JPH04268024A - Production of satisfactory electric steel plate - Google Patents

Abstract

PURPOSE:To produce a satisfactory electric steel plate. CONSTITUTION:Steel contg. limited amts. or less of C, Si, Mn, S, Al, N, O and H besides 0.02-0.20% P is heated to 950-1,150 deg.C, rolled in >=0.6 rolling shape ratio at >=800 deg.C and further rolled at >35-70% draft at <=800 deg.C. The resulting plate is subjected to dehydrogenation heat treatment, annealing or normalizing in accordance with the thickness to obtain a satisfactory electric steel plate having superior magnetic characteristics in a medium magnetic field and satisfactory machinability.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thick electromagnetic plate that has good machinability and excellent magnetic properties in a medium magnetic field.

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
) is required in a medium magnetic field near
Furthermore, good machinability during processing is also 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, such as 5Oe (400A/m
) There is a strong demand for the development of steel materials with high magnetic flux density in the vicinity. Conventionally, it has not been possible to stably obtain a high magnetic flux density in a medium magnetic field around 5 Oe.

0003

[Problems to be Solved by the Invention] The object of the present invention has been made in view of the above points, and is to provide a method for manufacturing a good electromagnetic thick plate that has good machinability and excellent magnetic properties in a medium magnetic field. be.

0004

[Means for Solving the Problems] The present invention provides C:
0.01% or less, Si: 0.02% or less, Mn: 0.2
0% or less, P: 0.02-0.20%, 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,
9 steel slabs or cast slabs with a steel composition in which the remainder is essentially iron
Heating to 50 to 1150°C, rolling at 800°C or higher with rolling shape ratio A of 0.6 or more at least once, and then rolling at 800°C or lower with a rolling reduction of more than 35% but not more than 70%. 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 950°C or 91°C as necessary.
Normalize at 0~1000℃, and annealing at 750~950℃ or 910~100℃ for plate thickness less than 50mm.
A method for manufacturing an electromagnetic thick plate that has good machinability and excellent magnetic properties in a medium magnetic field, which is characterized by normalization at 0°C.

[0005]

[Math 2]

[0006]

[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 high magnetic flux density in a medium magnetic field.

[0007] The inventors here discovered that in order to obtain a high magnetic flux density in a medium magnetic field, it is necessary to not only coarsen the crystal grains but also
It has been found that it is important that the directions of magnetization between adjacent crystal grains are aligned parallel to the rolling direction. Relatively coarse grains that are neither super coarse grains nor fine grains (ferrite grain size No. 0)
They found that the magnetic properties in a medium magnetic field were significantly improved by making the (100) direction random in parallel to the rolling direction. 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 plate thickness, and at the same time, the (100) crystal orientation can be made parallel to the rolling direction. It will be random.

FIG. 1 shows 0.005Si-0.06Mn-0
．． It shows the rolling reduction of 015Al steel at 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 to obtain high magnetic flux density in medium magnetic fields, we conducted detailed studies on the effects of elements and void defects that cause internal stress, and achieved the desired objective. Furthermore, as a result of various studies on the influence of void defects, it was found that those with a size of 100 μm or more significantly deteriorate the magnetic properties. It has been found that in order to eliminate harmful void defects of 100 μm or more, the rolling shape ratio A must be 0.6 or more.

[0009]

[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. Next, we found that the addition of P is very effective for improving the machinability of this high-purity steel, especially for reducing the surface roughness after cutting. Figure 3 shows 0.007C-0.10Mn-0.01
5Al steel, the surface roughness at a cutting length of 10 m is normal (indicated by △) of about 10 μm, good (indicated by ○) of about 5 μm,
A thickness of approximately 1 μm is defined as exhibiting particularly good machinability (indicated by ◎). As shown in the figure, it can be seen that good machinability with a surface roughness of 5 μm or less is exhibited when the amount of P added 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, particularly 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 magnetic aging, the lower the content, the less the deterioration over time, and it can be used permanently with good magnetic properties.For this reason, the content is limited to 0.01% or less. As shown in FIG. 2, an even higher magnetic flux density can be obtained by reducing the amount to 0.005% or less. It is preferable that Si and Mn be small in terms of magnetic flux density in a medium magnetic field, and that Mn should be small in terms of generating MnS-based inclusions. From this meaning, Si is 0.02%
Hereinafter, Mn is limited to 0.20% or less. Regarding Mn, it is more preferable to use 0 since MnS-based inclusions are generated.
．． It is preferably 10% or less. P is an element that reduces tool wear and increases machinability, and as shown in Figure 3, 0.020%
It is necessary to add more than 0.2%, but since adding more than 0.20% will reduce the magnetic properties in a low magnetic field, the upper limit should be set at 0.2%.
Set to 0%.

[0012] S and O form non-metallic inclusions in steel and have a detrimental effect on coarsening of crystal grains, and as their content increases, a decrease in magnetic flux density is observed, degrading magnetic properties, so the less the better. . Therefore, S was set to 0.010% or less, and O was set to 0.005% or less. Al is used as a deoxidizing agent, and if the amount is too large, it will generate inclusions and impair the properties of the steel, so the upper limit is set at 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. The upper limit is 0 because N increases the internal stress and AlN reduces the magnetic flux density in a medium magnetic field due to its crystal grain refinement effect.
．． 004%. Since H deteriorates the magnetic properties and prevents the reduction of void defects, it is limited to 0.0002% or less.

Next, the manufacturing method will be described. Regarding 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.

[0014] Regarding hot rolling, the above-mentioned porous defects may vary in size during the solidification process of steel, but they always occur, and the means to eliminate them must be through rolling, so the role of hot rolling is important. be. That is, hot rolling in which the amount of deformation per hot rolling is increased and the deformation extends to the center of the plate thickness is effective. Specifically, it is good for magnetic properties to perform high shape ratio rolling including one or more rolling passes with a rolling shape ratio A of 0.6 or more at 800° C. or higher and to reduce the size of void defects to 100 μm or less. 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 for performing high shape ratio rolling at 800°C or higher is that 80°C
This is because at a low temperature of less than 0° C., the deformation resistance is large and rolling is difficult with a normal rolling mill.

Next, by increasing the cumulative reduction rate to more than 35% 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, the (100) crystal orientation is made random parallel to the rolling direction. However, if the rolling reduction exceeds 70%, the grain size after heat treatment becomes non-uniform in the thickness direction, increasing the variation in magnetic flux density. Therefore, in order to obtain relatively coarse grains that are uniform in the thickness direction, the rolling reduction rate is 35%.
Must be over 70% or less.

Next, hot rolling is followed by grain coarsening, removal of internal strain, and dehydrogenation heat treatment for thick materials with a 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, and combined with the action of hydrogen itself, reduces the magnetic flux density in a low magnetic field. For this reason, dehydrogenation heat treatment is performed at 600°C.
If it is less than 750°C, the dehydrogenation efficiency will be poor, and if it exceeds 750°C, transformation will partially start, so it is carried out in the 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 grains and remove internal strain, but
At temperatures below 750°C, crystal grain coarsening does not occur;
If the temperature is 0°C or higher, the homogeneity of the crystal grains in the thickness direction cannot be maintained, so the annealing temperature is limited to 750 to 950°C.

Normalizing is performed in place of annealing in order to adjust grains in the thickness direction and remove internal strain, but the lower limit is 910°C or higher, which is the Ac3 point of the lower limit of the austenite region, and
If it exceeds 000°C, the homogeneity of the crystal grains in the thickness direction cannot be maintained, so the normalization temperature is limited to 910 to 1000°C. In addition,
It is possible to perform this annealing or normalization by dehydrogenation heat treatment performed on a thick material with a thickness of 50 mm or more. on the other hand,
When the plate thickness is less than 50 mm, hydrogen can easily diffuse, so dehydrogenation heat treatment is not necessary and only the above-mentioned annealing or normalizing is sufficient.

[0018]

[Examples] Next, examples of the present invention will be given along with comparative examples. Table 1 shows the manufacturing conditions for electromagnetic plate thickness, ferrite grain size, and magnetic flux density in a medium magnetic field.

[0019]

[Table 1]

[0020]

[Table 2]

Examples 1 to 6 illustrate embodiments of the invention, and Examples 7 to
23 shows a comparative example. Examples 1 to 3 were finished to a plate thickness of 100 mm, had a high magnetic flux density in a medium magnetic field, and had good machinability. Compared to Example 1, Example 2 has lower C and Example 3 has lower M.
n and exhibits higher magnetic properties. Example 4 is 40mm,
Example 5 is finished to 6 mm, and Example 6 is finished to 10 mm, which has a high magnetic flux density and good machinability. Examples 7 and 8 have low P and poor machinability. Example 9 has too high P, Example 10 has too much C, Example 11 has too much Mn, Example 12 has too much S, and Example 13 has too much A.
l is high, Example 14 is high in N, Example 15 is high in O, Example 1
No. 6 has a high H value and exceeds the upper limit, resulting in a low magnetic property value. In Example 17, the heating temperature exceeded the upper limit and the magnetic flux density was low. In Example 18, the heating temperature was outside the lower limit and the maximum shape ratio was small, resulting in a low magnetic flux density. Example 19
The rolling reduction rate of 800°C or less is outside the lower limit, resulting in a low magnetic flux density. In Example 20, the maximum shape ratio is outside the lower limit, and in Example 21
In Example 22, the annealing temperature was outside the lower limit, and in Example 23, there was no dehydrogenation heat treatment, so the magnetic flux density was low.

[0022]

[Effects of the Invention] According to the present invention, by appropriately limiting the ingredients, it has been possible to provide a thick steel plate with uniform high electromagnetic properties, making it applicable to structures that utilize magnetic properties due to direct current magnetization. Moreover, its manufacturing method is a method in which the above-mentioned ingredient restriction, 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. It is something to play.

[Brief explanation of the drawing]

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

FIG. 2 is a graph showing the influence of C content on magnetic flux density at 5 Oe.

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

Claims (1)

[Claims] Claim 1: In weight percent, C: 0.01% or less, Si: 0.02% or less, Mn: 0.20% or less, P: 0.02 to 0.20%, S: 0.010%. Hereinafter, a steel billet or slab having a steel composition consisting of Al: 0.040% or less, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, and the remainder substantially iron. 9
Heating to 50 to 1150°C, rolling at 800°C or higher with rolling shape ratio A of 0.6 or more at least once, and then rolling at 800°C or lower with a rolling reduction of more than 35% but not more than 70%. 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 950°C or 91°C as necessary.
Normalize at 0~1000℃, and annealing at 750~950℃ or 910~100℃ for plate thickness less than 50mm.
A method for manufacturing an electromagnetic thick plate that has good machinability and excellent magnetic properties in a medium magnetic field, which is characterized by normalization at 0°C. [Math 1]