TW201331384A - Method of producing a non-oriented electrical steel sheet - Google Patents

Abstract

A non-oriented electrical steel sheet having excellent magnetic properties in a cold rolling direction is obtained by subjecting a steel slab comprising C: not more than 0.005 mass%, Si: 2-7 mass%, Mn: 0.03-3 mass%, Al: not more than 0.01 mass%, N: not more than 0.005 mass%, S: not more than 0.005 mass%, Ca: 0.0005-0.01 mass%, provided that an atomic ratio of Ca to S (Ca(mass%)/40)/(S(mass%)/32) is within a range of 0.5-3.5, and the remainder being Fe and inevitable impurities to a hot rolling, a hot band annealing, a cold rolling and a recrystallization annealing to provide a crystal grain size d of not more than 70 μ m and further to a skin pass rolling at a rolling reduction of 1-15% and a stress relief annealing.

Description

Method for manufacturing non-directional electrical steel sheet

The present invention relates to a method for producing a non-oriented electrical steel sheet, and more particularly to a method for producing a non-oriented electrical steel sheet having superior magnetic characteristics in a rolling direction.

In recent years, in the world trend of reducing energy consumption, including electric power, it has been strongly desired to increase the efficiency and miniaturization in the field of electrical equipment. Non-directional electromagnetic steel sheets are widely used as core materials for electrical equipment. Therefore, in order to achieve miniaturization and high efficiency of the electric machine, the quality of the non-oriented electrical steel sheet is improved, that is, high magnetic flux density/low iron loss is indispensable.

The non-oriented electrical steel sheet is used in the prior art, or the type and amount of the alloying elements added are appropriately adjusted, or the particle size before cold rolling is increased as much as possible, or the cold rolling reduction ratio is optimized. In order to achieve a high magnetic flux density, an element which can increase the intrinsic impedance or a plate thickness can be added, thereby reducing the loss of iron.

However, the drive motor of the hybrid electric vehicle and the electric vehicle adopts a split core instead of one of the prior art core cores in terms of improving the core material yield. The split core is not the same as the prior art, the laminated core material is made into a ring shape by the material steel plate as a whole, but the tooth portion of the T-shaped core that has been divided in the circumferential direction is rolled in the rolling direction of the steel plate. After that, by assembling the core to the technology for improving the motor characteristics, the tooth portion where the magnetic flux is concentrated becomes electromagnetic steel. Since the direction of the plate is rolled, it is possible to achieve high torque and high efficiency of the motor.

As the material used for the split core, a grain-oriented electrical steel sheet having a good magnetic gas characteristic in the rolling direction can be considered. However, since a secondary recrystallization process is required in the manufacturing step, the manufacturing cost is high, so it is almost adopted to be divided. The core is made of a low-cost non-oriented electromagnetic steel sheet. Therefore, if the magnetic flux density in the rolling direction of the non-oriented electrical steel sheet can be increased, it is considered to be an optimum material for the split core.

As a technique for improving the magnetic gas characteristics in the rolling direction, for example, Patent Document 1 discloses that in-plane calendering can be obtained by controlling the crystal grain size after annealing the hot-rolled sheet and the rolling reduction ratio of cold rolling to an appropriate range. A method of magnetic gas characteristics superior in direction and direction. However, since this method requires obtaining a crystal grain size before cold rolling of 300 μm or more, it is necessary to reduce the concentration of impurities in the steel, or it is necessary to set the annealing temperature of the hot rolled sheet at a high temperature, so that manufacturability and cost are required. There is a problem on the surface.

Further, Patent Document 2 discloses a technique of performing hot rolling and hot-rolled sheet annealing on a steel material containing Si: 2.0% by mass or less, Mn: 3.0% by mass or less, and Al: 1.0 to 3.0% by mass. In the manufacturing steps of pickling, cold rolling, refining annealing, and skin rolling calendering, the steel sheet having the refining and annealing having a crystal grain size of 50 μm or less is subjected to rolling reduction of the skin at a rolling reduction of 3 to 10%. A non-oriented electrical steel sheet having excellent magnetic characteristics in the L direction is produced. However, the technique of Patent Document 2 is based on the addition of 1% by mass or more of Al. It is necessary, so there is a problem that the saturation magnetic flux density is lowered or the raw material cost is increased.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2004-332042

Patent Document 2: Japanese Patent Laid-Open Publication No. 2006-265720

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a non-oriented electrical steel sheet which is advantageous in producing a magnetic gas characteristic in a cold rolling direction.

The inventors of the present invention have carefully reviewed in order to solve the above problems. As a result, it was found that the crystal grain size of the cold-rolled steel sheet after recrystallization annealing in which Al is reduced and Ca is controlled to be in an appropriate range, and the skin rolling rolling of the appropriate rolling reduction ratio is performed, the cold rolling direction can be remarkably improved. The magnetic flux density (in the L direction) has been developed to develop the present invention.

According to the above findings, the present invention is a method for producing a non-oriented electrical steel sheet which is subjected to hot rolling, hot-rolled sheet annealing, cold rolling, and then subjected to recrystallization annealing to form a crystal grain size d of 70 μm. After that, the skin rolling reduction is performed at a rolling reduction ratio of 1 to 15%, and the strain relief annealing is performed. The steel embryo system contains C: 0.005 mass% or less and Si: 2 to 7 mass%. Mn: 0.03 to 3% by mass, Al: 0.01% by mass or less, N: 0.005% by mass or less, S: 0.005% by mass or less, further containing Ca: 0.0005 to 0.01% by mass, and atomic ratio with S (Ca (% by mass) ) / 40) / (S (% by mass) / 32) is in the range of 0.5 to 3.5, and the rest is Fe and unavoidable impurities.

The steel germ system used in the method for producing a non-oriented electrical steel sheet according to the present invention further contains Sn: 0.003 to 0.5% by mass, Sb: 0.003 to 0.5% by mass, and P: 0.03 to 0.15 in addition to the above-described component composition. One or more selected from %.

According to the present invention, since the non-oriented electrical steel sheet having superior magnetic characteristics in the rolling direction can be provided at a low price, by using the non-oriented electrical steel sheet of the present invention in the split core material, the oil-electric mixture is made The performance improvement of cars and electric cars is possible.

As described above, the inventors of the present invention examined the magnetic characteristics of the cold rolling direction (L direction) of the non-oriented electrical steel sheet, and found that the cold rolling was performed after recrystallization annealing by reducing Al and adding Ca. When the crystal grain size of the steel sheet is controlled to an appropriate range and the skin rolling rolling is performed at an appropriate rolling reduction ratio, the magnetic flux density in the cold rolling direction (L direction) can be remarkably improved, and the present invention has been developed. Hereinafter, an experiment regarding the above findings will be described.

<Experiment 1>

In order to investigate the influence of Al content on the magnetic characteristics of the rolling direction of the steel sheet It is a steel containing C: 0.0025 mass%, Si: 3.0 mass%, Mn: 0.15 mass%, Al: 0.001-1.5 mass%, N: 0.0019 mass%, S: 0.0020 mass%, and Ca: 0.0025 mass%. After the embryo was heated at 1100 ° C for 30 minutes, it was subjected to hot rolling to prepare a hot-rolled sheet having a thickness of 2.0 mm, and then subjected to hot-rolled sheet annealing at 1000 ° C for 30 seconds, and formed into a sheet thickness by one cold rolling: 0.368 The cold-rolled sheet of mm was subjected to recrystallization annealing at 800 ° C for 30 seconds to prepare a crystal grain size of 35 μm. Here, the crystal grain size is measured by the line division method to measure the average crystal grain size of the L section (the same applies hereinafter). Thereafter, a rolling reduction of 5% of the skin was carried out to obtain a sheet thickness of 0.35 mm, and after holding at 820 ° C for 2 hours, furnace annealing was performed by furnace cooling.

The cold rolled annealed sheet obtained therefrom was cut out in the L direction (rolling direction) sample having a length L of 180 mm × a width C of 30 mm, and the magnetic properties (magnetic flux density B _50-L , iron loss W) were measured by an Epstein test. _15/50-L ), the results are shown in Figures 1 and 2. As is apparent from the above figures, in the region where the Al content is 0.01% by mass or less, the magnetic gas characteristics in the L direction are improved. The reason why the magnetic properties in the L direction can be improved after the skin rolling and the strain relief annealing is not fully understood, but it is considered that the Al system forms AlN and is a suppressing element for suppressing grain boundary movement. By reducing Al, the difference in grain boundary orientation can be used to produce a difference in mobility at the grain boundary, and the difference in grain growth after de-strain annealing caused by this will increase the degree of integration for Goss orientation. .

<Experiment 2>

Next, in order to investigate the influence of the Ca content on the magnetic gas characteristics in the rolling direction of the steel sheet, C: 0.0028 mass%, Si: 3.3 mass%, Mn: 0.50 mass%, Al: 0.004 mass%, and N: 0.0022 mass are contained. Steels with %, S: 0.0024% by mass and Ca: 0.0001 to 0.015% by mass were heated at 1100 ° C for 30 minutes, then hot rolled to obtain a hot-rolled sheet having a thickness of 1.8 mm, and then subjected to 1000 ° C. The hot rolled sheet was annealed in seconds, and a cold rolled sheet having a thickness of 0.269 mm was formed by one cold rolling, and thereafter, recrystallization annealing was performed at 820 ° C for 30 seconds to prepare a crystal grain size of 40 μm. Thereafter, the skin was rolled and rolled at a rolling reduction ratio of 7%, and after the thickness was 0.25 mm, it was held at 750 ° C for 2 hours, and then subjected to furnace strain annealing.

The cold rolled annealed sheet obtained therefrom was cut out in the L direction (rolling direction) sample having a length L of 180 mm × a width C of 30 mm, and the magnetic properties (magnetic flux density B _50-L , iron loss W) were measured by an Epstein test. _15/50-L ), the results are shown in Figures 3 and 4. As can be seen from the above figures, in the range of (Ca (% by mass) / 40) / (S (% by mass) / 32) which is an atomic ratio of Ca to S, the magnetic properties in the L direction are obtained in the range of 0.5 to 3.5. Upgrade. When Ca is in the above range, the reason why the magnetic properties in the L direction can be improved after the skin rolling and the strain relief annealing is considered to be because Ca is fixed in the steel and is precipitated as CaS, so that it can be coarsely grown. Precipitation to improve the grain growth of the hot rolled sheet during annealing and strain relief annealing. If (Ca/40)/(S/32) is less than 0.5, the above effect is insufficient, and conversely, when (Ca/40)/( When S/32) exceeds 3.5, the amount of precipitation of CaS becomes excessive and the hysteresis loss is increased, thereby increasing the iron loss.

<Experiment 3>

Next, in order to investigate the influence of the crystal grain size before the skin rolling on the magnetic gas characteristics in the rolling direction of the steel sheet, C: 0.0025 mass%, Si: 3.0 mass%, Mn: 0.15 mass%, and Al: 0.001 mass% are contained. N: 0.0019 mass%, S: 0.0015 mass%, and Ca: 0.0020 mass% of steel embryos were heated at 1100 ° C for 30 minutes, and then hot rolled to obtain a hot-rolled sheet having a thickness of 2.0 mm at 1000 ° C. The hot-rolled sheet was annealed for 30 seconds, and a cold-rolled sheet having a thickness of 0.368 mm was formed by one cold rolling. Thereafter, a recrystallization annealing was performed for 30 seconds in a temperature range of 750 to 1050 ° C, and after the crystal grain size was changed to various sizes, a rolling reduction of 5% of the skin was performed, and the thickness was 0.35. After mm, after holding at 820 ° C for 2 hours, the furnace was subjected to strain relief annealing.

The cold rolled annealed sheet obtained therefrom was cut out in the L direction (rolling direction) sample having a length L of 180 mm × a width C of 30 mm, and the magnetic properties (magnetic flux density B _50-L , iron loss W) were measured by an Epstein test. _15/50-L ), the results are shown in Figs. 5 and 6. As is apparent from the above figures, the magnetic properties in the L direction are improved by using a particle diameter of 70 μm or less after recrystallization annealing (before rolling of the skin roll). This system is considered to be that when the particle size before the skin rolling exceeds 70 μm, since it is difficult to cause strain-induced grain growth after skin rolling and strain relief annealing, the aggregate structure is randomized, and the body mass of the Goss orientation is lowered. The resulting strain, or the strain introduced by the skin rolling, is still present after the strain relief annealing.

<Experiment 4>

In addition, in order to investigate the influence of the rolling reduction of the skin rolling on the magnetic characteristics of the rolling direction of the steel sheet, C: 0.0026 mass%, Si: 3.3 mass%, Mn: 0.50 mass%, and Al: 0.002 mass% are contained. N, 0.0022% by mass, S: 0.0018% by mass, and Ca: 0.0023% by mass of steel embryos were heated at 1100 ° C for 30 minutes, and then hot rolled to obtain a hot-rolled sheet having a thickness of 1.8 mm and then at 1000 ° C. The hot rolled sheet was annealed for 30 seconds, and a cold rolled sheet having a thickness of 0.251 to 0.313 mm was formed by one cold rolling. Thereafter, recrystallization annealing was performed at 800 ° C for 30 seconds to prepare a crystal grain size of 40 μm. Thereafter, the rolling reduction was changed in the range of 0.5 to 20%, and the skin roll rolling was carried out to obtain a sheet thickness of 0.25 mm, and then held at 750 ° C for 2 hours, and then subjected to furnace strain annealing.

The cold rolled annealed sheet obtained therefrom was cut out in the L direction (rolling direction) sample having a length L of 180 mm × a width C of 30 mm, and the magnetic properties (magnetic flux density B _50-L , iron loss W) were measured by an Epstein test. _15/50-L ), the results are shown in Figs. 7 and 8. As is apparent from the above figures, the magnetic properties in the L direction are improved by setting the rolling reduction ratio of the skin rolling after recrystallization annealing to a range of 1 to 15%. This system is considered to be because if the skin rolling reduction rate is less than 1%, the introduced strain energy is insufficient, so when the strain relief annealing is performed, the integration of the Goss orientation cannot be confirmed. On the other hand, when When the skin rolling reduction ratio exceeds 15%, the introduced strain energy becomes excessively large, and in the strain relief annealing, the preferential growth of the Goss orientation is not confirmed.

Further, as described above, regarding the mechanism of the increase in the body mass of the Goss orientation after the skin rolling calendering and the strain relief annealing, it is not clear, but it can be considered as the orientation selective particle of the Goss grain having a small internal strain. What is caused by growth, in addition to the above-mentioned Al reduction effect, is also to promote the integration of the Goss orientation.

Next, the reason for limiting the chemical composition of the non-oriented electrical steel sheet of the present invention will be described.

C: 0.005 mass% or less

When the C system contains more than 0.005% by mass, the product sheet causes magnetic aging and the iron loss characteristics are lowered. Therefore, the C system is set to 0.005 mass% or less. It is preferably set to 0.003 mass% or less.

Si: 2 to 7 mass%

Since the Si system is an element which increases the electrical resistance of steel and reduces iron loss, it is necessary to contain 2% by mass or more. On the other hand, when Si exceeds 7 mass%, the steel is hardened and the workability is lowered, and the saturation magnetic flux density is also lowered. Therefore, Si is set in the range of 2 to 7 mass%. It is preferred that the upper limit is 6.5% by mass.

Mn: 0.03~3 mass%

Mn is an element necessary for improving hot rolling workability, and if it is less than 0.03 mass%, the above effect cannot be obtained. On the other hand, addition of more than 3% by mass causes an increase in raw material cost. Therefore, the Mn is set to be in the range of 0.03 to 3% by mass. Wai. It is preferred that the lower limit is 0.05% by mass and the upper limit is 2% by mass.

Al: 0.01% by mass or less

When the Al system is more than 0.01% by mass, it is difficult to cause a difference in mobility at the grain boundary by the grain boundary orientation difference angle, so that the aggregate structure after annealing of the hot rolled sheet and after strain relief annealing is randomized. The Goss orientation failed to develop and it became impossible to obtain excellent magnetic characteristics. Therefore, Al is set to 0.01% by mass or less. It is preferably 0.005 mass% or less.

S: 0.005 mass% or less, and N: 0.005 mass% or less

In the present invention, in the case of the present invention, the impurity element which lowers the magnetic properties is contained, and when it exceeds 0.005 mass%, the above disadvantages become large. Therefore, S and N are each set to 0.005 mass% or less. It is preferably 0.003 mass% or less.

Ca: 0.0005 to 0.01% by mass, and (Ca (% by mass) / 40) / (S (% by mass) / 32): 0.5 to 3.5

Ca is an element which precipitates as S in the steel by fixing S in the steel, and has an effect of improving grain growth and improving magnetic properties. When the amount of Ca added is less than 0.0005 mass%, the above effects are insufficient. On the other hand, addition of more than 0.01 mass% causes excessive precipitation of CaS, which increases the hysteresis loss, which is not preferable. Therefore, Ca is set in the range of 0.0005 to 0.01% by mass. It is preferred that the lower limit is 0.001% by mass and the upper limit is 0.008% by mass.

Among them, in order to obtain the above-described effect of Ca, in addition to the above composition range, there is an atomic ratio of Ca to S (Ca (% by mass) / 40) / (S (quality) The amount %) / 32) is necessary to control the range of 0.5 to 3.5. If the atomic ratio of Ca to S is less than 0.5, the above effect cannot be sufficiently obtained. Conversely, when the atomic ratio of Ca to S exceeds 3.5, the precipitation amount of CaS becomes excessive, and hysteresis loss is increased, and iron is increased. loss. Therefore, it is necessary to add the atomic ratio of Ca to S in the range of 0.5 to 3.5. Preferably, the lower limit is 0.7 and the upper limit is 1.5.

The electromagnetic steel sheet according to the present invention may further contain one or two selected from the group consisting of Sn, Sb, and P in addition to the above-described component composition.

Sn: 0.003 to 0.5% by mass, Sb: 0.003 to 0.5% by mass

Sn and Sb are elements which not only improve the aggregate structure but also increase the magnetic flux density, and also suppress the growth of surface fine particles by the oxidation and nitridation of the surface layer of the steel sheet, thereby preventing various effects such as deterioration of magnetic characteristics. In order to exhibit the above effects, it is preferable to add at least one of Sn and Sb in an amount of 0.003% by mass or more. On the other hand, when the amount added exceeds 0.5% by mass, there is a concern that the grain growth property of the crystal grains is impeded and the magnetic gas characteristics are lowered. Therefore, in the case where Sn and Sb are added, it is desirable to be limited to the lower limit of 0.003 mass% and the upper limit of 0.5 mass%, respectively.

P: 0.03 to 0.15 mass%

P has an effect of improving the aggregate structure and improving the magnetic flux density, and preferably contains 0.03 mass% or more. However, when the content exceeds 0.15% by mass, the hardness of the steel sheet rises to cause embrittlement, which makes the cold rolling difficult. difficult. Therefore, it is preferable to set P to the lower limit of 0.03 mass% and the upper limit of 0.15 mass%.

Next, a method of producing the non-oriented electrical steel sheet of the present invention will be described.

The non-oriented electrical steel sheet according to the present invention is obtained by melt-manufacturing a steel having a composition of the above-described components suitable for the present invention through a conventional refining process using a converter, an electric furnace, a vacuum degassing device, etc., and then continuously casting or agglomerating. - a block calendering method for forming a steel preform, which is hot rolled by a conventional method, and subjected to hot rolling sheet annealing as required, followed by cold rolling, recrystallization annealing, skin rolling calendering, Fabrication is performed by strain annealing. In the above-described production step, the cold rolling may be carried out according to a usual method and is not particularly limited. For example, the cold rolling may be carried out once or in the form of intermediate annealing, and the rolling reduction ratio may be set to be generally The directional electromagnetic steel sheets are the same.

However, after recrystallization annealing, it is desirable to carry out under the following conditions.

Recrystallization annealing

The recrystallization annealing after the cold rolling is required to control the crystal grain size after annealing to 70 μm or less, and is preferably controlled to 60 μm or less. Further, in order to achieve this, it is preferred that the annealing temperature be set in the range of 700 to 900 °C. More preferably, the lower limit is 750 ° C and the upper limit is 850 ° C.

Skin rolling

The rolling reduction of the skin rolling after the recrystallization annealing is necessary to be set in the range of 1 to 15%. As mentioned above, if the skin rolling reduction is not full 1%, because the introduced strain energy is not sufficient, the integration of the Goss orientation at the time of strain relief annealing cannot be confirmed. On the other hand, when the skin rolling reduction ratio exceeds 15%, the strain energy introduced is excessively large, and the priority growth of the Goss orientation at the time of strain relief annealing cannot be confirmed. Preferably, the lower limit is 2% and the upper limit is 10%.

Strain annealing

The strain relief annealing is generally carried out under conditions of soaking for about 2 hours at a temperature of 700 to 900 ° C. In order to promote grain growth in the present invention, it is preferred to set the annealing temperature as high as possible. However, when the annealing temperature exceeds 900 ° C, the manufacturing cost rises. Therefore, the annealing temperature for the strain relief annealing is preferably in the range of 700 to 900 ° C, more preferably the lower limit is 750 ° C and the upper limit is 850 ° C.

[Examples]

The steel slab having the composition shown in Table 1 was melt-molded, and after heating at 1080 ° C for 30 minutes, hot rolling was performed to obtain a hot-rolled sheet having a thickness of 2.0 mm, and then hot-rolled sheet annealing was performed at 1000 ° C for 30 seconds. After a cold-rolled sheet having a final sheet thickness of 0.20 to 0.35 mm by one cold rolling, recrystallization annealing was applied for 10 seconds according to the annealing temperature shown in Table 2. At this time, a sample was taken from the steel sheet after recrystallization annealing, and the average crystal grain size of the L section was measured by a line division method. Thereafter, the skin rolling rolling was carried out according to the rolling reduction ratio shown in Table 2, and after the final thickness as shown in Table 2, the temperature was maintained at 780 ° C for 2 hours, and then subjected to furnace cooling to strain annealing, thereby producing For the product board.

From the product sheet thus obtained, a sample having an L length of 180 mm × width C: 30 mm in the L direction (rolling direction) was cut out, and magnetic characteristics (magnetic flux density B _50-L , iron loss W ₁₅ ) were measured by an Epstein test. _/50-L ), the results are shown in Table 2 together with the average crystal grain size.

As is clear from Table 2, the non-oriented electrical steel sheet produced by the production method of the present invention is excellent in magnetic gas characteristics in the rolling direction.

(industrial availability)

The use of the non-oriented electrical steel sheet of the present invention is not limited to a split core which is limited to a drive motor of a hybrid electric vehicle and an electric vehicle, and may be suitably used in other applications in which magnetic characteristics of a required rolling direction are superior, for example, As a core material for transportation, etc.

Fig. 1 is a graph showing the effect of the Al content on the magnetic flux density B _{50-L in} the rolling direction.

Fig. 2 is a graph showing the effect of the Al content on the iron loss W _{15/50-L in} the rolling direction.

Fig. 3 is a graph showing the effect of the atomic ratio of Ca to S (Ca/40) / (S/32) on the magnetic flux density B _{50-L in} the rolling direction.

Fig. 4 is a graph showing the effect of the atomic ratio of Ca to S (Ca/40) / (S/32) on the iron loss W _{15/50-L in} the rolling direction.

Fig. 5 is a graph showing the influence of the average particle diameter before rolling of the skin on the magnetic flux density B _{50-L in} the rolling direction.

Fig. 6 is a graph showing the effect of the average particle diameter before rolling of the skin on the iron loss W _{15/50-L in} the rolling direction.

Fig. 7 is a graph showing the effect of the skin rolling reduction on the magnetic flux density B _{50-L in} the rolling direction.

Fig. 8 is a graph showing the effect of the skin rolling reduction on the iron loss W _{15/50-L in} the rolling direction.

Claims (2)

A method for producing a non-oriented electrical steel sheet which is subjected to hot rolling, hot-rolled sheet annealing, cold rolling, and then subjected to recrystallization annealing to form a crystal grain size d of 70 μm or less, and then subjected to a rolling reduction ratio. 1 to 15% of the skin is rolled and rolled, and subjected to strain relief annealing; wherein the steel germ system contains C: 0.005 mass% or less, Si: 2 to 7 mass%, Mn: 0.03 to 3 mass%, and Al: 0.01% by mass or less, N: 0.005% by mass or less, S: 0.005% by mass or less, further containing Ca: 0.0005 to 0.01% by mass, and atomic ratio with S (Ca (% by mass) / 40) / (S (% by mass) ) / 32) In the range of 0.5 to 3.5, the rest is Fe and inevitable impurities. The method for producing a non-oriented electrical steel sheet according to the first aspect of the invention, further comprising, in addition to the component composition, Sn: 0.003 to 0.5% by mass, Sb: 0.003 to 0.5% by mass, and P: 0.03 to 0.15. One or two or more selected from the mass%.