KR100840833B1 - Process of manufacture of electrical sheet with high magnetic induction - Google Patents

Abstract

A method for manufacturing electromagnetic steel sheet having a high magnet flux density is provided to realize high magnet flux density by controlling the amount of segregation of sulfur on a surface of the steel plate removing particles having a plane index of 110 deviated from 001 direction. A method for manufacturing electromagnetic steel sheet having a high magnet flux density comprises the step of forming a silicon steel sheet through a hot rolling. The silicon steel sheet is subject to cold rolling such that final reduction ratio is not less than 30 percent and not more than 90 percent. The silicon steel sheet is subject to an annealing process such that steel sheet having a thickness of 0.35 or below is manufactured. When the temperature of treating the steel sheet is increased from 850 to 1350 degrees, an oxidizing atmosphere and a reduction atmosphere are changed in the temperature range of 600 to 1350 degrees. A final re-crystallization annealing is performed by separating the oxidizing atmosphere having a vacuum degree of 10-3 torr or less and the reduction atmosphere having a partial pressure of water to hydrogen of 10-3 torr or less by temperatures.

Description

Process of manufacture of electrical sheet with high magnetic induction

1A and 1B are examples of surface texture after general cold rolling.

(A) (b) is a schematic diagram which shows the relationship of the orientation of the number of {110} particle | grains after final heat processing.

Figure 3 is a graph of the correlation between the number of {110} particles and the saturation magnetic flux density after heat treatment according to the embodiment of the present invention.

The present invention relates to a method of manufacturing a high magnetic flux electrical steel sheet called an electrical or electronic steel sheet, and more particularly, to redoxing or changing a reducing oxidation atmosphere during an elevated temperature during heat treatment of an electrical steel sheet containing a certain amount of silicon. It relates to a method for producing a grain-oriented electrical steel sheet having a high magnetic flux density through.

The quality of electrical steel sheet should be high in saturation magnetic flux density and excellent iron loss characteristics. Basically, high saturation magnetic flux density should be expected to provide excellent iron loss characteristics.

FIG. 1 is a result of an orientation distribution function (ODF). FIG. 1A shows a surface texture after cold rolling at a reduction ratio of 60%, and FIG. 1B shows an example of surface texture immediately after recrystallization thereof in a vacuum atmosphere at 1200 ^° C. for 30 seconds. .

2 is a conceptual diagram showing the relationship between the number and orientation of {110} particles after the final heat treatment.

In general, as shown in FIG. 1A, the surface aggregate after cold rolling shows a strong {111} <112> element.

The contoured crystallographic direction and plane around it have elements slightly out of it. As shown in FIG. 1B, the initial recrystallized texture during heat treatment gives a strong {110} <001> structure. At this time, elements slightly out of {110} <001> coexist.

In order to achieve high saturation magnetic flux density, the particles deviating from these directions are removed during the heat treatment in the high temperature region so that they are composed only of particles very close to {110} <001>. Referring to this as a schematic diagram of Figure 2, even if the final structure of the electrical steel sheet is all composed of only {110} particles, as shown in Figure 2 (a), if the particle size is fine, it contains a lot of particles that are out of direction Saturation flux density is not good.

On the other hand, as shown in Figure 2 (b), As the particle size increases, the number of particles per unit area decreases, leaving only the {110} <001> structure, the strongest structure, to achieve a high saturation magnetic flux density.

In general, the recrystallization temperature of the heat treatment process of the electrical steel sheet, for example, in the case of the electrical steel sheet containing 3% silicon, the recrystallized structure resembling the cold-rolled texture immediately after about 650 ℃, the initial recrystallized structure not only {110} particles {100}, {111}, and other particles having various faces and directions are included together. As the heat treatment temperature increases, the growth of {110} particles prevails first and then {100}-> {111}-> {100}-> {110} In order.

The growth-preferred particles are usually determined because the surface energy of the particles is changed by surface segregation of impurities such as sulfur contained in the electrical steel sheet. {110} particles predominate with less segregation; growth of particles with {111} or higher surface index predominates with large segregation, with {100} in between. As a result, in order to reduce the number of {110} particles, the growth of {110} particles is suppressed at the beginning or the growth of {100} or {111} particles thereafter is controlled. The oxide film formed on the surface of the metal sheet absorbs sulfur and serves to reduce the amount of surface segregation of the steel sheet. In contrast, the reducing atmosphere does not reduce the amount of segregation because it serves to suppress or remove the surface oxide layer generation.

In the final heat treatment process of the conventional electrical steel sheet, the heat treatment atmosphere is mainly composed of dry hydrogen, wet hydrogen, mixed gas of hydrogen and nitrogen. This heat treatment atmosphere may be regarded as heat treatment conditions associated with the formation of a base coating, that is, forsterite, used in the production process.

Conventional electrical steel sheet is made of so-called Goss particles in which the microstructure of the rolled surface is the {110} plane and the rolling direction is parallel to the <001> crystal direction after the final heat treatment.

The final reason why Goss particles remain is that all particles other than {110}, such as {100}, {111} or higher surface index particles, are removed during the heat treatment and only {110} particles with the lowest surface energy remain. Because. At this time, the orientation of these particles is determined by the immediately cold rolling state, that is, the intermediate annealing condition or the like.

However, since the orientation of the initial recrystallized particles is more variously developed during the final heat treatment than the previous conditions, the removal of goth particles and other particles is essential to achieve high magnetic flux density.

Therefore, the larger the number of crystallographic {110} plane particles in the final texture, the higher the fraction of particles in the unaligned state and the lower the magnetic properties. On the contrary, when the number of {110} plane particles is low, {110} <001> As the fraction of the particles increases, the saturation magnetic flux density increases.

The process of removing grains other than {110} plane is a sulfur or similarly behaving element, which utilizes selective crystal growth using segregation of elements that lower the surface energy when segregated to the surface. It segregates to the surface during the process to lower the surface energy.

Therefore, it basically increases segregation amount, slows the growth by intergranular segregation at the time of growth of high surface index particles of {100} or {111}, and keeps the size small. This is to remove sulfur so that the Goth particles can grow smoothly.

An object of the present invention is to control the amount of segregation of sulfur on the surface of the steel sheet by the oxidizing atmosphere and reducing atmosphere formed during the temperature increase of the heat treatment process to remove the {110} particles deviated from the <001> direction to have a high magnetic flux density To manufacture.

The present invention for achieving the above object, Si ≤6.6% by weight, C ≤0.01% by weight, N ≤0.01% by weight, S ≤0.015% by weight, sol.Al ≤0.01% by weight, residual amount of Fe and other unavoidable impurities A silicon steel sheet prepared by melting and hot rolling was produced, and the cold rolled steel having a thickness of not more than 0.35 mm was obtained through intermediate annealing between one or more cold rolling and each cold rolling so that the final cold rolling rate was 30% or more and less than 90%. After manufacturing the rolled silicon steel sheet, the steel sheet is achieved by a process of final recrystallization annealing by changing the oxidizing atmosphere and the reducing atmosphere in the range of 600 to 1350 ^o C in the process of raising the final heat treatment temperature of 850 to 1350 ^o C.

In performing the final recrystallization annealing, the reducing atmosphere has a partial pressure (P _{H 2 O} / P _{H 2} ) of water vapor relative to hydrogen less than 10 ⁻³ , and the oxidizing atmosphere has a partial pressure of oxygen (P _{O 2} / P _{N 2 or Ar)} with respect to the gas. ) Is less than 10 ⁻³ , and the vacuum atmosphere causes the degree of vacuum to be less than or equal to 10 ⁻³ torr.

Looking at the content criteria of each component described above, if Si exceeds 6.6% by weight, the rollability is extremely poor, making cold rolling difficult, and when the content of other components except Fe, which is a known structure, exceeds the reference value, Recrystallization annealing interferes with the growth of selective goth aggregation. In particular, sulfur is segregated to the grain boundaries and the surface of the steel sheet in order to reduce the stress field formed in the structure due to the difference in atomic size between Fe and sulfur atoms during the final annealing, and the segregation behavior of sulfur has a great influence on the magnetic flux density.

In addition, the behavior of the segregated sulfur during annealing is closely related to the annealing temperature. When the annealing temperature is less than 850 ^o C, the recrystallization time is not only long, but also the evaporation and hydrogen sulfide gasification reaction of the segregated grain boundary and surface is smooth. As it prevents the formation of goth aggregates, the magnetic flux density is lowered. When it exceeds 1350 ^o C, the recrystallization speed becomes too high, making it difficult to control the recrystallization.

If the final cold rolling rate is less than 30%, the rolling capacity is low, and the driving force required for recrystallization is insufficient, which increases the annealing temperature by more than a certain time or significantly increases the annealing time and, in some cases, re-crystallization. In addition, when 90% or more is used, the amount of rolling processing is excessively reduced, so that the size of the recrystallized grains of the initial recrystallization is small and the grain growth of {100} and {111} is rapidly accelerated, and the growth of {110} <100> high grains is prevented. Density decreases.

Hereinafter, preferred embodiments of the present invention as described above will be described in more detail with reference to the accompanying drawings. As an example of application of the present invention is attached drawing Fig. 3 of 700 ^o C to 10 ^-6 torr of vacuum atmosphere, and then the temperature was raised to 1200 ^o and then to key a hydrogen atmosphere after C for 12 hours heat treatment at 1200 ^o C {110} grain This graph shows the correlation between the number and the saturation magnetic flux density (B ₁₀ ).

Example  1 and 2

The process of manufacturing high magnetic flux density electrical steel sheet by changing the atmosphere of redox or reduction oxidation heat treatment of the present invention is carried out by melting hot rolling 1st cold rolling 중간 intermediate annealing ((secondary or more cold rolling and intermediate annealing if necessary). → The final recrystallization annealing method in the general electrical steel sheet manufacturing process consisting of final recrystallization and annealing is to produce high magnetic flux density electrical steel sheet by changing the oxidizing or reducing atmosphere at an appropriate temperature during heating up to the heat treatment temperature.

That is, after melting and hot rolling, a hot rolled silicon steel sheet having a silicon content of 2.91 wt%, a sulfur content of 0.0072 wt%, and a thickness of 2 mm was cold rolled three times, and then manufactured by applying the heat treatment method of the present invention to a thickness of 0.1 mm. The result of measuring the magnetic flux density of the silicon steel sheet is shown in Figure 3, the details are summarized in Table 1. The temperature was heated to 1200 ^° C. at a heating rate of 400 ^° C./h, and the holding time at this temperature was fixed at 12 hours. The specimens were 5 mm wide and 100 mm long.

Table 1

division Cold rolling count Cold Rolling Rate (%) Final thickness (mm) Heat treatment atmosphere Atmosphere change temperature ( ^o C) Hydrogen Flow Rate (liter / min) {110} particle count Magnetic flux density (B ₁₀ , Tesla) Example 1 3 77-50-58 0.1 High vacuum-hydrogen 700 3 39 1.88 3 77-50-58 0.1 High vacuum-hydrogen 900 3 38 1.88 3 77-50-58 0.1 High vacuum-hydrogen 1100 3 23 1.89 3 77-50-58 0.1 High vacuum-hydrogen 1150 3 17 1.96 Example 2 3 77-50-58 0.1 High vacuum-hydrogen 700 10 45 1.84 3 77-50-58 0.1 High vacuum-hydrogen 900 10 43 1.83 3 77-50-58 0.1 High vacuum-hydrogen 1100 10 34 1.87 3 77-50-58 0.1 High vacuum-hydrogen 1150 10 20 1.97

* B ₁₀ represents the degree of magnetization under the magnetic flux density of 10 Orsted. For monocrystalline silicon steel, the theoretical value is 2.03 Tesla.

Looking at Table 1, it can be seen that the number of final {110} particles decreases and the magnetic flux density gradually increases as the atmosphere change temperature is changed from 700 ^° C. to 1150 ^° C. regardless of the flow rate of hydrogen gas. In addition, when the hydrogen flow rate is changed from 3 liters per minute to 10 liters, the number of {110} particles increases and the magnetic flux density generally decreases. This is a phenomenon in which the magnetic flux density decreases as the number of total {110} particles increases, so the number of particles which are out of the correct <001> direction also increases.

On the other hand, even in a high vacuum (10 ^-6 torr) atmosphere, this means that a small amount of oxygen exists, which results in a weak oxidation atmosphere and a thin oxide film formed on the surface of the steel sheet. The oxide film absorbs impurity sulfur to reduce the amount of surface sulfur segregation of the steel sheet. At this time, when the hydrogen atmosphere is changed, the oxide film is reduced and removed, and the amount of segregation of sulfur is increased again compared to the oxidation atmosphere.

Referring to FIG. 3, it can be seen that the number of {110} particles is decreased by changing the atmosphere change temperature. As the atmosphere change temperature is increased, the oxidation atmosphere is increased, so that the amount of segregation of the steel sheet is small, so that the {110} particles are kept. Increasing the number and decreasing the magnetic flux density, the increase in the flow rate of hydrogen will be able to remove the oxide film more quickly and leave more {110} particles.

Example  3,4,5

Examples 3 to 5 show the results of the heat treatment of a silicon steel sheet having a silicon steel content of 2.90-2.95% by weight, and a 2-mm hot rolled steel sheet having a sulfur content of 0.0018, 0.0072, and 0.015% by weight to 0.1mm.

The temperature was heated to 1200 ^° C. at a heating rate of 400 ^° C./h, and the holding time at this temperature was fixed at 12 hours. The specimens were 5 mm wide and 100 mm long.

TABLE 2

division Cold rolling count Cold Rolling Rate (%) Sulfur content (ppm) Heat treatment atmosphere Atmosphere change temperature ( ^o C) Hydrogen Flow Rate (liter / min) (110) particle count Magnetic flux density (B ₁₀ , Tesla) Example 3 2 89-63 18 High vacuum-hydrogen 700 10 10 2.02 Example 4 2 88-62 72 High vacuum-hydrogen 700 3 37 1.91 Example 5 2 89-61 150 High vacuum-hydrogen 700 10 0 1.45

According to Examples # 3 to # 5, it can be seen that the number of (110) particles changes according to the sulfur content and the flow rate of hydrogen, and thus the magnetic flux density also changes. In particular, when the sulfur content is 150 ppm (0.015% by weight) or more, even in the condition of leaving the most {110} particles, the {110} particles do not remain and the magnetic flux density becomes very poor.

This is because, as the concentration of sulfur in the phase increases under the same final cold rolling rate, the segregation range of sulfur increases, so that the surface energy, organic selective grain growth of the grains of the {100} and {111} grains becomes wider, thereby increasing the selective growth of the grains. Because it is disturbed.

Example  6 and 7

Examples 6 and 7 show the results of heat treatment of silicon steel sheets subjected to two-stage cold rolling.

The silicon content is 3.11 wt%, the sulfur content is 0.0007 wt%, Mn 0.093 wt%, Sn 0.043 wt%. The thickness of the hot rolled sheet is 2.3 mm and the 0.3 mm thick specimen after primary cold rolling is composed of {110} particles with an average particle diameter of 1 cm by 1200 ^° C high temperature annealing instead of intermediate annealing, and then cold rolled again to a thickness of 0.05 A steel sheet of mm or 0.069 mm was manufactured and heat-treated again at the final 1200 ^o C.

The temperature increase rate was 25 ^° C / h, and the heat-treated at 1200 ^° C 24 hours. Specimens are 10 mm wide and 100 mm long.

TABLE 3

division Cold rolling count Cold Rolling Rate (%) Sulfur content (ppm) Heat treatment atmosphere Atmosphere change temperature ( ^o C) Hydrogen Flow Rate (liter / min) (110) particle count Magnetic flux density (B ₁₀ , Tesla) Example 6 2 86-62 7 Hydrogen-High Vacuum 800 15 40 1.95 Example 7 2 86-75 7 Hydrogen-High Vacuum 800 15 80 1.93

According to Examples # 6 and 7, the aggregate structure immediately before the "final" cold rolling is {110}.

Cold rolling and final heat treatment leave a very large number of {110} particles. In this case, in order to increase the final magnetic flux density, a process of removing a lot of {110} particles should be adopted as opposed to the case of Examples 1 to 5.

In this case, the {110} particles should be removed by forming a reducing atmosphere at the initial stage during the final heat treatment and changing to high vacuum at 800 ^° C. or higher to remove the {110} particles. The result is a high magnetic flux density of more than 1.9 Tesla.

As discussed above, the method of manufacturing the electrical steel sheet of the present invention enables to obtain a very high magnetic flux density by controlling the number of {110} particles of the final texture. In the embodiment, the specimen results of 0.1 mm or less in thickness, but can also be applied to thicker electrical steel sheet to significantly improve the magnetic flux density by changing only the heat treatment atmosphere without major changes in the existing production equipment, the present invention is the embodiment described above It will not be limited to.

Claims (4)

A silicon steel sheet is produced by melting and hot rolling, and the cold rolled silicon steel sheet having a thickness of 0.35 mm or less through intermediate annealing between two or more cold rolling and each cold rolling so that the final cold rolling rate is 30% or more and less than 90%. After manufacturing In the process of increasing the steel sheet to the final heat treatment temperature of 850 to 1350 ^o C, an oxidizing atmosphere and a reducing atmosphere are applied in a range of 600 to 1350 ^o C, Performing a process for final recrystallization annealing by separating and changing the oxidizing atmosphere having a vacuum degree of 10 ^-3 torr or less and the reducing atmosphere having a partial pressure (P _{H 2 O} / P _{H 2} ) of water vapor to hydrogen below 10 ^-3. Method for producing a high magnetic flux density electrical steel sheet. delete delete The method of claim 1, The silicon steel sheet is composed of Si ≤6.6% by weight, C ≤0.01% by weight, N ≤0.01% by weight, S ≤0.015% by weight, sol.Al ≤0.01% by weight, residual amount of Fe and other unavoidable impurities Method of manufacturing high magnetic flux electrical steel sheet.

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