JPH06330255A - High tensile strength non-oriented silicon steel sheet and its production - Google Patents

Abstract

PURPOSE:To produce a non-oriented silicon steel sheet combining excellent mechanical properties and magnetic properties so as to withstand stress at the time of rotation or a change in stress at the time of acceleration-deceleration and used as an iron core material for the rotar of a rotary machine. CONSTITUTION:In the production of a non-oriented silicon steel sheet, steel contg. <=0.05% C, 2.0 to <4.0% Si, <=2.0% Al and <=0.2% P and contg. one or two kinds of Nb and Zr or one or two kinds of Ti and V in the range of 0.1<(Nb+Zr)/8(C+N)<1.0 and 0.4<(Ti+V)/4(C+N)<4.0 is subjected to hot rolling and in thereafter coiled at <=550 deg.C to regulate the ratio of the unrecrystallized part into >=40% and the average grain size in the unrecrystallized part into <=60mum. After cold rolling, the steel sheet is subjected to finish annealing at 700 to 900 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet used as an iron core material for a rotor of a rotating machine, and particularly to excellent mechanical properties and magnetic properties that can withstand stress during rotation or stress fluctuation during acceleration / deceleration. The present invention relates to a non-oriented electrical steel sheet for a rotating machine, which has high yield strength and also has characteristics.

[0002]

2. Description of the Related Art Recent advances in electronics have been remarkable, and various types of rotary drive control are becoming possible due to the sophistication of drive systems for rotating machines. That is, an increasing number of rotating machines are capable of variable speed operation and high speed operation at a commercial frequency or higher by controlling the frequency of the drive power source.
On the other hand, the development of mechatronics has accelerated the speeding up of rotating machines, and in the past, high-speed rotating machines have been limited to relatively small capacities, but are now expanding to medium and large-sized rotating machines.

In order to realize such a high-speed rotating machine, it is necessary to use a rotor having a structure capable of withstanding high-speed rotation. By the way, generally, the centrifugal force acting on the rotating body is proportional to the radius of rotation and is proportional to the square of the rotation speed. For this reason, in medium and large-sized high-speed rotating machines, the force acting on the rotor is, for example, 60
It may exceed kgf / mm ² . In addition, in the case of an ultra-large rotating machine, even if the number of rotations is relatively low, a very large stress may be applied as a result of the large diameter of the rotor. Is required. Furthermore, in rotating machines that require variable speed motion, acceleration and deceleration are frequently performed, so the material must not only have high tension, but must also have high limit stress (fatigue limit) for fatigue fracture against repeated stress. I have to.

Usually, laminated non-oriented electrical steel sheets are used for the rotor of a rotating machine. However, the rotating machine as described above may not satisfy the required mechanical strength. The cast steel rotor is used. But,
Since the rotor of the rotating machine utilizes an electromagnetic phenomenon, its material is required to have excellent mechanical properties as well as magnetic properties as described above. That is,
Since the rotor made of solid cast steel is an integral body, the eddy current loss is very large, and the efficiency as a rotating machine is several% compared to the case of using a rotor made by laminating electromagnetic steel sheets. Will also be lower. Also, if the magnetic flux density of the rotor core material is low,
The excitation ampere-turn must be increased in order to flow the magnetic flux required to generate the required torque to the rotor. This leads to an increase in copper loss in the exciting coil, which reduces the overall efficiency of the rotating machine.

As described above, the rotor core material of the rotating machine as described above has mechanically high tension and fatigue strength, and magnetically has low iron loss and high magnetic flux density at the same time. There must be. In the field of cold-rolled steel sheets, methods such as solid solution hardening, precipitation hardening, grain refining hardening, and transformation structure hardening are generally used as means for increasing the mechanical strength of steel sheets, but they have high mechanical strength and low iron loss and high magnetic flux density. However, it is extremely difficult to satisfy these requirements at the same time.

However, recently, some proposals have been made for a non-oriented electrical steel sheet having a high tensile strength. 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 having a large solid solution hardening is added to this to increase the tension. However, in this method, there is a problem in that warm rolling at 100 to 600 ° C. is necessary when rolling from the hot rolled sheet to the final cold rolled thickness, because the proportion that depends on the Si content is high. . Further, in Japanese Patent Application Laid-Open No. 61-9520, a molten steel obtained by increasing the Si content to 2.5 to 7.0% and adding an element having a large solid solution hardening to the steel is formed into a steel strip by a rapid solidification method. A method for manufacturing a high-strength non-oriented electrical steel sheet by hot or cold rolling and annealing is proposed. According to this method, even if the Si content is increased, since it is a rapid solidification method, the problem of embrittlement during rolling is mitigated, but a special casting method called rapid solidification method must be used,
There is a big problem that it cannot be applied to the ordinary rolling method widely used in industry.

Further, in Japanese Patent Laid-Open No. 62-256917, the Si content is 2.0 to 3.5%, the Ni content or the Ni and Mn content is increased, and ordinary cold rolling is performed and annealing conditions are applied. A method of manufacturing a high-strength non-oriented electrical steel sheet by controlling is proposed. However, this method has a problem in that the expensive Ni content must be increased, resulting in an increase in cost.

[0008]

In view of the above, the present invention is
It is intended to provide a non-oriented electrical steel sheet for a rotating machine, which is excellent in both mechanical properties and magnetic properties and has a high yield strength, and a manufacturing method thereof at low cost.

[0009]

Means for Solving the Problems In the silicon steel, the present inventors have used solid solution hardening, precipitation hardening, grain hardening, transformation structure hardening, work hardening, and other strengthening methods to improve mechanical properties and magnetic properties. I have been earnestly researching from the viewpoint that it is not possible to make the characteristics compatible. As a result, at the same time as containing Si in a high grade of a general non-oriented electrical steel sheet, at least one of Nb and Zr or Ti and V
By utilizing one or two types of carbonitrides and controlling hot rolling conditions and finish annealing conditions, it is possible to obtain non-oriented electrical steel sheets having high mechanical strength and magnetic properties and high yield strength. Found.

The present invention has been made based on the above findings, and the gist thereof is, in weight%, C: 0.05% or less,
Si: 2.0% or more and less than 4.0%, Al: 2.0% or less, P: 0.2% or less, and 1 out of Nb and Zr
1 or 2 kinds, or 1 or 2 kinds of Ti and V, 0.1 <(Nb + Zr) / 8 (C + N) <1.
0, 0.4 <(Ti + V) / 4 (C + N) <4.0, with the balance being Fe and unavoidable impurity elements, which are excellent in mechanical and magnetic properties It is found in electrical steel sheets. In addition, other gist is weight%
C: 0.05% or less, Si: 2.0% or more, 4.0%
Less than, including Al: 2.0% or less, P: 0.2% or less,
And one or two of Nb and Zr, or
One or two of Ti and V can be used as 0.1 <(Nb + Z
r) / 8 (C + N) <1.0, 0.4 <(Ti + V) /
Steel containing 4 (C + N) <4.0 with the balance Fe and unavoidable impurity elements is hot-rolled at 550 ° C.
Winding at the following temperature, the ratio of the unrecrystallized portion of the hot-rolled sheet is 40% or more, the average crystal grain size of the recrystallized portion is 60 μm or less, and then cold rolling is performed, and the temperature is 700 ° C. or more and 900 ° C. or less. It is in the place of finish annealing.

The present invention will be described in detail below. Si has a function of decreasing iron loss by increasing eddy current loss by increasing electrical resistance, and at the same time, is a component that also has a function of increasing the tension of steel by solution hardening, and in order to exert these functions. Must be contained at 2.0% or more.
On the other hand, if the content thereof increases, the magnetic flux density decreases, workability such as cold rolling deteriorates, and the cost increases, so the content is made less than 4.0%. Since Al also has an effect of reducing iron loss by increasing electrical resistance and reducing eddy current loss, in the case of achieving further excellent magnetic characteristics, especially low iron loss, the range is 2.0% or less. Added. If the content exceeds 2.0%, the magnetic flux density is lowered and the cost is increased. P is an element that has a very large effect of increasing the tension of steel, but it may cause grain boundary brittleness of steel because it segregates at grain boundaries. In order to avoid the problem of grain boundary brittleness and to enable continuous casting, hot rolling, and cold rolling on a normal industrial scale, it is added in a range of 0.2% or less.

Nb and Zr form fine carbonitrides and have the action of increasing the tension of steel by precipitation hardening and grain refining hardening. In order to achieve this effect, (Nb + Z
r) / 8 (C + N) must be more than 0.1, and even if the content thereof increases, the recrystallization temperature rises and the cost also increases, so (Nb + Zr) / 8 (C + N).
And less than 1.0. Ti and V also form fine carbonitrides, and have the action of increasing the tension of steel by precipitation hardening and grain refining hardening. In order to achieve this effect, (T
i + V) / 4 (C + N) must be greater than 0.4,
Moreover, since the recrystallization temperature rises and the cost increases even if the content increases, (Ti + V) / 4 (C + N)
And less than 4.0. When utilizing the above carbonitride forming elements such as Nb, Zr, Ti and V, C is set to 0.05% or less. If its content exceeds 0.05%, the deterioration of magnetism, particularly iron loss, becomes remarkable due to magnetic aging.

Iron and unavoidable impurity elements other than the above-mentioned components are included, but B may be added if necessary for the purpose of reducing the grain boundary brittleness due to P. In this case, B is 0.00
It is necessary to contain 10% or more. On the other hand, even if the content increases, it causes a decrease in magnetic flux density and hot brittleness.
It is 0.0070% or less. Further, Mn may be added, if necessary, for the purpose of increasing the electric resistance of steel to reduce the iron loss and increasing the tension by solid solution hardening. In this case, Mn must be contained by 0.1% or more, while
If the content thereof increases, the magnetic flux density will decrease and the cost will increase, so the content is made 2.0% or less.

The steel composed of the above components is melted in a converter or an electric furnace, and cast into a steel slab by continuous casting or slab rolling after ingot casting. The steel slab is then heated to the desired temperature and hot rolled. After hot rolling, it is wound up at a temperature of 550 ° C or less, and the ratio of the unrecrystallized portion of the hot rolled sheet is 40%.
As described above, the average crystal grain size of the recrystallized portion is set to 60 μm or less. If the winding temperature exceeds 550 ° C., grain boundary segregation of P may cause grain boundary embrittlement of the hot-rolled sheet, which will impede subsequent threading. When the ratio of the non-recrystallized portion of the hot-rolled sheet is less than 40% or the average crystal grain size of the recrystallized portion exceeds 60 μm, the grain boundary segregation of P becomes remarkable and the grain boundary of the hot-rolled sheet becomes large. Brittleness is likely to occur.

The hot-rolled sheet is then cold-rolled to a predetermined sheet thickness and subjected to continuous finish annealing for recrystallization. The finish annealing needs to be performed at a temperature of 700 ° C. or higher and 900 ° C. or lower. If the finish annealing temperature is less than 700 ° C., unrecrystallized portions remain, resulting in deterioration of magnetism and deterioration of shape. On the other hand, when the temperature exceeds 900 ° C., the crystal grains grow due to the crystal grain growth and the tension decreases.

[0016]

EXAMPLES Examples of the present invention will be described below. (Example 1) Steels having the components shown in Table 1 were hot-rolled to a thickness of 2.0 mm and wound at 500 ° C. In this case, the proportion of the non-recrystallized portion of the hot rolled sheet was 45%, and the average crystal grain size of the recrystallized portion was 48 μm. The hot rolled sheet was pickled, cold rolled to a thickness of 0.50 mm, and subjected to continuous finish annealing at 750 ° C. for 30 seconds. Epstein samples and JIS No. 6 tensile test pieces were sampled from the obtained product plates, and magnetic properties and mechanical properties were measured. The measurement results are also shown in the table. As is clear from Table 1, according to the present invention, it is possible to obtain a non-oriented electrical steel sheet having a high yield strength and having both excellent mechanical properties and magnetic properties.

[0017]

[Table 1]

(Example 2) C: 0.0302%, Si:
3.08%, Mn: 0.18%, P: 0.04%, A
1: 0.71%, N: 0.0010%, B: 0.003
Steel containing 2% and Ti: 0.021% [(Ti + V)
/(C+N)=0.673] by hot rolling to 2.3
It was made into a thickness of mm and wound up under the conditions shown in Table 2. This hot-rolled sheet is pickled, then cold-rolled to a thickness of 0.50 mm, and then rolled at 770 ° C for 3 hours.
A continuous finish annealing for 0 seconds was performed. Epstein samples and JIS No. 6 tensile test pieces were taken from the obtained product plate,
The magnetic and mechanical properties were measured. The measurement results are also shown in the table. As is clear from Table 2, the present invention provides a high-strength non-oriented electrical steel sheet having excellent mechanical properties and magnetic properties.

[0019]

[Table 2]

(Example 3) C: 0.0252%, Si:
3.16%, Mn: 0.25%, P: 0.03%, A
1: 0.58%, N: 0.0012%, B: 0.003
Steel containing 6%, V: 0.019% [(Ti + V) /
(C + N) = 0.72] was hot-rolled to a thickness of 2.2 mm and wound at 520 ° C. In this case, the ratio of the non-recrystallized portion of the hot-rolled sheet was 45%, and the average crystal grain size of the recrystallized portion was 52 μm. After pickling the hot rolled sheet, 0.5
It was cold rolled to a thickness of 0 mm and subjected to continuous finish annealing under the conditions shown in Table 3. Epstein samples and J
An IS6 tensile test piece was sampled and its magnetic properties and mechanical properties were measured. The measurement results are also shown in the table. Table 3
According to the above, it is understood that the present invention provides a high-strength non-oriented electrical steel sheet having excellent mechanical properties and magnetic properties.

[0021]

[Table 3]

[0022]

As described above, according to the present invention, there are provided a high tensile strength electromagnetic steel sheet for a rotating machine having excellent mechanical properties and magnetic properties and having a high yield strength, and a method for producing the same. In this movement, it is possible to sufficiently meet the demands made on the non-oriented electrical steel sheet that is the iron core material for the rotor, and its industrial value is extremely high.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeaki Takeshita 1-1 No. 1 Tobita-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works

Claims (2)

[Claims] 1. By weight%, C: 0.05% or less, Si: 2.0% or more and 4.0%
Less than, Al: 2.0% or less, P: including 0.2% or less,
And, one or two kinds of Nb and Zr, or one or two kinds of Ti and V, 0.1 <(Nb + Zr) / 8 (C + N) <1.0, 0.4 <( Ti + V) / 4 (C + N) <4.0, a high-strength non-oriented electrical steel sheet excellent in both mechanical and magnetic properties, characterized by being composed of the balance Fe and unavoidable impurity elements. 2. In% by weight, C: 0.05% or less, Si: 2.0% or more and 4.0%
Less than, Al: 2.0% or less, P: including 0.2% or less,
And, one or two kinds of Nb and Zr, or one or two kinds of Ti and V, 0.1 <(Nb + Zr) / 8 (C + N) <1.0 0.4 <(Ti + V ) / 4 (C + N) <4.0, with the balance Fe and unavoidable impurity elements, hot-rolled and rolled up at a temperature of 550 ° C. or lower to remove unrecrystallized portions of the hot-rolled sheet. Excellent mechanical and magnetic properties characterized by a ratio of 40% or more and an average crystal grain size of the recrystallized portion of 60 μm or less, followed by cold rolling and finish annealing at a temperature of 700 ° C. to 900 ° C. High strength non-oriented electrical steel sheet manufacturing method.