JPH0689401B2 - Manufacturing method of electromagnetic thick plate for non-directional DC magnetization - 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. Until now, electromagnetic plates have been manufactured with pure 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
There is a strong demand for the development of steel materials with high magnetic flux density at A / m. 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 for non-directional DC magnetization having a high magnetic flux density in a low magnetic field and a small magnetic characteristic difference in the plate thickness direction. 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)% by weight, C: 0.01% or less, Si: 0.02% or less, Mn: 0.20% or less, P: 0.01
5% or less, S: 0.010% or less, Cr: 0.05% or less, Mo: 0.01% or less, Cu: 0.01% or less, Ti: 0.005 to 0.03%, Ca: 0.0005 to 0.
01%, Al: 0.005% or less, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, the balance heating a steel slab or a slab of steel composition consisting essentially of iron to 1150 to 1300 ° C. Then, under the condition that the finishing temperature is 900 ° C. or higher, the rolling shape ratio A is 0.7 or more and the rolling is performed once or more to obtain a thick plate having a thickness of 50 mm or more. A method for producing an electromagnetic slab for non-directional DC magnetization, which has a magnetic characteristic of a magnetic flux density of 0.8 Tesla or more at a magnetic field of 80 A / m, characterized by performing a dehydrogenation heat treatment at a temperature.

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 plate thickness of 50 mm or more 750 to 950 ° C
The method for producing an electromagnetic thick plate for non-directional DC magnetization according to (1), characterized in that it is annealed at 910.degree.

(3) In% by weight, C: 0.01% or less, Si: 0.02% or less, Mn: 0.20% or less, P: 0.01
5% or less, S: 0.010% or less, Cr: 0.05% or less, Mo: 0.01% or less, Cu: 0.01% or less, Ti: 0.005 to 0.03%, Ca: 0.0005 to 0.
01%, Al: 0.005% or less, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, the balance heating a steel slab or a slab of steel composition consisting essentially of iron to 1150 to 1300 ° C. Then, under the condition that the finishing temperature is 900 ° C. or higher, rolling is performed with a rolling pass having a rolling shape ratio A of 0.7 or more one or more times to obtain a thick plate having a plate thickness of 20 mm or more and less than 50 mm, and the plate is 750 to 950. Of an electromagnetic slab for non-directional DC magnetization having magnetic characteristics of a magnetic flux density of 0.8 Tesla or more at a magnetic field of 80 A / m characterized by annealing at a temperature of ℃ or normalizing at a temperature of 910 to 1000 ℃ Manufacturing method.

A: Rolling shape ratio h _i : Inlet side plate thickness (mm) h _o : Outlet side 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 is further strengthened and the movement of the domain wall is completed, the direction of the magnetic force of the entire magnetic domain then changes direction. It is the ease of movement of the domain wall that determines the magnetic flux density in a low magnetic field during this magnetization process.

That is, it can be qualitatively said that in order to obtain a high magnetic flux density in a low magnetic field, it is necessary to reduce as much as possible the obstacles to the movement of the domain wall.

As a means for obtaining a high magnetic flux density in a low magnetic field, the inventors here have made a detailed study on the effect of the element on the grain size and the effect of the element and the void defect causing the internal stress, and Inventing a method for manufacturing a steel sheet having high magnetic flux density characteristics.

First, for coarsening, Al which has a grain refining effect
In order to reduce N, it is necessary to reduce Al and N.
In particular, for Al, grain growth of ferrite grains occurs as it is lowered as shown in FIG. 1, but it was found that abnormal grain growth of crystal grains occurs in a non-added region, that is, 0.005% or less. . However, if Al is not added, it is necessary to add another deoxidizer.

The present inventors used Ti and Ca as deoxidizing agents instead of Al and as elements that do not reduce the magnetic flux density in a low magnetic field.
It was found that the combined addition of

Further, as a manufacturing method, the heating temperature is raised as much as possible, the heating austenite grains are coarsened, and the rolling finishing temperature is raised as much as possible to prevent the grain refinement due to rolling and to carry out annealing after rolling.

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

Further, it was found that the presence of hydrogen in the steel is harmful, and as shown in FIG. 3, the magnetic properties are significantly improved by performing the dehydrogenation heat treatment. As shown in Fig. 3, 0.007C-
In 0.01Si-0.1Mn steel, by reducing the size of void defects to 100μ or less by high shape ratio rolling and reducing hydrogen in the steel by dehydrogenation heat treatment, internal stress is also reduced and magnetic flux at low magnetic field is reduced. It can be seen that the density 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 a rolled shape ratio A of 0.7 or more is sufficient to eliminate the void defects.

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

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, especially the magnetic flux density in a low magnetic field, and reducing it as much as possible 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. 2, a higher magnetic flux density can be obtained by further setting the content to 0.005% or less.

Si and Mn are preferably small in terms of magnetic flux density in a low magnetic field, and Mn is also preferably low in terms of producing MnS-based inclusions.
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, O form non-metallic inclusions in steel and segregate to impede the movement of the magnetic domain wall, and as the content increases, the magnetic flux density decreases and the magnetic properties deteriorate. So the less, the better. Therefore, P is 0.015
%, 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.

Since Ti and Ca are used as complex deoxidizing elements instead of Al, 0.005% and 0.0005% or more are added respectively, but 0.04%
And 0.01% or more lowers the magnetic flux density in a low magnetic field, so Ti is limited to 0.005 to 0.03% and Ca is limited to 0.0005 to 0.01%.

Since Al produces AlN and has a grain refining effect, it is necessary to reduce it as much as possible, so the content is made 0.005% or less.

N increases the internal stress and reduces the magnetic flux density in a low magnetic field due to the grain refining effect 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.

Regarding the rolling finishing temperature, at the finishing of 900 ° C or lower, the crystal grains become finer due to the low temperature rolling and the magnetic properties are deteriorated, so the temperature was set to 900 ° C or higher in order to increase the magnetic flux density due to the coarsening of the crystal grains.

Further, in the hot rolling, the above-mentioned void defects are large and small in the solidification process of steel, but they are always generated and the means for eliminating them must be done by rolling. Therefore, the role of hot rolling is important.

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, it is preferable for the electromagnetic characteristics to perform the high shape ratio rolling including one or more rolling passes with the rolling shape ratio A of 0.7 or more, and to make the size of the void defect 100 μm or less.

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, the 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 starts partially, so the dehydrogenation heat treatment is performed in the temperature range of 600 to 750 ° C.

As the dehydrogenation time, the results of various studies [0.6 (t-50) + 6
0] 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.

Normalizing is performed to adjust the crystal grains in the plate thickness direction and remove internal strain, but the normalizing temperature is limited to 910 to 1000 ° C. Below 910 ° C, the crystal grains become mixed grains due to the present in the austenite and ferrite regions, and above 1000 ° C, the homogeneity of the crystal grains in the plate thickness direction cannot be maintained. 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. Internal strain can be removed by dehydrogenation heat treatment for thick materials with a 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, when the plate thickness is 20 mm or more and less than 50 mm, hydrogen diffusion is easy, so dehydrogenation heat treatment is not necessary and the above-mentioned 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 12 show examples of the present invention, and Examples 13 to 35 show comparative examples. Examples 1 to 7 are finished to a plate thickness of 100 mm and show high magnetic characteristics with uniform and coarse grains. Compared to Example 1, further Example 4
Is low C, Examples 5 and 6 are low Mn, and Example 7 is low Al, showing higher magnetic properties.

Examples 8 to 10 were finished to 500 mm, Example 11 to 40 mm, and Example 12 to 20 mm, showing uniform and coarse grains and high magnetic properties. Example 13 is C
, Example 14 has high Si, Example 15 has high Mn, Example 16 has high P, Example 17 has high S, Example 18 has high Cr, Example 19 has high Mo, and Example 20 has high Cu. High, Example 21 has high Ti, Example 22 has high Ca, Example 23 has high both Ti and Ca, Examples 24 and 25 have high Al,
Example 26 has a high N value, Example 27 has a high O value, and Example 28 has a high H value.

In Example 29, the heating temperature is below the lower limit, in Example 30, the rolling finish temperature is below the lower limit, and in Example 31, the maximum shape ratio is below the lower limit.
In Example 32, the dehydrogenation heat treatment temperature is out of the lower limit, in Example 33, the annealing temperature is out of the lower limit, in Example 34, the normalizing temperature exceeds the upper limit, and in Example 35, the dehydrogenation heat treatment is absent, so that the magnetic property value is low.

[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 THE DRAWINGS FIG. 1 is a graph showing the effect of Al content on the ferrite grain size, and FIG. 2 is C on the magnetic flux density at 80 A / m.
FIG. 3 is a graph showing the influence of the content, and FIG. 3 is a graph showing the influence of the size of the void defects and the dehydrogenation heat treatment on the magnetic flux density at 80 A / m.

Claims (3)

[Claims] 1. By weight%, C: 0.01% or less, Si: 0.02% or less, Mn: 0.20% or less, P: 0.01
5% or less, S: 0.010% or less, Cr: 0.05% or less, Mo: 0.01% or less, Cu: 0.01% or less, Ti: 0.005 to 0.03%, Ca: 0.0005 to 0.
01%, Al: 0.005% or less, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, the balance heating a steel slab or a slab of steel composition consisting essentially of iron to 1150 to 1300 ° C. Then, under the condition that the finishing temperature is 900 ° C. or higher, rolling is performed by taking a rolling pass with a rolling shape ratio A of 0.7 or more one or more times to obtain a thick plate having a plate thickness of 50 mm or more, and the thick plate of 600 to 750 ° C. A method for manufacturing an electromagnetic slab for non-directional DC magnetization, which has a magnetic property of a magnetic flux density of 0.8 Tesla or more at a magnetic field of 80 A / m, characterized by performing a dehydrogenation heat treatment at a temperature. However, A: Rolling shape ratio h _i : Inlet plate thickness (mm) h _o : Outlet plate thickness (mm) R: Rolling roll radius (mm) 2. A 750-mm thick plate having a thickness of 50 mm or more after dehydrogenation heat treatment
2. The method for manufacturing an electromagnetic thick plate for non-directional DC magnetization according to claim 1, wherein the annealing is performed at .about.950.degree. C. or the temperature is normalized at 910.degree. 3. 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% or less, Mo: 0.01% or less. , Cu: 0.01% or less, Ti: 0.005 to 0.03%, Ca: 0.0005 to 0.01%, Al: 0.005% or less, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, and the balance substantially iron A steel slab or a slab with a steel composition consisting of 11
Rolling is performed by heating to 50 to 1300 ° C. and taking a rolling pass with a rolling shape ratio A of 0.7 or more at least once under the condition that the finishing temperature is 900 ° C. or more to obtain a thick plate having a plate thickness of 20 mm or more and less than 50 mm. Anneal the plate at a temperature of 750-950 ℃ or 910-1000
A method for manufacturing an electromagnetic slab for non-directional DC magnetization, which has a magnetic characteristic of a magnetic flux density of 0.8 Tesla or more at a magnetic field of 80 A / m, characterized by normalizing at a temperature of ℃. However A: Rolling shape ratio h _i : Inlet plate thickness (mm) h _o : Outlet plate thickness (mm) R: Rolling roll radius (mm)