JPS6253571B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing non-oriented electrical steel sheets with extremely low iron loss, and is concerned with the highest grade S9 specified by JIS C2552 (iron loss W _15/50 is 2.90w/Kg or less). 0.50mm thickness), 2.40w/Kg or less (0.35mm thickness)], relates to a method for manufacturing high-grade non-oriented electrical steel sheets of S8 grade or lower. S9 grade is currently available as a high-grade non-oriented electrical steel sheet, and is used as the magnetic core material of large rotating machines. However, even though non-oriented electrical steel sheets are high-grade products, they have low core loss but inferior magnetic flux density, so electrical equipment manufacturers do not necessarily use them sufficiently as magnetic core materials for large rotating machines. Some use electrical steel sheets. Recently, in order to reduce costs and improve the efficiency of large rotating machines, core materials for large rotating machines have been reviewed.
A higher grade product with even lower core loss and better magnetic flux density than the S9 grade is required. (Prior Art) By the way, several proposals have been made so far regarding the production of high-grade non-oriented electrical steel sheets of S8 and S7 grades. For example, in the method described in JP-A-55-97426, S is regulated to 0.005% or less and N to 0.004% or less to suppress the formation of fine inclusions and precipitates, thereby improving iron loss and magnetic flux density. In order to achieve this, the hot rolled sheet is annealed in a non-decarburizing atmosphere, and the final annealing is performed in a non-oxidizing atmosphere, or an alkali metal salt solution is applied to the steel sheet and the steel sheet is heated at 950 to 1100°C in a decarburizing atmosphere for 1 to 5
This treatment is carried out for several minutes to prevent internal oxidation and improve magnetic properties. In the method described in JP-A-54-68717, S
Sb is reduced to 0.007% or less, and Sb is contained in a range of 0.005 to 0.30% to improve crystal grain growth and texture, and the hot rolled sheet is further annealed to improve magnetic properties. (Problems to be Solved by the Invention) In addition to these proposals, attempts are being made to reduce iron loss in non-oriented electrical steel sheets by further increasing the content of Si and Al. However, when manufacturing on an industrial scale on a production line, it is difficult to stably produce high-grade non-oriented electrical steel sheets that are significantly higher than S8 grade, and the reality is that further research is needed in the future. It is. In particular, when manufacturing high-grade products of S8 grade or higher, the magnetic properties, especially iron loss, differ in the width direction of the steel plate, and the edge of the plate from the edge to 1/3 of the width of the plate is different compared to the center. The problem of iron loss being inferior by several percentage points has been seen here and there, and this has become a major bottleneck in the stable production of high-end products. The present invention is a method for stably manufacturing high-grade non-oriented electrical steel sheets of S8 grade or higher so that they have uniform and excellent magnetic properties across the width of the sheet, in other words, a method for stably manufacturing high-grade non-oriented electrical steel sheets of S8 grade or higher, in other words, a method for stably manufacturing high-grade non-oriented electrical steel sheets of S8 grade or higher so that they have uniform and excellent magnetic properties across the width direction. The purpose is to provide a method for manufacturing steel sheets. (Means for Solving the Problems) The present inventors have discovered that there is no deterioration of iron loss at the edge of the plate, and the iron loss is excellent throughout the width direction of the plate.
We conducted a study to stably produce high-grade non-oriented electrical steel sheets of S8 grade or higher. As a result, C
0.005% or less, S reduced to 0.0030% or less, Si:
2.5~4.0%, Al: 0.3~1.5%, Mn: 0.1~1.0%,
When final annealing a silicon steel plate containing N: 0.004% or less with the balance consisting of iron and unavoidable impurities after cold rolling to the final thickness, the final annealing is performed at over 1000°C to 1200°C for 5 seconds to 15 minutes. After cooling, annealing is performed in a dry atmosphere for 5 seconds or more at 600 to 1000°C, which is below the final annealing temperature, without performing any processing such as punching or _shearing .
Kg or less (0.35mm thickness) 2.30w/Kg or less (0.50mm thickness)
S6 and S7 grade products are manufactured with a significantly lower
It has been found that the manufacturing process is almost the same as in the central part, and that a product with low core loss can be stably manufactured across the entire board width direction. The present invention will be explained in detail below. First, let's talk about the steel components. C is a component that deteriorates magnetic properties, and if it is contained in an amount exceeding 0.005%, carbides will precipitate, increasing iron loss and causing magnetic aging, so it should be kept at 0.005% or less. The preferred content to lower iron loss is
It is 0.003% or less. Si increases the specific resistance of steel, reduces eddy current loss, and lowers iron loss, so it is contained in an amount of 2.5% or more. However, when its content increases, it makes the steel brittle,
Since it deteriorates cold rollability, it should be 4.0% or less. S forms fine sulfides, stains the steel matrix, and deteriorates iron loss, so the content should be 0.005% or less. Al has the effect of increasing the specific resistance of steel and lowering iron loss like the aforementioned Si, and requires 0.30% or more to exhibit this effect. On the other hand, if this content increases, the steel becomes brittle, so the upper limit is set at 1.5%. Since N is a component that deteriorates magnetic properties,
0.004% or less. Mn is 0.1 to 0.1 to prevent deterioration of hot workability.
The range shall be 1.0%. Note that it is preferable that the elements P, Ti, Zr, etc. that are unavoidably included are as small as possible. A steel slab containing the above-mentioned components, with the remainder being iron and unavoidable impurities, is melted in a converter and manufactured by continuous casting or ingot-blowing rolling. The steel slab is heated in a known manner and then hot rolled to a thickness of 1.5 to 3.5 mm. After hot rolling, hot rolled plate annealing is performed at e.g. 800~1050℃.
Then, the final plate thickness is made by one cold rolling, for example, 0.35 to 0.50 mm, or the final plate is made by cold rolling two or more times with annealing in the middle without hot-rolled plate annealing. Make it thick. Next, final annealing is carried out by heating to a temperature of over 1000°C to 1200°C and soaking at this temperature for 5 seconds to 15 minutes.
If the temperature is below 1000℃, the crystal grains will be small and the iron loss will deteriorate (increase), so the temperature should be higher than 1000℃. On the other hand, if the heating temperature is too high, an oxide film will form on the surface of the steel plate, leading to deterioration of the magnetic properties, so the upper limit has been set to 1200
℃. Also, if the soaking time is less than 5 seconds, there will be little improvement in iron loss, and if it exceeds 15 minutes, internal oxidation may occur even if the ambient gas is non-oxidizing.
minutes or less. After soaking, it is cooled. Next, without performing processing such as punching, reheating is performed, and annealing is performed by soaking for 5 seconds or more at a temperature of 600 to 1000° C., which is lower than the temperature of the final annealing. This annealing may be continuous annealing or box annealing. This annealing will be described with reference to experimental data. C: 0.0015%, Si: 3.07%, S: 0.0008%,
A steel slab specimen containing Al: 0.670%, Mn: 0.17%, N: 0.0017%, the balance consisting of iron and unavoidable impurities, is hot rolled, hot rolled sheet annealed, and then cold rolled, Cold-rolled sheets with thicknesses of 0.35 mm and 0.50 mm were used. Final annealing is performed at 1075℃ x 15 seconds, and after cooling, 550, 600, 650, 700, 750, 800, 850, 900,
It was reheated to a temperature of 1000°C and soaked for 60 minutes. The atmosphere gas in the final annealing and reheating annealing is 10% _H2.
Dry with +90% _N2 . After processing under these conditions, the iron loss value W _10/50 , W _15
/50 and magnetic flux density B ₅₀ were measured, and the results are shown in FIG. In this figure, the ● mark is the value for the plate thickness 0.05mm, and the ○ mark is the value for the plate thickness 0.35mm. Also, A is iron loss value _10/50 , B is iron loss value W _15/50 , and C is magnetic flux density.
Showing _B50 . As is clear from this figure, when reheating and annealing are performed after finish annealing, the iron loss is significantly reduced in both W _10/50 and W _15/50 . The magnetic flux density B ₅₀ is also improved. Since the effect of this reheating annealing is slight when heated at less than 600°C or more than 1000°C, in the present invention, the temperature is set at 600°C or more and 1000°C or less. Although iron loss improves even at temperatures exceeding 1000°C, variations occur in the width direction of the steel plate, so the upper limit is set at 1000°C. If this temperature is higher than the final annealing temperature, iron loss will deteriorate, so it is set below the final annealing temperature. If the soaking time in the annealing is less than 5 seconds, there will be no effect of reducing iron loss, so the soaking time should be set at 5 seconds.
It shall be more than seconds. The atmosphere gas used in this annealing is a mixed gas of H ₂ and N ₂ or a single gas thereof, Ar gas, etc., but it is preferably dry and non-oxidizing. (Example) Next, an example will be described. Example 1 C0.0024%, Si3.19%, Mn0.16%, S0.0013%,
A hot-rolled steel plate with a thickness of 1.8 mm is obtained by hot rolling a steel slab containing 0.665% Al and 0.0015% N, with the balance consisting of iron and unavoidable impurities. It was cold rolled to a thickness of 0.50mm. Subsequently, finish annealing was performed at 1075°C for 20 seconds, and after cooling, it was reheated without processing and annealed at 950°C for 30 seconds. The material before and after reheating was sheared into Epstein specimens of 30 mm x 320 mm by half each from the rolling direction and the right angle direction, and the iron loss of W _10/50 and W _15/50 was calculated.
The magnetic properties were measured regarding the magnetic flux density of _B50 . As shown in Table 1, it was found that the magnetism was significantly improved by reheating.

[Table] Example 2 C0.0014%, Si3.01%, Mn0.16%, S0.0002%,
A hot-rolled steel plate with a thickness of 1.9 mm is obtained by hot rolling a steel slab containing 1.032% Al, 0.0021% N, and the balance iron and unavoidable impurities such as 0.0019% Ti and 0.0003% Zr. Cold rolled to mm. Subsequently, after intermediate annealing at 980°C for 50 seconds, finish rolling was performed to a plate thickness of 0.35 mm, and final annealing was performed at 1060°C for 30 seconds. This material is reheated without any processing and heated to 900
Annealing was performed at ℃ for 60 seconds. Epstein measurement values before and after reheating are shown in Table 2. From the same table, the magnetism of the twice-cold-rolled material was also significantly improved by reheating.

[Table] Example 3 C0.0025%, Si3.25%, Mn0.18%, S0.0002%,
A hot-rolled steel plate with a thickness of 1.8 mm is obtained by hot rolling a steel slab containing 0.689% Al and 0.0012% N, with the balance consisting of iron and unavoidable impurities, and is annealed at 980°C for 100 seconds. After cold rolling to a plate thickness of 0.35 mm, finish annealing was performed at 1030°C for 30 seconds, and after cooling, reheating annealing was performed at 850°C for 30 seconds without performing processing such as punching or shearing. Width direction W _10/50 (w/Kg, 55
mm×55mmSST) is shown in Figure 2. Before annealing D, the iron loss at the edge of the plate (from the edge to about 1/3 of the width of the plate) was inferior to that at the center, but as shown in E, reheating annealed brought it to almost the same level as the center. Improved. That is, finish annealing, cooling, punching,
It has been confirmed that reheating and annealing without performing processing such as shearing is a means to stably produce a material with low core loss across the entire width of the plate.

[Brief explanation of the drawing]

Figures 1A, B, and C are diagrams showing the influence of reheating heat treatment on iron loss value and magnetic flux density, and Figures 2D and E are diagrams showing the influence of reheating heat treatment on iron loss value and magnetic flux density. ) and the rear (FIG. 2E) of iron loss in the plate width direction.

Claims (1)

[Claims] 1% by weight: C: 0.005% or less, Si: 2.5-4.0%,
S: 0.005% or less, Al: 0.3~1.5%, Mn: 0.1~
1.0%, N: 0.004% or less, with the balance consisting of iron and unavoidable impurities, after hot rolling a silicon steel slab, annealing the hot rolled sheet and cold rolling once, or by inserting annealing in between. In the manufacturing method of non-oriented electrical steel sheets, which involves cold rolling two or more times to achieve the final thickness and then final annealing, the final annealing is performed at a temperature of over 1000℃ to 1200℃.
℃ for 5 seconds to 15 minutes, and after cooling, the temperature is below the final annealing temperature without performing any processing such as punching and shearing.
A method for producing a non-oriented electrical steel sheet with extremely low core loss, characterized by annealing at 600 to 1000°C for 5 seconds or more.