of carbon steels.

Recent advances in continuous casting techniques have increased productivity. of the equipment used for the continuous jet cos? to match the capacity? of hot rolling mills. Continuous casting equipment can therefore now be directly combined with continuous rolling mills. When steels are fed from a continuous jet machine directly into a continuous rolling mill, the? continuous hot rolling mill pu? conduct the lamination without a waiting period.

Therefore, according to one of the advantageous methods of hot rolling which can? be used in the present invention, a plate is not cooled after continuous casting and is hot rolled directly using the sensible heat of the plate. Alternatively, according to another advantageous hot rolling method, a plate is loaded into a recovery oven when the temperature of the plate, especially the surface temperature, drops slightly. The plate is then heated in a very compact heating furnace for carbon steels for a short period of time and is then hot rolled.

These hot rolling processes are used for the production of carbon steels. Using these methods to produce a grain-oriented electrical steel strip, you can? obtain a high hot rolling efficiency, comparable to that of carbon steels.

When a continuous casting apparatus is directly combined with a continuous hot rolling mill, internal breakages can advantageously be avoided. A plate that holds a large amount? of silicon has a low conductivity? thermal and therefore a large temperature difference. It comes like this? created a thermal stress between the surface and internal portions of the plate. If it is cooled after the continuous casting, internal cracks are formed in the plate and so on. the yield is lowered. However since? a plate is not cooled in accordance with the advantageous method of hot rolling, internal breakages can be advantageously avoided. which constitutes a real advantage. specifically for hot rolled silicon steels.

According to a conventional method of heating the plate at high temperature, a plate usually has a thickness of from 150 mm to 300 mm and is hot rolled by rough lamination to form an intermediate product with a thickness of 30 to 70 cm. The intermediate product is then hot rolled through a plurality of products. of continuous finishing rolling mills, to form a hot rolled strip having a predetermined thickness.

According to this conventional method, you can not? use a plate with a small thickness, as the plate is deformed in the heating oven of the plate, given the high temperature, with the result that the plate cannot? be discharged from the oven, or because the plate heating oven must be extremely long.

According to the method of heating the plate at low temperature, s: pu? use a thin casting plate, as a casting plate can be directly hot rolled. In addition, a thin jet plate can? be directly laminated to finish, avoiding hot rough lamination, thus realizing? hot rolling very effectively. However if a plate? too thin, the production yield in continuous casting is low. On the other hand, if a plate is too thick, the load applied to the hot finishing mill is extremely high. The thickness of the plate therefore varies preferably from 30 mm to 70 mm.

The density of the magnetic flux is strongly influenced by the heating temperature of the plate. Continuous cast plates which contained 0.057% C, 3.50% Si, 0.25% Mn, 0.039% P, 0.033% acid-soluble Al and 0.0093% N were heated and mined hot-rolled by the single lamination method a to form hot-rolled strips with a thickness of 2.5mm. The following treatments were then carried out in succession: continuous annealing at 1T20 ° C for 2 minutes; cold rolling to form 0.30 mm cold rolled strip; decarburization-annealing at 850 ° C for 2 minutes in a humid atmosphere of hydrogen, application of MgO as a separator for annealing and final annealing at high temperature at 1200 ° C for 20 hours.

The density ; of the magnetic flux B of the products is shown in figure 6. As is evident from figure 6, can we? get a higher density? of magnetic flux B with plate heating temperatures above 1280 ° C. In many cases this density? pi? high magnetic flux is specifically desired. For example, a high density? of the magnetic flux? especially desirable when a laser beam irradiation technique is used to reduce watt loss, for grain oriented electrical steel strips produced by the process according to the present invention, since the reduction of watt loss? greater to greater density? of magnetic flux.

If the heating temperature of the plate -? extremely high, the heating equipment can not? withstand high temperature from an industrial point of view. The maximum heating temperature of the plate should therefore be 1430 ° C.

In the process according to the present invention, the hot rolled strip is annealed at a temperature of 850 ° C to 1200 ° C for a short period of time and then is rapidly cooled to control the state of the A1N precipitation. If the annealing temperature? less than 850? C you can not? obtain a high density of magnetic flux. On the other hand if the annealing temperature? higher than 1200 ° C, secondary recrystallization becomes incomplete. An annealing time of 30 seconds or more,? sufficient to achieve the purpose of annealing and an annealing time greater than 30 minutes? economically disadvantageous. The annealing time usually varies from 1 to 30 minutes.

The hot rolled annealing strip, which can? also be referred to as hot coil, it is then cold rolled. In cold rolling, heavy cold rolling with a degree or draft reduction of at least 80% is required to produce an oriented grain electric steel strip with a high density. of the magnetic flux.

cold rolled strip is then subjected to decarburization. The purpose of annealing - decarburization - is to decarburize and cause primary recrystallization of a cold rolled strip and simultaneously form an oxide layer which? necessary as an insulating film.

An annealing separator, which is required to form an insulating film on the product, is applied to the surface of the annealed-decarburized cold rolled strip. The annealing separator? mainly composed of MgO and pu? additionally include, if necessary, one or more? substances chosen from TiO2, ?? 2? 3, CaO, compounds of B, compounds of S, and compounds of N.

Then the final annealing at elevated temperature is carried out. The purpose of the final high temperature annealing consists in the secondary recrystallization and purification of the annealed-decarburized strip and in the formation of an insulating film composed mainly of forsterite. The final high temperature annealing is usually carried out at a temperature of 1100 ° C or more, in a hydrogen atmosphere, or in an atmospheric composition containing hydrogen. The temperature is then obviously raised to about 1200 ° C and the pufication annealing is carried out in such a way as to reduce N and the steel to a level as high as possible. low as possible.

After the final annealing at elevated temperature, a coating liquid consisting mainly of, for example, phosphoric acid, chromic acid anhydride and aluminum phosphate is applied to the steel strip and the flattening is carried out. Given the coating film, the insulating film is further strengthened and can? generate a high voltage. Finally, an insulating film is formed which consists essentially of MgO? SiO.

Regarding the conditions of the final annealing at elevated temperature, the speed? of heating in a range of temperatures in which secondary recrystallization takes place? preferably low? as there? ? effective to obtain a density? of stable and high magnetic flux. In metallurgical terms, in slow heating within the secondary recrystallization temperatures, a secondary recrystallization grain having a lower inclination than the [lloj <001> orientation is generated at the lower temperatures. Therefore slow heating can? improve the volumetric proportions of the secondary recrystallization grain that is generated at a low temperature and d? cos? close to the orientation 110 <001.>, with the result that the density is improved? of magnetic flux. Furthermore, since? the growth of the grain of the crystal? less prone to be repressed by the fine particles of MnS according to the present invention, in which? low the S content the inhibitory effect due to fine MnS is small and in comparison with the methods comparison with conventional methods, in which? high the quantity? of MnS, grain growth occurs relatively actively at low temperatures. What? slow heating? particularly effective in the case of steels with low S content, to increase the volume proportion of the secondary recrystallization grain which is generated at low temperature and which approaches so? to the orientation ^ 110 001>, thus improving? the density? of the magnetic flux.

From, figure 7 we note how the density? of magnetic flux B is influenced by the speed? of heating in a range of temperatures from 700 to 1100 ° C.

Cast steel was continuously cast, to form a bar, which contained 0.060% C, 3.35% Si, 0.25% Mn, 0.033% acid-soluble Al, 0.030% P, 0.005% S and 0.0085% N. Cut pieces of plates from a bar were heated to 1400 ° C and then hot rolled to form 2.3 mm thick hot rolled strip. The following treatments were then carried out in succession: continuous annealing at 1200 ° C for 2 minutes; cold rolling to form 0.30 mm cold rolled strip; decarburization-annealing at 550 ° C for 2 minutes in a humid atmosphere of hydrogen; application of an annealing separator and final annealing at elevated temperature at 1200 ° C for 20 hours. The rate of heating was varied in the final high temperature annealing.

As is evident from figure 7, the density? of magnetic flux B? higher when? lower the speed? of heating. The density of magnetic flux B? particularly high when the speed? heating? equal to 15? C / hour or less.

Secondary recrystallization is completed during slow heating to a temperature in the range of 700 ° C to 1100 ° C. With a speed? of heating less than 15? C / hour the density? of the magnetic flux does not vary greatly in function of the temperature, but the value of the dispersion of the density? of the magnetic flux decreases with a low speed? of heating. The speed? minimum heating? desirably equal to 7? C / hour in view of economic considerations. The temperature is then generally raised to about 1200 ° C and the purification annealing is carried out in this way. to reduce N and S in the steel to a level the most? possible low.

The electrical steel strip with oriented grain can? to contain. addition to the elements described above, quantity? mino-i of one or more? other elements, for example Cr.

They were heated to 1350 ° C and subjected to hot rolling, to form

hot rolled strips with thickness 2.3 mm, continuous jet plates which contained 0.06% of C, 3.33% of Si, 0.30% of Mn, 0.035% of P, 0.030% of Al sol? bile in acid, 0.0085% of N, 0.004% of S and a variable Cr content. The following treatments were then carried out in succession: continuous annealing at 1120 ° C for 2? Minutes'; cold rolling to form 0.30 mm cold rolled strip; decarburization-annealing in a humid atmosphere of hydrogen; application of an MgO annealing separator;

final annealing at elevated temperature at 1200? C for 20

hours. Cr pu? advantageously vary within the scope of A1

soluble in acid, in which a high density is obtained?

of the magnetic flux. From figure 8 you can? also understand

what Cr can? also decrease the watt loss per par

density of magnetic flux. However, a content of

Cr greater than 0.25%,? unsuitable as the effects

of Cr are not improved and the entity? of decarburization is lowered in annealing - decarburization.

Continuous jet plates containing 0.06% C,

3.33% Si, 0.04% S, 0.033% P, 0.032% soluble Al

in acid, 0.0090% of N and 0.15% of Cr, were heated

at 1150? C and 1350? C and then hot rolled to form

hot rolled strips with a thickness of 2.3 mm. They were

then conducted the following treatments in succession:

continuous annealing at 1150 ° C for 2 minutes; lamination

cold to form cold rolled strips of 0.30

mm; decarburization-annealing at 850 ° C for 2 minutes in a humid atmosphere of hydrogen; application of MgO as annealing separator and final annealing at high temperature

at 1200? C for 20 hours. A tension coating, which

was mainly composed of colloidal silica, it was applied to the products. The magnetic characteristics, illustrated in Figure 9, are those measured after formation of the tension coating.

As is evident from Figure 9, the heating temperature of the plate exerts an influence on the magnetic characteristics, i.e. lower heating temperatures of the plate allow a lower loss, at the same density. of magnetic flux.

The present invention is now further described by means of examples.

Example 1

Was it cast in the form of an ingot? cast steel which contained 0.053% C, 3.30% Si, 0.25% Mn, 0.030% P, 0.006% S, 0.027% acid-soluble Al and 0.0090% M. was subjected to hot rough rolling to form a plate with a thickness of 250 mm. The plate was heated to 1150 ° C and then was hot rolled to form 2.3mm thick hot rolled strips. The following treatments were then carried out in succession: continuous annealing at 1080 ° C for 2 minutes; cold rolling to form a cold rolled strip with a thickness of 0.30 mm; decarburization-annealing at 850? C in a humid atmosphere of hydrogen, application of MgO and final annealing at elevated temperature at? 1200? C for 20 hours.

The magnetic characteristics of the product in the rolling direction were as follows:

No incomplete secondary recrystallization took place.

Example 2

Cast steel containing 0.058% C, 3.45% Si, 0.20% Mn, 0.035% P, 0.005% S, 0.026% acid-soluble Al and 0.0090% N, was cast under shape of a bar with a thickness of 250 mm by continuous casting, followed by cooling up to 250? C. The cut plate was heated to 1200 ° C and then was hot rolled to form 2.3mm thick hot rolled strip. The following treatments were then carried out in succession: annealing at 1080 ° C for 2 minutes; cold rolling to form a 0.30 mm cold rolled strip; decarburization-annealing at 850 ° C in a humid atmosphere of hydrogen, application of MgO and final annealing at elevated temperature at 1200 ° C for 20 hours.

The magnetic characteristics of the product - in the rolling direction were as follows:

No incomplete secondary recrystallization took place.

Example 3

Cast steel containing 0.055% C, 3.35% Si, 0.20% Mn, 0.035% P, 0.006% S, 0.027% acid-soluble Al, 0.009% N, was cast by continuous casting using a mold with cavity? 250 mm thick mold. After solidification of the molten steel, cut plates were quickly loaded without cooling into a heat-retaining type furnace. When the temperature of the plate was homogenized, such that the average temperature of the plate was about 1130 ° C, hot rolling was carried out to form hot rolled strips with a thickness of 2.3 mm. The following treatments were carried out in succession: annealing at 1080 ° C for 2 minutes; cold rolling to form a 0.30 mm cold rolled strip; decarburization-annealing at 850eC in a humid atmosphere of hydrogen; application of l! g0; final annealing at elevated temperature at 1200 ° C for 20 hours.

The magnetic characteristics of the product in the rolling direction were as follows:

No incomplete secondary recrystallization took place!,.

Examples 4

Cast steel containing 0.060% C, 3.35% Si,

0.15% Mn, 0.030% P, 0.002% S, 0.028% Al soluble in acid, 0.0090% N, was cast by continuous casting using a cavity mold. of the mold of, thickness 250 mm. During the continuous casting, heat insulation was maintained in a casting apparatus

continuous. An end surface of the bar, which was

prone to cooling, it was heated with gas for a short time

period of time, cos? to decrease the cooling

at one level the pi? as low as possible, such cooling

occurring after solidification of the molten steel. The bars,

that is? plates, were quickly transferred to the side of

entrance of a hot rolling mill and hot rolling was started when the central part of the cross section and the surface part of the plates had a temperature of about 1200 ° C and about 1050 ° C respectively.

The plates were hot rolled to form

hot rolled strips with a thickness of 2.3 mm. They were

then conducted the following treatments in succession:

annealing at 1080 ° C for 2 minutes; cold rolling

to form a 0.30 mm cold rolled strip; decarburization-annealing at 850 ° C in a humid atmosphere of hydrogen; application of MgO; final annealing at high temperature

at 1200? C for 20 hours.

The magnetic characteristics of the product in the rolling direction were as follows

Example 5

Cast steel which contained 0.060% C, 3.30% Si, 0.20% Mn, 0.035% P, 0.006% S, 0.030% acid-soluble Al and 0.0080% N, was cast by continuous jet to form plates. The plates were heated to 1380 ° C and then hot rolled to form 2.3mm thick hot rolled strips. The following treatments were then carried out in succession: annealing at 1130 ° C for 2 minutes; cold rolling to form a 0.30 mn cold rolled sheet; decarburization-annealing at 850 ° C in a humid atmosphere of hydrogen; application of MgO; final annealing at high temperature? 1200? C for 20 hours. The speed? heating in the temperature range from 700 ° C to 1100 ° C was equal to 10 ° C / hour in the final annealing at high temperature. Face annealing was carried out and then the tension film composed mainly of chromic anhydride was applied to the surface of the strip.

The magnetic characteristics of the product in the rolling direction were as follows:

BIQ = 1.93 Tesl?

The product was then irradiated with a laser beam to form patch-type irradiation zones in the C direction (perpendicular to the rolling direction).

The magnetic characteristics of the laser irradiated product were excellent and are shown below:

Example 6

Cast steel which contained 0.057% C, 3.45% Si, 0.29% Mn, 0.039% P, 0.003% S, 0.032% acid-soluble Al and 0.0090% N, was cast by continuous casting in the form of plates. The plates were heated to 1380 ° C and then were hot rolled to form 2.3mm thick hot rolled strips. The following treatments were then carried out in succession: annealing at 1130 ° C for 2 minutes; cold rolling to form 0.30 cold rolled strip; decarburization-annealing at 850 ° C in a humid atmosphere of hydrogen; application of MgO; final annealing at high temperature at 1200? C for 20 hours. The speed? heating in the range of 700 ° C to 1100 ° C was 20 ° C / hour in the final high temperature annealing. Flattening annealing was carried out and a tension film composed mainly of chromic anhydride was then applied to the surface of the strip.

The magnetic characteristics of the product in the rolling direction were as follows:

Example 7

Cast steel which contained 0.060% C, 3.38% Si, 0.20% Mn, 0.040% P, 0.005% S, 0.033% acid-soluble Al, 0.0085% N and 0, 16% Cr, was cast by continuous casting to form plates. The plates were heated to 1400 ° C and then hot rolled to form 2.3 layer thick hot rolled strips. The following treatments were then carried out in succession: annealing at 1120 ° C for 2 minutes; cold rolling to form 0.30 mm cold rolled strips; decarburization-annealing at 850 ° C for 2 minutes in a humic atmosphere of hydrogen, application of MgO; final annealing at elevated temperature at 1200 ° C for 20 hours.

The speed? of heating under temperatures from 700 to 1100QC was 10? C / hour in the final annealing at high temperature. Face annealing was carried out and then a tension film composed mainly of chromic anhydride was applied to the surface of the strip

The magnetic characteristics of the product were the following in the rolling direction:

The product was then irradiated by a laser beam to form spot-type irradiation regions in the C direction (perpendicular to the rolling direction).

The magnetic characteristics of the laser irradiated product were excellent and are shown below:

Example 8

Cast steel which contained 0.053% C, 3.35% Si, 0.25% Mn, 0.035% P, 0.003% S, 0.029% acid-soluble Al, 0.0080% N and 0, 15% Cr, was cast by continuous casting to form plates. The plates were heated to 1150 ° C and were then hot rolled to form 2.3mm thick hot rolled strips. The following treatments were then carried out in succession: annealing at 1080 ° C for 2 minutes; cold rolling to form 0.30 mm cold rolled strips; decarburization-annealing at 850 ° C for 2 minutes in a humid atmosphere of hydrogen; application of MgO; final annealing at elevated temperature at 1200 ° C for 20 hours. The speed? heating in the range of temperatures from -700 to 1100 ° C was equal to 20 ° C / hour in the final annealing at high temperature. A tension film composed mainly of chromic anhydride was applied to the surface of the tape

The magnetic characteristics of the product were

the following in the rolling direction:

Example 9

Cast steel which contained 0.053% C, 3.45% Si, 0.23% Mn, 0.037% P, 0.003% S, 0.027% acid-soluble Al, 0.0090% M and 0, 20% Cr, was cast with a continuous jet to form plates using a mold with a cavity. of the mold with a thickness of 250 mn. The plates were heated to 1130 ° C and were then hot rolled to form 2.3mm thick hot rolled strips. The following treatments were then applied in succession: annealing at 1080 ° C for 2 minutes; cold rolling to form 0.30 mm cold rolled strip; decarburization-annealing at 850 ° C for 2 minutes in a humid atmosphere of hydrogen; application of MgO; final annealing at elevated temperature at 1200 ° C for 20 hours.

The speed? heating of a range of temperatures from 700 to 1100 ° C was equal to 10 ° C / hour in the final annealing at elevated temperature. A tension film composed mainly of chromic anhydride was applied to the surface of the tape.

the magnetic characteristics of the product were as follows in the rolling direction:

Example 10

Cast steel which contained 0.053% C, 3.45% Si, 0.23% Mn, 0.037% P, 0.003% S, 0.027% acid-soluble Al, 0.0090% N and 0, 20% Cr was cast in a continuous jet to form plates. During the continuous jet the heat insulation was maintained in a continuous jet apparatus and an end surface? of the bar, which was prone to cool, fti heated with gas, for a short period of time, so? to decrease the cooling to a level the most? as low as possible, such cooling occurring after solidification of the molten steel. Bars cut, that is? plates, were quickly transferred to the inlet side of a hot rolling mill and hot rolling was commenced when the cross-sectional part and the surface part of the plates had a temperature of about 1200 ° C and about 1050 ° C respectively. By hot rolling, hot rolled strips with a thickness of 2.5 mm were formed. The following were then conducted

Claims (8)

1. Process for producing an electrical steel strip with oriented grain, having a high density? of the magnetic flux in terms of B of 1.89 Tesla c pi ?, comprising the stages of: prepare a plate which has a temperature of 1430 ° C or less and which consists of: 0.025% to 0.075% C, 3.0% to 4.5% Si, 0.010% to 0.060% soluble aluminum acid, from 0.0030% to 0.0130% of N, not more? 0.007% of S, 0.08% to 0.45% of Mn and 0.015% to 0.045% of P, the remaining part being Fe and unavoidable impurities; subsequently hot rolling said plate to form a hot rolled strip; annealing said hot rolled strip in a temperature range of 85 ° C to 1200 ° C for a short period of time; then cold roll the annealed strip heavily with a reduction of not less than 80%, so? to obtain the final thickness of the strip; subjecting the cold rolled strip to continuous decarburization-annealing cos? obtained in a humid atmosphere of hydrogen and then applying an annealing separator on the belt; And subsequently carry out a final annealing at high temperature. 2. Process according to claim 1, characterized in that said plate is heated, in an oven, to a temperature higher than 1280 ° C up to 1430 ° C. 3. Process according to claim 1, characterized in that said plate is heated, in an oven, to a temperature not higher than 1280 ° C. 4. Process according to claims 1 or 2, characterized in that said plate is formed by continuous casting. 5. Process according to claim 4, further comprising the step of directly conveying said plate from a continuous casting apparatus to a hot rolling mill, avoiding cooling to ambient temperature and starting hot rolling at a temperature not exceeding 1280? C. 6. Process according to any one of claims 1 to 5, characterized in that in the final annealing stage at elevated temperature the speed? of heating under temperatures from 700 to 1100? C? not exceeding 15? C / hour. 7. Process according to any one of claims 1 to 5, characterized in that said plate further contains from 0.07 to 0.25% Cr, 8. Electrical steel tape with oriented grain with high density? of the magnetic flux in terms of B of 1.89 Tesla or more, essentially consisting of: 10 from 3.0 to 4.5% of Si, from 0.08 to 0.45% of Mn and from 0.015 to 0.045% of P, the remaining part being essentially made up of Fe, characterized by being produced by suppression, before final annealing at elevated temperature, secondary recrystallization by means of an inhibitor consisting essentially of A1N.