JPS60258413A - Production of non-oriented electrical steel sheet having low iron loss - Google Patents

Abstract

PURPOSE:To produce economically and stably a non-oriented electrical steel sheet having a less iron loss by subjecting the surface of the steel sheet to a treatment for applying fine traces of working during intermediate annealing in the stage of producing said sheet thereby forming coarse crystal grains. CONSTITUTION:The blank slab contg., by weight, <0.02% C, <3.5% Si, 0.1- 1.0% Mn, <1% Al and <0.02% S for the non-oriented electrical steel sheet is hot rolled and is worked to a hot rolled sheet. Such hot rolled sheet is subjected to >=2 passes of cold rolling including the intermediate annealing treatment to the steel sheet having the final sheet thickness and thereafter the steel sheet is subjected to the finish annealing, by which the non-oriented electrical steel sheet is manufactured. Surface indentations of 10<5>-10<7> pieces for each 1m<2> of the steel sheet surface having 2X10<-5>-2X10<-2>mm.<3> size or 0.5-40mum depth are formed on the surface thereof during the intermediate annealing treatment in the production process thereof. The crystal grains are grown to the coarse grains by such treatment. The non-oriented electrical steel sheet having low iron loss is thus produced at a low cost.

Description

[Detailed Description of the Invention] (Technical Field) The technical content described in this specification regarding the production of non-oriented electrical steel sheets is to reduce iron loss by special processing in the intermediate mirror annealing process of the so-called two-time cold rolling process. The aim is to propose development results aimed at significant improvements.

(Technical background) Non-oriented electrical steel sheets are generally used as iron cores for electrical equipment such as generators, motors, and small transformers, and according to Japanese Industrial Standards (JIS C2552, 2554), the iron loss value ranges from 89 to S60. It has been classified up to.

Since the iron loss value of electrical steel sheets is related to the amount of power consumed, a low iron loss value is required. In particular, in recent years, corporate demands for energy conservation have become even stronger, and electrical steel sheets of the same grade are required to have lower iron loss values.

By the way, it is known that the iron loss of a non-oriented electrical steel sheet depends on the recrystallized grain size of the finished product, and that the iron loss generally decreases as the grain size increases.

Therefore, in order to make the crystal grains sufficiently thick in the finished product, measures have been taken such as extremely minimizing inclusions that inhibit crystal grain growth, and annealing at high temperatures or for long periods of time. .

(Prior art and problems) For oxides, a deoxidizing agent is added, and 8β203 and Si
MnS is removed by agglomeration and floating as O□, and sulfides are removed by adding rare earth elements, Ca alloy, etc.
, CaS etc. to make it harmless and prevent fine precipitation in the subsequent process (JP-A-51-62115 (RBM), JP-A-52-2824 (Ce) and JP-A-53-96).
No. 796 (Ca) refer to each publication) and nitrides (AIIN
In the case of
(See Japanese Patent Publication Nos. 39-9668, 55-97426, and 50-98423).

However, all of these require the installation of expensive processing equipment or the use of additives in order to exhibit sufficient effects, which inevitably increases costs.

On the other hand, regarding continuous annealing of non-oriented electrical steel sheets,
According to Japanese Patent Publication No. 5B-1173, it is disclosed that the magnetic properties are improved by adjusting the elongation of the copper strip during continuous final annealing to within an appropriate range in relation to the annealing temperature. There is.

Providing a suitable elongation R using this method means that strain is spread evenly in the plate thickness and plate width directions, and therefore affects the crystal grains in both directions.

However, hot-rolled sheets, which are the raw materials for non-oriented electrical steel sheets, have relatively randomly oriented recrystallized grains in the surface layer, recrystallized grains,
It consists of a central layer with a strong 011〉 axis orientation in which deformed grains are mixed, so it is difficult to recrystallize during annealing.
011> Although it is more advantageous to grow grains in the surface layer than to coarsen grains in the center layer, which has many axially oriented crystal grains, after recrystallization, the grains do not grow uniformly as described above. If strain is applied to the inside, crystal grain growth from the inside will be encouraged and compete with growth from the surface layer, resulting in insufficient coarsening of the crystal grains.
The drawback remains that the magnetic properties as expected cannot be obtained.

(Start of the Invention) As a result of repeated research on how to economically coarsen crystal grains, the inventors found that by appropriately adding processing traces of minute indentations during intermediate annealing, It was discovered that crystal grains can be grown significantly and can be used to improve magnetic properties.

(Purpose of A) Based on the above knowledge, it is an object of the present invention to provide a method for economically and stably producing a non-oriented electrical steel strip having a much lower core loss value than conventional products. It is a purpose.

(Structure of the Invention) This object can be advantageously achieved by a procedure based on the following matters.

The weight percentage of the components in steel is simply expressed as %, C: 0.0
2% or less, Si: 3.5% or less, Mn 0.1-1.0%
,fart! : 1% or less, S: 0.02% or less is made into a hot-rolled sheet by hot rolling, and then cold-rolled two or more times with intermediate annealing in between. During the intermediate annealing process, in a series of steps in which the steel plate is finished to the final thickness, and then final annealing is performed, processing traces are applied to form fine skin indentations on the surface of the steel plate. This is a method for manufacturing a non-oriented electrical steel sheet.

This skin indentation is 105 to T per unit area of the plate surface.
h, and the size of these minute indentations is 2X10-' to 2X10 in terms of the volume per space surrounded by the concave surface and the virtual original plate surface covering it.
-'mm3, and the maximum depth of the indentation from the surface of the original plate is 0.
By adjusting the diameter to 5 to 40 μm, it is effective to promote the growth of the crystal grains, but this invention does not allow the crystal grains to develop significantly only when the processing pressure trace imparting treatment is performed during the intermediate annealing treatment. exhibits its greatest characteristics.

Generally, intermediate annealing treatment is performed to promote recrystallization of the cold-worked structure and grain growth, and the holding temperature thereof is usually in the range of 700 to 1050°C.

The processing trace imparting treatment of the present invention, which is performed in anticipation of remarkable development of crystal grains during the intermediate annealing treatment, can be performed during the temperature increase as long as the recrystallization temperature is higher than the recrystallization temperature that produces the effect of the annealing. It does not matter whether it is during retention, during temperature drop, or afterward.

Here, the recrystallization temperature is usually about 500°C or higher.

In this way, it is necessary to perform processing trace imparting treatment during the intermediate annealing process, and at a temperature higher than the recrystallization temperature during the intermediate annealing process, the strain causes noticeable crystal grains from the surface layer of the steel sheet. Growth is induced, which has a positive effect on the crystal grains of the finished product, improving its magnetic properties.

Now, a continuous annealing furnace is usually used for intermediate annealing, but here, processing marks are preferably applied as soon as possible after the temperature of the steel sheet passing through the furnace reaches the recrystallization temperature. It is desirable to apply it using a hearth roll or the like.

In this way, after the strain is applied, sufficient time for the above-mentioned remarkable grain growth can be easily obtained by taking special measures such as reducing the line speed in actual operation.

On the other hand, even if this type of treatment to impart minute processing marks is applied before intermediate annealing, the large strain stress from the preceding cold rolling remains, so the minute The effect of strain is virtually absent.

The reason why this process of creating minute machining marks makes a particularly significant contribution to coarsening of crystal grains compared to large deformation process is as follows.
It is based on the recrystallization behavior of electrical steel as follows.

That is, if strain stress is applied to a very limited area just below the surface of a recrystallized steel sheet, crystal grains will grow efficiently from the surface and will be effective. On the other hand, if strain stress is uniformly applied to the inside, crystal grains will grow from the center layer of the plate, competing with the growth of crystal grains from the surface layer, and as a result, the grain size will not be improved to a sufficient level. It will not be done.

By the way, in carrying out this invention, the starting material for the above-mentioned electrical steel sheet may be either a steel ingot or a continuously cast slab produced by melting by a known steel-making method and then cast, but the following ingredients may be used: Regulations shall be met.

That is, C: 0.02% or less, Sl: 3% or less, Aβ
: 1% or less, Mn: 0.1 to 1.0%, S: 0.02%
It is necessary to contain the following:

The reason for specifying the above components is as follows.

If C exceeds 0.02%, the magnetic properties will deteriorate, so C
must be 0.02% or less. sl has the effect of increasing resistivity and lowering iron loss, so it can be added according to the target iron loss value, but if the amount added increases, it becomes brittle and cold rolling becomes impossible, so Si is 3. It is necessary to keep it below 5%.

Mn is an element that contributes to preventing cracking during hot rolling, but if it is less than 0.1%, it will not have the effect of preventing cracking, while if it is more than 1.0%, the magnetic properties will deteriorate.
Mn needs to be in the range of 0.1 to 1.0%.

Aβ is an element that contributes to the improvement of magnetic properties, but if it exceeds 1%, it tends to break (so it is necessary to keep ^p below 1%).

Since S inhibits the growth of crystal grains and deteriorates magnetic properties, it is necessary to keep the content as low as 0.02% or less.

A steel ingot or continuously cast slab satisfying the above-mentioned compositional conditions is made into a hot-rolled plate having a thickness of 1.2 to 4.0 mm by conventional hot rolling.

After pickling, this hot-rolled sheet may be subjected to two or more cold rolling steps with intermediate annealing in between.

The purpose of intermediate annealing is generally for recrystallization and grain growth. Therefore, the holding temperature is 70
It is necessary to select an appropriate temperature so that it is 0° C. or higher and does not exceed the transformation point, which varies depending on the amount of Si, etc. On the other hand, if the Si content is 2.5% or more, no transformation will occur, but if the temperature exceeds 1050°C, the crystal grains will become too large and ridging will occur in the final cold rolling, so the intermediate mirror annealing is 700 to 1
A range of 0.050°C is desirable.

Now, the most important requirement in this invention is the machining trace imparting process performed during the intermediate mirror annealing process.

As mentioned above, hot-rolled sheets are subjected to two or more cold rolling processes with intermediate annealing in between to achieve the final thickness. , a processing trace imparting treatment is performed to form fine skin indentations on the surface of the steel plate. An example of the results is shown in FIG. 1 with a cross-sectional micrograph.As a result, the crystal grains of the steel sheet become significantly coarsened.

In addition, the same effect can be obtained if the above-mentioned machining mark imparting treatment is applied off-line to a steel sheet that has been heated above the recrystallization temperature during normal intermediate mirror annealing, and then intermediate mirror annealing is continued again. Ta.

In short, when the steel sheet is subjected to final cold rolling and final annealing after undergoing intermediate mirror annealing that includes such treatment to impart processing marks, a large crystal structure is obtained in the steel sheet.

Next, we will show the results of an investigation into the influence of the conditions of the machining trace imparting process during the intermediate mirror annealing process on the iron loss of the final product.

First, Figure 2 shows that a hot-rolled non-oriented electrical steel sheet containing 3.1% Si is subjected to two-time cold rolling to determine the degree of machining traces imparted during the intermediate mirror annealing process to the final plate thickness. The effect on a 0.50mm product is shown.

Here, intermediate mirror annealing is performed with an intermediate plate thickness of 1.0+ua+ (holding with a trowel at 980°C for 3 minutes, and during holding, only the size of the epidermal indentation shown on the horizontal axis in Figure 2 varies, The depth is 10μm1 and the degree of dispersion on the plate surface is 2.5XlO
Processing traces were applied at a rate of 5 pieces/m 2 at a substantially constant rate.

Note that this machining trace imparting treatment is performed by embedding carbide particles, such as silica with uniform grain size, on the outer peripheral surface of a hearth roll installed in a continuous annealing furnace at intervals of 2 mm on the circumference and in the width direction. Each band has a center spacing of 2
It was set so that a 111 m long skin indentation was transferred, and then finished by final cold rolling to a size of 0.50 mm, and then processed through conventional processes to reach the product stage.

As is clear from FIG. 2, the reduction in loss occurs particularly when the size of the epidermal indentation is 2X10-6 mm3 or more, and the effect is lost again when the size exceeds 2X10-3111113.

In addition, since an unnecessarily large skin indentation will impair the smoothness in the subsequent final cold rolling, it is recommended that the depth be 0.5 to 40.
2 xto-' ~ 2 Xl0-3 mm3 in μI
is desirable.

The above cemented carbide particles include SiO□, Al120. ,
SiC.

11c, 81N, BN, -, Mo, etc. may be used.

In addition to embedding cemented carbide particles on the circumferential surface of the hearth roll, it can also be achieved industrially by performing shot hitting with a peening machine off-line and continuing intermediate mirror annealing, but of course it can also be achieved off-line. Carrying this out is not preferable from an economic point of view due to increased manufacturing costs.

Next, Fig. 3 shows a hot-rolled sheet for non-oriented electrical steel sheet containing the same < 3.20% Si, which is subjected to the process mark imparting treatment during intermediate mirror annealing using the two-time cold rolling method, to create a surface indentation. the size of 7
X10-5mn+', depth 20μm, and the influence of the sheet surface distribution density on the magnetic properties was measured on one side of the steel sheet, approximately parallel to the rolling direction of the steel sheet, and approximately perpendicular to the rolling direction, respectively. A case is shown in which the epidermal indentations are arranged in a matrix so that the center distances are approximately the same.

As is clear from Figure 3, the center distance of the epidermal indentation is 3
The reduction in iron loss is remarkable in the range of mm or less, and the coughing distance can be made narrower as long as the epidermal impressions do not overlap.

Here, the machining mark imparting treatment is applied to one side of the steel plate, but if it is applied to both sides, the center distance may be extended to 6 marks.

After that, the steel plate of intermediate thickness is subjected to final cold rolling, and then the steel plate that has reached the product thickness through the final cold rolling process is subjected to final annealing according to a conventional method to prevent decarburization, recrystallization, and grain growth. proceed. Here, the final annealing is 700 to 1
It is carried out in a temperature range of 050℃, and the same method as before is followed by using a decarburizing atmosphere when the C content of the steel plate is high, and using a non-decarburizing atmosphere when the C content is low. can be done.

Based on the above description, the most preferred embodiment of the present invention can be summarized as follows.

The material contains less than 0.02% C and 3.5% Si as essential components.
Below, ^11% or less, Mn 0.1-1.0%, 30.
A non-oriented electrical steel ingot or continuous cast slab with a composition containing 0.02% or less is used, and after hot rolling, the product thickness is reduced by two or more cold rolling processes with intermediate annealing in between. When performing intermediate annealing at 700 to 1050°C,
During holding for 0 seconds to 20 minutes, especially in the recrystallization temperature range of usually 500°C or higher, extremely fine skin indentations are dispersed on the surface of the steel sheet within a range of 105 to 107 per unit area of the sheet surface. and the size of each epidermal indentation is 2 × 10−
'~2 x 10-3mm3 and depth 0.5~4
It is subjected to a treatment for forming processing traces under conditions that favor a range of 0 μm. The distance between each skin indentation is 3 +nn+ or less for single-sided construction, and 5 mm for double-sided construction.
The following is sufficient.

Then, final cold rolling is performed to the product thickness, followed by normal final annealing.

In this way, a non-oriented electrical steel sheet with low iron loss can be manufactured.

Example IC: 0.004%, si: 3.2%, Mn: 0.2
0%, l: 0.61%.

A slab containing 0.002% S and the remainder substantially Fe was heated at 1200° C. for 1 hour and hot rolled to obtain a 2.3 mm hot rolled plate.

This hot-rolled sheet is pickled and then subjected to a first cold rolling process.
．． (8265% after setting the intermediate plate thickness to 1+++m thickness.

Intermediate annealing was performed at 930° C. for 3 minutes in a dry atmosphere of 35% N2.

At this time, in the intermediate annealing furnace, 5 sets of heat-resistant hearth rolls in which spherical silica chips with a particle size of 60 μm were embedded and fixed were set, and ultrafine skin indentations were created on both sides of the steel plate while it was being annealed. , their average mutual spacing is 1ml11
With the irregular distribution, the size of each epidermal indentation is 5.7X
Processing traces were applied to give a width of 10 mm and a depth of 30 μm.

Next, the steel plate that has undergone this intermediate annealing is subjected to a final cold rolling to obtain a final thickness of 0.50111111, and then
Finish annealing was performed for 950 tons for 3 minutes in an atmosphere of 265% N2 and 35% N2 to produce a product. The magnetic properties of the product are shown in Table 1 in comparison with the conventional method (no processing during intermediate annealing).

Table 1 From Table 1, it is clear that the products produced by the method of the present invention have significantly lower W15150 values than those produced by the conventional method.

Example 2 C: 0.012%, Si: 1.85%, Mn:
0.15%, AI: 0.35%, S: 0.
A slab containing 0.007% and the remainder being essentially Fe was heated at 1200°C for 1 hour and hot rolled to 2.0m.
A hot-rolled sheet with +n thickness was obtained.

This hot-rolled sheet was pickled and first cold-rolled to a thickness of 1.0 mm, and then intermediately annealed at 880°C for 3 minutes in a dry atmosphere of 265%, N, and 35%. did.

At this time, in an intermediate annealing furnace, a hearth roll 10 in which spherical silica chips with a particle size of 60 μm were embedded and fixed.
The size of each skin indentation was 5.7
0'-4 mIno, 30 μm deep toner processing trace imparting treatment was performed.

Next, the steel plate that has undergone intermediate annealing is subjected to a final cold rolling to obtain a final thickness of 0.50+am, and then the i point is 30tH2.
Finish annealing was performed at 880 tons for 3 minutes in an atmosphere of 75% N2 and 25% N2 to produce a product. The resulting product magnetic properties are shown in Table 2 in comparison with those of the conventional method.

Table 2 As is clear from Table 2, it can be seen that the iron loss W15150 is significantly reduced even in single-sided processing of the steel plate.

(Effects of the Invention) As described above, according to the present invention, during the intermediate annealing treatment prior to the final cold rolling of the non-oriented electrical steel sheet during two or more cold rollings, the surface layer of the sheet surface is By adding processing traces that create fine skin indentations, it is possible to achieve remarkable improvements in the properties of the final product.
This can extremely advantageously contribute to higher performance, smaller size, and energy saving of electrical equipment.

[Brief explanation of the drawing]

Fig. 1 is a metallurgical micrograph of a cross section of a steel plate showing the coarsening behavior of grains in the surface layer of a steel plate due to intermediate annealing according to the present invention, and Fig. 2 is a metallurgical micrograph showing the coarsening behavior of grains in the surface layer of a steel plate due to intermediate annealing according to the present invention. FIG. 3 is a graph showing the effect of the size of skin indentations on iron loss improvement. FIG. 3 is a graph showing the effect of the average distance between skin indentations on iron loss improvement. Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Claims] 1. [:: 0.02 wt% or less, si: 3.5 wt% or less, Mn: 0.1 to 1. Owt% ＾＾! : 1 wt% or less S: A material for a non-oriented electrical steel sheet having a composition containing 0.02 wt% or less is hot-rolled into a hot-rolled sheet, and then cold-rolled twice or more with intermediate mirror annealing. In a series of steps in which the steel sheet is rolled to a final thickness and then finished annealed, during the intermediate mirror annealing treatment, a processing trace imparting treatment is performed in which fine skin indentations are formed on the surface of the steel sheet. A method for manufacturing a non-oriented electrical steel sheet, characterized by subjecting it to.