JPH0753883B2 - Manufacturing method of electromagnetic soft iron for thick plate - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for manufacturing electromagnetic soft iron for thick plates, which has excellent magnetic characteristics and is suitable for, for example, blocking leakage magnetism.

(Prior Art) With the remarkable progress of science and technology in recent years, for example, in the field of pharmaceutical equipment, a nuclear magnetic resonance tomography apparatus (MRI) utilizing a nuclear magnetic resonance phenomenon has been put into practical use and actively introduced. ing.

However, when using this nuclear magnetic resonance tomography apparatus, it is necessary to block a large amount of leakage magnetism that occurs. Therefore, the steel sheet used as a structural member of this nuclear magnetic resonance tomography apparatus is required to have magnetic blocking characteristics, and the thickness of the steel sheet is 20 mm or more from the necessity of having strength as an apparatus. Many.

On the other hand, electromagnetic soft iron for thick plates, which has excellent magnetic cutoff characteristics, that is, high magnetic permeability, is used not only for the above-mentioned nuclear magnetic resonance tomography equipment, but also for large scientific experimental equipment such as cyclotrons, nuclear fusion equipment, medical equipment, etc. It is also a material used as a structural member for magnetic shielding.

Therefore, in order to further advance the results of science and technology in recent years, the electromagnetic soft iron for thick plates is required to satisfy both originally excellent mechanical properties and magnetic properties represented by magnetic permeability or magnetic flux density. It is strongly desired from each field to do so.

An electromagnetic soft steel plate is known as a steel plate having such magnetic shutoff characteristics, and a thin plate generally used for a transformer is well known. As a steel material with excellent magnetic properties,
Electromagnetic soft iron bar specified in JIS C 2503 or JIS C 2504,
It is an electromagnetic soft iron plate. What is specified in JIS C 2503 is 1.0
It is a bar material with a diameter in the range of up to 16 mm, and also JIS C 25
What is specified in 04 is a thin plate with a thickness of 0.6 to 4.5 mm, both of which are intended for application to small parts for relays or electromagnets.

Also, using S10C, which is a carbon steel material for machine structure specified in JIS C 4051, which is not classified for magnetism, 250 mm
There is an example in which it is hot worked into width and used as a magnetic material.

Further, as disclosed in JP-A-60-96749, JP-B-63-45442 or JP-B-63-45443, the content of sol.Al is as large as 0.005-1.00% by weight, Si
In recent years, a thick plate for direct-current magnetization, which is an Al deoxidized ultra-low carbon steel with a certain reduction in Al, has been proposed.

(Problems to be Solved by the Invention) However, in these known means, a thick plate having excellent magnetic characteristics, for example, capable of blocking magnetic leakage when using a nuclear magnetic resonance tomography apparatus (MRI) It is impossible to provide a stable supply of electromagnetic soft iron. That is, (i) the electromagnetic soft iron bar or electromagnetic soft iron plate shown in JIS C 2503 or JIS C 2504 is intended for small parts as described above, and the mechanical characteristics as a structural member are taken into consideration at all. Not not. Therefore, when applying this electromagnetic soft iron plate to the above-mentioned nuclear magnetic resonance tomography apparatus, it is necessary to stack several tens of these electromagnetic soft iron plates in order to secure the strength of the apparatus, the manufacturing cost, the product In terms of quality, practical implementation cannot be achieved. (Ii) In the example of using the carbon steel material for machine structure shown in JIS C 4051, since no consideration was given to the magnetic properties, the maximum magnetic permeability μ was only 1800 (B / H) or less, which was an extremely low value. Not obtained. Therefore, it is still impossible to provide the desired electromagnetic soft iron for thick plates. Further (iii) the means proposed by JP-A-60-96749, JP-B-63-45442 or JP-A-63-45443, in order to improve the magnetic characteristics of the obtained electromagnetic soft iron, This is a means for significantly reducing impurities such as Cr in the steel during the refining stage.
In the means proposed by 60-96749, the Cr
The upper limit of the content is limited to 0.05% by weight.

However, when a refractory other than an acid refractory, such as a magnesia-chromium refractory, is used as the refractory used for the furnace wall or the like, impurities such as Cr inevitably mixed in the furnace wall or the like are contained in the molten steel. Since it is mixed, Cr in the molten steel is 0.05
% Or more will be contained.

Therefore, JP-A-60-96749 and JP-B-63-45442
In the means proposed by Japanese Patent Publication No. 63-45443 or No. 63-45443, the refractory used for the furnace wall and the like is xAl ₂ O ₃
It was supposed to be limited to ySiO ₂ or acidic refractory containing SiO ₂ as a main component.

On the other hand, magnesia-chromium refractories have a maximum usable temperature of about 1650 ° C of the above-mentioned acidic refractories, while they are generally said to be able to withstand high temperatures of 1870 ° C. As a refractory material, it has extremely suitable characteristics and its application is extremely wide.

Therefore, even when smelting steel for electromagnetic soft iron, if the magnesia-chromium refractory is used, the smelting temperature can be further raised and the life of the refractory can be extended. Is mixed in molten steel
The amount of impurities such as Cr increases. In other words, when magnesia / chromium refractory is used during melting of electromagnetic soft iron for thick plates, Cr will necessarily be contained in molten steel in an amount of 0.05% or more. If it is possible to sufficiently improve the magnetic characteristics of, it is not necessary to strictly control the amount of impurities mixed as in the past, in other words, for thick plates without deterioration of the magnetic characteristics even when impurities are mixed. It is possible to manufacture electromagnetic soft iron.

Here, an object of the present invention is to provide an electromagnetic soft iron for thick plates, which has excellent magnetic characteristics, such as capable of blocking leakage magnetism when using a nuclear magnetic resonance tomography apparatus (MRI). A thick plate that can be stably provided by using a magnesia-chromium refractory in the manufacturing stage, that is, it can be provided without deteriorating the magnetic properties even when mixed with more Cr than the conventional electromagnetic soft iron for thick plates. It is to provide a manufacturing method of electromagnetic soft iron for use.

(Means for Solving the Problems) As a result of various studies to solve the above problems, the present inventors have found that in order to improve the magnetic properties and to improve the homogeneity of the magnetic properties in the plate thickness direction, It is effective to reduce the content of components that increase the magnetic susceptibility as much as possible, and in the heat treatment after hot working, in order to facilitate the growth of crystal grains, processing strain is added to the crystal grains during hot working. It was noted that the above is effective, and that the heat treatment temperature is set just below the austenite-ferrite transformation temperature to prevent transformation.

Based on these facts, the present inventor has conducted further studies, and hot working a steel ingot having a specified composition such that the finishing temperature is a temperature at which the steel becomes a ferrite single phase, for example, After rolling, forging or drawing and processing to a predetermined size, in order to remove the processing strain of the crystal grains and to coarsen the crystal grains, heat and hold it just below the austenite-ferrite transformation temperature, and then gradually By cooling, for example, electromagnetic soft iron for thick plates having excellent magnetic characteristics that can block leakage magnetism when using a nuclear magnetic resonance tomography apparatus (MRI) is magnesia・ Stable with chrome refractory,
That is, it is possible to provide even if a larger amount of Cr is mixed in than in the conventional electromagnetic soft iron for thick plates, without degrading the magnetic characteristics. The present invention has been completed by finding that it is possible to provide a method for manufacturing electromagnetic soft iron for thick plates.

Here, the gist of the present invention is, in% by weight, C: 0.01% or less, Si: 0.30% or less, Mn: 0.50% or less, P: 0.01% or less, S: 0.01% or less, sol.Al: A steel ingot having a steel composition of 0.005 to 0.060%, Cr: more than 0.05% and 0.25% or less, the balance Fe and unavoidable impurities is finished at a finishing temperature of 650 to 900.
It is a method for producing electromagnetic soft iron for thick plates, characterized in that after hot working at ℃, it is heated to 750 ℃ ~ Ar ₃ points, held for 30 minutes or more and then gradually cooled.

In the present invention, "hot working" refers to rolling, forging, drawing or the like.

Further, in the present invention, the "steel ingot" is a base material of the product obtained by the hot working, specifically, a slab,
A steel ingot such as bloom.

(Operation) Hereinafter, the present invention will be described in detail together with operation effects. In this specification, "%" means "% by weight" unless otherwise specified.

First, the reason for limiting the composition of the steel ingot used in the present invention will be described.

C is an element having the highest magnetic property demagnetization rate, and it is desirable to reduce it as much as possible in order to improve the magnetic property. However, because it costs a lot of money to reduce it,
Content should be 0.01% or less.

In the Al deoxidizing type electromagnetic soft iron for thick plates, which is the object of the present invention, Si inhibits the coarsening of crystal grains during heat treatment due to the grain size regulating action. Therefore, the content should be 0.30% or less.

As is well known, Mn is an element that greatly contributes to ensuring the strength of steel, and, like C, is an element that increases the demagnetization rate.
Therefore, it is desirable to reduce the demagnetization rate from the viewpoint of reducing the demagnetization rate, but in order to secure the mechanical strength of the steel sheet obtained by the present invention, considering that it is used as a structural member of a large machine as described above. The upper limit is 0.50%.

P and S both exist in steel and form non-metallic inclusions,
Moreover, since the segregation occurs, the smaller the content, the better.
Further, it is an element that increases the coercive force with the increase of its content and deteriorates the magnetic characteristics. Therefore, the smaller the content, the more desirable, but the reduction of these elements always involves an increase in cost. Therefore, P is 0.01% or less and S is 0.01% or less.

Al is an element that acts as a deoxidizer in steel,
In order to exert such an effect, it is necessary to contain 0.005% or more, but if added in a large amount, inclusions are formed and the properties of steel are impaired, so the upper limit is made 0.060% or less. Therefore, the content of Al is set to 0.005 to 0.060%.

Since Cr is an element that deteriorates the magnetic properties, it has been conventionally considered desirable to reduce the amount. But Cr
Is an element that is inevitably mixed from the furnace wall and the like, and it takes a very large cost to remove Cr. Especially when magnesia / chromium refractory is used for the furnace wall, the refractory reacts with the molten steel and Cr, Ni, Mo, etc. are mixed in the steel. However, in the present invention, it is not necessary to reduce the Cr content by appropriately limiting the production conditions as described later. Therefore, the lower limit of the Cr content is
Over 0.05%. Further, the upper limit of the Cr content is 0.25% from the viewpoint of improving the magnetic properties. Therefore, the range of Cr content is
Limit to more than 0.05% and 0.25% or less.

A steel ingot having the above composition is manufactured under the following conditions. These conditions will be described in detail.

First, a steel ingot having the above composition is hot worked at a finishing temperature at which the steel structure becomes a ferrite single phase. Generally, adding work strain to crystal grains during hot working is disclosed in
As disclosed in Japanese Patent Laid-Open No. 208417, it is an effective means for growing crystal grains after heat treatment. Since the coarsening of crystal grains is one of the factors that improve the magnetic properties of steel products, it is also utilized in the present invention to improve the magnetic properties of the obtained products.

As an example of the hot working, any working method such as rolling, forging or drawing, which can give working strain to the steel ingot at the time of working, is not particularly limited. Further, in the present invention, the temperature at which the steel structure becomes a ferrite single phase is 900 ° C. or less from the Fe—C binary system phase diagram.

Thus, the finishing temperature for hot working is set to the ferrite-austenite transformation temperature or lower. In other words, the work strain is applied to the ferrite grains, and a heat treatment is performed after the work to release the work strain and coarsen the crystal grains.

Therefore, the finishing temperature is 650 ~ 900 ℃ from the above viewpoint.
And more preferably 650 to 800 ° C.
Is the range.

Next, the steel ingot thus hot-worked is heat-treated for the purpose of releasing work strain and coarsening crystal grains. The heating temperature of this heat treatment is preferably equal to or lower than the ferrite-austenite transformation temperature, and is preferably right below it. That is, when heated to the transformation temperature or higher, the structure becomes a transformation texture, and the presence of AlN causes the crystal grains to become finer, so that the magnetic properties are significantly deteriorated. Therefore, the heating temperature for heat treatment is set to ₃ Ar points or less. Also, below 750 ° C,
Since the processing strain cannot be removed, the temperature should be 750 ℃ or higher. Therefore, the heat treatment temperature is limited to 750 ° C. or higher and Ar ₃ point or lower. The upper limit of Ar ₃ can be 900 ° C., for example.

The holding time for heating is 30 min or more. This is the minimum value required to remove distortion.

Then, after this, gradual cooling, specifically, cover gradual cooling is performed to perform dehydrogenation treatment. Cooling rate of slow cooling is generally 30 ℃ / h
It is about r.

Thus, according to the present invention, by combining the composition and manufacturing conditions of a proper steel ingot, the electromagnetic soft iron for thick plates is melted using magnesia / chromium refractory, etc., and Cr in the steel is 0.
Even if a steel ingot containing more than 05% is used, it is possible to produce electromagnetic soft iron for thick plates having excellent magnetic properties.

Further, the present invention will be described in detail together with examples, but this is an exemplification of the present invention, and the present invention is not limited to this.

Example Steel ingots having the compositions shown in Table 1 (steel ingot No. 1 to steel ingot N
hot working (rolling) under the same conditions shown in Table 1.
Then, the sample was heat-treated under the heat-treatment conditions shown in Table 1, and then slowly cooled to obtain a sample (sample No. 1 to sample No. 31) of electromagnetic soft iron for thick plates. .

Regarding these sample No.1 to sample No.31, magnetic characteristics ・ B ₁ (magnetic flux density when magnetic field is 1 Oe) ・ μ _max (maximum magnetic permeability) Mechanical characteristics ・ YP (yield point) ・ TS (tensile strength・ El (elongation) low temperature toughness ・ vE ₀ ^Ave (V notch Charpy impact absorption energy value at 0 ° C) was measured. The results are summarized in Table 2. Also the first
In the figure, sample No.1 to sample No.8, sample No.24 to sample N
The relationship between the finishing temperature and the magnetic properties investigated for o.28 is shown. Further, FIG. 2 shows the relationship between the heat treatment temperature and the magnetic characteristics, which was investigated for sample No. 1 to sample No. 8 and sample No. 24 to sample No. 28. Furthermore, FIG. 3 shows the relationship between the holding time and the magnetic characteristics investigated for the same sample.

In Table 1, sample No. 1 to sample No. 11 and sample No. 24 to sample No. 28 are samples in which the amount of sol.Al was changed.

Of these, sample No. 1 to sample No. 8 and sample No. 24 to sample No. 28 were obtained from the same steel ingot (steel ingot No. 1), and only the finishing temperature was changed. It is a sample obtained by.

In addition, sample No.3 to sample No.7, sample No.24 to sample N
o.27 is a steel plate obtained after hot rolling at 780 ° C.
Further, it is a sample obtained by variously changing the heat treatment conditions.

Further, sample No. 9, sample No. 10 and sample No. 29 are samples obtained from steel ingots having a sol.Al content of 0.037%, and the finishing temperatures are variously changed.

Sample No. 11 is a sample containing 0.052% of sol.Al.

Sample No. 12, Sample No. 13 and Sample No. 14 are abbreviated Si.
This is a sample in which the sol.Al and Mn contents are changed by increasing it to 0.15%.

Sample No.15, Sample No.16, Sample No.17 and Sample No.18
Is a sample in which sol.Al and Mn are changed by further increasing Si to about 0.27%.

Further, sample No. 19 to sample No. 23 are samples of the comparative example, the content of sol.Al in sample No. 19 is P, and that in sample No. 20 is P.
Of Sample No. 21, the content of Mn of Sample No. 21, the content of Si of Sample No. 22, and the content of C of Sample No. 23 are outside the scope of the present invention.

As is clear from Table 2 and FIGS. 1 to 3,
It can be seen that the samples according to the invention have excellent magnetic properties, toughness and mechanical properties.

(Effects of the Invention) As described in detail above, according to the present invention, an electromagnetic soft iron for thick plates having excellent magnetic characteristics can be stably produced by using a magnesia / chromium refractory material in the melting stage, that is, the conventional method. It is now possible to provide it by containing more Cr than the electromagnetic soft iron for thick plates.

The practical significance of the present invention having such an effect is remarkable.

[Brief description of drawings]

1 is a graph showing the relationship between finishing temperature and magnetic properties in the example of the present invention; FIG. 2 is a graph showing the relationship between heat treatment temperature and magnetic properties in the example of the present invention; FIG. 3 is a graph showing the relationship between holding time and magnetic characteristics in the example of the present invention.

Claims (1)

[Claims] 1. By weight%, C: 0.01% or less, Si: 0.30% or less, Mn: 0.50% or less, P: 0.01% or less, S: 0.01% or less, sol.Al: 0.005-0.060%, Cr: A steel ingot having a steel composition of more than 0.05% and 0.25% or less and the balance Fe and unavoidable impurities is finished at a finishing temperature of 650 to 900
A method for manufacturing electromagnetic soft iron for thick plates, which comprises hot working at ℃, heating to 750 ℃ ~ Ar ₃ points, holding for 30 minutes or more and then gradually cooling.