JPH02258928A - Production of grain-oriented silicon steel sheet having controlled secondary recrystallized grain boundary - Google Patents

Abstract

PURPOSE:To control secondary recrystallized grain boundaries and to produce a grain- oriented silicon steel sheet with low iron loss by subjecting a slab of silicon steel with a specific composition to hot rolling, cold rolling, and decarburizing annealing, applying proper local strain to the resulting steel sheet, and then carrying out specific heat treatment. CONSTITUTION:A slab of a silicon steel having a composition consisting of, by weight, 0.025-0.075% C, 2.5-4.5% Si, <=0.012% S, 0.010-0.060% acid soluble AL, <=0.010% N, 0.05-0.45% Mn, and the balance Fe with inevitable impurities is heated to <=1200 deg.C and hot-rolled and is then cold-rolled once or cold-rolled twice or more while process- annealed between the cold rolling stages so as to be formed to the final sheet thickness. Subsequently, the resulting steel sheet is subjected to decarburizing annealing and then to high-temp. finish annealing after the application of a separation agent at annealing. At this time, after the decarburizing annealing, local strain is applied to the steel sheet to the extent causing no recrystallization and heat treatment consisting of local heating at 500-850 deg.C for a short time in a gaseous mixture of H2 and N2 containing NH3 is applied to the steel sheet. By this method, the size of secondary recrystallized grains formed in the course of finish annealing can be controlled, and the iron loss in the resulting grain-oriented silicon steel sheet can be reduced.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for controlling the secondary recrystallized grain size of a magnetic steel sheet, and more specifically, the present invention relates to a method for controlling the secondary recrystallized grain size of a magnetic steel sheet. This invention relates to a method for reducing iron loss in grain-oriented electrical steel sheets by controlling the grain size of secondary recrystallization.

(Prior Art) The core loss of a grain-oriented electrical steel sheet depends on the orientation and grain size of Goss grains.

Generally, in unidirectional electrical steel sheets, the magnetic flux density (B,
. As the value of B1 increases, the iron loss decreases.
When the 0 value is higher than 1.957 (Tesla),
The secondary recrystallized grain size also increases, eddy current loss increases despite the decrease in hysteresis loss, and no reduction in iron loss is seen even though the B10 value becomes high.

Furthermore, if the grain size is increased by annealing the material in the form of a strip coil, the sink angle with respect to the plate surface in the <001> orientation will increase, which will actually worsen core loss. Therefore,
Controlling the secondary recrystallized grain size to an appropriate size is an essential condition for obtaining a product with low iron loss.

Regarding techniques for controlling the grain size of secondary recrystallized grains, various means have already been disclosed in JP-A-50-137819. The prior art described in this patent publication is a method that uses means such as electron beam single shot peening and chemical coating, as seen in the examples thereof, and is quite difficult to employ in actual processes. On the other hand, Japanese Patent Laid-Open No. 59-100221 discloses a technique using high-frequency resistance heating and high-frequency induction heating, but it is also difficult to apply this prior art to an actual process.

(Problems to be Solved by the Invention) The present invention solves the problems in the prior art, stably and reliably controls the grain size of secondary recrystallized grains generated in the final annealing process, and manufactures products with low iron loss. The purpose was to provide a method for

(Means for solving problems) The gist of the present invention is as follows.

(1) C: 0.025-0.075% by weight,
Si: 2.5-4.5%, S≦0.012%, acid-soluble Aj=0.010-0.060%, N≦0.010%,
A magnetic steel slab containing 0.05 to 0.45% Mn and the balance consisting of Fe and unavoidable impurities was heated to 1200"
After heating to a temperature below C, hot rolling was performed, and cold rolling was performed once or twice or more with intervening intermediate annealing to give the final plate thickness, followed by decarburization annealing and application of an annealing separator. In a method for manufacturing unidirectional electrical steel sheets that is then subjected to high-temperature finish annealing, after decarburization annealing, the steel sheet is subjected to local strain to the extent that recrystallization does not occur (
It is characterized by controlling the grain boundaries of secondary recrystallized grains by applying heat treatment for a short time in a temperature range of 500 to 850"C in a hydrogen and nitrogen mixed gas atmosphere containing ammonia gas. A method for producing grain-oriented electrical steel sheets that controls secondary recrystallization grain boundaries.

(2) By weight, C: 0.025-0.075%, Si
:2.5-4.5%, S≦O, OI 2%, acid soluble A
I=0.010-0.060%, N≦0.010%, M
An electromagnetic steel slab containing n: 0.05 to 0.45% and the balance consisting of Fe and unavoidable impurities is heated to a temperature of 1200°C or less, then hot rolled, and one or intermediate annealing is performed. The final plate thickness is obtained by cold rolling two or more times,
Next, in a method for manufacturing a unidirectional electrical steel sheet in which decarburization annealing, application of an annealing separation agent, and high-temperature finish annealing are performed, after decarburization annealing, the temperature is 500 to 850 in a hydrogen and nitrogen mixed gas atmosphere containing ammonia gas. Method for producing grain-oriented electrical steel sheet for controlling secondary recrystallized grain boundaries, characterized in that grain boundaries of secondary recrystallized grains are controlled by local heating at ℃ (3)
) The introduction interval of local strain and local heating is 5 to 30 mm in the W4 plate (strip) rolling direction, and the width of local strain and local heating is 3
3. A method for producing a grain-oriented electrical steel sheet for controlling secondary recrystallization grain boundaries according to item 1 or 2 above, which is 00- or less.

The present invention will be explained in detail below.

The present invention differs from the conventional electrical steel sheet manufacturing process in that nitrogen is infiltrated into the steel sheet (strip) which has been made to the final thickness during the manufacturing process and has been primarily recrystallized in the decarburization sintering process.
AZ, St) This is a process that forms N and makes it function as an inhibitor, preventing the intrusion of nitrogen into steel sheets (
If this is done locally on the strip surface, the inhibitor strength will vary locally, and the grain size of the secondary recrystallized grains can be controlled more easily than in the case of conventional processes. Taking advantage of this, the present invention incorporates a means for locally changing the nitrogen concentration into the process after decarburization annealing and before finish annealing, thereby increasing the grain size of secondary recrystallized grains generated in the finish annealing process. The aim is to control this and reduce the iron loss of the product.

The inventors of the present invention have repeatedly conducted various experiments in order to locally change the inhibitor strength in a decarburized steel sheet consisting of the components specified in the present invention, and have found that laser irradiation,
After introducing strain to the steel plate to an extent that does not cause recrystallization using a toothed roll or the like, heat treatment is performed for a short time in a temperature range of 500 to 850°C in a mixed gas atmosphere of nitrogen and hydrogen containing ammonia gas, and then normal heat treatment is performed. The grain size of the secondary recrystallized grains can be changed by performing final annealing, or by performing local heating at 500 to 850°C in a mixed gas atmosphere of nitrogen and hydrogen containing ammonia gas after decarburization annealing, and then performing normal final annealing. We found that it is possible to control

The most suitable laser for introducing local strain into the steel plate is a YAG laser, and the beam energy needs to be 1 mJ or more at 0.3 mmφ.

If the beam energy is less than IIIJ, nitrogen penetration into the steel plate will be insufficient.

Since the nitrogen that enters the steel plate diffuses along the strain, the nitrogen concentration increases in the strained area, and as a result, the inhibitor strength becomes stronger in the strained area than in the non-strained area, and During secondary recrystallization, it is thought that the strain introduced area becomes a grain boundary because secondary recrystallization is delayed the most.

When introducing local strain into a steel plate using a toothed roll, an applied force of 50 to 70 kg/- is optimal. If the applied stress is less than 50 kg/m, it is not sufficient to locally infiltrate nitrogen into the steel plate, whereas if the applied stress is less than 70 kg/m
If it exceeds kg/-, the steel plate will be significantly deformed.

Means for locally heating the steel plate surface include carbon dioxide laser, microplasma heating, electron beam heating, and high frequency heating. However, in order to locally heat the steel plate surface in the above atmosphere, carbon dioxide laser Beam heating using

Next, a method of the present invention in which nitrogen is introduced into a steel plate in a mixed atmosphere of nitrogen and hydrogen containing ammonia gas after introducing local strain to a steel plate to a degree that does not involve recrystallization, and a method of introducing nitrogen containing ammonia gas into a steel plate in a mixed atmosphere of nitrogen and hydrogen; In the method of locally heating the steel plate surface in a hydrogen mixed atmosphere to infiltrate nitrogen into the steel plate, the temperature range when nitrogen is introduced into the steel plate is 500 to 850℃.
Explain the reason for this identification. At temperatures below 500° C., nitrogen diffusion becomes non-uniform. On the other hand, at a temperature exceeding 850°C, the grain size of the -next crystal grains changes, resulting in poor secondary recrystallization.

From an economic standpoint, the shorter the heating time, the better.

In the present invention, the effect can be obtained by heating for 20 seconds. By heating the steel plate to a temperature of 500 to 850° C., the strain may disappear, but from a microscopic point of view, the strain remains and is thought to serve as an effective bath for nitrogen diffusion.

The reason why nitrogen gas and hydrogen gas are mixed into the ammonia gas is that the surface of the steel sheet after decarburization annealing is covered with a thin film of fireite, and this thin film acts as a barrier when nitrogen enters the steel sheet. The purpose is to remove this thin film by reduction to facilitate nitriding.

The optimum concentration of ammonia is 1 to 10%, and if the concentration is less than 1%, the effect of grain boundary introduction will be small;
At a concentration exceeding , the difference in inhibitor strength between the strain-introduced part and the non-strain part becomes small, and the effect of grain boundary introduction disappears.

On the other hand, the reason why we specified the temperature range of 500 to 850 degrees Celsius when nitrogen penetrates into the steel sheet by locally heating the steel sheet surface in a nitrogen and hydrogen mixed atmosphere containing ammonia gas is
At temperatures below 850°C, nitrogen diffusion is insufficient.
This is because at temperatures exceeding .degree. C., the primary recrystallized grains become coarse, and fine grains as large as the beam remain in the heating section, deteriorating the magnetic flux density (Blo value) when secondary recrystallization occurs.

In both methods, the method of introducing local strain parts into the steel plate and the method of introducing local heating parts on the surface of the steel plate, the interval between the introduction parts should be 5 to 30 mm in the rolling direction of the steel plate, and the width of the introduction parts should be 300 μm or less. Explain the reason for the limitation.

The reason why the interval between the introduction parts is set to 5 to 30III11 in the rolling direction of the steel plate is that the interval between the introduction parts determines the grain size of the secondary recrystallized grains in the rolling direction of the steel plate, and the secondary recrystallized grains are set to 511II11. This is because if it is less than 30 degrees, the magnetic flux density (Bl. value) decreases and the iron loss worsens, and if it exceeds 30 degrees, the eddy current loss increases and the total iron loss increases.

The width of the introduction part was limited to 3006m or less because of 300μ.
If the width exceeds m, a defective secondary recrystallization area different from Goss grains will be generated at the inhibitor introduction part, and the magnetic flux density (Boo value) will decrease.
This is because iron loss deteriorates and the iron loss deteriorates.

Note that when strain is introduced by laser irradiation, it may be a series of points. In that case, the distance between the points in the width direction of the steel plate must be 0.5 am or less. 0.
If the spacing exceeds 5, a strain-free area will exist on a continuous line of points in the width direction of the steel sheet, making it impossible to control the secondary recrystallized grain size.

(Example) Example 1 By weight, C: 0.052%, Si: 3.3%, Mn:
0.12%, acid soluble AZ: 0.028%, S
: 0.006%, N: 0,0075%, balance: Fe and inevitable impurities.
After heating to ℃, hot rolling was performed to obtain a hot rolled sheet having a thickness of 2.3 mm. This hot-rolled sheet was annealed at 1120° C. for 3 minutes, and then cold-rolled to a final sheet thickness of 0.3 mm. This cold-rolled sheet was subjected to decarburization annealing at 850° C. for 120 seconds in a mixed gas atmosphere with a dew point of 60° cSHz, near 5%, and 10 Nz:25%. After decarburization annealing, strained portions with a width of 50/1111 extending in a direction perpendicular to the strip rolling direction were introduced using toothed rolls with an interval of 10 degrees in the rolling direction, and an application portion crab of 60 kg/-.

After introducing strain, the steel plate was heated under a mixed gas atmosphere of 5% Hz nia = 25% containing ammonia gas with a volume concentration of 5%.
Heat treated at 00°C for 30 seconds. Next, an annealing separator containing 5% by weight of ferromanganese nitride in MgO was applied to the steel plate, and then heat treated at 120°C at a heating rate of 10'C/hr.
Finish annealing was performed at 0° C. for 20 hours.

The magnetic properties of the product thus obtained are shown in Table 1.

Table 1 As is clear from Table 1, when the grain size of the secondary recrystallized grains is controlled according to the present invention, the iron loss is extremely superior to that according to the comparative example where the grain size is not controlled. product is obtained.

Example 2 By weight, C: 0:04% IsI: 3°5%, Mn:
0.12%, acid soluble A! : 0.030%, S:
0.008%.

An electromagnetic steel slab consisting of N: 0.0080%, balance di-Fe and unavoidable impurities was heated to 1200° C. and then hot rolled to form a hot rolled sheet with a thickness of 1.8 m. This hot-rolled sheet was subjected to two-step annealing at 1120° C. for 2 minutes and 900° C. for 2 minutes, and then cold rolled to a final sheet thickness of 0.20 am. Then, dew point = 55°C, Ht 75% 10N, :2
After decarburizing the steel plate at 830°C for 90 seconds in a 5% mixed gas atmosphere, it was annealed at 0.3 wn using a YAG laser.
A beam with a diameter of 3 mJ and an energy of 3 mJ was irradiated in a linear manner extending in a direction perpendicular to the rolling direction at an interval of 1 Oma in the rolling direction. After laser beam irradiation, the steel plate was exposed to 1% volume concentration of ammonia gas with 5% H and 10N! =25
Heat treatment was performed at 550° C. for 40 seconds in an atmosphere containing a mixed gas of 50%. After heat treatment? 5 in IgO! An annealing separator to which % of ferromanganese nitride was added was applied, followed by final annealing at 1200° C. at a heating rate of 10° C/hr for 20 hours.

The magnetic properties of the obtained product are shown in Table 2.

Table 2 As is clear from Table 2, when the grain size of the secondary recrystallized grains is controlled according to the present invention, the core loss is extremely superior to that according to the comparative example where the grain size is not controlled. product is obtained.

Example 3 By weight, C: 0.05%, Si: 3.0%, Mn
: 0.15%, acid soluble AI: 0.032%, S:
0.007%.

An electromagnetic steel slab consisting of 82% N:O, OO, balance Fe and unavoidable impurities was heated to 1150° C. and then hot rolled to form a hot rolled sheet with a thickness of 1.8 mm. This hot-rolled plate was annealed at 1120°C for 2 minutes + 900°C for 2 minutes (2
After performing stepwise annealing), it was cold rolled to a final thickness of 0.20 mm. Next, this cold-rolled sheet was heated to a dew point of 53°C, H
', 830 in a mixed gas atmosphere of near 5% and NZ 15%
Decarburization annealing was performed at ℃ for 90 seconds. After decarburization annealing, ammonia gas with a volume concentration of 2%, H, Nia 5% + Nt: 25
Local heating was performed using a carbon dioxide laser in an atmosphere containing a mixed gas of 50%.

Laser irradiation was performed at intervals of 15 am in the rolling direction of the steel plate.
The rolling process was performed in a linear manner extending in a direction perpendicular to the rolling direction. The diameter of the laser beam was 0.2 mm, the incident energy was 1.5 KW, and the beam was scanned with a wavelength of 10.6 mm so that the surface of the steel plate was locally heated to 500 to 850°C.

After heating by laser irradiation, 5% by weight in MgO was added to the steel plate.
Apply an annealing separator containing ferromanganese nitride,
Then, it was heated to 1200°C at a temperature increase rate of 8°C/hr for 2
Finish annealing was performed for 0 hours.

The magnetic properties of the product thus obtained are shown in Table 3.

have great value.

As is clear from Table 3, the product according to the present invention in which the grain size of the secondary recrystallized grains is controlled shows extremely superior iron loss compared to the comparative example in which the grain size is not controlled. .

(Effect of the invention)

Claims (3)

[Claims] (1) By weight, C: 0.025-0.075%, Si:
2.5-4.5%, S≦0.012%, acid-soluble Al:
0.010-0.060%, N≦0.010%, Mn:
An electromagnetic steel slab containing 0.05 to 0.45% and the balance consisting of Fe and unavoidable impurities is heated to a temperature of 1200 ° C. or less, then hot rolled, and one time or intermediate annealing is performed2. In a method for manufacturing unidirectional electrical steel sheets, the final thickness is achieved by cold rolling several times or more, followed by decarburization annealing, application of an annealing separator, and high-temperature finishing annealing. After introducing local strain to the steel plate (strip) to a degree that does not cause crystallization, secondary recrystallization is achieved by heat treatment for a short time in a temperature range of 500 to 850°C in a hydrogen and nitrogen mixed gas atmosphere containing ammonia gas. A method for producing a grain-oriented electrical steel sheet that controls secondary recrystallization grain boundaries, the method comprising controlling grain boundaries. (2) By weight, C: 0.025-0.075%, Si:
2.5-4.5%, S≦0.012%, acid-soluble Al:
0.010-0.060%, N≦0.010%, Mn:
An electromagnetic steel slab containing 0.05 to 0.45% and the balance consisting of Fe and unavoidable impurities is heated to a temperature of 1200 ° C. or less, then hot rolled, and one time or intermediate annealing is performed2. In a method for manufacturing unidirectional electrical steel sheets, in which the final plate thickness is obtained by cold rolling more than once, then decarburization annealing, application of an annealing separator, and high-temperature finish annealing, after decarburization annealing, ammonia A unidirectional method for controlling secondary recrystallized grain boundaries, characterized in that grain boundaries of secondary recrystallized grains are controlled by local heating at 500 to 850°C in a mixed gas atmosphere of hydrogen and nitrogen containing gas. Manufacturing method of electrical steel sheet. (3) The secondary recrystallization grain boundary according to claim 1 or 2, wherein the introduction interval of the local strain and local heating is 5 to 30 mm in the rolling direction of the steel plate (strip), and the width of the local strain and local heating is 300 μm or less. A controlled manufacturing method for unidirectional electrical steel sheets.