JP2005220373A - LAYER-HAVING Fe BASED ALLOY, AND ITS PRODUCTION METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a layer-having Fe based alloy in which the toughness of the surface layer part is improved and the concentration of stress is less liable to occur, thus brittle fracture is less liable to be generated, and to provide its production method. <P>SOLUTION: The surface of the small-sized part 16 of a preform 32 composed of SKH51 (Fe based alloy) is coated with the powder of a substance comprising an element(s) which is included in SKH51 and does not contribute to the increase in the hardness of SKH51. The coating is performed by applying a coating agent prepared in such a manner that powder is dispersed into an organic solvent. The coating agent may be mixed with a reducing agent. At the time when the preform 32 is heat-treated after the coating, W or the like included in SKH51 diffuse over the surface side. As a result, a diffused layer and a concentration-changed part 20 are formed on the surface of the small-sized part 16. In the concentration-changed part 20, the content of W or the like is lowest at the uppermost part side close to the diffused layer, thus the toughness in the uppermost part is made higher than that at the inside. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a layered Fe-based alloy whose toughness is improved from the inside to the surface layer portion and a method for producing the same.

  For the purpose of improving various properties such as wear resistance, corrosion resistance, and strength of steel materials that are Fe-based alloys, physical vapor deposition (PVD) method, chemical vapor deposition (CVD) method, plating, anodic oxidation, etc. A film may be provided on the surface of the steel material. However, in this case, there is a problem that it takes a long time to form a film and the film formation cost is high.

Therefore, various surface treatments such as carburizing, sulfiding, nitriding, carbonitriding, etc. are widely performed to improve various characteristics of the surface of the steel material without providing a coating (for example, Patent Document 1). 2). Further, in Patent Document 3, by applying a mechanical treatment such as shot peening or shot blasting and applying a compressive stress of 10 kgf / cm ² (approximately 0.1 MPa) to the surface, the wear resistance of the cutting tool and It has been proposed to improve fracture resistance.

JP 2003-129216 A JP 2003-239039 A JP-A-5-171442

  However, it is limited to the surface of a metal material that various characteristics improve by the conventional techniques as described in Patent Documents 1 to 3. For example, in nitriding or carburizing, the element diffuses from the surface of the metal material only a few μm and at most about 200 μm, and it is difficult to improve various internal characteristics. For this reason, it is difficult to say that the wear resistance and fracture resistance are remarkably improved.

  In addition, in the processing method according to the prior art, an interface exists between the formed nitride layer or the like and the metal material as the base material. For this reason, there is a concern that brittle fracture occurs from the interface under conditions where stress concentration occurs at the interface.

  Moreover, although the above-mentioned prior art is a processing method that mainly improves the hardness, in some cases, it is desired to improve the toughness. However, a simple treatment method for improving toughness is not known.

  The present invention has been made to solve the above-described problems, and provides a layered Fe-based alloy in which the toughness of the surface layer portion is improved and stress concentration is unlikely to occur, and brittle fracture is unlikely to occur, and a method for producing the same. Objective.

In order to achieve the above object, the present invention is a layered Fe-based alloy in which hardness is improved from the surface layer portion to the inside and a diffusion layer is present on the outer surface of the surface layer portion,
The diffusion layer includes a carbide obtained by carbideizing a first element having a property of increasing the hardness of the Fe-based alloy,
In the surface layer part, the amount of the second element other than the first element contained in the Fe-based alloy is larger than that in the interior,
The amount of the first element increases from the surface layer portion toward the inside.

  In the present invention, the amount of the first element that contributes to the increase in hardness of the Fe-based alloy is small on the surface layer side, and gradually increases toward the inside. A portion having a small amount of element contributing to an increase in hardness generally has high toughness. For this reason, a layered Fe-based alloy having a large toughness in the surface layer portion and a large internal hardness is formed.

  Moreover, this layered Fe-based alloy has no interface between the surface layer portion and the inside. For this reason, stress concentration is unlikely to occur, so that brittle fracture is less likely to occur.

  The carbide of the metal contained in the diffusion layer is not particularly limited as long as it is a carbide of the first element that improves the hardness of the Fe-based alloy, but carbide of Cr, W, Mo, V, Ni, Mn Can be cited as a suitable example.

  The carbide may be a carbide of a solid solution of at least one of Cr, W, Mo, V, Ni, and Mn and Fe. In this case, since the relative amount of the metal carbide as described above is reduced, it is possible to prevent the metal carbide from being excessively generated and the brittleness from being increased.

  On the other hand, preferable examples of the second element include C, Si, Cu, Ti, Al, and Mg.

In the present invention, the first element having the property that the hardness is improved from the surface layer portion to the inside, the diffusion layer is present on the outer surface of the surface layer portion, and the diffusion layer increases the hardness of the Fe-based alloy. In the surface layer portion, the amount of the second element other than the first element is larger than that in the inside, and the amount of the first element is from the surface layer portion to the inside. A method for producing a layered Fe-based alloy that increases as
Applying a powder of the substance containing the second element to the surface of the Fe-based alloy;
The Fe-based alloy coated with the powder is heat-treated to diffuse the first element into the surface layer portion, and the first element is present in the surface layer portion and reacts with carbon constituting the Fe-based alloy. And making it into carbide,
It is characterized by having.

  When the heat treatment is performed on the Fe-based alloy having the second element applied on the surface, the first element starts to diffuse toward the second element. That is, the first element that increases the hardness of the Fe-based alloy starts to diffuse to the surface side. This is presumably because the second element has an action of capturing the first element.

  Therefore, the first element can be diffused and unevenly distributed in the uppermost portion of the surface layer portion through the above-described steps. Thereby, the diffusion layer with the largest amount of the first element is provided on the outer surface of the surface layer portion.

  As a result of the uneven distribution of the first element on the outer surface of the surface layer portion in this way, the amount of the first element is the smallest immediately below the diffusion layer in the surface layer portion, and gradually increases toward the inside. That is, the hardness of the obtained layered Fe-based alloy is lowest immediately below the diffusion layer. As described above, since the portion having low hardness generally has high toughness, the toughness of the layered Fe-based alloy is larger on the surface layer side than on the inner side. In other words, it is possible to obtain a layered Fe-based alloy having high toughness on the surface layer side and high hardness on the inner side.

  That is, according to the present invention, a layered Fe-based alloy in which the toughness of the surface layer portion is improved can be easily obtained by performing a simple operation of performing a heat treatment after applying the powder.

  In addition, the powder of the substance containing a 1st element may be mix | blended with the powder. In this case, the blending ratio of the powder of the substance containing the first element and the powder of the substance containing the second element may be appropriately set according to the type of the Fe-based alloy and the heat treatment conditions.

  The powder is not particularly limited as long as it is a substance containing an element that is contained in the Fe-based alloy and does not contribute to the increase in hardness of the Fe-based alloy, but C, Si, Cu, Ti, Al, and Mg are preferable. In particular, C and Si are excellent in the effect of diffusing the first element, while Cu, Ti, Al, and Mg are excellent in the effect of blocking oxygen.

  Further, the diffusion layer may be removed, for example, as a machining allowance. In this case, the high hardness portion decreases and the high toughness portion remains, so that a layered Fe-based alloy that can be easily bent can be obtained.

  Further, the heat treatment may be performed in a nitrogen atmosphere to nitride the carbide to form a carbonitride. In this case, the hardness of the surface layer portion of the layered Fe-based alloy can be reduced and the toughness can be improved.

  According to the present invention, since the element that increases the hardness of the Fe-based alloy gradually decreases toward the surface layer portion, a layered Fe-based alloy having a large toughness on the surface layer side can be formed. In addition, since no interface exists between the surface layer portion and the inside, it is possible to avoid the occurrence of brittle fracture. That is, the effect that a layered Fe-based alloy excellent in various properties can be constituted is achieved.

  Hereinafter, preferred embodiments of a layered Fe-based alloy and a manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

  A schematic overall perspective view of a forging punch provided from a layered Fe-based alloy according to the present embodiment is shown in FIG. This forging punch 10 is manufactured using SKH51 as a raw material (base material), and has a large diameter portion 12, a reduced diameter portion 14 connected to the large diameter portion 12 and reduced in a taper shape, It has a small-diameter portion 16 and a curved projecting portion 18 that is formed to protrude from one end portion of the small-diameter portion 16 and is curved. Of these, the curved protrusion 18 and the tip of the small-diameter portion 16 press the work housed in a die cavity (not shown) to form the work into a predetermined shape. That is, the distal end portion of the small-diameter portion 16 and the curved protruding portion 18 are work pressing portions.

  Here, the cross section of the trunk | drum of the small diameter part 16 extended from a workpiece | work press site | part is expanded and shown in FIG. As can be seen from FIG. 2, a concentration changing portion 20 in which the concentration of the metal element in the base material SKH 51 changes exists in the surface layer portion of the workpiece pressing portion.

  The metal element whose concentration changes in the concentration changing portion 20 is a constituent element of SKH51 and contributes to the increase in hardness of SKH51, specifically, Cr, W, Mo, V, Ni, Mn, and the like. .

The metal elements as described above are usually present in the form of an alloy or carbide. The carbide may have a compositional formula represented by M ₆ C such as Cr ₆ C, W ₆ C, Mo ₆ C, or the like, or may be represented by M ₂₃ C _{6. If 6} C or M ₂₃ C ₆ is excessively present, the forging punch 10 becomes brittle. In order to avoid this, as a solid solution carbide of Fe and M, that is, a carbide represented by (Fe, M) ₆ C, (Fe, M) ₂₃ C _6, etc., the relative of M ₆ C and M ₂₃ C ₆ It is preferred to reduce the amount.

  The concentration of the metal element gradually increases from the top of the concentration changing portion 20 toward the inside. That is, the concentration of the metal element is the lowest at the top of the concentration changing portion 20, and therefore the hardness of the concentration changing portion 20 is the lowest at the top and increases toward the inside.

  As described above, the surface layer portion of the small diameter portion 16 is formed with the concentration changing portion 20 that gradually increases as the element that increases the hardness of the SKH 51 moves toward the inner side. As will be described later, the concentration changing portion 20 is provided by diffusing and discharging elements contained in the SKH 51 from the inside to the surface layer portion. At this time, the diffusion layer generated in the surface layer portion is removed by machining.

  Generally, hardness and toughness are in a trade-off relationship, and as hardness decreases, toughness improves. As described above, in the uppermost portion of the concentration changing portion 20, the amount of elements contributing to the increase in hardness is small, and therefore the toughness is increased on the outer surface of the small diameter portion 16 as compared with the inner side. That is, the surface layer portion of the small diameter portion 16 exhibits high toughness as compared with the SKH 51 in which the concentration changing portion 20 is not formed. For this reason, since the small diameter portion 16 itself also has improved toughness and is less likely to cause brittle fracture, cracks and the like are less likely to occur in the body portion of the small diameter portion 16 than in the work pressing portion where the concentration changing portion 20 does not exist. .

  In addition, the concentration of the above-described metal element, in other words, the alloy or carbide, is the lowest on the surface of the small-diameter portion 16 and gradually increases toward the inside. For this reason, there is no clear interface between the concentration changing portion 20 and the base material. Therefore, since it is possible to avoid stress concentration, it is possible to avoid an increase in brittleness due to the provision of the concentration changing portion 20. In FIG. 2, for the sake of clarity that the concentration changing portion 20 exists, a boundary line is provided between the concentration changing portion 20 and the base material for the sake of convenience.

  In the concentration changing portion 20, elements that are included in SKH51 and do not contribute to the hardness increase of SKH51, specifically, C, Si, Cu, Ti, Al, Mg, etc., exist in the form of an alloy or carbide, for example. . As will be described later, when such an element is present on the surface side during heat treatment, metal elements such as Cr, W, Mo, V, Ni, and Mn diffuse toward the outer surface side of the small diameter portion 16.

  The forging punch 10 configured as described above is used, for example, when a warm forging process is performed on a workpiece. In this case, the workpiece pressing portion of the forging punch 10 moves the workpiece. Press. Accordingly, a load is also applied to the body portion of the small diameter portion 16.

  As described above, the trunk portion has high toughness because the toughness of the surface layer portion is high. For this reason, even if this trunk part repeats a forge process, it is hard to produce a crack. That is, the lifetime of the forging punch 10 can be extended by providing the concentration changing portion 20 by diffusing and discharging elements contributing to the increase in hardness of the SKH 51 to the surface layer portion.

  This forging punch 10 can be manufactured as follows.

  First, as shown in FIG. 3B, the cylindrical workpiece W made of SKH 51 shown in FIG. 3A is cut by a cutting tool 30 to correspond to the shape of the forging punch 10. The preform 32 is shaped.

  Next, as shown in FIG. 3C, the surface of the preform 32 is an element contained in the SKH 51 and does not increase the hardness of the SKH 51, that is, Cr, W, Mo. The powder of the substance containing elements other than V, Ni, Mn, etc. is applied to the surface of the workpiece pressing part. Preferable examples of such powder include C, Si, Cu, Ti, Al, and Mg.

  Application of the powder as described above is performed by applying a coating agent 34 prepared by dispersing the powder in a solvent. As the solvent, it is preferable to select an organic solvent that easily evaporates, such as acetone or alcohol. And powder, such as C and Si, is disperse | distributed to this solvent.

  Here, an oxide film is usually formed on the surface of the SKH 51 that is the preformed body 32. In order to diffuse C, Si, and the like in this state, a great amount of heat energy must be supplied so that C and Si can pass through the oxide film. In order to avoid this, it is preferable to mix the coating agent 34 with a reducing agent capable of reducing the oxide film.

  Specifically, a substance that acts as a reducing agent on the oxide film and does not react with SKH51 is dispersed or dissolved in a solvent. Preferable examples of the reducing agent include nitrocellulose, polyvinyl, acrylic, melamine, and styrene resins, but are not particularly limited thereto. Note that the concentration of the reducing agent may be about 5%.

  The coating agent 34 in which the above substances are dissolved or dispersed is applied to the surface of the body portion of the small diameter portion 16 by a brush coating method using a brush 36 as shown in FIG. Of course, you may make it employ | adopt well-known coating techniques other than the brush coating method.

  Next, heat treatment is performed on the preform 32 in which the coating agent 34 is applied to the surface of the workpiece pressing portion. This heat treatment can be performed by applying a burner flame 38 from one end surface side of the preform 32 as shown in FIG. Of course, heat treatment may be performed in an inert atmosphere in a heat treatment furnace.

  In this temperature rising process, the reducing agent begins to decompose at about 250 ° C., and carbon and hydrogen are generated. The oxide film of the preform 32 is reduced and disappears under the action of carbon and hydrogen. For this reason, since it is not necessary for C, Si, etc. to pass through an oxide film, the time required for diffusion can be shortened and thermal energy can be reduced.

When the temperature is further increased, W, Cr, and the like, which are constituent elements of SKH51, react with C generated by the decomposition of the reducing agent and free C contained in SKH51, and as a result, W ₆ C and Cr ₆ C, W ₂₃ C ₆ , Cr ₂₃ C _{6 and the} like are generated. When Fe is mixed in the coating powder, (Fe, W) ₆ C, (Fe, Cr) ₆ C, (Fe, W) ₂₃ C ₆ , (Fe, Cr) ₂₃ which are solid solution carbides with Fe. C ₆ etc. are further generated. Here, the diffusion rate of Fe is higher than that of C, Si, Cu, Ti, Al, and Mg. Therefore, the concentration of Fe contained in the coating agent 34 is increased on the inner side of the concentration changing portion 20.

The generated carbides such as W ₆ C, Cr ₆ C, (Fe, W) ₆ C, and (Fe, Cr) ₆ C are immediately decomposed and returned to Fe, W, and Cr. Among these, W and Cr diffuse and move to the surface side. This reason is presumed to be because C, Si, etc. existing on the surface side have an action of capturing W, Cr, etc. In addition, when Cu, Ti, Al, and Mg are contained in the coating agent, these also serve to block oxygen. For this reason, it is possible to avoid the oxidation of SKH51.

In the above diffusion process, W and Cr are combined with C and Fe which are constituent elements of SKH51 existing on the surface side of the preform 32, and C which is present in a free state on the surface side, so that W ₆ C, Cr ₆ C, (Fe, W) ₆ C, (Fe, Cr) ₆ C, and the like are generated. These W ₆ C, Cr ₆ C, (Fe, W) ₆ C, and (Fe, Cr) ₆ C are also immediately decomposed and returned to W and Cr, and then C present on the one surface side of the preform 32. , Fe, and C present in a free state on the surface side to generate W ₆ C, Cr ₆ C, (Fe, W) ₆ C, (Fe, Cr) ₆ C, and the like again. Thus, by repeating decomposition | disassembly and a production | generation of a carbide | carbonized_material, this carbide | carbonized_material is diffused to the outer surface of the preforming body 32, As a result, the diffusion layer which consists of a carbide | carbonized_material is formed in this outer surface. This carbide is chemically stable. Therefore, the preform 32 is a layered Fe-based alloy having a diffusion layer on the outer surface of the surface layer portion. The thickness of the diffusion layer is about 0.5 mm.

Thus, W or Cr existing on the surface layer side diffuses as W ₆ C, Cr ₆ C, (Fe, W) ₆ C, (Fe, Cr) ₆ C, or the like on the outer surface of the preform 32. Is done. As a result, the concentration of W, Cr, etc. is lowest at the surface layer portion immediately below the diffusion layer and gradually increases as it goes to the inner side. That is, the density changing portion 20 is formed (see FIG. 2). Since the concentrations of W, Cr, etc. gradually increase, as described above, there is no clear interface between the terminal portion of the concentration changing portion 20 and the base material. Therefore, it is possible to avoid the occurrence of brittle fracture due to the provision of the concentration changing portion 20.

  On the other hand, C, Si, Cu, Ti, Al, Mg, etc. contained in the coating agent diffuse into the concentration changing portion 20 and remain in the concentration changing portion 20 as an alloy or carbide. Since these elements do not contribute to the increase in the hardness of SKH51, the hardness of the concentration changing portion 20 does not increase due to the diffusion of the elements.

  Finally, as shown in FIG. 3 (e), the preforming body 32 is finished with a cutting tool 30 to obtain a forging punch 10. In the small diameter portion 16, the diffusion layer is cut off at this time. As described above, since the thickness of the diffusion layer is about 0.5 mm, cutting and removal are relatively easy.

  As a result of the removal of the diffusion layer, the density changing portion 20 is exposed. As described above, the uppermost portion in the concentration changing portion 20 has the highest toughness, and therefore, the small diameter portion 16 has the largest toughness on the surface thereof.

  The forging punch 10 thus obtained was cut along the longitudinal direction, and the C-scale Rockwell hardness (HRC) measured from the surface side toward the inside in the cut surface of the body portion of the small diameter portion 16. ) Is shown in FIG. From FIG. 4, it is clear that in this case, the HRC increases from the surface to the inside to a depth of about 4 mm, in other words, the toughness in the surface layer portion is larger than the inside.

  The heat treatment may be performed in a nitrogen atmosphere in a heat treatment furnace. In this case, carbides such as W and Cr remaining in the concentration changing portion 20 are nitrided to become carbonitrides. This type of metal carbonitride particles has a rounded end. Since the brittle fracture is less likely to occur between particles having such a shape, the toughness of the concentration changing portion 20 is increased. That is, it is possible to obtain a layered Fe-based alloy with further improved toughness.

  In the same manner as described above, for example, Mo can be removed from molybdenum steel.

  In the above-described embodiment, the forging punch 10 has been described as an example of an Fe-based alloy. However, the present invention is not particularly limited to this, and other members may be used. Absent.

  In this embodiment, the diffusion layer is removed by cutting, but it may be used without removing the diffusion layer.

  Furthermore, the coating powder may contain a powder of a substance containing an element having a property of increasing the hardness of the Fe-based alloy. In this case, the blending ratio of the powder and C, Si, Cu, Ti, Al, and Mg may be set as appropriate according to the type of Fe-based alloy and heat treatment conditions.

  Using DH31, which is a steel for hot molds, a cylindrical body having a bottom diameter of 80 mm and a height of 80 mm was produced.

  On the other hand, a powder of a substance belonging to Group III-VIII of the periodic table (particle size 10-70 μm) is added to an acetone solution of 10% epoxy resin at a ratio shown in FIG. B was prepared. Here, the coating agent A mainly contains substances that improve the hardness of various steel materials including DH31, and the coating agent B mainly contains substances that are contained in various steel materials and do not contribute to an increase in hardness. include.

  Then, each of coating agent A and B was apply | coated to the different site | part in the surface of the same cylindrical body. In addition, application | coating was performed by brush coating and the thickness of the coating agents A and B was 1 mm.

  Each of the coating agents A and B was naturally dried and then quenched by holding at 1000 to 1180 ° C. for 2 hours, and then tempered by holding at 500 to 600 ° C. for 2 hours. .

  Next, the cylindrical body was cut in the height direction, and the HRC was measured every 0.5 mm along the height direction from the center of the bottom surface for each portion where the coating agent A or the coating agent B was applied. In addition, in the site | part which apply | coated the coating agent B, it measured, after removing all the diffusion layers by cutting.

  FIG. 6 shows the relationship between the distance from the surface and HRC at each site. The HRC of untreated DH31 is approximately 52 to 54, whereas the hardness increases when the coating agent A is applied, whereas the hardness decreases when the coating agent B is applied. It is clear that From the latter, it is understood that the toughness can be improved by applying the coating agent B.

  Further, from this, even when heat treatment is performed on the same member, by changing the type of the coating agent, it is possible to individually produce a portion with improved hardness and a portion with improved toughness. I understand.

It is a general | schematic whole perspective view of the punch for forging which is a layered Fe base alloy. FIG. 2 is an enlarged longitudinal sectional view of a main part of the forging punch in FIG. 1. FIG. 2 is a flow explanatory diagram illustrating a manufacturing process of the forging punch in FIG. 1. It is a graph which shows HRC measured toward the inside from the surface of the cut surface of the obtained forging punch. It is a chart which shows the composition and ratio of a coating agent. It is a graph which shows the relationship from the distance from the surface, and HRC in the test piece made from DH31.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Punch for forging process 12 ... Large diameter part 14 ... Reduced diameter part 16 ... Small diameter part 18 ... Curve protrusion 20 ... Concentration change part 30 ... Bit 32 ... Preliminary molded body 34 ... Coating agent 36 ... Brush

Claims (7)

A layered Fe-based alloy in which the hardness is improved from the surface layer part to the inside, and a diffusion layer is present on the outer surface of the surface layer part,
The diffusion layer includes a carbide obtained by carbideizing a first element having a property of increasing the hardness of the Fe-based alloy,
In the surface layer part, the amount of the second element other than the first element contained in the Fe-based alloy is larger than that in the interior,
A layered Fe-based alloy, wherein the amount of the first element increases from the surface layer portion toward the inside.   2. The layered Fe-based alloy according to claim 1, wherein the carbide is a carbide of Cr, W, Mo, V, Ni, Mn.   The layered Fe-based alloy according to claim 1 or 2, wherein the carbide is a carbide of a solid solution of at least one of Cr, W, Mo, V, Ni, and Mn and Fe. A featured layered Fe-based alloy.   The layered Fe-based alloy according to any one of claims 1 to 3, wherein the second element is C, Si, Cu, Ti, Al, or Mg. Hardness is improved from the surface layer part to the inside, a diffusion layer is present on the outer surface of the surface layer part, and the diffusion layer includes a carbide obtained by carbideizing the first element having a property of increasing the hardness of the Fe-based alloy, In the surface layer portion, the amount of the second element other than the first element contained in the Fe-based alloy is larger than that in the inside, and the amount of the first element increases as it goes from the surface layer portion to the inside. A method for producing a layered Fe-based alloy comprising:
Applying a powder of the substance containing the second element to the surface of the Fe-based alloy;
The Fe-based alloy coated with the powder is heat-treated to diffuse the first element into the surface layer portion, and the first element is present in the surface layer portion and reacts with carbon constituting the Fe-based alloy. And making it into carbide,
A method for producing a layered Fe-based alloy, comprising:   6. The method for producing a layered Fe-based alloy according to claim 5, wherein C, Si, Cu, Ti, Al, or Mg is used as the powder. 7. The method for producing a layered Fe-based alloy according to claim 5, further comprising a step of removing a part of the diffusion layer.

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