JPH07113128B2 - Method for manufacturing silicon steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a high silicon steel sheet having excellent soft magnetic properties, which is used for a magnetic core of a rotating machine, a generator, or the like.

[Conventional technology]

Silicon steel sheets have been used in large amounts as magnetic cores for electric power and materials for rotating machines because of their excellent soft magnetic properties, but in recent years, transformers and rotating machines have been used from the viewpoint of energy saving and resource saving. There has been a strong demand for efficiency and miniaturization of the electric equipment, and accordingly, the soft magnetic properties and the iron loss properties that are excellent in the silicon steel sheet which is the material for the iron core are also being demanded.

The soft magnetic properties of this silicon steel sheet improve with the amount of silicon added, and show the highest magnetic permeability, especially near 6.5 wt%.
Furthermore, since the specific electric resistance is high, it is known that the iron loss is also small. However, the silicon content is 4%
If it exceeds, the workability is rapidly deteriorated, and it has been considered extremely difficult to manufacture a thin plate on an industrial scale by the conventional rolling method.

In order to solve this problem, the inventors of the present invention have conducted various studies, and as a result, by selecting an appropriate rolling condition for the above-mentioned high silicon-containing steel having a high silicon content of 4%, it is possible to obtain a high cold workability. Knowing that silicon hot rolled steel sheets can be manufactured continuously,
The basic manufacturing method was presented in Japanese Patent Application No. 60-128323.

That is, this method achieves grain refinement by selecting appropriate rolling conditions when slab-rolling or rough-rolling an ingot or a continuous casting slab, and continuously finishing hot rolling them at a relatively low temperature. However, it is characterized by imparting excellent cold rolling property by adjusting the average grain boundary spacing in the thickness direction of the hot-rolled sheet according to the amount of Si added.

[Problems to be solved by the invention]

However, as a result of further tests and studies, the following facts were revealed. That is, in order to adjust the grain size in the plate thickness direction to a critical value or less according to the amount of Si added by the above method in the continuous hot rolling process, the required cumulative rolling reduction estimated from the grain size before hot rolling That is, there is a case where a high silicon steel sheet excellent in cold workability cannot be stably manufactured even if strain corresponding to is added.

[Means for solving problems]

The inventors of the present invention have conducted diligent experiments and researches to solve the above-mentioned problems, and as a result, the structure in the thickness direction of the hot-rolled sheet becomes non-uniform unless the strict control is applied during the finish hot-rolling, resulting in cold rolling property. The new hot-rolling method in the above-mentioned high silicon steel sheet manufacturing method in order to improve the new finding that it causes deterioration of the use of a hot rolling machine having an appropriate roll diameter during continuous hot-rolling. According to the present invention, a more uniform hot-rolled sheet structure can be obtained in the sheet thickness direction, and a high-silicon hot-rolled steel sheet excellent in cold workability can be stably and efficiently produced, and the present invention was accomplished. It is an ivy.

That is, the present invention is C: 1 wt% or less, Si: 4.0 ~ 7.0 wt%, M
n: 0.5wt% or less, Al: 2wt% or less, after melting an alloy consisting of balance iron and unavoidable impurities, cast by ingot casting or continuous casting, and slab rolling / rough rolling or rough rolling followed by finish hot rolling,
After removing the surface oxide film, cold rolling and annealing are performed to produce a silicon steel sheet. At the time of finish hot rolling, a diameter of 20 times or more of the charging thickness (hereinafter, the thickness before hot rolling) is applied. The basic feature is to roll using the rolls.

The method of the present invention will be described in detail below.

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

C is a harmful component that increases iron loss and causes magnetic aging. However, C is Fe
Since it is an element that expands the γ loop in the -Si system equilibrium diagram, an α-γ transformation point will appear during cooling when a fixed amount determined by the silicon content is added, and heat treatment using it will be possible. Therefore, it may be desirable to add C to some extent. In the present invention, C is 1 w from the viewpoint of workability.
Limited to t% or less.

Si is an element effective in increasing the specific electric resistance, reducing the eddy current loss, and reducing the iron loss. In the present invention, Si: 4.0wt
The target is a high silicon iron alloy containing at least%, and this is the lower limit. On the other hand, if the Si content exceeds 7.0 wt%, the manufacturing cost will increase and the magnetic properties, especially the maximum magnetic permeability will deteriorate, so this is the upper limit. For the above reasons, the limited range of Si is 4.0 to 7.0 wt%.

Mn is necessary to suppress hot embrittlement due to S, but if it exceeds 0.5 wt%, the workability deteriorates due to solid solution hardening, so the content is made 0.5 wt% or less.

Al effectively acts to fix N, which deteriorates the deoxidation and magnetic properties of steel, and is also a useful element to increase the specific electrical resistance and reduce the iron loss, like Si. However, if added in a large amount, the cold rolling property deteriorates and the cost increases, so the upper limit is made 2 wt%.

The molten steel whose composition has been adjusted as described above is made into a slab by the ingot-bulk rolling method or the continuous casting method (in some cases, continuous casting-bulk rolling), and the slab is recrystallized to refine the structure. Meanwhile, it is roughly hot rolled, and then finish hot rolled to a predetermined plate thickness according to the present invention. In the present invention in this finish hot rolling,
Rolling shall be carried out using a roll having a diameter 20 times or more the thickness of the charged sheet (thickness before hot rolling for finishing).

As a result, it is possible to improve the nonuniformity of the microstructure in the sheet thickness direction, which is likely to occur due to hot-rolling under high pressure in a non-recrystallization temperature range depending on the grain size before hot rolling, preferably at 500 to 1100 ° C. as a result,
It becomes possible to apply strain uniformly in the plate thickness direction according to the cumulative rolling reduction in the above temperature range, and it becomes easy to form a hot rolled sheet structure having excellent cold workability, and the cold rolled sheet of the obtained hot rolled sheet is cooled. The ductility is also extremely good.

In finish hot rolling using a roll having a diameter less than 20 times the thickness of the charged sheet, the strain distribution in the sheet thickness direction becomes non-uniform, resulting in a non-uniform structure in the sheet thickness direction of the hot-rolled sheet and cold rolling. The property also deteriorates.

That is, in order to produce a high silicon steel thin plate by cold rolling, if finish hot rolling is performed by the method of the present invention and the hot rolled sheet structure has a uniform structure in the plate thickness direction, an extremely good cold Ductility can be imparted.

〔Example〕

Example (1) A slab of slabs having a thickness of 150 mm and consisting of the chemical components shown in Table 1 was heated at 1150 ° C. for 3 hours and then rough-rolled to a thickness of 30 mm, and then 300 mm, 480 mm, 600 mm and 820 mm, respectively. Four types of rolls having the following roll diameters were used to finish hot-rolling each from 1080 ° C to a finishing temperature of 810 ° C to a thickness of 2 mm. Then, each of these was pickled and cold-rolled to 0.35 mm, and its cold-rollability (cold-rollability by 5-point evaluation) was evaluated. First
The figure shows the results, and it can be seen that the silicon steel sheet finished by hot rolling with a roll having a roll diameter of 20 times or more the thickness of the charging plate exhibits excellent cold workability.

Example (2) An ingot was prepared by adding C, Al, Mn, and P to an iron alloy containing Si at 6.5 wt% (target value) under various conditions, and the ingot was charged into a soaking blast furnace in a hot mass to produce an ingot. After soaking at 1250 ° C, slabbing with a rolling reduction of 60 to 80% was performed. After rolling, put one piece of heat into the heating furnace and start
Heated to 1250 ℃, rough rolling with a reduction rate of 60 to 90%, and
It was a 30 mm plate. Then, finishing hot rolling was started at a stage where the sheet temperature was 1100 to 900 ° C to obtain a hot rolled sheet having a sheet thickness of 2 mm. This finish hot rolling was performed using a roll having a roll diameter of 300 to 2100 mm. After descaling the hot-rolled sheet, cold rolling was performed at a reduction rate of 75%, and the cold rollability was evaluated according to the same criteria as in Example (1). The cold rolling was performed at a plate temperature of 20 to 250 ° C.

FIG. 2 shows a ratio (cold hot-rolling roll diameter / plate thickness) at which the cold rolling property (cold rolling property based on the 5-point evaluation in FIG. 1) becomes “rating 5”. According to this, as the content of each of Al, C, Mn, and P increases, the roll diameter required to obtain good cold rolling tends to increase, but according to the present invention, the (roll diameter / plate thickness) ratio is 20 It can be seen that by the above, a good cold rolling property can be obtained.

Example (3) An iron-silicon alloy having a composition range shown in Table 2 was melted. At this time, the component values of Fe, Si, C, Mn, P, and Al are analyzed to analyze other impurity elements (mainly Cr, Ti, W, Mo, Co, C
u, S, B, As) was obtained, and the total amount was varied to make various ingots having different total amounts of impurity elements. This ingot was charged into a soaking furnace with hot mass and soaked at 1100 to 1250 ° C.
Slab rolling with a reduction rate of 60 to 80% was performed. After rolling, heat pieces are put into a heating furnace and heated to 1100 to 1250 ℃, and the rolling reduction is 60 to 90%.
Was roughly rolled to obtain a plate having a thickness of 30 mm. And the plate temperature
Finishing hot rolling was started at a stage of 1100 to 900 ° C to obtain a 2 mm hot rolled sheet. This finish hot rolling was performed with a roll having a diameter of 700 mm. After descaling the hot-rolled sheet, cold rolling was performed at a sheet temperature in the range of 20 to 250 ° C and a reduction rate of 75%.

FIG. 3 shows the relationship between the total amount of impurity elements in the alloy and the cold workability (cold rollability based on a 5-point evaluation). When the total amount of impurity elements increases, cold ductility tends to deteriorate slightly. According to the present invention, it has been shown that good cold workability can be obtained by setting the (roll diameter / plate thickness) ratio to 20 or more.

[Effects of the Invention] As described above, according to the present invention, it becomes easy to control the hot rolling structure during finish hot rolling, and it is possible to stably and efficiently manufacture a high silicon steel sheet having dramatically excellent cold workability. .

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between (roll diameter / charging plate thickness) ratio and cold rollability. FIG. 2 shows the relationship between the concentration of each additional element in the alloy and the ratio (roll diameter / charging plate thickness) at which the cold rolling property becomes good. FIG. 3 shows the relationship between the total amount of impurities in the alloy and the cold rolling property.

Front Page Continuation (72) Inventor Junichi Inagaki Marunouchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Tube Co., Ltd. Co., Ltd. (72) Inventor Hironori Ninomiya 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Tube Co., Ltd.

Claims (2)

[Claims] 1. C: 1 wt% or less, Si: 4,0-7,0 wt%, Mn: 0.5 wt%
Below, Al: 2wt% or less, the alloy consisting of balance iron and unavoidable impurities is melted, then cast by ingot casting or continuous casting, and slab rolling / rough rolling or rough rolling followed by finish hot rolling to remove surface oxide film. After that, when producing a silicon steel sheet by performing cold rolling and annealing, finish production hot rolling using a roll having a diameter 20 times or more the thickness of the charged sheet Method. 2. The method for producing a silicon steel sheet according to claim 1, wherein the finish hot rolling is performed in a temperature range of 500 to 1100 ° C.