JPH0413811A - Production of grain-oriented electrical steel sheet having high magnetic flux density - Google Patents

Abstract

PURPOSE:To stably produce the above steel sheet by limiting the nitrogen partial pressure in an atmosphere at the time of secondary recrystallization annealing in the primary recrystallization process of a steel which is regulated in the contents of AlN and MnS as inhibitors, is limited in a cold draft and does not contain Si. CONSTITUTION:The hot rolled sheet contg., by weight %, <=0.06 C, 0.005 to 2.0 Mn, 0.001 to 0.02 S, 0.01 to 0.036 sol.Al, and 0.002 to 0.014N, and consists of the balance iron is subjected to >=1 passes of cold rolling including the final cold rolling of 50 to 80% draft to the final sheet thickness. This steel sheet is subjected to the final annealing in the temp. region where the transformation does not arise, after decarburization annealing, by which the grain-oriented electrical steel sheet is obtd. The atmosphere at the time of the final annealing is formed of a gaseous mixture composed of nitrogen and hydrogen contg. <=50% nitrogen in this method. The secondary recrystallization is generated in this way and the grain-oriented electrical steel sheet having the high magnetic flux density is stably obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet having an extremely high magnetic flux density.

In general, core materials for stationary equipment include pure iron, low carbon steel,
Alternatively, silicon steel to which about 3% St is added is widely used. Although pure iron and low carbon steel have higher saturation magnetic flux density than silicon steel, their magnetism is inferior. However, since they are cheaper than silicon steel, they are currently used depending on the purpose.

Among these, the present invention provides directionality to silicon-free steel, which has a higher saturation magnetic flux density than silicon steel, and is a unidirectional electrical steel sheet with superior magnetization properties and lower iron loss than pure iron or low carbon steel. The present invention provides a method for manufacturing.

(Prior technology) Until now, unidirectional electrical steel sheets have been used as core materials for transformers, so silicon steel containing about 3% St, which increases specific resistance and lowers iron loss, has been deeply researched. . However, in recent years, yoke materials, magnetic shield materials, etc. are required to have a magnetic flux density B higher than iron loss. Generally, the higher the purity of the iron mesh material, the higher the saturation magnetic flux density Bs. In addition, in single crystals, <100
It is well known that the > direction is most easily magnetized, and therefore oriented materials such as wrought iron are expected to have high magnetic flux densities. It is important to obtain such materials industrially in large quantities.

By the way, in conventional unidirectional silicon steel, by controlling the nitrogen partial pressure during annealing of valiant crystals (1i
0) <ool> Several attempts have been made to increase the degree of Goss orientation integration. For example, JP-A-55-47324
In the publication, by lowering the nitrogen partial pressure in the atmosphere before secondary recrystallized grain growth and utilizing coarse crystal grains in the surface layer,
It is stated that the degree of Goss accumulation increases after secondary recrystallization. Also, Tetsu to Hagane, Vol. 73. No, 14.1
746 (1987) states that lowering the nitrogen partial pressure during secondary recrystallization annealing weakens the inhibitor and increases the secondary recrystallization temperature. The mechanism of secondary recrystallization is described in which secondary recrystallization becomes difficult.

On the other hand, several studies have been conducted on the secondary recrystallization of so-called ordinary steel that does not contain silicon, and although the composition is different from the composition of the present invention, for example, M. Kohler (
J. Appl, Phys., 3B (1967) 1776
) is secondary recrystallization using MnS added with S at the time of final annealing as an inhibitor, using a 100% hydrogen atmosphere.

(Problems to be Solved by the Invention) The present invention provides a secondary recrystallization process for silicon-free steel in which the contents of AIN and MnS as inhibitors are specified and the further cold rolling rate is limited. It is an object of the present invention to provide a method for stably manufacturing grain-oriented electrical steel sheets with high magnetic flux density by limiting the nitrogen partial pressure in the atmosphere during annealing.

(Means for Solving the Problems) The gist of the present invention is that C≦0.06% by weight, Mn; 0
．． 005~2.0%, S;O,OO1~0.02%+
so 1. At+0.01~0.036. %,N,
The starting material is a hot-rolled plate containing 0.002 to 0.014%, with the remainder consisting of iron and unavoidable impurities, and the rolling reduction is 50%.
After undergoing one or more cold rollings, including ~80% final cold rolling,
The objective is to stably obtain a high magnetic flux density unidirectional electrical steel sheet by using a nitrogen/hydrogen mixed gas containing less than 50% nitrogen as the atmosphere during the final annealing during decarburization annealing and final annealing.

The hot rolled sheet used here may be obtained by known means, and neither the slab heating temperature nor the finishing temperature is particularly limited. The slab heating time may be set to a time that allows sufficient homogenization depending on the slab thickness; if it is too long, one grain of the slab will become coarse and secondary recrystallization failure will occur. Decarburization annealing is also performed by known means. For example, heat treatment may be performed in wet hydrogen.

The final annealing is preferably performed at a high temperature in a temperature range where α-γ transformation does not occur, and the annealing time is set to a time that allows sufficient growth of the gothic recrystallized grains. The nitrogen partial pressure in the atmosphere is also set by known means.

(for production) First, the component elements will be described.

It is desirable that C be suppressed to some extent in order to optimize the texture, but if its content is too large, it will not be removed in the decarburization process and will be harmful to the magnetic properties, so it should be kept at 0.06% or less.

Although Mn has the effect of lowering iron loss without deteriorating the magnetic flux density, if its content increases, the amount of solid solution of MnS decreases during heating of the hot-rolled slab, so it is set to 2.0% or less. Also, if the amount is too low, secondary recrystallization will not occur, so
The lower limit is set to 0.005%.

Since S acts as an inhibitor for secondary recrystallization in the form of MnS, it must be contained in an amount of 0.001% or more, but in order to dissolve MnS to some extent in the hot-rolled slab heating temperature range preferred in the present invention. , 0.02% or less, preferably 0.004% or less.

In addition to this S restriction, sol, AIo, 036
% or less. If the amount is larger than this, secondary recrystallization will not occur. Similarly, sol and AI need to be at least 0.01% to cause secondary recrystallization.

Since N precipitates in the steel in the form of AIN together with AI and acts as an inhibitor, it is required to be at least 0.002%, and if it is too large, secondary recrystallization will not occur, so it is 0.014%.
is the upper limit.

As other elements, it is permissible to add elements that do not act as inhibitors in steel, such as Si, for the purpose of improving core loss, although the magnetic flux density decreases.

Here, a cold rolling reduction ratio is an essential requirement for increasing magnetic flux density. If the cold rolling reduction is increased to 85%, B8
will drop considerably. This is because the grains are large due to secondary recrystallization, but grains with a large deviation from the Goss orientation grow.

Therefore, from the viewpoint of obtaining a high magnetic flux density, the upper limit of the rolling reduction ratio in the present invention is 80%.

Furthermore, regarding the nitrogen partial pressure in the atmosphere during final annealing, which is the gist of the present invention, it is necessary to make the nitrogen partial pressure less than 50% in order to cause secondary recrystallization. It is thought that secondary recrystallization did not occur in the final annealing temperature range of the present invention because increasing the nitrogen partial pressure increases the inhibitor strength in the steel as AIN. The reason for limiting the nitrogen partial pressure is to control the inhibitor level so that secondary recrystallization occurs in the final annealing temperature range of the present invention, and the nitrogen partial pressure is set low to utilize the sharp Goss grains on the surface. This is different from the conventional idea of silicon steel. Therefore, the component of the present invention does not have a high Goss accumulation degree at the lower limit of the nitrogen partial pressure.

Next, regarding the intermediate annealing temperature when cold rolling is performed two or more times, from the viewpoint of optimizing the next crystal texture and precipitation of AIN, the intermediate annealing is performed in a temperature range where at least a part of the steel sheet undergoes T transformation. For example, it was found that the magnetic properties were significantly superior.

(Example 1) C; 0.05%, MnHo, 18%, S; 0.00
7%, soZ, AZ; 0, 024%, N, 0.00
A hot-rolled sheet consisting of 9% Fe and unavoidable impurities was cold-rolled to 60% and then annealed at 830° C. for 2 minutes. After further cold rolling by 65%, decarburization annealing was performed at 850°C (in wet hydrogen), and secondary recrystallization annealing was performed under the atmospheric conditions shown in Table 1. In order to perform secondary recrystallization using the components of the present invention, it is important to keep the nitrogen partial pressure below 50%.

(Example 2) C, 0.04%, Mn; 0.15%, S, 0.00
4%.

sol, 81; 0.020%, N, 0.007
%, balance Fe and unavoidable impurities were cold rolled at the cold rolling rate shown in Table 2, decarburized annealed at 830°C (in wet hydrogen), and further annealed at 890°C in a 100% hydrogen atmosphere.
Secondary recrystallization annealing was performed for 20 hours.

Table 2 (Example 3) Hot rolled sheets having compositions No. 1 to 6 in Table 3 were cold rolled by 60%, annealed at 830°C, and further cold rolled by 70%. 8
After decarburization annealing at 30°C (in wet hydrogen), secondary recrystallization annealing was performed at 890°C for 15 hours in an atmosphere with a nitrogen partial pressure shown in Table 3.

(Example 4) After 60% cold rolling of a hot-rolled sheet with the same composition as in Example 2, N in Table 4
Intermediate annealing was performed at a temperature of 1 to 4 o. Another 65%
After cold rolling, decarburization annealing was performed at 830°C (in wet hydrogen), and secondary recrystallization annealing was performed at 890°C for 20 hours in an atmosphere with a nitrogen partial pressure shown in Table 4.

Table 4 Since a unidirectional electrical steel sheet can be stably obtained, its industrial effects are extremely significant.

(Effect of the invention) According to the invention, Higher magnetic flux density than silicon steel ■

Claims (2)

[Claims] (1) C≦0.06% by weight, Mn; 0.005-2
．． 0%S; 0.001-0.02%, sol. Al; 0
．． 01-0.036%, N; 0.002-0.014%
A hot-rolled sheet with the remainder consisting of iron and unavoidable impurities is cold-rolled one or more times including final cold-rolling at a rolling reduction of 50 to 80% to give the final sheet thickness, and after decarburization annealing, transformation In the production of unidirectional electrical steel sheets that are final annealed in a temperature range that does not
A method for producing a high magnetic flux density unidirectional electrical steel sheet, characterized in that the nitrogen partial pressure in the final annealing atmosphere is less than 50%. (2) The steel sheet according to claim 1, characterized in that the heat treatment during cold rolling when cold rolling is performed two or more times to obtain the final sheet thickness is performed in a temperature range at which γ transformation occurs in at least a part of the steel sheet. A method for manufacturing high magnetic flux density unidirectional electrical steel sheets.