JPH07300655A - Non-oriented electrical steel sheet having excellent magnetic properties and caulking property and method for producing the same - Google Patents

Abstract

(57) [Abstract] [Purpose] A non-oriented electrical steel sheet having excellent magnetism while sufficiently securing the crimping property in automatic caulking of non-oriented silicon steel sheets by customers. [Structure] (1) Si ≦ 4.0% by weight%, Al ≦ 2.
0%, balance: non-oriented silicon steel sheet having a steel composition consisting of Fe and unavoidable impurities before final cold rolling has an average crystal grain size of 80 μm or more and a standard deviation of grain size of 250 μm or less. And a method for producing a non-oriented silicon steel sheet having extremely excellent magnetism and crimping property. (2) Regarding the maximum value (HMAX), minimum value (HMIN) and average value (HAVE) of the surface hardness after the final annealing (HMAX-H
MIN) / HAVE × 100 ≦ 8% Non-oriented silicon steel sheet with excellent magnetism and crimping properties. [Effect] By using the method of the present invention, it is possible to manufacture a non-oriented silicon steel sheet having a uniform surface hardness and excellent not only caulking property but also magnetic property.

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 mainly used in rotating machines and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, demands for quality improvement of non-oriented electrical steel sheets have become stronger from the viewpoint of energy saving. Iron and steel manufacturers are also conducting intensive research and development to meet this demand, and industrially produce various grades of non-oriented electrical steel sheets specified by JIS. In particular, since the low Si-containing non-oriented electrical steel sheets for small rotating machines are used by laminating, the "caulking method" is adopted, and it is natural that the magnetic characteristics (iron loss, magnetic flux density) are important. The crimping property is also an extremely important property.

In order to improve the magnetic properties, the grain size before cold rolling is increased to reduce the area of the crystal grain boundaries, and the {111} plane, which has bad magnetic properties, is generated from the vicinity of the grain boundaries during recrystallization as much as possible. It is necessary to suppress. Therefore, various methods have been put into practical use for increasing the size of crystal grains before cold rolling. As one example thereof, Japanese Patent Laid-Open No. 54-7624
High temperature winding (750 ° C) during hot rolling disclosed in Japanese Patent No. 22
There is a method in which the material is wound in the above manner and held for a predetermined time (self-annealing). However, in this case, a large variation occurs in the size of the crystal grain size in the plate thickness direction before cold rolling, and subsequent cold rolling, a mottled pattern occurs on the surface of the steel plate after final annealing, and the caulking property deteriorates. There is a problem of doing.

As another method, a method of annealing before final cold rolling is also generally known. Also in this method, in the case of a component system having a transformation (Si ≦ 2.5 wt% (hereinafter simply referred to as%), Al ≦ 1.0% and Si + 2Al: 2.5 wt% or less), a short time in the α + γ region When annealed, there is a problem that a mottled pattern is generated on the surface of the steel sheet after self-annealing and the caulking property is deteriorated as in the above method.

[0005]

SUMMARY OF THE INVENTION The present invention is intended to provide a non-oriented electrical steel sheet having both good magnetic properties and good crimping properties and a method for producing the same.

[0006]

[Means for Solving the Problems] The inventors of the present invention have eagerly clarified the caulking deterioration phenomenon in a non-oriented electrical steel sheet to which a technique for improving magnetic properties such as self-annealing of a hot rolled sheet is applied. It was found that the mottled pattern corresponds to the grain boundary before cold rolling, and that it is composed of crystals having almost the same orientation within the range of one pattern. When the distribution of crystal grain size before cold rolling is wide, a nonuniform crystal pattern is generated on the surface of the steel sheet after final annealing. Crystals are formed in the crystal pattern portion, that is, the grain size before cold rolling is relatively large (the portion in which abnormal grain growth occurs) and in the portion that is not so, that is, the grain size is relatively small (in which the normal grain growth occurs). It was also found that there is a difference in hardness after annealing due to different orientations, and this difference deteriorates the crimping property. The present invention has been completed based on this finding.

That is, according to the present invention, (1) wt% Si ≦ 4.0.
%, Al ≦ 2.0%, maximum surface hardness HMAX
, The minimum value HMIN and the average value HAVE are (HMAX-HMIN
) / HAVE ≦ 0.08 and B ₅₀ ≧ 1.76T, which is a non-oriented electrical steel sheet having excellent magnetic properties and crimping properties, and (2) wt% Si ≦ 4.
The non-oriented electrical steel sheet containing 0% and Al ≦ 2.0% has a mean grain size of 80 μm or more and a standard deviation of 250 μm or less in the total thickness of the steel sheet before final cold rolling. It is a method for producing a non-oriented electrical steel sheet having excellent properties and crimping properties.

The present invention will be described in detail below. First, the components will be described. C: The non-oriented electrical steel sheet is mainly used for rotating machines, and it is required that the deterioration of magnetic characteristics (magnetic aging) does not occur during use from the viewpoint of stability of characteristics. In the case of the present invention, the usual range satisfying such requirements may be used, but 0.045 in consideration of the detoxification technology by annealing in the consumer.
% Or less is sufficient. S: S is an element that is inevitably mixed during melting. In order to obtain the predetermined magnetic characteristics, 0.020% or less is desirable. N: N, like S, if its content is large, it partially re-dissolves during slab heating during hot rolling, forms precipitates such as AlN during hot rolling, and causes the growth of recrystallized grains during finish annealing. It may interfere with the movement of the domain wall due to the pinning effect when the product plate is magnetized. In the case of the present invention, the usual range in which such an effect does not occur may be used, but 0.006% is preferable in order not to generate blowholes due to aggregation after the final annealing.

Si, Al: These are essential elements for increasing the specific resistance of the steel sheet. If Si exceeds 4.0% or Al exceeds 2.0%, actual production such as cold rolling becomes extremely difficult. Therefore, Si ≦ 4.0%, Al ≦ 2.0
Must be set to%.

If Mn is less than 0.1%, workability is deteriorated, and S is generally added to render it harmless.
If it exceeds 0%, the magnetic flux density deteriorates remarkably.
0% is desirable. P: It can be added up to 0.1% in order to improve the punchability of the steel sheet, and if it is 0.2% or less, there is no problem in terms of magnetic properties. B: Boron can be added to render N harmless. Since it is necessary to balance with the amount of N, it is desirable that the maximum amount be 0.005% when added. For improving the mechanical properties, magnetism, rust resistance, etc. of the steel of the present invention, or for other purposes, Mn, P, B, N
The effect of the present invention is not impaired even if one or more of i, Cr, Sb, Sn and Cu are contained.

Next, the distribution of surface hardness will be described. The maximum value of the surface hardness of the steel sheet after final annealing is HMAX, and the minimum value is H
When MIN is the average value and HAVE is the average value, a value ΔH = (HMAX-HMIN) / HAVE is defined as an index indicating the hardness unevenness. FIG. 1 shows the relationship between ΔH and the crimping defect rate. When ΔH rises and exceeds 8%, the crimping defect rate dramatically increases. Therefore, ΔH needs to be 8% or less.

Next, a manufacturing method for improving the crimping property and the magnetic characteristics (B ₅₀ ≧ 1.76T) will be described. FIG. 2 shows the relationship between the average grain size before cold rolling and the magnetic properties (B ₅₀ ). The value of the particle size is a circle-equivalent diameter obtained by image-processing an optical microscope image. If the average crystal grain size before cold rolling is 80 μm or more, good magnetic properties of B ₅₀ ≧ 1.76 T can be obtained. In addition, in FIG.
Is Si: 0.3%, Al: 0.2%, and Δ is Si: 0.5.
%, Al: 0.2%, □: Si: 0.5%, Al: 0.
It is 3%, and the difference in the reached B ₅₀ value is considered to be mainly due to the difference in the components.

Further, enormous tests and investigations were carried out on the relationship between various factors of particle size and caulking property in this case. As a result, ΔH, which is a factor that greatly affects the crimping property,
Has a deep relationship with the standard deviation of the grain size before cold rolling. The relationship is shown in FIG. By setting the standard deviation of the grain size before cold rolling to 250 μm or less, ΔH (8% or less) that can realize a low crimping defect rate (3% or less) can be obtained. Note that ●, △, and □ represent different materials as in FIG.

The method of obtaining the grain size distribution (average value and standard deviation) before cold rolling of the present invention is not particularly limited, but self-annealing in hot rolling and hot-rolled sheet annealing may be performed. In addition to the method of performing, it is also possible to perform annealing before cold rolling for a long time below the transformation point. Further, the method for obtaining the material before cold rolling may be any method as long as it is within the above-mentioned range of components. For example, there are a normal continuous hot rolling method, a reversible hot rolling method using a Steckel mill, a method of obtaining by a moving and renewing cooling body, and the like.

[0015]

【Example】

 (Example 1)

[Table 1] The slabs of the components shown in Table 1 (silicon slabs consisting of the balance Fe and unavoidable impurities) are heated to 2.5 mm by an ordinary method.
After the thickness was set and the hot rolling was completed at 980 ° C., it was processed under the following conditions. It was wound up at 750 ° C and air-cooled. It was wound at 860 ° C. and self-annealed at 830 ° C. for 30 minutes. After winding at 680 ° C., continuous annealing was performed at 925 ° C. for 5 minutes. After winding at 680 ° C., box-type annealing was performed at 1000 ° C. for 60 minutes and then furnace cooling. Then, it was pickled and cold-rolled to a thickness of 0.50 mm. Degreasing the cold-rolled steel sheet, and using a continuous annealing furnace,
Annealed at 50 ° C for 30 seconds. Then, the magnetic properties (average of L + C) and the surface hardness (Hv5) were measured by the Epstein method. The results are shown in Table 2.

[0016]

[Table 2]

(Example 2)

[Table 3] The slabs of the components shown in Table 3 (silicon slabs consisting of the balance Fe and unavoidable impurities) are heated by a usual method to 2.5 mm.
After the thickness was set and the hot rolling was completed at 980 ° C., it was processed under the following conditions. Wind up at 725 ° C. It was wound at 840 ° C. and self-annealed at 830 ° C. for 30 minutes. After winding at 700 ° C., continuous annealing was performed at 900 ° C. for 5 minutes. After winding at 690 ° C., box-type annealing was performed at 1000 ° C. for 60 minutes and then furnace cooling. Then, it was pickled and cold-rolled to a thickness of 0.50 mm. Degreasing the cold-rolled steel sheet, and using a continuous annealing furnace,
Annealed at 00 ° C for 30 seconds. Then, the magnetic properties (average of L + C) and the surface hardness (Hv5) were measured by the Epstein method. The results are shown in Table 4.

[0018]

[Table 4] The metallographic structure in the cross-sectional direction under the conditions shown in Table 4 is shown in FIG.
Fig. 4 shows the metallographic structure in the cross-sectional direction under the conditions shown in the table.
FIG. 4 (c) shows the metallographic structure in the cross-sectional direction under the conditions shown in FIG. 4 (b).

[0019]

As is clear from the above embodiments,
According to the present invention, it is possible to obtain a non-oriented electrical steel sheet having excellent magnetic properties and crimping properties.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between hardness unevenness and a crimping defect rate.

FIG. 2 is a diagram showing a relationship between an average crystal grain size and magnetic flux density before cold rolling.

FIG. 3 is a diagram showing a relationship between a grain size before cold rolling and ΔH.

FIG. 4 is a view showing electron micrographs (magnification of 300 times) of metal structures of an example of the present invention (FIG. C) and a comparative example (FIGS. A and b).

Claims (2)

[Claims] 1. Si ≤ 4.0% by weight%, Al ≤ 2.0
%, The maximum value HMAX of the surface hardness, the minimum value HMIN,
The average value HAVE is (HMAX-HMIN) / HAVE ≤ 0.0
8. A non-oriented electrical steel sheet having excellent magnetic properties and crimping properties, which satisfies B8 and B ₅₀ ≧ 1.76T. 2. Si ≦ 4.0% by weight%, Al ≦ 2.0
% Of the non-oriented electrical steel sheet containing 80% of the total thickness of the steel sheet before the final cold rolling is 80 μm or more, and the standard deviation is 2
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and caulking properties, which is characterized by having a thickness of 50 μm or less.