JP4427345B2 - Layered Fe-based alloy and method for producing the same - Google Patents

Description

  The present invention relates to a layered Fe-based alloy in which carbide is diffused on a surface of a base material made of an Fe-based alloy and a diffusion layer having a hardness higher than that of the base material is provided, and a method for manufacturing 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.

  The present invention has been made to solve the above-described problems, and has an object to provide a layered Fe-based alloy that has improved hardness and strength and is less likely to cause brittle fracture because stress concentration hardly occurs and a method for manufacturing the same. And

In order to achieve the above object, the present invention comprises a base material composed of an Fe-based alloy, and a diffusion layer formed by diffusing carbide in the base material and having a higher hardness than the base material. Have
Der thickness 0.5mm or more of the organic layer Fe group the diffusion layer was measured surface as the base point of the alloy is,
And said carbide is characterized der Rukoto those formed by diffusion inside the preform together with the metal to be coated on the surface of the base material to increase the hardness of the Fe-based alloy is carbonized.

  In the layered Fe-based alloy according to the present invention, the carbide diffuses deep inside the Fe-based alloy which is the base material, and therefore shows excellent hardness and strength up to the inside. Moreover, this layered Fe-based alloy has no interface between the diffused carbide and the base material. For this reason, stress concentration is unlikely to occur, so that brittle fracture is less likely to occur.

  The metal carbide is not particularly limited as long as it is a substance that improves the hardness of the Fe-based alloy, but preferred examples include carbides of Cr, W, Mo, V, Ni, and Mn.

In this case, when the metal element is represented by M, the composition formula of the carbide is preferably M ₆ C or M ₂₃ C ₆ . This is because the carbide whose composition formula is expressed in this way is particularly excellent in the effect of improving the hardness of the Fe-based alloy.

  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.

A preferred solid solution carbide is one in which the composition formula is represented by (Fe, M) ₆ C or (Fe, M) ₂₃ C ₆ when the metal element is represented by M.

The present invention also includes a base material made of an Fe-based alloy, and a diffusion layer formed by diffusing carbide in the base material and having a hardness higher than that of the base material. A method for producing a layered Fe-based alloy in which the thickness of the diffusion layer measured from the surface of the base alloy is 0.5 mm or more,
Applying a metal powder for increasing the hardness to the surface of the Fe-based alloy;
Heat-treating the Fe-based alloy coated with metal powder to react at least carbon constituting the Fe-based alloy with the metal to form a carbide, and to diffuse the carbide into the Fe-based alloy When,
It is characterized by having.

  Through such a process, a thick diffusion layer can be formed, and a layered Fe-based alloy in which no interface exists between the diffusion layer and the base material can be produced. The obtained layered Fe-based alloy has excellent hardness and strength due to the presence of the diffusion layer.

  As the metal, it is preferable to use Cr, W, Mo, V, Ni, or Mn because the hardness of the Fe-based alloy can be improved.

  Further, the heat treatment may be performed in a nitrogen atmosphere to nitride the carbide to form a carbonitride. Even in this case, the hardness of the Fe-based alloy can be improved.

  According to the present invention, since the diffusion layer is thick, the hardness and strength of the Fe-based alloy can be improved to the inside. That is, the effect that a layered Fe-based alloy having excellent hardness can be formed 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.

  FIG. 1 shows a schematic overall perspective view of a forging punch made of a layered Fe-based alloy according to the present embodiment. 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 workpiece pressing portion is enlarged and shown in FIG. As can be seen from FIG. 2, a diffusion layer 20 formed by diffusing metal carbide in the base material SKH 51 exists in the surface layer portion of the workpiece pressing portion.

  The metal element forming the carbide is not particularly limited as long as it improves the hardness of SKH51, and preferable examples include Cr, W, Mo, V, Ni, and Mn. The diffusion layer 20 formed by diffusing such metal element carbide exhibits high hardness and high strength. For this reason, in the punch 10 for a forging process, in the workpiece | work press site | part in which the diffused layer 20 exists, hardness and intensity | strength become high compared with the large diameter part 12, the reduced diameter part 14, etc. in which the diffused layer 20 does not exist. In other words, the workpiece pressing portion provided with the diffusion layer 20 has higher hardness and higher strength than other portions.

Carbides, when represents a metal element in M, tables in M ₆ C as may be carbide composition formula is represented by M ₇ C _{3 but, Cr 6 C, W 6 C} , Mo 6 C , etc. And a carbide represented by M ₂₃ C ₆ is preferred. In this case, it is because it is most excellent in the effect of improving hardness and strength.

If M ₆ C or M ₂₃ C ₆ is excessively present, the forging punch 10 becomes brittle. Therefore, it is preferable to generate a solid solution carbide of Fe and the above metal element. That is, the carbide may be represented by (Fe, M) ₆ C, (Fe, M) ₂₃ C ₆ or the like. When such a carbide is generated, the relative amounts of M ₆ C and M ₂₃ C ₆ are reduced, so that it is possible to reliably avoid the forging punch 10 from being brittle.

  Here, the thickness of the diffusion layer 20, in other words, the diffusion distance of carbides, the depth from the surface of the forging punch 10 has reached at least 0.5 mm (500 μm), and usually 3-7 mm ( 3000 to 7000 μm) and may reach 15 mm (15000 μm) at the maximum. This value is remarkably large while the diffusion distance of elements in nitriding, carburizing, etc. is several tens of μm, at most about 200 μm. That is, in the present embodiment, the carbide can be diffused to a deeper portion than the element introduced by the surface treatment method according to the prior art.

  In the workpiece pressing portion provided with such a diffusion layer 20, the hardness of the base material is improved to the depth at which the carbide is diffused. That is, the hardness and strength increase to the inside of the forging punch 10, and as a result, the internal wear resistance is improved and deformation is difficult.

  As will be described later, the diffusion layer 20 is formed by generating a carbide from a metal element diffused from the surface of the base material. For this reason, the carbide | carbonized_material density | concentration is the highest on the surface, and it reduces gradually as it goes inside the base material.

  Further, since the carbide concentration gradually decreases in this way, there is no clear interface between the diffusion layer 20 and the base material. For this reason, since it can avoid that stress concentration arises, it can avoid that brittleness increases with diffusing a metallic element. In FIG. 2, a boundary line is provided for convenience between the diffusion layer 20 and the base material in order to clarify that the diffusion layer 20 exists.

  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. As described above, the workpiece pressing portion has high hardness and high strength due to the presence of the diffusion layer 20, and toughness is ensured. Therefore, the workpiece pressing portion is not easily worn even when the forging process is repeatedly performed, and is not easily damaged. That is, a long life can be ensured.

  The carbide may be a carbonitride.

  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, a metal powder to be diffused is applied to the surface of the workpiece pressing portion on the surface of the preform 32. For example, if W is diffused, powder mixed with W powder may be applied, and if Cr is diffused, powder mixed with Cr powder may be applied. The coating amount of the powder may be, for example, to the amount W ₆ C and Cr ₆ C, etc. are produced.

  The powder is applied 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 W and Cr, is disperse | distributed to this solvent.

  Here, an oxide film is usually formed on the surface of the base material SKH 51. In order to diffuse W, Cr, etc. in this state, a great amount of heat energy must be supplied so that W, Cr, etc. 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 workpiece pressing portion 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, it is not necessary for W, Cr, or the like to pass through the oxide film, so that the time required for diffusion can be shortened and the thermal energy can be reduced.

When the temperature is further increased, C, Fe, which are constituent elements of SKH51, which is the base material, C generated by decomposition of the reducing agent, W, Cr, and the like react with each other, and W ₆ C, Cr ₆ C, W ₂₃ C ₆ , Cr ₂₃ C _{6 and the} like are generated. When Fe is involved, (Fe, W) ₆ C, (Fe, Cr) ₆ C, (Fe, W) ₂₃ C ₆ , (Fe, Cr) ₂₃ C _{6 and the} like are also generated.

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 are next combined with C and Fe, which are constituent elements of the base material existing on the inner side of the base material, and C existing in a free state on the inner side of the base material. Thus, W ₆ C, Cr ₆ C, (Fe, W) ₆ C, (Fe, Cr) ₆ C and the like are newly 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 the base material existing further inside the base material. Are combined with C and Fe, which are constituent elements of C, and C which is present in a free state on the inner side of the base material, and again W ₆ C, Cr ₆ C, (Fe, W) ₆ C, (Fe, Cr ) ₆ C etc. are generated. In this way, the carbide is repeatedly decomposed and produced, so that the carbide diffuses deep inside the base material.

In this way, W ₆ C, Cr ₆ C, (Fe, W) ₆ C, and (Fe, Cr) ₆ C can be diffused inside the base material, and as a result, the diffusion layer 20 is formed. (See FIG. 2). Note that the carbide concentration gradually decreases, and a clear interface does not occur between the carbide diffusion reaching end portion and the base material. Therefore, since brittle fracture can be avoided, it is possible to ensure the toughness of the workpiece pressing portion where the diffusion layer 20 is formed. The thickness of the diffusion layer 20, that is, the diffusion distance of carbides, extends up to a depth of about 15 mm from the surface.

  Finally, as shown in FIG. 3 (e), the preforming body 32 is finished with a cutting tool 30 to obtain a forging punch 10.

  The forging punch 10 thus obtained was cut along the longitudinal direction, and the C-scale Rockwell hardness (HRC) measured from the surface side to the inside of the cut surface was measured as the HRC of ordinary SKH51. In addition, FIG. From FIG. 4, it is clear that in this case, the hardness has increased from the surface to the inside of 2.5 mm.

  Similarly, the strength of the test piece of the JIS Z 2201 No. 4 test piece in which the diffusion layer 20 is formed is significantly improved as compared with the test piece of the same size in which the diffusion layer 20 is not formed. Specifically, the tensile strength of the test piece in which the diffusion layer 20 is not formed is about 1800 MPa, whereas the tensile strength of the test piece having the diffusion layer 20 is about 2200 MPa, which is about 1.2 times.

  Similarly to the above, carbides of Mo, V, and Ni can be diffused into the base material.

  In the above-described embodiment, the forging punch 10 has been described as an example of the layered Fe-based alloy. However, the forging punch 10 is not particularly limited, and other members may be used. Not too long.

Further, the carbide may have a compositional formula represented by M ₇ C ₃ or may be represented by another compositional formula.

  Further, the above heat treatment may be performed in a nitrogen atmosphere in a heat treatment furnace. In this case, the carbide is nitrided to become carbonitride. Even in this case, a layered Fe-based alloy showing high strength and high hardness is obtained in the same manner as described above.

  Using SKH51, which is a high-speed tool steel, and SKD11, which is a die steel, 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.

  Thereafter, coating agent A was applied to the entire surface of the cylindrical body of SKH51, and coating agent B was applied to the entire surface of the cylindrical body of SKD11. In addition, application | coating was performed by brush coating and the thickness of the coating agents A and B was 1 mm.

  After the coating agent was naturally dried, a quenching treatment was performed by holding at 1000 to 1180 ° C. for 2 hours, and then a tempering treatment was performed by holding at 500 to 600 ° C. for 2 hours.

  Each cylindrical body was cut in the height direction, and HRC was measured every 0.5 mm along the height direction from the center of the bottom surface. The relationship between the distance from the surface and HRC is shown in FIG. 6 or FIG. 7 together with uncoated SKH51 and SKD11 as a graph. Considering the measurement error of HRC, it is clear from these FIG. 6 or FIG. 7 that the hardness of each cylindrical body increases to a depth of about 6 mm from the bottom surface.

Moreover, when the produced carbide was identified, it was confirmed to be (Fe, W) ₆ C, (Fe, W) ₂₃ C ₆ , (Fe, Cr) ₆ C, (Fe, Cr) ₂₃ C ₆ . .

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 SKH51. It is a graph which shows the relationship between the distance from the surface, and HRC in the test piece made from SKD11.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Forging punch 16 ... Small diameter part 18 ... Curve protrusion 20 ... Diffusion layer 30 ... Bit 32 ... Preliminary molded body 34 ... Coating agent 36 ... Brush

Claims (5)

A base material composed of an Fe-based alloy, and a diffusion layer formed by diffusing carbides in the base material and having a higher hardness than the base material,
The thickness of the diffusion layer measured from the surface of the layered Fe-based alloy as a base point is 0.5 mm or more,
The carbide is applied to the surface of the base material, and when the metal that raises the hardness of the Fe-based alloy is carbonized and the metal element is represented by M, M ₆ C, M ₂₃ C ₆ , (Fe, M) A layered Fe-based alloy characterized by being formed by changing to carbides represented as ₆ C or (Fe, M) ₂₃ C ₆ and diffusing inside the base material.   2. The layered Fe-based alloy according to claim 1, wherein the carbide is a carbide of Cr, W, Mo, V, Ni, Mn. Characterized in claim 1 Symbol placement organic layer Fe-based alloy, the carbide, Cr, W, Mo, V, Ni, and at least any one of Mn, the solid solution of Fe is obtained by carbides of A layered Fe-based alloy. A base material composed of an Fe-based alloy, and a diffusion layer formed by diffusing carbide in the base material and having a hardness higher than that of the base material, and the surface of the layered Fe-based alloy A method for producing a layered Fe-based alloy in which the thickness of the diffusion layer measured as follows is 0.5 mm or more,
Table powder metal to increase the hardness on the surface of the Fe-based alloy, when represents a metal element in _{M, M 6 C, M 23} C 6, (Fe, M) 6 C or (Fe, M) as a ₂₃ C ₆ Applying in an amount that produces carbides to be produced ;
By heat-treating the Fe-based alloy metal powder is applied, as well as to the carbide by reacting the carbon metal constituting at least said Fe-based alloy, thereby diffusing the carbide during the Fe-based alloy Process,
A method for producing a layered Fe-based alloy, comprising: The manufacturing method according to claim 4 , wherein Cr, W, Mo, V, Ni, or Mn is used as the metal.

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