JP2002356718A - Method for producing nonoriented silicon steel sheet having excellent core loss and brittleness characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a nonoriented silicon steel sheet which has excellent core loss, brittle characteristics and productivity. SOLUTION: A hot rolled steel sheet having a composition containing, by mass, <=0.003% C, 2.0 to 4.5% Si, 0.1 to 3.0% Al, 0.07 to 3% Mn, <=0.05% P, <=0.002% S, <=0.003% N and <=0.004% O, and the balance inevitable components is subjected to continuous hot rolled sheet annealing, and then is subjected to cold rolling and recrystallization annealing to produce the nonoriented silicon steel sheet having excellent core loss and brittle characteristics. In a cooling step in the continuous hot rolled sheet annealing, the primary cooling rate to a holding temperature of >=450 deg.C is controlled to <=100 deg.C/sec, and the steel sheet is held at the above holding temperature for >=30 sec, and after that, the secondary cooling rate from the above holding temperature is controlled to <=50 deg.C/sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-oriented electrical steel sheet used for a motor or a small transformer.

[0002]

2. Description of the Related Art In recent years, demands for resource saving and energy saving have been increasing from the viewpoint of the global environment. For this reason, reduction of iron loss is strongly demanded also for non-oriented electrical steel sheets used for motors and small transformers. Conventionally, as a technology for manufacturing non-oriented electrical steel sheets, Si, Al
Attempts have been made to increase the electric resistance by adding the same, and to minimize the impurities, that is, S, N, O, Ti, Nb, V, etc., to increase the purity of the molten steel.

Further, high-temperature recrystallization annealing has been carried out in order to reduce the crystal grain size of a product to about 150 μm. Further, in order to increase the crystal grain size of the product or to obtain a texture having easy-axis orientation grains, the crystal grain size before cold rolling is coarsened, and the magnetization K High-temperature annealing of a hot-rolled sheet has been performed to reduce the hard-axis <111> orientation grains.

[0004] However, these techniques have been a major problem when viewed from the brittle side. That is, at present, the steel sheet after hot-rolled sheet annealing cracks at a location where bending deformation is applied or breaks during cold rolling. It is empirically known that a steel sheet having a problem of brittle rupture breaks once in a test using a bending apparatus (radius of 5 mm attached to a bend) with a small piece cut out from the original sheet. .

[0005] Various attempts have been made to solve the problem of brittle fracture. For example, JP-A-10-2517
In this method, the average cooling rate from the cooling start temperature (soaking temperature) to 100 ° C. is set to 40.
Since the cooling rate was set to ° C./sec, there were problems from the industrial point of view, such as the equipment of the cooling zone becoming too large, or the sheet passing speed being greatly reduced.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and provides a method for producing a non-oriented electrical steel sheet for a laminated iron core having excellent iron loss.

[0007]

The features of the present invention are as follows. That is, C ≦ 0.003%, Si: 2.0-4.5%, Al: 0.1-3.0%, Mn: 0.07-3%, P ≦ 0.05% by mass%. , S ≤ 0.002%, N ≤ 0.003%, O ≤ 0.004%, The hot-rolled steel sheet containing the balance of Fe and unavoidable components is subjected to continuous hot-rolled sheet annealing, then cold-rolled and re-rolled. In the method for producing a non-oriented electrical steel sheet in which crystal annealing is performed, in the cooling process of continuous hot-rolled sheet annealing, the primary cooling rate up to a holding temperature of 450 ° C. or more is 100 ° C./sec or less, and the holding temperature is 30 seconds or more. After holding, the secondary cooling rate from the holding temperature is set to 50
A method for producing a non-oriented electrical steel sheet having excellent iron loss and brittle properties, characterized in that the temperature is not more than ° C / sec.

The points of the present invention are the following three points. The first point is that the sheet is held at a temperature of 450 ° C. or more for 30 seconds or more in the hot rolled sheet annealing cooling process, the second point is that the cooling rate to the above-mentioned holding temperature is good up to 100 ° C./second, and the third point is the holding The subsequent cooling rate is good up to 50 ° C./sec.
According to the present invention, it has become possible to manufacture a non-oriented electrical steel sheet having excellent iron loss characteristics without causing a problem of brittle fracture and on an industrial production scale.

The idea of brittleness countermeasures is how to reduce the amount of residual strain, and more specifically, how to flatten the distribution of residual strain in the thickness direction. The technical points of the present invention are considered as follows. 450 ° C during the hot rolled sheet annealing cooling process
The holding at the above temperature for 30 seconds or more is for releasing the strain introduced by cooling to the holding holding temperature.

[0010] Further, due to the effect of the holding temperature, the cooling rate to the holding temperature can be applied to a speed range up to 100 ° C / sec as compared with the above-mentioned conventional technology of 40 ° C / sec. . Furthermore, the cooling rate after the holding temperature is
Since the strain remains as it is and is distributed in the thickness direction and becomes brittle properties of the steel sheet, it is limited to a certain range.
Since the strain is released by being held at a temperature of 50 ° C. or more for 30 seconds or more, it can be applied to a speed range up to 50 ° C./sec as compared with the above-described conventional technology of 40 ° C./sec.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The present inventors have conducted various studies in a method for producing a non-oriented electrical steel sheet having so-called hot-rolled sheet annealing, and as a result, by defining a cooling method after hot-rolled sheet annealing,
We succeeded in producing non-oriented electrical steel sheets with excellent iron loss characteristics without causing brittleness and on an industrial production scale.

First, the reasons for limiting the components in the present invention will be described. The amount of C is set to 0.003% or less because magnetic aging occurs when the amount exceeds this amount.

The reason why the amount of Si is specified to be 2.0 to 4.5% is that if it is less than 2.0%, the brittleness aimed at by the present invention hardly causes a problem. On the other hand, if it exceeds 4.5%, the problem of brittleness remains even if the brittleness measure of the present invention is taken.

The reason why the Al content is specified to be 0.1 to 3.0% is that if the Al content is less than 0.1%, there is a problem in iron loss characteristics, and 3.0%.
If the amount is too large, the cost of addition becomes a problem.

If the Mn content is less than 0.07%, ear roughness due to hot rolling becomes a problem, and if the Mn content is more than 3.0%, it is not preferable in terms of cost. Therefore, the Mn content is set to 0.07 to 3.0%.

If the P content exceeds 0.05%, the iron loss deteriorates, so the P content is set to 0.05% or less.

If the S content exceeds 0.002%, sulfides such as MnS increase, and the crystal grain size of the hot-rolled sheet decreases, and at the same time, the domain wall movement in the product is hindered and iron loss characteristics deteriorate. Therefore, the content is set to 0.002% or less.

The amount of N is limited to 0.003% or less. 0.
If the content exceeds 003%, blister-like surface defects called blisters occur.

O forms an oxide, impedes domain wall movement and degrades iron loss characteristics, so it must be 0.004% or less.

In addition to the above elements, known Sn, Ni, C
Even if u, Sb, Cr, etc. are added, the effect of the present invention is not impaired.

Next, the manufacturing method of the present invention will be described. The molten steel specified in the above range is finished into a slab or a hot-rolled steel sheet by an ordinary method. Although the slab heating temperature is not particularly specified, it is 950 to 120 to prevent generation of fine precipitates.
0 ° C. is preferred. The thickness of the hot-rolled sheet is also 0.8 to 2.5 m in consideration of the subsequent cold-rolling rate or industrial productivity.
m is preferred.

Next, continuous annealing of the hot-rolled sheet is performed. The annealing temperature is set to 800 to 1 to secure the crystal grain size before cold rolling.
150 ° C is required. In the subsequent cooling process, the temperature is held at a holding temperature of 450 ° C. or more for 30 seconds or more. Hold temperature 45
The reason why the temperature is set to 0 ° C. or higher is that strain release does not sufficiently occur at a temperature lower than 0 ° C. The same applies to the holding time.
If it is less than 0 second, it is not enough.

In the cooling step, the primary cooling rate up to a holding temperature of 450 ° C. or more is set to 100 ° C./sec or less. If the primary cooling rate to a holding temperature of 450 ° C. or more in the cooling process is set to more than 100 ° C./sec, the strain is not sufficiently released in the subsequent holding process, and the residual strain distribution in the thickness direction is not relaxed. Limited.

In addition, after holding at the holding temperature for 30 seconds or more, the secondary cooling rate from the holding temperature is set to 50 ° C./second or less. The secondary cooling rate from the holding temperature is 50 ° C
The reason why the cooling rate is not more than / sec is that if the cooling rate is higher than that, the introduced strain is large, so that the problem of brittleness that remains a problem in manufacturing on an industrial production scale remains.

After the hot-rolled sheet annealing, the sheet is finished to a predetermined thickness by cold rolling, and thereafter, recrystallization annealing and application of an insulating film are performed.
Regarding cold rolling, the method is not particularly specified. The effects of the present invention are not impaired by either tandem rolling or reverse rolling.

The recrystallization temperature is 900 to 125 as in the prior art.
Although 0 ° C. is adopted, it is particularly necessary to control the crystal grain size to about 150 μm. Annealing atmosphere is disclosed in JP-A-56-166.
As described in JP-A-23, a reducing atmosphere is preferred. As the insulating film, a mixture of organic and inorganic or inorganic components is applied and baked.

[0027]

EXAMPLE An ingot containing the components shown in Table 1 was prepared by vacuum melting, heated at 1050 ° C., and finished into a 2.0 mm thick hot rolled sheet.

[0028]

[Table 1]

The hot rolled sheets shown in Table 1 were treated under various annealing conditions and cooling conditions shown in Table 2. After the treatment, a small piece having a width of 30 mm and a length of 320 mm was cut out and subjected to JIS C 2550.
The number of times of bending was measured according to the bending test method described above. Assuming that the number n is 5, the minimum number was defined as the number of times of bending of the test piece.

On the other hand, the steel sheet after the hot-rolled sheet annealing is finished by reverse rolling to a thickness of 0.35 mm,
The recrystallization annealing at a soaking rate of 2 seconds was performed in a reducing atmosphere. The obtained steel plate was adjusted to a sample of 100 mm square and subjected to SST measurement. Note that iron loss (W _{15/5 0)} was used the average value of the L direction and C direction. Table 2 shows the results.

[0031]

[Table 2]

As can be seen from Table 2, in the cooling process of the continuous hot-rolled sheet annealing, the primary cooling rate to a holding temperature of 450 ° C. or more was set to 100 ° C./sec or less, and after the holding at the holding temperature for 30 seconds or more, The secondary cooling rate from the holding temperature is 50
By setting the temperature to not more than ° C./sec, a non-oriented electrical steel sheet excellent in iron loss and brittleness properties is obtained.

[0033]

The present invention provides a method for producing a non-oriented electrical steel sheet having excellent iron loss characteristics, brittleness characteristics and productivity, and its industrial effects are enormous.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Sadanobu Hirogami 1-Fuji-cho, Hirohata-ku, Himeji-shi F-term in Nippon Steel Corporation Hirohata Works (reference) 4K033 AA01 CA08 CA09 KA02 RA03 SA01 5E041 AA02 CA02 CA04 HB11 NN01 NN18

Claims (1)

[Claims] 1. Mass%, C ≦ 0.003%, Si: 2.0-4.5%, Al: 0.1-3.0%, Mn: 0.07-3%, P ≦ 0 0.05%, S ≤ 0.002%, N ≤ 0.003%, O ≤ 0.004%, The hot-rolled steel sheet containing the balance Fe and unavoidable components was subjected to continuous hot-rolled sheet annealing, and then cooled. In the method for producing a non-oriented electrical steel sheet that performs rolling and recrystallization annealing, in the cooling process of continuous hot-rolled sheet annealing, the primary cooling rate to a holding temperature of 450 ° C. or more is set to 100 ° C./sec or less. After holding for 30 seconds or more, the secondary cooling rate from the holding temperature is 50
A method for producing a non-oriented electrical steel sheet having excellent iron loss and brittle properties, characterized in that the temperature is not more than ° C / sec.