JP3084571B2 - High Si content steel plate with good workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an Si-containing steel sheet used for an iron core of a rotating machine and the like, which is excellent in iron loss characteristics and soft magnetic characteristics in a high frequency range, and which is used in electric equipment.
The present invention relates to a high-Si-containing steel sheet having excellent workability capable of extremely reducing noise during AC excitation.

[0002]

2. Description of the Related Art A so-called electromagnetic steel sheet containing Si is used as a soft magnetic material for an iron core of a transformer, a motor core, and the like. At this time, of the characteristics required for electrical steel sheets,
Most importantly, iron loss is low. It is an important issue to reduce iron loss during AC use from the viewpoint of reducing energy loss or improving the efficiency of electric equipment and preventing temperature rise for maintenance as conventionally known. Furthermore, in recent years, the frequency of devices using magnetic materials has been increasing in accordance with the trend of society, and social demands for reducing iron loss have been increasing.

[0003] The reduction of iron loss in an electromagnetic steel sheet is achieved by adding Si, controlling the orientation of crystal grains, and the like. Iron loss can be divided into DC iron loss and eddy current loss. Among them, the eddy current loss is an energy loss due to Joule heat of an eddy current induced by a magnetic flux density that changes with AC magnetization. The eddy current increases in proportion to the temporal change rate of the magnetic flux density. Therefore, the eddy current loss increases as the frequency increases. The eddy current can be reduced by increasing the electric resistance of the magnetic material. When Si is contained in the steel sheet, the electric resistance increases, so that the eddy current can be reduced. For this reason, Si has been conventionally contained in magnetic steel sheets.

However, when the Si content increases, the steel becomes brittle, and it becomes difficult to perform rolling and other processes for manufacturing a steel sheet. Process difficulties can be avoided by raising the processing temperature (such as warm rolling). However, when Si is contained up to about 6.5%, it becomes very brittle even at the product stage, and is used for, for example, a wound core. Bending at the time becomes difficult.

In a method of manufacturing a steel sheet in a usual mass production system, first, a steel ingot is melted to a predetermined component in a converter, an electric furnace, or the like, and then is subjected to continuous casting, ingot casting, or the like. The ingot is heated to a predetermined temperature and then wound into a coil. When a thin cast piece is manufactured by the twin roll method or the like, the cast piece may be wound as it is. The rolled hot-rolled sheet or thin slab is unwound and then the oxide layer on the surface is removed, and is subjected to cold rolling. The cold rolled sheet is also wound into a coil and subjected to annealing. As described above, the steel sheet manufacturing process includes many deformation and processing steps such as rolling and bending. Since steel containing a large amount of Si is brittle, it has been difficult to produce steel sheets through such a normal steel manufacturing process.

Conventionally, when rolling a steel sheet containing a large amount of Si, the steel sheet has been heated to about several hundred degrees centigrade to avoid cracking. However, at the time of rolling, since the heat is removed by the rolling rolls, it is inefficient to secure the temperature. Also, when unwinding the coil, it is necessary to heat the entire coil, which causes a decrease in productivity and an increase in manufacturing cost.

[0007]

SUMMARY OF THE INVENTION As described above, the present invention has been made for the purpose of improving the workability of a high-Si content steel having good magnetic properties as a soft magnetic material and increasing the productivity.

[0008]

The present invention has been made based on the findings obtained from the results of a series of experiments conducted to improve the toughness of high Si content steel. That is, the gist of the present invention is that Si: 5.0 to 8.0% by weight and C: 0.0
005-0.1%, and the element X (X is Ti, Nb
At least one of the above), the amount of which is represented by [Cwt%] ≦ [Tiwt%] / 5+ [Nbwt%] / 9, including other unavoidable impurities, and the balance substantially consisting of Fe. High Si with good processability
Contained steel sheet.

Next, the present invention will be described in detail. First, Si
The amount is 5.0 wt% or more as a minimum necessary amount for expressing iron loss characteristics better than the conventional Si-containing steel sheet, which is a feature of the high Si-containing steel. On the other hand, if the Si content exceeds 8%, not only the processing is difficult according to the present invention, but also a further improvement in the magnetic properties cannot be obtained with a decrease in the saturation magnetic flux density.

Next, the amount of C will be described. C is 0.00
When the content is less than 05 wt%, the toughness is not improved even when Ti and Nb are added, so the lower limit of the amount of C was set. If the content is more than 0.1 wt%, a γ phase is precipitated at a high temperature, and carbides are precipitated at a low temperature, and the magnetic properties are deteriorated. Next, the amounts of Ti and Nb will be described. In order to examine the effects of these elements, a Charpy impact test was performed by adding Ti to steel containing 6.5% of Si and 0.002% of C. The material of the component system shown in FIG. 1 was melted in a high frequency vacuum melting furnace,
After maintaining the thickness at 1000 ° C. for several minutes, it was gradually cooled. From now on, 55mm in length, 10mm in width and 1 in thickness
Cut out a 0 mm Charpy test piece and heat it at 300-600 ° C.
The test was performed between. The results are shown in FIGS. The addition of Ti greatly increased the absorbed energy in the ductile temperature range. In addition, the brittle fracture rate decreases. That is, Ti
The toughness could be improved by adding.
Similar effects were obtained for Nb.

However, the above-mentioned effect is apparent for steel containing C. For Ti, 5 times the amount of C by weight and N
The effect is saturated when b is added 9 times. Figures 3 and 4
7 shows the results of an impact test performed on steel containing 6.5% of Si while changing the amounts of C, Ti, and Nb added. Generally Ti
Since Nb and Nb combine with solid solution C in steel and precipitate in the form of TiC and NbC, solid solution C in steel can be reduced.
We believe that the addition of Ti improved the toughness this time because the same metallurgical phenomenon occurred.

Conventionally, there has been known a method of adding C to steel containing a large amount of Si to improve workability. (J. Ir
on. Steel. Inst. , Feb. 1967, 1
58) In this method, a large amount of C is added to precipitate a γ phase during hot rolling. When rolling is performed in the α-γ2 phase region, recrystallization easily occurs at the interface between the two phases, and the crystal grains are refined to improve toughness. However, according to this method, a large amount of the γ phase or the carbide phase precipitates and deteriorates the magnetic properties.

Therefore, the toughness of the high Si steel was examined within the range of the C content in which the α phase did not precipitate. The results are shown in FIGS. If the C content is small, the impact value is large and the brittle-ductile transition temperature is low. In particular, when the C content exceeds 0.01%, the impact value in a ductile temperature range is significantly deteriorated. This means that even warm working conventionally performed on high Si steels becomes difficult.
FIG. 5 shows a photograph of the metal structure of this test piece. No change in the metal structure such as the crystal grain size and the precipitated phase is observed even if the components and the test temperature are changed. Therefore, the present finding is that α-single-phase Fe-S
This is considered to be the effect of solid solution C in the i alloy.

[0014]

【Example】

Example 1 Table 1 shows the state of cracking when a material having different amounts of Si, C, Ti, and Nb was cold-rolled. It can be seen that the material of the present invention can be easily rolled even at a relatively low temperature, but the comparative material cracks and has poor toughness.

[0015]

[Table 1]

Example 2 Table 2 shows the results of bending tests on hot-rolled sheets and cold-rolled sheets when the components were changed. The bending test was performed at 150 ° C. for the hot-rolled sheet, but was performed at room temperature for the cold-rolled sheet.

[0017]

[Table 2]

Example 3 Table 3 shows the cracking properties when unwinding a hot-rolled coil having different components. The unwinding in a warm state was performed before the coil was completely cooled after hot rolling.

[0019]

[Table 3]

[0020]

According to the present invention, it is possible to improve the toughness of a high Si content steel and to improve the productivity or reduce the cost when using a conventional iron making process such as a conventional casting-rolling-coil winding. be able to. as a result,
For example, it is possible to easily provide a material which has been considered difficult to produce on a real machine while having excellent characteristics, such as 6.5% Si steel having extremely good soft magnetic characteristics.

[Brief description of the drawings]

FIG. 1 shows that a steel containing 6.5% of Si and 0.002% of C has a T content.
It shows the result of Charpy impact test with i added, and shows the relationship between impact value and test temperature.

[Fig. 2] T in steel containing 6.5% Si and 0.002% C
It shows the result of Charpy impact test performed by adding i, and shows the relationship between the brittle fracture impact rate and the test temperature.

FIG. 3 shows the results of an impact test performed on steel containing 6.5% of Si while changing the amounts of C and Ti added.

FIG. 4 shows the results of an impact test performed on steel containing 6.5% of Si while varying the amounts of C and Nb added.

FIG. 5 is a photograph of a metal structure of a test piece used in the toughness test shown in FIGS. 3 and 4.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiyuki Ushigami 1-1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu-city, Fukuoka Prefecture Inside Nippon Steel Corporation 3rd Research Institute (72) Inventor Shuji Kitahara Kitakyushu, Fukuoka Prefecture 1-1-1 Edamitsu, Hachiman-shi, Hachiman-shi Nippon Steel Corporation 3rd Technical Research Laboratories (56) References JP-A-56-112439 (JP, A) JP-A-62-267447 (JP, A) ( 58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00 303 C22C 38/02

Claims (1)

(57) [Claims] 1. Si: 5.0-8.0% by weight, C:
0.0005 to 0.1%, and the element X (X is T
i, Nb), the amount of which is represented by [Cwt%] ≦ [Tiwt%] / 5+ [Nbwt%] / 9, other unavoidable impurities are contained, and the balance is substantially less than Fe High Si with good workability characterized by becoming
Containing steel sheet.