JPH07258736A - Production of nonoriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To provide a method for producing a nonoriented silicon steel sheet excellent in magnetic properties. CONSTITUTION:This is a method for producing a nonoriented silicon steel sheet excellent in magnetic properties in which steel stock having a compsn. contg. <=4% Si, 0.1 to 4% sol. Al and <0.2% Mn, satisfying the following inequalities (1) and (2) as shown below, and in which the content of C in impurities is regulated to <=0.003%, N to <=0.003% and S to <=0.002% is subjected to hot rolling at 900 to 1000 deg.C finishing temp. and >=700 deg.C coiling temp., is descaled, is thereafter subjected to cold rolling at >=80% draft and is subsequently annealed. The inequalities (1) and (2) are [FT-900)/40]%<=(Si+sol. Al)<=6% and Mn/S>=10 (wherein FT denotes the finishing temp. ( deg.C) of the hot rolling). Thus, the nonoriented silicon steel sheet having low core loss and high magnetic flux density can be produced without being subjected to complicated stages such as high temp. slab heating, two time cold rolling and hot rolled sheet annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties, which is used as an iron core material for rotating equipment such as electric motors and generators.

[0002]

2. Description of the Related Art For magnetic steel sheets, there is a strong demand for improvement of magnetic characteristics such as reduction of iron loss and high magnetic flux density in order to reduce power loss and downsize equipment.

Above all, in a rotating machine, the magnetism is magnetized in all directions of the plate surface, and therefore the anisotropy of magnetic properties must be extremely small. Therefore, an electromagnetic steel sheet for rotating equipment is required to have low anisotropy in magnetic properties and low iron loss and high magnetic flux density as an average value in all directions of the plate surface.

In the case of non-oriented electrical steel, the measurement of iron loss and magnetic flux density is usually as specified in JIS-C-2550,
Although strip-shaped samples are taken from the rolling direction and the direction perpendicular to the rolling, this method cannot properly evaluate the ability to magnetize in any direction of the plate surface like the iron core of a rotating machine. When used for rotating equipment, it is important to evaluate the magnetic characteristics of a ring sample close to its excited state, and it is important that good characteristics be obtained by this test method.

For these reasons, in recent years, development of a non-oriented electrical steel sheet having good magnetic properties in in-plane non-direction, which can obtain good iron loss and magnetic flux density even when measured with a ring sample, is expected to proceed. Therefore, some proposals have been made regarding this manufacturing method.

For example, Japanese Laid-Open Patent Publication No. 64-55338 discloses that
C: 0.005% or less, Si: 4.0% or less, Mn: 0.2% or less,
sol.Al: Raw steel less than 0.002%, hot rolling finish temperature 700
It describes a method for producing a non-oriented electrical steel sheet which is characterized in that it is wound in a ferrite region of ℃ or higher and at a low temperature of 600 ℃ or lower.

In Japanese Patent Laid-Open No. 2-107719, Si + Al: 4.
Slabs containing 5% or less and Mn: 1.0% or less as main components, slab heating temperature 1300 to 1500 ° C, hot rolling finishing temperature 600 to 800 ° C
A method for producing a non-oriented electrical steel sheet having a high magnetic flux density in a ring sample by combining a cold rolling reduction of 40 to 85% is shown.

In Japanese Patent Laid-Open No. 3-24251, Si: 3.3%
Hereinafter, a magnetic steel sheet is shown by a method in which a material steel mainly containing Mn: 0.2% or less and Al: 1.5 to 8% is cold-rolled twice with intermediate annealing.

[0009]

In the method disclosed in Japanese Patent Laid-Open No. 64-55338, it is necessary to perform hot-rolled sheet annealing, which requires steps and costs and is economically disadvantageous.

In the method disclosed in Japanese Unexamined Patent Publication No. 2-107719, since the slab must be heated at a high temperature of 1300 to 1500 ° C., the surface of the slab is covered with a scale having a low melting point and melts down. It becomes difficult to remove the scale of the plate.
Furthermore, this method is economically disadvantageous.

According to the method disclosed in Japanese Patent Laid-Open No. 3-24251, since cold rolling is performed twice with intermediate annealing, the process becomes complicated and it is economically disadvantageous.

The present invention has been made to solve the above problems. An object of the present invention is to provide a method capable of producing a non-oriented electrical steel sheet having excellent magnetic properties, which is used as an iron core material of a rotating machine, by a simple process.

[0013]

The gist of the present invention resides in the following method for manufacturing a non-oriented electrical steel sheet.

In weight%, Si: 4% or less, Mn: less than 0.2% and sol.Al: 0.1 to 4% are satisfied, and the following formulas are satisfied, and the balance is Fe and inevitable impurities, C in the impurities is 0.003% or less, N is 0.003% or less, and S is
Steel material with 0.002% or less finishing temperature 900 ℃ to 1000 ℃
The non-oriented electrical steel sheet with excellent magnetic properties is characterized by hot rolling at a coiling temperature of 700 ° C or higher, descaling, cold rolling at a rolling reduction of 80% or higher, and subsequent annealing. Manufacturing method.

[(FT-900) / 40]% ≦ (Si + sol.Al) ≦ 6% ・ ・ ・ Mn / S ≧ 10 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ However, FT is heat Finishing temperature of hot rolling (° C) The present inventors have found that Mn, S and (Si + Al) which affect the magnetic properties.
As a result of detailed examination of the effect of the content of Al and the finishing temperature of hot rolling, it was found that the magnetic properties were further improved by performing the above-mentioned conditions without performing hot-rolled sheet annealing.

The above knowledge will be described with reference to FIGS.

FIG. 1 is a diagram showing the relationship between hot rolling finish temperature and magnetic properties. This has a base composition of C: 0.002.
%, Si: 3.2%, Mn: 0.17%, P: 0.01%, sol.Al: 0.
3%, S: 0.0013% steel material, heating temperature 1200 ℃,
Hot rolling is performed at a finishing temperature of 750 to 1050 ° C and a coiling temperature of 720 ° C. After descaling, cold rolling is performed at a reduction rate of 83% to a thickness of 0.5 mm, and then continuous annealing is performed at 1000 ° C for 30 seconds. The obtained steel plate was processed into a JIS ring (outer diameter 45 mm, inner diameter 33 mm) and the magnetic properties in the ring shape were investigated.

The magnetic characteristics are a frequency of 50 Hz and a magnetic flux density of 1.5.
The evaluation was made by iron loss W _{15/50 at} T and magnetic flux density B ₅₀ at a magnetizing force of 5000 A / m.

As shown in the figure, the iron loss is remarkably low when the finishing temperature of hot rolling is in the range of 900 to 1000 ° C. The magnetic flux density increases remarkably when the finishing temperature of hot rolling is in the range of 900 to 1000 ° C, but it decreases at temperatures below 900 ° C or above 1000 ° C. That is, the hot rolling finishing temperature is 900
It was found that the magnetic properties were well balanced in the range of up to 1000 ° C.

FIG. 2 is a diagram showing the relationship between hot rolling temperature and magnetic characteristics. This has a base composition of C: 0.002.
%, Si: 2.2%, Mn: 0.11%, P: 0.007%, sol.Al:
0.14%, S: 0.0011% steel material, heating temperature 1180
℃, finishing temperature 950 ℃, coiling temperature 600 ~ 800 ℃ hot rolling, after descaling, cold rolling to a thickness of 0.5 mm at a reduction of 85%, then continuous annealing at 970 ℃ for 30 seconds. The resulting steel plate was processed into a JIS ring (outer diameter 45 mm, inner diameter 33 mm),
This is the result of investigating the magnetic characteristics in the ring shape. The evaluation of the magnetic properties was the same as in the case of FIG.

As shown in the figure, iron loss is significantly reduced when the coiling temperature in hot rolling is 700 ° C. or higher.

The magnetic flux density is such that the coiling temperature in hot rolling is 700 ° C.
With the above, it becomes significantly large. That is, it was found that the magnetic properties were well balanced when the coiling temperature in hot rolling was in the range of 700 ° C or higher.

FIG. 3 is a diagram showing the relationship between the Mn content and the magnetic characteristics in the case of two types of S levels. This has a base composition of C: 0.002%, Si: 1.4%,
P: 0.011%, sol.Al: 0.6%, S 0.0004% and 0.00
At 2 levels of 37%, heating temperature 1150 ℃, finishing temperature for steel materials with Mn content changed in the range of 0.02 to 0.38%
After hot rolling at 1000 ℃ and coiling temperature of 750 ℃, descaling by pickling, cold rolling to a thickness of 0.5 mm with a reduction of 87%, and then continuous annealing at 950 ℃ for 30 seconds to obtain The obtained steel plate was processed into a JIS ring (outer diameter 45 mm, inner diameter 33 mm) and the magnetic properties of the ring were investigated. The evaluation of the magnetic properties was the same as in the case of FIGS.

As shown in the figure, iron loss tends to increase as the Mn content increases, and also increases as the S content increases. When the magnetic flux density is low S, Mn hardly changes up to 0.2%, but when Mn exceeds 0.2%, it tends to decrease. The magnetic flux density in the case of high S is smaller than that in the case of low S.

As described above, the contents of Mn and S are reduced, the finishing temperature of hot rolling is set in the range of 900 to 1000 ° C., and the winding temperature is set in the range of 700 ° C. or more. A steel plate is obtained. The reason for this is considered as follows.

By setting the finishing temperature of hot rolling within the range of 900 to 1000 ° C., recrystallization and grain growth of the hot rolled sheet proceed.

MnS forms a solid solution when the slab is heated, but since the contents of Mn and S are reduced, MnS does not precipitate up to the finishing temperature of hot rolling, and the grain growth of the hot-rolled sheet after finishing is easy. Proceed to.

By setting the coiling temperature to 700 ° C. or higher, the crystal grain growth of the hot rolled sheet easily proceeds.

[0029]

First, the reason why the chemical composition of the material steel to which the method of the present invention is applied is limited as described above will be explained. % Means% by weight.

Si: 4% or less Si is an element that increases the specific resistance and effectively contributes to the reduction of iron loss due to the reduction of eddy current loss. Especially for large rotating machines for which low iron loss is required, it is necessary to add it positively. The desired lower limit for obtaining these effects is 0.
It is 1%.

However, if the Si content exceeds 4%, the steel sheet becomes brittle and problems such as cracking occur during cold rolling, so the content was made 4% or less.

Mn: less than 0.2% Mn is one of the important elements in the present invention. Conventionally, from the viewpoint of preventing hot embrittlement due to S and coarsening of MnS described later, it was usual to add more than 0.2%, but in the present invention, the Mn content is made less than 0.2%. The reason for this is as follows.

Under a low S condition, the Mn content is 0.2%.
When the amount is less than the above, precipitation of MnS is suppressed through heating and finishing of hot rolling, and grain growth of the hot rolled sheet is easily performed. By coarsening the crystal grains before cold rolling, a texture advantageous for magnetic properties is formed through cold rolling and annealing, and magnetic properties are improved. Therefore, the lower limit of the desirable Mn content will be described later.
Determined by Mn / S.

On the other hand, when the Mn content is 0.2% or more, MnS is precipitated by the time hot-rolling is finished, grain growth of the hot-rolled sheet is suppressed, and the magnetic properties deteriorate. Therefore, the Mn content is set to less than 0.2%.

Sol.Al: 0.1 to 4% sol.Al is an element that increases the specific resistance and contributes to the reduction of iron loss like Si, but on the other hand, it forms AlN to improve the grain growth during annealing. It worsens and acts to increase iron loss. However, if AlN is coarsened by containing 0.1% or more, AI
It is possible to eliminate the adverse effect of N on the grain growth.

However, if sol.Al exceeds 4%, the steel sheet becomes brittle and problems such as cracking occur during cold rolling, so the content was made 4% or less.

Si + sol.Al: [(FT-900) / 40] -6% In the method of the present invention, recrystallization after finishing hot rolling.
Grain growth is essential. In this case, if the γ / α transformation occurs after the hot rolling finish, the crystal grains of the hot rolled sheet become fine, and the magnetic properties of the product deteriorate. Therefore, it is necessary that the γ / α transformation point is higher than the finishing temperature (FT) of hot rolling. Since Si and Al are both elements that affect the γ / α transformation point, the total content of Si and sol.Al is (FT
-900) / 40% or more. This (FT-900) / 40 is F
It is obtained from the result of experimentally determining the relationship between T and the γ / α transformation point.

On the other hand, if the total content of Si + sol.Al exceeds 6%, the workability deteriorates, so the upper limit was made 6%.

C: 0.003% or less C is an impurity that is preferably contained from the viewpoint of reducing iron loss.
When the C content exceeds 0.003%, iron loss increases due to magnetic aging, so the upper limit was made 0.003%.

N: 0.003% or less N is also an impurity that should be reduced from the viewpoint of reducing iron loss.
If the N content exceeds 0.003%, the amount of nitride such as AIN increases and the magnetic properties deteriorate, so the upper limit is 0.003%.
And

S: 0.002% or less When the S content exceeds 0.002%, MnS is formed between Mn and Mn to suppress grain growth of the hot rolled sheet after finish annealing. In addition, grain growth during annealing is also hindered, which acts to prevent reduction of iron loss and causes hot brittleness. Therefore, the S content is
It was set to 0.002% or less. Note that S does not require a lower limit because of its characteristics.

Mn / S: 10 or more Mn and S must be limited to the above range.
If S is less than 10, hot brittleness occurs. From the viewpoint of preventing hot brittleness, the relationship between Mn and S was set to 10 or more in Mn / S.

Incidentally, P is an impurity element contained inevitably, and it is not necessary to add it in particular.

However, if it exceeds 0.1%, the steel sheet becomes brittle,
It is desirable that the P content be 0.1% or less because cold rolling breakage easily occurs.

Next, the reasons for limiting the manufacturing process and conditions will be described.

The material steel having the above chemical composition is melted in a converter or the like according to a conventional method, and is continuously cast or ingot-slab-rolled into a slab.

Next, this slab is heated by a conventional method and hot-rolled at a finishing temperature of 900 to 1000 ° C. and a coiling temperature of 700 ° C. or higher, then after descaling, it is cold-rolled once at a rolling reduction of 80% or more. And then annealing. Each process after hot rolling will be described in detail below.

(1) Finishing temperature during hot rolling This step is conditioned on the finishing temperature being 900 ° C. or more and 1000 ° C. or less. In the method of the present invention, by promoting the recrystallization and grain growth of the hot rolled sheet after finishing the hot rolling,
Improving magnetic properties is essential. The finishing temperature is
If the temperature is lower than 900 ° C., a non-recrystallized part is formed especially in the central part of the steel sheet, and a desired recrystallized state cannot be obtained.

On the other hand, when the finishing temperature exceeds 1000 ° C., sufficient strain energy is not accumulated during rolling, only recovery occurs, and recrystallization does not occur. That is, desirable recrystallization occurs only when the finishing temperature is 900 ° C or higher and 1000 ° C or lower.

(2) Winding temperature after hot rolling This step is conditioned on the winding temperature being 700 ° C. or higher. If the winding temperature is lower than 700 ° C, grain growth cannot be sufficiently performed.

(3) Descaling Descaling is performed for the purpose of improving cold rolling property and preventing internal oxidation during annealing after cold rolling. This is often done by pickling, but it may be done by various mechanical descaling methods, such as a combination of shot blasting and roll bending.

(4) Cold rolling The cold rolling reduction is one of the important conditions of the present invention.
Must be 80% or higher. By performing cold rolling at such a high pressure reduction rate, the in-plane anisotropy of the magnetic properties of the product is reduced. The upper limit is not limited because it is determined solely by operational constraints. For example, in the case of the most common product with a plate thickness of 0.5 mm, at a reduction rate of 95%, the sheet thickness of the hot-rolled sheet is as high as 10 mm, and in actual operation it is virtually impossible to achieve a reduction rate higher than this. It is possible.

(5) Annealing after cold rolling This annealing is performed for the purpose of recrystallizing the worked structure after cold rolling and sufficiently growing the recrystallized grains, and is usually continuous annealing. Can be used under general conditions.

The non-oriented electrical steel sheet is a full-process product which is shipped with given magnetic characteristics, and a strain relief anneal (750 ° C. × 2 hr) after shipping and after processing such as punching by the user side. There is a semi-processed product that gives a predetermined magnetic property. However, even in the case of full process products, there are cases in which distortion relief annealing is naturally performed on the user side, and as a full process product, not only at the time of shipment,
It is required for the user to exhibit specified magnetic characteristics even when performing strain relief annealing.

The method of the present invention is intended for both such full-process products and semi-process products.
Annealing after cold rolling is generally 700-1000 for full process products.
℃ × 5 seconds or more, 650-900 ℃ × for semi-processed products ×
It is set to about 5 seconds or more, and the conditions according to this may be applied to the method of the present invention.

When a magnetic steel sheet is manufactured, a step of applying an insulating coating is usually added, but in the case of the method of the present invention, it is possible to add a coating step as a final step of manufacturing.

[0057]

EXAMPLE Steels having the respective compositions shown in Table 1 were vacuum-melted into 50 kg ingots. Then, the heating temperature was set to 1200 ° C., and hot rolling was performed under the conditions shown in Table 2. After that, descaling was performed and then cold rolling was performed under the conditions shown in Table 2.
No. 21 and No. 21 broke in the middle, and the subsequent process was terminated. If cold rolling was possible, the final strip thickness is 0.5 mm.

[0058]

[Table 1]

[0059]

[Table 2]

After cold rolling, No. 1 to 10 were 1050 ° C. ×
20 s continuous annealing, No. 12 to 20 was 900 ℃ × 20 s continuous annealing.

For each test steel plate thus obtained,
A punching ring test piece having an outer diameter of 80 mm and an inner diameter of 60 mm was sampled to investigate the magnetic properties. Magnetic characteristics are frequency 50Hz,
Iron loss W _15/50 and magnetizing force 5000 at magnetic flux density of 1.5 T
The magnetic flux density B ₅₀ at A / m was used for evaluation. The results are also shown in Table 2.

As is clear from Table 2, Nos. 1 to 4 and No. 1
Nos. 2 to 15 are cases in which the magnetic recording medium was manufactured under the conditions defined in the present invention, and in all cases, good magnetic characteristics excellent in iron loss / magnetic flux density balance were obtained.

On the other hand, in No. 5, since the C content is higher than the range of the present invention, the iron loss is particularly bad as compared with Nos. 1 to 4. No.6
However, since the Mn content is higher than the range of the present invention, MnS is precipitated during hot rolling and grain growth of the hot rolled sheet does not occur, and both core loss and magnetic flux density are worse than Nos. 1 to 4. Has become. In No. 7, since the S content is higher than the range of the present invention, MnS is precipitated during hot rolling and grain growth of the hot rolled sheet does not occur, and both iron loss and magnetic flux density are compared with No. 1 to 4. And is getting worse. In No. 8, since the N content is higher than the range of the present invention, the iron loss in particular is worse than Nos. 1 to 4.

In No. 9, since the finishing temperature of hot rolling is higher than the range of the present invention, recrystallization of the hot rolled sheet does not occur after finishing, and both iron loss and magnetic flux density are worse than Nos. 1 to 4. is doing.

In No. 10, the reduction ratio of cold rolling was too low, so that both iron loss and magnetic flux density were poor.

In No. 11, since the content of Si + sol.Al was too high than the range of the present invention, it fractured during cold rolling. No.16
, No. 17, the content of Si + sol.Al was too low than the range of the present invention, γ / α transformation occurred after hot rolling finishing, and the hot-rolled sheet became fine-grained, so compared with No. 12-15. And iron loss is getting worse.

In No. 18, the sol.Al content was too lower than the range of the present invention and AlN was finely precipitated, so that the iron loss and the magnetic flux density were worse than those of Nos. 12 to 15.

In No. 19, the finishing temperature of hot rolling was lower than the range of the present invention and recrystallization of the hot rolled sheet did not occur, and in No. 20, the winding temperature of hot rolling was the present invention. Since the grain growth of the hot-rolled sheet was not sufficient because it was lower than the range, both iron loss and magnetic flux density were worse than those of Nos. 12 to 15. In No. 21, since the Mn / S ratio was too low than the range of the present invention, cracking occurred during hot rolling.

[0069]

According to the method of the present invention, it is possible to manufacture a non-oriented electrical steel sheet having a low iron loss and a high magnetic flux density, which is suitable as an iron core material for a rotating machine, and moreover, as in the prior art. There is no need to take complicated steps such as high temperature slab heating, double cold rolling or hot rolled sheet annealing.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between hot rolling finish temperature and magnetic properties.

FIG. 2 is a diagram showing a relationship between hot rolling temperature and magnetic characteristics.

FIG. 3 is a diagram showing the relationship between Mn content and magnetic characteristics in the case of two types of S levels.

Claims (1)

[Claims] 1. By weight, Si: 4% or less, Mn: less than 0.2% and sol.Al: 0.1 to 4% are satisfied, and the following formulas and formulas are satisfied, and the balance is Fe and inevitable impurities. C in the impurities is 0.003% or less, N is 0.003% or less, and S is
Steel material with 0.002% or less finishing temperature 900 ℃ to 1000 ℃
The non-oriented electrical steel sheet with excellent magnetic properties is characterized by hot rolling at a coiling temperature of 700 ° C or higher, descaling, cold rolling at a rolling reduction of 80% or higher, and subsequent annealing. Manufacturing method. [(FT-900) / 40]% ≦ (Si + sol.Al) ≦ 6% ・ ・ ・ Mn / S ≧ 10 ・ ・ ・ ・ ・ ・ ・ ・ However, FT is the value of hot rolling. Finishing temperature (℃)