JPS59123715A - Production of non-directional electromagnetic steel - Google Patents

Abstract

PURPOSE:To produce inexpensively intra-surface non-directional electromagnetic steel plate having a high magnetic flux density and low iron loss characteristic by subjecting the slab having a specified compsn. of Si, Al and Fe to self-annealing at the specified coiling temp. in a hot rolling stage then subjecting the same to strong cold rolling. CONSTITUTION:A slab consisting of <=4.0wt% Si, <=1.0% Al and the balance Fe and unavoidable impurities is hot-rolled to a steel strip and the steel strip is subjected to self-annealing at the coiling temp. after the hot rolling specified within a range of 700-900 deg.C, whereby the crystal in the hot-rolled steel strip is made <=4 grain size number. The steel strip is further subjected to strong cold rolling at >=85% draft in cold rolling. It is necessary to hot roll the steel strip in such a way that the thickness t1 after the hot rolling attains (t1>=t2/0.15) according to the final thickness t2 by which the non-directional electromagnetic steel sheet having a uniformly high magnetic flux density in each direction of the plate surface and a low iron loss is thus obtd. at a low cost.

Description

Detailed Description of the Invention The present invention relates to a method for manufacturing a non-oriented electrical steel sheet suitable for the iron core of rotating equipment such as motors and generators, and in particular to a method for producing a non-oriented electrical steel sheet that has uniformly high magnetic flux density in each direction of the sheet surface and iron loss. The object of the present invention is to provide a method of obtaining a non-oriented electrical steel sheet with a low .

As is well known, non-oriented electrical steel sheets are used as iron core materials for so-called stationary equipment such as transformers and ballasts, and for so-called rotating equipment such as motors and generators used in household electrical appliances and industrial machinery. With the rise in energy costs in recent years, there has been a growing demand for energy saving and high efficiency in each of these applications, and for this reason, the magnetic flux density has increased even for non-directional vA steel sheets. There is a strong demand for improvement and reduction of iron loss.

By the way, as a method for measuring the magnetic flux density and iron loss of non-oriented type 11 steel sheet, as specified in J15-C-2550, the method is as follows: The method of cutting out and measuring an Epstein sample in the C direction (hereinafter referred to as the C direction) is generally widely applied, and in order to obtain high magnetic flux density and low iron loss values with this method, the values in the L direction and C direction must be becomes important. However, when electromagnetic steel sheets are used in rotating equipment such as motors, they are magnetized not only in the direction and the C direction, but also in all directions, so the magnetic flux density is uniformly high in each direction of the sheet surface, resulting in a so-called surface with low iron loss. A non-oriented electrical steel sheet is required. Therefore, just because the measurement value in the L+C direction is good as determined by the JIS method as mentioned above, it does not necessarily mean that it is suitable for rotating equipment. A ring-shaped sample is punched out, a primary winding and a secondary winding are applied to the ring-shaped sample, and the average iron loss and average magnetic flux density are measured in the entire circumferential direction, or an Epstein sample in a direction that is 45° to the rolling direction is measured. After cutting out and measuring the magnetized values in the L direction, C direction, and 45° direction, weights are applied and averaged to simply determine the average iron loss and average magnetic flux density in the entire circumferential direction. desirable.

Various methods have been proposed as methods for producing non-oriented electrical steel sheets. We are proposing a manufacturing method for non-oriented electrical steel sheets. The invention of JP-A No. 57-35628 discloses that the temperature after hot rolling is determined by Δr determined according to the raw material components.
The invention of Japanese Patent Application No. 57-18909 sets the hot rolling end temperature to the γ phase region just above the transformation point, and then annealing for a short time. It is characterized by raising the heating temperature, and all of these are aimed at improving magnetic properties by enlarging the crystal grains of the hot rolled steel strip before cold rolling. In addition, as shown in JP-A-54-76422, a method has also been proposed in which the coiling temperature during hot rolling is increased to improve the magnetic properties of the hot rolled steel strip through grain growth through self-annealing. has been done.

However, with these methods, although the magnetism in the L+C direction is certainly improved, the magnetism in the direction approximately 55°C from the rolling direction is conversely lower than that of ordinary electromagnetic steel strips, and therefore electromagnetic steel strips for rotating machines It turns out that this is not necessarily appropriate.

On the other hand, Japanese Patent Publication No. Sho 51-942 describes a method for manufacturing an in-plane non-oriented electrical steel sheet suitable for use in rotating machines. O
A method has been proposed in which a hot-rolled material of II+m is subjected to one round of strong cold rolling at a reduction rate of 85% or less to finish it to a thickness of 0.35RI11 or less, and then subjected to annealing that also serves as decarburization. .

However, since a plate thickness of 0.50 mm is often used as an ordinary rotating machine material, this proposed method is not suitable for practical use.

In addition, in the case of this proposed method, when hot rolling is performed according to the conventional method and the hot-rolled coil is wound up at about 500 to 700°C, a strong reduction of 85% or more is required in the cold rolling as described above. In addition, although the degree of in-plane non-direction was improved, it was found that the average magnetic properties were inferior to conventional products.

This invention was made in view of the above circumstances, and an object of the present invention is to provide at a low cost a non-oriented 11a steel plate which has uniformly high magnetic flux density in all directions in the plane and has low iron loss, and is particularly suitable for rotating machines. The purpose is to

In other words, the inventors of the present invention have carried out extensive experiments and examinations to achieve the above-mentioned purpose, and have found that in order to have uniform magnetism in each direction within the plane and a high level of magnetism as a whole,
By self-annealing at a coiling temperature of 700°C or higher in the hot rolling process, the average grain size of the hot rolled steel strip is increased to A.
S T M Nα4 or less (average grain size 100JJII
+ or more) and cold rolling with a reduction rate of 85%.
It was discovered that it was necessary to combine the above two conditions of intense cold rolling, and this invention was completed.

Specifically, this invention applies to 9i 4.0% or less, to Q1.
A slab consisting of 0% or less Fe and unavoidable impurities is hot-rolled into a copper strip, the hot-rolled steel strip is cold-rolled once to achieve the final thickness, and then annealed to grow grains. In the method for producing a grain-oriented electrical steel sheet, hot rolling is performed so that the hot-rolled plate thickness tl satisfies t1≧j2/0.15 according to the final plate thickness t2, and the coiling temperature after hot rolling is The grain size of the hot rolled steel strip is reduced to 4 or less by self-annealing at a temperature of 700°C or more and 950°C or less, and is roughly cold rolled with a reduction rate of 85% or more. That is.

The method of the present invention will be explained in more detail below.

First, to explain the reason for limiting the ingredients of the material slab used in the method of this invention, Si is an element effective in lowering iron loss by increasing specific resistance and reducing eddy current loss. If it exceeds 4.0%, the steel strip becomes brittle and problems such as cold opening pressure M and plate cracking occur.
It needs to be 4.0% or less. Note that the lower limit of Si is not particularly limited, but the S1 content may be determined as appropriate depending on the application.

△Q is an effective element for developing texture,
If it exceeds 1.0%, it becomes brittle like Sl, leading to an increase in cost, so it is necessary to keep it below 1.0%.

In addition, since it is necessary for non-oriented silicon steel sheets to grow crystal grains by annealing after cold rolling, thereby lowering the dawn loss among iron loss components, impurity elements such as C1S, ○, and N are It is desirable to reduce the amount of precipitates such as N and MnS as much as possible to suppress inclusions and grain growth.

A steel material having the above-mentioned composition is melted according to a conventional method by controlling the composition using a converter, a subsequent degassing device, etc., and is made into a slab by an ingot-blowing method or a continuous casting method. The crystal grains at this slab stage do not pose much of a problem if the Si content is 1.5% or less, where transformation is observed.
When the Si content is 1.5% or more, it is desirable to lower the casting temperature or use ultrasonic stirring or electromagnetic stirring during casting to prevent crystal grains from coming out.

The slab obtained as described above is heated to around 1200° C. and then hot-rolled to a desired hot-rolled plate thickness by rough rolling and finish rolling. In this hot rolling, in order to keep the rolling reduction ratio in the subsequent cold rolling to 85% or more, the finished hot rolling thickness tl is determined by the following formula according to the product thickness (thickness after cold rolling) t2. Must be satisfied.

t1≧t2/ (1-0,85) The product thickness of non-oriented silicon steel plate is 0.3 according to JIS.
5L1m, 0.50111m, 0.65m
Three types of m are defined, and in Al5I, 0
．． 35mm, 0.471Il11.0.635+
Three types of nm are specified, but the most commonly used are o and somm. In order to obtain a product of somm, the finished hot rolling thickness tl must be 3.34 mrA or more from the above formula,
It is preferably 4.5 to 5.5+nm. Note that the hot-rollable thickness in the conventional normal process is about 2.0 to 2.6 mm due to the ease of cold rolling in the subsequent process, ease of handling, or the conventional normal cold rolling reduction rate. Therefore, in the case of the present invention, the finished hot-rolled thickness is considerably thicker than that of the conventional method.

The coiling temperature in the above hot rolling is 700°C or higher, 950°C
Temperature below ℃. Conventional normal winding temperature is 600℃
Therefore, in the case of the present invention, the hot rolling winding temperature is higher than that of the conventional method. The reason why we set the hot rolling coiling temperature to a high temperature of 700°C or higher is as follows.
by. That is, when the finished thickness of the hot-rolled sheet is increased and the reduction ratio during cold rolling is increased as described above, although the uniformity of magnetism in each in-plane direction increases, the magnetic flux density Bs usually increases.

(Magnetic flux density at a magnetizing force of 5000 A/m) will decrease. In particular, when the rolling reduction in cold rolling is 80% or more, B50 decreases significantly. On the other hand, by setting the coiling temperature to a particularly high temperature of 700°C or higher and self-annealing after coiling, the average grain size of the hot rolled steel strip is changed to ASTM grain size number 4.
If the grain size is grown to an average grain size of 100 JJI or more, it is possible to prevent the 850 value of the product from decreasing even if the cold rolling reduction is 85% or more as described above.

If the coiling temperature during hot rolling is less than 700°C, the crystal grains of the hot rolled steel strip will be small and the Bso value will decrease.

In particular, if the cold rolling reduction ratio is set to a value of 85% or more as in the present invention, the degree of decrease in magnetic flux density becomes significant, and the designed magnetic flux of the stator teeth portion becomes insufficient for use in a rotating machine. This is thought to be because in the case of fine grains with an average grain size of 4 or more, the number of crystals with the (111) orientation, which is said to be generated from grain boundaries and is difficult to magnetize, is further increased by intense cold rolling. . On the other hand, if the coiling temperature exceeds 950°C, the crystal grains in the hot rolled steel strip will become too large due to self-annealing, causing problems such as cracks and breaks during cold rolling, and the uneven surface of the product. There is a risk that the scale formed on the surface of the hot-rolled steel strip may become too thick, making it difficult to remove the scale before cold rolling. Therefore, in this invention, the coiling temperature of hot rolling is set to 70
It was defined in the range of 0 to 950'C.

The optimum value for the hot rolling coiling temperature depends on the steel components, especially the Si content; if the Si content is approximately 2.5% or more and there is no γ transformation, the coiling temperature is approximately 800 to 950°C. Desirably, if the Si content is less than this, 750
The temperature is preferably about 800°C.

After hot rolling as described above, descaling treatment is usually performed using hydrochloric acid, sulfuric acid, etc. before cold rolling.

In the case of this invention, as mentioned above, the thickness of the hot-rolled steel strip is thick, so the coil length is relatively short, and as a result, the surface area to be descaled is reduced, so the efficiency of the descaling process is Becomes good.

In the cold rolling after the descaling treatment, the rolling reduction is 85% or more. By performing strong cold rolling in this manner, the in-plane anisotropy of the product is reduced, and the magnetism is uniformly improved in each in-plane direction. Therefore, in the method of this invention, the coiling temperature during hot rolling is set to a high temperature of 700°C or higher, the crystals in the hot rolled steel strip are grown into large grains with a grain size number of 4 or less by self-annealing, and the cold rolling is performed at a rolling reduction rate of 85°C. It is only when these two conditions are combined, that is, hard rolling of % or more, that magnetism is uniform in all directions within the plane, and overall magnetic flux density is high and iron loss is low, making it suitable for rotating machines. A steel plate is obtained. Note that the cold rolling reduction ratio is preferably 87% or more and 95% or less, even within the range of 85% or more.

Next, embodiments of the invention will be described.

Example 1 Molten steel containing Co, oos%, Si 1.05%, and 90.2% Si was made into a slab by continuous casting, and after heating to 1250°C, material A was hot rolled to a thickness of 4.8 mm.
After being rolled up at 00°C, it was allowed to cool naturally and was self-annealed.

On the other hand, material B was hot rolled to a thickness of 4.8 mm in the same manner as described above, but after finish rolling, it was water cooled and wound at 680°C.

Material C was hot rolled to a thickness of 2.3IllIll, wound at 780°C, and self-annealed. Furthermore, material D was finished to a thickness of 2.30III by hot rolling, and
It was wound at 0'C. Each hot-rolled coil of these A-D materials was subjected to descaling treatment by pickling, and then cold-rolled to form a plate having a thickness of 0.50 nu+. Therefore, the cold rolling reduction ratio for materials A and B is 90%, and the cold rolling reduction ratio for materials C and D is 78%. Next, continuous finish annealing was performed at 850° C. for 30 seconds, and the magnetic properties at the central portion in the longitudinal direction of the coil were measured. Table 1 shows the L+C magnetic properties of each sample, and Fig. 1 shows the relationship between the angle from the rolling direction of each sample and 850. (
B) shows the (201 pole figure) of material C.

From Table 1, the magnetic properties of L+C are AI, which has a high winding temperature,
It is clear that material C is much superior to materials B and D, which have a lower winding temperature, and that the magnetic flux density B50 is particularly high. On the other hand, from Figure 1, in the case of C and DI materials with a low cold rolling reduction of 78%, the angle dependence of B50 is strong, with 85° around 55°.
An extremely low point of 0 can be seen, and this tendency is particularly strong in C material, which has strong anisotropy, whereas A material has a high cold rolling reduction of 90%.
It is clear that materials B and B have small anisotropy and are uniformly magnetized. From these magnetic I11 constant results,
It is clear that only material A obtained by the method of the present invention has small in-plane anisotropy and exhibits excellent overall magnetism. Furthermore, from the pole figure shown in Figure 2, A
In the case of C material, the axis of easy magnetization [200
] is clearly uniformly and strongly accumulated in the circumferential direction, making it suitable for rotating machines.

Example 2 CO, 011%, SiO, 27%, Mn 0.25%
, 1200 continuous cast slabs containing ΔQ 0.0005%
℃, hot rolled to a thickness of 4.0 mm for slab a and coiled at 770 ℃, and 3.0 mm for slab b. Slab C was hot rolled to 2.5 mm and wound at 730°C, and self-annealed by natural cooling.

On the other hand, slabs d, e, and f are each 4. OmI!
l.

Hot rolled to 3.0mm, 2.5mm, water cooled, 6
It was wound at 50'C. After descaling each hot rolled steel strip by pickling, it was cold rolled to a thickness of 0.5n+m, and after cleaning the cold rolling oil, final annealing was performed at 800° C. for 30 seconds. Thereafter, ring samples having an inner diameter of 55 mm and an outer diameter of 85 mm were punched out, 12 pieces were stacked, and the magnetic properties of the ring samples were measured. However, since the stators of small motors are generally annealed to remove strain, 750
'CX After 2 hours of strain relief annealing, magnetic characteristics were performed. The results are shown in Table 2. Furthermore, from the results shown in Figure 3 and Table 2, which show the relationship between the Bso value, cold rolling reduction and hot rolling finish thickness of each sample, the ring sample It is clear that the magnetism is extremely excellent. Also, from Figure 3, when the cold rolling reduction is 85% or more, the winding temperature is less than 700°C, B50
It is clear that 850 decreases markedly, but conversely 850 increases when the winding density is 700° C. or higher.

Example 3 CO, 005%, Si 2.85%, ΔQ O, 35%
, So, a slab containing 002% was heated to 1230°C,
Hot-rolled steel strips with plate thicknesses of 3.5I and 2.0III were produced. Here, the hot-rolled steel strip with a thickness of 3.5n+n was hot-rolled in 5 stands where it should originally be hot-rolled in 6 stands, and coiled at 910°C immediately after the final stand, while 2.0III
A hot-rolled steel strip having a thickness of I11 was coiled at 570° C. while being water-cooled. After descaling each hot rolled steel strip, 0.35
+am, and after degreasing, finish annealing was performed at 950° C. for 2 minutes. When a normal Epstein sample was cut and its magnetic properties were measured, the results shown in Table 3 were obtained. However, in Table 3, the value of C/L is C of W 150.
The ratio of the values in the direction and L direction.

From Table 3, the magnetic properties of the present invention material are excellent, especially L/C
It is clear that the ratio is very small and that it is easy to be uniformly magnetized in both the L and C directions.

As is clear from the above explanation, according to the method of this invention,
Magnetic flux density is uniformly high in all directions within the plane, and iron loss is low.
A remarkable effect is obtained in that a non-oriented electrical steel sheet suitable for rotating machines can be produced practically and at low cost.

[Brief explanation of the drawing]

Figure 1 shows an angle from the rolling direction and magnetic flux density B5 when the hot rolling winding temperature and cold rolling reduction ratio are changed in Example 1.
Figure 2 shows the (200) pole figure of each village obtained in Example 1, where (A) is the pole figure of the invention material A, and (B) is the pole figure of the comparative material. Showing the pole figure of B,
FIG. 3 is a graph showing the relationship between the cold rolling reduction ratio, the finished hot rolled plate thickness, and the magnetic flux density B50 of each sample obtained in Example 2 at different hot rolling winding temperatures. Applicant Kawasaki Steel Co., Ltd. agent Patent attorney Takehisa Toyota (one idiot) Figure 2 (A) (B) □2×≦ [z1] IX plan, Ku2× □1×> Figure 3 A thousand dirty toys rod(%)

Claims (1)

[Claims] Si 4.0% (weight %, same hereinafter) or less, △Q1.0
% or less, the balance Fe and unavoidable impurities are hot-rolled into a copper strip, the hot-rolled steel strip is cold-rolled once to achieve the final thickness, and then annealed to grow grains. In the method for manufacturing a magnetic steel sheet, the sheet thickness t1 after hot rolling is determined according to the final sheet thickness t2 [I≧t
2 / 0.15, and by self-annealing the coiling temperature after hot rolling within the range of 700°C to 950°C, the grain size of the crystals in the hot rolled steel strip is reduced. A method for producing a non-oriented electrical steel sheet, characterized in that the number is 4 or less, and heavy cold rolling is performed at a reduction rate of 85% or more in rough cold rolling.