KR20010086846A - Production method of Si-steel strip having single-preferred orientation and properties of low core loss and high magnetic induction - Google Patents

Abstract

PURPOSE: A method for manufacturing flat rolled magnetic steel sheets and strip is provided which improves productivity and reduces production costs by increasing rolling productivity and enabling heat treatment under the non-vacuum atmosphere. CONSTITUTION: In manufacturing ultra-thin silicon flat rolled magnetic steel sheets and strip having a thickness of 0.23 mm or less by passing a hot rolled silicon steel sheet manufactured by melting and hot rolling through processes of first cold rolling, first intermediate annealing, second cold rolling and recrystallization annealing under the dry hydrogen atmosphere, the method for manufacturing an ultra-thin oriented silicon steel sheet having low watt loss and high magnetization properties is characterized in that a rolling ratio of the second cold rolling is 30 to 80%, and an atmospheric temperature of the recrystallization annealing under the dry hydrogen atmosphere is ranging from 850 to 1350 deg.C, wherein the hot rolled silicon steel sheet comprises 4 wt.% or less of Si, 0.01 wt.% or less of C, 0.01 wt.% or less of N, 0.05 wt.% or less of S, 0.01 wt.% or less of sol.Al and a balance of Fe and other inevitable impurities, and wherein the dry hydrogen atmosphere has a partial pressure of vapor for hydrogen (PH2O/PH2) which is less than 10¬-3.

Description

Production method of Si-steel strip having single-preferred orientation and properties of low core loss and high magnetic induction

The present invention relates to a silicon steel sheet, also referred to as an electrical or electronic steel sheet, and more particularly, to a silicon steel containing less than 4.0wt.silicon steel is made into a sheet of 0.23mm or less by hot rolling and two or more cold rolling. After recrystallization at a temperature of 850 ° C. or higher in dry hydrogen or a vacuum atmosphere, a Goss texture having a directionality of {110} <100> was formed to obtain ultra-thin silicon steel sheet having low iron loss and high magnetic flux density characteristics. It relates to a manufacturing method.

Magnetic materials are classified into soft magnetic materials and hard magnetic materials. The former is characterized by a narrow and long magnetic hysteresis loop, which is used as a core of a transformer or a motor, and the latter is magnetized. It is used as a permanent magnet because it has a large magnetic field-a wide hysteresis curve.

In the soft magnetic material, which is an iron core material, ferromagnetic elements include iron, nickel, and cobalt, but the most inexpensive iron-based materials are used. Iron core materials used in transformers, generators, and motors must have high saturation magnetic flux density. In the case of iron, it may be quite high, but the low resistivity causes magnetization by alternating current, which causes a large energy loss due to eddy currents, which is a problem as an iron core material of an alternating current device. Therefore, an electronic steel sheet having a thin plate or adding silicon to increase resistivity is widely used.

When the magnetic flux changes in the iron core of a transformer or generator, a current called eddy current flows in the iron core, and the power loss due to this eddy current is called the eddy current loss, and the energy corresponding to the area of the curve each time a hysteresis curve is formed. This loss is called hysteresis loss.

In order to reduce the iron loss combined with the eddy current loss and the hysteresis loss as described above, a thin iron plate may be insulated and stacked to increase efficiency, but there is a limit to such a method.

Unlike the simple physical method described above, the addition of silicon to iron increases the electrical resistance, reduces the eddy current loss, and also reduces the hysteresis loss and aging. It is developed and used as a steel plate.

When more than 3wt of silicon is added to low carbon steel, transformation point is eliminated and crystal grains can be increased by increasing the annealing temperature, which can reduce hysteresis loss and increase the permeability at low flux density, but increasing the amount of silicon makes processing difficult. Due to the problem of low saturation magnetic flux density, currently produced silicon steel sheet is a cold rolled steel sheet having a silicon content of 3wt or less.

When the magnetization curves of the <100> direction, the <110> direction, and the <111> direction, which are the three-direction crystalline directions of the silicon steel sheet single crystal, were measured, the <100> direction was most easily magnetized, and thus, it was saturated with a very low magnetization force and <111. It can be seen that the direction is most difficult to magnetize.

That is, since the degree of magnetization varies depending on the crystallization direction, the material used for the iron core should be properly controlled to obtain the optimum recrystallization texture by controlling the rolling and annealing during the steel sheet manufacturing process.

The electronic steel sheet has a grain-oriented electrical steel sheet and a non-oriented electrical steel sheet. The latter has a very irregular crystal arrangement, and thus has low directionality of magnetic properties, and a high-grade product containing about 3wt of silicon to a low-grade product containing little silicon. have.

This type of electronic steel sheet is mainly used for rotating machines such as generators and electric motors, and high-grade products of low iron loss are used for large-sized rotors, and low-priced low-grade products having high magnetic flux densities are used even for small rotors.

In the grain-oriented electrical steel sheet, as shown in FIG. 1, the most easily magnetized <100> crystal direction is parallel to the rolling direction 1, and the {110} plane is arranged parallel to the rolling surface 2, so that the magnetic properties of the rolling direction are obtained. This is very good.

The electrical steel sheet as described above is manufactured through a process of cold rolling → decarburization annealing in a hydrogen hydrogen atmosphere (decarburization and primary recrystallization) → complete annealing in a dry hydrogen atmosphere (desulfurization, denitrification and secondary recrystallization) → phosphoric acid coating. At this time, the phosphate coating has an effect of exerting an external tension in the rolling direction, thereby reducing iron loss, excitation current, and noise.

The steel sheet produced by the conventional method is usually 0.23 ~ 0.27mm thickness, the silicon content of 3wt oriented silicon steel sheet manufacturing method, in the hydrogen atmosphere suppressed grain growth by precipitates such as AlN, MnS, etc. Prepared with the accompanying secondary recrystallization.

The silicon steel sheet manufactured as described above has high magnetic flux density and is currently used in most small and large transformers, but there is a limit to reducing the thickness of the steel sheet in order to reduce iron loss caused by eddy current loss.

In order to satisfy the low iron loss, high magnetic flux density and low distortion required for core materials for electronic parts as well as transformers, the silicon content is increased, and the thickness of the steel sheet is reduced to the thickness of the steel sheet while having the above-mentioned direction. Should.

Therefore, in order to reduce the iron loss by reducing the thickness of the silicon steel sheet, an amorphous iron core material having a thickness of 0.02 to 0.04 mm of Fe ₈₁ B _13.5 Si _3.5 C ₂ component was developed by the melt spinning method. Although it has been used in some transformers, because of the low-velocity density characteristics, there is a problem that the volume of the iron core becomes larger than 20 to compensate for this when used as an iron core material.

In addition, ultrathin oriented trisilicon steel sheets were developed by Nippon Steel and Northeast Asia, but these were manufactured by three cold rolling and three recrystallization. As a result, the productivity is lowered, and since the third recrystallization is carried out in a vacuum, it is difficult to increase the size of the vacuum equipment, making mass production difficult.

As discussed above, the ultra-thin grain-oriented electrical steel sheet has a problem that the cold rolling property decreases with increasing silicon content and the heat treatment cost increases to selectively grow the orientation of the matrix structure. It is an object of the present invention to provide a method for manufacturing an electronic steel sheet which can reduce the productivity and production cost by heat treatment possible.

1 is a manufacturing process diagram of the method of the present invention.

2 is a conceptual diagram showing the directional relationship between the rolled surface and crystal grains.

3 is a correlation graph of segregation and magnetic flux density of sulfur

((Explanation of symbols for main part of drawing))

1. Rolling direction 2. Rolled surface

The object of the present invention is to dissolve and hot-roll a silicon steel sheet composed of Si ≤4wt, C ≤0.01wt, N ≤0.01wt, S ≤0.05wt, sol.Al ≤0.01wt, the balance of Fe and other unavoidable impurities. The cold rolled silicon steel sheet having a thickness of 0.23 mm or less was manufactured by two cold rolling and one intermediate annealing, or three cold rolling and two intermediate annealing so that the final cold rolling rate was 30 or more and less than 80. Thereafter, the steel sheet is achieved by final recrystallization annealing in dry hydrogen at 850 to 1350 ° C. or in a vacuum atmosphere.

Looking at the content standards of the above components, when Si exceeds 4, the rollability becomes extremely poor and the cold rolling rate becomes small, making ultra-thin rolling difficult by secondary rolling, and the content of other components except Fe, which is a matrix structure. Exceeding this threshold will hinder the growth of the selective goth set upon final recrystallization annealing.

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, this segregation behavior of sulfur has a very significant effect on the magnetic flux density.

Figure 3 shows the correlation between the segregation behavior of sulfur and the magnetic flux density in accordance with the annealing time in the final recrystallization annealing process of 30ppm sulfur-containing cold rolled silicon steel sheet, the magnetic flux density rises rapidly as the segregation amount of sulfur decreases Able to know.

Therefore, the final recrystallization annealing should be carried out in dry hydrogen or vacuum atmosphere because not only the sulfur content should be lowered below the standard but also the sulfur segregated to the grain boundary or surface of the steel sheet should be removed by hydrogen sulfide gasification or evaporation. atmosphere and the partial pressure (P _H2P / P _H2) of the steam to hydrogen is less than 10 ^-3, a vacuum atmosphere is to be such that the 10 ^-3 torr (torr) less than the degree of vacuum.

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 ° C., the recrystallization time is not only long, but also the evaporation and hydrogen sulfide gasification reaction of the segregated sulfur at the grain boundary and the surface is smooth. As a result, the magnetic flux density decreases as it interferes with the formation of goth aggregated tissues, and when the temperature exceeds 1350 ° C., the recrystallization rate is too high, making it difficult to control the recrystallization.

In addition, if the final cold rolling rate is less than 30, the amount of rolling work is small and the driving force required for recrystallization is insufficient, thereby increasing the annealing temperature or the annealing time considerably, and in some cases, recrystallization may not occur. When the amount is 80 or more, the amount of rolling work is excessive, the size of the recrystallized grains at the initial stage of recrystallization is small, so that the {100} and {111} grains grow faster, and the growth of {110} <100> Goth grains is hindered and the magnetic flux density is increased. Will decrease.

Details of the technical configuration and specific effects of the method for producing ultra-thin silicon steel sheet having low iron loss and high magnetization properties of the present invention will be clearly explained by the following description with reference to the drawings showing preferred embodiments of the present invention. Will be understood.

The manufacturing process of the ultra-thin silicon steel sheet of the present invention is melted → hot rolling → primary cold rolling → intermediate annealing → secondary cold rolling → final recrystallization annealing or melting → hot rolling → primary as shown in the process flow chart of FIG. There are two processes consisting of cold rolling → 1st intermediate annealing → 2nd cold rolling → 2nd intermediate annealing → 3rd cold rolling → final recrystallization annealing.

Through the melting and hot rolling, a hot rolled silicon steel sheet having a silicon content of 2.98 wt, a sulfur content of 0.003 wt%, and a thickness of 2 mm was subjected to cold and rolled silicon steel sheets having a thickness of 0.1 mm through two processes of secondary and tertiary cold rolling. Table 1 shows the results of measuring the working conditions and the magnetic flux density of the silicon steel sheet at that time.

division Cold Rolling Count Cold Rolling Rate () Final thickness (mm) Recrystallization annealing temperature (℃) Recrystallization Recrystallization time (hrs) Magnetic flux density (B ₁₀ , Tesla) Example 1 2 92-40 0.1 1000 Dry hydrogen 62 1.90 2 92-40 0.1 1100 Dry hydrogen 8 1.91 2 92-40 0.1 1200 Dry hydrogen 4 1.92 2 92-40 0.1 1300 Dry hydrogen 4 1.95 Example 2 2 88-60 0.1 1000 Dry hydrogen 62 1.88 2 88-60 0.1 1100 Dry hydrogen 8 1.93 2 88-60 0.1 1200 Dry hydrogen 4 1.97 2 88-60 0.1 1300 Dry hydrogen 4 1.96 Example 3 2 84-70 0.1 1200 Dry hydrogen 4 1.94 2 75-80 0.1 1200 Dry hydrogen 4 1.68 Example 4 3 50-50-80 0.1 1200 Dry hydrogen 4 1.66 3 80-37-60 0.1 1200 Dry hydrogen 4 1.93 3 80-50-50 0.1 1200 Dry hydrogen 4 1.97 3 80-55-44 0.1 1200 Dry hydrogen 4 1.96 3 90-64-30 0.1 1200 Dry hydrogen 4 1.94

* B ₁₀ ; Indicates the degree of magnetization under a magnetic density of 10 Oersted,

For single crystal silicon steel, the theoretical value is 2.03 Tesla.

Referring to Table 1, regardless of the secondary or tertiary cold rolling, if the final cold rolling rate is less than 80, after the final recrystallization annealing, the magnetic flux density of the silicon steel sheet shows a high value of 1.9 Tesler or more, but when it is 80 or more Can be seen to be significantly lower.

As the final rolling ratio increases, the initial grains decrease during final annealing as described above, so that the surface energy organic selective crystal growth rate of the {100} and {111} directional grains is increased to be {110} <001> in the second half of the annealing. This is because the selective growth process of goth grains is suppressed.

In addition, the magnetic flux density by tertiary rolling is similar to that of secondary rolling, and the process by secondary rolling is preferable from an economical viewpoint.

Table 2 shows the results of another example in which the silicon and sulfur content of the hot rolled silicon steel sheet, which is the material of the example, was changed to 2.97 wt% and 0.03 wt%.

division Cold Rolling Count Cold Rolling Rate () Final thickness (mm) Recrystallization annealing temperature (℃) Recrystallization Recrystallization time (hrs) Magnetic flux density (B ₁₀ , Tesla) Example 5 2 92-40 0.1 1000 Dry hydrogen 62 1.90 2 92-40 0.1 1100 Dry hydrogen 8 1.92 2 92-40 0.1 1200 Dry hydrogen 4 1.93 2 92-40 0.1 1300 Dry hydrogen 4 1.94 Example 6 2 88-60 0.1 1000 Dry hydrogen 62 1.89 2 88-60 0.1 1100 Dry hydrogen 8 1.92 2 88-60 0.1 1200 Dry hydrogen 4 1.93 2 88-60 0.1 1300 Dry hydrogen 4 1.94 Example 7 2 84-70 0.1 1200 Dry hydrogen 4 1.70 2 75-80 0.1 1200 Dry hydrogen 4 1.69

Looking at the magnetic flux density of Examples 5 to 7, it can be seen that the magnetic flux density is significantly reduced at 70 or more, unlike Examples 1 to 4, where the magnetic flux density is significantly reduced when the final cold rolling rate is 80 or more.

This means that under the same final cold rolling rate, the {110} <001> Goth grains were expanded by increasing the surface energy organic selective crystal growth region of {100} and {111} grains as the segregation range of sulfur increased as the sulfur concentration of the parent phase increased. Their selective growth was hampered.

In order to examine the effect of the final recrystallization annealing atmosphere, the results of the second cold rolling and final vacuum annealing of the Example hot rolled steel sheet having a sulfur content of 0.03 are shown in Table 3 below.

division Cold Rolling Count Cold Rolling Rate () Final thickness (mm) Recrystallization annealing temperature (℃) Recrystallization annealing atmosphere Recrystallization time (hrs) Magnetic flux density (B ₁₀ , Tesla) Example 8 2 92-40 0.1 1200 vacuum 4 1.98 2 88-60 0.1 1200 vacuum 4 1.68

In the case of Example 8, although the final rolling rate is 60, the magnetic flux density is very low. This is the result of longer selective crystal growth time of {100} and {111} grains and relatively hindered growth of {110} <100> grains due to the wider time range in which sulfur segregates in vacuum than in a dry hydrogen atmosphere.

Therefore, when the final recrystallization annealing is carried out in a vacuum atmosphere, the segregation time of sulfur becomes longer than in the dry hydrogen atmosphere, thus suppressing selective crystal growth of {100} and {111} grains as much as possible, and in the absence of segregation of {110} < 100> In order to promote grain growth, the initial grain size should be largely controlled by relatively reducing the amount of processing of the matrix. Therefore, when performing final recrystallization annealing in vacuum, it is preferable to apply two cold rollings instead of three, and to make the secondary cold rolling rate less than 70.

As described above, since the ultra-thin electrical steel sheet manufacturing method of the present invention can be produced by secondary cold rolling, not only can the rolling productivity be improved, but also the final vacuum annealing is carried out in a dry hydrogen atmosphere. The cost of production can be lowered by solving problems that must be in place.

Claims (6)

In the process of primary cold rolling → primary intermediate annealing → secondary cold rolling → dry hydrogen atmosphere recrystallization annealing of hot-rolled silicon steel sheet produced by melting and hot rolling, the secondary silicon steel sheet having a thickness of 0.23 mm or less is prepared. A method for producing ultra-thin silicon steel sheet having low iron loss and high magnetization characteristics, characterized in that the cold rolling rate is 30 or more and less than 80, and the atmosphere temperature of dry hydrogen atmosphere recrystallization annealing is 850-1350 ° C. The method of claim 1, wherein the hot-rolled silicon steel sheet is composed of Si ≤ 4wt, C ≤0.01wt, N ≤0.01wt, S ≤0.05wt, sol.Al ≤0.01wt, remaining amount of Fe and other unavoidable impurities Method for producing ultra-thin silicon steel sheet having low iron loss and high magnetization characteristics. The method of claim 1, wherein the hydrogen atmosphere is very thin gun method for producing a grain-oriented silicon steel sheet having a low iron loss and want Characterization characterized in that the partial pressure (P _H2P / P _H2) is less than 10 ^-3 in water vapor to hydrogen. The hot rolled silicon steel sheet produced by melting and hot rolling is first cold rolled → first intermediate annealing → second cold rolling → second intermediate annealing → third cold rolling → dry hydrogen atmosphere recrystallization annealing In manufacturing the silicon steel sheet, the third cold rolling rate is 30 or more and less than 80, and the ultra-thin directional property having low iron loss and high magnetization characteristics, characterized in that the atmosphere temperature of dry hydrogen recrystallization annealing is 850 ~ 1350 ℃ Method of manufacturing silicon steel sheet In the process of primary cold rolling → primary intermediate annealing → secondary cold rolling → vacuum atmosphere recrystallization annealing of hot rolled silicon steel sheet produced by melting and hot rolling, secondary cold rolling A method for producing ultra-thin silicon steel sheet having low iron loss and high magnetization characteristics, characterized in that the rolling ratio is 30 or more and less than 70, and the atmospheric temperature of vacuum recrystallization annealing is 850 to 1350 ° C. 6. The method of claim 5, wherein the vacuum degree of the vacuum atmosphere is 10 ⁻³ Torr or less.