JPH028346A - High tensile electrical steel sheet and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture the title steel sheet having high yield strength and excellent magnetic characteristics by subjecting a slab of a steel having specific compsn. constituted of C, Si, Al, P, Mn, Ni, Nb, Zr and Fe to cold rolling end thereafter to recrystallization at specific temp. CONSTITUTION:A steel constituted of, by weight, <=0.04% C, 2.0 to <4.0% Si, 42.0% Al, 40.2% P, 0.3<=Mn+Ni<10% and 0.1<(Nb+Zr)/8(C+N)<1.0, furthermore of 40+ or -30 ppm B and/or 0.4<(Ti+V)/4(C+N)<4.0 according to necessary and the balance Fe with inevitable impurities is converted into a slab by continuous casting or ingot-blooming. The slab is hot-rolled, and, as it is, or after subjected to annealing, pickled and cold rolled into the final sheet thickness. After that, the cold rolled sheet is recrystallized in the temp. range of 700 to <900 deg.C. By this method, the high tensile nonoriented electrical steel sheet having the mechanical characteristics of >=70kgf/mm<2> yield strength (YP) and having low iron loss and high magnetic flux density can be obtd.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to an electromagnetic steel sheet used as an iron core in the rotating part of a rotating machine, which has excellent mechanical properties that can withstand stress during rotation or stress fluctuations during acceleration and deceleration. The present invention relates to an electromagnetic steel sheet for rotating machines with high yield strength and magnetic properties.

[Prior Art] In recent years, with the development of electronics, the functions of drive systems for rotating machines have become more sophisticated, and various rotational drive controls have become possible. That is, by controlling the frequency of the drive power source, there has been an increase in the number of rotating machines that are capable of variable speed operation and high speed operation at or above the commercial frequency.

On the other hand, the development of mechatronics has increased the demand for faster rotating machines, and although high-speed rotating machines have traditionally been limited to relatively small capacities, this trend is expanding to the field of medium- and large-sized rotating machines. .

In order to realize such a high-speed rotating machine, the rotor must have a structure that can withstand high-speed rotation.

In general, the centrifugal force acting on a rotating object is proportional to the radius of rotation and increases in proportion to the square of the rotation speed, so in medium to large high-speed rotating machines, the force acting on the rotor is BOkg.
/rrf may be exceeded.

In addition, in the case of ultra-large rotating machines, even if the rotation speed is relatively low, the diameter of the rotating part is large, so a stress of 80 kg/- or more may be applied as a result, and the rotor has a high tensile strength. Materials are required.

Furthermore, since acceleration and deceleration are frequently performed in rotating machines that require variable speed operation, the material must not only have high tensile strength, but also a high limit stress (fatigue limit) that can cause fatigue failure under repeated stress. It won't happen.

Normally, laminated non-oriented electrical steel plates are used for the rotor of rotating machines, but there are cases where the above-mentioned rotating machine cannot satisfy the required mechanical strength, and in that case, a solid cast steel rotating plate is used. Children are being employed.

However, since the rotor of a rotating machine utilizes electromagnetic phenomena, its material is required to have excellent magnetic properties as well as the mechanical properties mentioned above.

Of the magnetic properties required of rotor core materials, the most important are iron loss and magnetic flux density.

The main iron loss that occurs in the rotor is loss caused by high-frequency magnetic flux called ripple loss that occurs on the surface of the rotor core, and its frequency fR is expressed by the following equation.

fR=2-fo-M/P where fo: Frequency M of driving power supply: Number of teeth of stator core - Number of magnetic poles of rotating machine - As an example, set the frequency of driving power supply to about twice the commercial frequency. Considering the case of a two-pole rotating machine, the frequency of the ripple magnetic flux is in the range of 1 to 1 kHz.

Therefore, it is desirable that such a rotor core material has a small iron loss in the above frequency range. However, since the solid cast steel rotor mentioned above is a one-piece piece, the eddy current loss becomes extremely large in the high frequency range, and compared to the case of using a rotor made of laminated electromagnetic steel plates, the rotating machine It is said that the efficiency is several percent lower.

Another important magnetic property is the excitation property.

If the magnetic flux density of the rotor core material is low, the excitation ampere turns must be increased to flow the necessary magnetic flux through the rotor to generate the required torque. This leads to an increase in copper loss in the excitation coil, resulting in a decrease in the overall efficiency of the rotating machine.

In other words, replacing a rotor made of solid cast steel with a rotor made of laminated materials with excellent mechanical properties and iron loss will definitely reduce iron loss, but if the magnetic flux density of that material is low, copper loss will increase. However, in some cases, the decrease in iron loss is offset,
There may be no improvement in efficiency.

In this way, the rotor core material for such a rotating machine is
Mechanically, it must have high tensile strength and fatigue strength, and magnetically, it must simultaneously satisfy the requirements of low iron loss at high frequencies and high magnetic flux density.

Methods commonly used in the field of cold-rolled steel sheets to increase the mechanical strength of steel sheets include solid solution hardening, precipitation hardening, hardening by grain refinement, and hardening by transformed structure. Strength and excellent magnetic properties such as low core loss and high magnetic flux density are in a contradictory relationship, and it has been difficult to satisfy both at the same time.

As a known technique, for example, as in JP-A-60-238421, a method has been proposed in which the Si content is increased to 3.5 to 7.0% and an element with high solid solution hardening is added to increase the tensile strength. However, this method has the disadvantage that warm rolling at 100 to 600°C is required when rolling the hot-rolled sheet to the final cold-rolled thickness because the ratio is highly dependent on the Si content. . Furthermore, there was a major problem in that the magnetic flux density B50 of the steel plate obtained by this technique was extremely low at 1.56 to 1.61T.

Furthermore, in Japanese Patent Application Laid-open No. 81-9520, molten steel with increased Si content and addition of elements with high solid solution hardening is formed into a copper strip by rapid solidification, which is then cold or warm rolled and further annealed. A method has been proposed for producing a high tensile strength non-oriented electrical steel sheet with high tensile strength and low iron loss. According to this technique, even if the Si content is increased, the rapid solidification method is used, so that the constraints caused by material embrittlement, which are required in the conventional manufacturing method by rolling, are alleviated.

However, as with the previous technology, in order to obtain a high tensile strength of, for example, 70 kg/- or more, the S1 content must be increased to 4 to 4.5%, and the problem is that the magnetic flux density "50" becomes extremely low. was there.

On the other hand, as proposed in Japanese Unexamined Patent Publication No. 55-65349, there is a technology to manufacture sendust-based magnetic materials with extremely high hardness and high magnetic permeability, but these materials are mainly used in magnetic heads. Alternatively, it can be used for static devices such as small high-frequency transformers.

The rotor core of a rotating machine, which is the object of the present invention, is usually processed by punching and then laminated and bundled.

In the actual operating state of a rotating machine, it is subjected to repeated stress due to rotation, stopping, acceleration and deceleration.

Therefore, such a rotor core material must be free from cracking during punching and must have high fracture strength to withstand repeated stress. Sendust-based materials have high mechanical strength and excellent wear resistance, but on the other hand, they are extremely brittle, so they could not be used for rotating machines from the above point of view.

Therefore, the present inventors proposed a high tensile strength non-oriented electrical steel sheet for rotating machines and a method for manufacturing the same in Japanese Patent Application Laid-Open No. 62-258917. This enabled the industrial production of non-oriented electrical steel sheets with YP≧60 kg f /− class.

After that, as a result of working on developing something with even higher YP,
Minimizes the negative effect on magnetic properties\, YP≧70k
It has now become possible to industrially produce g f /- grade high tensile strength non-oriented electrical steel sheets.

[Problems to be Solved by the Invention] The object of the present invention is to provide YP≧70kgf/
III! The purpose of the present invention is to provide a high tensile strength non-oriented electrical steel sheet and a method for manufacturing the same.

[Means for solving the problem] Strengthening mechanisms for steel include solid solution strengthening, precipitation strengthening, strengthening by grain refinement, strengthening by transformed structure, and strengthening by processing. It is inevitable that the soft magnetic properties of the material will be impaired.

However, in contrast to solid solution strengthening, precipitation strengthening, and strengthening by grain refinement, strengthening by transformed structures and strengthening by processing have a very large negative effect on magnetism, so the former three are used in combination. By doing so, we developed a high-strength non-oriented electrical steel sheet with good magnetic properties.

The present invention will be explained in detail below.

First, the reason for limiting the ingredients will be explained.

Si: 2.0% or more to less than 4.0% St increases the specific resistance of steel and reduces eddy current, so
It is the most effective element in reducing iron loss.

At the same time, is St an effective element for increasing tensile strength?
If the amount added is less than 2%, the effect will be insufficient.

On the other hand, St makes steel brittle and lowers the saturation magnetic flux density of the product. Therefore, in the present invention, in order to enable production on an industrial scale using current rolling technology and to ensure high magnetic flux density,
The upper limit is set at 4.0%.

A, 17: 2.0% or less AΩ also has the same effect as St, so it is added in an appropriate amount. However, since it is not necessary to add it at all, the upper limit is set at 2.0% due to the problem of brittleness.

P: 0.2% or less P is an element that has a very large effect of increasing strength, but it is known that it causes grain boundary brittleness in steel because it segregates at grain boundaries. In order to avoid this problem of grain boundary brittleness and enable continuous casting, hot rolling, and cold rolling on an industrial scale, the upper limit is set to 0.2%.

Mn, Ni: 0.3%≦Ml+Ni<1
Both 0% Mn and Ni have a relatively small adverse effect on magnetic properties, and also have a large strength-increasing effect due to the solid solution effect.

The reason why the addition amount of Mn and Ni is defined as the total amount is that the effect of both elements on strength and the negative effect on magnetic flux density are the same, and the addition effect is clearly determined by the total addition amount. , from 3% or more to less than 10%, which is the allowable limit for the decrease in magnetic flux density.

Nb, Zr: As shown in Example 5, Nb/8 (C+N) is 0.
If it is less than 1, the effect of increasing the tension is insufficient;
．． If it is more than 0, there are disadvantages such as increase in addition cost and recrystallization temperature, and Zr can be expected to have the same effect as Nb, so (Nb + Zr)/8 (C + N) is set to 0.1
It was limited to more than 1.0.

Ti, V: As shown in Example 6, Tj /4 (C+N) is 0.
If it is less than 4, the effect of increasing the tension is insufficient;
If it is more than 0, there are disadvantages such as an increase in addition cost and recrystallization temperature, and since V can be expected to have the same effect as Ti, (Ti 10 V)/4 (C 0 N) should be set to more than 0.4.
It was limited to less than 40.

In addition, when carbonitride-forming elements such as Nb, Zr, Ti, V, etc. mentioned above are used, C is limited to 0.04% or less. This is because if it exceeds 0.04%, the deterioration of magnetism becomes too large.

In order to avoid grain boundary embrittlement due to P, it is effective to add an appropriate amount of B, and the amount added was limited to 40±30 ppm.

Next, the reasons for limitations regarding the manufacturing method will be described.

Continuous casting and hot rolling can be carried out by known methods. Whether or not to apply hot-rolled sheet annealing may be determined by taking into consideration requirements regarding magnetic properties and requirements regarding mechanical properties.

Further, although cold rolling can be carried out by a known method, warm rolling or the like may be preferable depending on the steel composition.

The most important point is the annealing conditions that define the crystal grain size of the product plate, and it is necessary to recrystallize at a temperature range of 700°C or higher and lower than 900°C.

Although there are no cases in which the samples were annealed at less than 750°C, the lower limit of the temperature range was set at 700°C in consideration of the industrially equivalent annealing temperature x annealing time. Also, the upper limit is 90
Considering the annealing temperature x annealing time equivalent to less than 0°C x 30 seconds, high-temperature short-time annealing at 900°C or higher is acceptable, but considering the range that can be industrially stably manufactured, the upper limit has been set to 900°C.
℃.

[Example] Example 1 Each steel having the composition shown in Table 1 was cast into a steel ingot and heated at 1100°C.
It was heated to , and then bloomed and rolled to form a slab. Then 110
After heating to 0℃, hot rolling is performed to make the plate thickness 2.3+
After a+a, pickling was performed, and then cold rolling was performed to obtain a plate thickness of 0.5 mm to 0.65 m11.

Subsequently, this cold-worked steel strip was heated at a temperature of 750°C to 800°C for 3
Annealed for 0 seconds.

Table 1 shows the mechanical properties and magnetic properties obtained as a result.

Example 2 Each steel having the composition shown in Table 2 was cast into a steel ingot and heated at 1100°C.
The material was heated and bloomed into a slab.

Next, after heating to 1100°C and hot rolling to a thickness of 1.8 mm or 2.0 mm, as shown in Table 2, some were left as they were, while others were rolled at 900°C.
The hot rolled plate was annealed for 1 minute, then pickled and cold rolled to a thickness of 0.5 mm.

Subsequently, this cold rolled steel strip was annealed at a temperature of 750°C to 800°C for 30 seconds.

Table 2 shows the mechanical properties and magnetic properties obtained as a result.

[Effects of the Invention] As described above, the present invention makes it possible to obtain a high-strength electrical steel sheet that has high yield strength, low core loss, and high magnetic flux density, and that enables ultra-high speed rotation of small rotating machines. , it can fully meet the demand for higher tensile strength of rotor materials accompanying the higher rotation speeds of medium and large-sized rotating machines, and its industrial effects are extremely large.

Agent Patent Attorney Tatsuo Chanoki Procedural Amendment (
(Voluntary) August 18, 1988

Claims (1)

[Claims] 1. C: 0.04% or less, Si: 2.0% or more to less than 4.0%, Al: 2.0% or less, P: 0.2% or less in weight%. , and one or two of Mn and Ni at 0.3%≦Mn+N
i < 10%, and one or two of Nb and Zr are controlled to achieve a content of 0.1 < (
Nb+Zr)/8(C+N)<1.0 Yield strength (YP) with balance Fe and unavoidable impurity elements ≧70 kgf/
High tensile strength electrical steel sheet with mechanical properties of mm^2 and excellent magnetic properties. 2. C: 0.04% or less, Si: 2.0% or more to less than 4.0%, Al: 2.0% or less, P: 0.2% or less, and contains Mn, Ni 0.3%≦Mn+N of one or two of them
i < 10%, and one or two of Nb and Zr are controlled to achieve a content of 0.1 < (
Nb+Zr)/8(C+N)<1.0 B: 40±300ppm The balance is Fe and unavoidable impurity elements (YP
) High tensile strength electrical steel sheet with mechanical properties of 70 kgf/mm^2 and excellent magnetic properties. 3. C: 0.04% or less, Si: 2.0% or more to less than 4.0%, Al: 2.0% or less, P: 0.2% or less, and contains Mn, Ni 0.3%≦Mn+N of one or two of them
Contain in the range of i<10%, and control one or two of Ti and V to achieve 0.4<(Ti+V)/4(C+N)<4.0 balance Fe
and yield strength (YP) ≧70 consisting of unavoidable impurity elements
A high-tensile electrical steel sheet with mechanical properties of kgf/mm^2 and excellent magnetic properties. 4. C: 0.04% or less, Si: 2.0% or more to less than 4.0%, Al: 2.0% or less, P: 0.2% or less, and contains Mn, Ni 0.3%≦Mn+N of one or two of them
Contains in the range of i < 10%, controls one or two of Ti and V to 0.4 < (Ti + V) / 4 (C + N) < 4.0, and B: 40 ± 30 ppm, the balance being Fe and unavoidable Yield strength due to impurity elements (YP
) High tensile strength electrical steel sheet with mechanical properties of 70 kgf/mm^2 and excellent magnetic properties. 5. Steel comprising the components described in claims 1 to 4 is made into a slab by continuous casting or steel ingot-blubber rolling, then hot-rolled as it is or after annealing, pickling, and cold-rolling. After making the final plate thickness, it is recrystallized at a temperature range of 700°C or more and less than 900°C.It has mechanical properties of yield strength (YP) ≧70kgf/mm^2 and has excellent magnetic properties. A method for manufacturing high-strength electrical steel sheets.