JPH01309924A - Grain-oriented magnetic steel sheet and its production - Google Patents

Abstract

PURPOSE:To stably produce the subject grain-oriented magnetic steel sheet having a high magnetic characteristic at a low cost by hot-rolling a slab consisting of C, Si, Mn, S, Al, N, and Fe and having a specified composition, annealing, then cold-rolling, and annealing the obtained sheet under specified conditions. CONSTITUTION:A slab contg., by weight, <=0.01% C, 1.8-4.0% Si, 0.05-0.20% Mn, 0.003-0.015% S, 0.003-0.015% soluble Al, 0.0010-0.0100% N, the balance Fe, and inevitable impurities is heated at <=1270 deg.C, hot-rolled at the finish temp. of 700-900 deg.C, and wound at <=600 deg.C. The hot-rolled sheet is then continuously annealed at 950-1050 deg.C for 10sec-10min. The hot-rolled sheet is cold-rolled once or >=2 times with process annealing to the final thickness. The cold-rolled sheet is then continuously annealed at 950-1050 deg.C for 10sec-10min to cause primary recrystallization. The cold-rolled sheet is further finish-annealed at 800-1000 deg.C to cause secondary recrystallization. By this method, a grain-oriented magnetic steel sheet having an excellent magnetic characteristic in the rolling direction is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a directional magnetic MS plate at low cost and having good magnetic properties in the rolling direction.

(Prior Art) Grain-oriented electrical steel sheets are 7!1 magnetic materials with excellent excitation characteristics in the rolling direction and iron bJ characteristics, and are widely used in various electrical equipment applications including transformer cores.

By the way, the manufacturing process for grain-oriented steel sheets is more complex and special than that of general cold-rolled steel sheets or non-oriented electrical steel sheets.
The cost is very high. For these reasons, cost reduction by improving the manufacturing process has become an important issue for grain-oriented electrical steel sheets.

The general manufacturing process for grain-oriented electrical steel sheets is to first heat a slab to a high temperature of 1,300°C or higher, solutionize AIN and MnS, hot-roll it, and then annealing the hot-rolled sheet and then rolling it once or twice with intermediate annealing. The above cold rolling is performed to obtain the final plate thickness. Then, C in the steel is lowered to a low level by decarburization annealing, and crystals are adjusted. Finally, in the batch furnace, 1
Final annealing is performed at 100 to 1200°C to cause secondary recrystallization and to purify the steel (desulfurization and denitrification).
That's why.

High-temperature heating of slabs is essential for optimizing the dispersion state of AIN and MnS, which are inhibitors of secondary recrystallization, but heating above 1300°C requires a special dedicated furnace and requires scale loss. There are also problems in terms of energy costs.

In addition, decarburization annealing uses AI!
, N, and MnS in order to reduce the amount of C necessary for the purpose of optimizing the dispersion state of MnS to a level that does not cause problems in terms of magnetic properties, but it is very costly.

Furthermore, high-temperature, long-term annealing as final annealing is required to remove precipitates that are harmful to the magnetic properties of the finished product, especially MnS, but long-term treatment at high temperatures of 1100 to 1200°C is costly. This is a major cause of the increase. That is, in order to reduce the cost of grain-oriented F iff steel sheets, it is essential to reduce the cost of these heat treatments.

As an attempt to reduce the cost of heat treatment, there is, for example, a method shown in Japanese Patent Application Laid-open No. 100627/1983.

This is less than 0.02% CO, less than 5% Si, and SO.

015% or less, Ai, 01-0.08%, No, 01%
The following steel materials are slab-heated at 1270°C or less, hot-rolled, hot-rolled plate annealed, cold-rolled, and crystal annealed.
Annealing is performed to provide a temperature difference of 2° C. or more per 1 cn+ parallel to the four-plate mask to cause secondary recrystallization.

In this method, the slab can be heated at a temperature of less than 1300° C., so a special dedicated furnace is not required, and scale loss and energy costs are reduced.

Furthermore, since Cl can be lowered in advance, there are advantages such as no need for decarburization treatment during the process.

[Problem to be solved by the invention]

However, in this method, the inhibitory effect of Ap and N is not sufficiently exhibited, and it is difficult to obtain stable secondary recrystallization. This cannot be said to be a practical method as it requires a special annealing process that applies a temperature difference to the plane of the IL plate face plate.

By the way, the present inventors have been conducting research on grain-oriented electrical steel sheets for some time, and have already proposed several useful manufacturing methods. One of them is JP-A-62-83421.
(hereinafter referred to as "first application").

This is basically an extremely low carbon (C50,010%) and A
A steel material containing a very small amount of L (0,003 to 0.015%) is used as a raw material, and after hot rolling and cold rolling, it is finished by annealing to perform primary recrystallization under the required conditions and secondary recrystallization. Annealing is performed. This method can effectively bring out the inhibitor effect of AIN, can omit decarburization annealing, and can generate secondary recrystallization with low-temperature annealing in the α region for final annealing, so it is cost effective. Very advantageous.

The method of the earlier application is thus highly effective, but
Regarding magnetic properties, there are many demands for better performance than this.
Further improvement is desired.

The present invention further develops the technology of the prior application and aims to provide a method for manufacturing a grain-oriented electrical steel sheet that can ensure higher and more stable magnetic properties while taking advantage of its advantages.

[Means to solve the problem]

The inventors of the present invention have described the work when applying the prior art.

In order to find an effective means to improve the secondary recrystallization behavior in the upper annealing process, that is, the Goss orientation fl101 <001> integration degree of the secondary recrystallized grains, we have conducted intensive experiments and research, and have found the following knowledge. Obtained.

In order to increase the degree of Goss orientation integration of secondary recrystallized grains, it is necessary to utilize a small amount of MnS as an inhibitor in addition to AIN.

In order to effectively bring out the inhibitor effect of MnS under a low temperature condition where the slab heating temperature is 1270°C or less, Mn 0.05% to 0.20%, 30.003
It is important that the content be in the range of 0.015%.

In this case, the processing conditions include a hot rolling finishing temperature of 7.
It is necessary to set the temperature in the range of 00 to 900 °C, and furthermore, the hot rolled Fi annealing and the primary recrystallization annealing after cold rolling should be carried out in the range of 950 to 900 °C.
Continuous high temperature annealing at 1050°C is effective.

The present invention is based on the above findings, and its gist is the method described below.

C0.01% or less, Si1.8-4.0%, Mr+0.
05-0.20%, 30.003-0.015%, S,
ol・Aβa, oos~0.015%, N0.0010
A slab containing 100% -0゜0 with the remainder consisting of Fe and unavoidable impurities is heated to 1270℃ or less, hot rolled at a finishing temperature of 700 to 900''C, and then heated to 600℃.
After coiling at the following temperature, hot-rolled plate is annealed by continuous annealing at a temperature of 950℃ and 1050℃ for 10 seconds or more and 10 minutes, followed by cold annealing once or twice or more with intermediate annealing. After rolling to obtain the final plate thickness, continuous annealing is performed at a temperature of 950°C to 1050°C for 10 seconds or more and 10 minutes to control primary recrystallization, and then further annealed at 800°C -
1. A method for producing a grain-oriented electrical steel sheet, characterized in that secondary recrystallization is caused by final annealing of 1 o o o'c.

[For production]

Hereinafter, each constituent feature of the present invention will be explained specifically and in detail, and its effects will be clarified.

○ First, the reasons for limiting the steel composition of the slab used are as follows.

C: When the amount of C in the steel exceeds 0.01%, unfavorable phenomena in terms of magnetic properties, such as deterioration of the strength of the iron and deterioration of magnetic aging, become noticeable. Therefore, C was set to 0.01% or less. In addition,
The lower limit of C is not specified because it is more advantageous to have less C in terms of magnetic properties.

Incidentally, conventional grain-oriented electrical steel sheets usually contain about 0.025 to 0.085% C at the raw material (hot rolled sheet) stage, and this is added in the process after cold rolling. The amount of C in the product is reduced by decarburization annealing. This is based on the idea that the C content up to the middle of the process optimizes the dispersion state of AfN and MnS as inhibitors and helps improve the magnetism of the final product, but the present invention does not include such C. TomoAl! This allows N and MnS to act effectively as inhibitors, and there is no need to include C in the steel material. Rather, it is necessary to keep it extremely low in advance in order to omit decarburization annealing.

Sl: Effective in reducing iron content by increasing specific resistance, 1
．． The effect is noticeable when the content is 8% or more. However, a content exceeding 4% makes cold rolling difficult. Therefore, it was set at 1.8 to 4.0%.

Incidentally, in practice, Sil is determined so that the required magnetic properties (iron loss, magnetic flux density) can be obtained within this specified range.

Mn: Mn acts as an inhibitor together with S
It generates nS and plays an important role in stabilizing secondary recrystallization. However, when the Mn content exceeds 0.20%, 1270
``If the slab is heated below C, MnS may not be sufficiently dissolved, and the inhibitor effect of MnS may not be exhibited.Furthermore, in the case of 0.05% grooves, brittleness during hot rolling due to FeS may be a problem. Therefore, Mn@ is 0.05
~0.20%.

SO3 is an important element that forms the aforementioned Mn and MnS and stabilizes secondary recrystallization.

Figure 1 shows the 6f1 flux density B in the rolling direction by changing the S view.
(Magnetic flux density when magnetized with a magnetizing force of 800 A/m) was investigated.

That is, as the sample material, C0,001-0.003%,
Si2.9~3.1%, Mn0.010~0.015%
, S o 1. Aj20.006~o, o o s
%, No. 0025 to 0.0035% (range of the present invention), slabs were heated at a slab heating temperature of 1230°C.
1 Finishing temperature of hot rolling 820-880℃ 1 Coiling temperature 5
After hot-rolling the sheet to a thickness of 2.3 m at 10 to 570°C, the hot-rolled sheet was continuously annealed at 950°C for 1 hour and descaled by pickling, and then cold-rolled to 0.30a. 9
Continuous annealing was performed at 50°C for 30 seconds, and after applying the annealing separation material, 9
Finish annealing was performed in a batch annealing furnace soaking at 00° C. for 24 hours.

There is a large variation in the value of B in the range where the amount of S added exceeds 0.003% and 0.015%. This is considered to be because such an amount of S makes the amount and precipitation form of MnS, which acts as an inhibitor, inappropriate. On the other hand, when sl is in the range of 0.003 to 0.015%, the value of B is always at a high level, and it is understood that the secondary recrystallization is stable. Therefore, sl was set to 0.003 to 0.015%.

Sol, Al: Al is an element necessary to form AlN, which is the main inhibitor of the present invention, and to suppress grain growth of primary recrystallized grains, and the regulation of its addition amount has an important meaning in the present invention.

The Al content is Sof, A/! The reason why the amount was set at 0.0.03% to 0.015% is that if it is less than the lower limit, the absolute amount of AffiNl as an inhibitor will be insufficient and a sufficient effect cannot be expected, whereas if it exceeds the positive limit, the inhibitor This is because the distribution form of the steel becomes inappropriate, and stable secondary recrystallization cannot be obtained in final annealing.

N: An element essential for the formation of AlN as an inhibitor, and from this point of view, it is required to be at least 0.0010%. However, even if the content exceeds 0.0100%, there is no meaning in terms of inhibitor effect. Therefore, N is 0
．． It was determined to be 0.0010% to 0.0100%.

Next, the manufacturing process will be described.

The method of the present invention basically uses a slab that conforms to the above-mentioned component conditions, and performs continuous annealing (slab heating - 0 hot rolling - + coiling screaming hot rolled plate annealing intermediate cold rolling) (continuous annealing (after cold rolling) A grain-oriented electrical steel sheet is manufactured through the process of finishing annealing (annealing).

Each step will be explained below.

■ Slab heating direction! Slab heating in the manufacture of magnetic steel sheets requires 1300
It was customary to carry out at very high temperatures of ~1400°C. This is because in order for AlN and MnS to precipitate in a state (size, dispersion state) that is effective as an inhibitor in the process after hot rolling, it is necessary to sufficiently dissolve AIN%MnS at the slab heating stage. This is because we recognize that there is. However, such high-temperature heating of slabs is fraught with problems, such as reduced yields due to slag generation, increased energy costs, and problems with the heating furnace, and the implementation cost is high due to the need to prepare a special dedicated furnace. Very descendant.

One aim of the present invention is to reduce costs by lowering the heating temperature of this slab heating.

For this purpose, a method is adopted in which the amount of AIN and MnS in the steel is made smaller than usual, and a small amount of AIN and MnS is efficiently utilized as an inhibitor.

According to this method, the heating temperature of the slab is sufficient to be 1270°C or lower, which is the same as that for cold-rolled steel sheets, and by heating at this low temperature, the inhibitor effect is sufficiently expressed, and the secondary recrystallization is stable in the final annealing process. It will be ensured that Therefore, in the present invention, the heating temperature of the slab is set to 12
The temperature was limited to 70°C or lower.

Incidentally, at such a low temperature, direct charging (roll), which has been popularly used in recent years from the perspective of energy conservation, is necessary.
That is, it is also possible to adopt a method in which the slab is directly charged into a heating furnace without being cooled, subjected to heating and recuperation treatment, and immediately subjected to hot rolling.

The lower limit of the slab heating temperature is not particularly limited, but heating to 1000° C. or higher is desirable in view of actual operation such as the capacity of the rolling mill.

■ Finishing temperature of hot rolling This is an important manufacturing condition for stabilizing secondary recrystallization. If the finishing temperature exceeds 900°C, secondary recrystallization becomes unstable, causing variations in magnetic properties.

This is due to the precipitation state of /IN and MnS during hot rolling, or the aggregated texture of the hot rolled sheet is Goss-oriented ((1101<
It is thought that this is because it becomes unsuitable for secondary recrystallization where 001>1, but the details are not yet clear.

On the other hand, when the finishing temperature falls below 700°C, problems arise in shape control, etc. with current hot rolling equipment. Therefore, the hot rolling finishing temperature was set in the range of 700 to 900°C.

(2) Coiling temperature In the present invention, AIN precipitated during hot-rolled sheet annealing and subsequent steps plays an important role as an inhibitor. Therefore, when the coiling temperature exceeds 600° C. and precipitation of AlN progresses in the coiled state, the amount of AffiN precipitated in the steps after cold rolling decreases, and secondary recrystallization becomes unstable. Therefore, the winding temperature was set to 600° C. or lower. In addition,
The lower limit is not set because it does not pose a problem in terms of magnetic properties.

■ Hot-rolled sheet annealing Hot-rolled sheet annealing is necessary to prevent the occurrence of flashing and to precipitate and disperse AlN. Ridging is a surface undulation extending linearly in the rolling direction that occurs when a hot-rolled sheet of high-Si steel such as the steel of the present invention is cold-rolled with unrecrystallized portions remaining. To prevent this, it is necessary to completely recrystallize the hot rolled sheet, which requires continuous annealing at 800° C. for 10 seconds or more.

In addition, AIN precipitated during hot-rolled sheet annealing is important as an inhibitor for secondary recrystallization, and in order to achieve this appropriate dispersed precipitation state and increase the degree of accumulation of Goss-oriented grains, rapid heating to 950 °C is necessary. Exceeding annealing is suitable. Also 1
Hot-rolled sheet annealing above 0.050 is inappropriate for AIN dispersion. In addition, there is no practical meaning even if the soaking time for hot-rolled sheet annealing exceeds 10 minutes.
The temperature was 10 seconds or more and 10 minutes or less at 05°C or lower.

■Cold rolling Cold rolling is cold rolling once, but it does not matter if it is cold rolling twice or more with intermediate annealing. The conditions for intermediate annealing are preferably continuous annealing at 800 to 950°C, but are not particularly specified.

■ In order to generate secondary recrystallization with a high degree of accumulation in the Goss orientation after continuous annealing after cold rolling, it is necessary to need to be an appropriate combination.

This is achieved by continuous annealing after achieving the final plate thickness. This annealing requires rapid and rapid heating, and continuous annealing is suitable. As conditions for annealing, a heating rate of 5° C./S or higher is desirable.

If the annealing temperature is below 950℃ or 1050℃,
The aforementioned texture, ferrite grain size, inhibitor precipitation, etc. are not appropriate, and the degree of Goss orientation accumulation in secondary recrystallization becomes low. Further, if the annealing time is less than 10 seconds, the annealing effect cannot be obtained, and soaking for more than 10 minutes is actually unnecessary.

From the above, the continuous annealing conditions after cold rolling were set at 950°C.
The temperature was 10 seconds or more and 10 minutes or less at a temperature of 1050°C or less.

(2) Final annealing The present invention is mainly aimed at producing stable secondary recrystallization through low-temperature final annealing through proper ratio of components, and final annealing does not include so-called high-temperature purification annealing of 1000° C. or higher. This leads to cost reduction.

If the final annealing temperature is less than 800°C, secondary recrystallization will not occur and good magnetic properties cannot be expected. Further, in the present invention, relatively small amounts of AP, N, and MnS are used as inhibitors, and secondary recrystallization is sufficient at less than io o o'c. Therefore, it was annealed at 800 to 1000°C.

Although the atmosphere for final annealing is not particularly limited, it is desirable to use an atmosphere containing nitrogen until the secondary recrystallization is completed in order to strengthen the inhibitory effect of AP and N.

Note that before final annealing, there is generally a step of applying a surface treatment such as an annealing separation material to prevent seizure.

[Example] Continuously cast slabs with various component systems shown in Table 1 were directly charged into a slab heating furnace without being cooled to room temperature, and subjected to hot rolling → hot rolled sheet annealing → cooling under the conditions shown in the table. Inter-rolling → continuous sintering →
Finish annealing was performed, and the iron tJIW1-150 in the rolling direction and the magnetic flux density B were measured. In addition, each test material was descaled before or after hot-rolled plate annealing. Furthermore, an annealing separation material was applied before final annealing. Magnetic measurement is 30 mm wide and 280 mm long according to JIS C2550.
An Epstein specimen was cut and collected from the rolling direction.
“This was done after strain relief annealing of CX2h.

Explain the test results.

Seeds 1 to 4 are examples in which all conditions except sl are substantially the same (satisfying the conditions of the present invention), and sl is varied in various ways.

With respect to Nα2.3 of the present invention example, sl deviated from the range of the present invention at low and high levels (hereinafter, "deviated" means "deviated from the range of the present invention"). ..., the magnetic flux density is greatly inferior.

Nα5 to Nα7 have the same composition but have different finishing temperatures during hot rolling, and Nα5 with a higher finishing temperature is inferior to N116.7 under proper conditions in both iron loss and f11 east density.

Nf18-13 are hot-rolled sheets with the same composition but with different annealing conditions.Among the strips 8-12 that adopted continuous annealing, Nf18-13 had a lower annealing temperature and had good magnetic properties. However, occurrence of ridging is observed.

On the other hand, at an appropriate temperature of klO~12, both the ridging properties and magnetic properties are good. In addition, Nα13, which was subjected to hot-rolled sheet annealing by batch annealing, has good ridging properties, but the secondary recrystallization is not stable and the magnetic properties are poor. The method can stably produce grain-oriented electrical steel sheets with high-level magnetic properties without performing costly heat treatments such as high-temperature slab heating, decarburization annealing, and high-temperature finishing annealing.

[Brief explanation of the drawing]

FIG. 1 is a plot of experimental data showing the relationship between S content and magnetic flux density B.

Claims (1)

[Claims] 1. In weight%, C 0.01% or less, Si 1.8 to 4.0
%, Mn0.05-0.20%, S0.003-0.0
15%, Sol. Al0.003-0.015%, N0
．． 0010 to 0.0100%, with the remainder being Fe and unavoidable impurities, is heated to below 1270°C,
Hot rolling is carried out at a finishing temperature of 700 to 900°C,
After winding at a temperature below ℃, 950℃ and 1050℃
Hot-rolled plate is annealed by continuous annealing for 10 seconds to 10 minutes at the following temperature, and then cold rolled once or twice or more with intermediate annealing to obtain the final thickness, and then heated to 950°C.
Continuous annealing for 10 seconds to 10 minutes at a temperature of 1050°C or lower to cause primary recrystallization, and further
A method for producing a grain-oriented electrical steel sheet, characterized in that secondary recrystallization is caused by final annealing at 000°C.