JPH03111516A - Production of grain-oriented electrical steel sheet - Google Patents

Abstract

PURPOSE:To stably produce a grain-oriented electrical steel sheet having high magnetic flux density at a low cost by annealing at a specific temp. before or after cold-rolling of a hot-rolled steel sheet with an extremely low carbon content and a specific composition of C, Si, Mn, S, Al, N and Fe. CONSTITUTION:The hot-rolling is executed to a steel with extremely low carbon content composed of <=0.01wt.% C, 1.5-3.0% Si, 1.0-2.0% Mn, <=0.010% S, 0.003-0.015% sol.Al, 0.001-0.010% N and the balance Fe with inevitable impurities. This hot-rolled steel sheet is made to the finished sheet thickness by the cold- rolling at one time or two or more times including intermediate annealing in alpha range at >=700 deg.C. Successively, the cold-rolled steel sheet is continuously annealed in the alpha range at >=700 deg.C and desirably at a heating velocity of >=about 5 deg.C to generate a suitable primary recrystallization. After that, finish annealing is executed to the steel sheet to sufficiently develope the secondary recrystallization having (110) Miller indices direction. By this method, the grain- oriented electrical steel sheet having high magnetic flux density is obtd. without executing the decarbonizing annealing, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to a magnetic steel plate having excellent magnetic properties with flol <001> orientation as the main orientation. ! It is related to the method of sending.

(Prior Art) Directional IM steel plates are magnetic materials that are widely used as core materials and magnetic shielding materials for power transformers, generators, electric motors, and the like. Among these, those containing around 3% by weight of silicon are used relatively often. The grain-oriented electrical steel sheet has -C Goss orientation (Miller index (1101<o
It is composed of crystal grains with a crystal orientation called ot> orientation), and the axis of easy magnetization is <00 in the rolling direction.
1> Since the axes are parallel, it has extremely good magnetization characteristics and iron loss characteristics in the rolling direction.

In order to obtain such a crystal ml whose main orientation is the Goss orientation, a method is used that utilizes so-called secondary recrystallization, in which primary recrystallized grains selectively grow during finish annealing after cold rolling. There is. Therefore, the key point in manufacturing a directional electromagnetic wA plate is how to generate stable and accurate secondary recrystallization in the Goss orientation during finish annealing. In order to generate secondary recrystallization in the Goss orientation, fine precipitates called inhibitors are required to suppress the growth of grains other than in the Goss orientation, and precipitates such as MnS, MnSe, or AlN are generally used as inhibitors. .

For example, Japanese Patent Publication No. 40-15644 and Japanese Patent Publication No. 4
Japanese Patent No. 6-23820 discloses a method for producing a grain-oriented electrical steel sheet using AlN as a main inhibitor.

In these manufacturing methods, ordinary steel containing a certain amount of C is used as the base material in order to control the structure of the rolled plate and the dispersion state of AIN. However, if a steel with a high C content is used as the base material, there are problems such as deterioration of the magnetic properties of the final product and difficulty in secondary recrystallization during final annealing. A costly decarburization annealing is performed before the final annealing, which causes secondary recrystallization.

On the other hand, several manufacturing methods have been proposed that do not require such costly decarburization annealing and allow AlN to be appropriately dispersed and exert an inhibitor effect even in ultra-low carbon steel. Publication No. 58-100627 discloses that a slab containing 0.02% or less of C is used as the base material, and 101 mm parallel to the surface of the steel plate is subjected to finish annealing to allow secondary recrystallization.
A method for manufacturing a grain-oriented electrical steel sheet that provides a temperature difference of 2° C. or more per 11°C has been proposed. However, it is very difficult to carry out such special finish annealing in actual production, and it is thought that the magnetic properties of the obtained grain-oriented electrical steel sheets will also vary widely.

By the way, the inventor of the present application previously discovered that c:o, o1% or less, S
i: 0.5-2.5%, Mn: 1.0-2.0
%, Sol, Al: 0°003 to 0.015% as a base material, and the final plate is cold rolled once or twice or more with intermediate annealing in between. We proposed a method for manufacturing grain-oriented electrical steel sheets in which after the thickness is increased, continuous annealing is performed to achieve crystallization and finish annealing is performed to perform secondary recrystallization (Japanese Patent Application Laid-Open No. 1-119644).
issue).

In the prior invention, since the base metal hot-rolled steel sheet is an ultra-low carbon steel with a C content of 0.01% or less, there is no need to perform costly decarburization annealing before final annealing, and the above-mentioned AffiN becomes an inhibitor even after special finish annealing.
Since it is possible to stably form the appropriate finely dispersed form, it is possible to obtain a directional it if it has excellent magnetic properties in the rolling direction.
f steel plate is obtained. The reason for this is presumed to be that Mn in the steel homogenizes the dispersion state of AlN, which is an inhibitor of primary recrystallization, and promotes stability of secondary recrystallization.

However, in recent years, in order to reduce costs, generators,
As electrical equipment such as electric motors continues to become smaller, grain-oriented electrical steel sheets with higher magnetic flux density are required. It is difficult to achieve sufficient density.

(Problems to be Solved by the Invention) An object of the present invention is to meet the above-mentioned needs. Specifically, it is possible to inexpensively and stably achieve higher magnetic flux density without decarburizing annealing or special finishing annealing. An object of the present invention is to provide a method capable of manufacturing a grain-oriented electrical steel sheet having the following properties.

(Means for Solving the Problem) As disclosed in the prior invention mentioned above, in order to eliminate the need for decarburization annealing, the C content in the steel should be reduced to 0.01% or less, and stable secondary recrystallization should be achieved. Sol to generate.

0.003-0.015% of AJ2 and 1.0% of FIn.
It is necessary to use ultra-low carbon steel containing 0 to 2.0% as the base material. However, with this alone, it is difficult to satisfy the magnetic flux density that has been required in recent years. However, the present inventors conducted various studies based on this prior invention and found that if a hot-rolled steel sheet is annealed in the alpha region of 700°C or higher before cold rolling, the magnetic flux density of the final product is significantly improved. I discovered that.

Here, the gist of the present invention is ``in weight %, c: o, ot% or less, Si: 1.5 to 3.0%, Mn: 1.0 to 2
．． 0%, S: 0.010% or less, So j! , A l
: 0.003~0.015%, N:0.001~0
．． 010%, the balance being Fe and unavoidable impurities. After annealing in the α region of 700°C or higher, cold rolling is performed once or twice or more with intermediate annealing in between. The method J for producing a grain-oriented electrical steel sheet is characterized in that the final sheet J7 is obtained by heating, followed by continuous annealing in the α region of 700° C. or higher, followed by finish annealing.

Hereinafter, the present invention will be described in detail (effects) First, the reason why each component of the base material hot rolled steel sheet is limited as described above will be explained together with the effects.

■　C: In the present invention, it is not necessary to actively include C.

Conventional production of oriented 1m steel sheet required some degree of metal &ll shadow formation to cause good secondary recrystallization to occur. Therefore, it has been necessary to perform decarburization annealing before final annealing in order to eliminate the adverse effects of C, which deteriorate the magnetic properties of the final product and make secondary recrystallization difficult to occur in final final annealing.

In the present invention, such decarburization treatment is not actively performed in the processes after hot rolling, so C is reduced as much as possible at the steelmaking stage to the extent that it does not adversely affect secondary recrystallization in finish annealing or magnetic aging of the final product. It is necessary to do so. If the C content in the steel exceeds 0.01% when carbon removal during the steelmaking stage is insufficient, secondary recrystallization during final annealing becomes difficult to occur, and deterioration due to air aging in the final product becomes significant. From, the C content is o, o
i% or less.

■Si: Si is an element that affects magnetic properties, and as the content increases to -1, iron loss improves. However, if the content is less than 1.5%, the effect of reducing iron loss is poor;
If the Si content is less than 0%, secondary recrystallization becomes unstable and workability decreases, making cold rolling difficult. Therefore, the Si content was set to 1.5 to 3.0%.

■ In ultra-low C materials like the present invention, PINs Mn promotes homogenization of hot-rolled steel plate &11 weave, hot-rolled steel plate annealing structure, and -next crystal structure, resulting in a high degree of accumulation in the Goss orientation. It is a preferable element that facilitates the occurrence of subsequent recrystallization. Also, Mn includes Mn5tNt, Mn, Si, Aj! , promotes the precipitation of nitrides containing Fe at the same time, and these precipitates become AIN
It is also thought that it exerts an inhibitory effect on secondary recrystallization and causes secondary recrystallization with a high degree of accumulation in the Goss orientation.

These effects cannot be sufficiently obtained with a content of less than 1.0%, while on the other hand, if it exceeds 2.0%, workability will decrease and cold rolling will be delayed. 1.0～
It was limited to 2.0.

■ S: In the present invention, iN, MnSi N, and -n, Si
, Aj! Since nitride containing Fe at the same time is used as an inhibitor to prevent crystal grain coarsening before secondary recrystallization, a large amount of S (0.020 to 0.030 %) is not required.

Rather, if a large amount of MnS is present, secondary recrystallization becomes unstable and iron 1-member deterioration occurs, so the content is preferably 0.010% or less to avoid such negative effects.

■Sol, A I Al is an important element that forms A2, which is the main inhibitor. ^2 content is 5 off, Al content is 0
．． The reason why it was set at 0.003% to 0.015% is that if it is less than 0.003%, the absolute amount of 8βN as an inhibitor is insufficient.
This is because a sufficient inhibitor effect cannot be expected, and 0
．． This is because if it exceeds 0.015%, the number of inhibitors becomes too large and the distribution form becomes inappropriate, making it difficult for stable secondary recrystallization to occur.

■ N N is AlN, Mr+SiNx, Mn, Si, ^
2. It is an important element that forms nitrides containing Fe at the same time and acts as an inhibitor that suppresses grain growth until secondary recrystallization occurs. However, if the N content is less than o, ooi%, the desired inhibitor effect cannot be obtained, and even if the content exceeds 0.010%, the inhibitory effect is saturated. The range was set at 0.010%.

Note that the remainder is Fe and unavoidable impurities.

In the present invention, a hot rolled steel plate having the above chemical composition is used as a base material,
After annealing this in the alpha range of 700°C or higher, it is cold rolled once or twice or more with an intermediate annealing in between to obtain the final plate thickness, and then at 700° for crystallization.
Continuous annealing in the α region of C or higher and final annealing for secondary recrystallization are performed to make the orientation a magnetic S plate.

The reason why each annealing condition is limited as described above is as follows.

(a) Hot-rolled steel sheet annealing base material The manufacturing process of the hot-rolled steel sheet does not need to be particularly limited; it may be obtained by any method as long as it has the above chemical composition.0 Important points: , the hot-rolled steel sheet having the above chemical composition is annealed in the alpha range of 700° C. or higher prior to the next cold rolling.

Figure 1 shows C: 0.002%, Si: 2.25%
, Mn: 1.51%, S: 0.004%, So
j! , All bow 0.008%, N: 0.00
A hot-rolled steel plate with a thickness of 2.3 mm obtained by hot rolling a slab consisting of 38% and the remainder consisting of PE and unavoidable impurities was subjected to continuous annealing at various temperatures for 1 minute, and then pickled. After cold rolling to obtain a cold rolled steel plate with a plate thickness of 0.51,
Magnetic flux density B in the rolling direction of a test piece obtained by continuous annealing at 00°C for 30 seconds and final annealing at 870°C for 48 hours
*This is the result of measuring (magnetic flux density when magnetized with a magnetizing force of 800 A/s).

In addition, for the first 24 hours of finish annealing, 50% N8 and 50
It was carried out in a mixed gas atmosphere of %US, and the second half was 10
0% ■ Conducted in an earthquake atmosphere.

As is clear from Figure 1, the hot rolled steel plate annealing temperature is 700
Below ℃, the improvement in magnetic flux density is small, but? There is a significant improvement at temperatures above 00°C. The reason why the magnetic flux density increases greatly when hot-rolled steel sheet is annealed at 700°C or higher is that the recrystallization of the hot-rolled steel sheet progresses and the homogenization of the structure is promoted, and the inhibitors AffiN, MnSi N 2 and Mn,
This is considered to be because the dispersion state of nitrides containing 5iSAffi and Fe at the same time is improved, and as a result, secondary recrystallization of Goss-oriented grains occurs with high precision in final annealing.

For the above reasons, in the present invention, hot rolled steel sheet annealing is performed at 700°C.
It was set to above °C.

Note that hot-rolled steel sheets may be annealed at a temperature exceeding 1000°C, but the effect of annealing is saturated and no improvement in magnetic flux density is observed, which is rather economically disadvantageous, so the desirable annealing temperature is 7.
00-1000°C. In addition, this hot rolled steel plate annealing may be continuous annealing or box annealing, and in the case of continuous annealing, 800~
In the case of one-box annealing at 1000°C, the desired temperature range is 700 to 850°C for uniformity of the structure.

(b) Intermediate annealing Intermediate annealing is performed for the purpose of softening the rolled material between cold rolling when a hot rolled steel plate is cold rolled twice or more to reach its final thickness. Although there is no need to particularly limit the conditions for intermediate annealing, it is desirable that the intermediate annealing temperature be the same as the continuous annealing temperature after cold rolling described below.

(C) Continuous annealing after cold rolling This continuous annealing to cause primary recrystallization is performed at 700°
Conducted in the α range of C or higher. -AIN, MnSi N, and Mn, Si, Aj in the next crystal annealing! , F
The precipitation of nitrides containing e at the same time, the secondary recrystallization grain size, and the primary recrystallization texture are important for causing desirable secondary recrystallization in the subsequent final annealing. For this purpose, it is preferable to set the annealing temperature in the α range of 700° C. or higher and perform continuous annealing at a heating rate of 5° C./sec or higher.

If the annealing temperature is less than 700°C, primary recrystallization may not occur sufficiently. On the other hand, when annealing is performed at a high temperature that produces the T phase, a good A7! The dispersion state of N, the -order recrystallized grain size, and the first-order recrystallization texture cannot be obtained.

Although it is desirable to hold this annealing temperature for 5 seconds or more, holding it for 10 minutes or more does not make any difference in the effect and only reduces the productivity of the continuous annealing furnace.

(d) Finish annealing Finish annealing can of course be carried out by the steel sheet manufacturer, but it can also be carried out by the user as strain relief annealing.

In final annealing, it is important to sufficiently develop secondary recrystallization in the Goss orientation. As conditions for final annealing, it is common to maintain the temperature in the α region of 800° C. or higher for about 10 to 60 hours.

Finish annealing is preferably carried out in an Nz-containing atmosphere until secondary recrystallization is completed.In the present invention, AIN and Mn5
Since a nitride containing iNz and Mn, Si, Al, and Fe at the same time is used as an inhibitor, if denitrification occurs before secondary recrystallization occurs, the amount of nitride precipitation decreases, and secondary recrystallization becomes ineffective. It becomes stable.

The present invention will be further explained below with reference to Examples.

(Example 1) Hot-rolled steel plate with the chemical composition shown in Table 1 (plate thickness 2.3ma+)
was continuously annealed at 900°C for 1 minute, then cold-rolled once while pickling to give a plate thickness of 0.35I1m, and then continuously annealed at 900°C for 1 minute for next crystallization. After annealing and applying an annealing separator, heat to 880°C.
Finish annealing was performed to perform secondary recrystallization for 48 hours. Finish annealing is the first half of soaking where secondary recrystallization occurs.
The annealing was performed in a mixed gas atmosphere of 75% N and 25% x8, and the latter 24 hours was performed in a 100% H2 atmosphere for the purpose of purification annealing.

Regarding the magnetic properties of the thus obtained grain-oriented electrical steel sheet, the magnetic flux density and iron loss in the rolling direction were investigated. The results are also shown in Table 1.

(Hereinafter, blank space) In Table 1, test steels (a) to (e) are Sol, A
The contents of all the other elements except 1 are the same.

Among them, Sol, AI! Test steel (a) with a lower value than the range specified by the present invention and sample N (e with a higher value)
) and those of test Nαl and 5 produced from Nαl and 5 had significantly inferior magnetic properties. Similarly, test steels (f) and (g) are S and test M
(h) and (i) have almost the same content of N, and the test steels (j) and (k) have almost the same content of other elements except -〇, but S
Test NQ7 where N is high, test Nα8 where N is low, and test Na1l where in is low are all inferior in magnetic properties. The steel type (1) of test Nα12 has a low Si content. Although this product has no difference in magnetic flux density from the example of the present invention, it has inferior iron loss, and test k1
Steel type (b) of the present invention example, which has almost the same composition except for C, has a high C value.
, (C), and (d) are compared with tests Nα2 to Nα4 using iron. In contrast to these comparative examples, all of the inventive examples have good magnetic properties.

(Example 2) Plate thickness 2.3 m1 with the same composition as steel type 0 used in Example 1
After using the hot rolled sheet of No. 1 as the base material and making it to the final thickness under various conditions as shown in Table 2, annealing is performed to cause crystallization, and an annealing separator is applied. Finish annealing was performed to perform secondary recrystallization.

The final annealing was performed in the same atmosphere as in Example 1.

Regarding the magnetic properties of the thus obtained grain-oriented electrical steel sheet, the magnetic flux density and iron loss in the rolling direction were investigated. The results are also shown in Table 2.

(Hereinafter, blank space) As is clear from Table 2, all of the inventive examples of Test Nos. 16 to 19 had good magnetic properties, whereas
Comparative examples of Test No. 14 in which hot-rolled steel sheet annealing was omitted, Test Nα15 in which hot-rolled steel sheet annealing temperature was low, and Test No. 20 in which primary recrystallization annealing temperature was low were inferior in magnetic properties.

(Effects of the Invention) As explained above, according to the method of the present invention, it is possible to stably produce a grain-oriented electrical steel sheet having excellent magnetic properties and having secondary recrystallized Mi fibers with a highly accurate Goss orientation.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between hot rolled steel sheet annealing temperature and magnetic flux density of the final product.

Claims (1)

[Claims] In weight%, C: 0.01% or less, Si: 1.5 to 3.0%, Mn:
1.0-2.0%, S: 0.010% or less, Sol. A
l: 0.003-0.015%, N: 0.001-0.
010%, remainder: Fe and unavoidable impurities A hot-rolled ultra-low carbon steel plate is annealed in the alpha range of 700°C or higher, and then cold-rolled once or twice or more with an intermediate annealing in between to form the final product. A method for producing a grain-oriented electrical steel sheet, comprising: reducing the thickness of the sheet, then continuously annealing in the α region at 700° C. or higher, and then finishing annealing.