JP4829025B2 - Method for producing layered Fe-based alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for improving the hardness and compressive residual stress of an Fe-base alloy to an internal depth; and to provide an Fe-based alloy produced by the method. <P>SOLUTION: The surface of a pre-molded article made of SKH51(Fe based alloy) is coated with a powder of Al, Cr and the like. The coating may be performed by applying a coating agent which is prepared by dispersing the powder in an organic solvent. The coating agent can contain a reducing agent. After coating, the pre-molded article is subjected to heat treatment to form a carbonized product of the metal. The pre-molded article can be further subjected to salt bath nitriding treatment, thereby forming a layered Fe-based alloy which has a diffusion layer 20 which is formed by the diffusion of the carbonized product, a nitrided product and AlN in the base material. Subsequently, the article can be subjected to finishing process to give a punch having a predetermined shape for use in a hot-roll forging process. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

The present invention, on the surface of the base material made of Fe-based alloy, the diffusion layer is a method of manufacturing organic layer Fe-based alloy gold provided a high hardness compared to and the base material include carbides and nitrides.

  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.

  Further, in Patent Documents 4 and 5, attention is paid to the corrosion resistance of the Fe—Al alloy, and it is attempted to diffuse and infiltrate the steel material by heat treatment. In order to realize this, Patent Document 4 proposes to apply Al powder or Al alloy powder and Ti powder or Ti alloy powder to a steel material and heat-treat, while Patent Document 5 discloses Al powder. Alternatively, it has been proposed to apply a heat treatment by applying a mixed powder of an Al alloy powder and at least one of a metal oxide, a metal nitride, a metal carbide, and a metal boride to a steel material.

JP 2003-129216 A JP 2003-239039 A JP-A-5-171442 Japanese Patent No. 3083292 JP 2004-323891 A

  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.

  Also in the techniques described in Patent Documents 4 and 5, since the diffusion and penetration depth of Al is about 100 μm, it is difficult to improve various characteristics deep inside the metal material.

The present invention has been made in order to solve the above-described problems. The layered Fe which is hard to cause brittle fracture because the hardness and strength are improved deep inside, and the change in physical properties is gentle, so that stress concentration hardly occurs. and to provide a method of manufacturing-based alloy gold.

In order to achieve the above object, a layered Fe-based alloy according to the present invention is formed by diffusion of carbide and nitride from a base material made of an Fe-based alloy and a surface side of the base material. It has a diffusion layer with high hardness compared to the material,
The nitride includes at least AlN,
The diffusion layer is characterized in that the concentration of the carbide and the nitride gradually decreases as the depth increases in the depth direction.

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

  In addition, although compressive residual stress is imparted with the presence of nitride, carbide, etc., in the present invention, carbide and nitride are diffused to a depth of 0.5 mm or more starting from the outermost surface. . Therefore, the compressive residual stress can be increased deep inside. In addition, since the density | concentration of a carbide | carbonized_material and nitride reduces gradually as it goes inside from the outermost surface, a compressive residual stress also reduces gradually. Also from this point, stress concentration is avoided.

  Preferable examples of the metal carbide include carbides of Cr, W, Mo, V, Ni, and Mn. In addition, preferable examples of nitrides other than AlN include nitrides of these metals.

In the carbides in this, when the metal element is represented by M, the composition formula 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 and nitride in the base material and having a hardness higher than that of the base material, A method for producing a layered Fe-based alloy containing at least AlN as a nitride,
Applying a metal powder containing Al powder on the surface of the Fe-based alloy;
Heat treating the Fe-based alloy coated with the powder;
Nitriding the Fe-based alloy subjected to heat treatment;
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.

  The reason why the thickness of the diffusion layer, and thus the diffusion distance of each component becomes large, is that a lattice defect is generated in the steel by applying Al and heat treatment, and each component can be easily penetrated deep inside the steel through the lattice defect. It is guessed that it is to spread.

  Further, the carbide contained in the diffusion layer is formed by combining the metal applied as powder and the carbon constituting the Fe-based alloy during the heat treatment, while the nitride remains as an unreacted material during the heat treatment. It is considered that the metal and Al are formed by nitriding during nitriding.

  As the metal powder to be applied, nitrides can be formed by diffusing deeply into the Fe-based alloy together with Al, and since it can also be diffused deeply inside as a carbide, Cr, W, Mo, V Ni, Mn powder is preferably used.

  According to the present invention, since Al is applied, lattice defects are generated in the steel material. For this reason, Al and other metals diffuse deep inside, and thereafter these components are nitrided. For this reason, since the thickness of the diffusion layer is large, 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, like the preferred embodiment for the production method of the organic layer Fe-based alloy gold according to the present invention will be described in detail with reference to the accompanying drawings.

  A schematic overall perspective view of a hot forging punch made of a layered Fe-based alloy according to the present embodiment is shown in FIG. This hot forging punch 10 is manufactured using SKH51 as a raw material (base material), and has a large diameter portion 12 and a reduced diameter portion 14 connected to the large diameter portion 12 and reduced in a taper shape. And a small-diameter portion 16 and a curved protruding portion 18 that is formed to protrude from one end portion of the small-diameter portion 16 and is curved. Of these, the curved protruding portion 18 and the side wall portion at 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 molding portions that press the workpiece.

  Here, the cross section near the forming portion is enlarged and shown in FIG. As understood from FIG. 2, a diffusion layer 20 formed by diffusing metal carbide and nitride in the base material SKH 51 exists in the surface layer portion of the formed portion.

  Further, nitrogen is further diffused and penetrated in the vicinity of the outermost surface of the molded part. That is, in the vicinity of the outermost surface in the diffusion layer 20, in addition to carbide and nitride, nitrogen is contained in the base material as a base in the form of a so-called nitride layer (nitrogen diffusion layer) formed by nitriding.

  Preferable examples of the metal element that forms carbide or nitride include Cr, W, Mo, V, Ni, and Mn. The diffusion layer 20 in which the carbides and nitrides of such metal elements are diffused exhibits high hardness and high strength based on the same mechanism as that of the precipitation hardening type composite material.

  Further, in the vicinity of the outermost surface in the diffusion layer 20, there is a nitride layer formed by diffusion and permeation of nitrogen as described above. For this reason, in the hot forging punch 10, the molded portion where the diffusion layer 20 exists has higher hardness and strength than the large diameter portion 12 and the reduced diameter portion 14 where the diffusion layer 20 does not exist. In other words, the molded part provided with the diffusion layer 20 has higher hardness and higher strength than other parts.

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.

Note that when M ₆ C and M ₂₃ C ₆ are present in an excessively large amount, the hot 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 the hot forging punch 10 can be reliably prevented from showing brittleness.

For example, when the C amount of the steel material is large, WC, VC, Mo ₂ C, Cr ₃ C _{4 and the} like may be present as carbides in addition to those represented by these composition formulas.

  Moreover, as a suitable example of nitride, the nitride of Cr, W, Mo, V, Ni, Mn mentioned above is mentioned. Among these, Cr is particularly preferable. Further, in the present embodiment, in addition to these nitrides, AlN is also included in the diffusion layer 20. Such a nitride exists so as to be interposed between fine carbides and precipitated austenite.

  Here, the thickness of the diffusion layer 20, in other words, the diffusion distance of carbide and nitride, the depth from the outermost surface of the hot forging punch 10 reaches at least 0.5 mm (500 μm), Usually, it may reach 3 to 7 mm (3000 to 7000 μm), and 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, carbides and nitrides can be diffused to a deeper site than the elements introduced by the surface treatment method according to the prior art.

  Further, in the present embodiment, AlN is diffused to a depth substantially equal to the thickness of the diffusion layer 20. In other words, AlN reaches a depth of at least 0.5 mm from the outermost surface, and thus the diffusion layer 20 has a form containing AlN. AlN may be diffused to a deeper position than carbides and other nitrides.

  In the molded part provided with such a diffusion layer 20, the hardness of the base material is improved to the depth at which the carbides are diffused. That is, the hardness and strength increase to the inside of the hot forging punch 10, and as a result, the internal wear resistance is improved and the deformation becomes difficult.

  The diffusion layer 20 may contain carbonitrides such as Cr, W, Mo, V, Ni, Mn, etc. in addition to the above-described carbides and nitrides.

  As will be described later, the diffusion layer 20 is formed by generating carbide and nitride by a metal element diffused from the surface of the base material. For this reason, the concentration of carbide and nitride is highest on the surface and gradually decreases toward the inside of the base material.

  Further, since the concentrations of carbide and nitride gradually decrease 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 hot forging punch 10 configured in this manner is used when hot forging is performed on a workpiece. At this time, the forming portion of the hot forging punch 10 is used as a workpiece. Press. As described above, since the diffusion layer 20 is present, the molded portion has high hardness and high strength, and toughness is ensured. Therefore, the molded part is not easily worn even if the forging process is repeatedly performed, and is not easily damaged. That is, a long life can be ensured.

  The hot forging punch 10 can be manufactured as follows.

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

  Next, as shown in FIG. 3C, a metal powder to be diffused is applied to the surface of the molding portion of the preform 32.

  The metal powder to be diffused is a metal that forms carbides and nitrides and increases the hardness of the steel material, and Al. Suitable examples of metals other than Al are Cr, W, Mo, V, Ni, and Mn as described above. In particular, when Cr is present, the nitride layer becomes deep, which is preferable. In addition, the presence of Mo and Ni provides an advantage that the elongation of the hot forging punch 10 is improved.

  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 Al, Cr, etc. in this state, a great amount of thermal energy must be supplied so that Al, 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 molded part 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 molding part. This heat treatment can also be performed by applying a burner flame 38 from one end face 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 Al, Cr, or the like to pass through the oxide film, so that the time required for diffusion can be shortened and thermal energy can be reduced.

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

A part of the generated carbides such as Cr ₆ C and (Fe, Cr) ₆ C are immediately decomposed and returned to Fe and Cr. Among these, Cr is then combined with C, 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, Newly produced are Cr ₆ C, (Fe, Cr) ₆ C, and the like. This Cr ₆ C, (Fe, Cr) ₆ C also immediately decomposes and returns to Cr, and then C, Fe, which are constituent elements of the base material existing on the inner side of the base material, and the base material It combines with C existing in a free state on the inner layer side, and again produces Cr ₆ C, (Fe, Cr) ₆ C and the like. In this way, the carbide is repeatedly decomposed and produced, so that the carbide diffuses deep inside the base material.

  On the other hand, Al causes lattice defects in the crystal structure of SKH51 and promotes diffusion through the lattice defects. Unreacted metals other than Al also diffuse through these lattice defects. In other words, Al causes lattice defects so that a part of the metal diffuses into the preform 32 before forming carbide.

In this way, Cr ₆ C, Al, Cr, etc. can be diffused inside the base material.

  Next, for example, salt bath nitriding is performed on the preform 32. In this case, the nitriding conditions may be 550 ° C. and 14 hours.

  The molten salt used for the salt bath nitriding has good convection properties, uniform heat transfer, and high density, so that the preform 32 and the coating agent 34 can be heated quickly. . In addition, since the thermal conductivity is high, the preform 32 is heated deep inside. For this reason, a large amount of N is diffused deep inside the preform 32 using N that has penetrated the surface of the preform 32 as a source. It becomes possible to make it. Furthermore, there is an advantage that capital investment can be reduced.

  By salt bath nitriding, Al, Cr, or the like diffused inside the preform 32 is nitrided to produce AlN or CrN. Further, part of the carbide is also nitrided to become carbonitride. Thereby, the diffusion layer 20 is formed (see FIG. 2). Further, as nitrogen diffuses and penetrates into the preform 32, a nitride layer is also formed near the outermost surface of the diffusion layer 20.

  Note that the concentrations of carbide, nitride, and carbonitride gradually decrease, and no clear interface is formed between the diffusion reaching termination portion and the base material. For this reason, since compressive residual stress changes gently, it is avoided that stress concentrates on a specific location. As a result, the occurrence of brittle fracture can be avoided, so that the toughness of the molded part in which the diffusion layer 20 is formed can be ensured.

  Here, the depth and compressive residual stress in the steel material that has been subjected to the salt bath nitriding treatment without being coated with the metal powder, and the steel material that has undergone the above procedure after the mixed powder containing Al and Cr is applied as the metal powder. The relationship is shown in a graph in FIG. In addition, the numerical value of Al in FIG. 4 is weight% which Al occupies in mixed powder. From FIG. 4, it is clear that the compressive residual stress can be improved by applying a nitriding treatment after applying a mixed powder containing Al and Cr.

  Of course, ion nitriding may be performed instead of salt bath nitriding. In this case, for example, a DC voltage of a predetermined voltage is applied using the nitriding furnace as an anode and the preformed body 32 as a cathode, while a nitriding gas such as nitrogen is supplied at a predetermined pressure and held at 520 ° C. for 10 hours. In ion nitriding, nitriding proceeds by causing a sputtering phenomenon in which nitriding gas ions are accelerated at high speed and collide with the preform 32.

  Due to the above nitriding treatment, a large amount of nitride is present in the diffusion layer 20, so that the compressive residual stress of the preform 32 increases and the hardness increases. As a result, the hot forging punch 10 with improved resistance to cracks and cracks is obtained.

  The hot forging punch 10 preferably has a large compressive residual stress because a compressive pressure is applied along the pressing direction as it is subjected to pressing from the workpiece during forging. That is, according to the nitriding treatment, the hot forging punch 10 suitable for forging can be provided.

  Before the nitriding treatment, the metal powder and impurities remaining on the surface may be removed, or the surface (diffusion layer 20) may be slightly ground. As a result, the nitriding process proceeds smoothly and efficiently. This is because N easily diffuses from the surface. As a result, the film quality can be easily controlled and the time required for the nitriding treatment can be shortened. This effect is particularly remarkable in the case of ion nitriding.

  Further, the nitriding treatment may be performed a plurality of times.

  When the hot forging punch 10 is subjected to pressing from a workpiece when performing hot forging, the hot forging punch 10 is expanded along a direction substantially perpendicular to the pressing direction. In other words, tensile stress acts. As described above, according to the present embodiment, since the compressive residual stress can be increased deep inside the hot forging punch 10, resistance to tensile stress during the hot forging process is increased. be able to.

  The thickness of the diffusion layer 20, particularly the diffusion distance of AlN, extends up to a depth of about 15 mm from the surface, and the compressive residual stress at the outermost surface may reach 1200 MPa.

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

  In the same manner as described above, Mo, V, and Ni carbides and nitrides can be diffused into the base material.

  The hot forging punch 10 thus obtained was cut along the longitudinal direction, and the Vickers hardness measured from the surface side to the inside of the cut surface was nitrided without applying metal powder. It is shown in FIG. 5 together with SKH51. In this case, the coated material was mixed in a weight ratio of Group III metal: Group IV metal: Group VI metal: Group VII metal: Group VIII metal: Al = 2: 13: 26: 20: 31: 4. The product was prepared by adding it to an acetone solution of 10% epoxy resin. Moreover, application | coating was performed by brush coating and the thickness of the coated material was 1 mm. Furthermore, after air-drying a coating material, the hardening process was performed by hold | maintaining at 1000-1180 degreeC for 2 hours, and the tempering process was then hold | maintained at 500-600 degreeC for 2 hours.

  From FIG. 5, the normal nitriding treatment increases the hardness only to about 0.07 mm from the outermost surface, and thereafter shows a substantially constant hardness, whereas in the present embodiment, it exceeds 0.5 mm from the outermost surface. It is clear that it shows high hardness and decreases gradually.

  FIG. 5 also shows the case where the nitriding treatment is performed twice. In this case, an increase of about 50 in Vickers hardness was observed compared with the case where the nitriding treatment was performed only once. That is, by performing the nitriding treatment a plurality of times, it becomes possible to further improve the compressive residual stress on the surface, and as a result, it becomes more preferable as the hot forging punch 10.

  In the above-described embodiment, the hot forging punch 10 has been described as an example of the layered Fe-based alloy. However, the present invention is not limited to this, and cold or warm including the punch is not limited thereto. Needless to say, it may be a forging die or other members.

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

It is a schematic whole perspective view of the hot forging punch which is a layered Fe-based alloy. FIG. 2 is an enlarged vertical cross-sectional view of a main part of the hot forging punch in FIG. 1. FIG. 2 is a flow explanatory diagram illustrating a manufacturing process of the hot forging punch of FIG. 1. It is a graph which shows the relationship between the depth and compressive residual stress in each steel material after nitriding was performed. It is a graph which shows the Vickers hardness measured toward the inside from the surface of the cut surface of the obtained punch for hot forging.

Explanation of symbols

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

Claims (1)

A base material made of an Fe-based alloy, and a diffusion layer formed by diffusing carbide and nitride from the surface side of the base material and having a hardness higher than that of the base material. However, when M is represented by at least one of Cr, W, Mo, V, Ni, and Mn), the composition formula of the carbide is M ₆ C, M ₂₃ C ₆ , (Fe, M) ₆ C or (Fe, M) ₂₃ C ₆ , and the nitride includes AlN and at least one of nitrides of Cr, W, Mo, V, Ni, and Mn, and the diffusion layer has a depth of A method for producing a layered Fe-based alloy in which the concentration of the carbide and the nitride gradually decreases as the depth increases in the direction,
Metal powder containing Al powder and at least one of Cr, W, Mo, V, Ni, and Mn on the surface of the Fe-based alloy, M ₆ C, M ₂₃ C ₆ , (Fe, M) Applying in an amount to produce a carbide represented as ₆ C or (Fe, M) ₂₃ C ₆ ;
Heat treating the Fe-based alloy coated with the metal powder;
Nitriding the Fe-based alloy subjected to heat treatment;
A method for producing a layered Fe-based alloy, comprising:

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