WO2016072244A1 - Stainless steel material for diffusion bonding - Google Patents

Stainless steel material for diffusion bonding Download PDF

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Publication number
WO2016072244A1
WO2016072244A1 PCT/JP2015/079342 JP2015079342W WO2016072244A1 WO 2016072244 A1 WO2016072244 A1 WO 2016072244A1 JP 2015079342 W JP2015079342 W JP 2015079342W WO 2016072244 A1 WO2016072244 A1 WO 2016072244A1
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Prior art keywords
stainless steel
less
diffusion bonding
phase
steel material
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PCT/JP2015/079342
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French (fr)
Japanese (ja)
Inventor
淳史 須釜
景岡　一幸
芳明 堀
一成 今川
学 奥
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日新製鋼株式会社
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Application filed by 日新製鋼株式会社 filed Critical 日新製鋼株式会社
Priority to ES15857850T priority Critical patent/ES2886446T3/en
Priority to EP15857850.0A priority patent/EP3216888B1/en
Priority to CN201580056844.0A priority patent/CN107002189B/en
Priority to SG11201703499XA priority patent/SG11201703499XA/en
Priority to KR1020177015017A priority patent/KR102384698B1/en
Priority to US15/523,882 priority patent/US20170321311A1/en
Publication of WO2016072244A1 publication Critical patent/WO2016072244A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a duplex stainless steel material used for a molded product to be diffusion bonded.
  • Stainless steel diffusion bonding products assembled by diffusion bonding are applied to various uses such as heat exchangers, machine parts, fuel cell parts, household appliance parts, plant parts, decorative component members, and building materials.
  • the diffusion bonding method includes “insert material insertion method” in which an insert material is inserted into the bonding interface and bonded by solid phase diffusion or liquid phase diffusion, and “directly” in which the surfaces of both stainless steel materials are in direct contact with each other. Law ".
  • the insert material insertion method is advantageous in that reliable diffusion bonding can be realized relatively easily.
  • this method since this method uses an insert material, it is disadvantageous compared to the direct method in that the cost increases and the joint portion is formed of a different type of metal from the base material, which may reduce the corrosion resistance. It becomes.
  • the direct method is generally difficult to obtain sufficient bonding strength as compared with the insert material insertion method.
  • this direct method since this direct method has the possibility of being advantageous in terms of reducing manufacturing costs, various methods have been studied. For example, in Patent Document 1, the amount of S in stainless steel is 0.01% by weight or less and diffusion bonding is performed in a non-oxidizing atmosphere at a predetermined temperature to avoid deformation of the material and A technique for improving diffusion bonding is disclosed.
  • Patent Document 2 discloses a method of using a stainless steel foil material having irregularities on the surface by pickling treatment.
  • Patent Document 3 discloses a method in which stainless steel with a suppressed Al content is used as a material to be joined so that an alumina coating that becomes an impediment to diffusion bonding is difficult to form during diffusion bonding.
  • Patent Document 4 discloses a method of promoting diffusion using a stainless steel foil that has been deformed by cold working.
  • Patent Documents 5 and 6 describe ferritic stainless steel for direct diffusion bonding with an optimized component composition.
  • Patent Document 7 a method for manufacturing a diffusion bonded article by the direct method, which can be carried out with a work load equivalent to that of the insert material insertion method without applying heating or high surface pressure.
  • Patent Documents 9 and 10 a method for manufacturing a diffusion bonded article by the direct method, which can be carried out with a work load equivalent to that of the insert material insertion method without applying heating or high surface pressure.
  • Patent Documents 9 and 10 a method for manufacturing a diffusion bonded article by the direct method, which can be carried out with a work load equivalent to that of the insert material insertion method without applying heating or high surface pressure.
  • Patent Documents 9 and 10 a method for manufacturing a diffusion bonded article by the direct method, which can be carried out with a work load equivalent to that of the insert material insertion method without applying heating or high surface pressure.
  • Patent Documents 9 and 10 a method for controlling the surface roughness before joining of the used stainless steel material in order to ensure good joining properties. Therefore, further improvement in bondability is required for stainless steel materials used for diffusion bonding
  • An object of the present invention is to provide a stainless steel material that is not affected by the degree of surface roughness and that is suitable for a diffusion bonding molded product having further improved diffusion bonding properties.
  • the present inventors have controlled the average crystal grain size, ⁇ max amount, and creep elongation before diffusion bonding for a duplex stainless steel material having a duplex structure consisting of at least two of a ferrite phase, a martensite phase, and an austenite phase. As a result, it was found that good diffusion bondability was obtained without being affected by the surface roughness of the steel material, and the present invention was completed as a stainless steel material for diffusion bonding. Specifically, the present invention provides the following.
  • the present invention is a dual-phase stainless steel material in which the metal structure before diffusion bonding has a multi-phase structure composed of at least two of a ferrite phase, a martensite phase, or an austenite phase, and the average of the multi-phase structure
  • the crystal grain size is 20 ⁇ m or less
  • ⁇ max represented by the following formula (a) is 10 to 90
  • the creep elongation is 0.2% or more when a 1.0 MPa load is applied at 1000 ° C. for 0.5 h. It is a stainless steel material for diffusion bonding.
  • ⁇ max 420C-11.5Si + 7Mn + 23Ni-11.5Cr-12Mo + 9Cu-49Ti-47Nb-52Al + 470N + 189 (a) where the element symbol in the above formula (a) means the content (mass%) of each element. To do.
  • the stainless steel material is mass%, C: 0.2% or less, Si: 1.0% or less, Mn: 3.0% or less, P: 0.05% or less, S: 0.03% or less, Ni: 10.0% or less, Cr: 10.0 to 30.0%, N: 0.3% or less, Ti: 0.15% or less, Al: 0.15% or less
  • the balance is the stainless steel material for diffusion bonding according to (1), wherein the balance is made of Fe and inevitable impurities, and the total amount of Ti and Al is 0.15% or less.
  • the stainless steel material further includes, in mass%, Nb: 4.0% or less, Mo: 0.01 to 4.0%, Cu: 0.01 to 3.0%, V: The stainless steel material for diffusion bonding according to (1) or (2) above, comprising one or more of 0.03 to 0.15%.
  • the stainless steel material for diffusion bonding according to any one of the above (1) to (3), wherein the stainless steel material further contains B: 0.0003 to 0.01% by mass%. It is.
  • a duplex stainless steel having a duplex structure composed of at least two of a ferrite phase, a martensite phase, and an austenite phase is obtained by creeping at an average crystal grain size and ⁇ max before diffusion bonding, and at a bonding temperature.
  • a stainless steel material having excellent diffusion bonding properties is provided, and thus a diffusion bonding molded product exhibiting a good bonding interface is provided.
  • a diffusion bonded molded article with improved diffusion bonding properties can be obtained.
  • diffusion bonding by a direct method of stainless steel material is (i) a process in which the unevenness of the joint surface is deformed and brought into close contact, and the joint area of the joined part increases, and (ii) joining at the tight part
  • the process is considered to be completed by three processes: a process in which the surface oxide film of the former steel material disappears and (iii) a process in which the residual gas in the void which is an unjoined part reacts with the base material. ing.
  • the inventors have so far focused on the process of (ii) above to regulate the base material component, the component contained in the passive film, and the surface roughness of the joint surface, and the industrial productivity becomes a bottleneck.
  • the step (ii) is controlled, it may be difficult to ensure industrially stable bondability, and in order to obtain stable bondability in consideration of the step (i).
  • Much research has been conducted on steel materials. As a result, it has been found that when the stainless steel used for diffusion bonding is a dual phase stainless steel having a double phase structure, it is extremely effective to make the crystal grain size before diffusion bonding fine.
  • Multiphase structure Stainless steel is generally classified into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and the like based on the metal structure at room temperature.
  • the “multiphase structure” of the present invention has a metal structure composed of at least two of a ferrite phase, a martensite phase, and an austenite phase.
  • the “multi-phase stainless steel material” of the present invention has such a multi-phase structure, and refers to a steel having an austenite + ferrite two-phase structure in the joining temperature range.
  • Such a two-phase stainless steel may include a stainless steel classified as a ferritic stainless steel or a martensitic stainless steel.
  • the stainless steel material used for diffusion bonding has a multiphase structure composed of at least two types of ferrite phase, martensite phase, and austenite phase.
  • Use duplex stainless steel in this stainless steel, in the temperature range where diffusion bonding proceeds, a part of the ferrite phase and the martensite phase is transformed into the austenite phase, and a two-phase structure of austenite phase + ferrite phase is obtained.
  • a fine structure is maintained, and creep deformation estimated to be caused by grain boundary sliding can easily occur.
  • easy deformation is promoted in the concavo-convex portion of the bonding surface, and the bonding area of the bonded portion is increased, thereby enabling diffusion bonding by a direct method at a low temperature and low surface pressure.
  • the duplex stainless steel material of the present invention can be used for both or one of the stainless steel materials that are brought into direct contact and integrated by diffusion bonding.
  • the stainless steel material of the present invention can be applied, other two-phase steel types, austenitic steel types that become austenite single phase in the heating temperature range of diffusion bonding, ferritic steel types that become ferrite single phase Etc. can be applied.
  • the component elements other than Ti and Al are not particularly required from the viewpoint of diffusion bonding properties, and various component compositions can be adopted depending on the application.
  • the present invention targets an austenite + ferrite two-phase structure in the temperature range where diffusion bonding proceeds, it is necessary to employ a steel having a component composition satisfying ⁇ max of 10 to 90 represented by the following formula (a). is there.
  • Specific examples of the component composition range include the following.
  • Nb 4.0% or less
  • Mo 0.01-4.0%
  • Cu 0.01-3.0%
  • V 0.03-0.15%
  • B 0.0003 to 0.01% by mass%.
  • the C improves the strength and hardness of steel by solid solution strengthening.
  • the C content is preferably 0.2% by mass or less, and more preferably 0.08% by mass or less.
  • Si is an element used for deoxidation of steel. On the other hand, if the Si content is excessive, the toughness and workability of steel are reduced. In addition, a strong surface oxide film is formed to inhibit diffusion bonding. Therefore, the Si content is preferably 1.0% by mass or less, and more preferably 0.6% by mass or less.
  • Mn is an element that improves high-temperature oxidation characteristics. On the other hand, if the Mn content is excessive, the steel is work-hardened and the cold workability of the steel is reduced. Therefore, the Mn content is preferably 3.0% by mass or less.
  • the P content is preferably 0.05% by mass or less, and more preferably 0.03% by mass or less.
  • the S content is preferably 0.03% by mass or less.
  • Ni is an austenite-forming element and has the effect of improving the corrosion resistance of steel in a reducing acid environment.
  • the Ni content is excessive, the austenite phase becomes stable and the growth of ferrite crystals cannot be suppressed. Therefore, a stable austenite single phase is formed to suppress the growth of ferrite crystals. Therefore, the Ni content is preferably 10.0% or less.
  • Cr is an element that forms a passive film and imparts corrosion resistance. If the Cr content is less than 30.0% by mass, the effect of imparting corrosion resistance is not sufficient. When it exceeds 10.0 mass%, workability will fall. Therefore, the Cr content is preferably 10.0 to 30.0% by mass.
  • N is an unavoidable impurity and is preferably 0.3% by mass or less in order to deteriorate the cold workability.
  • Ti has an effect of fixing C and N, and is therefore an effective element for improving corrosion resistance and workability.
  • Al is often added as a deoxidizer.
  • Ti and Al are easily oxidizable elements, Ti oxide and Al oxide contained in the oxide film on the surface of the steel material are difficult to be reduced in the heat treatment of vacuum diffusion bonding. Therefore, if these Ti oxides and Al oxides are large, the progress of the process (ii) may be hindered during diffusion bonding, so the Ti content is 0.15% by mass or less, and the Al content is 0.15 mass% or less is preferable, and 0.05 mass% is more preferable.
  • the total content of Ti and Al is preferably 0.15% by mass or less, and more preferably 0.05% by mass or less.
  • Nb is an element that forms carbides or carbonitrides and refines the crystal grains of steel to increase the toughness.
  • the Nb content is preferably 4.0% by mass or less.
  • Mo is an element that has the effect of improving the corrosion resistance without reducing the strength. If the Mo content is excessive, the workability of the steel is reduced, so the Mo content is preferably 0.01 to 4.0% by mass.
  • Cu is an element that is effective in improving the corrosion resistance and has an action of generating a ferrite phase.
  • the Cu content is preferably 0.01 to 3.0% by mass.
  • V is an element that contributes to improving the workability and toughness of steel by fixing solute C as carbide.
  • the V content is preferably 0.03 to 0.15%.
  • B is an element that contributes to improvement of corrosion resistance and workability by fixing N.
  • the B element is contained excessively, the hot workability of the steel is lowered, so the B content is preferably 0.0003 to 0.01%.
  • ⁇ max 420C-11.5Si + 7Mn + 23Ni-11.5Cr-12Mo + 9Cu-49Ti-47Nb-52Al + 470N + 1189 (a) where, in the above equation (a), the element symbols such as C and Si are the contents of each element. (Mass%) is meant.
  • ⁇ max is an index representing the amount (volume%) of the austenite phase that is generated when heated and held at about 1100 ° C.
  • ⁇ max is 100 or more, it can be regarded as a steel type that becomes an austenite single phase.
  • ⁇ max is 0 or less, it can be regarded as a steel type that becomes a ferrite single phase.
  • ⁇ max is 10 to 90, the two phases become austenite + ferrite in the temperature range where diffusion bonding proceeds, and these two phases suppress the growth of crystal grains at high temperatures. Therefore, it is effective for obtaining a fine crystal structure. More preferably, ⁇ max is 50-80.
  • the process (i) can be rapidly advanced. Therefore, the average crystal grain size before bonding is preferably 20 ⁇ m or less, and more preferably 10 ⁇ m or less.
  • the surface of the stainless steel material is preferably smooth, and the surface roughness Ra is preferably 0.3 ⁇ m or less.
  • the stainless steel material of the present invention provides a diffusion bonded product with good bondability by performing vacuum diffusion bonding by a direct method.
  • a specific diffusion bonding treatment for example, in a state of direct contact at a contact surface pressure of 0.1 to 1.0 MPa, a pressure of 1.0 ⁇ 10 ⁇ 2 Pa or less, preferably 1.0 ⁇ 10 ⁇ Diffusion bonding can be advanced by heating and maintaining at 900 to 1100 ° C. in a furnace having a pressure of 3 Pa or less and a dew point of ⁇ 40 ° C. or less.
  • the holding time can be adjusted in the range of 0.5 to 3 h.
  • the stainless steel having the chemical composition shown in Table 1 was melted by 30 kg of vacuum melting, and the obtained steel ingot was forged into a 30 mm thick plate, followed by hot rolling at 1230 ° C. for 2 hours and 3.0 mm. A thick hot-rolled sheet was obtained. Subsequently, annealing, pickling, and cold rolling were performed to obtain a cold-rolled sheet having a thickness of 1.0 mm. Then, the cold-rolled sheet was annealed as described later to produce a cold-rolled sheet, which was used as a test material.
  • Table 1 shows a plurality of steel materials.
  • the metal structure before diffusion bonding is a ferrite + martensite duplex steel ( ⁇ + M phase).
  • the metal structure before diffusion bonding is a ferrite + austenite dual phase steel ( ⁇ + ⁇ phase).
  • the metal structure before diffusion bonding is a ferritic single phase steel ( ⁇ phase).
  • the metal structure before diffusion bonding is an austenitic single phase steel ( ⁇ phase).
  • M-1 steel is martensitic single phase steel (M phase) before diffusion bonding.
  • Each steel plate was obtained by changing the annealing temperature after cold rolling between 900 ° C. and 1200 ° C. to obtain test materials having different average crystal grain sizes.
  • the test material from which surface roughness Ra differs was obtained by changing the finishing process of a cold-rolled annealing board using some steel plates.
  • the average crystal grain size ( ⁇ m) of the steel sheet before diffusion bonding was measured by a quadrature method as shown below.
  • the metal structure of the plate thickness cross section parallel to the cold rolling direction was observed at 1 mm 2 or more continuously, and the number of crystal grains contained in the unit area was calculated using the quadrature method.
  • the average area per crystal grain was calculated
  • Creep elongation was measured by the method shown below.
  • a JIS 13B test piece was cut out from each steel plate, and a hole of ⁇ 5 mm was formed in the center of one gripping part.
  • the test piece was attached to a high-temperature tensile tester so that the test piece was marked with a mark of 50 mm between the marks, so that the grip portion having a hole was positioned downward.
  • the temperature between the gauge points is raised to 1000 ° C., and after soaking for 15 minutes at that temperature, a wire made of SUS310S having a weight calculated so as to apply a stress of 1.0 MPa is attached to the grip portion. Attached to the hole and held for 0.5 h. Thereafter, the SUS310S wire was removed from the test piece, and further cooled to room temperature by air cooling.
  • the length L between the gauge points was measured, and (L-50) / 50 ⁇ 100 was calculated as the creep elongation (%).
  • the jig and the laminate are inserted into a vacuum furnace and evacuated to obtain an initial vacuum of 1.0 ⁇ 10 ⁇ 3 to 1.0 ⁇ 10 ⁇ 4 Pa, and then raised to 1000 ° C. in about 1 h. Warm and hold at that temperature for 2 h. Then, it moved to the cooling chamber and cooled. The said vacuum degree was maintained to 900 degreeC after that, Ar gas was introduce
  • Thickness measurements were made at points. The probe diameter was 1.5 mm. If the measured thickness at a given measurement point indicates the total thickness of the two steel materials, it is assumed that both steel materials are integrated by diffusion of atoms at the interface position of both steel materials corresponding to the measurement point. Can do. On the other hand, when the plate thickness measurement value is different from the total plate thickness of both steel materials, it can be considered that an unjoined portion (defect) exists at the interface position of both steel materials corresponding to the measurement point. When the correspondence between the cross-sectional structure of the laminate after the heat treatment and the measurement results obtained by this measurement method was examined, the number of measurement points at which the measurement results were the total plate thickness of both steel materials was 49 in total.
  • Table 2 shows the average grain size and ⁇ max, surface roughness, creep elongation, and bondability evaluation results after cold rolling annealing of each steel.
  • Examples 1 to 6 of the present invention have a bonding rate of 90% or more, and exhibit good diffusion bonding properties even at a relatively low temperature of 1000 ° C. and a low surface pressure of 0.1 MPa. It was. Inventive Examples 1 to 6 showed good diffusion bonding properties regardless of the degree of the surface roughness Ra, and no influence of the surface roughness was observed. In the multiphase stainless steel material having the configuration of the present invention, the diffusion bondability does not decrease even when the surface roughness is increased, so that it can be understood that the diffusion bondability is not restricted by the surface property of the steel material.
  • Comparative Examples 1 to 10 since the average crystal grain size, ⁇ max, and creep elongation were out of the scope of the present invention, the deformation of the concavo-convex portion of the joint surface in the two-phase high temperature region was small, and The bonding area did not increase. Therefore, most of the joining ratios were slightly poor or poor at less than 80%. Further, regarding the ferrite single phase steels of Comparative Examples 5 to 7 and the austenite single phase steels of Comparative Examples 8 to 9, according to the change in the joining rate due to the surface roughness Ra, Comparative Example 7 and Comparative Example with extremely small surface roughness No. 9 showed a bonding rate of 90% or more.

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
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Abstract

Provided is a stainless steel material suitable for diffusion bonded moldings in which diffusion bondability has been further improved without being affected by the extent of surface roughness. The present invention is a stainless steel material for diffusion bonding in which the metal structure before diffusion bonding has a multi-phase structure obtained from two or more of a ferrite phase, a martensite phase and an austenite phase, wherein: the mean crystal grain diameter in the multi-phase structure is not more than 20 µm; γmax represented by formula (a) is 10-90; and creep elongation when a 1.0 MPa load is applied at 1000°C for 0.5 h is at least 0.2%. γmax=420C-11.5Si+7Mn+23Ni-11.5Cr-12Mo+9Cu-49Ti-47Nb-52Al+470N+189 ∙∙∙ Formula (a) The element notations in formula (a) represent the contents (mass%) of the respective elements.

Description

拡散接合用ステンレス鋼材Stainless steel for diffusion bonding
　　本発明は、拡散接合される成型品に用いられる複相系ステンレス鋼材に関する。 The present invention relates to a duplex stainless steel material used for a molded product to be diffusion bonded.
　ステンレス鋼材同士の接合方法の一つに拡散接合がある。拡散接合によって組み立てられたステンレス鋼拡散接合製品は、熱交換器、機械部品、燃料電池部品、家電製品部品、プラント部品、装飾品構成部材、建材など、種々の用途に適用されている。拡散接合方法には、インサート材を接合界面に挿入し、固相拡散または液相拡散により接合する「インサート材挿入法」と、双方のステンレス鋼材の表面同士を直接接触させて拡散接合する「直接法」がある。 One method of joining stainless steel materials is diffusion bonding. Stainless steel diffusion bonding products assembled by diffusion bonding are applied to various uses such as heat exchangers, machine parts, fuel cell parts, household appliance parts, plant parts, decorative component members, and building materials. The diffusion bonding method includes “insert material insertion method” in which an insert material is inserted into the bonding interface and bonded by solid phase diffusion or liquid phase diffusion, and “directly” in which the surfaces of both stainless steel materials are in direct contact with each other. Law ".
　前記インサート材挿入法は、確実な拡散接合を比較的簡便に実現できる点で有利である。しかし、この方法は、インサート材を用いるので、コストが増大する点や、接合部分が母材と異なる種類の金属で形成されるので、耐食性が低下する場合がある点で、直接法よりも不利となる。
　他方、前記直接法は、インサート材挿入法に比べて、一般に十分な接合強度を得ることが難しいと言われている。しかし、この直接法は、製造コストを低減できる面で有利となる可能性を含んでいることから、種々の方法が検討されてきた。
　例えば、特許文献１には、ステンレス鋼中のＳ量を０．０１重量％以下にするとともに、所定温度の非酸化性雰囲気中で拡散接合することにより、材料の変形を回避してステンレス鋼材の拡散接合性を向上させた技術が開示されている。特許文献２には、酸洗処理によって表面に凹凸が付与されたステンレス鋼箔材を使用する方法が開示されている。特許文献３には、拡散接合の阻害要因となるアルミナ皮膜が拡散接合時に生成しにくいように、Ａｌ含有量を抑制したステンレス鋼を被接合材として用いる方法が開示されている。特許文献４には、冷間加工によって変形を付与されたステンレス鋼箔を用いて、拡散を促進させる方法が開示されている。特許文献５、６には、成分組成を適正化した直接拡散接合用のフェライト系ステンレス鋼が記載されている。 The insert material insertion method is advantageous in that reliable diffusion bonding can be realized relatively easily. However, since this method uses an insert material, it is disadvantageous compared to the direct method in that the cost increases and the joint portion is formed of a different type of metal from the base material, which may reduce the corrosion resistance. It becomes.
On the other hand, it is said that the direct method is generally difficult to obtain sufficient bonding strength as compared with the insert material insertion method. However, since this direct method has the possibility of being advantageous in terms of reducing manufacturing costs, various methods have been studied.
For example, in Patent Document 1, the amount of S in stainless steel is 0.01% by weight or less and diffusion bonding is performed in a non-oxidizing atmosphere at a predetermined temperature to avoid deformation of the material and A technique for improving diffusion bonding is disclosed. Patent Document 2 discloses a method of using a stainless steel foil material having irregularities on the surface by pickling treatment. Patent Document 3 discloses a method in which stainless steel with a suppressed Al content is used as a material to be joined so that an alumina coating that becomes an impediment to diffusion bonding is difficult to form during diffusion bonding. Patent Document 4 discloses a method of promoting diffusion using a stainless steel foil that has been deformed by cold working. Patent Documents 5 and 6 describe ferritic stainless steel for direct diffusion bonding with an optimized component composition.
特開昭６２－１９９２７７号公報JP 62-199277 A 特開平２－２６１５４８号公報JP-A-2-261548 特開平７－２１３９１８号公報Japanese Patent Laid-Open No. 7-213918 特開平９－２７９３１０号公報JP-A-9-279310 特開平９－９９２１８号公報JP-A-9-99218 特開２０００－３０３１５０号公報JP 2000-303150 A 特開２０１３－１０３２７１号公報JP 2013-103271 A 特開２０１３－１７３１８１号公報JP 2013-173181 A 特開２０１３－２０４１４９号公報JP 2013-204149 A 特開２０１３－２０４１５０号公報JP2013-204150A
　上述した接合技術などにより、ステンレス鋼材の拡散接合は、直接法を用いても実施可能となった。しかし、工業的には、直接法は、ステンレス鋼材の拡散接合方法の主流として定着するには至っていない。その主たる理由は、接合強度や密着性などの接合部における信頼性を確保すること、接合装置や接合時間などの製造上の負荷を抑制すること、という２つ課題の両立が難しい点にある。従来の技術的知見によると、直接法で製造される接合部が十分な信頼性を確保するには、接合温度を１１００℃を超える高温にする工程、または、ホットプレスやＨＩＰ等により高い面圧を付与する工程などの製造負荷の大きい工程を採用する必要があり、それによるコスト増大が避けられなかった。直接法によるステンレス鋼材の拡散接合を、通常のインサート材挿入法と同等の作業負荷で実施しようとすると、接合部の信頼性を十分に確保することは難しいのが現状である。 Due to the joining technique described above, diffusion joining of stainless steel materials can be carried out using the direct method. However, industrially, the direct method has not been established as the mainstream of the diffusion bonding method of stainless steel materials. The main reason is that it is difficult to satisfy both of the two problems of ensuring the reliability of the bonded portion such as bonding strength and adhesion and suppressing the manufacturing load such as the bonding apparatus and bonding time. According to the conventional technical knowledge, in order to ensure sufficient reliability of the joint manufactured by the direct method, a high surface pressure by a process of increasing the bonding temperature to over 1100 ° C. or by hot pressing, HIP, or the like Therefore, it is necessary to adopt a process with a large production load such as a process for imparting, and an increase in cost is unavoidable. If diffusion welding of a stainless steel material by the direct method is performed with a work load equivalent to that of a normal insert material insertion method, it is difficult to sufficiently secure the reliability of the joint.
　そこで、拡散接合時において、フェライト相がオーステナイト相へ変態するときの駆動力を利用すること（特許文献７）や、結晶粒成長の駆動力を利用すること（特許文献８）により、特別な高温加熱や高い面圧を付与することなく、インサート材挿入法と同等の作業負荷で実施できる、直接法による拡散接合品の製造方法が提案された。また、拡散接合に供するステンレス鋼材の表面酸化物をできるだけ低減して拡散接合性を高める方法（特許文献９、１０）が提案された。これらの方法は、良好な接合性を確保するためには、使用されるステンレス鋼材の接合前の表面粗さを規制する必要がある。そこで、拡散接合製品に使用されるステンレス鋼材においては、一層の接合性の向上が求められている。 Therefore, at the time of diffusion bonding, by using the driving force when the ferrite phase is transformed to the austenite phase (Patent Document 7) or by using the driving force of crystal grain growth (Patent Document 8), a special high temperature There has been proposed a method for manufacturing a diffusion bonded article by the direct method, which can be carried out with a work load equivalent to that of the insert material insertion method without applying heating or high surface pressure. In addition, a method (Patent Documents 9 and 10) has been proposed in which the surface oxide of a stainless steel material used for diffusion bonding is reduced as much as possible to enhance diffusion bonding properties. In these methods, it is necessary to regulate the surface roughness before joining of the used stainless steel material in order to ensure good joining properties. Therefore, further improvement in bondability is required for stainless steel materials used for diffusion bonding products.
　本発明は、表面粗さの程度に影響されず、かつ、拡散接合性をさらに向上させた拡散接合成型品に適したステンレス鋼材を提供することを目的とする。 An object of the present invention is to provide a stainless steel material that is not affected by the degree of surface roughness and that is suitable for a diffusion bonding molded product having further improved diffusion bonding properties.
　本発明者らは、フェライト相、マルテンサイト相、オーステナイト相の少なくとも２種以上からなる複相組織を有する複相系ステンレス鋼材について、拡散接合前の平均結晶粒径、γｍａｘ量、クリープ伸びを制御することによって、鋼材の表面粗さに影響されることなく、良好な拡散接合性が得られることを見出し、拡散接合用ステンレス鋼材として本発明を完成するに至った。具体的には、本発明は、以下のようなものを提供する。 The present inventors have controlled the average crystal grain size, γmax amount, and creep elongation before diffusion bonding for a duplex stainless steel material having a duplex structure consisting of at least two of a ferrite phase, a martensite phase, and an austenite phase. As a result, it was found that good diffusion bondability was obtained without being affected by the surface roughness of the steel material, and the present invention was completed as a stainless steel material for diffusion bonding. Specifically, the present invention provides the following.
　（１）　本発明は、拡散接合前の金属組織がフェライト相、マルテンサイト相またはオーステナイト相の少なくとも２種以上からなる複相組織を有する複相系ステンレス鋼材であって、前記複相組織の平均結晶粒径が２０μｍ以下であり、下記（ａ）式で示されるγｍａｘが１０～９０であり、１．０ＭＰａの負荷を１０００℃、０．５ｈで加えたときのクリープ伸びが０．２％以上である、拡散接合用ステンレス鋼材である。
　γｍａｘ＝４２０Ｃ－１１．５Ｓｉ＋７Ｍｎ＋２３Ｎｉ－１１．５Ｃｒ－１２Ｍｏ＋９Ｃｕ－４９Ｔｉ－４７Ｎｂ－５２Ａｌ＋４７０Ｎ＋１８９　・・・（ａ）式
　ここで、上記（ａ）式における元素記号は、各元素の含有量（質量％）を意味する。 (1) The present invention is a dual-phase stainless steel material in which the metal structure before diffusion bonding has a multi-phase structure composed of at least two of a ferrite phase, a martensite phase, or an austenite phase, and the average of the multi-phase structure The crystal grain size is 20 μm or less, γmax represented by the following formula (a) is 10 to 90, and the creep elongation is 0.2% or more when a 1.0 MPa load is applied at 1000 ° C. for 0.5 h. It is a stainless steel material for diffusion bonding.
γmax = 420C-11.5Si + 7Mn + 23Ni-11.5Cr-12Mo + 9Cu-49Ti-47Nb-52Al + 470N + 189 (a) where the element symbol in the above formula (a) means the content (mass%) of each element. To do.
　（２）　本発明は、前記ステンレス鋼材は、質量％で、Ｃ：０．２％以下、Ｓｉ：１．０％以下、Ｍｎ：３．０％以下、Ｐ：０．０５％以下、Ｓ：０．０３％以下、Ｎｉ：１０．０％以下、Ｃｒ：１０．０～３０．０％、Ｎ：０．３％以下、Ｔｉ：０．１５％以下、Ａｌ：０．１５％以下を含み、残部がＦｅおよび不可避的不純物からなり、ＴｉとＡｌの合計量が０．１５％以下である、上記（１）に記載の拡散接合用ステンレス鋼材である。 (2) In the present invention, the stainless steel material is mass%, C: 0.2% or less, Si: 1.0% or less, Mn: 3.0% or less, P: 0.05% or less, S: 0.03% or less, Ni: 10.0% or less, Cr: 10.0 to 30.0%, N: 0.3% or less, Ti: 0.15% or less, Al: 0.15% or less The balance is the stainless steel material for diffusion bonding according to (1), wherein the balance is made of Fe and inevitable impurities, and the total amount of Ti and Al is 0.15% or less.
　（３）　本発明は、前記ステンレス鋼材は、さらに、質量％で、Ｎｂ：４．０％以下、Ｍｏ：０．０１～４．０％、Ｃｕ：０．０１～３．０％、Ｖ：０．０３～０．１５％の１種または２種以上を含む、上記（１）または上記（２）に記載の拡散接合用ステンレス鋼材である。 (3) In the present invention, the stainless steel material further includes, in mass%, Nb: 4.0% or less, Mo: 0.01 to 4.0%, Cu: 0.01 to 3.0%, V: The stainless steel material for diffusion bonding according to (1) or (2) above, comprising one or more of 0.03 to 0.15%.
　（４）　本発明は、前記ステンレス鋼材は、さらに、質量％で、Ｂ：０．０００３～０．０１％を含む、上記（１）～（３）のいずれかに記載の拡散接合用ステンレス鋼材である。 (4) In the present invention, the stainless steel material for diffusion bonding according to any one of the above (1) to (3), wherein the stainless steel material further contains B: 0.0003 to 0.01% by mass%. It is.
　本発明によれば、フェライト相、マルテンサイト相、オーステナイト相の少なくとも２種以上からなる複相組織を有する複相系ステンレス鋼が、拡散接合前の平均結晶粒径およびγｍａｘ、接合温度でのクリープ伸びを最適な範囲で備えたことにより、優れた拡散接合性を有するステンレス鋼材が提供されるため、良好な接合界面を呈する拡散接合成型品が提供される。さらに、ＴｉおよびＡｌの合計含有量を抑制することにより、拡散接合性が向上した拡散接合成型品が得られる。 According to the present invention, a duplex stainless steel having a duplex structure composed of at least two of a ferrite phase, a martensite phase, and an austenite phase is obtained by creeping at an average crystal grain size and γmax before diffusion bonding, and at a bonding temperature. By providing the elongation within the optimum range, a stainless steel material having excellent diffusion bonding properties is provided, and thus a diffusion bonding molded product exhibiting a good bonding interface is provided. Furthermore, by suppressing the total content of Ti and Al, a diffusion bonded molded article with improved diffusion bonding properties can be obtained.
接合性試験で使用した測定試験体を示す図である。It is a figure which shows the measurement test body used by the bondability test.
　以下、本発明の実施形態について説明する。本発明は、この説明に限定されない。 Hereinafter, embodiments of the present invention will be described. The present invention is not limited to this description.
　ステンレス鋼材の直接法による拡散接合は、従来の手法に従えば、（ｉ）接合面の凹凸が変形して密着し、接合した箇所の接合面積が増大する過程、（ｉｉ）密着した箇所で接合前鋼材の表面酸化物皮膜が消失する過程、（ｉｉｉ）未接合部であるボイド内の残留ガスが母材と反応する過程、という３種の過程が並行して進行することにより完了すると考えられている。 According to the conventional method, diffusion bonding by a direct method of stainless steel material is (i) a process in which the unevenness of the joint surface is deformed and brought into close contact, and the joint area of the joined part increases, and (ii) joining at the tight part The process is considered to be completed by three processes: a process in which the surface oxide film of the former steel material disappears and (iii) a process in which the residual gas in the void which is an unjoined part reacts with the base material. ing.
　発明者らは、これまで、上記（ｉｉ）の過程に着目して母材成分、不動態皮膜中に含まれる成分、接合面の表面粗さを規制し、工業的にネックとなる生産性の低下を回避すべく検討してきた。しかし、上記（ｉｉ）の工程を制御しても、工業的に安定した接合性を確保することが困難な場合があり、上記（ｉ）の工程も加味して安定した接合性を得るための鋼材に関して多くの研究を重ねてきた。その結果、拡散接合に供するステンレス鋼が複相組織を有する複相系ステンレス鋼である場合、拡散接合前の結晶粒径を微細にすることが極めて有効であることを見出した。 The inventors have so far focused on the process of (ii) above to regulate the base material component, the component contained in the passive film, and the surface roughness of the joint surface, and the industrial productivity becomes a bottleneck. We have studied to avoid the decline. However, even if the step (ii) is controlled, it may be difficult to ensure industrially stable bondability, and in order to obtain stable bondability in consideration of the step (i). Much research has been conducted on steel materials. As a result, it has been found that when the stainless steel used for diffusion bonding is a dual phase stainless steel having a double phase structure, it is extremely effective to make the crystal grain size before diffusion bonding fine.
［複相組織］
　ステンレス鋼は、一般に、常温での金属組織に基づいてオーステナイト系ステンレス鋼、フェライト系ステンレス鋼、マルテンサイト系ステンレス鋼などに分類される。本発明の「複相組織」は、フェライト相、マルテンサイト相、オーステナイト相の少なくとも２種以上からなる金属組織を有するものである。本発明の「複相系ステンレス鋼材」は、このような複相組織を有するものであり、接合温度域でオーステナイト＋フェライト２相組織となる鋼をいうものとする。このような２相系のステンレス鋼の中には、フェライト系ステンレス鋼やマルテンサイト系ステンレス鋼に分類されるステンレス鋼が含まれることもある。 [Multiphase structure]
Stainless steel is generally classified into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and the like based on the metal structure at room temperature. The “multiphase structure” of the present invention has a metal structure composed of at least two of a ferrite phase, a martensite phase, and an austenite phase. The “multi-phase stainless steel material” of the present invention has such a multi-phase structure, and refers to a steel having an austenite + ferrite two-phase structure in the joining temperature range. Such a two-phase stainless steel may include a stainless steel classified as a ferritic stainless steel or a martensitic stainless steel.
　本発明では、低温および低面圧下で直接法による拡散接合を実現するために、拡散接合に供するステンレス鋼材として、フェライト相、マルテンサイト相、オーステナイト相の少なくとも２種以上からなる複相組織を有する複相系ステンレス鋼を用いる。このステンレス鋼は、拡散接合が進行する温度域では、フェライト相およびマルテンサイト相の一部がオーステナイト相へ相変態し、オーステナイト相＋フェライト相の２相組織となる。当該２相組織における互いの相が高温下で生じる結晶粒成長を抑制することにより、微細な組織が維持されて、粒界すべりを起因すると推定されるクリープ変形が容易に生じ得る。その結果、接合面の凹凸部において容易な変形が促進され、接合した箇所の接合面積が増大することにより、低温および低面圧下で直接法による拡散接合が可能となる。 In the present invention, in order to realize diffusion bonding by a direct method under low temperature and low surface pressure, the stainless steel material used for diffusion bonding has a multiphase structure composed of at least two types of ferrite phase, martensite phase, and austenite phase. Use duplex stainless steel. In this stainless steel, in the temperature range where diffusion bonding proceeds, a part of the ferrite phase and the martensite phase is transformed into the austenite phase, and a two-phase structure of austenite phase + ferrite phase is obtained. By suppressing the crystal grain growth in which the mutual phases in the two-phase structure are generated at a high temperature, a fine structure is maintained, and creep deformation estimated to be caused by grain boundary sliding can easily occur. As a result, easy deformation is promoted in the concavo-convex portion of the bonding surface, and the bonding area of the bonded portion is increased, thereby enabling diffusion bonding by a direct method at a low temperature and low surface pressure.
　本発明の複相系ステンレス鋼材は、直接接触させて拡散接合により一体化させるステンレス鋼材の双方あるいはその一方に使用できるものである。一体化させる相手材としては、本発明のステンレス鋼材を適用できる他、それ以外の２相系鋼種、拡散接合の加熱温度域でオーステナイト単相となるオーステナイト系鋼種、フェライト単相となるフェライト系鋼種などを適用することができる。 The duplex stainless steel material of the present invention can be used for both or one of the stainless steel materials that are brought into direct contact and integrated by diffusion bonding. As a counterpart material to be integrated, the stainless steel material of the present invention can be applied, other two-phase steel types, austenitic steel types that become austenite single phase in the heating temperature range of diffusion bonding, ferritic steel types that become ferrite single phase Etc. can be applied.
［成分組成］
　本発明で適用対象となる複相系ステンレス鋼は、Ｔｉ、Ａｌ以外の成分元素については、拡散接合性の観点からは、特にこだわる必要はなく、用途に応じて種々の成分組成を採用できる。ただし、本発明は、拡散接合が進行する温度域でオーステナイト＋フェライト２相組織を対象にするので、下記（ａ）式で示されるγｍａｘが１０～９０を満たす成分組成の鋼を採用する必要がある。具体的な成分組成範囲として、以下のものを例示することができる。 [Ingredient composition]
In the multiphase stainless steel to be applied in the present invention, the component elements other than Ti and Al are not particularly required from the viewpoint of diffusion bonding properties, and various component compositions can be adopted depending on the application. However, since the present invention targets an austenite + ferrite two-phase structure in the temperature range where diffusion bonding proceeds, it is necessary to employ a steel having a component composition satisfying γmax of 10 to 90 represented by the following formula (a). is there. Specific examples of the component composition range include the following.
　質量％で、Ｃ：０．２％以下、Ｓｉ：１．０％以下、Ｍｎ：３．０％以下、Ｐ：０．０５％以下、Ｓ：０．０３％以下、Ｎｉ：１０．０％以下、Ｃｒ：１０．０～３０．０％、Ｎ：０．３％以下、Ｔｉ：０．１５％以下、Ａｌ：０．１５％以下を含み、残部がＦｅおよび不可避的不純物からなり、ＴｉとＡｌの合計量が０．１５％以下である。 In mass%, C: 0.2% or less, Si: 1.0% or less, Mn: 3.0% or less, P: 0.05% or less, S: 0.03% or less, Ni: 10.0% Hereinafter, Cr: 10.0 to 30.0%, N: 0.3% or less, Ti: 0.15% or less, Al: 0.15% or less, with the balance being Fe and inevitable impurities, Ti And the total amount of Al is 0.15% or less.
　さらに、質量％で、Ｎｂ：４．０％以下、Ｍｏ：０．０１～４．０％、Ｃｕ：０．０１～３．０％、Ｖ：０．０３～０．１５％の１種または２種以上を含むことができる。さらに、質量％で、Ｂ：０．０００３～０．０１％を含むことができる。 Further, by mass%, Nb: 4.0% or less, Mo: 0.01-4.0%, Cu: 0.01-3.0%, V: 0.03-0.15% Two or more types can be included. Further, it may contain B: 0.0003 to 0.01% by mass%.
　以下、ステンレス鋼材に含まれる成分について説明する。 Hereinafter, the components contained in the stainless steel material will be described.
　Ｃは、固溶強化により鋼の強度、硬さを向上させる。一方で、Ｃ含有量が多くなると、鋼の加工性及び靱性を低下させるため、Ｃ含有量は、０．２質量％以下が好ましく、０．０８質量％以下がより好ましい。 C improves the strength and hardness of steel by solid solution strengthening. On the other hand, when the C content is increased, the workability and toughness of the steel are reduced, so the C content is preferably 0.2% by mass or less, and more preferably 0.08% by mass or less.
　Ｓｉは、鋼の脱酸に使用される元素である。一方で、Ｓｉ含有量が過多であると、鋼の靭性及び加工性を低下させる。また、強固な表面酸化膜を形成して、拡散接合性を阻害する。そのため、Ｓｉ含有量は、１．０質量％以下が好ましく、０．６質量％以下がより好ましい。 Si is an element used for deoxidation of steel. On the other hand, if the Si content is excessive, the toughness and workability of steel are reduced. In addition, a strong surface oxide film is formed to inhibit diffusion bonding. Therefore, the Si content is preferably 1.0% by mass or less, and more preferably 0.6% by mass or less.
　Ｍｎは、高温酸化特性を向上させる元素である。一方で、Ｍｎ含有量が過多であると、鋼を加工硬化させて、鋼の冷間加工性を低下させる。そのため、Ｍｎ含有量は、３．０質量％以下が好ましい。 Mn is an element that improves high-temperature oxidation characteristics. On the other hand, if the Mn content is excessive, the steel is work-hardened and the cold workability of the steel is reduced. Therefore, the Mn content is preferably 3.0% by mass or less.
　Ｐは、不可避的不純物であり、粒界腐食性を高めるとともに、鋼の靭性の低下を招く。そのため、Ｐ含有量は、０．０５質量％以下が好ましく、０．０３質量％以下がより好ましい。 Ｐ P is an unavoidable impurity, which increases the intergranular corrosion resistance and causes a decrease in the toughness of the steel. Therefore, the P content is preferably 0.05% by mass or less, and more preferably 0.03% by mass or less.
　Ｓは、不可避的不純物であり、鋼の熱間加工性を低下させる。そのため、Ｓ含有量は、０．０３質量％以下が好ましい。 S is an unavoidable impurity and reduces the hot workability of steel. Therefore, the S content is preferably 0.03% by mass or less.
　Ｎｉは、オーステナイト生成元素であり、また、還元性酸環境中での鋼の耐食性を向上させる作用を有する。一方で、Ｎｉ含有量が過多であると、オーステナイト相が安定となり、フェライト結晶の成長を抑制することができないため、安定なオーステナイト単相を形成してフェライト結晶の成長を抑制する。そのため、Ｎｉ含有量は、１０．０％以下が好ましい。 Ni is an austenite-forming element and has the effect of improving the corrosion resistance of steel in a reducing acid environment. On the other hand, if the Ni content is excessive, the austenite phase becomes stable and the growth of ferrite crystals cannot be suppressed. Therefore, a stable austenite single phase is formed to suppress the growth of ferrite crystals. Therefore, the Ni content is preferably 10.0% or less.
　Ｃｒは、不働態被膜を形成して耐食性を付与する元素である。Ｃｒ含有量は、３０．０質量％未満では、耐食性を付与する効果が十分でない。１０．０質量％を超えると、加工性が低下する。そのため、Ｃｒ含有量は、１０．０～３０．０質量％が好ましい。 Cr is an element that forms a passive film and imparts corrosion resistance. If the Cr content is less than 30.0% by mass, the effect of imparting corrosion resistance is not sufficient. When it exceeds 10.0 mass%, workability will fall. Therefore, the Cr content is preferably 10.0 to 30.0% by mass.
　Ｎは、不可避的不純物であり、冷間加工性を劣化させるため、０．３質量％以下が好ましい。 N is an unavoidable impurity and is preferably 0.3% by mass or less in order to deteriorate the cold workability.
　Ｔｉは、Ｃ、Ｎを固定する作用を有するため、耐食性や加工性を改善するうえで有効な元素である。Ａｌは、脱酸剤として添加されることが多い。他方、ＴｉおよびＡｌは、易酸化性元素であるから、鋼材表面の酸化皮膜中に含まれるＴｉ酸化物やＡｌ酸化物は、真空拡散接合の熱処理において還元されにくい。そのため、これらのＴｉ酸化物やＡｌ酸化物が多いと、拡散接合時に上記（ｉｉ）の過程の進行を妨げるおそれがあることから、Ｔｉ含有量は、０．１５質量％以下、Ａｌ含有量は、０．１５質量％以下が好ましく、より好ましくは０．０５質量％である。そして、ＴｉとＡｌの合計含有量は、０．１５質量％以下とすることが好ましく、より好ましくは０．０５質量％以下である。 Ti has an effect of fixing C and N, and is therefore an effective element for improving corrosion resistance and workability. Al is often added as a deoxidizer. On the other hand, since Ti and Al are easily oxidizable elements, Ti oxide and Al oxide contained in the oxide film on the surface of the steel material are difficult to be reduced in the heat treatment of vacuum diffusion bonding. Therefore, if these Ti oxides and Al oxides are large, the progress of the process (ii) may be hindered during diffusion bonding, so the Ti content is 0.15% by mass or less, and the Al content is 0.15 mass% or less is preferable, and 0.05 mass% is more preferable. The total content of Ti and Al is preferably 0.15% by mass or less, and more preferably 0.05% by mass or less.
　Ｎｂは、炭化物または炭窒化物を形成し、鋼の結晶粒を微細化して靭性を高める効果を付与する元素である。一方で、Ｎｂ含有量が過多であると、鋼の加工性の低下を招くため、Ｎｂ含有量は、４．０質量％以下が好ましい。 Nb is an element that forms carbides or carbonitrides and refines the crystal grains of steel to increase the toughness. On the other hand, if the Nb content is excessive, the workability of the steel is reduced, so the Nb content is preferably 4.0% by mass or less.
　Ｍｏは、強度を低下させることなく耐食性を向上させる作用を有する元素である。Ｍｏ含有量が過多であると、鋼の加工性の低下を招くため、Ｍｏ含有量は、０．０１～４．０質量％が好ましい。 Mo is an element that has the effect of improving the corrosion resistance without reducing the strength. If the Mo content is excessive, the workability of the steel is reduced, so the Mo content is preferably 0.01 to 4.0% by mass.
　Ｃｕは、耐食性を向上させるのに効果的であり、また、フェライト相を生成する作用を有する元素である。一方で、Ｃｕ含有量が過多であると、鋼の加工性が低下するため、Ｃｕ含有量は、０．０１～３．０質量％が好ましい。 Cu is an element that is effective in improving the corrosion resistance and has an action of generating a ferrite phase. On the other hand, if the Cu content is excessive, the workability of the steel decreases, so the Cu content is preferably 0.01 to 3.0% by mass.
　Ｖは、固溶Ｃを炭化物として固定することにより、鋼の加工性や靭性の向上に寄与する元素である。一方で、Ｖ元素を過剰に含有すると、製造性の低下を招くので、Ｖ含有量は、０．０３～０．１５％が好ましい。 V is an element that contributes to improving the workability and toughness of steel by fixing solute C as carbide. On the other hand, if the V element is contained excessively, the productivity is lowered, so the V content is preferably 0.03 to 0.15%.
　Ｂは、Ｎを固定することにより、耐食性や加工性の改善に寄与する元素である。一方で、Ｂ元素を過剰に含有すると、鋼の熱間加工性の低下を招くので、Ｂ含有量は、０．０００３～０．０１％が好ましい。 B is an element that contributes to improvement of corrosion resistance and workability by fixing N. On the other hand, if the B element is contained excessively, the hot workability of the steel is lowered, so the B content is preferably 0.0003 to 0.01%.
　上記化学組成を有する複相系ステンレス鋼として、特に下記（ａ）式で示されるγｍａｘが１０～９０である鋼を適用することができる。
γｍａｘ＝４２０Ｃ－１１．５Ｓｉ＋７Ｍｎ＋２３Ｎｉ－１１．５Ｃｒ－１２Ｍｏ＋９Ｃｕ－４９Ｔｉ－４７Ｎｂ－５２Ａｌ＋４７０Ｎ＋１８９　・・・（ａ）式
　ここで、上記（ａ）式における、Ｃ、Ｓｉ等の元素記号は、各元素の含有量（質量％）を意味する。 As the duplex stainless steel having the above chemical composition, steel having a γmax of 10 to 90 represented by the following formula (a) can be applied.
γmax = 420C-11.5Si + 7Mn + 23Ni-11.5Cr-12Mo + 9Cu-49Ti-47Nb-52Al + 470N + 1189 (a) where, in the above equation (a), the element symbols such as C and Si are the contents of each element. (Mass%) is meant.
　γｍａｘは、１１００℃程度に加熱保持した場合に生成するオーステナイト相の量（体積％）を表す指標である。γｍａｘが１００以上の場合は、オーステナイト単相となる鋼種であるとみなすことができる。γｍａｘが０以下の場合は、フェライト単相となる鋼種であるとみなすことができる。
　本発明の複相系ステンレス鋼は、γｍａｘが１０～９０であるときは、拡散接合が進行する温度域でオーステナイト＋フェライト２相となり、この２相が互いに高温下での結晶粒成長を抑制するため、微細結晶組織を得るのに有効である。γｍａｘが５０～８０であるとさらに好ましい。 γmax is an index representing the amount (volume%) of the austenite phase that is generated when heated and held at about 1100 ° C. When γmax is 100 or more, it can be regarded as a steel type that becomes an austenite single phase. When γmax is 0 or less, it can be regarded as a steel type that becomes a ferrite single phase.
In the duplex stainless steel of the present invention, when γmax is 10 to 90, the two phases become austenite + ferrite in the temperature range where diffusion bonding proceeds, and these two phases suppress the growth of crystal grains at high temperatures. Therefore, it is effective for obtaining a fine crystal structure. More preferably, γmax is 50-80.
［接合前の平均結晶粒径］
　本発明の複相系ステンレス鋼は、細粒組織であるほど、上記（ｉ）の過程を迅速に進行させることができる。そのため、接合前の平均結晶粒径は、２０μｍ以下が好ましく、１０μｍ以下がより好ましい。 [Average crystal grain size before bonding]
As the duplex stainless steel of the present invention has a finer grain structure, the process (i) can be rapidly advanced. Therefore, the average crystal grain size before bonding is preferably 20 μm or less, and more preferably 10 μm or less.
［表面粗さ］
　本発明の微細結晶粒を有する複相系ステンレス鋼は、上記（ｉ）の過程が迅速に進行するので、上記（ｉｉ）の過程による影響が小さく、表面粗さＲａの程度によって接合性が制約される可能性は低い。ただ、拡散接合に供するステンレス鋼材の表面粗さが大きくなると、上記（ｉｉ）の過程における酸化皮膜の消失が遅くなる傾向にある。そのため、ステンレス鋼材の表面は、平滑であることが好ましく、表面粗さＲａとしては０．３μｍ以下が好ましい。 [Surface roughness]
In the multi-phase stainless steel having fine crystal grains according to the present invention, since the process (i) proceeds rapidly, the influence of the process (ii) is small, and the bondability is limited by the degree of the surface roughness Ra. It is unlikely to be done. However, when the surface roughness of the stainless steel material used for diffusion bonding increases, the disappearance of the oxide film in the process (ii) tends to be delayed. Therefore, the surface of the stainless steel material is preferably smooth, and the surface roughness Ra is preferably 0.3 μm or less.
［拡散接合製品の製造方法］
　本発明のステンレス鋼材は、直接法による真空拡散接合を行うことにより、接合性の良好な拡散接合品が得られる。具体的な拡散接合処理としては、例えば、接触面圧０．１～１．０ＭＰａで直接接触させた状態であって、圧力１．０×１０－２Ｐａ以下、好ましくは１．０×１０－３Ｐａ以下、露点－４０℃以下の炉内で、９００～１１００℃に加熱保持することにより、拡散接合を進行させることができる。保持時間は、０．５～３ｈの範囲で調整することができる。 [Diffusion bonding product manufacturing method]
The stainless steel material of the present invention provides a diffusion bonded product with good bondability by performing vacuum diffusion bonding by a direct method. As a specific diffusion bonding treatment, for example, in a state of direct contact at a contact surface pressure of 0.1 to 1.0 MPa, a pressure of 1.0 × 10 −2 Pa or less, preferably 1.0 × 10 − Diffusion bonding can be advanced by heating and maintaining at 900 to 1100 ° C. in a furnace having a pressure of 3 Pa or less and a dew point of −40 ° C. or less. The holding time can be adjusted in the range of 0.5 to 3 h.
　以下、本発明の実施例について説明する。本発明は、以下の実施例に限定されるものではなく、発明の要旨の範囲内で適宜変更して実施できる。 Hereinafter, examples of the present invention will be described. The present invention is not limited to the following examples, and can be implemented with appropriate modifications within the scope of the gist of the invention.
　表１に示す化学組成を有するステンレス鋼について、３０ｋｇの真空溶解で溶製し、得られた鋼塊を３０ｍｍ厚の板に鍛造した後、１２３０℃で２ｈの熱間圧延を行って３．０ｍｍ厚の熱延板を得た。次いで、焼鈍、酸洗、冷間圧延を行って、１．０ｍｍの厚さの冷延板を得た。その後、該冷延板に後述する焼鈍処理を施して冷延焼鈍板を製造し、これを供試材とした。 The stainless steel having the chemical composition shown in Table 1 was melted by 30 kg of vacuum melting, and the obtained steel ingot was forged into a 30 mm thick plate, followed by hot rolling at 1230 ° C. for 2 hours and 3.0 mm. A thick hot-rolled sheet was obtained. Subsequently, annealing, pickling, and cold rolling were performed to obtain a cold-rolled sheet having a thickness of 1.0 mm. Then, the cold-rolled sheet was annealed as described later to produce a cold-rolled sheet, which was used as a test material.
Figure JPOXMLDOC01-appb-T000001
  
 
Figure JPOXMLDOC01-appb-T000001
  
 
　表１に複数の鋼材が示されている。ＦＭ－１鋼～ＦＭ－４鋼は、拡散接合前の金属組織がフェライト＋マルテンサイト２相鋼（α＋Ｍ相）である。ＦＡ－１鋼およびＦＡ－２鋼は、拡散接合前の金属組織がフェライト＋オーステナイト２相鋼（α＋γ相）である。Ｆ－１鋼は、拡散接合前の金属組織がフェライト単相鋼（α相）である。Ａ－１鋼は、拡散接合前の金属組織がオーステナイト単相鋼（γ相）である。Ｍ－１鋼は、拡散接合前の金属組織がマルテンサイト単相鋼（Ｍ相）である。
　各鋼板は、冷延後の焼鈍温度を９００℃～１２００℃の間で変化させることにより、平均結晶粒径の異なる供試材を得た。また、表面粗さの影響を調査するため、一部の鋼板を用いて冷延焼鈍板の仕上げ処理を変更することにより、表面粗さＲａの異なる供試材を得た。 Table 1 shows a plurality of steel materials. In FM-1 steel to FM-4 steel, the metal structure before diffusion bonding is a ferrite + martensite duplex steel (α + M phase). In FA-1 steel and FA-2 steel, the metal structure before diffusion bonding is a ferrite + austenite dual phase steel (α + γ phase). In F-1 steel, the metal structure before diffusion bonding is a ferritic single phase steel (α phase). In the A-1 steel, the metal structure before diffusion bonding is an austenitic single phase steel (γ phase). M-1 steel is martensitic single phase steel (M phase) before diffusion bonding.
Each steel plate was obtained by changing the annealing temperature after cold rolling between 900 ° C. and 1200 ° C. to obtain test materials having different average crystal grain sizes. Moreover, in order to investigate the influence of surface roughness, the test material from which surface roughness Ra differs was obtained by changing the finishing process of a cold-rolled annealing board using some steel plates.
（平均結晶粒径）
　鋼板の拡散接合前の平均結晶粒径（μｍ）は、以下に示すように求積法により測定した。冷間圧延方向に平行な板厚断面の金属組織を連続した１ｍｍ２以上で観察し、求積法を用いて単位面積内に含まれる結晶粒の個数を算出した。そして、結晶粒１つ当たりの平均面積を求めて、これを１／２乗した値を平均結晶粒径として用いた。 (Average crystal grain size)
The average crystal grain size (μm) of the steel sheet before diffusion bonding was measured by a quadrature method as shown below. The metal structure of the plate thickness cross section parallel to the cold rolling direction was observed at 1 mm 2 or more continuously, and the number of crystal grains contained in the unit area was calculated using the quadrature method. And the average area per crystal grain was calculated | required, and the value which carried out this 1/2 power was used as an average crystal grain diameter.
（表面粗さ）
　表面粗さＲａ（μｍ）については、表面粗さ測定装置（東京精密社製；ＳＵＲＦＣＯＭ２９００ＤＸ）を用いて、圧延方向に対する直角方向の表面粗さＲａを測定した。 (Surface roughness)
About surface roughness Ra (micrometer), surface roughness Ra of the orthogonal | vertical direction with respect to the rolling direction was measured using the surface roughness measuring apparatus (The Tokyo Seimitsu company make; SURFCOM2900DX).
（クリープ伸び）
　クリープ伸びは、以下に示す方法で測定した。各鋼板から、ＪＩＳ１３Ｂ試験片を切り出し、一方のつかみ部中央にφ５ｍｍの穴を開けた。当該試験片に標点間５０ｍｍのけがきを入れた後、穴を有する前記つかみ部が下方となるように、当該試験片を高温引張試験機に取り付けた。前記標点間内の温度が１０００℃になるまで昇温し、その温度で１５ｍｉｎ均熱した後、１．０ＭＰａの応力が加わるように算出された錘を備えたＳＵＳ３１０Ｓ製ワイヤを当該つかみ部の穴に取り付けて、０．５ｈ保持した。その後、当該ＳＵＳ３１０Ｓ製ワイヤを当該試験片から取り外し、さらに空冷により常温まで冷却した。そして、前記標点間の長さＬを測定し、クリープ伸び（％）として、（Ｌ－５０）／５０×１００を算出した。 (Creep elongation)
Creep elongation was measured by the method shown below. A JIS 13B test piece was cut out from each steel plate, and a hole of φ5 mm was formed in the center of one gripping part. The test piece was attached to a high-temperature tensile tester so that the test piece was marked with a mark of 50 mm between the marks, so that the grip portion having a hole was positioned downward. The temperature between the gauge points is raised to 1000 ° C., and after soaking for 15 minutes at that temperature, a wire made of SUS310S having a weight calculated so as to apply a stress of 1.0 MPa is attached to the grip portion. Attached to the hole and held for 0.5 h. Thereafter, the SUS310S wire was removed from the test piece, and further cooled to room temperature by air cooling. The length L between the gauge points was measured, and (L-50) / 50 × 100 was calculated as the creep elongation (%).
（接合性試験）
　各鋼板から２０ｍｍ×２０ｍｍの平板試験片を取り出し、以下の方法で拡散接合を行った。同一鋼材２枚の試験片を、互いに表面同士が接触するように積層した状態とした。錘を有する冶具を用いて、これら２枚の試験片の接触表面に付与される面圧を０．１ＭＰａとなるように調整した。以下、積層された平板試験片を「鋼材」という。当該鋼材が積層された状態のものを「積層体」という。次いで、冶具と積層体を真空炉に挿入し、真空引きを行って圧力１．０×１０－３～１．０×１０－４Ｐａの初期真空度とした後、１０００℃まで約１ｈで昇温し、その温度で２ｈ保持した。その後、冷却室に移して冷却した。当該冷却は、９００℃まで上記真空度を維持し、その後、Ａｒガスを導入して９０ｋＰａのＡｒガス雰囲気中で約１００℃以下まで冷却した。上記の熱処理を終えた積層体について、超音波厚さ計（オリンパス社製；Ｍｏｄｅｌ３５ＤＬ）を用いて、図１に示すように２０ｍｍ×２０ｍｍの積層体表面上に３ｍｍピッチで設けた４９箇所の測定点において厚さ測定を行った。プローブ径は１．５ｍｍとした。ある測定点での板厚測定値が２枚の鋼材の合計板厚を示す場合には、その測定点に対応する両鋼材の界面位置では原子の拡散によって両鋼材が一体化しているとみなすことができる。一方、板厚測定値が両鋼材の合計板厚と異なる場合には、その測定点に対応する両鋼材の界面位置に未接合部（欠陥）が存在するとみなすことができる。加熱処理後の積層体の断面組織と、この測定手法により得られた測定結果との対応関係を調べたところ、測定結果が両鋼材の合計板厚となった測定点の数を測定総数４９で除した値（これを、以下「接合率」という。）によって、接触面積に占める接合部分の面積率が精度良く評価できることを確認した。そこで、以下の評価基準で拡散接合性を評価した。
　　Ａ：接合率１００％（優秀）
　　Ｂ：接合率９０～９９％（良好）
　　Ｃ：接合率６０～８９％（やや良好）
　　Ｄ：接合率０～５９％（不良）
　種々の検討の結果、評価Ａ及びＢにおいて拡散接合部の強度が十分に確保され、かつ両部材間のシール性（連通する欠陥を介する気体の漏れが生じない性質）も良好であることから、評価Ａ及びＢを合格と判定した。 (Jointability test)
A plate test piece of 20 mm × 20 mm was taken out from each steel plate and diffusion bonded by the following method. Two test pieces of the same steel material were laminated so that the surfaces were in contact with each other. Using a jig having a weight, the surface pressure applied to the contact surfaces of these two test pieces was adjusted to 0.1 MPa. Hereinafter, the laminated flat plate test piece is referred to as “steel material”. A state in which the steel materials are laminated is referred to as a “laminated body”. Next, the jig and the laminate are inserted into a vacuum furnace and evacuated to obtain an initial vacuum of 1.0 × 10 −3 to 1.0 × 10 −4 Pa, and then raised to 1000 ° C. in about 1 h. Warm and hold at that temperature for 2 h. Then, it moved to the cooling chamber and cooled. The said vacuum degree was maintained to 900 degreeC after that, Ar gas was introduce | transduced and it cooled to about 100 degrees C or less in 90 kPa Ar gas atmosphere. About the laminated body which finished said heat processing, as shown in FIG. 1, it measured 49 places provided in 3 mm pitch on the surface of a 20 mm x 20 mm laminated body using the ultrasonic thickness meter (Olympus company make; Model35DL). Thickness measurements were made at points. The probe diameter was 1.5 mm. If the measured thickness at a given measurement point indicates the total thickness of the two steel materials, it is assumed that both steel materials are integrated by diffusion of atoms at the interface position of both steel materials corresponding to the measurement point. Can do. On the other hand, when the plate thickness measurement value is different from the total plate thickness of both steel materials, it can be considered that an unjoined portion (defect) exists at the interface position of both steel materials corresponding to the measurement point. When the correspondence between the cross-sectional structure of the laminate after the heat treatment and the measurement results obtained by this measurement method was examined, the number of measurement points at which the measurement results were the total plate thickness of both steel materials was 49 in total. It was confirmed that the area ratio of the joint portion occupying the contact area can be accurately evaluated by the value obtained by dividing (hereinafter referred to as “joining ratio”). Therefore, diffusion bonding properties were evaluated according to the following evaluation criteria.
A: Joining rate 100% (excellent)
B: Joining rate 90 to 99% (good)
C: Joining rate 60 to 89% (slightly good)
D: Joining rate 0 to 59% (defect)
As a result of various studies, the strength of the diffusion bonding portion is sufficiently ensured in the evaluations A and B, and the sealing performance between the two members (property that gas does not leak through a communicating defect) is good. Evaluations A and B were determined to be acceptable.
　表２に各鋼の冷延焼鈍後の平均結晶粒径およびγｍａｘ、表面粗さ、クリープ伸び、接合性評価結果を示す。 Table 2 shows the average grain size and γmax, surface roughness, creep elongation, and bondability evaluation results after cold rolling annealing of each steel.
Figure JPOXMLDOC01-appb-T000002
  
 
Figure JPOXMLDOC01-appb-T000002
  
 
　表２に示すように、本発明例１～６は、接合率が９０％以上であり、１０００℃という比較的低温でかつ０．１ＭＰａという低い面圧であっても良好な拡散接合性を示した。また、本発明例１～６は、表面粗さＲａの程度にかかわらず、良好な拡散接合性を示しており、表面粗さによる影響が見られなかった。本発明の構成を備えた複相系ステンレス鋼材は、表面粗さが増大しても拡散接合性が低下しないので、その拡散接合性が鋼材表面性状に制約されないことが分かる。 As shown in Table 2, Examples 1 to 6 of the present invention have a bonding rate of 90% or more, and exhibit good diffusion bonding properties even at a relatively low temperature of 1000 ° C. and a low surface pressure of 0.1 MPa. It was. Inventive Examples 1 to 6 showed good diffusion bonding properties regardless of the degree of the surface roughness Ra, and no influence of the surface roughness was observed. In the multiphase stainless steel material having the configuration of the present invention, the diffusion bondability does not decrease even when the surface roughness is increased, so that it can be understood that the diffusion bondability is not restricted by the surface property of the steel material.
　それに対し、比較例１～１０は、平均結晶粒径、γｍａｘ、クリープ伸びが本発明の範囲から外れていたので、２相高温域での接合面の凹凸部の変形が小さく、接合した箇所の接合面積が増加しなかった。そのため、その多くの接合率は、８０％未満のやや不良または不良であった。
　また、比較例５～７のフェライト単相鋼、比較例８～９のオーステナイト単相鋼については、表面粗さＲａによる接合率の変化によると、表面粗さが極めて小さい比較例７及び比較例９は、９０％以上の接合率を示した。その一方で、それ以外の比較例は、表面粗さが大きく、接合率が低下した。このように、単相系の鋼では、表面粗さが大きいと、接合率が不良となり、その拡散接合性が表面粗さにより制約されることが分かる。 On the other hand, in Comparative Examples 1 to 10, since the average crystal grain size, γmax, and creep elongation were out of the scope of the present invention, the deformation of the concavo-convex portion of the joint surface in the two-phase high temperature region was small, and The bonding area did not increase. Therefore, most of the joining ratios were slightly poor or poor at less than 80%.
Further, regarding the ferrite single phase steels of Comparative Examples 5 to 7 and the austenite single phase steels of Comparative Examples 8 to 9, according to the change in the joining rate due to the surface roughness Ra, Comparative Example 7 and Comparative Example with extremely small surface roughness No. 9 showed a bonding rate of 90% or more. On the other hand, in other comparative examples, the surface roughness was large and the bonding rate was lowered. Thus, it can be seen that, in a single-phase steel, when the surface roughness is large, the bonding rate becomes poor, and the diffusion bonding property is restricted by the surface roughness.

Claims (4)

  1. 　拡散接合前の金属組織がフェライト相、マルテンサイト相またはオーステナイト相の少なくとも２種以上からなる複相組織を有する複相系ステンレス鋼材であって、
    　前記複相組織の平均結晶粒径が２０μｍ以下であり、
    　下記（ａ）式で示されるγｍａｘが１０～９０であり、
    　１．０ＭＰａの負荷を１０００℃、０．５ｈで加えたときのクリープ伸びが０．２％以上である、拡散接合用ステンレス鋼材。
    　γｍａｘ＝４２０Ｃ－１１．５Ｓｉ＋７Ｍｎ＋２３Ｎｉ－１１．５Ｃｒ－１２Ｍｏ＋９Ｃｕ－４９Ｔｉ－４７Ｎｂ－５２Ａｌ＋４７０Ｎ＋１８９　・・・（ａ）式
    　ここで、上記（ａ）式における元素記号は、各元素の含有量（質量％）を意味する。     A metal structure before diffusion bonding is a duplex stainless steel material having a duplex structure consisting of at least two of a ferrite phase, a martensite phase or an austenite phase,
    The average crystal grain size of the multiphase structure is 20 μm or less,
    Γmax represented by the following formula (a) is 10 to 90,
    A stainless steel material for diffusion bonding having a creep elongation of 0.2% or more when a load of 1.0 MPa is applied at 1000 ° C. for 0.5 h.
    γmax = 420C-11.5Si + 7Mn + 23Ni-11.5Cr-12Mo + 9Cu-49Ti-47Nb-52Al + 470N + 189 (a) where the element symbol in the above formula (a) means the content (mass%) of each element. To do.
  2. 　前記ステンレス鋼材は、質量％で、Ｃ：０．２％以下、Ｓｉ：１．０％以下、Ｍｎ：３．０％以下、Ｐ：０．０５％以下、Ｓ：０．０３％以下、Ｎｉ：１０．０％以下、Ｃｒ：１０．０～３０．０％、Ｎ：０．３％以下、Ｔｉ：０．１５％以下、Ａｌ：０．１５％以下を含み、残部がＦｅおよび不可避的不純物からなり、ＴｉとＡｌの合計量が０．１５％以下である、請求項１に記載の拡散接合用ステンレス鋼材。 The stainless steel material is, by mass, C: 0.2% or less, Si: 1.0% or less, Mn: 3.0% or less, P: 0.05% or less, S: 0.03% or less, Ni : 10.0% or less, Cr: 10.0 to 30.0%, N: 0.3% or less, Ti: 0.15% or less, Al: 0.15% or less, the balance being Fe and inevitable The stainless steel material for diffusion bonding according to claim 1, comprising impurities and having a total amount of Ti and Al of 0.15% or less.
  3. 　前記ステンレス鋼材は、さらに、質量％で、Ｎｂ：４．０％以下、Ｍｏ：０．０１～４．０％、Ｃｕ：０．０１～３．０％、Ｖ：０．０３～０．１５％の１種または２種以上を含む、請求項１または請求項２に記載の拡散接合用ステンレス鋼材。 The stainless steel material is further mass%, Nb: 4.0% or less, Mo: 0.01-4.0%, Cu: 0.01-3.0%, V: 0.03-0.15 The stainless steel material for diffusion bonding according to claim 1 or 2, comprising 1% or 2 or more of%.
  4. 　前記ステンレス鋼材は、さらに、質量％で、Ｂ：０．０００３～０．０１％を含む、請求項１～３のいずれかに記載の拡散接合用ステンレス鋼材。 The stainless steel material for diffusion bonding according to any one of claims 1 to 3, wherein the stainless steel material further contains B: 0.0003 to 0.01% by mass%.
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