JPH03274247A - Nonoriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To effectively prevent the nitriding and internal oxidation at the time of high temp. annealing in a steel sheet and to obtain good growability in its crystalline grains by adding a trace amt. of B to a steel contg. a relatively large amt. of Al as a base and furthermore adding Sb and Sn thereto. CONSTITUTION:The compsn. of a nonoriented silicon steel sheet is formed of, by weight, <=0.005% C, 1.5 to 3.5% Si, 0.1 to 1.5% Mn, <=0.005% S, 0.15 to 1.5% Al, <=0.005% N, 0.0005 to 0.0050% B, total 0.01 to 0.20% of one or two kinds of Sb and Sn and the balance Fe with inevitable impurities. By this compsn., nitriding and internal oxidation are not produced, so that its magnetic properties are made excellent. This nonoriented silicon steel sheet has low core loss and is suitable for an iron core of a large sized motor, a generator or the like.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a so-called high-grade non-oriented electrical steel sheet with a Si content of 1.5 to 3.5%, particularly for use in large rotating parts such as large motors and generators. Low core loss non-directional II suitable for machine cores
This relates to m-steel plates.

(Prior Art) Non-oriented electrical steel sheets are used as core materials for rotating machines such as motors, taking advantage of their small in-plane anisotropy in magnetic properties. As for the magnetic properties, iron loss is particularly important, and the JIS standard (revised C-2552) classifies them by plate thickness and iron ti value. Iron loss represents the heat loss that occurs when iron is magnetized, and it goes without saying that the smaller the value, the better, but the grade is selected according to the purpose based on economic efficiency and the size of the A-ware. Generally, as equipment gets larger, the amount of heat generated by iron loss increases in proportion to its volume, while the amount of heat dissipated is only proportional to its surface area.
It becomes difficult to cool the equipment. For this reason, the larger the equipment, the more materials with low iron loss are required.

Iron loss is controlled by two factors: eddy current loss and hysteresis loss. Eddy electric fjti is a vortex ffl induced by magnetization
The loss is due to droplets and depends on the plate thickness and the electrical resistance of the steel. The thinner the plate, the better, but if it is too thin, problems such as the labor-intensive work of laminating the core will occur, so the JIS standard specifies three types: 0.65, 0.50, and 0.35+u+. ing. The higher the electrical resistance of steel, the better, and Si is often used as an alloying element because it has a large electrical resistance increase rate per unit addition amount and is inexpensive. This is why electrical steel sheets are also called silicon steel sheets, and high-grade magnetic sheets with high Si content and low core loss are called magnetic sheets. Since Al and JIn have similar effects, they are often used in high-grade electromagnetic TM plates.

On the other hand, the hysteresis loss becomes smaller as there are fewer fine precipitates and grain boundaries that impede movement of domain walls during the magnetization process. Therefore, it is important to grow crystal grains using steel of as high a purity as possible. Fi, in terms of quantity, it is necessary to reduce impurity elements such as C, N10 (oxygen), and S that cause fine precipitates as low as possible.Also, Ti, Nb, ■, Zr, etc. In addition to the harmful effects of precipitates, precipitates inhibit crystal grain growth and degrade hysteresis loss, so it is necessary to strictly limit the inclusion of these elements.

^e is also a minute AI! ,N, and have a similar adverse effect, so it is generally not added to low-grade electrical steel sheets.
Al is added to high-grade IT magnetic steel sheets to increase electrical resistance, but in this case, it is usually added in large amounts of 0.1% or more to coarsen the precipitates and avoid adverse effects on hysteresis loss. . That is, it is common knowledge that it is better not to add An at all, or to add it in a large amount. B (boron) is also an element that forms strong nitrides, but BN is said to have a weaker effect on crystal grain growth than ^IN, and Al
It has been reported that good magnetic properties can be obtained by adding B to steel with a B content of 0.1% or less with a quantitative balance with the N content within a certain range (for example,
-1172 publication), Shikashi, and the effect of adding B.
Other than the economical advantage of reducing the amount of ^e added when used in combination with 8L, no significant effectiveness has been found, and B is added to materials with an Al content exceeding 0.1%. However, it is said that the effect of B will not be fully obtained, as it will only increase the cost.

Adjustment of grain size is also an important point in reducing iron loss.
It is known that the hysteresis loss decreases as the crystal grains become larger.In order to achieve zero-grain growth, it is desirable to anneal as high a temperature as possible, and electrical steel sheets containing a large amount of Si are
Since there is no transformation, there is no restriction on the annealing temperature in principle. However, when steel sheets containing a large amount of Si, Mn, or Al are annealed at high temperatures, internal oxidation and nitridation occur on the surface of the m-plate, which deteriorates the magnetic properties. In order to improve the magnetic properties of high-grade electrical steel sheets, high-temperature hot-rolled sheet annealing or high-temperature intermediate annealing using a double cold rolling method is often performed, and the risk of nitridation and internal oxidation is lower than that of lower-grade products. Sb, Sn, etc. are considered to be effective in preventing nitriding at high temperatures.
Including ti! Each steel plate is disclosed. On the other hand, the most common method for preventing internal oxidation is to adjust the dew point of the annealing atmosphere, and methods such as applying special substances to the surface of the steel sheet have also been proposed, but these methods are not necessarily perfect.

In order to reduce the iron loss of high-grade non-directional electromagnetic m-plates, many improvements have been made to the composition, manufacturing conditions, etc., but these are not necessarily sufficient, and the factors governing iron loss are intricately intertwined. ,Even if a method is effective from a certain point of view, it often leads to the opposite result in reality.The high-temperature annealing mentioned above is a good example, and unless nitridation and internal oxidation are prevented, it will not be effective. In order to adjust the grain size to an appropriate level while preventing nitridation and internal oxidation, it is necessary to strictly control many factors such as the strength of the steel and annealing conditions. It is extremely difficult to manufacture products stably.

(Issues to be Solved by the Invention) In view of the above-mentioned circumstances, the present invention can be manufactured in an industrial and easy manner without having to precisely limit the manufacturing method to narrow conditions as in the past. The purpose is to provide a high-grade non-oriented electrical steel sheet with low iron loss.

(Means for Solving Problem I1) The present inventors conducted a detailed study on the influence of various alloying elements on grain growth, nitriding and internal oxidation behavior when electrical steel sheets are annealed at high temperatures.

As a result, it was found that nitridation and internal oxidation during high-temperature annealing can be effectively prevented by adding a small amount of B to a steel containing a relatively large amount of A1, and further adding one or more of Sb or Sn. It has also been found that good grain growth properties can be obtained at the same time.

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

In weight%: CF 0.005% or less, Si: 1.5-3.
5%, Hn: 0.1% to 1.5%, S: 0.
005% or less, ^1: 0.15-1.5%, N:
0.005% or less, B: 0.0005% to 0.00
50%, and a total of 0.50% and one or both of Sb and Sn. A patented magnetic steel sheet characterized by containing 1 to 0.20% O, with the remainder consisting of Fe and unavoidable impurities.

Conventionally, B has been thought to have the effect of improving magnetic properties through BN, and in addition, ^j! Since it has relatively little adverse effect on grain growth compared to N, attempts have been made to improve the magnetic properties by adding B to low ANliil, which is cheap but has poor grain growth. Also, Sb and S
Although n is an element that repels N and is said to be effective in preventing nitridation during high-temperature annealing, these elements may segregate at grain boundaries and promote internal oxidation.

The present inventors conducted a detailed study on the effects of B, Sb, and Sn on grain growth and internal oxidation in high-grade 1tKf steel sheets with high Si and i contents. As a result, the ^l content is 0
．． They found that adding B to high-Al steel with a content of 15% or more prevents internal oxidation during high-temperature annealing and further promotes grain growth, without the negative effects of Sb and Sn. In this case, since the pace has a high ^E content,
Most of the N is fixed in ^l, and there is a high probability that B exists in a solid solution state. B dissolved in solid solution is more likely to segregate at grain boundaries than Sb and Sn, and is thought to suppress the adverse effects of Sb and Sn and prevent internal oxidation during high-temperature annealing.

In addition, it is thought that grain growth is further promoted because BN partially generated during the heating and cooling steps of the manufacturing process becomes a nucleus and the AlN is lengthened.

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

■ CC C is an element that forms carbides and deteriorates all magnetic properties, so it is desirable to reduce it as much as possible. In particular, in order to prevent magnetic aging, the content must be 0.005% or less, and more preferably 0.003% or less.

■Si The Si content should be 1.5% or more to obtain the core loss required for high-grade non-oriented electrical steel sheets. If Si is less than 1.5%, the eddy current loss will be large and the iron loss will not be as low as the target.
On the other hand, if Si is contained in an amount exceeding 3.5%, the cold rolling property will be significantly deteriorated, so the Si content should be less than this.

■Mn Mn is contained in an amount of 0.1% or more to prevent hot skin properties caused by S. Mn is also effective in increasing electrical resistance and reducing eddy current loss. However, the Mn content is 1
．． If it exceeds 5%, the steel will become weak and the growth of crystal grains will deteriorate, so the content should be less than this.

(2) S S produces sulfide-based precipitates and increases hysteresis loss, so it is best to suppress it to 0.005% or less, preferably 0.002% or less.

■ N N forms nitrides and contributes to magnetic properties, so 0, 0
0.05% or less, preferably 0.002% or less.

■ ^i High-grade non-oriented electrical steel sheets generally have increased electrical resistance and
B is often contained in an amount of 0.15% or more for the purpose of coarsening ffiN, but in the present invention, in addition to these effects, B is contained in an amount of 0.1% or more in order to completely fix N and fully exhibit the effects of B.
Affi content is O.
If it is less than tS%, there is a high probability that B becomes BN, and solid IB, which is effective in 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, so the content should be less than this.

■ B In the steel sheet of the present invention, B does not combine with N, and most of B exists in a solid solution state. B dissolved in solid solution segregates at grain boundaries and prevents internal oxidation during high-temperature annealing. The content of B is o,
If the amount of solid iB is less than 0.005%, the effect of preventing internal oxidation is small.On the other hand, if B is contained in excess of 0.0050%, the effect will be saturated and the price will only increase. The following shall apply.

■Sb, Sn: Sb and Sn segregate on the surface of the steel sheet and have the effect of preventing nitridation during high temperature annealing. It is thought that these elements repel each other with N and thus prevent nitrogen molecules from adsorbing on the surface of the steel sheet, thereby preventing nitridation.

The content of Sb and Sn is 0.01 in total of 1 type or 2 types
If the content is less than 0.20%, the above-mentioned effect cannot be obtained.On the other hand, even if the total content of one or both of them exceeds 0.20%, the effect will be saturated, so the content should be less than this.

Note that Sb and Sn tend to segregate at grain boundaries as well, and usually promote internal oxidation, but in the IT electrical steel sheet of the present invention, as mentioned above, B segregates at grain boundaries first. Sb and Sn have little adverse effect on internal oxidation.

The 1i magnetic 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 process is 1100-12
It is better to heat in the range of 50°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 finishing temperature, and the temperature within the coil will increase. 1150~! Approximately 200°C is suitable. In hot rolling, the higher the finishing temperature, the better the magnetic properties, so it is better to finish rolling at a temperature of 800"C or higher.It is also better to use a higher temperature for 0 winding, but in consideration of pickling properties,
Appropriate winding temperature is around 00'C.

After hot rolling, hot-rolled processing & hot-rolled plate annealing is performed to recrystallize the 11tIs, 9 times are carried out at 800'C or higher. When this hot-rolled sheet is annealed at a high temperature, the crystal grains become larger, which is advantageous for achieving low hysteresis and low acupuncture.However, in the case of box annealing, the upper limit for conventional electrical steel sheets is 85"C due to nitridation and internal oxidation. is suppressed.

On the other hand, the ILTM steel sheet of the present invention is less prone to nitriding and internal oxidation and can be annealed at high temperatures. However, if the temperature is too high, the crystal grains will become coarser,
Because cracks are likely to occur in the gaps during the next cold rolling, 110
It is better to keep it below 0'C.

Cold rolling is performed by a single rolling method to achieve the final thickness at a reduction rate of 60 to 90%. If it is important to reduce iron loss, cold rolling may be performed two or more times including intermediate annealing.
The final annealing is preferably carried out at a temperature of 850"C to 1100"C.

(Example) The &lI strength rope shown in Table 1 was melted in a laboratory and made into a thin plate with a thickness of 0.5V+m using the manufacturing process described below.In addition, in this example, changes in hysteresis loss due to manufacturing conditions are clearly explained. In order to achieve this, the electrical resistance values were matched and the components were adjusted so that the eddy current loss was almost the same.

〔Manufacturing process〕

■Hot rolling heating temperature: 1150°C Finishing rolling temperature: 850"C Finished sheet thickness: 2.3a+s Coiling temperature: 550"C ■Hot rolled sheet annealing after pickling As shown in Table 2 ■Cold rolling Rolling ratio = 78% Finished plate thickness: 0.5mm ■First step after cold rolling! As shown in Annealing Table 2, from the steel plate after final annealing, the L direction (rolling direction) and T direction (
A test piece was cut out (perpendicular to the rolling direction) and the iron loss was measured. Table 3 shows the average values of iron loss values in the L direction and the T direction.

The steels (1 to 5) of the present invention exhibit good core loss values under any annealing conditions, and the properties improve as 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 properties even when subjected to high-temperature annealing, and on the contrary, properties sometimes deteriorate, and it is clear that the effects of nitridation and internal oxidation are large.

(The following is a margin.) (Effects of the invention) The non-oriented electrical steel sheet of the present invention does not undergo nitridation or internal oxidation even when annealed at high temperatures, so it can be industrially and stably manufactured with excellent magnetic properties. be able to.

By using the electromagnetic tI4 plate of the present invention in an iron core, the performance of large motors, starter tlIa, etc. can be improved.

Claims (1)

[Claims] In weight%, C: 0.005% or less, Si: 1.5 to 3.5%, Mn
: 0.1% to 1.5%, S: 0.005% or less, Al:
0.15-1.5%, N: 0.005% or less, B: 0.
0005% to 0.0050%, and a total of 0.0% of one or both of Sb and Sn
A non-oriented electrical steel sheet with excellent magnetic properties, characterized by containing 1 to 0.20% of Fe, and the balance consisting of Fe and unavoidable impurities.