JPH04293722A - Production of grain nonoriented electrical steel plate having superior machinability - Google Patents

Abstract

PURPOSE:To produce a grain nonoriented electrical steel plate excellent in magnetic properties in a medium magnetic field and machinability and having high specific resistance value by working an Si-containing extremely low carbon steel into a plate at respectively specified temp. and rolling conditions and then performing dehydrogenation heat treatment, annealing, or normalizing according to plate thickness. CONSTITUTION:A slab of a steel for silicon steel having a composition containing, by weight, <0.008% C, 0.1-3.0% Si, <0.20% Mn, 0.02-0.2% P, <0.010% S, <0.040% Al, <0.004% N, <0.005% O, and <0.O002% H is subjected to heating up to 950-1150 deg.C before rolling. After high rolling shape ratio hot rolling including more than one rolling pass where rolling shape ratio A represented by an equation is regulated to >=0.6 is performed at >=800 deg.C, rolling of 35-70% cumulative reduction of area is successively exerted at <=800 deg.C to refine crystalline grains. A plate of >=50mm thickness is subjected to dehydrogenation heat treatment at 600-750 deg.C and, as necessary, to annealing at 750-1150 deg.C or normalizing at 910-1200 deg.C. A plate of <=50mm thickness is annealed at 750-1150 deg.C or normalized at 910-1200 deg.C.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention provides a method for manufacturing a non-oriented electromagnetic thick plate which has high magnetic properties in a medium magnetic field, a high resistivity value, and excellent machinability.

0002

BACKGROUND OF THE INVENTION In recent years, with advances in elementary particle research and medical equipment, which are cutting-edge science and technology, devices that use magnetism are being used in large structures, and there is a demand for improved performance. The magnetic pole material and return yoke material for particle accelerators used under DC magnetization conditions have a high saturation magnetic flux density of 5Oe (400A/m
) A high magnetic flux density in a medium magnetic field is required. It is well known that many materials such as silicon steel sheets and electromagnetic soft iron sheets have been provided in the field of thin plates as electromagnetic steel sheets with excellent magnetic flux density. However, when used as a structural member, there are problems with assembly and strength, and it becomes necessary to use thick steel plates. Until now, electromagnetic plates have been manufactured using pure iron-based components. For example, JP-A-6
0-96749 is publicly known.

However, in recent years, as devices have become larger and their capabilities have improved, devices with even better magnetic properties, especially in medium magnetic fields, have been developed.
For example, there is a strong demand for the development of steel materials with high magnetic flux density around 5 Oe (400 A/m). With the steel materials developed in the above-mentioned patents, it is not possible to stably obtain a high magnetic flux density in the medium magnetic field near 5 Oe. Furthermore, steel plates used as magnetic pole materials and return yoke materials for particle accelerators are often subjected to cutting, but electromagnetic thick plates made of pure iron have a problem of poor machinability.

0004

[Problems to be Solved by the Invention] The object of the present invention has been made in view of the above points, and has high magnetic properties in a medium magnetic field.
It is an object of the present invention to provide a method for manufacturing a non-oriented electromagnetic thick plate having a high resistivity value and excellent machinability.

[0005]

[Means for Solving the Problems] The present invention provides C:
0.008% or less, Si: 0.1% or more, 3.0% or less, Mn: 0.20% or less, P: 0.02% or more, 0.2
% or less, S: 0.010% or less, Al: 0.040% or less, N: 0.004% or less, O: 0.005% or less, H
: 0.0002% or less, the remainder being substantially iron, a steel slab or cast slab is heated to 950 to 1150°C, and
Rolling pass with rolling shape ratio A of 0.6 or more at 00℃ or higher
Rolling is performed for at least 3 times, and then rolling is performed at 800°C or less with a rolling reduction of more than 35% and less than 70%, and the plate thickness is 5.
For thick plates of 0 mm or more, after dehydrogenation heat treatment at 600-750°C, heat treatment at 750-1150°C as necessary.
or normalized at 910-1200°C, and for plates less than 50mm thick, annealed at 750-1150°C or normalized at 910-1200°C, which has high magnetic properties in a medium magnetic field. , and a method for manufacturing a non-oriented electromagnetic thick plate having a high specific resistance value.

[0006]

[Math 2]

[0007]

[Operation] First, the process of magnetization will be described. When demagnetized steel is placed in a magnetic field and the field is strengthened, the orientation of the magnetic domains gradually changes, and the magnetic domains that are close to the direction of the magnetic field become dominant and merge with other magnetic domains. In other words, movement of the domain wall occurs. When the magnetic field becomes stronger and the movement of the domain wall is completed, the entire magnetic domain changes direction in the direction of magnetization. In this magnetization process, the ease with which domain walls move determines the magnetic flux density in low magnetic fields. In other words, it can be said qualitatively that in order to obtain a high magnetic flux density in a low magnetic field, it is necessary to reduce as much as possible what impedes the movement of domain walls. From this point of view, coarsening of crystal grains that impede movement of domain walls has traditionally been an important technique (Japanese Patent Laid-Open No. 60-96749). On the other hand, there was no knowledge of a method for obtaining the steel magnetic flux density in a medium magnetic field.

The inventors here discovered that in order to obtain a high magnetic flux density in a medium magnetic field, it is necessary not only to coarsen the crystal grains but also to
It has been found that it is important that the easy-to-magnetize [100] orientation of the crystal grains is aligned parallel to the rolling surface. It is not necessary to make ultra-coarse grains in particular, but relatively coarse grains (ferrite grain size No.
．． They found that the magnetic properties in a medium magnetic field can be significantly improved by having a texture in which the number is about 0 to 4) and the [100] orientation is parallel to the rolling surface. As a hot rolling condition for this purpose, by taking a rolling reduction of more than 35% and less than 70% at 800°C or less, the grains before heat treatment after rolling are made finer and easier to recrystallize, and the steel is strained. By introducing this strain and using this strain as a driving force for recrystallization during heat treatment, relatively large crystal grains can be stably obtained throughout the sheet thickness, and at the same time, the [100] crystal orientation is parallel to the rolling surface. It is possible to obtain a collective structure. Figure 1 shows 0.003%C
-1.3%Si-0.055%P steel showing the rolling reduction of 800°C or less and the magnetic flux density at 5Oe. A high magnetic flux density can be obtained by a reduction of more than 35% and less than 70%.

Furthermore, as a means of obtaining a high magnetic flux density in a medium magnetic field, various studies were conducted on the influence of void defects, and it was found that defects with a size of 100 μm or more significantly deteriorate the magnetic properties. It is. And this one
It has been found that in order to eliminate harmful void defects of 0.00 μm or more, the rolled shape ratio A needs to be 0.6 or more.

0010

[Math 3]

Furthermore, it has been found that the presence of hydrogen in steel is also harmful, and that magnetic properties can be significantly improved by dehydrogenation heat treatment. By reducing the size of void defects to 100 μm or less through high shape ratio rolling and reducing hydrogen in the steel through dehydrogenation heat treatment, the magnetic flux density in a medium magnetic field increases significantly. Furthermore, as shown in FIG. 2, it has been found that Si is the most suitable element to give steel a high resistivity value and to be used as a deoxidizing agent in place of Al in a region where no Al is added.

[0012] As an element that improves the machinability of steel sheets for magnetic shielding, S etc.
142028). However, S forms MnS, which significantly impedes crystal grain coarsening by the above method and greatly reduces magnetic properties. Here, the inventors have discovered that P is effective as an element that improves the machinability of steel materials and does not hinder crystal grain coarsening by the above method. Also S
Although i, Al, P, etc. reduce toughness, it has been found that toughness can be ensured by setting extremely low C and also reducing S. Figure 3 shows 0.004% C-1.
This figure shows the influence of the amount of P on the machinability of 8% Si steel. In other words, a high-speed steel drill with a diameter of 10.2 mm was used at a rotation speed of 700 rpm and a feed rate of 140 m.
This is the relationship between the wear width of the drill flank and the amount of P when 20 holes with a depth of 30 m are drilled under the condition of m/min. The machinability is particularly good when the wear width is 0.2 mm or less (indicated by ◎). ,0
．． Good machinability from 2mm to 0.3mm (indicated by ○), 0
．． 3 mm or more is defined as having normal machinability (indicated by △). It can be seen that the machinability is good when P is 0.02% or more.

Next, the reason for limiting the ingredients will be described. C is an element that increases the internal stress in steel and lowers the magnetic properties, especially the magnetic flux density in a low magnetic field, the most, and reducing it as much as possible contributes to not lowering the magnetic flux density in a medium magnetic field. In addition, from the viewpoint of ensuring toughness, the lower the content, the better. Because of this, 0.00
Limited to 8% or less. As shown in FIG. 2, Si is an essential element for increasing the specific resistance value, and needs to be added in an amount of 0.1% or more. However, if added excessively, the magnetic flux density in a medium magnetic field will decrease and the toughness will also decrease, so the upper limit has been set to 3.0.
%.

[0014] The lower the Mn content, the better from the viewpoint of magnetic flux density in a medium magnetic field, and the lower the Mn content from the viewpoint of generating MnS-based inclusions. From this point of view, Mn is limited to 0.20% or less. Regarding Mn, it is more desirable to keep it at 0.10% or less from the point of view of forming MnS-based inclusions. S and O form non-metallic inclusions in steel, hinder the coarsening of crystal grains, and as their content increases, the magnetic flux density decreases and the magnetic properties deteriorate, so the smaller the content, the better. Therefore, S should be 0.010% or less, and O should be 0.005% or less. Al is used as a deoxidizing agent, and if the amount of Al is too large, inclusions will be formed and the properties of the steel will be impaired, so the upper limit is set to 0.040%. Furthermore, in order to reduce AlN, which is a precipitate that prevents crystal grain coarsening, the lower the content, the better, and preferably 0.020% or less. Since N increases internal stress and AlN reduces the magnetic flux density in a medium magnetic field due to its crystal grain refining effect, the upper limit is set to 0.004%. H
Since it lowers the magnetic properties and prevents the reduction of void defects, it is set to 0.0002% or less.

Next, the manufacturing method will be described. Regarding the rolling conditions, first of all, the pre-rolling heating temperature should be set to 1150°C or less. At heating temperatures exceeding 1150°C, there will be large variations in the heated γ grain size in the thickness direction, and this variation will remain even after rolling and cause the final result. Since the crystal grains become non-uniform, the upper limit is set to 1150.
℃. If the heating temperature is less than 950°C, the deformation resistance during rolling will increase, and the rolling load for rolling with a high shape ratio to eliminate void defects described below will increase.
The lower limit is 50°C. The role of hot rolling is important because the above-mentioned porosity defects, which vary in size during the solidification process of steel, always occur during hot rolling, and rolling is the only way to eliminate them. That is, hot rolling in which the amount of deformation per hot rolling is increased and the deformation extends to the center of the sheet thickness is effective. Specifically, high shape ratio rolling including one or more rolling passes with rolling shape ratio A of 0.6 or more is performed at 800°C or higher to reduce the size of void defects to 100μ.
The following is good for magnetic properties. By eliminating void defects during rolling by this high shape ratio rolling, the dehydrogenation efficiency in the subsequent dehydrogenation heat treatment is dramatically increased. The reason why high shape ratio rolling is carried out at 800° C. or higher is that deformation resistance is large at low temperatures below 800° C., and deterioration is difficult to achieve with a normal rolling mill.

Next, by increasing the cumulative reduction rate to 35% or more at a temperature of 800° C. or lower, crystal grains are made finer and strain is introduced, thereby promoting recrystallization during the subsequent heat treatment. Further, by this rolling, a texture in which the [100] crystal orientation is aligned parallel to the rolling surface is obtained. However, 70%
If the rolling reduction ratio is too high, the grain size after heat treatment becomes non-uniform in the thickness direction of the plate, increasing the variation in magnetic flux density. Therefore, in order to obtain relatively coarse grains that are uniform in the thickness direction, the reduction ratio is set to more than 35% and less than 70%.

Next, following hot rolling, grain coarsening, internal strain removal, and dehydrogenation heat treatment is performed as necessary for thick materials with a plate thickness of 50 mm or more. If the plate thickness is 50 mm or more, it is difficult for hydrogen to diffuse, which causes void defects.
In addition, combined with the action of hydrogen itself, it lowers the magnetic flux density in a low magnetic field. For this reason, a dehydrogenation heat treatment is performed, but at a temperature lower than 600°C, the dehydrogenation efficiency is poor and a part of transformation starts at a temperature higher than 750°C, so the dehydrogenation heat treatment is carried out in a temperature range of 600 to 750°C. As a result of various studies, the dehydrogenation time was [0.6 (
t-50)+6] time (t: plate thickness) is appropriate. Annealing is performed as necessary to coarsen the crystal grains and remove internal strain, but at temperatures below 750°C, no coarsening of the grains occurs, and at temperatures above 1150°C, the homogeneity of the grains in the thickness direction is maintained. Therefore, the annealing temperature is 750 to 1150℃.
limited to.

Normalizing is performed in place of annealing to adjust grains in the thickness direction and remove internal strain, but the lower limit is 910°C, which is the Ac3 point at the lower limit of the austenite region, and 1200°C.
Since the homogeneity of the crystal grains in the thickness direction cannot be maintained above, the normalization temperature is limited to 910°C to 1200°C. Note that this annealing or normalizing can be performed by dehydrogenation heat treatment performed on a thick material having a thickness of 50 mm or more. On the other hand, plate thickness 5
If the diameter is less than 0 mm, hydrogen can easily diffuse, so dehydrogenation heat treatment is not necessary and only the above-mentioned annealing or normalizing is sufficient.

[0019]

[Example] Table 1 shows the manufacturing conditions of the electromagnetic thick plate and the evaluation of the ferrite grain size, magnetic flux density in a medium magnetic field, specific resistance value, toughness and machinability.

[0020]

[Table 1]

[0021]

[Table 2]

Examples 1 to 8 illustrate embodiments of the invention; Examples 9 to 8 illustrate examples of the invention;
26 shows a comparative example. Examples 1 to 3 have a plate thickness of 100 mm, Example 4
- 6 were finished to 500 mm, Example 7 to 40 mm, and Example 8 to 6 mm, all of which had high magnetic flux density in a medium magnetic field, high specific resistance, and good machinability. Example 9 has high C,
In Example 10, the magnetic flux density is low because the Si content is low. In Example 11, since Si exceeds the upper limit, the toughness is low and the magnetic flux density is also low. Example 12 has a high Mn content, so the magnetic flux density is low. Example 13 has poor machinability because P is low. Example 14 has low toughness because P exceeds the upper limit. In Example 15, the magnetic flux density is low because S is high. Example 16 has low toughness due to high Al content. Example 17 has a high N content, Example 18 has a high O content, and Example 19 has a high H content, so the magnetic flux density is low. In Example 20, the heating temperature exceeded the upper limit and the magnetic flux density was low. In Example 21, the heating temperature was outside the lower limit, so the magnetic flux density was low. In Example 22, the rolling reduction of 800° C. or less is outside the lower limit and the magnetic flux density is low. In Example 23, the maximum shape ratio is outside the lower limit, in Example 24, the dehydrogenation heat treatment temperature is outside the lower limit, in Example 25, the annealing temperature is outside the lower limit, and in Example 26, the magnetic flux density is low because there is no dehydrogenation heat treatment.

[0023]

[Effects of the Invention] According to the present invention, by appropriately limiting the ingredients, a thick steel plate can be provided with uniform high electromagnetic properties, a high resistivity value, and good machinability. This method was successful and can be applied to structures that undergo cutting using the magnetic properties of direct current magnetization. Moreover, the manufacturing method thereof is a method in which the above-mentioned ingredient limitation, grain adjustment after hot rolling, and dehydrogenation heat treatment are performed simultaneously, and it provides an extremely economical manufacturing method and has great industrial effects.

[Brief explanation of drawings]

FIG. 1 is a graph showing the influence of a reduction rate of 800° C. or less on magnetic flux density at 5 Oe.

FIG. 2 is a graph showing the influence of Si content on specific resistance.

FIG. 3 is a graph showing the influence of the amount of P on machinability.

Claims (1)

[Claims] Claim 1: In weight%, C: 0.008% or less, Si: 0.1% or more and 3.0% or less, Mn: 0.20% or less, P: 0.02% or more, 0.2 % or less, S: 0.010% or less, Al: 0.040% or less, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, the remainder substantially consisting of iron. 9 steel slabs or cast slabs of steel composition
Heating to 50 to 1150°C, rolling at least once at 800°C or higher with a rolling shape ratio A of 0.6 or more, and then rolling at 800°C or lower with a rolling reduction of more than 35% to 70% or more. After rolling and dehydrogenation heat treatment at 600 to 750°C for plates with a thickness of 50 mm or more, annealing at 750 to 1150°C or 9
Normalize at 10-1200℃, and annealing at 750-1150℃ for plate thickness less than 50mm or 910-1200℃.
A method for producing a non-oriented electromagnetic thick plate with good machinability, which has high magnetic properties in a medium magnetic field and has a high specific resistance value, which is characterized by normalizing at 200°C. [Math 1]