JP5850763B2 - Stainless steel diffusion bonding products - Google Patents
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- 238000009792 diffusion process Methods 0.000 title claims description 119
- 229910001220 stainless steel Inorganic materials 0.000 title claims description 58
- 239000010935 stainless steel Substances 0.000 title claims description 54
- 239000000463 material Substances 0.000 claims description 76
- 239000013078 crystal Substances 0.000 claims description 69
- 229910000831 Steel Inorganic materials 0.000 claims description 61
- 239000010959 steel Substances 0.000 claims description 61
- 238000005304 joining Methods 0.000 claims description 21
- 239000002436 steel type Substances 0.000 claims description 12
- 229910001566 austenite Inorganic materials 0.000 claims description 10
- 229910000859 α-Fe Inorganic materials 0.000 claims description 9
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 8
- 239000011800 void material Substances 0.000 claims description 8
- 230000013011 mating Effects 0.000 claims description 7
- 229910052759 nickel Inorganic materials 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 5
- 229910052758 niobium Inorganic materials 0.000 claims description 5
- 229910052791 calcium Inorganic materials 0.000 claims description 4
- 230000033001 locomotion Effects 0.000 claims description 4
- 229910052749 magnesium Inorganic materials 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims description 4
- 229910052717 sulfur Inorganic materials 0.000 claims description 4
- 229910052721 tungsten Inorganic materials 0.000 claims description 4
- 229910052727 yttrium Inorganic materials 0.000 claims description 4
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 230000009545 invasion Effects 0.000 claims description 3
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- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 6
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- 238000005260 corrosion Methods 0.000 description 3
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- 239000011888 foil Substances 0.000 description 3
- 239000007791 liquid phase Substances 0.000 description 3
- 239000002932 luster Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
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- 238000005482 strain hardening Methods 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 238000012935 Averaging Methods 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
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- IARVUEAKHFHUNB-UHFFFAOYSA-N nitric acid propane-1,2,3-triol hydrofluoride Chemical compound OCC(O)CO.[N+](=O)(O)[O-].F IARVUEAKHFHUNB-UHFFFAOYSA-N 0.000 description 1
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Description
本発明はステンレス鋼材同士をインサート材なしで直接拡散接合した製品であって、特にオーステナイト単相ステンレス鋼種またはフェライト単相ステンレス鋼種を適用して密着性に優れた拡散接合部を形成したステンレス鋼拡散接合製品に関する。 The present invention is a product in which a stainless steel material is directly diffusion bonded without an insert material, and in particular, a stainless steel diffusion in which an austenite single phase stainless steel type or a ferrite single phase stainless steel type is applied to form a diffusion bonded portion having excellent adhesion. Related to bonded products.
ステンレス鋼材同士を拡散接合する手法は、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、種々の用途で利用されている。拡散接合にはインサート材挿入法と直接法がある。インサート材挿入法は、接合するステンレス鋼材と馴染みがよい異別の金属材料からなる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双方のステンレス鋼材を接合する手法である。直接法は、インサート材を用いずに双方のステンレス鋼材の表面同士と直接接触させ、固相拡散により接合する手法である。 The technique of diffusion bonding stainless steel materials is used in various applications such as heat exchangers, machine parts, fuel cell parts, home appliance parts, plant parts, decorative component members, and building materials. For diffusion bonding, there are an insert material insertion method and a direct method. The insert material insertion method is a method in which an insert material made of a different metal material that is familiar to the stainless steel material to be joined is inserted into the joining interface, and both stainless steel materials are joined by solid phase diffusion or liquid phase diffusion. The direct method is a technique in which the surfaces of both stainless steel materials are brought into direct contact with each other without using an insert material and are joined by solid phase diffusion.
インサート材挿入法としては、例えば２相ステンレス鋼をインサート材に使用する方法（特許文献１）、ＮｉとＡｕをめっきしたステンレス鋼箔をインサート材に用いて液相拡散により接合する方法（特許文献２）、Ｓｉを多量に含むオーステナイト系ステンレス鋼をインサート材に使用する方法（特許文献３）をはじめ、種々の手法が知られている。また、ニッケル系や銅系のろう材をインサート材に用いる「ろう付け」も液相拡散による拡散接合の一種と見ることができる。これらの技術は比較的簡便に、しかも確実に拡散接合を行うことができる点で優位性がある。しかし、インサート材を用いることによるコスト増や、接合箇所に異種金属が存在することによる耐食性の低下が問題となりやすい。 As an insert material insertion method, for example, a method of using duplex stainless steel as an insert material (Patent Document 1), a method of joining Ni and Au plated stainless steel foil as an insert material by liquid phase diffusion (Patent Document) 2) Various methods are known, including a method of using austenitic stainless steel containing a large amount of Si as an insert material (Patent Document 3). In addition, “brazing” using nickel or copper brazing material as an insert material can be regarded as a kind of diffusion bonding by liquid phase diffusion. These techniques are advantageous in that diffusion bonding can be performed relatively easily and reliably. However, an increase in cost due to the use of the insert material and a decrease in corrosion resistance due to the presence of dissimilar metals at the joints tend to be problems.
インサート材を用いない直接法としては、例えば鋼中のＳ量を０.０１％以下としたステンレス鋼を非酸化雰囲気中の特定温度域に加熱することで変形を回避する方法（特許文献４）、酸洗処理により表面に凹凸を付与したステンレス鋼箔を拡散接合して自動車排ガス浄化装置用触媒担体を得る方法（特許文献５）、拡散接合の阻害要因となるアルミナ皮膜の生成を抑えるためにＡｌ含有量を不純物レベル〜０.８％に抑えたステンレス鋼を用いて触媒用ハニカムを得る方法（特許文献６）、冷間加工によるひずみを付与したステンレス鋼を用いて拡散接合性を向上させる方法（特許文献７）、クロム炭窒化物の形成を軽減するためにＴｉやＮｂを所定量添加したフェライト系ステンレス鋼箔を重ねて巻回して触媒用メタル担体を得る方法（特許文献８）、特定の組成を有する直接拡散接合用のフェライト系ステンレス鋼を用いる方法（特許文献９）などが知られている。 As a direct method not using an insert material, for example, a method of avoiding deformation by heating stainless steel having an S content in steel of 0.01% or less to a specific temperature range in a non-oxidizing atmosphere (Patent Document 4). , A method of obtaining a catalyst carrier for an automobile exhaust gas purification device by diffusion bonding of a stainless steel foil having surface irregularities by pickling treatment (Patent Document 5), in order to suppress the formation of an alumina film which becomes an obstruction factor of diffusion bonding Method of obtaining honeycomb for catalyst using stainless steel with Al content suppressed to impurity level to 0.8% (Patent Document 6), improving diffusion bonding using stainless steel imparted with strain by cold working Method (Patent Document 7), a method of obtaining a metal carrier for a catalyst by overlapping and winding a ferritic stainless steel foil to which a predetermined amount of Ti or Nb is added in order to reduce the formation of chromium carbonitride (special Document 8), a method using a ferritic stainless steel for diffusion bonding directly with a specific composition (Patent Document 9) are known.
ステンレス鋼材の直接法による拡散接合については上述のように種々の技術が提案されている。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、接合部の信頼性（接合強度や密封性）確保と、製造負荷抑制の両立が難しいことにある。従来の知見によると、直接法により接合部の信頼性を確保するためには接合温度を１１００℃を超える高温としたり、ホットプレスやＨＩＰ等により高い面圧を付与したりする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い。一方、ステンレス鋼材の直接法による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にて実施すると、接合部の信頼性を十分に確保することは難しい。 As described above, various techniques have been proposed for diffusion bonding of stainless steel materials by the direct method. However, industrially, the direct method has not yet been established as the mainstream diffusion bonding method for stainless steel materials. The main reason is that it is difficult to ensure the reliability of the joint (joint strength and sealability) and suppress the production load. According to the conventional knowledge, in order to ensure the reliability of the joint part by the direct method, the process of making the joint temperature higher than 1100 ° C. or applying a high surface pressure by hot press, HIP or the like is a heavy load process. It is necessary to employ it, and the cost increase by it is inevitable. On the other hand, if diffusion bonding by a direct method of stainless steel material 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.
また、ステンレス鋼の拡散接合製品においては、材料特性等の観点からオーステナイト単相鋼やフェライト単相鋼を適用したい場合もある。しかし、発明者らの検討によれば、このような鋼種については直接法により信頼性に優れた健全な拡散接合部を得ることは一層難しい。 In addition, in stainless steel diffusion bonding products, it may be desired to apply austenite single-phase steel or ferrite single-phase steel from the viewpoint of material properties and the like. However, according to the examination by the inventors, it is more difficult to obtain a sound diffusion bonded portion excellent in reliability by a direct method for such a steel type.
本発明は、従来のインサート材挿入法と同等の作業負荷による「直接法」によって構築可能なステンレス鋼材の拡散接合製品であって、特にオーステナイト単相鋼やフェライト単相鋼を適用した場合に接合部の優れた信頼性が得られるステンレス鋼拡散接合製品を提供しようというものである。 The present invention is a diffusion bonding product of a stainless steel material that can be constructed by a “direct method” with a work load equivalent to that of a conventional insert material insertion method, particularly when austenite single phase steel or ferritic single phase steel is applied. It is intended to provide a stainless steel diffusion bonding product that can obtain excellent reliability of parts.
上記目的は、ステンレス鋼材同士を直接接触させて拡散接合により一体化した拡散接合製品であって、接合前の接触界面（以下「接合前界面」という）に垂直な断面において、
（１）拡散接合時の結晶粒界移動によって接合前界面を跨いで相手側の鋼材中へと侵入して接合前界面より相手側の位置に粒界三重点を形成した結晶粒のうち、前記粒界三重点における粒界の夾角が１５０°以下である結晶粒を「侵入結晶粒」と呼ぶとき、接合前界面に接するか接合前界面を跨ぐ結晶粒の総数に占める前記侵入結晶粒の個数割合が２０％以上であること、
（２）接合前界面位置上に占めるボイド存在箇所の長さ割合が５％以下であること、
を満たすステンレス鋼拡散接合製品によって達成される。
The above purpose is a diffusion bonding product in which stainless steel materials are brought into direct contact with each other and integrated by diffusion bonding, and in a cross section perpendicular to a contact interface before bonding (hereinafter referred to as “interface before bonding”),
(1) Among the crystal grains that have penetrated into the mating steel material across the interface before bonding by the grain boundary movement during diffusion bonding, and formed a grain boundary triple point at the position on the mating side from the interface before bonding, When a crystal grain having a grain boundary depression angle of 150 ° or less at the grain boundary triple point is referred to as an “invasion crystal grain”, the number of the intrusion crystal grains in the total number of crystal grains in contact with or across the interface before bonding The proportion is 20% or more,
(2) The length ratio of the void existing location on the interface position before joining is 5% or less,
Achieved by satisfying stainless steel diffusion bonding products.
ここで、「接合前界面に接するか接合前界面を跨ぐ結晶粒の総数」をｎtotalとするとき、ｎtotalは以下のようにして定めることができる。接合前界面に垂直な断面において、接合前界面の位置上に長さＬのラインを想定し、結晶粒の少なくとも一部が当該ラインの長さＬの部分に接しているライン両側の結晶粒の数ｎ1、および結晶粒内に当該ラインの長さＬの部分の少なくとも一部分を含む結晶粒の数ｎ2を求め、下記〔１〕式によりｎtotalを定める。ただし、Ｌは３００μｍ以上とする。相互拡散により接合前界面上の結晶粒界の一部または全部が不明確となっている結晶粒は、一方の鋼材側から他方の鋼材側へと粒界移動を伴いながら成長した結晶粒である場合を除き、接合前界面に相当するライン上に結晶粒界が存在するとみなして当該ラインの両側の結晶粒をそれぞれｎ1のカウント対象とする。
ｎtotal＝ｎ1＋ｎ2−［ｎ1とｎ2に重複してカウントされた結晶粒の数］ …〔１〕
このｎtotalに占める侵入結晶粒の個数割合は、上記ｎ2のカウントに採用した結晶粒のうち侵入結晶粒であるもの（すなわち前記粒界三重点の粒界の夾角１５０°以下の条件を満たすもの）の個数を、ｎtotalで除することにより求まる。
Here, when “total number of crystal grains in contact with or across the interface before bonding” is n total , n total can be determined as follows. In a cross section perpendicular to the interface before bonding, a line having a length L is assumed on the position of the interface before bonding, and crystal grains on both sides of the line in which at least a part of the crystal grains are in contact with the length L portion of the line are assumed. The number n 1 and the number n 2 of crystal grains including at least a part of the length L of the line in the crystal grain are obtained, and n total is determined by the following formula [1]. However, L is 300 μm or more. A crystal grain in which a part or all of the crystal grain boundary on the interface before bonding is unclear due to interdiffusion is a crystal grain that is grown with grain boundary movement from one steel material side to the other steel material side. Except for the case, it is assumed that there is a crystal grain boundary on the line corresponding to the interface before bonding, and the crystal grains on both sides of the line are each counted as n 1 .
n total = n 1 + n 2 − [number of crystal grains counted redundantly in n 1 and n 2 ] ... [1]
The ratio of the number of invading crystal grains in n total is that of the invading crystal grains among the crystal grains employed in the counting of n 2 (that is, satisfying the condition that the included angle of the grain boundary triple point is 150 ° or less. The number of items is divided by n total .
また、「接合前界面位置上に占めるボイド存在箇所の長さ割合」は、接合前界面の位置上に上述の長さＬのラインを想定し、そのライン上に存在するボイド（未接合部）のトータル長さをＬで除することにより算出することができる。ボイドは未接合部を形成している空隙であり、残存酸化物とは異なる。 In addition, “the ratio of the length of the void existing portion on the interface position before bonding” is assumed to be the above-mentioned length L line on the interface position before bonding, and the void (unbonded portion) existing on the line Can be calculated by dividing the total length of L by L. Voids are voids that form unjoined parts and are different from residual oxides.
「ステンレス鋼」は、ＪＩＳ Ｇ０２０３：２００９の番号３８０１に示されているように、Ｃｒ含有量を十分に確保して耐食性を向上させた合金鋼である。ここではＣｒ含有量９.０質量％以上の鋼を対象とすることできるが、Ｃｒ含有量１０.５質量％以上を確保した鋼がより好適な対象となる。 “Stainless steel” is an alloy steel that sufficiently secures the Cr content and improves the corrosion resistance, as indicated by the number 3801 of JIS G0203: 2009. Here, steel with a Cr content of 9.0% by mass or more can be targeted, but steel with a Cr content of 10.5% by mass or more is more suitable.
接合する双方のステンレス鋼材をオーステナイト単相鋼とする場合、Ｃｒ含有量が９.０〜４０.０質量％好ましくは１０.５〜４０.０質量％、Ｎｉ含有量が６.０〜３０.０％であり、８００〜１２５０℃でオーステナイト単相組織を呈する鋼種を対象とすることができる。より好ましい成分組成範囲を例示すると、質量％で、Ｃ：０.０００１〜０.１５％、Ｓｉ：０.００１〜４.０％、Ｍｎ：０.００１〜２.５％、Ｐ：０.００１〜０.０４５％、Ｓ：０.０００５〜０.０３％、Ｎｉ：６.０〜２８.０％、Ｃｒ：１５.０〜２６.０％、Ｍｏ：０〜７.０％、Ｃｕ：０〜３.５％、Ｎｂ：０〜１.０％、Ｔｉ：０〜１.０％、Ａｌ：０〜０.１％、Ｎ：０〜０.３％、Ｂ：０〜０.０１％、Ｖ：０〜０.５％、Ｗ：０〜０.３％、Ｃａ、Ｍｇ、Ｙ、ＲＥＭ（希土類元素）の合計：０〜０.１％、残部Ｆｅおよび不可避的不純物からなる組成を有するオーステナイト系鋼種を挙げることができる。 When both stainless steel materials to be joined are austenitic single phase steels, the Cr content is 9.0 to 40.0 mass%, preferably 10.5 to 40.0 mass%, and the Ni content is 6.0 to 30. The steel grade that is 0% and exhibits an austenite single phase structure at 800 to 1250 ° C. can be targeted. More preferable component composition ranges are exemplified by C: 0.0001 to 0.15%, Si: 0.001 to 4.0%, Mn: 0.001 to 2.5%, and P: 0.005% by mass. 001 to 0.045%, S: 0.0005 to 0.03%, Ni: 6.0 to 28.0%, Cr: 15.0 to 26.0%, Mo: 0 to 7.0%, Cu : 0-3.5%, Nb: 0-1.0%, Ti: 0-1.0%, Al: 0-0.1%, N: 0-0.3%, B: 0-0. 01%, V: 0 to 0.5%, W: 0 to 0.3%, Ca, Mg, Y, REM (rare earth element) total: 0 to 0.1%, remaining Fe and unavoidable impurities Examples include austenitic steel types having a composition.
接合する双方のステンレス鋼材をフェライト単相鋼とする場合、Ｃｒ含有量が９.０〜４０.０質量％好ましくは１０.５〜４０.０質量％であり、８００〜１２５０℃でフェライト単相組織を呈する鋼種を対象とすることができる。より好ましい成分組成範囲を例示すると、質量％で、Ｃ：０.０００１〜０.１５％、Ｓｉ：０.００１〜１.２％、Ｍｎ：０.００１〜１.２％、Ｐ：０.００１〜０.０４％、Ｓ：０.０００５〜０.０３％、Ｎｉ：０〜０.６％、Ｃｒ：１１.５〜３２.０％、Ｍｏ：０〜２.５％、Ｃｕ：０〜１.０％、Ｎｂ：０〜１.０％、Ｔｉ：０〜１.０％、Ａｌ：０〜０.２％、Ｎ：０〜０.０２５％、Ｂ：０〜０.０１％、Ｖ：０〜０.５％、Ｗ：０〜０.３％、Ｃａ、Ｍｇ、Ｙ、ＲＥＭ（希土類元素）の合計：０〜０.１％、残部Ｆｅおよび不可避的不純物からなる組成を有するフェライト系鋼種を挙げることができる。 When both stainless steel materials to be joined are ferritic single phase steel, the Cr content is 9.0 to 40.0% by mass, preferably 10.5 to 40.0% by mass, and the ferrite single phase is 800 to 1250 ° C. Steel types that exhibit a structure can be targeted. More preferable component composition ranges are illustrated by mass%, C: 0.0001 to 0.15%, Si: 0.001 to 1.2%, Mn: 0.001 to 1.2%, P: 0.00. 001 to 0.04%, S: 0.0005 to 0.03%, Ni: 0 to 0.6%, Cr: 11.5 to 32.0%, Mo: 0 to 2.5%, Cu: 0 -1.0%, Nb: 0-1.0%, Ti: 0-1.0%, Al: 0-0.2%, N: 0-0.025%, B: 0-0.01% , V: 0 to 0.5%, W: 0 to 0.3%, Ca, Mg, Y, REM (rare earth element) total: 0 to 0.1%, balance Fe and inevitable impurities The ferritic steel grades that can be mentioned.
また、上記のステンレス鋼拡散接合製品の製造法として、
拡散接合に供する双方のステンレス鋼材（以下「接合前鋼材」という）として、接合面となる表面の表面粗さＲａが０.３０μｍ以下に調整された鋼材を使用し、
拡散接合条件として、双方の接合前鋼材とも平均結晶粒径ｒ0が５０μｍ以下に調整された状態から拡散接合温度に到達し、拡散接合温度に保持した後に平均結晶粒径ｒ1が８０μｍ以下となり、かつ（ｒ1−ｒ0）／ｒ0が０.２０以上となるヒートパターンを適用する手法が提供される。
Also, as a method for producing the above-mentioned stainless steel diffusion bonded products,
As both stainless steel materials used for diffusion bonding (hereinafter referred to as “steel materials before bonding”), steel materials having a surface roughness Ra of the bonding surface adjusted to 0.30 μm or less are used,
As diffusion bonding conditions, both of the steel materials before bonding reach the diffusion bonding temperature from the state where the average crystal grain size r 0 is adjusted to 50 μm or less, and after maintaining the diffusion bonding temperature, the average crystal grain size r 1 becomes 80 μm or less. In addition, a method of applying a heat pattern in which (r 1 −r 0 ) / r 0 is 0.20 or more is provided.
ここで、平均結晶粒径は、接合面に垂直な断面について顕微鏡組織観察を行った場合の円相当径を採用することができる。観察視野は厚さ中心部を含む９００００μｍ2以上の矩形領域とし、その矩形内に結晶粒の全部が収まっている結晶粒を対象として測定すればよい。上記ヒートパターンにより双方の鋼材のｒ0およびｒ1が上記の規定に合致するかどうかは、双方の接合前鋼材について当該ヒートパターンでの加熱試験を施すことによって判定することができる。 Here, as the average crystal grain size, a circle-equivalent diameter in the case where the microstructure is observed on a cross section perpendicular to the joint surface can be adopted. The observation field of view may be a rectangular region of 90000 μm 2 or more including the center of thickness, and measurement may be performed on crystal grains in which all of the crystal grains are contained within the rectangle. Whether or not r 0 and r 1 of both steel materials meet the above-mentioned rules by the heat pattern can be determined by performing a heating test with the heat pattern on both steel materials before joining.
本発明に従うステンレス鋼拡散接合製品は接合箇所の信頼性（接合強度や密封性）が高い。また、インサート材を使用していないので、適用するステンレス鋼種本来の特性（耐食性等）を活かすことができる。特に、オーステナイト単相系ステンレス鋼やフェライト単相系ステンレス鋼を用いた拡散接合製品の普及に貢献しうる。 The stainless steel diffusion bonded product according to the present invention has high reliability (bonding strength and sealing performance) at the bonded portion. Moreover, since the insert material is not used, the original characteristics (such as corrosion resistance) of the stainless steel to be applied can be utilized. In particular, it can contribute to the spread of diffusion bonding products using austenitic single-phase stainless steel or ferritic single-phase stainless steel.
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）ボイド内の残留ガスが母材と反応する過程、が並行して進行することにより完了すると考えられる。しかし、このような従来のメカニズムで拡散接合させる場合、特に（ii）の反応を完全に終了させるために高温、高面圧、長時間を要し、これが直接法による拡散接合を工業的に生産性良く実施するためのネックとなっていることがわかった。 The diffusion bonding by the direct method of stainless steel materials, according to the conventional method, (i) the process of increasing the bonding area of the bonded area, (ii) bonding at the bonded area, and (ii) bonding at the bonded area It is considered that the process in which the surface oxide film of the front steel material disappears and (iii) the process in which the residual gas in the void reacts with the base material progress in parallel. However, when diffusion bonding is performed by such a conventional mechanism, in particular, high temperature, high surface pressure, and a long time are required to complete the reaction (ii), and this produces industrial diffusion bonding by the direct method. It turned out that it became the bottleneck for implementing well.
発明者らは、直接法による拡散接合（以下「直接拡散接合」ということがある）でステンレス鋼材同士を接合する際に、特に上記（ii）の過程がネックとなる生産性の低下を回避すべく、種々研究を重ねてきた。その結果、一方の鋼材側の結晶粒が接合前界面を超えて相手側に侵入するように成長している箇所が多々存在する拡散接合構造を実現したとき、上記（ii）の過程における表面酸化物皮膜の消失を待つことなく信頼性の高い拡散接合部を構築することができることが明らかとなった。 The inventors avoid a decrease in productivity particularly when the above-mentioned process (ii) becomes a bottleneck when joining stainless steel materials by diffusion bonding by a direct method (hereinafter also referred to as “direct diffusion bonding”). Therefore, various researches have been repeated. As a result, the surface oxidation in the process of (ii) above was achieved when a diffusion bonding structure in which there were many places where the crystal grains on one steel material side had grown so as to penetrate the mating side beyond the interface before bonding was achieved. It became clear that a highly reliable diffusion junction can be constructed without waiting for the disappearance of the material film.
図１（ａ）に、従来一般的な直接拡散接合により形成されたステンレス鋼拡散接合製品の接合前界面に垂直な断面の組織形態を模式的に例示する。接合前界面の位置を夾んで双方の鋼材側の結晶粒同士が対面することにより接合している。この接合部は上記（ii）の過程により接合前鋼材の表面酸化物皮膜に起因する酸化物層が拡散により消失していき双方の鋼素地同士が結合したものであり、基本的に接合前界面上に結晶粒界を有する。ただし、拡散により接合前界面上の明確な結晶粒界が部分的に消失している場合もある。また、接合前界面位置にあった双方の鋼材間の結晶粒界が、どちらかの鋼材側にシフトしている箇所が存在する場合もある。 FIG. 1A schematically illustrates a structure form of a cross section perpendicular to the interface before joining of a stainless steel diffusion bonding product formed by conventional general direct diffusion bonding. It is joined by crystal grains on both sides facing each other with the position of the interface before joining. In this joint, the oxide layer resulting from the surface oxide film of the steel material before joining disappears by diffusion through the process of (ii) above, and both steel substrates are basically bonded to each other. It has a grain boundary on the top. However, a clear crystal grain boundary on the interface before bonding may partially disappear due to diffusion. Moreover, there may be a location where the crystal grain boundary between the two steel materials at the interface position before joining is shifted to either steel material side.
従来の直接拡散接合によって、表面酸化物皮膜に起因する残存酸化物やボイドが十分に消失している状態となっていれば、接合強度や密封性に問題はない。しかし、そのような信頼性の高い接合部を得るためには上述の（i）〜（iii）の過程を十分に完了させる必要があり、工業的な実施には多大なコストを要するという問題があった。 If the residual oxides and voids resulting from the surface oxide film are sufficiently eliminated by the conventional direct diffusion bonding, there is no problem in the bonding strength and the sealing performance. However, in order to obtain such a highly reliable joint, it is necessary to sufficiently complete the processes (i) to (iii) described above, and there is a problem that industrial implementation requires a great deal of cost. there were.
図１（ｂ）に、本発明に従う直接拡散接合により形成されたステンレス鋼拡散接合製品の接合前界面に垂直な断面の組織形態を模式的に例示する。接合前界面に面していた結晶粒のなかには接合前界面を乗り越えて相手側鋼材の方へ侵入するように成長して、その相手側の領域において粒界三重点（図中の矢印で示した箇所）を形成しているものが存在する。そのような結晶粒（図中の矢印を内包するもの）の当該粒界三重点の粒内側に生じる粒界の夾角（図中α）をここでは「侵入角」と呼ぶ。前記の「侵入結晶粒」はその侵入角が１５０°以下である結晶粒である。接合前界面上には表面酸化物皮膜に起因する残存酸化物が存在しても構わない。また、少量のボイド（図示せず）が残存する場合もある。 FIG. 1 (b) schematically illustrates a cross-sectional structure perpendicular to the interface before joining of a stainless steel diffusion bonding product formed by direct diffusion bonding according to the present invention. Some of the crystal grains that faced the interface before bonding grew over the interface before bonding and penetrated into the mating steel, and in the region of the mating boundary, the grain boundary triple point (indicated by the arrows in the figure) There is something that forms a part). The angle of depression of the grain boundary (α in the figure) generated inside the grain boundary triple point of such a crystal grain (including the arrow in the figure) is referred to herein as the “penetration angle”. The “penetrating crystal grains” are crystal grains having an intrusion angle of 150 ° or less. Residual oxides resulting from the surface oxide film may be present on the interface before bonding. In addition, a small amount of voids (not shown) may remain.
このような本発明に従う拡散接合部は、後述のように粒成長の駆動力を与えることによって、上記（ii）の表面酸化物皮膜の完全消失を待たずに形成させることができる。したがって、拡散接合条件がインサート材挿入法と同程度に緩和される。また、この拡散接合部の形態はオーステナイト単相鋼種やフェライト単相鋼種など、本来、直接拡散接合が難しいとされていた鋼種に対しても形成させることができる。 Such a diffusion bonding portion according to the present invention can be formed without waiting for the complete disappearance of the surface oxide film of the above (ii) by providing a driving force for grain growth as described later. Therefore, the diffusion bonding conditions are relaxed to the same extent as in the insert material insertion method. In addition, the form of the diffusion bonded portion can be formed even for a steel type that is originally considered to be difficult to perform direct diffusion bonding, such as an austenite single phase steel type or a ferrite single phase steel type.
侵入結晶粒は相手側の鋼材中へ侵入角１５０°以下でくさびのように侵入しているので接合部でアンカー効果を発揮し、接合強度の向上に寄与する。侵入角１５０°未満の結晶粒は接合強度向上にあまり有効でない。種々検討の結果、自動車部品等での十分な密封性（ガス成分が拡散接合部を出入りしない性能）を確保するためには、上述の「接合前界面に接するか接合前界面を跨ぐ結晶粒の総数」に占める侵入結晶粒の個数割合が２０％以上であることが必要である。侵入結晶粒は拡散接合時に一方の鋼材側から相手鋼材側へと粒界移動を伴いながら成長した結晶粒である。これは、長時間の拡散により接合前界面上の粒界が徐々に移動または消失したのではなく、ある程度勢いよく結晶粒が接合前界面を乗り越えて成長することによって生じたものであると考えられる。 Since the invading crystal grains penetrate into the counterpart steel material like a wedge at an invasion angle of 150 ° or less, an anchor effect is exhibited at the joint and contributes to an improvement in joint strength. Crystal grains having a penetration angle of less than 150 ° are not very effective in improving the bonding strength. As a result of various studies, in order to secure sufficient sealing performance (performance in which gas components do not enter and exit the diffusion bonded portion) in automobile parts, etc., the above-mentioned “ It is necessary that the number ratio of the invading crystal grains in the “total number” is 20% or more. An intruding crystal grain is a crystal grain that has grown while accompanying grain boundary movement from one steel material side to the other steel material side during diffusion bonding. This is thought to be caused by the fact that the grain boundaries on the interface before bonding did not gradually move or disappear due to long-term diffusion, but rather that the crystal grains grew over the interface before bonding to some extent. .
このような侵入結晶粒は上記（ii）の表面酸化物皮膜の完全消失を待たずに形成させることができることから、多くの場合、接合前界面位置には残存酸化物が観測される。この残存酸化物は存在して構わない。しかし、接合前界面位置に多数のボイド（未接合部）が残存していると接合部の信頼性を損なう要因となる。詳細な検討の結果、上述の「接合前界面位置上に占めるボイド存在箇所の長さ割合」が５％以下であることが重要である。 Since such interstitial crystal grains can be formed without waiting for the complete disappearance of the surface oxide film of (ii) above, residual oxide is often observed at the interface position before bonding. This residual oxide may be present. However, if a large number of voids (unjoined parts) remain at the interface position before joining, the reliability of the joined parts is impaired. As a result of detailed investigation, it is important that the above-mentioned “ratio of the length of the void existing portion on the interface position before bonding” is 5% or less.
〔ステンレス鋼種〕
本発明は種々のステンレス鋼種に適用できるが、なかでも拡散接合の加熱温度域を含む８００〜１２５０℃の温度域でオーステナイト単相あるいはフェライト単相となるステンレス鋼種に適用することが効果的である。これらのオーステナイト単相系またはフェライト単相系の鋼種は本来直接法による拡散接合は必ずしも容易でないが、後述の手法に従えば上述の接合組織構造を実現することが可能であり信頼性の高い拡散接合製品を得ることができる。これらの鋼種の具体的な成分組成範囲は前述のとおりである。
[Stainless steel grade]
Although the present invention can be applied to various stainless steel types, it is effective to apply to a stainless steel type that becomes an austenite single phase or a ferrite single phase in a temperature range of 800 to 1250 ° C. including a heating temperature range of diffusion bonding. . These austenitic single-phase or ferritic single-phase steel grades are not necessarily easy to be diffusion-bonded by the direct method. However, according to the method described below, the above-mentioned joint structure can be realized and diffusion is highly reliable. Joined products can be obtained. Specific component composition ranges of these steel types are as described above.
〔拡散接合方法〕
拡散接合部に上記の侵入結晶粒を生成させるためには、双方の鋼材の接触界面に介在して拡散障壁となる酸化物皮膜を乗り越えて結晶粒が成長する必要がある。そのためには前記の結晶粒成長に必要な駆動力を何らかの手法により与えなければならない。その手法として、例えば、拡散接合に供する鋼材に予め冷間加工歪を付与しておく方法や、通電加熱等により瞬間的に加熱する方法などが考えられる。しかし、前者は接合に供する鋼材に対する制約が大きく、また後者は工業的規模での安定した実施は容易でない。そこで発明者らは研究を進めたところ、平均結晶粒径ができるだけ小さい組織状態で拡散接合の加熱に供し、拡散接合時に平均結晶粒径の大幅な増大を伴いながら粒成長させる手法が極めて有効であることを見出した。また、双方の鋼材のミクロ的な接触表面積を十分に確保するために接合面となる表面はできるだけ平滑化されていることが重要である。具体的には以下の条件を採用すればよい。
(Diffusion bonding method)
In order to generate the above-described intruding crystal grains in the diffusion bonding portion, it is necessary to grow the crystal grains over the oxide film serving as a diffusion barrier interposed between the contact interfaces of both steel materials. For that purpose, the driving force necessary for the crystal grain growth must be given by some method. As the method, for example, a method of preliminarily imparting cold working strain to a steel material to be used for diffusion bonding, a method of instantaneously heating by energization heating, or the like can be considered. However, the former has great restrictions on the steel materials used for joining, and the latter is not easy to perform stably on an industrial scale. Therefore, the inventors conducted research and found that a technique in which the average crystal grain size is subjected to heating in diffusion bonding in a microstructure state as small as possible and the grain growth is performed while the average crystal grain size is greatly increased at the time of diffusion bonding is extremely effective. I found out. Further, it is important that the surfaces to be joined surfaces are made as smooth as possible in order to sufficiently secure the microscopic contact surface area of both steel materials. Specifically, the following conditions may be adopted.
双方の接合前鋼材として、接合面となる表面の表面粗さＲａが０.３０μｍ以下に調整された鋼材を使用する。Ｒａが０.２０μｍ以下に調整された鋼材を使用することがより好ましい。表面粗さが大きくなると接合前界面位置のボイドを効率的に減少させるうえで不利となる。 As both steel materials before joining, steel materials whose surface roughness Ra of the surface to be the joining surface is adjusted to 0.30 μm or less are used. It is more preferable to use a steel material with Ra adjusted to 0.20 μm or less. When the surface roughness is increased, it is disadvantageous in efficiently reducing voids at the interface position before bonding.
拡散接合の具体的な加熱条件としては、双方の接合前鋼材とも平均結晶粒径ｒ0が５０μｍ以下に調整された状態から拡散接合温度に到達し、拡散接合温度に保持した後に平均結晶粒径ｒ1が８０μｍ以下となり、かつ（ｒ1−ｒ0）／ｒ0が０.２０以上となるヒートパターンを適用することが極めて有効である。ｒ0が５０μｍより大きい場合や、（ｒ1−ｒ0）／ｒ0が０.２０以上とならない場合は、拡散障壁である酸化物皮膜を乗り越えるに足る粒成長の駆動力を得ることが難しくなる。また、ｒ1が８０μｍを超えて粗大化する場合は粒界三重点での侵入角αが１５０°を超えやすくなり、結果的にアンカー効果に優れる侵入結晶粒の個数割合が低減する。 Expansion as the dispersion Specific heating conditions of the joint, both steel before bonding of reaching the diffusion bonding temperature from the state in which the average crystal grain size r 0 is adjusted to 50μm or less, the average crystal grain after holding the diffusion bonding temperature It is extremely effective to apply a heat pattern in which the diameter r 1 is 80 μm or less and (r 1 −r 0 ) / r 0 is 0.20 or more. When r 0 is larger than 50 μm or (r 1 −r 0 ) / r 0 does not become 0.20 or more, it is difficult to obtain a driving force for grain growth sufficient to overcome the oxide film that is a diffusion barrier. Become. In addition, when r 1 exceeds 80 μm and becomes coarser, the penetration angle α at the grain boundary triple point tends to exceed 150 °, and as a result, the number ratio of the penetrating crystal grains excellent in the anchor effect is reduced.
拡散接合温度に到達する前の段階における平均結晶粒径ｒ0は拡散接合の熱処理に供する前の接合前鋼材の段階で既に調整されていてもよいが、拡散接合の昇温過程を利用して熱処理を施すことによってｒ0を５０μｍ以下に調整し、その後さらに拡散接合温度まで昇温するヒートパターンを採用することもできる。実際の操業に際しては、接合前鋼材の成分組成、加工度などに応じて予備実験により適切なヒートパターンの条件を予め把握しておけばよい。 The average grain size r 0 in the stage before reaching the diffusion bonding temperature may have already been adjusted in the stage of the pre-bonding steel material before being subjected to the heat treatment for diffusion bonding. It is also possible to adopt a heat pattern in which r 0 is adjusted to 50 μm or less by performing heat treatment, and then the temperature is further raised to the diffusion bonding temperature. In actual operation, an appropriate heat pattern condition may be grasped in advance by preliminary experiments in accordance with the component composition of the steel material before joining, the degree of processing, and the like.
その適切なヒートパターン条件は通常、拡散接合温度９００〜１２５０℃、好ましくは９８０〜１２００℃、保持時間０.５〜３.０ｈの範囲内にて見つけることができる。この範囲内において、双方の鋼材とも平均結晶粒径ｒ1が８０μｍ以下かつ（ｒ1−ｒ0）／ｒ0が０.２０以上となるような条件であれば、侵入結晶粒の個数割合が２０％以上、かつ接合前界面位置上に占めるボイド存在箇所の長さ割合が５％以下である適切な拡散接合部の組織状態を実現することができる。拡散接合時の雰囲気は通常、真空引きによりガスの全圧を１０-1Ｐａ以下とすれば十分である。 The appropriate heat pattern conditions can usually be found within the range of diffusion bonding temperature 900 to 1250 ° C., preferably 980 to 1200 ° C. and holding time 0.5 to 3.0 h. Within this range, if both steel materials are in such a condition that the average crystal grain size r 1 is 80 μm or less and (r 1 -r 0 ) / r 0 is 0.20 or more, the number ratio of invading crystal grains is It is possible to realize an appropriate structure of the diffusion bonded portion in which the length ratio of the void existing portion occupying 20% or more and on the interface position before bonding is 5% or less. The atmosphere during diffusion bonding is usually sufficient if the total pressure of the gas is 10 −1 Pa or less by evacuation.
表１に示す化学組成の鋼を溶製し、熱間圧延にて板厚３〜４ｍｍの熱延板とし、焼鈍、酸洗、冷間圧延により板厚１.０ｍｍの冷延板とし、その後必要に応じて仕上焼鈍および酸洗を施し、供試鋼板とした。γ−１〜γ−３は８００〜１２５０℃でオーステナイト単相組織となるオーステナイト単相系ステンレス鋼、α−１、α−２は８００〜１２５０℃でフェライト単相組織となるフェライト単相系ステンレス鋼である。 Steel having the chemical composition shown in Table 1 is melted and hot rolled into a hot rolled sheet with a thickness of 3 to 4 mm, then cold rolled with a thickness of 1.0 mm by annealing, pickling and cold rolling, and then Finish annealing and pickling were performed as necessary to obtain test steel plates. γ-1 to γ-3 are austenite single phase stainless steels that form an austenite single phase structure at 800 to 1250 ° C, and α-1 and α-2 are ferrite single phase stainless steels that form a ferrite single phase structure at 800 to 1250 ° C. It is steel.
供試鋼板の表面粗さＲａの調整は、必要に応じて＃１８０〜＃２０００のエメリー紙で鋼板表面を湿式研磨する工程を冷間圧延後または仕上焼鈍後の酸洗前に挿入することにより行った。仕上焼鈍を行った供試鋼板では、その仕上焼鈍温度を９００〜１２００℃の範囲で変えることにより拡散接合前の平均結晶粒径ｒ0を種々のサイズに調整した。仕上焼鈍を行っていない供試鋼板では、後述のように拡散接合の昇温過程を利用して熱処理を施すことによりｒ0を調整した。 The surface roughness Ra of the test steel sheet is adjusted by inserting a step of wet polishing the steel sheet surface with emery paper of # 180 to # 2000 as necessary before cold pickling or after pickling after finish annealing. went. In the test steel sheet that was subjected to finish annealing, the average crystal grain size r 0 before diffusion bonding was adjusted to various sizes by changing the finish annealing temperature in the range of 900 to 1200 ° C. In the test steel sheet that was not subjected to finish annealing, r 0 was adjusted by performing heat treatment using the temperature raising process of diffusion bonding as described later.
各供試鋼板から切削加工により１００ｍｍ角の「平板材」を作製した。また、切削加工により１００ｍｍ角の平板材の中央をくりぬいて幅５ｍｍの枠を有する「枠材」を作製した。これらの切削加工後にバリは除去していない。平板材と枠材には対角線上端部付近２箇所にφ６ｍｍの穴を形成した。図３（ａ）の［１］［５］に平板材の寸法・形状を、同［２］〜［４］に枠材の寸法・形状をそれぞれ模式的に示してある。図３（ａ）に示すように３枚の枠材を重ね、その両側を平板材で蓋をするように［１］〜［５］の積層順でこれらの鋼材を重ね合わせて積層体とし、各鋼材を連通する上記穴にＡｌｌｏｙ６００製のφ５ｍｍのピンを差し込み、水平に置かれたこの積層体の上面に質量５ｋｇの錘を乗せ、真空拡散接合に供した。このとき鋼材間の接触面には約０.０５ＭＰａの面圧が付与されている。１つの積層体において［１］〜［５］は平均結晶粒径ｒ0および接触表面の表面粗さＲａが共通の同一鋼種とした。 A 100 mm square “flat plate” was prepared from each test steel sheet by cutting. Further, a “frame material” having a frame with a width of 5 mm was produced by cutting the center of a 100 mm square flat plate material by cutting. The burrs are not removed after these cutting operations. In the flat plate member and the frame member, φ6 mm holes were formed at two locations near the upper end of the diagonal line. In FIG. 3A, [1] and [5] schematically show the size and shape of the flat plate, and [2] to [4] schematically show the size and shape of the frame material. As shown in FIG. 3 (a), three frame members are stacked, and these steel members are stacked in a stacking order of [1] to [5] so that both sides are covered with a flat plate, A φ5 mm pin made of Alloy 600 was inserted into the holes communicating with each steel material, and a weight of 5 kg was placed on the upper surface of the horizontally placed laminate, and subjected to vacuum diffusion bonding. At this time, a contact pressure of about 0.05 MPa is applied to the contact surface between the steel materials. In one laminate, [1] to [5] are the same steel type having the same average grain size r 0 and surface roughness Ra of the contact surface.
拡散接合は、上記積層体を真空炉に装入して１０-2Ｐａ以下の圧力となるまで真空引きした後、９００〜１１００℃の範囲に設定した拡散接合温度まで昇温してその温度に所定時間保持し、その後、炉中で放冷する手法にて行った。仕上焼鈍を行っていない供試鋼板を使用した例では拡散接合温度への昇温過程を利用して途中の温度で保持する熱処理を加え、この熱処理で拡散接合前の平均結晶粒径ｒ0を調整した。表２中にはこの熱処理を※印にて表示してある。供試鋼板の組合せおよび拡散接合条件が同一であるステンレス鋼拡散接合製品（図３（ｂ）の形状のもの）を２個ずつ作製し、それぞれ後述の断面観察と拡散接合性評価に使用した。 In diffusion bonding, the above laminate is charged into a vacuum furnace and evacuated to a pressure of 10 −2 Pa or less, and then heated to the diffusion bonding temperature set in the range of 900 to 1100 ° C. to reach that temperature. It hold | maintained for the predetermined time, and performed by the method of cooling in a furnace after that. In the case of using the test steel sheet not subjected to finish annealing, a heat treatment is used to maintain the intermediate temperature using the temperature raising process to the diffusion bonding temperature, and the average grain size r 0 before diffusion bonding is determined by this heat treatment. It was adjusted. In Table 2, this heat treatment is indicated by *. Two stainless steel diffusion bonded products (in the shape of FIG. 3 (b)) having the same combination of test steel plates and diffusion bonding conditions were prepared and used for cross-sectional observation and diffusion bonding evaluation described below, respectively.
〔平均結晶粒径ｒ0およびｒ1の確認〕
接合前鋼材に相当する各供試鋼板に対して、上記の各拡散接合の条件と同じヒートパターンで加熱試験を施すことにより、拡散接合前の平均結晶粒径ｒ0、および拡散接合のヒートパターンを終えた時点の平均結晶粒径ｒ1を測定した。ｒ0については、拡散接合の昇温過程を利用して熱処理を行うヒートパターンの場合は当該熱処理後の段階の試験片を急冷したのち組織観察を行うことにより測定し、それ以外では拡散接合の昇温に供する前の供試鋼板について組織観察を行うことにより測定した。平均結晶粒径ｒ0およびｒ1の測定は、圧延方向に垂直な断面（Ｃ断面）について光学顕微鏡による組織観察を行い、金属組織写真を画像処理して各結晶粒の円相当径を求め、それを平均することにより行った。
[Confirmation of average crystal grain size r 0 and r 1 ]
By subjecting each test steel plate corresponding to the steel material before joining to a heat test in the same heat pattern as the conditions of each of the above-mentioned diffusion bonding, the average crystal grain size r 0 before diffusion bonding, and the heat pattern of diffusion bonding The average crystal grain size r 1 at the time of finishing was measured. In the case of a heat pattern in which heat treatment is performed using the temperature rise process of diffusion bonding, r 0 is measured by quenching the test piece at the stage after the heat treatment and then observing the structure. It measured by performing structure | tissue observation about the test steel plate before using for temperature rising. The average crystal grain sizes r 0 and r 1 are measured by observing the structure with an optical microscope for the cross section (C cross section) perpendicular to the rolling direction, image processing of the metal structure photograph, and obtaining the equivalent circle diameter of each crystal grain, This was done by averaging.
〔拡散接合製品の断面観察〕
得られたステンレス鋼拡散接合製品について図３（ｂ）のａ−ａ’の位置で積層方向に切断し、その断面（［１］〜［５］の鋼材のＣ断面に相当）をバフ研磨後、フッ酸−硝酸−グリセリン混合溶液中でエッチングしたのち組織観察を行った。その際、図３（ｂ）のａ側およびａ’側の断面に形成されている計８箇所の拡散接合部について、各接合前界面上に長さＬ＝３００μｍのラインを想定して上述〔１〕式のｎtotalに占める侵入結晶粒の個数割合を求め、８箇所の平均値を算出することにより「接合前界面に接するか接合前界面を跨ぐ結晶粒の総数に占める前記侵入結晶粒の個数割合Ａ（％）」を求めた。また、同時に「接合前界面位置上に占めるボイド存在箇所の長さ割合Ｂ（％）」を求めた。
[Section observation of diffusion bonding products]
The obtained stainless steel diffusion bonding product was cut in the laminating direction at the position aa ′ in FIG. 3B, and the cross section (corresponding to the C cross section of the steel materials [1] to [5]) was buffed. The structure was observed after etching in a hydrofluoric acid-nitric acid-glycerin mixed solution. At that time, a total of 8 diffusion bonding portions formed in the cross sections on the a side and a ′ side in FIG. 3B are described above assuming a line of length L = 300 μm on each pre-bonding interface. 1] The number ratio of the invading crystal grains in n total in the formula is calculated, and the average value of 8 points is calculated, thereby obtaining “the number of intruding crystal grains in the total number of crystal grains in contact with or straddling the interface before joining”. The number ratio A (%) was determined. At the same time, “the length ratio B (%) of the void existing portion on the interface position before bonding” was determined.
侵入結晶粒の生成程度については上記Ａ値が２０％以上であるものを○（良好）、それ以外を×（不良）と評価した。
ボイドの消失程度については上記Ｂ値が５％以下であるものを○（良好）、それ以外を×（不良）と評価した。
As for the degree of formation of the intruding crystal grains, the case where the A value was 20% or more was evaluated as ◯ (good), and the others were evaluated as x (bad).
Regarding the disappearance degree of voids, the case where the B value was 5% or less was evaluated as ◯ (good), and the others were evaluated as × (bad).
〔拡散接合性評価〕
各ステンレス鋼拡散接合製品について、大気中８００℃で２４ｈの加熱試験を施した。その後、図３（ｂ）のａ−ａ’の位置で積層方向に切断し、内部の空洞表面（内表面）の酸化の有無を目視で調査した。拡散接合部に外部と繋がる空隙が存在していた場合や、当該加熱処理時に拡散接合部に破損が生じた場合には、内部に酸素が侵入するため加熱試験後の内表面は酸化され、当初の金属光沢が失われる。一方、拡散接合部の健全性が維持され内部が高真空の状態に保たれている場合は加熱試験後の内表面はステンレス鋼特有の金属光沢を呈する。そこで、内表面が当初の金属光沢を維持しているステンレス鋼拡散接合製品を○（拡散接合性；良好）、それ以外を×（拡散接合性；不良）と評価した。結果を表２に示す。
(Diffusion bonding evaluation)
Each stainless steel diffusion bonding product was subjected to a heating test in the atmosphere at 800 ° C. for 24 hours. Then, it cut | disconnected in the lamination direction in the position of aa 'of FIG.3 (b), and the presence or absence of the oxidation of the internal cavity surface (inner surface) was investigated visually. If there is a gap connected to the outside in the diffusion bonding part or if the diffusion bonding part is damaged during the heat treatment, the inner surface after the heating test is oxidized because oxygen penetrates into the inside. The metallic luster is lost. On the other hand, when the soundness of the diffusion bonded portion is maintained and the inside is kept in a high vacuum state, the inner surface after the heating test exhibits a metallic luster unique to stainless steel. Therefore, a stainless steel diffusion bonding product whose inner surface maintained the original metallic luster was evaluated as ◯ (diffusion bonding property: good), and the others were evaluated as x (diffusion bonding property: poor). The results are shown in Table 2.
表２からわかるように、本発明例のものは侵入結晶粒の個数割合Ａが２０％以上、かつボイドの存在割合Ｂが５％以下である拡散接合部が形成され、その拡散接合部は信頼性の高いものであった。 As can be seen from Table 2, in the examples of the present invention, diffusion junctions in which the number ratio A of intruding crystal grains is 20% or more and the existence ratio B of voids is 5% or less are formed. It was highly probable.
これに対し、比較例Ｎｏ.１は拡散接合温度が低かったため、またＮｏ.５は仕上焼鈍時間が短く、拡散接合温度が低かったため、これらはいずれも（ｒ1−ｒ0）／ｒ0が０.２０以上となる結晶粒成長が起こらず、侵入結晶粒の個数割合Ａが不十分となった。その結果、拡散接合性に劣った。Ｎｏ.４、１３は接合前鋼材の表面粗さＲａが大きかったのでボイドの存在割合Ｂが多くなり、拡散接合性に劣った。Ｎｏ.６、１４は拡散接合後の平均結晶粒径ｒ1が過大となる拡散接合条件であったため、またＮｏ.８はさらに拡散接合前の平均結晶粒径ｒ0が大きすぎたため、これらはいずれも侵入結晶粒の個数割合Ａが不十分となり、拡散接合性に劣った。 On the other hand, since Comparative Example No. 1 had a low diffusion bonding temperature, and No. 5 had a short finish annealing time and a low diffusion bonding temperature, both of these were (r 1 −r 0 ) / r 0. Grain growth of 0.20 or more did not occur, and the number ratio A of invading crystal grains was insufficient. As a result, the diffusion bonding property was inferior. In Nos. 4 and 13, since the surface roughness Ra of the steel material before joining was large, the presence ratio B of the voids was increased and the diffusion bonding property was inferior. Nos. 6 and 14 were diffusion bonding conditions in which the average crystal grain size r 1 after diffusion bonding was excessive, and No. 8 was further because the average crystal grain size r 0 before diffusion bonding was too large. In all cases, the number ratio A of invading crystal grains was insufficient, and the diffusion bonding property was inferior.
Claims (5)
（１）拡散接合時の結晶粒界移動によって接合前界面を跨いで相手側の鋼材中へと侵入して接合前界面より相手側の位置に粒界三重点を形成した結晶粒のうち、前記粒界三重点における粒界の夾角が１５０°以下である結晶粒を「侵入結晶粒」と呼ぶとき、接合前界面に接するか接合前界面を跨ぐ結晶粒の総数に占める前記侵入結晶粒の個数割合が２０％以上であること、
（２）接合前界面位置上に占めるボイド存在箇所の長さ割合が５％以下であること、
を満たすステンレス鋼拡散接合製品。 It is a diffusion bonding product in which stainless steel materials are brought into direct contact with each other and integrated by diffusion bonding, and in a cross section perpendicular to the contact interface before bonding (hereinafter referred to as “the interface before bonding”),
(1) Among the crystal grains that have penetrated into the mating steel material across the interface before bonding by the grain boundary movement during diffusion bonding, and formed a grain boundary triple point at the position on the mating side from the interface before bonding, When a crystal grain having a grain boundary depression angle of 150 ° or less at the grain boundary triple point is referred to as an “invasion crystal grain”, the number of the intrusion crystal grains in the total number of crystal grains in contact with or across the interface before bonding The proportion is 20% or more,
(2) The length ratio of the void existing location on the interface position before joining is 5% or less,
Meet stainless steel diffusion bonding products.
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