JP2019056160A - Joined iron-based component and method for manufacturing the same - Google Patents

Abstract

To provide a method for manufacturing a joined iron-based component exhibiting a high joining strength.SOLUTION: A method for manufacturing a joined iron-based component in the present invention comprises a fitting step of obtaining an assembly in which, on an outer peripheral side of a first iron-based substance, a close-ringed second compact formed by press-forming a second base powder containing a second iron-based powder is fit, and a sinter-joining step of heating the assembly to obtain a joined iron-based component formed by joining a first iron-based component consisting of a first iron-based substance and a second iron-based component consisting of a second sintered body formed by sintering the second compact at a close-ringed joint interface. The second iron-based powder contains C:0.5-1.8% and a carbide-forming element consisting of W and/or V:6-16% provided that the powder entirety is taken 100 mass%. The second iron-based powder preferably contains further one or more of Si:0.1-1%, Mn:0.1-0.7% or Co:0.1-12%. The base powder may contain a carbon source powder (graphite powder, etc.) meeting C:0.01-0.8 mass%.SELECTED DRAWING: Figure 3A

Description

  The present invention relates to a bonded iron base member obtained by bonding at least two iron base members and a method for manufacturing the same.

  A member having a complicated shape used in the automobile field or the like is often made of an iron-based sintered body (simply referred to as “sintered body”) obtained by sintering a formed body made of iron-based powder. As a result, the so-called near-net shape of the member can be achieved, and the manufacturing cost can be significantly reduced by reducing machining or improving the yield.

  However, the shape of the sintered body obtained by one molding and sintering is limited to a shape that can be removed from the molding die. In addition, the sintered body is usually homogeneous as a whole, and it is difficult to change the material and properties (Young's modulus, strength, etc.) depending on the part.

  However, if the sintered body can be firmly joined to the other member, it is possible to manufacture a member having a more complicated shape or a member having different materials and characteristics depending on the part at low cost. The description relevant to this is, for example, in the following patent document.

JP-A-56-10859 Japanese Patent Publication No.58-13603 Japanese Patent Publication No. 2009-91609 JP 2010-215951 A

  Patent Document 1 proposes a camshaft in which a cam or the like made of an iron-based material to which P is added (Japanese Patent Application No. 52-128120) is liquid-phase sintered and integrated with a stem.

  Patent Document 2 discloses that a pre-sintered cam piece made of an iron-based material containing C: 1% (graphite powder) and P: 1.2% (ferroalloy) is liquid-phase sintered after being press-fitted and fixed to a camshaft. A method for manufacturing a camshaft is proposed.

  Patent Document 3 discloses a pre-sintered outer member compact made of a mixed powder of Fe-25% Cr-20% Ni powder and Co-28% Mo-8% Cr-2.5% Si powder not containing C. A method for manufacturing a sintered composite sliding member in which a body is solid-phase diffusion bonded after being inserted into molten stainless steel is proposed.

  In Patent Document 4, after pre-sintered outer member green compact composed of mixed powder composed of graphite powder (1%), iron-phosphorus alloy powder and high Cr iron alloy powder (remainder) is inserted into melted stainless steel. A method of manufacturing a sintered composite sliding member that is solid phase diffusion bonded is proposed.

  The present invention has been made in view of such circumstances, and is a bonded iron base member obtained by bonding a sintered body (outer member) made of a raw material powder having a composition different from the conventional one to another member (inner member). It aims at providing the manufacturing method of this.

  As a result of diligent research to solve this problem, the present inventor succeeded in obtaining a high-performance bonded iron-base member by using an iron-base powder containing a predetermined amount of C and a carbide-forming element. By developing this result, the present invention described below has been completed.

<< Method for Manufacturing Bonded Iron Base Member >>
In the method for producing a bonded iron base member of the present invention, an assembly in which a closed second molded body formed by pressure-molding a second raw material powder containing a second iron base powder is fitted on the outer peripheral side of the first iron base. A fitting step for obtaining the first iron base member made of the first iron base and the second iron base member made of the second sintered body obtained by sintering the second molded body by heating the assembly. And a sintered joining step of obtaining a joined iron base member joined at a closed annular joining interface portion, and the second iron base powder is 100% by mass (hereinafter simply referred to as “%”). C): 0.5 to 1.8%, and carbide forming elements composed of W and / or V (total): 6 to 16%.

  According to the manufacturing method of the present invention, at the time of the sintering joining process, the second molded body becomes a dense second sintered body while maintaining substantially the shape, and joined with the first iron base disposed inside the second sintered body. To do. A composite iron base member in which the first iron base member (inner member) and the second iron base member (outer member) are firmly joined in this way has a complex shape and different characteristics that cannot be obtained with a simple sintered body. The member can be provided.

  The details of the mechanism that is firmly bonded to the ferrous substrate when the second molded body becomes the second sintered body by the manufacturing method of the present invention is not clear at present, but in addition to the diffusion of carbon generated at the bonding interface Thus, it is presumed that an Fe—C-based (eutectic) liquid phase that can appear at least near the bonding interface in the second sintered body is also involved. Specifically, it is considered as follows.

  Conventionally, the Fe—C liquid phase (also simply referred to as “liquid phase”) has often appeared using graphite powder, Fe—C powder, or Fe—C—P powder. However, when such a powder is used, a liquid phase tends to appear pinpointly near the eutectic point (around 1140 ° C. for Fe—C). As a result, the amount of the liquid phase in the vicinity of the bonding interface cannot be controlled, and it is difficult to ensure stable bonding strength, or the appearance of the liquid phase is rapid. It was difficult to obtain a net-shaped bonded iron base member.

  On the other hand, in the present invention, the iron-based powder (also simply referred to as “base iron powder”) serving as the base of the second iron-based member contains C and a specific carbide-forming element (Cr, W, Mo, or V). Contains the proper amount at the same time. Since the carbide forming element forms a stable carbide, at least during the sintering joining process, C is not rapidly released at a pinpoint. Therefore, the liquid phase appears gently in the second molded body or the second sintered body, and an appropriate amount of the liquid phase in the vicinity of the joining interface between the second sintered body and the first iron base can be maintained. Thus, the first iron base member and the second iron base member are uniformly bonded at the bonding interface, and high bonding strength can be exhibited. In addition, since the appearance of the liquid phase in the second molded body or the second sintered body is moderate, at least the second iron base member can be formed into a near net shape.

《Bonded iron base member》
The present invention can also be grasped as a bonded iron base member. That is, the present invention is a joined iron base member comprising a first iron base member and a closed annular second iron base member joined to the outer peripheral surface of the first iron base member, the second iron base The member is 100% by mass (hereinafter, simply referred to as “%”) of the entire ferric base member, and C: 0.5 to 2.5%, and a carbide forming element composed of W and / or V: 6 to It may be a bonded iron base member made of a second sintered body containing 16%.

<Others>
(1) In this specification, for convenience of explanation, “first” or “second” is given to each member (molded body, sintered body, etc.) arranged in order from the inside (center side) to the outside. But the ordinal numbers themselves have no special meaning. In addition, the “iron group” in the present specification indicates that Fe is 50% by mass or more with respect to the entire object.

  The first iron base to be fitted with the second molded body may be any of a molded body, a sintered body, molten steel, and the like. In this specification, the first iron base after the sintering joining process is referred to as the first iron base member. That's it. The first iron base (iron base member) is not limited to a solid shape, and may be hollow or annular. Further, the first iron base member (first sintered body) and the second iron base member (second sintered body) may have the same alloy composition and characteristics (density, Young's modulus, strength, etc.).

The true density (ρ ₀ ) referred to in the present specification is a pore-free density (PFD) calculated from the blending composition of the raw material powder and the specific gravity of each blended powder. Note that the PFD of an existing sintered body is obtained by actually measuring the volume and weight of a compressed body obtained by forging / setting the sintered body.

  The molten steel referred to in this specification includes pure iron or a steel material close thereto (C: less than 0.2%), carbon steel, alloy steel (particularly alloy steel containing C), stainless steel, and the like.

(2) Unless otherwise specified, “x to y” in this specification includes a lower limit value x and an upper limit value y. A range such as “a to b” can be newly established with any numerical value included in various numerical values or numerical ranges described in the present specification as a new lower limit value or upper limit value.

It is a schematic diagram which shows the assembly before sintering. It is explanatory drawing of the extraction test which measures joining strength. It is an external appearance photograph of the sintered outer simple substance. It is the external appearance photograph which concerns on the sample 1 after a extraction test, and the metal structure photograph of the joining interface vicinity. It is an external appearance photograph concerning sample C2 after an extraction test. It is a metal structure photograph of the joint interface vicinity which concerns on the sample 23 after an extraction test. It is an external appearance photograph of each sample from which an inner (melting steel) and an outer dimension difference (inside and outside diameter difference) differ. It is a scatter diagram which shows the outer dimension change (outer diameter change) in each of these samples.

  The contents described in this specification can be applied not only to the bonded iron base member of the present invention but also to the manufacturing method thereof. A component related to the manufacturing method can also be a component related to an object. One or two or more components arbitrarily selected from the present specification may be added to the above-described components of the present invention.

(1) Raw material powder The raw material powder contains one or more iron-based powders, and one of the iron-based powders contains at least a predetermined amount of C and a carbide-forming element. C in the iron-based powder is preferably contained in an amount of 0.5 to 1.8%, more preferably 0.8 to 1.6%, based on 100% by mass (simply referred to as “%”) of the entire iron-based powder. It is preferable that a total of 6 to 16%, 7 to 15%, and further 7.5 to 14.5% of carbide forming elements composed of W and / or V are included in the iron-based powder. In particular, W is preferably contained in 6 to 13%, more preferably 7 to 11%, and V is contained in 1 to 5%, more preferably 1.5 to 4%. Such a carbide forming element contributes to control of the amount of liquid phase appearing at the time of sintering joining, densification and high rigidity of the sintered body, and the like.

  In addition to C and carbide forming elements, the iron-based powder is Si: 0.1 to 1%, further 0.2 to 0.6%, Mn: 0.1 to 0.7%, and further 0.2 to 0. 0.5%, Co: 0.1 to 12%, or 8 to 11% may be included. These elements contribute to securing strength and wear resistance at high temperatures.

  An example of the overall composition of the iron-based powder is as follows: C: 0.5 to 1.8%, carbide forming element: 6 to 16%, Si: 0.1 to 1%, Mn: 0.1 to 0.7%, The balance: Fe and impurities. Furthermore, Co: 0.1 to 12% may be included.

  The raw material powder may be only one kind of iron-based powder having the above-described composition, or may include iron-based powder, carbon source powder, alloy element powder and the like having different compositions. However, it is preferable that 95 mass% or more, further 98 mass% or more of the iron-based powder (ferric iron-based powder) having the above-described composition is included with respect to the entire raw material powder.

In addition to the iron-based powder, a carbon source powder may be added to the raw material powder. By adding the carbon source powder, it is possible to adjust the amount of liquid phase that appears at the time of sintering joining. As the carbon source powder, an alloy containing C (for example, an iron-based alloy), a compound (for example, Fe ₃ C), graphite (Gr) powder, or the like can be used. As an example, 0.1 to 1%, further 0.2 to 0.8% of graphite powder may be added to the entire raw material powder (100% by mass). However, when the added amount of graphite powder or the like is excessive, it is difficult to control the liquid phase, and joint strength and shape retention can be reduced.

  In the present invention, the liquid phase is controlled by the cooperation of C and the carbide forming element to ensure the bonding strength and shape retention of the bonded iron base member. For this reason, the raw material powder may be P: less than 0.1%, less than 0.05%, or even 0.01% or less, based on 100% by mass as a whole. Further, from the viewpoint of increasing the rigidity of the ferrous base member, V may be 6% or less, further 5% or less, respectively, and the amount of W may be relatively increased.

  The iron-based powder may have a general particle size of 212 μm or less (−212 μm), but the average particle size (median diameter: D50) is 1 to 20 μm, further 5 to 15 μm, or a particle size determined by sieving. It is preferable that the particles be classified to 45 μm or less (−45 μm) because the sintered body can be densified. In addition, you may mix and use the coarse powder with a large particle size (or average particle diameter) and the small fine powder.

(2) Molding step The second compact is obtained by pressing a raw material powder containing iron-based powder. The molding pressure is preferably 350 to 1000 MPa, more preferably 450 to 850 MPa. When the molded bodies are joined to each other, the molding pressure of each molded body may be the same or different. As the molding pressure of the first molded body disposed on the inner side is increased, higher bonding strength is easily obtained.

  The forming process may be cold forming (room temperature forming) or warm forming. The lubrication between the powder and the mold may be performed by blending an internal lubricant with the powder, or may be performed by mold lubrication. When performing mold lubrication, it is preferable to use a mold lubrication warm pressure molding method (refer to Japanese Patent No. 3309970 for details).

(3) Insertion process Before the sintering joining, an assembly is prepared in which the second compact is inserted on the outer peripheral side of the first iron base (molded body, sintered body or melted steel). The fit between the first iron base and the second molded body may be an interference fit that does not collapse the second molded body, or may be a gap fit. However, since the second molded body is densified at the time of sintering joining and the inner dimension is slightly shrunk, the fitting process may be a process of gap fitting the second molded body to the first iron base. By fitting the gap, press-fitting work or the like can be omitted, and the second molded body can be prevented from collapsing.

  As the ratio of the outer dimension (for example, outer diameter) of the first iron base to the inner dimension (for example, inner diameter) of the second molded body (also simply referred to as “dimension ratio”) increases, the gap (clearance) between the fitting surfaces increases. It becomes small and it is easy to improve joint strength. Conversely, the smaller the dimensional ratio, the greater the clearance and the easier it is to retain shape retention. When the dimensional ratio is 88 to 93%, more preferably 89 to 92%, both the joint strength and the shape retention can be achieved (particularly when the ferrous substrate is made of molten steel).

  The clearance described above can be appropriately adjusted according to the reference dimension between the fitting surfaces, the material of the first iron base, the composition and density of the second molded body, the sintering (joining) conditions, and the like. For example, in the case of sintered joining between molded bodies, the clearance may be about 1 to 100 μm, further about 5 to 50 μm. The clearance with respect to the reference dimension is preferably about 0.05 to 1%, more preferably about 0.1 to 0.5%.

(4) Sinter bonding step By heating the assembly, the second molded body becomes the second sintered body, and the bonded iron base member in which the first iron base member and the second iron base member are (diffusion) bonded is provided. can get.

  The heating temperature (sintering temperature) is preferably 1140 ° C. or higher that generates an Fe—C-based liquid phase, for example, 1140 ° C. to 1350 ° C., 1180 to 1300 ° C., further 1200 to 1280 ° C.

  The heating time (time for maintaining the temperature) is preferably 0.1 to 3 hours, and more preferably 0.1 to 1 hour, for example. The heating atmosphere is preferably a nitrogen atmosphere in addition to a vacuum atmosphere or an inert gas (Ar gas or the like) atmosphere. N in the atmosphere acts on carbides (or its forming elements: W or V) in the iron-based powder, contributes to the appearance of a liquid phase, and can increase the bonding strength.

(5) Others The assembly described above may be a multiple assembly in which another third molded body or the like is inserted inside the first iron base or the second molded body. Increasing the cooling rate after the sintering joining step is preferable because it can suppress the coarsening of the metal structure of the sintered body. The bonded iron base member may be further subjected to a heat treatment step such as annealing, normalizing, aging, tempering (quenching, tempering), carburizing, and nitriding after the sintering bonding step.

《Bonded iron base member》
(1) Second iron base member (second sintered body)
The ferrous base member is formed by sintering the above-described raw material powder compact. Considering the case where carbon source powder (graphite powder or the like) may be included in the raw material powder, the ferric iron-based member has C: 0.5 to 2.5%, W and It is preferable that the second sintered body contains a carbide forming element composed of V and / or V: 6 to 16%. The second sintered body may include one or more of Si: 0.1 to 1%, Mn: 0.1 to 0.7%, or Co: 0.1 to 12%. Further, the second sintered body may be P: less than 0.1% or V: 6% or less.

In the second sintered body, the relative density (100 × ρ / ρ ₀ ), which is the ratio of the bulk density (ρ) to the true density (ρ ₀ ), can be 97% or more, 98% or more, and even 99% or more. As the second sintered body becomes denser, the mechanical properties (strength, rigidity, etc.) of the second sintered body can be improved. For example, if it is a high-density second sintered body having the above-described composition, the Young's modulus can be about 200 to 240 GPa, further about 210 to 230 GPa.

(2) According to the present invention, it becomes easy to provide a member having a complicated shape or a member having different characteristics for each part. Since the first iron base member may be sintered or melted, an attachment (gear, cam lobe, counterweight, etc.) made of sintered material is provided on the shaft made of melted steel, for example. There are transmission shaft, camshaft, crankshaft and so on.

  A number of samples were prepared with different raw material powder composition, molding conditions, sintering conditions, etc., and their measurements, observations and evaluations were performed. Through these, the contents of the present invention will be described more specifically.

[Example 1 / Jointing of molded bodies]
<Production of sample>
(1) Raw material powder As shown in Table 1, a plurality of base iron powders (iron-based powders) having different component compositions were prepared. Each of the base iron powders shown in Table 1 is atomized powder, SKH powder and SKH2 powder are made by Kobe Steel, and FCM1 powder, FM1 powder, FNCM1 powder and FC1 powder are made by Höganäs AB. FCM2 powder and FM2 powder are manufactured by Epson Atmix Co., Ltd. The component composition shown in Table 1 is a mass ratio with respect to the entire base iron powder.

  The “particle size” shown in Table 1 was determined by sieving or average particle size. The classification using a sieve is specified according to JIS Z 8801, and “−a μm (a μm or less)” means a powder having passed through a sieve having a nominal opening: a μm. The “average particle size” was a median diameter (D50) based on particle size distribution measurement using a laser diffraction particle size distribution analyzer.

  In addition to the base iron powder, graphite (Gr) powder (JCPB manufactured by Nippon Graphite Co., Ltd., average particle size: 5 μm) was also prepared. When graphite powder was added to the base iron powder, each powder was weighed and blended in the proportions shown in Table 2 and Tables 3A and B, then premixed for 3 minutes in a mortar, and further rotationally mixed in a ball mill for 30 minutes. The mixed powder thus obtained was used as a raw material powder. In addition, the compounding quantity of the graphite powder shown in each table | surface is a mass ratio with respect to the whole raw material powder (mixed powder).

(2) Molding process Two types of molds having different cavity shapes were prepared. One is a cylindrical shape (φ14 mm × H10 mm) for obtaining a molded body (first molded body) that becomes a cylindrical shaft-shaped inner (first iron base, first iron base member). The other is a ring mold (φ14 mm × φ23 mm × H6 mm) for obtaining a molded body (second molded body) to be an annular outer (second iron base member).

  Unless otherwise specified, the inner diameter of the cylindrical mold and the ring mold so that the outer peripheral surface of the inner molded body and the inner peripheral surface of the outer molded body according to this example are fitted with a gap with respect to the reference dimension φ14 mm. The inner diameter (the outer diameter of a cylindrical core disposed at the center) was set.

  Molding is performed without using an internal lubricant by using a mold lubrication warm pressure molding method (see Japanese Patent No. 3309970), while the raw material powder filled in the cavity of each mold is warm (mold temperature: 150 ° C.). ) Under pressure. The molding pressure was adjusted in the range of 392 to 980 MPa. Unless otherwise specified, the inner molded body was molded at 392 MPa, and the outer molded body was molded at 490 MPa. Thus, various molded articles for inner and outer molded articles were obtained.

(3) Sintering process Prior to joining the molded body for the inner and the molded body for the outer, as shown in Table 2, a sintered body obtained by sintering each molded body independently is also prepared and used for density measurement. did.

  Sintering (including sintering joining described later) was performed using a batch-type sintering furnace (PVSGgr 20/20 manufactured by Shimadzu Mektem Co., Ltd.). The sintering atmosphere was a vacuum atmosphere or a nitrogen atmosphere, and heating was performed at 1250 ° C. for 30 minutes (soaking time). After the heating, the furnace was cooled to 1000 ° C., and then quenched by introducing 400 kPa of nitrogen gas.

(4) Sintering step As shown in FIG. 1A, the inner molded body and the outer molded body were fitted to form an assembly. This assembly was heated under the same conditions as in the above-described sintering step. Thus, as shown in Table 3A and Table 3B (both are simply referred to as “Table 3”), an axial inner (first sintered body, first iron base member) and an annular outer (second sintered) The various joined bodies (joined iron base member) were obtained by joining the body and the second iron base member) at the joint interface of the closed ring.

<Measurement>
(1) Relative density Relative density (density ratio) was determined for each sample (molded body and sintered body) shown in Table 2. The relative density was calculated as a ratio (100 × ρ / ρ ₀ ) of the bulk density (ρ) to the true density (ρ ₀ ). The bulk density (ρ) was calculated from the size and weight obtained by actually measuring the molded body and the sintered body. For the true density (ρ ₀ ), PFD calculated based on the composition and specific gravity of each raw material powder was used. The relative density of each sample thus obtained is also shown in Table 2.

(2) Dimensional Difference For each sample shown in Table 3, the inner diameter (R2) of each outer molded body and the outer diameter (R1) of each inner molded body were measured. These measured values and the dimensional difference (ΔR = R2−R1) that becomes the clearance when both molded bodies are fitted are shown in Table 3.

(3) Bonding strength (extraction test)
The bonding strength between the inner and outer was measured by an extraction test using an extraction jig as shown in FIG. 1B. Specifically, first, the inner side convex portion is fitted into an annular holding jig to hold the joined body. Next, a load is applied from above to a cylindrical pressing jig fitted in the recess on the inner side.

  The load (F) is measured when the outer and inner parts are separated or when one of them breaks. The joint strength was determined by dividing this load by the cylindrical area (d: φ14 mm × H: 4 mm) of the joint interface between the outer and inner joints obtained in advance. The results are also shown in Table 3.

<< Observation >>
FIG. 2 shows the appearance of a sintered body obtained by sintering the outer molded body independently for a part of the samples shown in Table 2.

  A part of the sample shown in Table 3 is shown in FIG. 3A and FIG. 3B (appearance “figure 3” together) as the appearance after the pull-out test and the metal structure photograph in the vicinity of the bonding interface. In addition, the metallographic photograph was observed with an optical microscope after cutting the sample, filling it with resin, and mirror polishing.

<Evaluation>
(1) Densification For each sample shown in Table 2, the following can be seen by comparing the relative density of the compact and the relative density of the sintered body. It was found that when the base iron powder is SKH, the sintered body is densified substantially to a level close to the true density regardless of whether graphite powder is added, molding pressure, and sintering atmosphere. Further, as apparent from the appearance photographs (samples R1 and R5) shown in FIG. 2, these sintered bodies were free from surface roughness and shape deformation, and maintained the shape during molding.

  On the other hand, when a base iron powder other than SKH is used, a dense sintered body cannot be obtained with graphite powder: 0.4 to 0.6%, and graphite powder: addition of 1.5% or more is required for the densification. Was necessary. Further, as apparent from the appearance photographs (samples R9 and R10) shown in FIG. 2, it was also found that the sintered body of graphite powder: 1.5% or more causes surface roughness and shape collapse.

(2) Bonding strength As is clear from Table 3, all samples using SKH or SKH2 for the outer, regardless of the type of base iron powder used for the inner, molding pressure, sintering atmosphere of the assembly, etc. It was found that sufficient bonding strength was obtained without breaking (separating) at the bonding interface. FIG. 3A shows an example (sample 1) in which the bonding strength is sufficient and the base material is broken by the extraction test.

  Conversely, any sample using powder other than SKH or SKH2 for the outer layer has insufficient bonding strength. As shown in an example (sample C2) in FIG. Separated and destroyed.

(3) Graphite powder and sintering atmosphere As can be seen from samples 1 to 12 shown in Table 3, when the amount of graphite powder on the outer side is small, the sample sintered in a nitrogen atmosphere is sintered in a vacuum atmosphere. It was found that the bonding strength is likely to be higher than that of the prepared sample. This is presumably because the carbide forming element contained in SKH or its carbide contributed to Fe-C liquid phase formation and C diffusion by acting with nitrogen in the atmosphere.

  On the other hand, as can be seen from Samples 13 to 18 or Samples 31 to 38 shown in Table 3, it has also been found that when the amount of graphite powder on the outer side is relatively large, the sintering atmosphere hardly affects the bonding strength.

(4) Inner As can be seen from samples 22 and 23 shown in Table 3, when SKH is used for both the outer and inner, it is sufficient regardless of the amount of graphite powder added, the molding pressure on the inner side, the sintering atmosphere, etc. It was also found that a sufficient bonding strength was ensured.

Example 2 Joining Molten Steel and Molded Body
<Production and measurement of sample>
A sample was produced in which the inner made of the sintered body used in Example 1 was changed to an inner machined from molten steel (JIS SCM435). The outer diameter (R1) of the inner was changed as shown in Table 4. Other than that, the sample was manufactured, measured and observed in the same manner as in Example 1. The production conditions, bonding strength, etc. of each sample are also shown in Table 4. Table 4 also shows the dimensional ratio (R1 / R2) in addition to the dimensional difference (ΔR) between the outer (R2) and the inner (R1).

  Incidentally, the molten steel (SCM435) used for the inner is an alloy steel for machine structure, and its main component composition (mass%) is SCM435: Fe- (0.33-0.38)% C- (0.15-0.35)% Si- (0.6-0.9)% Mn- (0.9-1.2)% Cr- (0.15-0.3)% Mo.

<Evaluation>
(1) Joining strength As is clear from Table 4, it was confirmed that if the dimensional difference or the dimensional ratio was appropriately set, the outer made of the sintered material of SKH was strongly joined to the inner from the melted material. Specifically, in order to ensure high bonding strength, for example, the dimensional ratio may be 88% or more, further 89% or more. Speaking with respect to the standard dimension (φ14 mm), for example, the dimensional difference may be 1.6 mm or less.

  FIG. 4 shows the metal structure of the sample 23 after the extraction test, in which the vicinity of the bonding interface was observed with an optical microscope. As is clear from FIG. 4, no cracks or the like were observed in the vicinity of the bonding interface, and it was confirmed that the bonding state of the outer and inner was homogeneous.

(2) Deformation of outer The appearance of each sample shown in Table 4 after sintered joining is shown in FIG. Moreover, the outer diameter change from the center part of an outer part to an edge part was shown in FIG. As is clear from FIGS. 5 and 6, it was found that the outer dimension is more easily deformed into a drum shape as the dimensional difference becomes smaller (as the dimensional ratio becomes larger). From this viewpoint, when at least the inner is made of molten steel, the dimensional ratio is preferably 93% or less, and more preferably 91% or less. With respect to the reference dimension (φ14 mm), for example, it is preferable that the dimensional difference is 1.1 mm or more, further 1.3 mm or more.

  Incidentally, the reason why the outer becomes easier to deform into a drum shape as the dimensional difference becomes smaller (as the dimensional ratio becomes larger) is presumed as follows. First, during the sintering (joining) step, the outer inner peripheral surface and the inner outer peripheral surface come into contact, and carbon diffuses (moves) from the outer inner peripheral surface side to the inner outer peripheral surface side. As a result, in the vicinity of the inner peripheral surface where the carbon content has increased, liquid phase is likely to occur and shrinkage is likely to occur. The outer side of the outer side tends to have a lower density at the center side in the compression axis direction than the both end sides at the time of molding. In this way, it is considered that the outer has a contraction amount larger at the center side in the axial direction than both ends, and deforms into a drum shape.

Claims (16)

A fitting step of obtaining an assembly in which a second annular molded body formed by press-molding a second raw material powder containing a second iron-based powder is fitted on the outer peripheral side of the first iron base;
The assembly is heated so that the first iron base member made of the first iron base and the second iron base member made of the second sintered body obtained by sintering the second molded body are in a closed annular joint interface. And a sintered joining step for obtaining a joined iron base member joined at a portion,
The ferric base powder is 100% by mass (hereinafter simply referred to as “%”) of the entire ferric base powder.
C: 0.5-1.8%
Carbide forming elements consisting of W and / or V (total): 6-16%,
The manufacturing method of the joining iron base member containing.   2. The method for producing a bonded iron base member according to claim 1, wherein the second raw material powder contains 95% by mass or more of the second iron base powder with respect to the entire second raw material powder.   3. The method for manufacturing a bonded iron base member according to claim 2, wherein the second raw material powder is P: less than 0.1% with the entire second raw material powder being 100 mass% (simply referred to as “%”).   The ferric-based powder further includes one or more of Si: 0.1 to 1%, Mn: 0.1 to 0.7%, or Co: 0.1 to 12%. A method for producing a bonded iron base member according to claim 1.   The said 2nd raw material powder is a manufacturing method of the joining iron base member in any one of Claims 1-4 containing the carbon source powder different from the said 2nd iron base powder. The carbon source powder is a graphite powder,
The method for producing a bonded iron base member according to claim 5, wherein the graphite powder is contained in an amount of 0.1 to 1 mass% with respect to the entire second raw material powder.   The method for manufacturing a bonded iron base member according to any one of claims 1 to 6, wherein the inserting step is a step of fitting the second molded body into the gap with the first iron base.   The said insertion process is a manufacturing method of the joining iron base member of Claim 7 which sets the ratio of the outer dimension of the said 1st iron base | substrate with respect to the inner dimension of the said 2nd molded object to 88 to 93%.   The said 2nd molded object is a manufacturing method of the joining iron base member in any one of 1-8 formed by pressurizing the said 2nd raw material powder at 350-1000 MPa.   The said sintered joining process is a process of heating the said assembly at 1140-1350 degreeC, The manufacturing method of the joining iron base member in any one of Claims 1-9.   The method for manufacturing a bonded iron base member according to any one of claims 1 to 10, wherein the sintered bonding step is a step of heating the assembly in a nitrogen atmosphere. A first iron base member;
A closed annular second iron base member joined to the outer peripheral surface of the first iron base member;
A bonded iron base member comprising:
The second ferrous base member is composed of 100% by mass (hereinafter simply referred to as “%”) of the second ferrous base member, and C: 0.5 to 2.5%, and a carbide composed of W and / or V. Forming element: A bonded iron base member made of a second sintered body containing 6 to 16%.   The joined iron base member according to claim 12, wherein the second sintered body is further P: less than 0.1%.   The second sintered body further includes at least one of Si: 0.1 to 1%, Mn: 0.1 to 0.7%, or Co: 0.1 to 12%. Bonded iron base member. 15. The second sintered body has a relative density (100 × ρ / ρ ₀ ) that is a ratio of a bulk density (ρ) to a true density (ρ ₀ ) of 97% or more. Bonded iron base member.   The bonded iron base member according to claim 12, wherein the first iron base member is made of a sintered material or a melted material.