JPS61124527A - Manufacture of nonoriented electrical steel sheet - Google Patents

Abstract

PURPOSE:To improve the magnetic characteristics of a rolled steel strip contg. prescribed percentages of C, Si, Mn, sol. Al and P by forming a rapid heating and rapid cooling region in a soaking zone so as to facilitate the growth of crystal nuclei when the steel strip is continuously annealed. CONSTITUTION:A steel strip contg. <=0.02% C, 0.1-1% Si, 0.1-0.3% Mn, <=0.001% sol. Al and <=0.2% P is hot rolled and cold rolled to obtain a steel strip. When the steel strip is continuously annealed, in a rapid heating and rapid cooling region formed in a soaking zone, the steel strip is rapidly heated from the furnace temp. of the soaking zone and then it is rapidly cooled to the furnace temp. of the soaking zone.

Description

[Detailed description of the invention] 11 Ω month j difference! The present invention relates to a method for manufacturing a non-oriented electrical steel sheet.

More specifically, the present invention relates to the improvement of a continuous annealing method for cold-rolled steel sheets for electrical steel sheets, which has excellent magnetic properties and is free from indentation and heat buckling caused by build-up of oxides and the like on hearth rolls. The present invention relates to a method for manufacturing grain-oriented electrical steel sheets.

BACKGROUND ART Non-oriented electrical steel sheets are usually subjected to final annealing in a continuous annealing furnace, and subjected to treatments such as coating to become products.

In that case, the larger the crystal grains of the material, the more advantageous the magnetic properties of the negative product become. Therefore, the higher the final annealing temperature, ie, the furnace temperature in the soaking zone of the continuous annealing furnace, is as high as possible in the range below the Ar= point, the larger the crystal grains can be obtained, and therefore the better the magnetic properties can be obtained.

However, in the case of a vertical continuous annealing furnace, if the furnace temperature in the soaking zone is raised, there is a problem that quality defects may occur due to intrusion due to build-up of oxides etc. on the hearth roll, heat buckling, etc.

Build-up is generally a foreign matter on the hearth roll that grows when oxides on the steel surface come into contact with the hearth roll and are transferred onto the roll, which causes so-called "push-in" defects on the steel surface. Therefore, the higher the temperature of the soaking zone, the more likely they are to occur.On the other hand, even if there is build-up on the hearth roll, if the temperature of the steel plate is low when it comes into contact with the hearth roll, push-in scratches due to build-up are less likely to occur.

On the other hand, a heat buckle is a "deflection" defect in a steel sheet due to contact with a hearth roll. This is thought to be because the hearth roll has a crown, so when the steel plate comes into contact with the hearth roll, the strength of the steel plate is low, and the steel plate undergoes plastic deformation when the temperature is high. Therefore, the temperature of the heat buckle is high, and if the plate thickness is thin and the material has low mechanical strength, cracks are likely to occur.

On the other hand, the magnetic properties of electrical steel sheets are extremely sensitive to strain, and even the slightest strain deteriorates the magnetic properties, so if push-in or heat buckling occurs due to build-up during final annealing,
To correct these, it is not possible to apply light reduction using a temper mill or the like.

For the above reasons, in the conventional vertical continuous annealing furnace, in order to improve the magnetic properties, final annealing is performed at a soaking temperature of 800°C or higher, and distortions such as indentation and heat buckling are avoided as much as possible. To avoid this, it is sometimes necessary to perform annealing at a soaking temperature of about 700°C, making it extremely difficult to manufacture high-quality non-oriented electrical steel sheets with excellent magnetic properties by continuous annealing. .

Problems to be solved regarding H generation The purpose of the present invention is to solve the above-mentioned drawbacks of the prior art.More specifically, in annealing non-oriented electrical steel sheets in a continuous annealing furnace, Provided is a method for manufacturing a non-oriented electrical steel sheet that can impart magnetic properties equivalent to continuous annealing at high temperatures without causing heat buckling of the steel sheet due to indentation due to build-up of oxides, etc. and contact with hearth rolls. It's about doing.

Still another object of the present invention is to provide a simple and economical method for manufacturing a non-oriented electrical steel sheet that has excellent magnetic properties, a beautiful surface and no distortion.

Means for Solving the Problems In order to achieve the above object, according to the present invention, C:0
．． 02% or less, Si: 0.10-1.00%, Mn: 0.1-0.3%, Sol, Al: 0.0% or less, P: 0.2% or less, and the remainder When steel consisting of iron and unavoidable impurities is hot rolled, pickled and cold rolled, and the resulting copper strip is continuously annealed in a continuous annealing furnace, a rapid heating and cooling zone is provided in the soaking zone, and the steel is A method is provided for producing a non-oriented electrical steel sheet with good magnetic properties by rapidly heating a strip above the furnace temperature in a soaking zone and then rapidly cooling it to the furnace temperature in a soaking zone.

It is desirable that the maximum temperature in the rapid heating and cooling zone in the soaking zone be 100 to 300 degrees Celsius higher than the furnace temperature in other parts of the soaking zone.

An induction heating method or a resistance heating method can be adopted as a heating method for the rapid heating and cooling zone. However, in the method of resistively heating a copper strip by rolling current, the current-carrying roll reaches a high temperature, so care must be taken to avoid build-up of oxides on the current-carrying roll and heat buckling. Heating is preferred.

Further in accordance with an aspect of the invention, it is preferred that the furnace temperature in other portions of the soaking zone be equal to the recrystallization temperature of the copper strip to minimize build-up and heat buckling in these portions.

The reason for limiting the conditions of the method for manufacturing a non-oriented electrical steel sheet according to the present invention described above will be explained.

■Reason for limiting the range of components C: C precipitates as a carbide during annealing and deteriorates the magnetic properties. If the C content exceeds 0.02%, desired magnetic properties cannot be obtained, so it was decided to reduce the C content as low as possible within the range of 0.02% or less to provide good magnetic properties.

Sl: Sl is an element effective in reducing iron loss and is a necessary element for electrical steel sheets. If the Si content is less than 0.10%, the above-mentioned iron loss reduction effect will be insufficient. On the other hand, if the Si content exceeds 1.00%, weldability and descaling properties in a continuous line will be significantly deteriorated. In order to maintain the magnetic properties required for a non-oriented electrical steel sheet and to take into consideration weldability, the Si content was set in the range of 0.10 to 1.00%.

Mn: Mn is an effective element for imparting strength, and 0.1%
If the Mn content is less than that, it is difficult to provide a predetermined strength that can withstand punching. On the other hand, since Mn, as MnS, is an element that inhibits the growth of crystal grains and deteriorates magnetic properties, the upper limit of its content was set to 0.3%.

Sol, Al: AI is an element that combines with N in steel to form AIN and inhibits the growth of crystal grains during annealing. Therefore, Sol,A
A lower I content is desirable from the viewpoint of improving magnetic properties.

However, the addition of A1 is necessary in order to economically carry out deoxidation treatment in the steel manufacturing stage and to secure the casting temperature during continuous casting. Therefore, the content of Sol and AI is 0.0
01% or less.

P: P is an effective element for imparting strength and improving punching properties, but if it is contained in a large amount, problems such as cracking of the slab and reduction in rollability will occur, so for manufacturing process reasons, the P content is reduced to 0. It was set to 2% or less.

(2) Regarding rapid heating and cooling in the soaking zone: According to the method of the present invention, a rapid heating and cooling zone is provided in the soaking zone of a continuous annealing furnace for non-oriented electrical steel sheets to promote the growth of crystal grains.

The present invention will now be described in detail with reference to the accompanying FIG.

FIG. 1 is a schematic diagram of a vertical continuous annealing furnace used to carry out the method of the present invention. As shown in the figure, the vertical continuous annealing furnace is composed of a heating zone Z1, a soaking zone Z2, and a cooling zone Z. The steel strip S sequentially travels in the direction of the arrow through a heating zone Z1, a soaking zone Z2, and a cooling zone Z3 via hearth rolls R1, R2, . . . R3.

According to the present invention, in the illustrated example, a rapid heating and cooling zone P is provided between the hearth rolls R7 and R in the soaking zone Z2.

Figure 2 is an enlarged view of the rapid heating and cooling area. As shown in the figure, the rapid heating and cooling zone P for carrying out the method of the present invention is provided in the running portion of the steel strip C running between the two hearth rolls Ri and Rl+1. This rapid heating and cooling zone P is composed of an induction coil (2) and a group of gas nozzles N that inject cooling gas onto the surface of the steel strip S. As the cooling gas, inert gas such as N, Ar, etc. is preferably used.

In the example shown in Fig. 2, only the portion of the steel strip S surrounded by the induction coil is rapidly heated, and the cooling gas is immediately cooled down to the furnace temperature in the soaking zone, so that the temperature rise of the hearth roll R1 is suppressed. It never happens.

In other words, the growth of crystal grains in the copper strip S is significantly promoted by the rapid heating by induction heating, and as a result, the furnace temperature in other parts of the soaking zone can be set much lower than in normal cases, which reduces the oxidation of the hearth roll. Build-up of objects, heat buckling, etc. can be effectively prevented.

Through many years of experiments, the present inventors have found that the growth of crystal grains, which affects magnetic properties, is controlled by the heating temperature rather than the soaking time. Based on the findings. Therefore, the length of the rapid heating and quenching zone employed in the method of the present invention, that is, the time for holding the high temperature after rapid heating, is not so important, and may be about 10 seconds, and the length of the rapid heating and quenching zone employed in the method of the present invention is not so important. The burden is also small.

The rapid heating temperature is within the range of ^r1 point of the steel to be treated, and the higher the temperature, the greater the grain growth effect. On the other hand, even if the furnace temperature in the soaking zone is about 100° C. lower than the conventionally required 800° C., magnetic properties almost the same as those of the conventional method can be obtained by the rapid heating and cooling process. Therefore, in a preferred embodiment of the present invention, the furnace temperature in the soaking zone is approximately 700°C, and the rapid heating temperature is approximately 800°C.
〜900℃.

The rapid heating and cooling zone for implementing the method of the present invention described above is not limited to the exit side of the soaking zone as shown in FIG. 1, but may be provided at any location.

Figure 3 shows the case where the rapid heating and cooling area is provided at the entrance of the soaking area (
The heat patterns are shown for I), when it is provided in the center (II), and when it is provided on the exit side (III). Each rapid heating and cooling process is completed in about 10 seconds and can be carried out without heating the hearth roll. In addition, the results of improving the magnetic properties are almost the same regardless of the heat pattern treatment.

Hereinafter, the present invention will be explained with reference to Examples, but these Examples are merely illustrative of the present invention and do not limit the technical scope of the present invention in any way.

Example Molten steel refined in a converter was vacuum degassed and decarburized by the RH method, ^l was added to the treated molten steel to raise the molten steel temperature, the molten steel temperature was adjusted, and continuous casting was performed. The obtained slab was heated to a temperature of 1250°C or higher, and hot rolled at a finishing temperature of 790°C and a winding temperature of 630°C to obtain 2.3
A copper strip having a thickness of mm was prepared, and after pickling treatment, it was cold rolled to a thickness of 0.5 mm.

The cold rolled steel strips thus obtained each had a chemical composition shown in Table 1, and were subjected to continuous annealing under the conditions shown in Table 1 according to the method of the present invention and the method of the prior art. In the table, the heat pattern refers to any of the heat patterns shown in FIG.

The magnetic properties of the steel strip after continuous annealing were measured by the Epstein method according to JIS C2550, and the results are shown in Table 1. Furthermore, the crystal grain size was measured and is also shown in Table 1.

As can be understood from the results shown in Table 1, in the method of the present invention, the furnace temperature in the soaking zone is as low as 700°C, which is a temperature that does not cause build-up to the nozzle roll or heat buckling, compared to the conventional method. Almost the same magnetic properties as those obtained by soaking at furnace temperatures of 800°C and 900°C can be obtained. Furthermore, the copper strips after continuous annealing produced by the method of the present invention had a beautiful appearance and a constant shape, and no heat buckling was observed, which was observed in the case of the prior art.

As explained above, in the method of the present invention, a rapid heating and cooling zone is provided in the soaking zone of the continuous annealing furnace, and grain growth is promoted by heating the copper strip to a high temperature in the zone. At the same time, by setting the furnace temperature in the entire soaking zone to a low level, this technology succeeded in solving the problems of build-up on hearth rolls and heat buckling, which were problems with conventional technology. Therefore, the method of the present invention has made it possible to economically produce non-oriented electrical steel sheets with excellent magnetic properties and no distortion.

Furthermore, in order to carry out the method of the present invention, it is sufficient to provide a heating means and a cooling means in any part of the soaking zone of the continuous annealing furnace.
The burden on equipment is also small.

Furthermore, the method of the present invention can be applied not only to full-processed products that are manufactured by applying insulation coating and -ting after annealing and punching, but also to manufacturing semi-processed products in which strain relief annealing is performed after punching. Furthermore, it can be applied to the production of cold-rolled steel sheets for deep drawing which require high-temperature annealing without increasing the furnace temperature in the soaking zone of a continuous annealing furnace.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a vertical continuous annealing furnace used to carry out the method of the present invention, FIG. 2 is a schematic diagram of a rapid heating and cooling zone provided in a soaking zone, and FIG. It is a graph which shows various heat patterns of the soaking zone in continuous annealing in the method of this invention. (Main reference symbols) S: Adjustment zone, Zl: Heating zone of continuous annealing furnace, Z2: Soaking zone of continuous annealing furnace, Z3: Primary cooling zone of continuous annealing furnace, R1... ...
...R9, Ri, Rial ... Hearth roll, P ... Rapid heating and rapid cooling area, N ... Cooling nozzle, ■ ... Induction coil

Claims (3)

[Claims] (1) C: 0.02% or less, Si: 0.10-1.00%, Mn: 0.1-0.3%, Sol. A steel containing Al: 0.001% or less, P: 0.2% or less, with the remainder consisting of iron and unavoidable impurities is hot rolled, pickled and cold rolled, and the obtained steel strip is When continuously annealing in a continuous annealing furnace, a rapid heating and cooling zone is provided in the soaking zone, and the steel strip is rapidly heated above the furnace temperature in the soaking zone, and then rapidly cooled to the furnace temperature in the soaking zone, resulting in good magnetic properties. A method of manufacturing non-oriented electrical steel sheets. (2) The method according to claim 1, characterized in that the maximum temperature of the coil in the rapid heating and cooling zone is 100 to 300 degrees Celsius higher than the furnace temperature in the soaking zone. (3) The method according to claim 1 or 2, characterized in that the lowest temperature in the soaking zone is the recrystallization temperature of the coil.