JPH0686647B2 - Non-oriented electrical steel sheet with excellent magnetic properties - Google Patents

Description

The present invention relates to a so-called high-grade non-oriented electrical steel sheet having a Si content of 1.5 to 3.5%, and particularly to an iron core of a large rotating machine such as a large motor or a generator. The present invention relates to a suitable low iron loss non-oriented electrical steel sheet.

(Prior Art) A non-oriented electrical steel sheet is used as an iron core material of a rotating machine such as a motor, taking advantage of the small in-plane anisotropy of magnetic properties. Iron loss is particularly important as magnetic characteristics, and is classified according to sheet thickness and iron loss value in the JIS standard (C-2552). Iron loss represents the heat loss that occurs when magnetizing iron. The smaller the value, of course, the better, but the grade is selected according to the purpose from the viewpoint of economy and size of equipment. Generally, as the size of a device increases, the amount of heat generated by iron loss increases in proportion to the volume of the device, whereas the amount of heat radiation increases only in proportion to the surface area, making it difficult to cool the device. Therefore, the larger the equipment, the more the material with lower iron loss is required.

Iron loss is governed by two factors: eddy current loss and hysteresis loss. The eddy current loss is a loss due to the eddy current induced by the magnetization and depends on the plate thickness and the electric resistance of the steel. It is better to have a thin plate, but if it is too thin, problems such as labor for laminating iron cores will occur, so JIS standard 0.65, 0.5
Three types of 0, 0.35 mm are specified. The higher the electric resistance of steel is, the better it is, and as an alloying element, the increase rate of electric resistance per unit addition amount is large and it is cheap.
Si is often used. It is for this reason that the electrical steel sheet is also called a silicon steel sheet, and the higher the Si content, the higher the electrical loss of the high-grade electrical steel sheet. Al and Mn, which have similar effects, are often used in high-grade electrical steel sheets.

On the other hand, the hysteresis loss becomes smaller as the number of fine precipitates and grain boundaries that hinder the movement of the domain wall during the magnetization process decreases. Therefore, the point is to grow crystal grains after using steel with the highest possible purity. Componentally, C
It is necessary to minimize the impurity elements such as N, O (oxygen), and S that cause fine precipitates. Also, Ti
, Nb, V, Zr, etc. are elements that generate fine carbonitrides.
In addition to the damage of the precipitates, the precipitates hinder the crystal grain growth and deteriorate the hysteresis loss. Therefore, it is necessary to strictly limit the mixing of these elements.

Al also produces fine AlN and has a similar adverse effect. Therefore, it is generally not added to low grade electrical steel sheets. In medium to high grade electrical steel sheets, Al is added to increase the electric resistance, but in this case, a large amount of 0.1% or more is usually added to coarsen the precipitates, thereby avoiding the adverse effect on the hysteresis loss. That is, it is a general common sense that Al should not be added at all, or conversely, it should be contained in a large amount. In addition, B (boron) is also an element that forms a strong nitride, but BN is considered to have a weaker degree of inhibiting grain growth than AlN, and B is contained in steel with an Al content of 0.1% or less. It has been reported that good magnetic characteristics can be obtained by adding the N in a quantitative balance within a certain range (for example, Japanese Patent Publication No. 58-1172). However, regarding the effect of adding B, no significant effect has been found except for the economic merit that the amount of Al added can be reduced when used in combination with Al, and the Al content exceeds 0.1%. It is said that even if B is added to the material, the effect of B is not sufficiently obtained only because the cost is increased.

Also, adjusting the grain size is an important point for reducing iron loss.
It is known that the hysteresis loss decreases as the crystal grain size increases. It is desirable to anneal as high a temperature as possible for grain growth, and since the electrical steel sheet containing a large amount of Si does not have α / γ transformation, there is no limit in principle to the annealing temperature. However, when a steel sheet containing a large amount of Si, Mn, or Al is annealed at a high temperature, internal oxidation or nitridation occurs on the surface of the steel sheet, and magnetic properties are often deteriorated. In order to improve the magnetic properties of high-grade electromagnetic steel sheets, high-temperature hot-rolled sheet annealing or high-temperature intermediate annealing is often performed by the double cold-rolling method, and the risk of nitriding and internal oxidation is far greater than that of low-grade products. Sb for nitriding prevention at high temperature
And Sn are considered effective. For example, Japanese Patent Publication Sho 56-5437
No. 0 discloses a magnetic steel sheet containing Sb, and Japanese Patent Publication No. 58-3027 discloses a magnetic steel sheet containing Sn. on the other hand,
The most common method of preventing internal oxidation is to adjust the dew point of the annealing atmosphere, and a method of applying a special substance to the surface of the steel sheet has been proposed, but this is not always perfect.

Since the iron loss of a high-grade non-oriented electrical steel sheet has been reduced, many improvements have been conventionally made regarding the composition, manufacturing conditions, etc., but this is not always sufficient. The controlling factors of iron loss are intricately entwined with each other, and even if it is an effective method from a certain aspect, it often causes the opposite result in reality. The above-mentioned high temperature annealing is a good example, and its effect is not exhibited unless nitriding or internal oxidation is prevented. In order to adjust the grain size to an appropriate level while preventing nitriding and internal oxidation, it is necessary to strictly control many factors such as the composition of steel and annealing conditions. It is extremely difficult to manufacture.

(Problems to be Solved by the Invention) In view of the above circumstances, the present invention is an iron that can be manufactured by an industrial and easy method without precisely limiting the manufacturing method to narrow conditions as in the conventional iron. It is an object of the present invention to provide a high-grade non-oriented electrical steel sheet with low loss.

(Means for Solving the Problem) The present inventors have made detailed studies on the influence of various alloying elements on the crystal grain growth property and nitriding and internal oxidation behavior when an electrical steel sheet is annealed at a high temperature. As a result, a small amount of B was added to the steel containing a relatively large amount of Al, and
Further, it has been found that by adding at least one kind of Sn, nitriding and internal oxidation during high temperature annealing can be effectively prevented, and at the same time, good grain growth can be obtained.

The gist of the present invention resides in the following non-oriented electrical steel sheet.

% By weight, C: 0.005% or less, Si: 1.5 to 3.5%, Mn: 0.1% to 1.5%, S: 0.005% or less, Al: 0.15 to 1.5%, N: 0.005% or less B: 0.0005% to 0.0050% , And one or two of Sb and Sn in total of 0.01 to 0.20
%, And the balance Fe and unavoidable impurities, which is a non-oriented electrical steel sheet with excellent magnetic properties.

Conventionally, B is thought to have the effect of improving magnetic properties through BN, and since it has relatively less adverse effect on grain growth compared to AlN, it is less costly but for low Al steel with poor grain growth, Attempts have been made to improve the magnetic characteristics by adding B. Also, Sb and Sn are elements that repel N and are said to be effective in preventing nitriding during high temperature annealing. However, these elements may segregate at grain boundaries and, on the contrary, promote internal oxidation. .

The present inventors have studied in detail the effects of B, Sb and Sn on the grain growth property and internal oxidation, targeting high grade electrical steel sheets with high Si and Al contents. As a result, it was found that when B is added to high Al steel having an Al content of 0.15% or more, internal oxidation during high temperature annealing is prevented, grain growth is further promoted, and the adverse effects of Sb and Sn do not appear. Of. in this case,
Due to the high Al content of the base, it is highly probable that most N is fixed with Al and B exists in solid solution. The solid solution B is
It is considered that segregation is more likely to occur at the grain boundaries than Sb and Sn, which suppresses the adverse effects of Sb and Sn and prevents internal oxidation during high temperature annealing. Further, it is considered that grain growth is further promoted because AlN grows with BN partially formed in the heating and cooling processes of the manufacturing process as nuclei.

(Function) Hereinafter, the function and effect of the alloying elements in the electrical steel sheet of the present invention will be described together with the reason for limiting the content.

C C is an element that forms carbides and deteriorates all magnetic properties, and it is desirable to make it as low as possible. In particular, in order to prevent magnetic aging, it is necessary to set it to 0.005% or less, and more preferably 0.003% or less.

Si Si is to obtain the iron loss required for high grade non-oriented electrical steel sheet.
The content should be 1.5% or more. If the Si content is less than 1.5%, the eddy current loss is large and the iron loss cannot be reduced as desired. On the other hand, Si
If the content exceeds 3.5%, the cold rolling property deteriorates significantly.

Mn Mn is contained in an amount of 0.1% or more in order to prevent hot embrittlement due to S. Mn is also effective in increasing electrical resistance and reducing eddy current loss. However, if the Mn content exceeds 1.5%, the steel becomes brittle and the growth of crystal grains deteriorates.

Since S S produces sulfide-based precipitates and increases hysteresis loss, it is preferable to suppress S S to 0.005% or less, preferably 0.002% or less.

N N forms nitrides and impairs magnetic properties, so 0.005%
Hereafter, it is preferably 0.002% or less.

Al High-grade non-oriented electrical steel sheet generally has an increase in electrical resistance and Al
It is often contained in an amount of 0.15% or more for the purpose of coarsening N, but in the present invention, in addition to these effects, an amount of 0.15% or more is contained in order to completely fix N and sufficiently exert the action effect of B. Let If the Al content is less than 0.15%, the probability of B becoming BN becomes high, and the solid liquid B effective for preventing internal oxidation during high temperature annealing is insufficient. On the other hand, if the content exceeds 1.5%, the effect will be saturated and the price will only increase.

B In the steel sheet of the present invention, B does not bond with N, and most of it exists in a solid solution state. The solid solution B segregates at the crystal grain boundaries and prevents internal oxidation during high temperature annealing. B content is 0.
If it is less than 0005%, the amount of solid solution B is insufficient and the effect of preventing internal oxidation is small. On the other hand, even if B is contained in an amount of more than 0.0050%, the above effect is saturated and only the price rises, so the content is made less than this.

Sb, Sn: Sb and Sn have the effect of segregating on the surface of the steel sheet and preventing nitriding during high temperature annealing. Since these elements repel each other with N, it is considered that nitrogen molecules are prevented as a result of preventing nitrogen molecules from adsorbing on the surface of the steel sheet. If the content of Sb and Sn is less than 0.01% in total of one kind or two kinds, the above effect cannot be obtained. On the other hand, the effect is saturated even if the content of more than 0.20% in total of 1 type or 2 types is saturated, so the content is made less than this.

It should be noted that Sb and Sn are likely to segregate also at grain boundaries and usually promote internal oxidation, but in the electrical steel sheet of the present invention, B segregates first at grain boundaries as described above, so The adverse effects of Sb and Sn on oxidation are small.

The electrical steel sheet of the present invention having the composition as described above can be manufactured by the following method.

The slab heating temperature in the hot rolling step is preferably in the range of 1100 to 1250 ° C. Low temperature heating is better to prevent deterioration of magnetic properties due to fine precipitation of MnS, but if the temperature is too low, it will be difficult to secure the hot rolling finish temperature, and variations in magnetic properties within the coil will increase, and surface defects will occur. Since it easily occurs, about 1150 to 1200 ° C is preferable. In hot rolling, the higher the finishing temperature, the better the magnetic properties, so it is better to finish rolling at 800 ° C or higher. The higher the winding temperature is, the better the pickling temperature is.

After hot rolling, hot rolled sheet annealing is performed to recrystallize the hot rolled work structure. It is usually performed above 800 ℃. When this hot-rolled sheet annealing is performed at high temperature, the crystal grains become larger and it is advantageous in reducing hysteresis loss.However, the conventional electromagnetic steel sheet has nitriding and internal oxidation, so in case of box annealing the upper limit is kept at 850 ° C. Has been. On the other hand, since the electrical steel sheet of the present invention is less likely to undergo nitriding and internal oxidation, it can be annealed at high temperature. However, if the temperature is too high, the crystal grains become coarse and cracks are likely to occur in the next cold rolling, so it is better to keep the temperature below 1100 ° C.

Cold rolling is carried out by a single rolling method to a final strip thickness with a reduction rate of 60 to 90%. When it is important to reduce iron loss, cold rolling including intermediate annealing may be performed twice or more. The final annealing is preferably performed at a temperature of 850 ° C to 1100 ° C.

(Example) A steel having the composition shown in Table 1 was melted in an experimental quality and made into a thin plate having a thickness of 0.5 mm by the following manufacturing process. In this example, in order to clarify the change in hysteresis loss due to manufacturing conditions,
The components were adjusted so that the eddy current loss was almost the same by adjusting the electric resistance levels.

[Manufacturing process] Hot rolling Heating temperature: 1150 ° C Rolling finishing temperature: 850 ° C Finished sheet thickness: 2.3mm Winding temperature: 550 ° C Hot rolled sheet annealing after pickling As shown in Table 2, Cold rolling Reduction rate: 78% Finished plate thickness: 0.5 mm Final annealing after cold rolling As shown in Table 2, test pieces in the L direction (rolling direction) and T direction (right angle to the rolling direction) were cut out from the steel sheet after final annealing and ironed. The loss was measured. Table 3 shows the average iron loss values in the L and T directions.

The steels of the present invention (1 to 5) show good core loss values under any annealing conditions, and the properties are improved as the hot-rolled sheet annealing and final annealing are performed at higher temperatures. On the other hand, the comparative steels (6 to 9) show no improvement in the characteristics even if they are annealed at a high temperature, and the characteristics may deteriorate on the contrary, and it is clear that the effects of nitriding and internal oxidation are large.

(Effects of the Invention) The non-oriented electrical steel sheet of the present invention does not undergo nitriding or internal oxidation even when annealed at a high temperature, and therefore it is possible to industrially produce one having excellent magnetic properties.

By using the electromagnetic steel sheet of the present invention for the iron core, it is possible to improve the performance of large motors, generators and the like.

Claims (1)

[Claims] 1. By weight%, C: 0.005% or less, Si: 1.5 to 3.5%, Mn: 0.1% to 1.5%, S: 0.005% or less, Al: 0.15 to 1.5%, N: 0.005% or less B: 0.0005% to 0.0050%, and one or two of Sb and Sn in total of 0.01 to 0.20
%, And the balance Fe and unavoidable impurities, which is a non-oriented electrical steel sheet with excellent magnetic properties.