Method of manufacturing pressed part and steel sheet for press working

Abstract

 Provided is a method of manufacturing a pressed part, which imparts excellent formability on a steel sheet, and the steel sheet for press working used in the manufacturing of the pressed part when the pressed part is manufactured with a silicon steel sheet.
A manufacturing method includes a process of siliconizing a low-silicon steel sheet (14) which becomes a material of a high-silicon steel sheet in a state where a surface of a to-be-pressed portion (16) is coated with a mask (30); and a process of pressing the to-be-pressed portion (16) of the siliconized high-silicon steel sheet as a workpiece. Since the surface of the to-be-pressed portion (16) is coated with the mask (30) and the siliconizing treatment is performed, it is possible to obtain the high-silicon steel sheet in which the to-be-pressed portion (16) is softer than other portions. Since the high-silicon steel sheet is pressed, the steel sheet is excellent in formability during the press working.

Description

BACKGROUND OF THE INVENTION

Incorporation by Reference

[0001] Priority is claimed to Japanese Patent Application No. 2013-103763, filed May 16, 2013, the entire content of each of which is incorporated herein by reference.

Field of the Invention

[0002] The present invention relates to a method of manufacturing a pressed part such as a motor core or a transformer core with a silicon steel sheet, and a steel sheet for press working used in the manufacturing of the pressed part.

Description of Related Art

[0003] A core such as a motor core or a transformer core requires a low core loss and a high magnetic flux density as characteristics thereof. In particular, a silicon steel sheet having the Si content of 4.0% by weight or greater is widely used as a material that satisfies a low core loss. There are a siliconizing treatment, direct casting and the like as a method of acquiring the silicon steel sheet (refer to Japanese Unexamined Patent Application Publication No. 2000-178699).

[0004] The silicon steel sheet has excellent low core loss characteristics, and the steel sheet becomes hardened to the extent that the Si content increases, and press formability sharply deteriorates. Since the steel sheet becomes hardened, a metallic mold such as a punch and a die used for press working is likely to wear or be damaged, and a frequency of maintenance of the metallic mold increases.

SUMMARY OF THE INVENTION

[0005] The present invention is made in light of the problems, and an object of the present invention is to provide a method of manufacturing a pressed part, which imparts excellent formability on a steel sheet, and a steel sheet for press working used in the manufacturing of the pressed part when the pressed part is manufactured with a silicon steel sheet.

[0006] An aspect of the present invention relates to a method of manufacturing a pressed part. The method of manufacturing a pressed part includes a process of pressing a to-be-pressed portion of a silicon steel sheet as a workpiece in which the to-be-pressed portion is softer than other portions.

[0007] According to the aspect, since the silicon steel sheet in which the to-be-pressed portion is softer than the other portions is pressed, the steel sheet is excellent in formability during the press working.

[0008] A method of manufacturing a pressed part according to another aspect of the present invention includes a process of pressing a low-silicon steel sheet which becomes a material of a high-silicon steel sheet; and a process of siliconizing the low-silicon steel sheet to obtain the high-silicon steel sheet.

[0009] According to the aspect, since the low-silicon steel sheet, which is softer and is better in formability than the high-silicon steel sheet, is pressed and then undergoes the siliconizing treatment, the steel sheet is excellent in formability during the press working.

[0010] Still another aspect of the present invention relates to a steel sheet for press working. In the steel sheet for press working, a to-be-pressed portion of a silicon steel sheet is softer than other portions thereof.

[0011] According to the aspect, since the to-be-pressed portion is softer than the other portions, the steel sheet is excellent in formability during the press working.

[0012] The method of manufacturing a pressed part according to the aspect of the present invention imparts excellent formability on the steel sheet during the press working.

[0013] The steel sheet for press working according to the aspect of the present invention is excellent in formability during the press working.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 

Fig. 1 is a plan view illustrating a high-silicon steel sheet used as a workpiece to obtain a pressed part according to a first embodiment.

Fig. 2 is a cross-sectional side view illustrating a state where a low-silicon steel sheet undergoes a siliconizing treatment as an intermediate process of the manufacturing method according to the first embodiment.

Fig. 3 is a cross-sectional side view illustrating a state where the high-silicon steel sheet undergoes press working as an intermediate process of the manufacturing method according to the first embodiment.

Fig. 4 is a cross-sectional side view illustrating a state where the high-silicon steel sheet undergoes etching as an intermediate process of a manufacturing method according to a second embodiment.

Fig. 5 is a cross-sectional side view illustrating a state where the high-silicon steel sheet undergoes press working as an intermediate process of the manufacturing method according to the second embodiment.

Fig. 6 is a cross-sectional side view illustrating a state where the high-silicon steel sheet undergoes a heat treatment using a de-siliconizing steel product as an intermediate process of a manufacturing method according to a third embodiment.

Fig. 7 is a view illustrating an intermediate process of a manufacturing method according to a fourth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(First Embodiment)

[0015] A pressed part which can be obtained by a manufacturing method according to a first embodiment is made of a high-silicon steel sheet. The high-silicon steel sheet contains Si of 4.0% by weight or greater. Si is an element which is effective for improving core loss characteristics, and when the Si content is equal to or greater than 4.0% by weight, excellent low core loss characteristics are obtained. In contrast, when the Si content is equal to or greater than 4.0% by weight, there is a problem in that the steel sheet becomes hardened to the extent that the Si content increases, and press formability deteriorates. The high-silicon steel sheet can be obtained by a siliconizing treatment or direct casting. An upper limit value of the Si content is not particularly limited. However, when the upper limit value exceeds 7.0% by weight, a saturation magnetic flux density remarkably decreases, and thus the upper limit value is preferably equal to or less than 7.0% by weight. When a lower limit value of the Si content is equal to or greater than 6.0% by weight, more excellent low core loss characteristics are obtained, and thus the lower limit value is preferably equal to or greater than 6.0% by weight.

[0016] In components of the high-silicon steel sheet, components other than Si and ranges of the other components' contents are not particularly limited. However, the high-silicon steel sheet may contain components and ranges of components' content which can be obtained in a widely known steel manufacturing process. The following is an example of the components other than Si and the ranges of the other components' content: the high-silicon steel sheet may contain the C content of 0.01% by weight or less, the Mn content of 0.5% by weight or less, the P content of 0.01% by weight or less, the S content of 0.01% by weight or less, and the remainder may be formed of Fe and unavoidable impurities. In addition, the high-silicon steel sheet may contain alloy elements such as Al, Cr, Mo, W, V, Ti and Sb, each of which is contained so as not to degrade the core loss characteristics and the formability.

[0017] Fig. 1 illustrates a high-silicon steel sheet 18 as a workpiece 10 used for obtaining a pressed part according to the first embodiment. It is possible to obtain the pressed part by forming the workpiece 10 into a predetermined shape by means of press working such as punching. Hereinafter, a case where a stator core of a motor is obtained as the pressed part will be described. Fig. 1 illustrates a portion 12 by a two-dot chain line, which becomes an exterior shape of the stator core seen from the top.

[0018] In the manufacturing method according to the first embodiment, first, the high-silicon steel sheet 18 is obtained by siliconizing a low-silicon steel sheet whichbecomes a material of the high-silicon steel sheet 18. The low-silicon steel sheet contains Si of less than 4.0% by weight. In components of the low-silicon steel sheet, components other than Si and ranges of the other components' contents are not particularly limited. However, the low-silicon steel sheet may contain components and ranges of components' content that can be obtained in a widely known steel manufacturing process. In the low-silicon steel sheet, when an upper limit value of the Si content is equal to or less than 3.5% by weight, formability becomes good, and thus the Si content is preferably equal to or less than 3.5% by weight.

[0019] The siliconizing treatment is performed using a chemical vapor deposition method (a CVD method). The siliconizing treatment is performed by disposing a steel sheet in a non-oxidizing atmosphere that contains source gas such as SiCl₄ or SiH₄ which is a source of Si, by heating the steel sheet to a predetermined temperature, and by retaining the steel sheet at the heated temperature. Accordingly, Si penetrates into a surface layer of the steel sheet, and Si in the surface layer of the steel sheet diffuses in a steel-sheet thickness direction. When SiCl₄ is used as a source of Si, the heated temperature of the steel sheet is, for example, 1023°C to 1230°C.

[0020] Fig. 2 illustrates a state where the low-silicon steel sheet 14 undergoes the siliconizing treatment. An example in Fig. 2 illustrates a state where the low-silicon steel sheet 14 is disposed on a stage 20 provided in a chamber, and the low-silicon steel sheet 14 undergoes the siliconizing treatment via a single surface in a steel-sheet thickness direction thereof.

[0021] A surface of a to-be-pressed portion 16 (hereinafter, referred to as a to-be-worked portion 16) of the low-silicon steel sheet 14 is coated with a mask 30, and the siliconizing treatment is performed on the low-silicon steel sheet 14. Herein, the to-be-worked portion 16 indicates a portion which undergoes a plastic deformation during press working. If the press working is punching, the to-be-worked portion 16 is a portion which is sheared by a cutting edge of a punch and a cutting edge of a die. In the example of Fig. 2, the to-be-worked portion 16 is illustratively surrounded by a two-dot chain line to simplify a description.

[0022] A mechanical mask such as a metallic foil formed in a predetermined pattern is used as the mask 30. The pattern is formed in such a manner that the surface of the to-be-worked portion 16 of the low-silicon steel sheet 14 is coated with the pattern, and that surfaces of other portions of the low-silicon steel sheet 14 are exposed. A metallic material such as pure iron or silicon steel, or a ceramic material such a glass is used as a material of the mechanical mask so as to resist heating during the siliconizing treatment.

[0023] In the siliconizing treatment using the mask 30, Si progressively penetrates into portions other than the to-be-worked portion 16, which are not coated with the mask 30, and Si is prevented frompenetrating into the to-be-workedportion 16 that is coated with the mask 30. That is, the to-be-worked portion 16 is not siliconized, and the portions other than the to-be-worked portion 16 are siliconized. Accordingly, it is possible to obtain the high-silicon steel sheet 18 in which the to-be-worked portion 16 has the Si content less than that of the other portions. The steel sheet becomes hardened to the extent that the Si content increases, and thus it is possible to obtain the high-silicon steel sheet 18 in which the to-be-worked portion 16 is softer than the other portions.

[0024] In the high-silicon steel sheet 18, siliconizing treatment conditions are adjusted in such a manner that the Si content of the to-be-worked portion 16 becomes less than 4.0% by weight and the Si contents of the other portions become equal to or greater than 4.0% by weight. More preferably, the siliconizing treatment conditions are adjusted in such a manner that the Si content of the to-be-worked portion 16 becomes equal to or less than 3.5% by weight and the Si contents of the other portions become equal to or greater than 6.0% by weight. The adjusted siliconizing treatment conditions are a concentration of the source gas in the non-oxidizing atmosphere in which the steel sheet is disposed, a heated temperature of the steel sheet, and a time period of retaining the heated steel sheet.

[0025] The to-be-worked portion 16 of the low-silicon steel sheet 14 is provided to extend along an in-plane direction of the low-silicon steel sheet 14. When a direction A is defined as a direction that is perpendicular to the direction in which the to-be-worked portion 16 extends, and is the in-plane direction of the low-silicon steel sheet 14, the low-silicon steel sheet 14 is preferably coated with the mask 30 in a range in the direction A greater than the to-be-worked portion 16. The coating range of the mask 30 indicates a range in the direction A, within which the to-be-worked portion 16 is interposed, and the to-be-worked portion 16 is disposed at a substantially center position in the direction A. Accordingly, when Si penetrates into the surface layer of the steel sheet to diffuse in the steel-sheet thickness direction, Si is prevented from diffusing to the to-be-worked portion 16, and thus it is possible to stablyperformpress working without requiring high accuracy of locating positions of the workpiece and the metallic mold during the press working. For example, when the coating range of the mask 30 is set to be equal to or greater than 3.0 mm, Si is reliably prevented from diffusing to the to-be-worked portion 16.

[0026] Subsequently, in the high-silicon steel sheet 18 which can be obtained as the workpiece 10 by the siliconizing treatment, the to-be-worked portion 16 is pressed so as to form the shape of the stator core. That is, the to-be-worked portion 16 is pressed so as to form the predetermined shape of the pressed part.

[0027] Fig. 3 illustrates a state where the to-be-worked portion 16 of the workpiece 10 is pressed. In an example illustrated in Fig. 3, the to-be-worked portion 16 of the workpiece 10 is disposed between a cutting edge 31a of a punch 31 and a cutting edge 33a of a die 33. When the punch 31 moves in a vertical direction, it is possible to obtain a press formed part with the shape of the stator core by shearing and punching the workpiece 10 along the to-be-worked portion 16 by the cutting edge 31a of the punch 31 and the cutting edge 33a of the die 33.

[0028] In the manufacturing method according to the first embodiment, since the high-silicon steel sheet 18 in which the to-be-pressed portion 16 is softer than the other portions is pressed, the steel sheet is excellent in formability during the press working. Since the to-be-pressed portion 16 is softer than the other portions, the metallic mold such as the punch and the die used for the press working is unlikely to wear or be damaged, and a frequency of maintenance of the metallic mold decreases.

(Second Embodiment)

[0029] In the following embodiment, the same symbols are assigned to the same elements as those described in the first embodiment, and duplicated descriptions thereof will be omitted.

[0030] In a manufacturing method according to a second embodiment, first, the high-silicon steel sheet 18 is obtained by siliconizing the low-silicon steel sheet 14 which is a material of the high-silicon steel sheet 18. The siliconizing treatment is performed in a state where the surface of the low-silicon steel sheet 14 is not coated with a mask, and descriptions on other points are the same as those in the first embodiment.

[0031] Subsequently, as illustrated in Fig. 4, the high-silicon steel sheet 18 which can obtained by the siliconizing treatment is coated with the mask 30 in such a manner that the surface of the to-be-worked portion 16 is exposed, and the high-silicon steel sheet 18 is etched. A mechanical mask formed in a predetermined pattern is used as the mask 30. The pattern is formed in such a manner that the surface of the to-be-worked portion 16 of the high-silicon steel sheet 18 is exposed, and that surfaces of other portions of the high-silicon steel sheet 18 are coated with the mask 30.

[0032] The etching is performed by painting or spraying an etching solution such as FeCl₃. In the etching as illustrated in Fig. 5, etching conditions are adjusted in such a manner that a concave portion 16a is formed in the to-be-worked portion 16 of the high-silicon steel sheet 18, and that the to-be-worked portion 16 is not penetrated. The adjusted etching conditions are a time period of exposure to the etching solution, the type of the etching solution or the like.

[0033] According to the etching using the mask 30, the etching makes progress in the to-be-worked portion 16 that is not coated with the mask 30. In contrast, the etching is prevented in the portions other than the to-be-worked portion 16, which is coated with the mask 30. Accordingly, it is possible to obtain the high-silicon steel sheet 18 in which the to-be-worked portion 16 has a thickness thinner than that of the other portions. Since a portion becomes softened to the extent that a thickness of the portion is thin, it is possible to obtain the high-silicon steel sheet 18 in which the to-be-worked portion 16 is softer than the other portions. That is, according to the etching using the mask 30, the to-be-worked portion 16 of the high-silicon steel sheet 18 becomes softened.

[0034] The range of the etching of the high-silicon steel sheet 18 is preferably in the direction A wider than the to-be-worked portion 16 of the high-silicon steel sheet 18. The etching range indicates a range in the direction A, within which the to-be-worked portion 16 is interposed, and the to-be-worked portion 16 is disposed at a substantially center position in the direction A. It is possible to stably perform press working without requiring high accuracy of locating positions of the workpiece and the metallic mold during the press working.

[0035] For example, when a thickness of the etched portion of the high-silicon steel sheet 18 is t x 1/4 or greater and t x 3/4 or less with respect to a thickness t of the other portions of the high-silicon steel sheet 18, it is possible to limit a time period of the etching and to obtain effects by which the to-be-worked portion 16 is sufficiently softened.

[0036] Subsequently, similarly to in the first embodiment, the to-be-worked portion 16 of the high-silicon steel sheet 18 as the workpiece 10 is pressed so as to form a shape of a pressed part.

[0037] Similarly to in the first embodiment, the manufacturing method according to the second embodiment imparts excellent in formability on the steel sheet during the press working, and a frequency of maintenance of the metallic mold decreases. Since the concave portion 16a is formed in the to-be-pressed portion 16 of the high-silicon steel sheet 18 by the etching, it is possible to easily recognize the position of the to-be-pressed portion 16 by visual observation, and it becomes an easy task to locate the positions of the workpiece and the metallic mold during the press working.

(Third Embodiment)

[0038] In a manufacturing method according to a third embodiment, first, the high-silicon steel sheet 18 is obtained by siliconizing the low-silicon steel sheet 14 which is a material of the high-silicon steel sheet 18. The siliconizing treatment is performed in a state where the surface of the low-silicon steel sheet 14 is not coated with the mask 30, and descriptions on other points are the same as those in the first embodiment.

[0039] Subsequently, as illustrated in Fig. 6, in the high-silicon steel sheet 18 that can be obtained by the siliconizing treatment, a steel product 40 for de-siliconizing is brought into contact with the surface of the to-be-worked portion 16, and a heat treatment is performed in such a manner that Si diffuses from the high-silicon steel sheet 18 to the steel product 40 for de-siliconizing.

[0040] The steel product 40 for de-siliconizing is a steel product that has the Si content less than that of the high-silicon steel sheet 18, and for example, is made of the low-silicon steel sheet 14 that contains the Si content of less than 4.0% by weight. The steel product 40 for de-siliconizing is formed to coat the surface of the to-be-worked portion 16 of the high-silicon steel sheet 18 with the steel product 40 for de-siliconizing. That is, the steel product 40 for de-siliconizing is formed to be shaped along the to-be-worked portion 16 of the high-silicon steel sheet 18.

[0041] The heat treatment is performed by disposing the steel product 40 for de-siliconizing and the high-silicon steel sheet 18 in a non-oxidizing atmosphere, by heating the steel product 40 for de-siliconizing and the high-silicon steel sheet 18 to a predetermined temperature, and by retaining the steel product 40 for de-siliconizing and the high-silicon steel sheet 18 which are heated at the temperature. The heated temperature is set to a temperature, for example, 1000°C to 1200°C, at which Si can diffuse from the high-silicon steel sheet 18 to the steel product 40 for de-siliconizing.

[0042] According to the heat treatment described above, it is possible to obtain the high-silicon steel sheet 18 in which the to-be-worked portion 16 in contact with the steel product 40 for de-siliconizing has the Si content less than those of the other portions. That is, according to the heat treatment using the steel product 40 for de-siliconizing, the to-be-worked portion 16 of the high-silicon steel sheet 18 becomes softened.

[0043] In the high-silicon steel sheet 18, heat treatment conditions or components and a size of the steel product 40 for de-siliconizing are adjusted in such a manner that the Si content of the to-be-worked portion 16 becomes less than 4.0% by weight and the Si contents of the other portions become equal to or greater than 4 . 0% by weight . More preferably, the heat treatment conditions and the like are adjusted in such a manner that the Si content of the to-be-worked portion 16 becomes equal to or less than 3.5% by weight and the Si contents of the other portions become equal to or greater than 6.0% by weight. The adjusted heat treatment conditions are a heated temperature of the steel sheet, and a time period of retaining the heated steel sheet. The adjusted components of the steel product 40 for de-siliconizing are the Si content of the steel product 40 for de-siliconizing and the like, and Si is likely to diffuse from the high-silicon steel sheet 18 to the steel product 40 for de-siliconizing to the extent that the Si content is small. The adjusted sizes of the steel product 40 for de-siliconizing are a thickness of the steel product 40 for de-siliconizing and the like relative to the thickness of the high-silicon steel sheet 18. The Si content, which can diffuse from the high-silicon steel sheet 18 to the steel product 40 for de-siliconizing, increases, and Si is likely to diffuse to the extent that the thickness of the steel product 40 for de-siliconizing is great.

[0044] Subsequently, similarly to in the first embodiment, the to-be-worked portion 16 of the high-silicon steel sheet 18 as the workpiece 10 is pressed so as to form a shape of a pressed part.

[0045] Similarly to in the first embodiment, the manufacturing method according to the third embodiment imparts excellent formability on the steel sheet during the press working, and a frequency of maintenance of the metallic mold decreases.

(Fourth Embodiment)

[0046] In a manufacturing method according to a fourth embodiment, first, as illustrated in Fig. 7, the low-silicon steel sheet 14, which is a material of the high-silicon steel sheet 18, is pressed as the workpiece 10 into a predetermined shape of a pressed part 19.

[0047] Subsequently, the high-silicon steel sheet 18 is obtained by siliconizing the low-silicon steel sheet 14 which is formed in the shape of the pressed part as a material. The siliconizing treatment is performed in a state where the surface of the low-silicon steel sheet 14 is not coated with a mask. In other points, the siliconizing treatment is the same as that described in the first embodiment.

[0048] In the manufacturing method according to the fourth embodiment, the low-silicon steel sheet 14, which is softer and is better in formability than the high-silicon steel sheet 18, is pressed as the workpiece 10 and then undergoes the siliconizing treatment, and thus the steel sheet is excellent in formability during the press working. Since the low-silicon steel sheet 14 softer than the high-silicon steel sheet 18 is pressed, the metallic mold such the punch and the die used for the press working is unlikely to wear and be damaged, and a frequency of maintenance of the metallic mold decreases.

[0049] As such, the present invention is described based on the embodiments, but the embodiments are intended only to illustrate a principle and applications of the present invention. Various modifications or changes of the disposition can be made to the embodiments insofar as the modifications or the changes do not depart from the scope of the present invention which is specified in the claims.

[0050] In each embodiment described above, the stator core of the motor is exemplified as the pressed part manufactured by the manufacturing method according to the present invention. However, the present invention is not limited to the embodiment, and the pressed part may be a core or other part of electrical equipment such as a generator or a transformer.

[0051] In each embodiment described above, the siliconizing treatment method using the CVD method is described, but the siliconizing treatment is not limited to the CVD method. For example, as disclosed in Publication No. WO2004/044251, the siliconizing treatment using another method may be performed by painting a coating composite which contains Si as a main component on the low-silicon steel sheet, and by annealing the low-silicon steel sheet in a non-oxidizing atmosphere.

[0052] In each of the embodiments described above, the punching is exemplified as the press working, but the press working may be bending, drawing or the like in addition to the punching.

[0053] In the first and the second embodiments described above, the mechanical mask is exemplified as the mask 30. However, a part of the surface of the steel sheet can be preferably coated with the mask 30, and for example, the mask 30 may be photoresist or the like. When the photoresist is used as the mask 30, the steel sheet is coated with the photoresist, the pattern of which is formed by a photolithography method.

[0054] In the second embodiment described above, the siliconizing treatment is performed in a state where the surface of the low-silicon steel sheet 14 is not coated with the mask 30. However, as in the first embodiment, the surface of the low-silicon steel sheet 14 is coated with the mask 30, the siliconizing treatment is performed, and then the etching may be performed. In this case, it is possible to obtain the high-silicon steel sheet 18 in which the to-be-worked portion 16 has the Si content less than that of the other portions, and the thickness thinner than that of the other portions.

[0055] In the second embodiment described above, the siliconizing treatment is performed, and then the etching is performed. However, the siliconizing treatment may be performed while the etching is being performed. That is, if the steel sheet used as the workpiece 10 for press working is coated with the mask 30 in such a manner that the surface of the to-be-worked portion 16 is exposed, and the etching process is performed, the siliconizing treatment may be performed either before or after the etching process.

[0056] In the second and the third embodiments described above, the method of siliconizing the low-silicon steel sheet 14 is exemplified as the method of obtaining the high-silicon steel sheet 18. However, the method of obtaining the high-silicon steel sheet 18 is not limited to the siliconizing treatment, and widely known methods may be used. For example, there is direct casting in which the high-silicon steel sheet is obtained by cooling molten steel which contains the same components as those of the high-silicon steel sheet 18, and by forming the molten sheet into a sheet shape by a plurality of rolls or the like.

[0057] In the first embodiment described above, the to-be-worked portion 16 is not siliconized by using the mask 30 and the other portions are siliconized. However, means for preventing the to-be-worked portion 16 from being siliconized is not limited to the mask 30. In the second and the third embodiments described above, the to-be-worked portion 16 is softened by using the etching or the steel product 40 for de-siliconizing, but means for softening the to-be-worked portion 16 is not limited to the etching or the steel product 40 for de-siliconizing.

[0058] The manufacturing method according to the present invention may be realized by a batch process in which each process is sequentially performed on a steel sheet with predetermined unit dimensions, or may be realized by a continuous process in which each process is performed on a steel strip that is continuously transported.

Claims

1. A method of manufacturing a pressed part, the method comprising:

a process of pressing a to-be-pressed portion of a silicon steel sheet as a workpiece in which the to-be-pressed portion is softer than other portions.

2. The method of manufacturing a pressed part according to claim 1, further comprising:

a process of siliconizing a low-silicon steel sheet which becomes a material of a high-silicon steel sheet used as the workpiece,

wherein in the siliconizing process, the to-be-pressed portion is not siliconized, and the other portions are siliconized.

3. The method of manufacturing a pressed part according to claim 2,
wherein in the siliconizing process, a surface of the to-be-pressed portion of the low-silicon steel sheet is coated with a mask, and the low-silicon steel sheet undergoes the siliconizing treatment.

4. The method of manufacturing a pressed part according to any one of claims 1 to 3, further comprising:

a process of softening the to-be-pressed portion of the steel sheet used as the workpiece.

5. The method of manufacturing a pressed part according to claim 4,
wherein in the softening process, the steel sheet used as the workpiece is coated with a mask in such a manner that a surface of the to-be-pressedportion is exposed, and etching is performed.

6. The method of manufacturing a pressed part according to claim 4,
wherein in the softening process, a steel product for de-siliconizing is brought into contact with a surface of the to-be-pressed portion, and a heat treatment is performed on the steel sheet used as the workpiece in such a manner that Si diffuses from the steel sheet to the steel product for de-siliconizing.

7. The method of manufacturing a pressed part according to any one of claims 1 to 6,
wherein the to-be-pressedportion of the silicon steel sheet has a Si content less than that of the other portions thereof.

8. The method of manufacturing a pressed part according to any one of claims 1 to 7,
wherein the to-be-pressedportion of the silicon steel sheet has a sheet thickness thinner than that of the other portions thereof.

9. A method of manufacturing a pressed part, comprising:

a process of pressing a low-silicon steel sheet which becomes a material of a high-silicon steel sheet; and

a process of siliconizing the low-silicon steel sheet to obtain the high-silicon steel sheet.

10. A steel sheet for press working,
wherein a to-be-pressed portion of a silicon steel sheet is softer than other portions thereof.

11. The steel sheet for press working according to claim 10,
wherein the to-be-pressed portion of the silicon steel sheet has a Si content less than that of the other portions thereof.

12. The steel sheet for press working according to claim 10 or 11,
wherein the to-be-pressed portion of the silicon steel sheet has a thickness thinner than that of the other portions thereof.

Drawing