JPH0745690B2 - Manufacturing method of good electromagnetic thick plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] In recent years, along with the progress of elementary particle research and medical equipment, which are the most advanced science and technology, devices that use magnetism for large structures are used, and it is necessary to improve their performance. Has been.

The present invention relates to a method for manufacturing an electromagnetic thick steel plate having a high magnetic flux density for an iron core of a magnet used under a DC magnetization condition or for a magnetic shield necessary for shielding a magnetic field.

[Prior Art] As magnetic steel sheets having excellent magnetic flux density, it is well known that a number of materials such as silicon steel sheets and electromagnetic soft iron sheets have been provided in the field of thin sheets. However, there are problems in assembly processing and strength when used as a structural member,
It becomes necessary to use thick steel plates. Up to now, electromagnetic thick plates have been manufactured with blunt iron-based components. For example, JP-A-60-96749 is known.

However, with the recent increase in size of equipment and improvement in performance, magnetic properties are even better, especially in low magnetic fields, such as 80
The magnetic flux density at A / m is high and the coercive force is low, for example, 65 A / m or less, and there is a strong demand for steel material development. The steel materials developed by the above patents cannot stably obtain a high magnetic flux density at a low magnetic field of 80 A / m.

[Problems to be Solved by the Invention] The object of the present invention is made in view of the above points, and is good in that the magnetic flux density is high in a low magnetic field, the coercive force is low, and the magnetic characteristic difference in the plate thickness direction is small. It is to provide a manufacturing method of an electromagnetic thick plate.

[Means for Solving the Problems] The gist of the present invention is as follows.

(1) In% by weight, C: 0.01% or less, Si: 0.02% or less, Mn: 0.
20% or less, P: 0.015% or less, S: 0.010% or less, Cr: 0.05%
Below, Mo: 0.01% or less, Cu: 0.01% or less, Ni: 0.1 to 2.0
%, Al: 0.005 to 0.040%, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, the balance is a steel composition of steel or a slab heated to 1150 to 1300 ° C. Then, under the condition that the finishing temperature is 900 ° C or higher, rolling with a rolling shape ratio A of 0.7 or more and one or more rolling passes is performed, and a dehydrogenation heat treatment at 600 to 750 ° C is performed as a plate with a thickness of 50 mm or more. A method of manufacturing a good electromagnetic thick plate having magnetic properties with a magnetic flux density of 0.8 Tesla or more at a magnetic field of 80 A / m and a low coercive force.

However, A: Rolling shape ratio h _i : Inlet side plate thickness (mm) h _o : Outlet side plate thickness (mm) R: Rolling roll radius (mm) (2) After dehydrogenation heat treatment of plates with a thickness of 50 mm or more, 750 to 950
The magnetic flux density at a magnetic field of 80 A / m described in (1) is 0.8, which is characterized by annealing at ℃ or normalizing at 910 to 1000 ℃.
A method of manufacturing a good electromagnetic thick plate with magnetic characteristics superior to Tesla and low coercive force.

(3) C: 0.01% or less, Si: 0.02% or less, Mn: 0.
20% or less, P: 0.015% or less, S: 0.010% or less, Cr: 0.05%
Below, Mo: 0.01% or less, Cu: 0.01% or less, Ni: 0.1 to 2.0
%, Al: 0.005 to 0.040%, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, the balance is a steel composition of steel or a slab heated to 1150 to 1300 ° C. Then, under the condition that the finishing temperature is 900 ℃ or more, the rolling shape ratio A is 0.7 or more, and the rolling pass takes at least one rolling pass, and the plate thickness is 20mm or more and 50mm or more.
For thick plates of less than 750-950 ℃, or 91
A method for manufacturing a good electromagnetic thick plate having magnetic properties with a magnetic flux density of 0.8 Tesla or more at a magnetic field of 80 A / m and low coercive force, characterized by normalizing at 0 to 1000 ° C.

However, A: Rolling shape ratio h _i : Inlet plate thickness (mm) h _o : Outlet plate thickness (mm) R: Rolling roll radius (mm) [Operation] First, the magnetization process to increase the magnetic flux density in a low magnetic field. For example, when demagnetized steel is put in a magnetic field and the magnetic field is strengthened, the direction of the magnetic domain gradually changes, and the magnetic domain close to the direction of the magnetic field becomes dominant and the other magnetic domains are annealed. That is, the domain wall moves.

When the magnetic field becomes stronger and the movement of the domain wall is completed, the direction of the magnetic force of the entire magnetic domain changes direction. It is the ease of movement of the domain wall that determines the magnetic flux density in the low magnetic field in this magnetization process. In other words, it can be qualitatively said that in order to obtain a high magnetic field density in a low magnetic field, it is necessary to reduce as much as possible what hinders the movement of the domain wall.

The inventors here have a high magnetic flux density in a low magnetic field, and as a means for obtaining a thick steel sheet having a low coercive force,
We have made detailed studies on the utilization of elements that cause internal stress, void defects, and alloying elements, and have succeeded in achieving the intended purpose.

That is, for coarsening, Al having a grain refining effect is used.
To reduce N, reduce Al, N, and as a manufacturing method, raise the heating temperature as much as possible, coarsen the heating austenite grains, raise the rolling finishing temperature as much as possible, and prevent the grain refinement due to rolling. And annealing after rolling.

Next, in order to reduce the internal stress, it is necessary to reduce C.
It can be seen that in the 0.01Si-0.1Mn-0.01Al steel shown in Fig. 1, the magnetic flux density in a low magnetic field (80A / m) decreases as the C content increases.

Furthermore, it was found that the presence of hydrogen in the steel is also harmful, and as shown in FIG. 2, the magnetic properties are significantly improved by performing the dehydrogenation heat treatment.

As shown in Fig. 2, in 0.007C-0.01Si-0.1Mn steel, the size of void defects is reduced to 100μ or less by high shape ratio rolling, and the hydrogen content in the steel is reduced by dehydrogenation heat treatment. It can be seen that the stress also decreases and the magnetic flux density in a low magnetic field increases significantly.

As a result of various studies on the effect of void defects, it was found that the magnetic properties were significantly reduced when the size was 100 μ or more. It was found that the rolled shape ratio A needs to be 0.7 or more in order to eliminate the harmful void defects of 100 μ or more.

Furthermore, it is important to ensure the homogeneity of the magnetic properties, but the method according to the present invention is an extremely effective means for this.

Furthermore, as a result of various studies as an element that reduces the coercive force and does not reduce the magnetic flux density in a low magnetic field, it was found that Ni is optimal as shown in FIG.

Next, the reasons for limiting the components of the present invention will be given.

C is an element that increases the internal stress in steel and lowers the magnetic characteristics, particularly the magnetic flux density in a low magnetic field, and the lowest reduction contributes to not lowering the magnetic flux density in a low magnetic field. In addition, the lower the magnetic aging is, the less the deterioration with time is, and the permanent magnet can be used with good magnetic properties. Therefore, the content is limited to 0.010% or less. As shown in FIG. 1, a higher magnetic flux density can be obtained by further reducing the content to 0.005% or less.

Si and Mn are preferably as small as possible from the viewpoint of magnetic flux density in a low magnetic field, and Mn is preferably as low as MnS-based inclusions are generated. From this meaning, Si is limited to 0.02% or less and Mn is limited to 0.20% or less. Mn is more preferably 0.10% or less from the viewpoint of forming MnS inclusions.

P, S and O form non-metallic inclusions in steel and segregate to hinder the movement of the domain wall, and as the content increases, the magnetic flux density decreases and the magnetic properties decrease. The less the better. Therefore, P is 0.015%
Hereinafter, S is 0.010% or less and O is 0.005% or less.

Cr, Mo, Cu decrease the magnetic flux density in a low magnetic field, so the smaller the better, and it is necessary to make it as low as possible in order to reduce the degree of segregation. From this meaning, Cr is 0.05% or less, Mo is 0.01%. Hereinafter, Cu is 0.01% or less.

Ni is indispensable as an element that lowers the coercive force and does not lower the magnetic flux density in a low magnetic field, and it is necessary to add 0.1% or more in order to lower the coercive force. Addition of 2.0% or more lowers the coercive force and the magnetic flux density in a low magnetic field, so the content is limited to 0.1 to 2.0%. Further, this makes it possible to increase the strength without deteriorating the magnetic characteristics, and is preferably 1.0 to 2.0%.

Al is used as a deoxidizing agent and is an element indispensable for homogenizing the internal quality when the plate thickness is large as in the present invention.
% Is added, but if it is too much, inclusions are formed and the properties of the steel are impaired, so the upper limit is made 0.040% or less. Further, in order to reduce AlN having a grain refining effect, 0.020% or less is desirable.

N increases the internal stress and reduces the magnetic flux density in a low magnetic field by the grain refining action of AlN, so the upper limit is 0.00.
4% or less.

H reduces the electromagnetic characteristics and prevents the reduction of void defects, so H content is set to 0.0002% or less.

Next, the manufacturing method will be described.

Regarding the rolling conditions, first, the heating temperature before rolling is set to 1150 ° C. or higher in order to coarsen the heated austenite grains and improve the magnetic properties. Heating above 1300 ° C is unnecessary from the viewpoints of preventing scale loss and saving energy, so the upper limit was made 1300 ° C.

The rolling finishing temperature was set to 900 ° C in order to increase the magnetic flux density due to the coarsening of the crystal grains because the crystal grains become finer and the magnetic properties deteriorate due to the low temperature rolling in the finish of 900 ° C or less.

Further, in the hot rolling, the above-mentioned void defects are always generated in the solidification process of steel, but they always occur, and the role of hot rolling is important because the means for eliminating them must be done by rolling. That is, it is effective to increase the amount of deformation per hot rolling so that the deformation reaches the center of the plate thickness.

Specifically, high shape ratio rolling including one or more rolling passes with a rolling shape ratio A of 0.7 or more is performed to reduce the size of void defects to 10
Setting it to 0 μ or less is good for electromagnetic characteristics. By eliminating the void defects by the high shape ratio rolling during rolling, the dehydrogenation efficiency in the dehydrogenation heat treatment to be performed later is dramatically increased.

Then, following hot rolling, grain coarsening, internal strain removal, and dehydrogenation heat treatment are applied to thick materials with a plate thickness of 50 mm or more.
When the plate thickness is 50 mm or more, it is difficult for hydrogen to diffuse, which causes void defects and, together with the action of hydrogen itself, reduces the magnetic flux density in a low magnetic field.

For this reason, dehydrogenation heat treatment is performed, but if the dehydrogenation heat treatment temperature is less than 600 ° C, the dehydrogenation efficiency is poor, and if it exceeds 750 ° C, the transformation partially starts, so the temperature is in the range of 600 to 750 ° C. As the dehydrogenation time, various examination results [0.6 (t-5
0) +6] Time (t: plate thickness) is appropriate.

Annealing is performed for grain coarsening and internal strain removal.
If the temperature is lower than 0 ° C., the crystal grains do not coarsen, and if the temperature is 950 ° C. or higher, the uniformity of the crystal grains in the plate thickness direction cannot be maintained. Therefore, the annealing temperature is limited to 750 to 950 ° C.

Normalization is performed to adjust the crystal grains in the plate thickness direction and remove internal strain, but if the temperature is not less than 910 ° C and not more than 1000 ° C of the Ac ₃ point, the uniformity of the crystal grains in the plate thickness direction cannot be maintained. Sub-temperature is 910
Limited to ~ 1000 ° C. Below 910 ° C, the austenite and ferrite regions are mixed and the crystal grains become mixed.
If the temperature exceeds ℃, the homogeneity of the crystal grains in the plate thickness direction cannot be maintained. In addition,
In order to improve the magnetic properties, coarsening of crystal grains and removal of internal strain can be considered, but removal of internal strain is an essential condition. For removing internal strain, dehydrogenation heat treatment can be performed on a thick material having a plate thickness of 50 mm or more. Therefore, in the thick material of the present invention, the dehydrogenation heat treatment can also serve as the above-mentioned annealing or normalization.

On the other hand, a sheet having a plate thickness of 20 mm or more and less than 50 mm can be easily dehydrogenated, so dehydrogenation heat treatment is not necessary and the above annealing or normalization may be performed.

[Examples] Table 1 shows the manufacturing conditions of the electromagnetic thick plate, the ferrite grain size, and the magnetic flux density in a low magnetic field.

Examples 1 to 10 show examples of the present invention, and Examples 11 to 31 show comparative examples. Examples 1 to 5 are finished to a plate thickness of 100 mm and have uniform and coarse grains, high magnetic flux density in a low magnetic field, and low coercive force. Example 1
Compared to the above, Example 2 has low C, Examples 3 and 4 have low Mn, and Example 5 has low Al.
And the magnetic flux density in a lower magnetic field is high. Example 6-8 is 50
0 mm, Example 9 is 40 mm, and Example 10 is 20 mm, and it is uniform and coarse and has a high magnetic flux density in a low magnetic field and a low coercive force.

Has high magnetic flux density and specific resistance.

Example 11 has high C, Example 12 has high Si, and Example 13 has high Mn.
14 has a high P, Example 15 has a high S, Example 16 has a high Cr, and Example 17
Has a high Mo content, and Example 18 has a high Cu content, and each exceeds the upper limit, so that the magnetic flux density in a low magnetic field is low and the coercive force is high. In Example 19, since Ni is low and exceeds the lower limit, the magnetic flux density is high in a low magnetic field but the coercive force is high.

In Example 20, since Ni is high and exceeds the upper limit, the magnetic flux density in a low magnetic field is low and the coercive force is high. Example 21 is high in Al, and Example 22 is N
Is high, Example 23 has a high O, and Example 24 has a high H, and since the respective upper limits are exceeded, the magnetic flux density in a low magnetic field is low.
In Example 25, the heating temperature is below the lower limit, in Example 26, the rolling finish temperature is below the lower limit, and in Example 27, the maximum shape ratio is below the lower limit.
In 28, the dehydrogenation heat treatment temperature is out of the lower limit, in Example 29, the normalization temperature is out of the lower limit, in Example 30, the normalization temperature exceeds the upper limit, and in Example 31, there is no dehydrogenation heat treatment, so the magnetic flux density is low in a low magnetic field. Has become.

[Effects of the Invention] As described in detail above, according to the present invention, it has been possible to provide a thick steel plate having a large thickness with uniform high electromagnetic characteristics by appropriately limiting the components, and to utilize the magnetic properties of direct current magnetization. It is applicable to a structure that has the above-mentioned structure, and its manufacturing method is a method of simultaneously limiting the above-mentioned components and simultaneously performing crystal grain adjustment and dehydrogenation heat treatment after hot rolling, which provides an extremely economical manufacturing method. It has a great industrial effect.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of C content on the magnetic flux density at 80 A / m, and FIG. 2 is a graph showing the effect of void defect size and dehydrogenation heat treatment on the magnetic flux density at 80 A / m. The figure is a graph showing the effect of Ni content on coercive force.

Claims (3)

[Claims] 1. By weight%, C: 0.01% or less, Si: 0.02% or less, Mn: 0.20% or less, P: 0.015% or less, S: 0.010% or less, Cr: 0.05% or less, Mo: 0.01% or less. , Cu: 0.01% or less, Ni: 0.1 to 2.0%, Al: 0.005 to 0.040%, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, the balance is steel having a steel composition consisting essentially of iron. 11 pieces or pieces
Rolling is performed by heating to 50 to 1300 ° C, and with a finishing temperature of 900 ° C or more, with a rolling shape ratio A of 0.7 or more and at least one rolling pass, and as a thick plate of 50 mm or more, 600 to 750
A method for manufacturing a good electromagnetic thick plate having magnetic properties with a magnetic flux density of 0.8 Tesla or more at a magnetic field of 80 A / m and low coercive force, which is characterized by performing dehydrogenation heat treatment at ℃. However, A: Rolling shape ratio h _i : Strip thickness (mm) h _o : Strip thickness (mm) R: Rolling roll radius (mm) 2. After dehydrogenation heat treatment of a thick plate having a thickness of 50 mm or more, 75
The magnetic material having a magnetic flux density of 0.8 Tesla or more at a magnetic field of 80 A / m according to claim 1, which is annealed at 0 to 950 ° C or normalized at 910 to 1000 ° C, and has a low coercive force. Manufacturing method of electromagnetic plate. 3. By weight%, C: 0.01% or less, Si: 0.02% or less, Mn: 0.20% or less, P: 0.015% or less, S: 0.010% or less, Cr: 0.05% or less, Mo: 0.01% or less. , Cu: 0.01% or less, Ni: 0.1 to 2.0%, Al: 0.005 to 0.040%, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, the balance is steel having a steel composition consisting essentially of iron. 11 pieces or pieces
Rolling is performed by heating to 50 to 1300 ° C and rolling at a finishing shape temperature of 900 ° C or more with at least one rolling pass with a rolling shape ratio A of 0.7 or more, and as a thick plate of 20 mm or more and less than 50 mm,
A method for manufacturing a good electromagnetic thick plate having magnetic properties with a magnetic flux density of 0.8 Tesla or more at a magnetic field of 80 A / m and low coercive force, characterized by being annealed at 750 to 950 ℃ or normalized at 910 to 1000 ℃ . However, A: Rolling shape ratio h _i : Strip thickness (mm) h _o : Strip thickness (mm) R: Rolling roll radius (mm)