JPH0353022A - Manufacture of low core loss-high magnetic flux density nonoriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To manufacture the low core loss-high magnetic flux density nonoriented silicon steel sheet by subjecting a steel having specified compn. of C, Si, Al, Mn, P and Fe to hot rolling, thereafter executing the recrystallization of ferrite and the introduction of specified plastic strains and coiling the steel at a high temp. CONSTITUTION:A slab contg., by weight, <=0.01% C, 2.0 to 4.0% Si or Si+Al, <=1.0% Mn, <=0.1% P and the balance Fe with inevitable impurities is hot-rolled. At this time, the hot rolling is completed at >=900 deg.C and the recrystallization of ferrite is executed. After that, until coiling is executed, 5 to 30% plastic strains are introduced by a leveller or the like, and the steel is coiled at >=700 deg.C. In this way, the above strains work as a driving force, and by a self annealing effect in the stage of high temp. coiling, coarse crystals grow in the steel. After that, the hot rolled sheet is cold-rolled and is annealed. In this way, the middle grade to high grade nonoriented silicon steel sheet having low core loss and high magnetic flux density can be obtd.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a non-oriented electrical steel sheet, and more particularly, to a method for manufacturing an intermediate to high-grade non-oriented electrical steel sheet having low iron loss and high magnetic flux density. (Prior art and problems to be solved) Non-oriented electrical steel sheets are used as iron cores for rotating machines such as motors, and stationary devices such as small transformers and ballasts. In recent years, in order to improve efficiency and reduce size and weight, there has been an increasing demand for non-oriented electrical steel sheets with low iron loss and high magnetic flux density. Generally, non-oriented electrical steel sheets are manufactured by hot rolling steel slabs with predetermined chemical precepts, pickling, cold rolling, annealing, and subjecting them to the required surface treatment. It is already well known that in order to lower the crystal grain size in the final annealing step, it is necessary to increase the grain size. In order to increase the grain size in the final annealing process, the first method is to wind the material at a high temperature after hot rolling in the ferrite-austenite region, and the second method is to increase the grain size in the final annealing step. A third method of annealing a hot-rolled sheet has been proposed, such as a method of introducing a slight plastic strain to a hot-rolled sheet at room temperature and then annealing it. However, in the first method, since the crystal grain size is still small,
The magnetic properties are not sufficient, and the second and third methods
Since annealing is performed after hot rolling, the number of steps increases, and
It is unavoidable that manufacturing costs will be high. In order to solve these problems, the present inventors previously regulated hot rolling conditions and coiling temperature for steel slabs having γ-α transformation in JP-A No. 60-258414, and By introducing a predetermined plastic strain into the hot-rolled sheet during coiling after hot rolling, and performing cold rolling and annealing after coiling, a coarse grain size is obtained, thus reducing iron loss. We proposed a method to obtain non-oriented electrical steel sheets with low and high magnetic flux density. The present invention is based on the method related to the above proposal,
Si or Si and Af used in high-grade non-oriented electrical steel sheets
The object of the present invention is to provide a method for obtaining a non-oriented electrical steel sheet having a low iron loss and a high magnetic flux density in steel having a total amount of 1 of 2.0% or more. (Means for Solving the Problems) In order to achieve the above object, the present inventors have conducted intensive research on a method for manufacturing intermediate to high grade non-oriented electrical steel sheets having the above-mentioned Si or Si and Al content. The present invention was achieved by discovering a method for improving the iron loss and magnetic flux density of these products. That is, in the present invention, C: 0.01% or less, Si or S
Total amount of i and Afl: 2.0 to 4.0%, Mn: 1.
0% or less, P: 0.1% or less, and the balance is iron and unavoidable impurities.
After hot rolling is completed at 0°C or higher, 5 to 30% plastic strain is introduced between ferrite recrystallization and winding of the coil, and the coil is wound at a temperature of 700°C or higher.
The gist of this invention is a method for manufacturing a non-oriented electrical steel sheet with low iron loss and high magnetic flux density, which is characterized by cold rolling and then annealing. The present invention will be explained in further detail below. (Function) First, the reason for limiting the chemical separation of steel materials in the present invention will be explained. C: C is an element that has a large effect on magnetic properties, but if it is contained in large amounts in steel materials, magnetic properties such as iron loss and magnetic flux density will be greatly degraded, so the content should be 0.01% or less. Particularly preferably, the C content is 0.005% or less in order to further improve the magnetic properties. Si. AI2: Si is an important element for increasing the resistivity of steel and obtaining low core loss, and Al is an element that has the same effect as SL and at the same time has the effect of improving grain growth. . In intermediate to high grade non-oriented electrical steel sheets, in order to achieve a predetermined core loss, it is essential to use steel with a total content of Si or SL and Al of 2.0% or more. However, if the total amount of Si or Si and Afl exceeds 4.0%, cold rolling becomes difficult, so it needs to be 4.0% or less. Mn: Mn is contained in order to suppress hot embrittlement, but 1.
If it exceeds 0%, it will have an adverse effect on the magnetic properties and will make steel manufacturing difficult in the case of ultra-low C steel produced by the method according to the present invention. Therefore, the Mn content should be 1.0% or less. P: P is an element that improves punchability by increasing hardness, but if it is included in an excessive amount, it will cause cracks to occur during welding after laminating the iron core, so the P content should be 0. 1%
The following shall apply. Next, the method of the present invention will be explained. The method according to the present invention uses a steel billet having the above-mentioned chemical content as a raw material and hot-rolls it at a temperature of 900°C or higher, recrystallizes the ferrite, and then winds the coil. Introducing 5-30% plastic strain and heating at 700℃
By winding at the above temperature and thus coarsening the crystal grains of the hot-rolled sheet, a non-oriented electrical steel sheet having better magnetic properties than conventional ones, in particular, high magnetic flux density, can be obtained. That is, in the method of the present invention, α in the worked structure is recrystallized at an intermediate stage of hot rolling of steel without γ-α transformation,
Plastic strain is introduced into the hot-rolled sheet in this state, and the so-called strained grain growth is completed by the self-annealing effect during high-temperature coiling using this strain as a related force. By coarsening the crystal grains of the hot-rolled sheet using this method, it is possible to achieve low core loss and high magnetic flux density. At the same time. m will reduce the flux density (1
This is considered to be because the accumulation of (1 1 1) planes became weaker because the grain boundary area, which is the generation site of 1 1) planes, decreased. To do this, first, as shown in Figure 1 below,
It is necessary to finish hot rolling at 0°C or higher. A recrystallized structure cannot be obtained at temperatures below 900°C. The amount of plastic strain introduced into the hot rolled sheet after hot rolling and before winding is in the range of 5 to 30%. If the amount of plastic strain is less than 5%, it is difficult to coarsen the crystal grains during high-temperature coiling, while if it exceeds 30%, the obtained crystal grains will become finer, which is not preferable. In particular, from the viewpoint of magnetic properties, 5 to 20% is desirable. The method for introducing plastic strain may be any method such as rolling, leveler, tensile force, etc., and is not particularly limited. After plastic strain is introduced into the hot-rolled sheet in this way, in order to fully exhibit the self-annealing effect and complete strained grain growth during coiling, it is desirable that the coiling temperature is as high as possible. In the invention, this temperature is set to 700°C or higher. This is because if the winding temperature is less than 700°C, coarsening of crystal grains is insufficient. The cold rolling and annealing after high-temperature coiling as described above can be carried out by conventional and usual methods, and the cold rolling may be carried out in a single pass, or the cold rolling may be carried out in two passes with intermediate annealing in between. You may go. Note that the final annealing may be either N annealing or continuous annealing, but in order to obtain a high magnetic flux density, it is preferable to perform rapid heating by continuous annealing. Moreover, processes such as continuous casting, direct rolling, and slab low-temperature heating can be employed as necessary. (Example) Examples of the present invention are shown below. Loss of success C: O. OO4%, Si:2.4%, Mn:0.23%
, P: 0.01 1% and Al: 0.26%, the balance being iron and unavoidable impurities.After heating a steel piece (20a+m thick) to 1200℃, the hot rolling finishing temperature was 750~10
It was rolled to a thickness of 2n+m at a temperature of 70°C, left to cool, and then water-cooled for 2 seconds or 20 seconds to Iltm the crystal structure. The results are shown in FIG. As is clear from Figure 1, the hot rolling finishing temperature is 900℃.
In the above case, recrystallized grains were obtained whether the cooling time was 2 seconds or 20 seconds, but a non-recrystallized structure was obtained when the cooling time was less than 900°C. Therefore, after finishing hot rolling in the current hot rolling mill,
When considering recrystallizing α on a run-out table, it is sufficient to let it cool for at most 20 seconds, but the aim of the present invention is to recrystallize α after hot rolling.
In order to improve the magnetic properties of the final product by introducing plastic strain and coarsening the crystal grains by high-temperature coiling, it is necessary to raise the hot-rolling finishing temperature to 900°C or higher. Using a steel billet having the same composition as in Example 1, hot rolling was completed at a finishing temperature of 950°C to a thickness of 3 mm, and then left to cool for about 15 seconds. (Temperature is about 810℃), 2-60%
The material was rolled (introduced plastic strain), inserted into a 730° C. furnace, soaked for 30 minutes, and then cooled in the furnace, thereby performing heat treatment to simulate winding. The crystal structure of these materials is
The obtained crystal grain size numbers are shown in FIG. In Figure 2, the amount of plastic strain introduced - (rolling ratio) is 5
If it is less than 30%, a mixed grain structure will result, and if it exceeds 30%, the crystal grains will become finer. On the other hand, in the range of 5 to 30%, a coarse grain structure with a grain size number of 4 or less is obtained, and excellent magnetic properties are obtained as described later. Using steel pieces having the same composition as in Example 1 and Example 2, a 2.0 mm thick material before cold rolling was manufactured under the manufacturing conditions shown in Table 1. After cold rolling these materials to a thickness of 0.5,
Annealing was performed at 950°C for 1 minute. Table 1 shows the grain size number of the material before cold rolling and the magnetic properties of the product. In Table 1, the hot rolling finishing temperature of Comparative Example Nα is low. This is a case where the material before cold rolling has a slightly recrystallized structure, and its magnetic properties are extremely poor. Comparative Example Nα2 is a case of high-temperature coiling, and Comparative Example &3 is a case of hot-rolled sheet annealing, but in both cases, the grain size number of the material before cold rolling is about 7, and coarse grains are not obtained. Its magnetic properties are inferior to those of the inventive examples described below. Comparative Example 44 is a case where a hot rolled sheet is rolled at room temperature by 6% (N strain introduced) and then annealed at 760°C for 2 hours, resulting in low iron loss and high magnetic flux density. It has been obtained. In this case, the grain size number of the material before cold rolling was 1.8. However, this method is expensive because it involves annealing the hot-rolled sheet. In contrast to these comparative examples, the present invention examples, Nn5, No.
No. 6 was hot rolled at about 930°C and left to cool to about 85°C.
After 10% or 30% rolling at 0℃, 740℃
This is the case when Xlhr winding simulation processing is applied,
It can be seen that the magnetic properties are the same or better than Comparative Example &4. The grain size number of the material before cold rolling was approximately 3. Comparative example Nα7 is a case where the amount of plastic strain introduced (rolling rate) is large, and comparative example NllL8 is a case where the coiling temperature is low. The structures of the materials before cold rolling are fine grains and mixed grains, respectively, and their magnetic properties are inferior to those of the examples of the present invention.

[Left below]

(Effects of the Invention) As detailed above, according to the present invention, an intermediate to high grade non-oriented electrical steel sheet with a total content of SL or Si and Al of 2.0% or more has a low iron loss and a magnetic flux density. A product with high quality can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the hot rolling finishing temperature and the grain size number, and FIG. 2 is a diagram showing the relationship between the rolling wheel (that is, the amount of plastic strain) and the grain size number after ferrite recrystallization.

Claims (1)

[Claims] In weight% (the same applies hereinafter), C: 0.01% or less, Si or total amount of Si and Al: 2.0 to 4.0%, Mn: 1.
0% or less, P: 0.1% or less, and the balance is iron and unavoidable impurities.
After finishing hot rolling at 0°C or higher, 5 to 30% plastic strain is introduced between ferrite recrystallization and coil winding, and the coil is wound at a temperature of 700°C or higher, and then
A method for producing a non-oriented electrical steel sheet with low core loss and high magnetic flux density, which comprises cold rolling and then annealing.