JP2773951B2 - Manufacturing method of electromagnetic thick plate with excellent low-field magnetic properties - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an electromagnetic thick plate having excellent low-field magnetic properties.

(Prior Art) In recent years, the need for a magnetic shield has been increasing more and more, and in particular, a magnetic shield in a lower magnetic field has become a problem. For example, considering the effects on pacemakers around the MRI diagnostic room in hospitals and the effects of elevator motors on computer equipment in intelligent buildings, etc., sufficient shielding properties against magnetic fields of tens of gauss or less are considered. is required.

An electromagnetic thick plate used for a magnetic shield is required to have a high magnetic flux density even at a very low magnetic field, for example, a magnetizing force of 20 A / m or less, and to have good uniformity in the thickness direction.

It is well known that many materials such as silicon steel sheets and soft magnetic iron sheets have been provided in the field of thin sheets as electromagnetic steel sheets having excellent magnetic flux density. However, when used as a structural member, there are problems in terms of assembly processing and strength, and it becomes necessary to use a thick steel plate. Until now, electromagnetic thick plates have been disclosed in JP-A-60-96749 and JP-A-1-142.
No. 028 is known.

In order to exhibit effective shielding properties for magnetic fields of tens of gauss or less, it is necessary to have a high magnetic flux density in a very low magnetic field of, for example, a magnetizing force of about 20 A / m,
Conventionally developed steel materials do not consider this level of characteristics, and therefore high magnetic flux densities cannot be obtained with a magnetizing force of 20 A / m.

(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 manufacture an electromagnetic thick plate having a magnetic flux density of 0.6 Tesla or more at a magnetizing force of 20 A / m and excellent in low magnetic field magnetic properties. Is to provide cheeks.

(Means for Solving the Problems) The gist of the present invention is as follows.

1. By weight%, C: 0.005% or less, Si: more than 0.2%, 3.5% or less, Al: more than 0.2%, 3.5% or less, the sum of the weight% of Si and Al is 1.5% or more, Mn: 0.5% or less, S: 0.010% or less, N: 0.00
Rolling a steel slab or slab having a steel composition of 8% or less, O: 0.006% or less, and the balance substantially consisting of iron at least one rolling pass at 900 ° C or more and a rolling shape ratio A of 0.6 or more. And continuously reduce the rolling reduction from 35% to 70 at 700 ° C to 900 ° C.
%. A method for producing an electromagnetic thick plate excellent in low magnetic field magnetic properties, characterized in that rolling is carried out to not more than 10% and annealing is performed at 950 ° C. to 1150 ° C.

However, A: Rolling shape ratio h _i : Incoming plate thickness (mm) h _o : Outgoing plate thickness (mm) R: Rolling roll radius (mm) 2. By weight%, C: 0.005% or less, Si: Exceeding 0.2%, 3.5% or less, Al: more than 0.2%, 3.5% or less, the sum of the weight percentages of Si and Al is 1.5% or more, Mn: 0.5% or less, S: 0.010% or less, N: 0.00
Rolling a steel slab or slab having a steel composition of 8% or less, O: 0.006% or less, and the balance substantially consisting of iron at least one rolling pass at 900 ° C or more and a rolling shape ratio A of 0.6 or more. And continuously reduce the rolling reduction from 35% to 70 at 700 ° C to 900 ° C.
%. A method for producing an electromagnetic thick plate excellent in low magnetic field magnetic properties, characterized in that rolling is carried out to at most 1000% and normalizing is performed at 1000 ° C. to 1200 ° C.

However, A: rolling shape ratio h _i: thickness at entrance side (mm) h _o: thickness at delivery side (mm) R: rolling roll radius (mm) (action) will be described first magnetization process.

In the demagnetized state, the magnetic domains inside the steel are finely divided within one crystal grain, each of which takes one of the magnetic domain easy directions, and is totally disordered as a whole. When the steel is magnetized in a certain direction, the magnetic domain having a direction close to the direction of magnetization from the outside gradually expands by combining other magnetic domains with silkworms. In other words, the domain wall moves.
In a low magnetic field, this mainly promotes magnetization.

Therefore, it is easy to move the domain wall that determines the magnetic flux density in the low magnetic field. It has been qualitatively said that, in order to obtain a high magnetic flux density, it is important to reduce the crystal grain boundaries which hinder domain wall movement, that is, to make the crystal grains coarser (Japanese Patent Application Laid-Open No. 60-96749). Gazette).

However, in the case of a thick plate, a method for stably obtaining coarse particles over the entire thickness has not been established. Conventionally, recrystallization by heat treatment after rolling has been used for coarsening the crystal grains of an electromagnetic thick plate (Japanese Patent Application Laid-Open No. 60-96749). Becomes coarse. However, when the heat treatment is performed at a temperature exceeding the Ac ₁ transformation point, the particles are refined during the transformation, so that the heat treatment temperature limit is around 900 ° C.

Here, the inventors succeeded in stably obtaining extremely large crystal grains over the entire sheet thickness when a detailed study was performed on the chemical composition, rolling conditions, and heat treatment conditions for obtaining coarse grains. .

Very low C of 0.005% or less, and the sum of the weight percentages of Si and Al is 1.5%
In the above case, it has been found that even after the rolling, heat treatment is performed at a temperature exceeding the Ac ₁ transformation point, whereby remarkable coarsening can be achieved without fineness. Specifically, coarse grains can be obtained by annealing at 950 ° C. or higher or normalizing at 1000 ° C. or higher. It has been found that the toughness decreases when the amount of Si + Al increases, but it is found that toughness can be ensured by decreasing the S and reducing the S to extremely low.

Furthermore, by taking a rolling reduction of 35% or more and 70% or less at 900 ° C. or less during rolling, the crystal grains before high-temperature heat treatment are refined to facilitate recrystallization, and strain is introduced into the steel. By using the strain as a driving force for recrystallization during heat treatment, it was found that extremely large crystal grains can be stably obtained over the entire thickness.

Fig. 1 shows 700 ° C in 0.004% C-0.7% Si-1.2% Al steel.
The relationship between the rolling reduction at ℃ 900 ° C. and the crystal grain size No. is shown.

It can be seen that the grains become extremely coarse at a rolling reduction of 35% or more. However, when the rolling reduction exceeds 70%, the crystals on the surface become rather fine, and the variation in the grain size in the thickness direction increases.

FIG. 2 shows the reduction ratio of the same steel at 700 ° C. to 900 ° C., and the variation of the magnetic flux density at a magnetizing force of 20 A / m and the magnetic flux density in the thickness direction.

It can be seen that a high magnetic flux density was obtained at a rolling reduction of 35% or more, which corresponds to the crystal grain size No. in FIG. At a rolling reduction of more than 70%, the variation in the magnetic flux density in the thickness direction also increases, corresponding to the variation in the grain size.

FIG. 3 shows the relationship between the annealing and normalizing temperatures and the magnetic properties at 20 A / m when the reduction ratio is 40% at 900 ° C. or less for steel materials having the same composition and 5 mm, 60 mm, and 100 mm sheet pressure. .

High magnetic flux densities are obtained in both annealing at 950 ° C or higher and normalizing at 1000 ° C or higher.

In other words, take the reduction of 35-70% at 700-900 ° C,
By annealing at 950 ° C or higher or normalizing at 1000 ° C or higher,
It becomes coarse grains with a grain size of No.-2 or less, and a magnetic flux density of 0.6 Tesla or more can be obtained at a magnetizing force of 20 A / m.

Furthermore, as a result of a detailed study of the action of the void defects, it was found that those having a size of 100 μm or more significantly reduce the magnetic properties in a low magnetic field. It has been found that the rolling shape ratio A is required to be 0.6 or more in order to eliminate the harmful void defects of 100 μm or more.

However, A: Rolling shape ratio h _i : Incoming plate thickness (mm) h _o : Outgoing plate thickness (mm) R: Rolling roll radius (mm) As shown in Fig. 4, 0.004% C-0.7% Si-1.2% Al steel It can be seen that the magnetic properties in a low magnetic field are improved by reducing the size of the void defect to 100 μ or less by high shape ratio rolling.

 Next, the reasons for limiting the components will be described.

C has elements that greatly affect the transformation temperature, and it is necessary to add a large amount of Si and Al in order to eliminate γ transformation when the amount of C increases. Therefore, the upper limit is 0.005%.

Si and Al are important elements in the present invention, and Si + Al ≧ 1.5% is required to eliminate the γ transformation.
However, if each exceeds 3.5%, it is difficult to secure toughness, so this is set as the upper limit.

P and S are each set to 0.01% or less from the viewpoint of securing toughness.

Mn should be low in terms of magnetic flux density at low magnetic field,
0.5% or less.

Since N is an element which makes crystal grains fine by AlN and is very harmful to low-field magnetic properties, it is necessary to reduce it as much as possible. The upper limit is 0.008%, preferably 0.004%.
The following is assumed.

O forms nonmetallic inclusions in the steel, hinders the movement of the domain wall and lowers the magnetic flux density.

 Next, the manufacturing conditions will be described.

The heating temperature before rolling is not particularly limited.

In hot rolling, although the above-mentioned void defects have a large or small size during the solidification process of steel, they always occur, and the means for eliminating them must be by rolling. That is, hot rolling, in which the amount of deformation per rolling is increased and the deformation reaches the center of the sheet thickness, is effective. Specifically, the rolling shape ratio A is
It is good for magnetic properties that high-form rolling including at least one rolling pass of 0.6 or more is performed to reduce the size of void defects to 100 μ or less.

Next, at a temperature of 700 ° C. to 900 ° C., the crystal grains are refined with a rolling reduction of 35% or more and a strain is introduced, thereby promoting recrystallization during the subsequent high-temperature heat treatment. But 70
%, The grain size after heat treatment becomes non-uniform in the sheet thickness direction, and the variation in magnetic flux density increases. Therefore, in order to obtain uniform coarse grains in the thickness direction, the rolling reduction is
35% to 70%.

Annealing and normalizing are performed for coarsening the crystal grains and removing internal strain. However, at 950 ° C. and 1000 ° C. or less, the coarsening of the crystal grains is insufficient. Further, since annealing at 1150 ° C or higher and normalizing at 1200 ° C or higher are unnecessary from the viewpoint of scale loss prevention and energy saving, the upper limit is set to 1150
℃, 1200 ℃.

(Examples) Table 1 shows the components of the electromagnetic thick plate, Table 2 shows the manufacturing conditions and the size of void defects, ferrite grain size, magnetic flux density at a magnetizing force of 20 A / m, and variations in the magnetic flux density in the thickness direction. , And the absorbed energy vEo of the Charpy test at 0 ° C. as an index of toughness.

Examples 1 to 11 show examples of the present invention, and Examples 12 to 25 show comparative examples.

Examples 1 to 7 were finished to a plate thickness of 60 mm, and Examples 8 to 9 were
Example 10 was finished to 20 mm, Example 10 was finished to 5 mm, and Example 11 was finished to 5 mm. All of these have a high magnetic flux density at a magnetizing force of 20 A / m and have little variation in the thickness direction.

In Example 12, C exceeded the upper limit, and in Examples 13 and 14, the sum of the Si amount and the Al amount
Since it is less than 1.5%, a γ region exists at any high temperature, and becomes fine grains due to transformation during heat treatment, resulting in low magnetic flux density. Example 15 has low toughness because Si exceeds the upper limit in Example 16 and Al in Example 16 exceeds the upper limit. Example 17 has Mn, Example 18 has S, Example 19 has N, and Example 20 has O which exceeds the upper limit.
In the case of 18, the toughness is low. In Example 21, the rolling shape ratio was insufficient, and the magnetic properties were low due to large void defects. Example 22 is 70
Since the rolling reduction at 0 ° C. to 900 ° C. is less than the lower limit, the magnetic flux density is low. In Example 23, since the rolling reduction at 700 ° C. to 900 ° C. exceeds the upper limit, the variation in the magnetic flux density is large. In Example 24, the annealing temperature was lower than the lower limit, and in Example 25, the grain growth was insufficient because the normalizing temperature was lower than the lower limit, and the magnetic flux density was low.

(Effects of the Invention) As described above in detail, according to the present invention, the magnetic flux density is 0.6 Tesla or more in a low magnetic field of 20 A / m and uniform in the thickness direction by limiting the appropriate components and the manufacturing method. It succeeds in providing magnetic properties and can be applied to a magnetic shield for a magnetic field of several tens of gauss or less, and has a great industrial effect.

[Brief description of the drawings]

FIG. 1 is a chart showing the effect of the reduction at 700 ° C. to 900 ° C. on the grain size No., and FIG. 2 is a graph showing the reduction at 700 ° C. to 900 ° C. FIG. 3 is a graph showing the effect of the magnetic flux density on variation, FIG. 3 is a graph showing the effect of annealing and normalizing temperature on the magnetic flux density at a magnetizing force of 20 A / m, and FIG. 20
4 is a chart showing the effect on magnetic flux density at A / m.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C21D 8/12

Claims (2)

(57) [Claims] (1) In weight%, C: 0.005% or less, Si: more than 0.2%, 3.5% or less, Al: more than 0.2%, 3.5% or less, and the sum of the weight percentages of Si and Al is
1.5% or more, Mn: 0.5% or less, S: 0.010% or less, N: 0.008% or less, O: 0.006% or less The balance of a steel slab or slab consisting essentially of iron
Rolling is performed at least once at a rolling pass having a rolling shape ratio A of 0.6 or more at 0 ° C or more, and then rolling at a rolling reduction of 35% to 70% at 700 ° C to 900 ° C is performed. 1
A method for producing an electromagnetic thick plate having excellent low-field magnetic properties, characterized by annealing at 150 ° C. However, A: Rolling shape ratio h _i : Inlet thickness (mm) h _o : Outlet thickness (mm) R: Rolling roll radius (mm) 2. Rolling is performed at least once in a rolling pass at a rolling shape ratio A of 0.6 or more at 900 ° C. or more, followed by rolling at a rolling reduction of 35% to 70% at 700 ° C. to 900 ° C. The method for producing an electromagnetic thick plate excellent in low magnetic field magnetic properties according to claim 1, wherein the heat treatment is performed at a temperature of 1000 ° C to 1200 ° C.