JPH0726325A - Manufacturing method of good electromagnetic thick plate - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a method of manufacturing a good electromagnetic thick plate. [Constitution] C: 0.01% or less, Si: 0.02% or less, S: 0.02 to 0.20%, Al: 0.040% or less, heated to 950 to 1150 ° C., 800 ° C. As described above, rolling with a rolling shape ratio of 0.6 or more and rolling with a rolling reduction of 35 to 70% are performed, and by performing dehydrogenation heat treatment, annealing or normalization depending on the plate thickness, good machinability is obtained, and in a medium magnetic field. A method for manufacturing good electromagnetic thick plates with excellent magnetic properties. [Effect] Good machinability and excellent magnetic characteristics in medium magnetic field.

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 good electromagnetic thick plate used for large structural members and the like.

[0002]

2. Description of the Related Art In recent years, along with the progress of elementary particle research and medical equipment, which are the most advanced science and technology, a device using magnetism for a large structure is used, and its performance is required to be improved. In particular, for the particle accelerator magnetic pole material and return yoke material used under DC magnetization conditions, in addition to high saturation magnetic flux density, 5 Oe (400 A /
Although a high magnetic flux density in a medium magnetic field near m) is required, good machinability during processing is also required.

It is well known that, as magnetic steel sheets having excellent magnetic flux density, many materials such as silicon steel sheets and electromagnetic soft iron sheets have been conventionally provided in the thin sheet field. However, there are problems in assembling and strength when used as a structural member, and it becomes necessary to use thick steel plates. Heretofore, as an electromagnetic thick plate, for example, JP-A-60-96 has been used.
It is manufactured with pure iron-based components as disclosed in Japanese Patent Publication No. 749. However, with the recent increase in the size of equipment and improvement in performance, there is a strong demand for the development of steel materials having excellent magnetic properties along with machinability, and particularly high magnetic flux density in a medium magnetic field, for example, around 5 Oe (400 A / m). . With the steel materials presented in the above publications, etc., a high magnetic flux density of a medium magnetic field near 5 Oe has not been stably obtained.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object thereof is to provide a method for manufacturing a good electromagnetic thick plate which has good machinability and excellent magnetic characteristics in a medium magnetic field. To do.

[0005]

According to the present invention, in% by weight, C: 0.01% or less, Si: 0.02% or less,
Mn: 0.20% or less, S: 0.02% or more,
0.20% or less, Al: 0.040% or less, N:
0.004% or less, O: 0.005% or less, H
: 0.0002% or less, with the balance being a steel slab having a steel composition substantially consisting of iron, or a slab, being heated to 950 to 1150 ° C.,
Rolling is performed at 800 ° C. or higher at least one rolling pass in which the rolling shape ratio A calculated by the following formula (1) is 0.6 or higher,
Subsequently, rolling is performed at a temperature of 800 ° C. or lower at a rolling reduction of 35 to 70%, and a thick plate having a plate thickness of 50 mm or more is subjected to a dehydrogenation heat treatment at 600 to 750 ° C. if necessary, and then 7
Anneal at 50-950 ° C or 910-1000
Normalize at ℃, 750-950 for plate thickness less than 50mm
It is a method for producing a good electromagnetic thick plate having good machinability and excellent magnetic properties in a medium magnetic field, which is characterized by annealing at ℃ or normalizing at 910 to 1000 ℃.

[0006]

[Equation 2]

[0007]

The present invention will be described in detail below. First, the magnetization process will be described. When degaussed steel is put into 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 entire magnetic domain next turns to the magnetization 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. 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. From this point of view, it has conventionally been an important technique to coarsen the crystal grains, which hinders the movement of the domain wall (see JP-A-60-96749).
On the other hand, there was no knowledge about a method for obtaining a high magnetic flux density in a medium magnetic field.

In order to obtain a high magnetic flux density in a medium magnetic field, the present inventors not only make the crystal grains coarser, but also make the magnetization directions between adjacent crystal grains parallel to the rolling direction. Have found that it is important. The magnetic characteristics of medium magnetic field are significantly improved by being relatively coarse particles (ferrite grain size No. 0 to 4) that are neither ultra-coarse grains nor fine grains, and the [100] direction being random parallel to the rolling direction. We found that it would improve. As a hot rolling condition for this purpose, a rolling reduction of not less than 35% and not more than 70% at 800 ° C. or less facilitates refining and recrystallization of crystal grains before heat treatment after rolling and strain in steel. By introducing this strain as a driving force for recrystallization during heat treatment, relatively large crystal grains can be stably obtained over the entire plate thickness, and at the same time, the [100] crystal orientation becomes parallel to the rolling direction. It will be random. 0.006Si-0.07 in FIG.
Rolling ratio of Mn-0.014Al steel at 800 ° C or lower and 5
The relationship with the magnetic flux density at Oe is shown. As is clear from the figure, a high magnetic flux density can be obtained by the reduction of 35 to 70%.

Further, as a means for obtaining a high magnetic flux density in a medium magnetic field, the effects of elements causing internal stress and the effects of void defects were examined in detail, and the intended purpose was achieved. Further, as a result of various studies on the influence of void defects, it was found that those having a size of 100 μm or more significantly deteriorate the magnetic characteristics. And this 10
It was found that the rolling shape ratio A in the following formula (1) needs to be 0.6 or more in order to eliminate harmful void defects of 0 μ or more.

[0010]

[Equation 3]

Further, it has been found that the presence of hydrogen in steel is also harmful and that the magnetic properties are significantly improved by performing the dehydrogenation heat treatment. The high-shape-ratio rolling reduces the size of void defects to 100 μm or less, and the dehydrogenation heat treatment reduces hydrogen in the steel, thereby significantly increasing the magnetic flux density in a medium magnetic field.

Next, it was found that S addition is very effective for the machinability of high purity steel in the present invention, especially for reducing the surface roughness after cutting. Fig. 2 shows 0.006C-0.0
The relationship between the surface roughness and the S content at a cutting length of 10 m in 9Mn-0.014Al steel was shown. In the figure, the surface roughness at a cutting length of 10 m is normally about 10 μm (indicated by Δ), 5 μm
The degree was defined as good (indicated by ◯), and approximately 1 μm was defined as particularly good (indicated by ⊚). From the figure, it can be seen that good machinability with a surface roughness of 5 μm or less is exhibited when the S addition amount is in the range of 0.02% or more.

Next, the reasons for limiting the components will be described. 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 not to decrease the magnetic flux density in a medium magnetic field. Also, from the viewpoint of magnetic aging, the lower it is, the less the deterioration with time is, and it can be used permanently with good magnetic characteristics. Therefore, the content is limited to 0.01% or less. As shown in FIG. 3, which shows the effect of C on the magnetic flux density at 5 Oe,
It is clear that a higher magnetic flux density can be obtained by setting the content to be not more than%.

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

S is an element that reduces the amount of tool wear and increases the machinability, and it is necessary to add 0.020% or more as shown in FIG. 2, but if it is added in excess of 0.20%, a low magnetic field is generated. The upper limit is made 0.20% in order to reduce the magnetic properties of. O forms a non-metallic inclusion in the steel, has a harmful effect on the coarsening of crystal grains, and the magnetic flux density decreases as the content increases. Therefore, O is set to 0.005% or less.

Al is used as a deoxidizing agent. If Al is too much, inclusions are formed and the properties of the steel are impaired, so the upper limit is made 0.040%. Furthermore, in order to reduce AlN, which is a precipitate that hinders crystal grain coarsening, the lower the better, the better, and preferably 0.020% or less. N increases the internal stress and reduces the magnetic flux density in a medium magnetic field due to the grain refining effect of AlN, so the upper limit is made 0.004%. H reduces the magnetic properties and hinders the reduction of void defects, so the content is made 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 lower. At heating temperatures higher than 1150 ° C., the variation of the heating γ grain size in the plate thickness direction is large, and this variation remains after rolling and the final Since the crystal grains become non-uniform, the upper limit is 1150.
℃. If the heating temperature is lower than 950 ° C., the deformation resistance of rolling increases, and the rolling load of rolling having a high shape ratio to eliminate void defects described below increases.
The lower limit is 50 ° C.

In the hot rolling, the above-mentioned void defects are large and small in the solidification process of steel, but they always occur and means for eliminating them must be done by rolling. Therefore, the role of hot rolling is important. is there. 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 0.6 or more is performed,
It is good for the magnetic properties that the size of the void defects is 100 μm or less. By eliminating the void defects by this high shape ratio rolling during rolling, the dehydrogenation efficiency in the dehydrogenation heat treatment to be performed later is dramatically increased.

Next, at a temperature of 800 ° C. or lower, the cumulative rolling reduction is set to 35% or more, whereby the crystal grains are made finer and strain is introduced to promote 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 crystal grain size after heat treatment becomes non-uniform in the plate thickness direction, and variations in magnetic flux density increase. Therefore, in order to obtain relatively coarse grains that are uniform in the plate thickness direction, the reduction rate is set to 3
5 to 70%.

Next, hot rolling is followed by coarsening of crystal grains, removal of internal strain, and dehydrogenation heat treatment as necessary for thick materials having a plate thickness of 50 mm or more. When the plate thickness is 50 mm or more, hydrogen is difficult to diffuse, which causes void defects and also reduces the magnetic flux density in a low magnetic field in combination with the action of hydrogen itself. For this reason, dehydrogenation heat treatment is performed, but at that time, if the temperature is lower than 600 ° C., the dehydrogenation efficiency is poor, and if it exceeds 750 ° C., a part of the transformation starts, so the temperature is 600 to 750 ° C. As the dehydrogenation time, various examination results [0.6 (t
-50) +6] hours (t: plate thickness) are suitable.

Annealing is carried out for grain coarsening and internal strain removal, but grain coarsening does not occur below 750 ° C., and homogeneity in the plate thickness direction of crystal grains cannot be maintained above 950 ° C. Therefore, the annealing temperature is limited to 750 to 950 ° C. Normalization is performed to adjust crystal grains in the plate thickness direction and remove internal strain, but the lower limit is Ac, which is the lower limit of the austenite range.
_Since the homogeneity of the crystal grains in the plate thickness direction cannot be maintained at _three points of 910 ° C or higher and 1000 ° C or higher, the normalizing temperature is limited to 910 to 1000 ° C. The annealing or the normalization can be performed by the dehydrogenation heat treatment performed on a thick material having a plate thickness of 50 mm or more. On the other hand, if the plate thickness is less than 50 mm, hydrogen can be easily diffused, and thus dehydrogenation heat treatment is not necessary and only annealing or normalizing as described above is required.

[0022]

EXAMPLES Next, examples of the present invention will be given together with comparative examples. Table 1 shows the chemical composition of the steel, and Table 2 shows the manufacturing conditions of the electromagnetic thick plate, the ferrite grain size, and the magnetic flux density in a medium magnetic field.

[0023]

[Table 1]

[0024]

[Table 2]

Examples 1 to 6 show examples of the present invention, and Examples 7 to
22 shows a comparative example. Examples 1 to 3 are finished to a plate thickness of 100 mm, have a high magnetic flux density in a medium magnetic field, and have good machinability. Compared to Example 1, Example 2 has lower C, and Example 3 has lower Mn.
And shows higher magnetic properties. Example 4 is 40 mm, Example 5
Is 6 mm and Example 6 is 10 mm, and has a high magnetic flux density and good machinability. Examples 7 to 8 have low S and poor machinability. Example 9 has too high S, Example 10 has high C, Example 11
Has a high Mn, Example 12 has a high Al, Example 13 has a high N, Example 14 has a high O, and Example 15 has a high H, both of which exceed the upper limits and thus have low magnetic characteristic values. In Example 16, the heating temperature exceeds the upper limit and the magnetic flux density is low. Example 17 has a low magnetic flux density because the heating temperature is below the lower limit. In Example 18, the rolling reduction below 800 ° C is below the lower limit and the magnetic flux density is low. In Example 19, the maximum shape ratio is below the lower limit,
In Example 20, the dehydrogenation heat treatment temperature is below the lower limit, in Example 21, the annealing temperature is below the lower limit, and in Example 23, there is no dehydrogenation heat treatment, so the magnetic flux density is low.

[0026]

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 a uniform high electromagnetic characteristic by appropriately limiting the components, and to utilize the magnetic characteristic of direct current magnetization. It is applicable to structures.
Moreover, the production method also provides the method of producing extremely economically, which can simultaneously perform the above-described component limitation, grain adjustment after hot rolling and dehydrogenation heat treatment, and has a great industrial effect. It is a thing.

[Brief description of drawings]

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

FIG. 2 is a graph showing the effect of S content on machinability.

FIG. 3 is a graph showing the effect of C content on the magnetic flux density at 5 Oe.

Claims (2)

[Claims] 1. By weight%, C: 0.01% or less, Si: 0.02% or less, Mn: 0.20% or less, S: 0.02% or more, 0.20% or less, Al: 0. 0.040% or less, N: 0.004% or less, O: 0.005% or less, H: 0.0002% or less, and the balance 9 or 9
Heat to 50-1150 ° C, and at 800 ° C or higher, the following (1)
The rolling shape ratio A in the formula is such that a rolling pass having a rolling ratio of 0.6 or more is performed once or more, and subsequently rolling is performed at 800 ° C. or less to a rolling reduction of 35 to 70%, and then 750 to 950.
A method for producing a good electromagnetic thick plate having good machinability and excellent magnetic properties in a medium magnetic field, characterized by being annealed at ℃ or normalized at 910 to 1000 ℃. [Equation 1] 2. After rolling at 800 ° C. or lower according to claim 1 at a reduction ratio of 35 to 70%, dehydrogenation heat treatment at 600 to 750 ° C. is performed on a thick plate having a thickness of 50 mm or more, and further 750 The method for producing a good electromagnetic thick plate having good machinability and excellent magnetic properties in a medium magnetic field according to claim 1, characterized in that annealing is performed at 950C to 950C or normalizing is performed at 910C to 1000C.