JPH10183311A - Non-oriented silicon steel sheet excellent in blanking workability and magnetic characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon steel sheet excellent in blanking workability and magnetic characteristic by specifying component composition and surface Vickers hardness and further specifying the content of either Sb or Sn or both of them. SOLUTION: The component composition of the objective steel sheet is, by weight, <=0.01% C, 0.1-2.0% Si, 0.1-1.5% Mn, 0.5-2.5% Al, <=0.1% P and <=0.01% S, and satisfies the relation, Si+0.60Al>=0.80 and the surface Vickers hardness of <=160HV. In addition, the steel preferably contains 0.005-0.20% either Sb or Sn or the total of both of them. Further, it is desired that the sulfide inclusions in the steel sheet are mostly calcium-sulfide or calcium- oxysulfide and the oxygen surface density in the surface layer of ferrite after finish annealing is <=1.0g/m<2> .

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 for a motor, a small transformer, or the like by performing a punching process, in particular, to improve the punching processability and iron loss characteristics. .

[0002]

2. Description of the Related Art In recent years, as the demand for energy saving has increased, the efficiency of electric equipment has been increased. In order to cope with this trend of energy saving, steel sheet manufacturers have improved magnetic properties, particularly iron loss properties, of magnetic steel sheets used for electric appliances by various means.

[0003] That is, Si is the most effective element for reducing iron loss by increasing the specific resistance of a steel sheet,
Widely used. In addition, Al is known to have the same effect as Si. About this Al, for example, JP-A-53-668
No. 16 proposes the positive addition of Al in order to increase the specific resistance of the steel sheet and avoid the effect of suppressing the grain growth due to the precipitation of fine AIN. Also, in JP-A-55-73819,
Good high magnetic field characteristics are achieved by adding Al and adjusting the annealing atmosphere to reduce the internal oxide layer on the steel sheet surface. Further, in JP-A-54-68716 and JP-A-58-25427, iron loss is improved by improving the texture by adding Al and adding REM and Sb in combination or purifying them. Has been reduced. Similarly, in addition to the addition of Al,
Japanese Patent Application Laid-Open No. 61-87823 discloses that the cooling rate of a steel sheet during finish annealing is controlled.
b, Sn combined addition to prevent oxynitridation, JP-A-3-2
In JP 94422, controlling the cold rolling to reduce the LC characteristic ratio of the steel sheet, in JP-A-4-63252, Mn and Al are added in combination, and in JP-A-4-136138, the extremely low By improving the texture by adding Si and adding P and Sb, the magnetic properties are all improved. Both technologies improve the properties of the electrical steel sheet itself,
The aim was to improve the efficiency of electrical equipment using it.

On the other hand, as the performance of semiconductors has been improved and the price has been reduced, peripheral technologies have been dramatically improved. As a result, control technology for small rotating devices has been advanced, and excellent permanent magnet materials have been developed. This has made it possible to manufacture high-efficiency rotating machines such as DC brushless motors. In the manufacture of this type of motor, the processing accuracy of the rotor is particularly required, and especially in the case of a core in which a permanent magnet is embedded in a punched iron core, it is necessary to withstand extremely severe punching. However, although the magnetic steel sheet according to the prior art described above achieves improvement in magnetic properties, warpage occurs after punching when performing punching, which is required for the above uses, and the desired shape is maintained after processing. There were problems such as not being able to do so.

[0005] In addition, while the rotor of the motor is usually used as it is in a punching process, the stator is not subjected to the severer punching process than the rotor. Many. In addition, in the electromagnetic steel sheet to be provided to the stator, in addition to the above-described method of adding Al, by optimizing the crystal grain size after strain removal of the product sheet, the iron loss property is improved, and the stator property is improved. Can be.

[0006] This iron loss largely depends on the recrystallized grain size obtained by finish annealing after cold rolling. In order to obtain a product with low iron loss, it is basically necessary to increase the crystal grain size. It is said. By the way, the recrystallized particle size is 150-250 μm
It is known that low iron loss can be obtained at the time.

[0007] Here, the growth of the crystal grains is greatly affected by the second phase dispersed in the steel, ie, the precipitates and inclusions, and greatly depends on the components, the size distribution, and the dispersed state. Since these precipitates and inclusions have the effect of pinning the movement of the crystal grain boundaries, reducing them as much as possible is effective for improving the grain growth. Therefore, in order to recrystallize to such a particle size, it is effective to reduce fine precipitates such as nitrides and sulfides as much as possible.

However, at the current industrial technology level, it is extremely difficult to melt high-purity steel in which precipitates and inclusions in the steel are reduced to such an extent that they do not affect the grain growth, and general-purpose practical materials are used. In the production of steel, the problem of cost cannot be neglected, and it is substantially impossible to melt such high-purity steel.

For this reason, some precipitates and inclusions remain in the steel inevitably, and as a result, the magnetic properties have to be deteriorated. In particular, when precipitates having a relatively low solid solution temperature, such as MnS, are formed, they are once dissolved in the process of slab heating, hot-rolled sheet annealing, recrystallization annealing after cold rolling, and then cooled. The fine precipitates have a remarkable effect of suppressing the grain growth, so that the magnetic properties are remarkably deteriorated.

As means for avoiding the solid solution and reprecipitation,
There is a method of lowering the slab heating temperature, the hot rolled sheet annealing temperature, and the recrystallization annealing temperature after cold rolling. However, although lowering the slab heating temperature has the effect of preventing solid solution of precipitates, it also lowers the hot rolling temperature, which not only makes rolling difficult, but also makes the hot rolled sheet unrecrystallized. Since the grain size is small even if a part remains or is recrystallized, the texture of the product sheet is deteriorated by subsequent cold rolling and recrystallization, which is not preferable for the product characteristics of the non-oriented electrical steel sheet. Similarly, in the method of lowering the annealing temperature of the hot-rolled sheet, recrystallization and grain growth become insufficient, and deterioration of the texture of the product sheet is inevitable.
Further, when the recrystallization annealing temperature is lowered, the grain growth rate is rather lowered due to the low temperature, and a sufficient grain size cannot be obtained with a limited annealing time. As described above, there is a limit in obtaining a product having good magnetic properties without dissolving and re-precipitating a precipitate, and no particular effect can be expected.

As a means for avoiding adverse effects such as precipitates, there is a method of controlling the form of precipitates. As such a method of controlling the form of precipitates, S in steel is made of REM sulfide, Sb sulfide or the like. Method of fixing as a precipitate having a high solid solution temperature (JP-A-51-62115)
Method for fixing S using Ca (Japanese Patent Publication No. 58-17248,
JP-B-58-17249 and JP-A-59-74213),
Method of adding Zr (Japanese Patent Publication No. 1-52448, JP-A-51-6)
0624)

[0012] However, in order to obtain a sufficient effect by these methods, it is necessary to add a large amount of expensive auxiliary raw materials, and there is a major problem of an increase in product cost. Not only that, REM sulfide is (REM, Mn, Al, Si) (O, S)
In addition to the fact that it takes a very complicated precipitation form as described above, it is difficult to float during melting and has a disadvantage that it remains in a large amount in steel. Therefore, even though the solid solution temperature of REM sulfide (mainly Ce sulfide) alone is high, it is actually a composite precipitate, and partially solid solution and reprecipitate.

As described above, in order to obtain good magnetic properties in a non-oriented electrical steel sheet, it is necessary to secure sufficient grain growth, and it is important to control the precipitates affecting the grain growth. To date, no technique has been developed to properly control the precipitates.

[0014]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and is particularly excellent in punching.
Another object of the present invention is to provide a non-oriented electrical steel sheet having good magnetic properties. It is a further object of the present invention to provide a means for improving magnetic properties after strain relief annealing.

[0015]

Means for Solving the Problems The inventors conducted various studies on the punching workability of non-oriented electrical steel sheets. As a result, the inventors optimized the content balance of Si and Al and further reduced the hardness of the steel sheet surface. By controlling, it was found that satisfactory punching workability was realized while satisfying magnetic properties, and the present invention was completed. It has also been newly found that the magnetic properties after strain relief annealing are improved by controlling the form of the sulfide-based inclusions and further controlling the surface state of the steel sheet.

That is, according to the present invention, C: 0.01 wt% or less, Si: 0.1 to 2.0 wt%, Mn: 0.1 to 1.5 wt%, Al: 0.
5 to 2.5 wt%, P: 0.1 wt% or less, and S: 0.01 wt% or less, with a component composition containing Si + 0.60Al ≧ 0.80 wt% and Vickers hardness of the surface is HV160 or less. This is a non-oriented electrical steel sheet having excellent punching workability and magnetic properties.

Here, in addition to the above components, one or both of Sb and Sn are added in a total amount of 0.005 to 0.20 wt%.
That the sulfide-based inclusions in the steel sheet are mainly calcium-sulfide or calcium-oxysulfide, and that the basis weight of the surface iron layer after finish annealing is 1.0 g / m ² or less; Are advantageous for improving magnetic properties. The fact that the sulfide-based inclusion is mainly calcium-sulfide or calcium-oxysulfide specifically means that the Mn weight ratio in the sulfide-based inclusion is suppressed to 10 wt% or less.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be specifically described based on experimental results which have led to the present invention. The inventors first obtained various commercially available DC brushless motors, created a mold that could be processed into the same shape as the rotor used for these motors, and performed a punching test on a steel sheet material using this mold. Was. Specifically, in evaluating the shape after punching, a ring having an outer diameter of 50 mm and an inner diameter of 48 mm was punched from a test steel sheet, and the warp of the ring after this punching was at most 5 mm.
It was confirmed that, if the material was not more than mm, punching with any of the molds did not result in a defective shape, and this was used as an evaluation index of the punching shape. Various steel sheet materials were evaluated by this evaluation method.

That is, FIG. 1 shows that C: 0.0020 wt%, Mn:
A non-oriented electrical steel sheet having a thickness of 0.50 mm and manufactured in accordance with a conventional method with 0.50 wt%, P: 0.05 wt% and S: 0.003 wt% as basic components, and further with various contents of Si and Al. And the evaluation results of the punching workability are shown. From FIG. 1, it can be seen that if Si + 0.6 Al ≧ 0.80 wt%, almost satisfactory punching workability can be obtained.

However, as shown in FIG.
Even in the region satisfying 6Al ≧ 0.80 wt%, there was one having poor workability. Therefore, when a good material and a defective material in this region were compared in detail, it was found that the surface hardness of the steel plate of the defective material was higher than that of the good material.

That is, FIG. 2 shows that C: 0.0020 wt%, Mn:
0.50wt%, P: 0.05wt%, S: 0.003wt%, Si: 1.3wt
% And Al: 1.0 wt% in producing a non-oriented electrical steel sheet according to a conventional method, by changing the atmosphere dew point during final annealing from + 30 ° C to -50 ° C, and increasing the annealing temperature by 700 ° C.
℃ ~ 1000 ℃, or by changing the pickling time with hydrochloric acid for the steel sheet after intermediate annealing, when adjusting the surface hardness of the steel sheet variously, the effect of the steel sheet surface hardness on the punching workability Show the effect. FIG. 2 shows that when the surface hardness exceeds HV160, the punching workability deteriorates.

Although the reason why the punching workability is improved by controlling the balance between the contents of Si and Al and controlling the surface hardness of the steel sheet has not been clearly elucidated, the inventors have found that. Thinks as follows. First, hardness governs the shape after punching. That is, if it is too soft, the adverse effect of the texture is reflected on the steel sheet, and in particular, when punching is performed in a direction where the yield strength is low, the drooping and crushing relatively increase, and the strength difference from a direction different from the above direction. As a result, the stress becomes locally non-uniform and the processed shape cannot be maintained.
On the other hand, if the hardness is too high, the stress applied to the mold during processing increases, causing excessive stress on the material and promoting non-uniform deformation of the material. Therefore, by optimizing the Si and Al content balance, the strength anisotropy of the material is reduced, and by optimizing the surface hardness, excess reaction to the material is reduced, resulting in improved workability. it is conceivable that.

Next, the results of an experiment conducted to improve magnetism after strain relief annealing will be described in detail. That is,
C: 0.003 wt%, Si: 1.0 wt%, Mn: 0.3 wt%, P: 0.
The composition of steel containing 03 wt% and Al: 1.7 wt% was adjusted by converter and vacuum degassing. Then add CaSi alloy or
Alternatively, by adding a normal desulfurization flux containing a mixture of CaO and CaF ₂ as a main component, S: 0.00
It was desulfurized to 7 wt%. Next, the obtained steel slab was heated to 1150 ° C. in a normal gas heating furnace, and then hot-rolled into a hot-rolled sheet having a thickness of 2.6 mm. Thereafter, hot-rolled sheet annealing was performed or omitted, and after cold rolling to a thickness of 0.5 mm, the dew point was set to -15 ° C and recrystallization annealing was performed to obtain a product sheet. The conditions for hot-rolled sheet annealing and recrystallization annealing are as shown in Table 1.

A part of the product plate thus obtained was subjected to punching workability evaluation, and the remaining product plate was annealed at 750 ° C. for 2 hours in a nitrogen atmosphere gas, and then the magnetic properties were measured. . The evaluation results are also shown in Table 1. In addition, regarding the Mn weight ratio in the sulfide-based inclusions after desulfurization, the results of investigations on the product sheet after finish annealing,
It is shown in Table 1.

[0025]

[Table 1]

From Table 1, it can be seen that under all conditions, CaSi
Steel with a Mn weight ratio of 10 wt% or less in sulfide-based inclusions, compared with conventional steel sheets with a high MnS content in sulfide-based inclusions, has particularly high iron loss characteristics. It turns out that it is favorable.

Although the reason why good magnetic properties can be obtained by controlling the sulfide-based inclusions is not necessarily clear, the low solid solution temperature (Mn, Fe) formed when a normal desulfurization flux is added is formed. ) S is finely dispersed by re-precipitation in slab heating, hot-rolled sheet annealing, and recrystallization annealing, which hinders grain growth, whereas CaS formed by CaSi desulfurization is stable in steel. Therefore, it is considered that the particles have extremely low solubility and do not undergo refining without solid solution reprecipitation, so that grain growth is improved.

Here, as the Ca alloy used as the desulfurizing agent, a wire-like material in which metallic calcium is covered with an iron hoop, or a calcium-silicon alloy whose particle size has been adjusted to a size suitable for injection, and the like are preferable.

Next, the reasons for limiting each component range will be described. C: 0.01 wt% or less C expands the γ region and lowers the α-γ transformation point. During annealing, the γ phase is formed in the form of a film at the α grain boundary to suppress the growth of the α grains, so that C must be basically reduced. Also, C content should be 0.01 wt% or less because it contains a large amount of α-phase stabilizing elements such as Si and Al, and causes aging deterioration of iron loss characteristics even when γ-phase is not generated in all temperature ranges. There is. The lower limit is not particularly limited, but is preferably 0.0005 wt% or more from the viewpoint of cost and the like.

Si: 0.1 to 2.0 wt% Si is an element that increases the specific resistance of steel and reduces iron loss, and at least 0.1 wt% is required to obtain the effect. On the other hand, excessive content increases the hardness and deteriorates the cold rollability, so the upper limit is 2.0 wt%.

Al: 0.5 to 2.5 wt% Al is an element that, like Si, increases the specific resistance of steel and reduces iron loss, and at least 0.5 wt% is required to obtain its effect. On the other hand, if the content is too large, the lubricity with the mold in continuous casting is reduced and casting becomes difficult, so the upper limit is set to 2.5 wt%.

Mn: 0.1 to 1.5 wt% Mn has the effect of increasing the specific resistance of the steel to reduce iron loss, though not so much as Si and Al, and also has the effect of improving hot rolling properties. 0.1% by weight or more is necessary to achieve the effect. However, if contained in a large amount, the cold rolling property is degraded, so the upper limit is 1.5 wt%.

P: 0.1 wt% or less P, although not as much as Si and Al, has the effect of increasing the specific resistance of steel and reducing iron loss. Further, there is an effect that the texture after cold rolling recrystallization is improved by the grain boundary segregation to improve the magnetic flux density. However, excessive grain boundary segregation hinders grain growth and rather deteriorates iron loss, so the upper limit is 0.1 wt%.

S: 0.01 wt% or less S is an element to be reduced as much as possible because it forms precipitates and inclusions and inhibits grain growth. In the present invention, the harmlessness of S is realized by controlling the precipitation form of S. However, when the amount of S remaining in the steel is large, the number of inclusions increases and the S is fixed. If Ca is relatively insufficient, the proportion of MnS in the inclusions increases, which also adversely affects the grain growth. Therefore, the upper limit of S is set to 0.01 wt%.

Further, Sb and Sn not only improve the texture and improve the magnetic flux density, but also suppress the oxynitridation of Al particularly on the surface layer of the steel sheet, and further suppress the generation of fine particles on the surface layer. Is added to suppress the increase in surface hardness and improve the punching workability. If one or both of them is less than 0.005 wt% in total, the effect is not obtained. On the other hand, if more than 0.2 wt%, grain growth is inhibited and magnetism is deteriorated. .

Although the essential components have been described above, various other known elements can be added. For example, B, Ni, Cu, Sn, Sn, Bi, Ge, and the like are added as magnetic property improving components. can do.

Next, the manufacturing method will be described. In the present invention, the manufacturing method is not particularly limited, and a conventionally known method can be applied. For example, in hot rolling, slab heating is desirably performed at 1200 ° C. or less from the viewpoint of energy saving, rolling is performed, and subsequent hot-rolled sheet annealing is not essential, but in order to improve magnetic flux density, 750 ° C. ~ 1050 ℃
It is preferable to anneal within the range. In addition, the final annealing after cold rolling, especially to prevent the oxynitriding of the surface layer of the steel sheet and the accompanying generation of fine particles in the surface layer and to suppress an excessive increase in surface hardness, the atmosphere dew point is -10 ° C or less. It is recommended that

[0038]

【Example】

Example 1 A steel having a component composition shown in Table 2 was adjusted by a converter and vacuum degassing to smelt the steel at an oxygen content of 0.007 wt% or less, and then the molten steel was mixed with various desulfurizing agents shown in Table 2. Using S: 0.
Desulfurized to less than 01%. After that, width 1100 by continuous casting
The slab was の 1250 mm thick and 225 mm thick. After heating these slabs in a normal gas heating furnace, hot rolling is performed,
Thereafter, hot-rolled sheet annealing was performed or omitted, and after cold rolling to a thickness of 0.5 mm, recrystallization annealing was performed in an atmosphere having a dew point of 20 ° C. to obtain a product sheet. The magnetic properties of the product sheet thus obtained are also shown in Table 2. In addition, for each steel plate,
Table 2 also shows the results of investigation of the warpage of the ring after punching when a ring having a diameter of 50 mm and an inner diameter of 48 mm was punched from the test steel sheet.

[0039]

[Table 2]

As is evident from the results shown in Table 2, the steel sheet according to the present invention is superior to the comparative example in terms of punching workability, and is also excellent in magnetic properties, particularly iron loss properties.

Example 2 A steel having the same composition as steel Nos. 6 and 10 in Table 2 was used as a slab, heated to 1150 ° C. in a normal gas heating furnace, subjected to hot rolling, and then hot rolled at 900 ° C. After performing sheet annealing, cold rolling was performed to obtain a thickness of 0.5 mm, and then recrystallization annealing was performed at 800 ° C. with a dew point changed from −50 ° C. to + 50 ° C. to obtain a product sheet.
A part of the obtained product sheet was subjected to punching property evaluation, and the remaining steel sheet was subjected to strain relief annealing at 750 ° C. for 2 hours, and then its magnetic properties were examined. The results are shown in Table 3 together with the measurement results of the basis weight of oxygen on the surface layer of the base steel after the finish annealing.

[0042]

[Table 3]

From Table 3, the dew point in the recrystallization annealing was adjusted.
The basis weight of oxygen on the surface layer of ground iron is 1.0 g / m ^TwoTo be
Therefore, the magnetic characteristics obtained in the first embodiment can be further improved.
You can see that you can. This is a steel plate with relatively high Al content
The surface scale generated during finish annealing (recrystallization annealing)
Is affecting the nitriding phenomenon during strain relief annealing.
It is. In other words, finish baking is performed by increasing the Al content.
The scale that easily forms on the steel sheet surface during dulling
Surface area oxygen weight is 1.0 g / m^TwoBeyond the limit, nitriding proceeds
This causes a magnetic degradation phenomenon. I don't know why
However, as the oxygen weight increases, the surface scale property increases.
Is considered to have changed the state and affected the nitriding phenomenon.
available.

[0044]

Thus, according to the present invention, Si and Al
By controlling the content balance and controlling the surface hardness of the steel sheet, the punching workability can be improved with satisfactory magnetic properties. Further, when the sulfide-based inclusions in the steel sheet are mainly calcium-sulfide or calcium-oxysulfide, and when the basis weight of oxygen of the ground iron surface layer after the finish annealing is 1.0 g / m ² or less, further magnetic The characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the contents of Si and Al on punching workability.

FIG. 2 is a graph showing the effect of steel sheet surface hardness on punching workability.

Claims (4)

[Claims] 1. C: 0.01 wt% or less, Si: 0.1 to 2.0 wt
%, Mn: 0.1 to 1.5 wt%, Al: 0.5 to 2.5 wt%, P: 0.
Punching workability characterized by having a component composition containing 1 wt% or less and S: 0.01 wt% or less under Si + 0.60Al ≧ 0.80 wt% and having a Vickers hardness of HV160 or less on the surface. Non-oriented electrical steel sheet with excellent magnetic properties. 2. The non-oriented electrical steel sheet according to claim 1, further comprising a component composition containing 0.005 to 0.20 wt% of one or both of Sb and Sn in total. Electrical steel sheet. 3. The non-oriented electrical steel sheet according to claim 1, wherein the sulfide-based inclusions in the steel sheet are mainly calcium-sulfide or calcium-oxysulfide. 4. The oxygen basis weight of the surface steel layer after finish annealing is
The non-oriented electrical steel sheet according to claim 1, 2 or 3, having a weight of 1.0 g / m ² or less.