WO2015145808A1 - Method for processing surface of stainless steel, and heat exchanger obtained using same - Google Patents

Method for processing surface of stainless steel, and heat exchanger obtained using same Download PDF

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Publication number
WO2015145808A1
WO2015145808A1 PCT/JP2014/073606 JP2014073606W WO2015145808A1 WO 2015145808 A1 WO2015145808 A1 WO 2015145808A1 JP 2014073606 W JP2014073606 W JP 2014073606W WO 2015145808 A1 WO2015145808 A1 WO 2015145808A1
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Prior art keywords
stainless steel
heat transfer
microstructure
treatment
processing method
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PCT/JP2014/073606
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French (fr)
Japanese (ja)
Inventor
利則 川村
明紀 田村
広 中野
和明 木藤
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株式会社日立製作所
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Priority to EP14886931.6A priority Critical patent/EP3124650B1/en
Publication of WO2015145808A1 publication Critical patent/WO2015145808A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
    • B24C1/06—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods for producing matt surfaces, e.g. on plastic materials, on glass
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
    • C21D7/06—Modifying the physical properties of iron or steel by deformation by cold working of the surface by shot-peening or the like
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F1/00—Etching metallic material by chemical means
    • C23F1/10—Etching compositions
    • C23F1/14—Aqueous compositions
    • C23F1/16—Acidic compositions
    • C23F1/18—Acidic compositions for etching copper or alloys thereof
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F1/00—Etching metallic material by chemical means
    • C23F1/10—Etching compositions
    • C23F1/14—Aqueous compositions
    • C23F1/16—Acidic compositions
    • C23F1/28—Acidic compositions for etching iron group metals
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/18—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by applying coatings, e.g. radiation-absorbing, radiation-reflecting; by surface treatment, e.g. polishing
    • F28F13/185—Heat-exchange surfaces provided with microstructures or with porous coatings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
    • F28F19/02—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings
    • F28F19/06—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings of metal
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
    • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
    • F28F21/081—Heat exchange elements made from metals or metal alloys
    • F28F21/082—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys
    • F28F21/083—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys from stainless steel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D7/00—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
    • F28D7/16—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being arranged in parallel spaced relation

Definitions

  • the present invention relates to a surface processing method for stainless steel.
  • Stainless steel is widely used as a material for building members, sanitary members, electrical equipment and the like because it is excellent in strength and corrosion resistance.
  • it is often used by laminating a paint or a resin film on the surface.
  • it is necessary to roughen the surface of the stainless steel in order to improve adhesion to the stainless steel.
  • the surface roughening technology for stainless steel there are a blasting process for physically forming unevenness, a roughening etching process for forming unevenness chemically or electrically, or a method of combining them.
  • Patent Document 1 proposes a method of chemically and uniformly roughening the surface of stainless steel with an etching solution mainly composed of sulfuric acid, chlorine ions, and cupric ions.
  • Patent Document 2 proposes a method of chemically etching with hydrofluoric acid, nitric acid, hydrochloric acid, phosphoric acid aqueous solution or the like after sandblasting.
  • the concavo-convex structure is formed by preferentially etching the crystal grain boundaries. Therefore, the size of the concavo-convex structure such as width and height depends on the crystal grain size of stainless steel. Therefore, since the crystal grain size of general stainless steel is 10 to 200 ⁇ m, it is difficult to form the size of the uneven structure to about 10 ⁇ m or less. In addition, it is possible to reduce the etching amount to reduce the height of the convex portion, but the surface area decreases with a decrease in height. When a fine structure having a height of 5 ⁇ m is formed by a surface roughening technique using an etching process, the surface area is limited to about 14 times that of a smooth surface, and it is difficult to increase the surface area. .
  • a complex concavo-convex structure can be formed by combining sandblasting and etching, but a large concavo-convex structure as a base is formed by sandblasting using an abrasive having a diameter of about 100 ⁇ m. It is difficult to form a size of 10 ⁇ m or less.
  • the present invention provides a surface processing method for stainless steel that forms a fine and high surface area uneven structure (roughened surface) on the surface of stainless steel.
  • the present invention includes a plurality of means for solving the above-described problems.
  • the surface processing method for stainless steel according to the present invention forms a microstructure on the surface of stainless steel.
  • FIG. 6 is a structural diagram of a shell and tube heat exchanger according to Embodiment 2.
  • FIG. 1 is a procedural diagram showing a surface microstructure forming process of stainless steel according to the present invention.
  • the crystal grain refinement process (first process) and the rough etching process (second process) are performed in this order.
  • the feature of the surface processing method of the stainless steel for forming a fine structure on the surface of the stainless steel of the present invention is that the crystal grain boundary inside the surface of the stainless steel is refined and then the grain boundaries are preferentially etched. is there.
  • the concavo-convex structure formed by the crystal grain refining process in the first step is R1
  • the concavo-convex structure formed by the roughening etching process in the second step is R2
  • the third step When the concavo-convex structure formed by the replacement deposited metal removal treatment is R3, the final surface microstructure obtained in the present invention is R2 or R3.
  • the surface fine structure obtained by the present invention does not include the uneven structure (R1) formed by the crystal grain refining treatment in the first step.
  • the size of the concavo-convex structure is R3 ⁇ R2 ⁇ R1, but R2 and R3 are substantially the same, and a sufficiently fine concavo-convex structure can be obtained. With these features, a fine and high surface roughened surface can be formed on stainless steel.
  • the crystal grain refining process (first step) is a process of refining crystal grains inside the surface of stainless steel to form a fine crystal layer on the surface layer. Since the final surface microstructure obtained in the present invention is highly dependent on the thickness and grain size of the fine crystal layer formed by the crystal grain refinement process, the fine crystal layer has a thickness of 1 ⁇ m or more. The particle size is preferably 1 ⁇ m or less. The crystal grain size of general stainless steel is 10 ⁇ m or more.
  • the crystal grain refinement processing method is not particularly limited, and known peening, polishing, turning, or machining by a grinder can be used. Suitable is a peening process in which the thickness and crystal grain size of the fine crystal layer can be adjusted according to the processing conditions such as the abrasive size and pressure.
  • the rough etching process (second process) is a process for preferentially etching the crystal grain boundaries of the fine crystal layer formed in the first process. Therefore, it is preferable that the liquid composition of the rough etching treatment is strongly acidic and contains chloride ions and transition metal ions that can be deposited by substitution on iron.
  • the effect of chloride ions is to destroy the passive film mainly composed of chromium oxide formed on the stainless steel surface.
  • the chloride ion is not particularly limited, and hydrochloric acid, sodium chloride, potassium chloride and the like can be used.
  • transition metal ions that can be substituted and deposited on iron are copper (+0.34 (V)) and silver (+0.80 (V) which are noble than the standard potential of iron -0.44 (V) and can obtain a high potential difference. )), Palladium (+0.99 (V)), platinum (+1.19 (V)), gold (+1.50 (V)). Particularly suitable are inexpensive copper ions.
  • the replacement deposited metal removal process (third process) is a process of selectively etching the metal deposited on the stainless steel surface in the second process.
  • An etching process without selectivity is not preferable because the surface microstructure of stainless steel is also etched together. Therefore, it is important that the liquid composition used in the replacement deposited metal removal treatment does not contain chloride ions or nitric acid that promotes etching of stainless steel, or has a large dissolution rate ratio with respect to stainless steel.
  • the liquid composition also varies depending on the type of substitutional deposited metal. When the substitution deposition metal is copper, the liquid composition containing persulfate or hydrogen peroxide is good.
  • the liquid composition containing potassium cyanide or ammonium peroxosulfate is good.
  • the third step is performed in the case where there is an adverse effect due to the presence of substitutional deposited metal in the microstructure of the stainless steel surface due to the characteristics of the product. For example, when the surface microstructure is required to have corrosion resistance, it is preferable to perform the replacement deposited metal removal treatment when the replacement deposited metal is copper that is easily oxidized. On the other hand, the third step is omitted when it is not necessary to remove the substituted deposited metal, such as when there is no adverse effect even if the substituted deposited metal is present in the surface microstructure.
  • Passive film evaluation method For evaluation of the passive film, the surface chromium concentration was measured using Auger electron spectroscopy. The measured surface chromium concentration was evaluated as a surface chromium concentration ratio based on a smooth test piece not subjected to the surface microstructure formation process.
  • Fine crystal layer observation method Electron beam backscatter diffraction (EBSD) was used for the observation of the fine crystal layer. As crystal orientation analysis software, OSL-Analysis manufactured by TSL was used.
  • Corrosion resistance evaluation method For the corrosion resistance evaluation, a combined cycle test based on JISK5600-7-9 “Neutral salt spray cycle test method” was used. The number of test cycles was 42 cycles.
  • the determination of the corrosion state was performed by the rating number method of JISZ2371 Appendix 1 (normative). (Adhesion evaluation method) The adhesion evaluation was performed by applying polyimide (Hitachi Chemical Co., Ltd.) to a test piece to a thickness of 50 ⁇ m and peeling it off with an adhesive tape.
  • Example 1 the transition metal ions that can be substituted and deposited on iron are used as the copper ions in the wet peening process and the rough etching process (second process) in the crystal grain refining process (first process) in FIG.
  • SUS304 was used for the test piece.
  • (1) Grain refinement process (first step) Wet peening processing conditions were as follows: spherical glass having a diameter of about 50 ⁇ m was used as an abrasive, air pressure was 0.33 MPa, and conveyance speed was 20 mm / sec.
  • wet peening conditions appropriately correspond to the required crystal grain size and the thickness of the fine crystal layer.
  • the composition of the rough etching solution was 500 g / l sulfuric acid, 90 g / l sodium chloride, and 30 g / l cupric chloride dihydrate.
  • the liquid temperature was 40 ° C. and the treatment time was 5 min.
  • substitutional precipitation metal removal treatment liquid was 200 g / sodium persulfate that can selectively remove copper because copper was used as the transition metal ion capable of substitutional precipitation on iron in the roughening etching treatment liquid in the second step. 1 and sulfuric acid 50 ml / l.
  • the liquid temperature was 30 ° C. and the treatment time was 10 minutes.
  • processing time it is preferable to respond
  • test piece of Example 1 For the test piece of Example 1, surface and cross-sectional SEM observation, surface area evaluation, and fine crystal layer observation were performed.
  • FIG. 3 shows the results of surface and cross-sectional SEM observation and surface area evaluation. From the surface of FIG. 3 and the cross-sectional SEM image, it can be confirmed that a fine structure having a width of 1 ⁇ m or less and a height of about 3 ⁇ m is formed. Moreover, the surface area by this fine structure was 21 times with respect to the smooth surface. Thus, a surface microstructure having a height of 5 ⁇ m or less and a surface area ratio of 15 times or more can be formed on stainless steel.
  • FIG. 4 shows the observation result of the fine crystal layer after the wet peening process.
  • the fine crystal layer was formed with a depth of about 7 ⁇ m from the surface of the stainless steel, and the crystal grain size was about 0.8 ⁇ m.
  • a fine crystal layer having a crystal grain size of 1 ⁇ m or less and a thickness of 1 ⁇ m or more can be formed inside the surface of stainless steel by wet peening.
  • a fine structure was formed on the surface of the test piece under the same conditions as in Example 1 except that the processing time of the rough etching process (second step) in Example 1 was changed to 3 min.
  • the processing time of the rough etching process (second step) in Example 1 was changed to 3 min.
  • FIG. 3 shows the results of surface and cross-sectional SEM observation and surface area evaluation. From the surface of FIG. 3 and the cross-sectional SEM image, it can be confirmed that a fine structure having a width of 1 ⁇ m or less and a height of about 1 ⁇ m is formed. Moreover, the surface area by this fine structure was 15 times with respect to the smooth surface.
  • the surface area ratio is smaller because the height of the fine structure is lower than that of Example 1, but it is possible to realize a surface area ratio of 15 times even at a height of 1 ⁇ m of the fine structure. there were.
  • Fig. 5 shows the evaluation of the passive film after forming the surface microstructure. It was confirmed that the chromium concentration on the surface of the stainless steel was 1.5 times higher than before forming the surface microstructure. The cause of this is thought to be that chromium dispersed in the stainless steel remains on the surface by the surface processing method of this example.
  • Fig. 6 shows the corrosion resistance evaluation before and after the formation of the surface microstructure.
  • the rating number was 10 (corrosion area 0.0%) after formation of the surface microstructure, compared to 6 (corrosion area 0.5 to 1.0%) before formation of the surface microstructure.
  • the cause of this is thought to be due to the fact that the chromium concentration on the surface is increased by the surface microstructure formation process from the passive film evaluation result.
  • Comparative Example 1 In Comparative Example 1, a case where wet blasting is used as a method for forming the surface microstructure of stainless steel will be described. In addition, SUS304 was used for the test piece.
  • the wet blasting conditions were an air pressure of 0.2 MPa using a polygonal alumina having a diameter of about 15 ⁇ m as the abrasive.
  • FIG. 3 shows the results of surface and cross-sectional SEM observation and surface area evaluation.
  • Comparative Example 1 it can be confirmed from the surface of FIG. 3 and the cross-sectional SEM image that a fine structure having a width of 2 to 3 ⁇ m and a height of about 0.5 ⁇ m is formed.
  • the surface area of Comparative Example 1 was 3 times that of the smooth surface.
  • Comparative Example 2 In Comparative Example 2, a case where a rough etching process is used as a method for forming a surface microstructure of stainless steel will be described. In addition, SUS304 was used for the test piece.
  • the roughening etching process conditions were the same as in Example 1.
  • the liquid composition was 500 g / l sulfuric acid, 90 g / l sodium chloride, 30 g / l cupric chloride dihydrate, the liquid temperature was 40 ° C., and the treatment time was 5 min. I went there.
  • FIG. 3 shows the results of surface and cross-sectional SEM observation and surface area evaluation.
  • Comparative Example 2 it can be confirmed from the surface of FIG. 3 and the cross-sectional SEM image that a fine structure having a width of 2 to 5 ⁇ m and a height of about 3 ⁇ m is formed.
  • the surface area of Comparative Example 2 was 10 times that of the smooth surface.
  • part of the polyimide film was peeled off.
  • Comparative Example 1 When Examples 1 and 2 are compared with Comparative Examples 1 and 2, the surface microstructure formed by wet blasting in Comparative Example 1 affects the abrasive size, but the distance between the microstructures is somewhat small. Large and dense. Further, the surface fine structure formed by the roughening etching process of Comparative Example 2 has a large width of the fine structure depending on the crystal grain size of the base material due to the grain boundary etching. As described above, it is difficult to form a surface microstructure having a height of 5 ⁇ m or less and a surface area ratio of 15 times or more in stainless steel by wet blasting and roughening etching, which are conventional surface structure forming methods.
  • heat transfer performance was evaluated by a shell-and-tube heat exchanger using a stainless steel heat transfer tube having a surface microstructure formed by the surface processing method of Example 1.
  • FIG. 7 is a structural diagram of a shell-and-tube heat exchanger according to the fourth embodiment.
  • Tube plates 202 are installed on both sides of the circular or polygonal shell 200 to support the heat transfer tubes 201 that are heat transfer portions.
  • a large number of holes for passing the heat transfer tubes 201 are arranged in a staggered pattern in the tube plate 202, and the heat transfer tubes 201 are inserted into these tube holes and fixed to the tube plate 202 at both ends.
  • the length of the heat transfer tube 201 is 25 times or more of the representative length D of the flow.
  • the representative length D of the flow along the tube group of the present embodiment takes a hydraulic equivalent diameter.
  • the fine structure 203 is formed on the outer surface of the heat transfer tube 201.
  • Air 204 which is a low-temperature fluid, flows into the heat exchanger from a nozzle 205 provided on the side surface of the lower portion of the heat exchanger, rises outside the heat transfer tube 201, and steam 206, which is a high-temperature fluid, through the heat transfer tube wall.
  • Steam 206 which is a high-temperature fluid, flows into the heat exchanger from the nozzle 207 at the top of the heat exchanger, and flows down through the heat transfer tube 201 via the water chamber 208 at the top of the heat exchanger.
  • the water vapor 206 is condensed by exchanging heat with the air 204, which is a low-temperature fluid, through the heat transfer tube wall and becomes compressed water.
  • the compressed water flows out of the heat exchanger from the nozzle at the bottom of the heat exchanger via the water chamber at the bottom of the heat exchanger.
  • the heat transfer performance is improved by about 6% compared to the shell and tube heat exchanger not subjected to the surface processing. I was able to.
  • the stainless steel having the surface microstructure formed by the surface processing method of the present invention to the heat transfer tube, the heat transfer performance can be improved without increasing the number of heat transfer tubes. That is, when obtaining the target heat transfer performance, the number of heat transfer tubes can be reduced, and the cost of the heat exchanger can be reduced.
  • the heat transfer performance is higher than that of the shell and tube heat exchanger not subjected to the surface processing. About 2.5% improvement. From this result, it was confirmed that the heat transfer performance is improved as the surface area ratio of the heat transfer tube 201 is increased.
  • the height of the fine structure it is preferable that the height is lower if the surface area of the fine structure is the same. This is because the pressure loss increases as the microstructure increases. When the height of the microstructure exceeds the boundary layer, a high heat transfer acceleration effect can be expected, but the pressure loss increases in a trade-off manner. As a result, the heat transfer performance may not improve as a whole due to an increase in pressure loss.
  • the boundary layer is a thin layer that exists in the vicinity of the contact surface with which the gas is in contact and cannot ignore the viscosity of the gas (it is strongly influenced by the viscosity of the gas).
  • the thickness of the boundary layer varies depending on various requirements such as heat exchanger specifications, that is, gas flow velocity and flow method, heat transfer section shape, and the like. Therefore, from the viewpoint of reliably reducing the pressure loss, it is desirable that the height of the fine structure is lower and the surface area ratio is large. According to the surface processing method of the present invention, it is possible to form a surface microstructure having a height of 5 ⁇ m or less and a surface area ratio of 15 times or more, which has been difficult in the prior art. By adopting the heat transfer section, it is possible to obtain higher heat transfer performance than before.
  • the chromium concentration on the surface of the stainless steel is increased and the corrosion resistance is excellent. Therefore, it is suitable for the heat transfer part of a heat exchanger that requires corrosion resistance.
  • Example 4 demonstrated the shell and tube type heat exchanger as an example as a heat exchanger
  • the heat exchanger applicable by this invention is not necessarily limited to this.
  • heat exchangers that perform heat exchange in contact with gas such as fin-type heat exchangers (heat sinks) for power semiconductors, cross fin-type heat exchangers for air conditioners and radiators of automobiles, etc. It can be implemented in a heat exchanger whose part is stainless steel.

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Abstract

Provided is a method for processing a surface of a stainless steel, the method being a method for forming a refined structure in the surface of a stainless steel, i.e., for forming a rugged structure (roughened surface) that is refined and has a large surface area. This method for processing a surface of a stainless steel is a method for forming a refined structure in a surface of a stainless steel, and is characterized by including: a first step in which the stainless steel is subjected to crystal-grain refinement in which the crystal grains inside the surface thereof are refined; and a second step in which after the first step, the surface of the stainless steel is etched for roughening with an etchant.

Description

ステンレス鋼の表面加工方法とそれを用いた熱交換器Surface treatment method of stainless steel and heat exchanger using the same
　本発明は、ステンレス鋼の表面加工方法に関する。 The present invention relates to a surface processing method for stainless steel.
　ステンレス鋼は、強度や耐食性に優れるため建築部材、衛生部材、電気機器などの材料として多用途に使用されている。近年では、ステンレス鋼の耐食性を更に向上させるため表面に塗料や樹脂フィルムなどを積層させて使用される場合も多い。ステンレス鋼に塗料や樹脂フィルムを積層する際には、ステンレス鋼との密着性を向上させるためにステンレス鋼の表面を粗化する必要がある。このステンレス鋼の表面粗化技術としては、物理的に凹凸を形成するブラスト加工や化学的あるいは電気的に凹凸を形成する粗化エッチング処理、または、それらを組み合わせた方法がある。例えば、特許文献１では、硫酸、塩素イオン、第二銅イオンを主成分とするエッチング液により、ステンレス鋼の表面を化学的に均一に粗化する方法が提案されている。また、特許文献２では、サンドブラスト加工後に弗化水素酸、硝酸、塩酸、燐酸水溶液などで化学的にエッチングする方法が提案されている。 Stainless steel is widely used as a material for building members, sanitary members, electrical equipment and the like because it is excellent in strength and corrosion resistance. In recent years, in order to further improve the corrosion resistance of stainless steel, it is often used by laminating a paint or a resin film on the surface. When laminating a paint or a resin film on stainless steel, it is necessary to roughen the surface of the stainless steel in order to improve adhesion to the stainless steel. As the surface roughening technology for stainless steel, there are a blasting process for physically forming unevenness, a roughening etching process for forming unevenness chemically or electrically, or a method of combining them. For example, Patent Document 1 proposes a method of chemically and uniformly roughening the surface of stainless steel with an etching solution mainly composed of sulfuric acid, chlorine ions, and cupric ions. Patent Document 2 proposes a method of chemically etching with hydrofluoric acid, nitric acid, hydrochloric acid, phosphoric acid aqueous solution or the like after sandblasting.
特開２００１－１１６６２号公報Japanese Patent Laid-Open No. 2001-11662 特開平５－２６４０４５号公報JP-A-5-264045
　特許文献１等に記載されたエッチング処理を利用した表面粗化技術では、結晶粒界が優先的にエッチングされることによって凹凸構造が形成される。そのため、凹凸構造の幅や高さなどのサイズはステンレス鋼の結晶粒径サイズに依存する。したがって、一般的なステンレス鋼の結晶粒径は１０～２００μｍであることから、凹凸構造のサイズを約１０μｍ以下に形成するのは困難である。また、エッチング量を少なくして凸部の高さを低くすることも可能であるが、高さの低下とともに表面積が低下する。エッチング処理を利用した表面粗化技術で高さ５μｍの微細構造を形成した場合には表面積は平滑面に対して１４倍程度が限度であり、これよりも表面積を大きくすることは困難であった。 In the surface roughening technique using the etching process described in Patent Document 1 or the like, the concavo-convex structure is formed by preferentially etching the crystal grain boundaries. Therefore, the size of the concavo-convex structure such as width and height depends on the crystal grain size of stainless steel. Therefore, since the crystal grain size of general stainless steel is 10 to 200 μm, it is difficult to form the size of the uneven structure to about 10 μm or less. In addition, it is possible to reduce the etching amount to reduce the height of the convex portion, but the surface area decreases with a decrease in height. When a fine structure having a height of 5 μm is formed by a surface roughening technique using an etching process, the surface area is limited to about 14 times that of a smooth surface, and it is difficult to increase the surface area. .
　特許文献２では、サンドブラスト加工とエッチング処理を組み合わせることにより複雑な凹凸構造を形成可能であるが、ベースとなる大きな凹凸構造は直径約１００μｍの研磨材を用いたサンドブラスト加工により形成されるため凹凸構造のサイズを１０μｍ以下に形成するのは困難である。 In Patent Document 2, a complex concavo-convex structure can be formed by combining sandblasting and etching, but a large concavo-convex structure as a base is formed by sandblasting using an abrasive having a diameter of about 100 μm. It is difficult to form a size of 10 μm or less.
　そこで、本発明は、ステンレス鋼の表面に微細で且つ高表面積な凹凸構造（粗化面）を形成するステンレス鋼の表面加工方法を提供する。 Therefore, the present invention provides a surface processing method for stainless steel that forms a fine and high surface area uneven structure (roughened surface) on the surface of stainless steel.
　本発明は上記課題を解決する手段を複数含んでいるが、その一例を挙げるならば、本発明のステンレス鋼の表面加工方法は、ステンレス鋼の表面に微細構造を形成するものであって、ステンレス鋼の表面内部の結晶粒を微細化する結晶粒微細化処理を施す第一の工程と、前記第一の工程の後に、エッチング処理液でステンレス鋼の表面を粗化エッチングする第二の工程と、を有することを特徴とする。 The present invention includes a plurality of means for solving the above-described problems. To give an example, the surface processing method for stainless steel according to the present invention forms a microstructure on the surface of stainless steel. A first step of applying a crystal grain refining process for refining crystal grains inside the surface of the steel; and a second step of roughening and etching the surface of the stainless steel with an etching treatment liquid after the first step; It is characterized by having.
　本発明によれば、ステンレス鋼に微細で且つ高表面積な凹凸構造（粗化面）の形成が可能なステンレス鋼の表面加工方法を提供することができる。 According to the present invention, it is possible to provide a surface processing method for stainless steel capable of forming a fine and high surface area uneven structure (roughened surface) on stainless steel.
表面微細構造形成プロセスの概略図である。It is the schematic of a surface microstructure formation process. 表面微細構造形成プロセスにおける基材の断面図である。It is sectional drawing of the base material in a surface fine structure formation process. 表面微細構造の表面と断面ＳＥＭ像および表面積比の結果である。It is the result of the surface of a surface microstructure, a cross-sectional SEM image, and a surface area ratio. 結晶粒微細化処理後の断面結晶観察の結果である。It is a result of cross-sectional crystal observation after crystal grain refinement processing. 表面微細構造形成前後の不動態被膜評価の結果である。It is a result of a passive film evaluation before and after surface fine structure formation. 表面微細構造形成前後の耐食性評価の結果である。It is a result of corrosion resistance evaluation before and after surface fine structure formation. 実施例２に係るシェルアンドチューブ型熱交換器の構造図である。6 is a structural diagram of a shell and tube heat exchanger according to Embodiment 2. FIG.
　以下、図面を参照して本発明の実施の形態を説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
　図１は、本発明に係るステンレス鋼の表面微細構造形成プロセスを示す手順図である。 FIG. 1 is a procedural diagram showing a surface microstructure forming process of stainless steel according to the present invention.
　本発明では、図１に示すように、結晶粒微細化処理（第一の工程）、粗化エッチング処理（第二の工程）をこの順序で行う。なお、必要に応じて、粗化エッチング処理（第二の工程）の後に、置換析出金属を除去する除去処理（第三の工程）を行っても良い。 In the present invention, as shown in FIG. 1, the crystal grain refinement process (first process) and the rough etching process (second process) are performed in this order. In addition, you may perform the removal process (3rd process) which removes a substituted precipitation metal after a roughening etching process (2nd process) as needed.
　本発明のステンレス鋼の表面に微細構造を形成するステンレス鋼の表面加工方法の特徴は、ステンレス鋼の表面内部の結晶粒径を微細化させてから、結晶粒界を優先的にエッチングすることである。また、図２に示すように、第一の工程の結晶粒微細化処理で形成される凹凸構造をＲ１、第二の工程の粗化エッチング処理で形成される凹凸構造をＲ２、第三の工程の置換析出金属除去処理で形成される凹凸構造をＲ３とした場合、本発明で得られる最終的な表面微細構造はＲ２またはＲ３となる。すなわち、本発明で得られる表面微細構造には、第一の工程の結晶粒微細化処理で形成される凹凸構造（Ｒ１）は含まれない。なお、凹凸構造のサイズとしては、Ｒ３＜Ｒ２≪Ｒ１となるが、Ｒ２とＲ３はほぼ同等であり、十分に微細な凹凸構造を得ることが可能である。これらの特徴により、ステンレス鋼に微細で且つ高表面積な粗化面を形成することができる。 The feature of the surface processing method of the stainless steel for forming a fine structure on the surface of the stainless steel of the present invention is that the crystal grain boundary inside the surface of the stainless steel is refined and then the grain boundaries are preferentially etched. is there. In addition, as shown in FIG. 2, the concavo-convex structure formed by the crystal grain refining process in the first step is R1, the concavo-convex structure formed by the roughening etching process in the second step is R2, and the third step When the concavo-convex structure formed by the replacement deposited metal removal treatment is R3, the final surface microstructure obtained in the present invention is R2 or R3. That is, the surface fine structure obtained by the present invention does not include the uneven structure (R1) formed by the crystal grain refining treatment in the first step. The size of the concavo-convex structure is R3 <R2 << R1, but R2 and R3 are substantially the same, and a sufficiently fine concavo-convex structure can be obtained. With these features, a fine and high surface roughened surface can be formed on stainless steel.
　結晶粒微細化処理（第一の工程）は、ステンレス鋼の表面内部の結晶粒を微細化して表層に微細結晶層を形成する処理である。本発明で得られる最終的な表面微細構造は、この結晶粒微細化処理で形成される微細結晶層の厚さや粒径の依存性が高いため、この微細結晶層は、厚さが１μｍ以上で粒径は１μｍ以下であるのが好ましい。なお、一般的なステンレス鋼の結晶粒径は１０μｍ以上である。結晶粒微細化処理方法は、特に限定は無く公知のピーニング加工、研磨、ターニングまたはグラインダによる機械加工などを用いることができる。好適なのは、研磨材サイズや圧力などの加工条件により、微細結晶層の厚さや結晶粒径を調整可能なピーニング加工である。 The crystal grain refining process (first step) is a process of refining crystal grains inside the surface of stainless steel to form a fine crystal layer on the surface layer. Since the final surface microstructure obtained in the present invention is highly dependent on the thickness and grain size of the fine crystal layer formed by the crystal grain refinement process, the fine crystal layer has a thickness of 1 μm or more. The particle size is preferably 1 μm or less. The crystal grain size of general stainless steel is 10 μm or more. The crystal grain refinement processing method is not particularly limited, and known peening, polishing, turning, or machining by a grinder can be used. Suitable is a peening process in which the thickness and crystal grain size of the fine crystal layer can be adjusted according to the processing conditions such as the abrasive size and pressure.
　粗化エッチング処理（第二の工程）は、第一の工程で形成された微細結晶層の結晶粒界を優先的にエッチングする処理である。そのため、粗化エッチング処理の液組成は、強酸性で、塩化物イオンと、鉄に置換析出可能な遷移金属イオンを含むことが好ましい。塩化物イオンの効果は、ステンレス鋼表面に生成されている酸化クロムを主成分とする不動態被膜を破壊することである。塩化物イオンは、特に限定はなく、塩酸、塩化ナトリウム、塩化カリウムなどを用いることができる。鉄に置換析出可能な遷移金属イオンの効果は、ステンレス鋼の主成分である鉄に金属が置換析出し、エッチングを抑制することによって、結晶粒界部のエッチングを促進することである。鉄に置換析出可能な遷移金属イオンは、鉄の標準電位－０．４４（Ｖ）より貴で、且つ、高電位差を得られる銅（＋０．３４（Ｖ））、銀（＋０．８０（Ｖ））、パラジウム（＋０．９９（Ｖ））、白金（＋１．１９（Ｖ））、金（＋１．５０（Ｖ））が良好である。特に好適なのは安価な銅イオンである。 The rough etching process (second process) is a process for preferentially etching the crystal grain boundaries of the fine crystal layer formed in the first process. Therefore, it is preferable that the liquid composition of the rough etching treatment is strongly acidic and contains chloride ions and transition metal ions that can be deposited by substitution on iron. The effect of chloride ions is to destroy the passive film mainly composed of chromium oxide formed on the stainless steel surface. The chloride ion is not particularly limited, and hydrochloric acid, sodium chloride, potassium chloride and the like can be used. The effect of transition metal ions that can be substituted and deposited on iron is to promote the etching of the crystal grain boundaries by the metal being deposited and deposited on iron, which is the main component of stainless steel, and suppressing the etching. Transition metal ions that can be deposited on iron are copper (+0.34 (V)) and silver (+0.80 (V) which are noble than the standard potential of iron -0.44 (V) and can obtain a high potential difference. )), Palladium (+0.99 (V)), platinum (+1.19 (V)), gold (+1.50 (V)). Particularly suitable are inexpensive copper ions.
　置換析出金属除去処理（第三の工程）は、第二の工程でステンレス鋼表面に析出した金属を選択的にエッチングする処理である。選択性の無いエッチング処理では、ステンレス鋼である表面微細構造も一緒にエッチングされるため好ましくない。したがって、置換析出金属除去処理で用いる液組成は、ステンレス鋼のエッチングを促進させる塩化物イオンや硝酸系を含まないこと、または、ステンレス鋼に対して溶解速度比の大きいことが重要である。なお、置換析出金属の種類によっても液組成は異なる。置換析出金属が銅の場合は、過硫酸塩または過酸化水素を含む液組成が良好である。置換析出金属が金、白金、パラジウム、銀の場合には、シアン化カリウムやペルオキソ硫酸アンモニウムを含む液組成が良好である。 
　なお、第三の工程は、製品の特性上、ステンレス鋼表面の微細構造に置換析出金属が存在することによって悪影響を及ぼす場合に実施される。例えば、表面微細構造に耐食性が求められる際に、置換析出金属が酸化しやすい銅である場合に置換析出金属除去処理を行うことが好適である。一方、表面微細構造に置換析出金属が存在していても悪影響を及ぼさない場合など、置換析出金属の除去が必要でない場合には第三の工程は省略される。
（表面と断面観察方法）
　表面微細構造体の表面と断面の観察には、走査型電子顕微鏡（ＳＥＭ）を用いた。なお、表面微細構造体の高さと幅は断面ＳＥＭ象より求めた。ここでは、断面ＳＥＭ像で観察される凸部のうち、高さ、幅の大きい５箇所の凸部の値を測定し、その平均値を表面微細構造体の凸部の高さと幅とした。
（表面積評価方法）
　表面積測定には、クリプトンガス吸着法を用いた。測定した表面積は、表面微細構造形成プロセスを施していない平滑な試験片を基準とした表面積比として評価した。
（不動態被膜評価方法）
　不動態被膜評価には、オージェ電子分光分析法を用いて表面クロム濃度を測定した。測定した表面クロム濃度は、表面微細構造形成プロセスを施していない平滑な試験片を基準とした表面クロム濃度比として評価した。
（微細結晶層観察方法）
　微細結晶層観察には、電子線後方散乱回折法（ＥＢＳＤ）を用いた。なお、結晶方位解析ソフトはＴＳＬ製ＯＩＭ－Ａｎａｌｙｓｉｓを用いた。
（耐食性評価方法）
　耐食性評価には、ＪＩＳＫ５６００－７－９「中性塩水噴霧サイクル試験法」に準拠した複合サイクル試験を用いた。試験サイクル数は４２サイクルとした。腐食状態の判定には、ＪＩＳＺ２３７１付属書１（規定）レイティングナンバー法により行った。
（密着性評価方法）
　密着性評価は、試験片にポリイミド（日立化成（株））を厚さ５０μｍに塗布し、粘着テープにて引き剥がす方法により行った。 The replacement deposited metal removal process (third process) is a process of selectively etching the metal deposited on the stainless steel surface in the second process. An etching process without selectivity is not preferable because the surface microstructure of stainless steel is also etched together. Therefore, it is important that the liquid composition used in the replacement deposited metal removal treatment does not contain chloride ions or nitric acid that promotes etching of stainless steel, or has a large dissolution rate ratio with respect to stainless steel. The liquid composition also varies depending on the type of substitutional deposited metal. When the substitution deposition metal is copper, the liquid composition containing persulfate or hydrogen peroxide is good. When the substituted deposited metal is gold, platinum, palladium, or silver, the liquid composition containing potassium cyanide or ammonium peroxosulfate is good.
Note that the third step is performed in the case where there is an adverse effect due to the presence of substitutional deposited metal in the microstructure of the stainless steel surface due to the characteristics of the product. For example, when the surface microstructure is required to have corrosion resistance, it is preferable to perform the replacement deposited metal removal treatment when the replacement deposited metal is copper that is easily oxidized. On the other hand, the third step is omitted when it is not necessary to remove the substituted deposited metal, such as when there is no adverse effect even if the substituted deposited metal is present in the surface microstructure.
(Surface and cross-section observation method)
A scanning electron microscope (SEM) was used to observe the surface and cross section of the surface microstructure. Note that the height and width of the surface microstructure were determined from a cross-sectional SEM image. Here, among the convex portions observed in the cross-sectional SEM image, the values of the five convex portions having a large height and width were measured, and the average values were taken as the height and width of the convex portions of the surface microstructure.
(Surface area evaluation method)
The krypton gas adsorption method was used for the surface area measurement. The measured surface area was evaluated as a surface area ratio based on a smooth test piece not subjected to the surface microstructure formation process.
(Passive film evaluation method)
For evaluation of the passive film, the surface chromium concentration was measured using Auger electron spectroscopy. The measured surface chromium concentration was evaluated as a surface chromium concentration ratio based on a smooth test piece not subjected to the surface microstructure formation process.
(Fine crystal layer observation method)
Electron beam backscatter diffraction (EBSD) was used for the observation of the fine crystal layer. As crystal orientation analysis software, OSL-Analysis manufactured by TSL was used.
(Corrosion resistance evaluation method)
For the corrosion resistance evaluation, a combined cycle test based on JISK5600-7-9 “Neutral salt spray cycle test method” was used. The number of test cycles was 42 cycles. The determination of the corrosion state was performed by the rating number method of JISZ2371 Appendix 1 (normative).
(Adhesion evaluation method)
The adhesion evaluation was performed by applying polyimide (Hitachi Chemical Co., Ltd.) to a test piece to a thickness of 50 μm and peeling it off with an adhesive tape.
　実施例１では、図１における結晶粒微細化処理（第一の工程）にウェットピーニング加工、粗化エッチング処理（第二の工程）に、鉄に置換析出可能な遷移金属イオンを銅イオンとした粗化エッチング処理液、置換析出金属除去処理（第三の工程）に過硫酸塩を含んだ置換析出金属除去処理液を用いた場合について説明する。なお、試験片にはＳＵＳ３０４を用いた。
（１）結晶粒微細化処理（第一の工程）
　ウェットピーニング加工条件は、研磨材に直径約５０μｍの球形ガラスを用いて、エア圧力０．３３ＭＰａ、搬送速度２０ｍｍ／ｓｅｃとした。なお、ウェットピーニング加工条件は、必要とする結晶粒径や微細結晶層の厚さに応じて適宜対応するのが好ましい。
（２）粗化エッチング処理（第二の工程）
　粗化エッチング処理液の組成は、硫酸５００ｇ/ｌ、塩化ナトリウム９０ｇ/ｌ、塩化第二銅二水和物３０ｇ/ｌとした。また、液温は４０℃、処理時間は５ｍｉｎで行った。なお、処理時間については、必要とするエッチング量に応じて適宜対応するのが好ましい。（３）置換析出金属除去処理（第三の工程）
　置換析出金属除去処理液の組成は、第二の工程の粗化エッチング処理液に鉄に置換析出可能な遷移金属イオンとして銅を用いたため、銅を選択的に除去可能である過硫酸ナトリウム２００ｇ/ｌ、硫酸５０ｍｌ/ｌとした。また、液温は３０℃、処理時間は１０ｍｉｎで行った。なお、処理時間については、置換析出金属量に応じて適宜対応するのが好ましい。 In Example 1, the transition metal ions that can be substituted and deposited on iron are used as the copper ions in the wet peening process and the rough etching process (second process) in the crystal grain refining process (first process) in FIG. The case where the substitutional precipitation metal removal treatment liquid containing persulfate is used for the roughening etching treatment liquid and the substitutional precipitation metal removal treatment (third step) will be described. In addition, SUS304 was used for the test piece.
(1) Grain refinement process (first step)
Wet peening processing conditions were as follows: spherical glass having a diameter of about 50 μm was used as an abrasive, air pressure was 0.33 MPa, and conveyance speed was 20 mm / sec. In addition, it is preferable that wet peening conditions appropriately correspond to the required crystal grain size and the thickness of the fine crystal layer.
(2) Roughening etching process (second step)
The composition of the rough etching solution was 500 g / l sulfuric acid, 90 g / l sodium chloride, and 30 g / l cupric chloride dihydrate. The liquid temperature was 40 ° C. and the treatment time was 5 min. In addition, about processing time, it is preferable to respond | correspond suitably according to the etching amount required. (3) Displacement deposited metal removal treatment (third step)
The composition of the substitutional precipitation metal removal treatment liquid was 200 g / sodium persulfate that can selectively remove copper because copper was used as the transition metal ion capable of substitutional precipitation on iron in the roughening etching treatment liquid in the second step. 1 and sulfuric acid 50 ml / l. The liquid temperature was 30 ° C. and the treatment time was 10 minutes. In addition, about processing time, it is preferable to respond | correspond suitably according to the amount of substitutional precipitation metal.
　実施例１の試験片について、表面と断面ＳＥＭ観察、表面積評価、細結晶層観察を行った。 For the test piece of Example 1, surface and cross-sectional SEM observation, surface area evaluation, and fine crystal layer observation were performed.
　図３に表面と断面ＳＥＭ観察および表面積評価の結果を示す。図３の表面と断面ＳＥＭ像から、幅１μｍ以下で高さ約３μｍの微細な構造体が形成されていることが確認できる。また、この微細構造による表面積は平滑面に対して２１倍であった。このように、ステンレス鋼に高さ５μｍ以下で、且つ表面積比１５倍以上の表面微細構造を形成可能である。 FIG. 3 shows the results of surface and cross-sectional SEM observation and surface area evaluation. From the surface of FIG. 3 and the cross-sectional SEM image, it can be confirmed that a fine structure having a width of 1 μm or less and a height of about 3 μm is formed. Moreover, the surface area by this fine structure was 21 times with respect to the smooth surface. Thus, a surface microstructure having a height of 5 μm or less and a surface area ratio of 15 times or more can be formed on stainless steel.
　図４にウェットピーニング加工後の微細結晶層の観察結果を示す。微細結晶層はステンレス鋼の表面から深さ方向に約７μｍ形成されており、その結晶粒径は約０．８μｍであった。このように、ウェットピーニング加工によりステンレス鋼の表面内部に結晶粒径１μｍ以下で、厚さ１μｍ以上の微細結晶層を形成可能である。 FIG. 4 shows the observation result of the fine crystal layer after the wet peening process. The fine crystal layer was formed with a depth of about 7 μm from the surface of the stainless steel, and the crystal grain size was about 0.8 μm. Thus, a fine crystal layer having a crystal grain size of 1 μm or less and a thickness of 1 μm or more can be formed inside the surface of stainless steel by wet peening.
　本実施例では、実施例１の粗化エッチング処理（第二の工程）の処理時間を３ｍｉｎに変更した以外は実施例１と同様の条件で試験片の表面に微細構造体を形成した。実施例２の試験片について、表面と断面ＳＥＭ観察、表面積評価を行った。図３に表面と断面ＳＥＭ観察および表面積評価の結果を示す。図３の表面と断面ＳＥＭ像から、幅１μｍ以下で高さ約１μｍの微細な構造体が形成されていることが確認できる。また、この微細構造による表面積は平滑面に対して１５倍であった。このように、ウェットピーニング加工、エッチング処理の条件を変更することで微細構造体のサイズや表面積を調整することが可能である。また、実施例１と比較して微細構造体の高さが低くなったことから表面積比が小さくなっているが、微細構造体の高さ１μｍにおいても表面積比１５倍を実現することが可能であった。 In this example, a fine structure was formed on the surface of the test piece under the same conditions as in Example 1 except that the processing time of the rough etching process (second step) in Example 1 was changed to 3 min. About the test piece of Example 2, surface and cross-sectional SEM observation and surface area evaluation were performed. FIG. 3 shows the results of surface and cross-sectional SEM observation and surface area evaluation. From the surface of FIG. 3 and the cross-sectional SEM image, it can be confirmed that a fine structure having a width of 1 μm or less and a height of about 1 μm is formed. Moreover, the surface area by this fine structure was 15 times with respect to the smooth surface. As described above, it is possible to adjust the size and the surface area of the fine structure by changing the conditions of the wet peening process and the etching process. In addition, the surface area ratio is smaller because the height of the fine structure is lower than that of Example 1, but it is possible to realize a surface area ratio of 15 times even at a height of 1 μm of the fine structure. there were.
　本実施例では、実施例１で作製した試験片について、不動態被膜評価、耐食性評価、密着性評価を行った結果について説明する。 In this example, the results of performing passive film evaluation, corrosion resistance evaluation, and adhesion evaluation on the test piece prepared in Example 1 will be described.
　図５に表面微細構造を形成した後の不動態被膜評価を示す。ステンレス鋼表面のクロム濃度は、表面微細構造を形成する前に対して１．５倍高くなっていることが確認された。この原因は、本実施例の表面加工方法によって、ステンレス鋼内部に分散していたクロムが表面に残留するためではないかと考えられる。 Fig. 5 shows the evaluation of the passive film after forming the surface microstructure. It was confirmed that the chromium concentration on the surface of the stainless steel was 1.5 times higher than before forming the surface microstructure. The cause of this is thought to be that chromium dispersed in the stainless steel remains on the surface by the surface processing method of this example.
　図６に表面微細構造の形成前後の耐食性評価を示す。レイティングナンバーは、表面微細構造形成前の６（腐食面積０．５～１．０％）に対して、表面微細構造形成後は１０（腐食面積０．０％）であった。このように、本実施例の表面加工方法によって表面微細構造を形成することで、耐食性が向上していることが確認された。この原因は、不動態被膜評価結果から、表面微細構造形成プロセスによって、表面のクロム濃度が高くなるためではないかと考えられる。 Fig. 6 shows the corrosion resistance evaluation before and after the formation of the surface microstructure. The rating number was 10 (corrosion area 0.0%) after formation of the surface microstructure, compared to 6 (corrosion area 0.5 to 1.0%) before formation of the surface microstructure. Thus, it was confirmed that the corrosion resistance was improved by forming the surface microstructure by the surface processing method of this example. The cause of this is thought to be due to the fact that the chromium concentration on the surface is increased by the surface microstructure formation process from the passive film evaluation result.
　表面微細構造形成プロセス後の密着性評価の結果、ポリイミド膜の剥がれは発生しなかった。このように、表面微細構造形成プロセスを施すことによって高い密着力を得ることが可能である。
〔比較例１〕
　比較例１では、ステンレス鋼の表面微細構造の形成方法としてウェットブラスト加工を用いた場合について説明する。なお、試験片にはＳＵＳ３０４を用いた。 As a result of the adhesion evaluation after the surface microstructure formation process, peeling of the polyimide film did not occur. Thus, it is possible to obtain a high adhesion force by performing the surface fine structure forming process.
[Comparative Example 1]
In Comparative Example 1, a case where wet blasting is used as a method for forming the surface microstructure of stainless steel will be described. In addition, SUS304 was used for the test piece.
　ウェットブラスト加工条件は、研磨材に直径約１５μｍの多角径アルミナを用いて、エア圧力０．２ＭＰａとした。 The wet blasting conditions were an air pressure of 0.2 MPa using a polygonal alumina having a diameter of about 15 μm as the abrasive.
　比較例１の試験片について、表面と断面ＳＥＭ観察、表面積評価を行った。図３に表面と断面ＳＥＭ観察および表面積評価の結果を示す。比較例１は、図３の表面と断面ＳＥＭ像から、幅２～３μｍで高さ約０．５μｍの微細構造体が形成されていることが確認できる。比較例１の表面積は平滑面に対して３倍であった。 The test piece of Comparative Example 1 was subjected to surface and cross-sectional SEM observation and surface area evaluation. FIG. 3 shows the results of surface and cross-sectional SEM observation and surface area evaluation. In Comparative Example 1, it can be confirmed from the surface of FIG. 3 and the cross-sectional SEM image that a fine structure having a width of 2 to 3 μm and a height of about 0.5 μm is formed. The surface area of Comparative Example 1 was 3 times that of the smooth surface.
　また、表面微細構造形成プロセス後の密着性評価の結果、全面でポリイミド膜の剥がれが生じた。
〔比較例２〕
　比較例２では、ステンレス鋼の表面微細構造の形成方法として粗化エッチング処理を用いた場合について説明する。なお、試験片にはＳＵＳ３０４を用いた。 Further, as a result of the adhesion evaluation after the surface microstructure forming process, the polyimide film was peeled off on the entire surface.
[Comparative Example 2]
In Comparative Example 2, a case where a rough etching process is used as a method for forming a surface microstructure of stainless steel will be described. In addition, SUS304 was used for the test piece.
　粗化エッチング処理条件は、実施例１と同様とし、液組成は硫酸５００ｇ/ｌ、塩化ナトリウム９０ｇ/ｌ、塩化第二銅二水和物３０ｇ/ｌ、液温は４０℃、処理時間は５ｍｉｎで行った。 The roughening etching process conditions were the same as in Example 1. The liquid composition was 500 g / l sulfuric acid, 90 g / l sodium chloride, 30 g / l cupric chloride dihydrate, the liquid temperature was 40 ° C., and the treatment time was 5 min. I went there.
　比較例２の試験片について、表面と断面ＳＥＭ観察、表面積評価を行った。図３に表面と断面ＳＥＭ観察および表面積評価の結果を示す。比較例２は、図３の表面と断面ＳＥＭ像から、幅２～５μｍで高さ約３μｍの微細構造体が形成されていることが確認できる。比較例２の表面積は平滑面に対して１０倍であった。 The test piece of Comparative Example 2 was subjected to surface and cross-sectional SEM observation and surface area evaluation. FIG. 3 shows the results of surface and cross-sectional SEM observation and surface area evaluation. In Comparative Example 2, it can be confirmed from the surface of FIG. 3 and the cross-sectional SEM image that a fine structure having a width of 2 to 5 μm and a height of about 3 μm is formed. The surface area of Comparative Example 2 was 10 times that of the smooth surface.
　また、表面微細構造形成プロセス後の密着性評価の結果、ポリイミド膜に一部剥がれが生じた。 Also, as a result of the adhesion evaluation after the surface microstructure formation process, part of the polyimide film was peeled off.
　実施例1、２と比較例１、２を比較してみると、比較例１のウェットブラスト加工で形成される表面微細構造は、研磨材サイズにも影響するが微細構造体間の距離がやや大きく緻密性が低い。また、比較例２の粗化エッチング処理で形成される表面微細構造は、結晶粒界エッチングのため基材の結晶粒径に依存し微細構造体の幅が大きい。このように、従来の表面構造形成方法であるウェットブラスト加工と粗化エッチング処理では、ステンレス鋼に高さ５μｍ以下で、且つ表面積比１５倍以上の表面微細構造を形成することは困難である。 When Examples 1 and 2 are compared with Comparative Examples 1 and 2, the surface microstructure formed by wet blasting in Comparative Example 1 affects the abrasive size, but the distance between the microstructures is somewhat small. Large and dense. Further, the surface fine structure formed by the roughening etching process of Comparative Example 2 has a large width of the fine structure depending on the crystal grain size of the base material due to the grain boundary etching. As described above, it is difficult to form a surface microstructure having a height of 5 μm or less and a surface area ratio of 15 times or more in stainless steel by wet blasting and roughening etching, which are conventional surface structure forming methods.
　次に、本発明の表面加工方法によって表面微細構造を形成したステンレス鋼の適用例について説明する。微細で且つ高表面積な凹凸構造が形成されたステンレス鋼が適用可能な好適な例として、気体で熱交換を行う空冷熱交換器が挙げられる。空冷熱交換器の伝熱部に本発明の表面加工が施されたステンレス鋼を適用することによって、表面積の増加による伝熱性能が向上し、さらに凹凸構造が非常に微細であることから圧力損失が抑制され、高い伝熱促進効果を得ることができる。 Next, an application example of stainless steel having a surface microstructure formed by the surface processing method of the present invention will be described. As a suitable example to which a stainless steel having a fine uneven structure with a high surface area can be applied, there is an air-cooled heat exchanger that performs heat exchange with gas. By applying the surface-treated stainless steel of the present invention to the heat transfer part of the air-cooled heat exchanger, the heat transfer performance is improved by increasing the surface area, and the uneven structure is very fine, resulting in pressure loss. Is suppressed, and a high heat transfer promoting effect can be obtained.
　本実施例では、実施例１の表面加工方法により表面微細構造を形成したステンレス鋼の伝熱管を用いたシェルアンドチューブ型熱交換器により伝熱性能を評価した。 In this example, heat transfer performance was evaluated by a shell-and-tube heat exchanger using a stainless steel heat transfer tube having a surface microstructure formed by the surface processing method of Example 1.
　図７は実施例４に係るシェルアンドチューブ型熱交換器の構造図である。円形または多角形のシェル２００の両側に伝熱部である伝熱管２０１を支えるための管板２０２が設置されている。管板２０２には伝熱管２０１を通すための多数の穴が千鳥状に配列されており、伝熱管２０１はこれらの管穴に挿入されて両端で管板２０２に固着される。伝熱管２０１の長さは、流れの代表長さＤの２５倍以上である。なお、本実施例の管群に沿った流れの代表長さＤは、水力等価直径を取る。伝熱管２０１の長さを、流れの代表長さＤの２５倍以上とすることで、気流状態が乱流の場合に伝熱性能をより向上することができる。 FIG. 7 is a structural diagram of a shell-and-tube heat exchanger according to the fourth embodiment. Tube plates 202 are installed on both sides of the circular or polygonal shell 200 to support the heat transfer tubes 201 that are heat transfer portions. A large number of holes for passing the heat transfer tubes 201 are arranged in a staggered pattern in the tube plate 202, and the heat transfer tubes 201 are inserted into these tube holes and fixed to the tube plate 202 at both ends. The length of the heat transfer tube 201 is 25 times or more of the representative length D of the flow. In addition, the representative length D of the flow along the tube group of the present embodiment takes a hydraulic equivalent diameter. By setting the length of the heat transfer tube 201 to 25 times or more of the typical flow length D, the heat transfer performance can be further improved when the airflow state is turbulent.
　微細構造体２０３は伝熱管２０１の管外表面に形成する。低温流体である空気２０４は熱交換器下部の側面に設けられたノズル２０５より熱交換器内に流入し、伝熱管２０１外を上昇し、伝熱管壁を介して高温流体である水蒸気２０６と熱交換する。高温流体である水蒸気２０６は熱交換器上部のノズル２０７から熱交換器内に流入し、熱交換器上部の水室２０８を経由して伝熱管２０１内を流下する。水蒸気２０６は伝熱管壁を介して低温流体である空気２０４と熱交換して凝縮し、圧縮水となる。圧縮水は熱交換器下部の水室を経由し、熱交換器下部のノズルから熱交換器外へ流出する。 The fine structure 203 is formed on the outer surface of the heat transfer tube 201. Air 204, which is a low-temperature fluid, flows into the heat exchanger from a nozzle 205 provided on the side surface of the lower portion of the heat exchanger, rises outside the heat transfer tube 201, and steam 206, which is a high-temperature fluid, through the heat transfer tube wall. Exchange heat. Water vapor 206, which is a high-temperature fluid, flows into the heat exchanger from the nozzle 207 at the top of the heat exchanger, and flows down through the heat transfer tube 201 via the water chamber 208 at the top of the heat exchanger. The water vapor 206 is condensed by exchanging heat with the air 204, which is a low-temperature fluid, through the heat transfer tube wall and becomes compressed water. The compressed water flows out of the heat exchanger from the nozzle at the bottom of the heat exchanger via the water chamber at the bottom of the heat exchanger.
　伝熱管２０１に実施例１の表面加工方法により表面微細構造を形成したステンレス鋼を用いた結果、表面加工処理を施していないシェルアンドチューブ型熱交換器に比べ伝熱性能を約６％向上させることができた。このように本発明の表面加工方法により表面微細構造を形成したステンレス鋼を伝熱管に適用することにより、伝熱管本数を増加せずに伝熱性能を向上することができる。すなわち、目標の伝熱性能を得る際には、伝熱管本数を削減でき、熱交換器のコストを削減できる。 As a result of using the stainless steel in which the surface microstructure is formed by the surface processing method of Example 1 for the heat transfer tube 201, the heat transfer performance is improved by about 6% compared to the shell and tube heat exchanger not subjected to the surface processing. I was able to. Thus, by applying the stainless steel having the surface microstructure formed by the surface processing method of the present invention to the heat transfer tube, the heat transfer performance can be improved without increasing the number of heat transfer tubes. That is, when obtaining the target heat transfer performance, the number of heat transfer tubes can be reduced, and the cost of the heat exchanger can be reduced.
　比較のため、伝熱管２０１に比較例２の表面加工方法により表面微細構造体を形成したステンレス鋼を用いた結果、表面加工処理を施していないシェルアンドチューブ型熱交換器に比べ伝熱性能は約２．５％向上した。この結果から、伝熱管２０１の表面積比が大きいほど伝熱性能を向上することが確認された。 For comparison, as a result of using the stainless steel in which the surface microstructure is formed by the surface processing method of Comparative Example 2 for the heat transfer tube 201, the heat transfer performance is higher than that of the shell and tube heat exchanger not subjected to the surface processing. About 2.5% improvement. From this result, it was confirmed that the heat transfer performance is improved as the surface area ratio of the heat transfer tube 201 is increased.
　また、微細構造体の高さに関しては、微細構造体の表面積が同じであればその高さはより低い方が好ましい。これは、微細構造体が高くなると圧力損失が増大するためである。微細構造体の高さが境界層を超えると高い伝熱促進効果が期待できるものの、これとトレードオフするかたちで圧力損失が大きくなる。この結果、圧力損失の増加によってトータルとしては伝熱性能が向上しない場合がある。なお、境界層とは、気体が接触する接触面の近傍に存在する、気体の粘性を無視することができない（気体の粘性の影響を強く受ける）薄い層をいう。境界層の厚さは熱交換器の仕様、すなわち気体の流速や流れ方、伝熱部の形状等の様々な要件によって変化する。そのため、確実に圧力損失を低減するという観点からは微細構造体の高さがより低く、かつ、表面積比が大きいことが望ましい。本発明の表面加工方法によれば、従来困難であった高さ５μｍ以下で、且つ表面積比１５倍以上の表面微細構造を形成できることから、この微細構造体を表面に有するステンレス鋼を熱交換器の伝熱部に採用することによって、従来よりも高い伝熱性能を得ることができる。 Also, regarding the height of the fine structure, it is preferable that the height is lower if the surface area of the fine structure is the same. This is because the pressure loss increases as the microstructure increases. When the height of the microstructure exceeds the boundary layer, a high heat transfer acceleration effect can be expected, but the pressure loss increases in a trade-off manner. As a result, the heat transfer performance may not improve as a whole due to an increase in pressure loss. Note that the boundary layer is a thin layer that exists in the vicinity of the contact surface with which the gas is in contact and cannot ignore the viscosity of the gas (it is strongly influenced by the viscosity of the gas). The thickness of the boundary layer varies depending on various requirements such as heat exchanger specifications, that is, gas flow velocity and flow method, heat transfer section shape, and the like. Therefore, from the viewpoint of reliably reducing the pressure loss, it is desirable that the height of the fine structure is lower and the surface area ratio is large. According to the surface processing method of the present invention, it is possible to form a surface microstructure having a height of 5 μm or less and a surface area ratio of 15 times or more, which has been difficult in the prior art. By adopting the heat transfer section, it is possible to obtain higher heat transfer performance than before.
　また、図５、６に示したようにステンレス鋼表面のクロム濃度が高くなり、耐食性に優れるという特徴を有する。そのため、耐食性が要求される熱交換器の伝熱部に好適である。 In addition, as shown in FIGS. 5 and 6, the chromium concentration on the surface of the stainless steel is increased and the corrosion resistance is excellent. Therefore, it is suitable for the heat transfer part of a heat exchanger that requires corrosion resistance.
　なお、実施例４では熱交換器としてシェルアンドチューブ型熱交換器を例として説明したが、本発明で適用可能な熱交換器はこれに限定されるわけではない。例えば、パワー半導体のフィン型熱交換器（ヒートシンク）、空調機や自動車のラジエータのクロスフィン型熱交換器など、気体と接触して熱交換を行う熱交換器において、前記気体と接触する伝熱部がステンレス鋼である熱交換器に実施可能である。 In addition, although Example 4 demonstrated the shell and tube type heat exchanger as an example as a heat exchanger, the heat exchanger applicable by this invention is not necessarily limited to this. For example, in heat exchangers that perform heat exchange in contact with gas, such as fin-type heat exchangers (heat sinks) for power semiconductors, cross fin-type heat exchangers for air conditioners and radiators of automobiles, etc. It can be implemented in a heat exchanger whose part is stainless steel.
　１００　ステンレス鋼
　１０１　微細結晶層
　１０２　置換析出金属
　Ｒ１　　結晶粒微細化処理後の凹凸構造
　Ｒ２　　粗化エッチング処理後の凹凸構造
　Ｒ３　　置換析出金属除去処理後の凹凸構造
　２００　シェル
　２０１　伝熱管
　２０２　管板
　２０３　微細構造体
　２０４　空気
　２０５　ノズル
　２０６　水蒸気
　２０７　ノズル
　２０８　水室 DESCRIPTION OF SYMBOLS 100 Stainless steel 101 Fine crystal layer 102 Substitution precipitation metal R1 Concavity and convexity structure after crystal grain refinement processing R2 Concavity and convexity structure after roughening etching processing R3 Concavity and convexity structure after substitution precipitation metal removal processing 200 Shell 201 Heat transfer tube 202 Tube plate 203 Fine Structure 204 Air 205 Nozzle 206 Water vapor 207 Nozzle 208 Water chamber

Claims (15)

  1. 　ステンレス鋼の表面に微細構造を形成するステンレス鋼の表面加工方法であって、
    　ステンレス鋼の表面内部の結晶粒を微細化する結晶粒微細化処理を施す第一の工程と、
    　前記第一の工程の後に、エッチング処理液でステンレス鋼の表面を粗化エッチング処理する第二の工程と、を有することを特徴とするステンレス鋼の表面加工方法。     A surface processing method for stainless steel that forms a microstructure on the surface of stainless steel,
    A first step of applying a crystal grain refining process for refining crystal grains inside the surface of stainless steel;
    And a second step of roughening and etching the surface of the stainless steel with an etching solution after the first step.
  2. 　前記結晶粒微細化処理が、ピーニング加工、機械加工、研磨のいずれかであることを特徴とする請求項１に記載のステンレス鋼の表面加工方法。  The stainless steel surface processing method according to claim 1, wherein the crystal grain refining treatment is any one of peening, machining, and polishing.
  3. 　前記第一の工程の結晶粒微細化処理でステンレス鋼の表面内部に形成された微細結晶層の厚さが１μｍ以上であり、前記微細結晶層の結晶粒の粒径が１μｍ以下であることを特徴とする請求項１または２に記載のステンレス鋼の表面加工方法。 The thickness of the fine crystal layer formed inside the surface of the stainless steel by the grain refinement treatment in the first step is 1 μm or more, and the grain size of the crystal grain of the fine crystal layer is 1 μm or less. The surface processing method for stainless steel according to claim 1 or 2, characterized in that:
  4. 　前記第二の工程の粗化エッチング処理は、ステンレス鋼の表面の結晶粒界を優先的にエッチングすることを特徴とする請求項１に記載のステンレス鋼の表面加工方法。 2. The surface processing method for stainless steel according to claim 1, wherein the roughening etching treatment in the second step preferentially etches crystal grain boundaries on the surface of the stainless steel.
  5. 　前記エッチング処理液は、塩化物イオンと鉄の標準電位より貴な遷移金属イオンを含み酸性であることを特徴とする請求項１に記載のステンレス鋼の表面加工方法。  2. The method of surface treatment of stainless steel according to claim 1, wherein the etching treatment liquid contains a transition metal ion noble from a standard potential of chloride ion and iron and is acidic.
  6. 　前記遷移金属イオンは、銅、銀、パラジウム、金、白金のいずれか１種類以上であることを特徴とする請求項５に記載のステンレス鋼の表面加工方法。 The stainless steel surface processing method according to claim 5, wherein the transition metal ion is one or more of copper, silver, palladium, gold, and platinum.
  7. 　前記第二の工程の後に、エッチング処理によってステンレス鋼の表面に析出した置換析出金属を除去する第三の工程を有することを特徴とする請求項４に記載のステンレス鋼の表面加工方法。 5. The method for surface treatment of stainless steel according to claim 4, further comprising a third step of removing substitutional deposited metal deposited on the surface of the stainless steel by etching treatment after the second step.
  8. 　前記第三の工程において、ステンレス鋼を溶解しにくく置換析出金属を優先的に溶解する金属除去処理液によって置換析出金属をエッチングすることを特徴とする請求項７に記載のステンレス鋼の表面加工方法。 8. The surface treatment method for stainless steel according to claim 7, wherein in the third step, the substitutional precipitation metal is etched with a metal removal treatment solution that hardly dissolves the stainless steel and preferentially dissolves the substitutional precipitation metal. .
  9. 　前記置換析出金属が銅であり、前記金属除去処理液が、過硫酸塩、過酸化水素のいずれかを含むことを特徴とする請求項８に記載のステンレス鋼の表面加工方法。  The method for surface processing a stainless steel according to claim 8, wherein the substitutional deposited metal is copper, and the metal removal treatment liquid contains one of persulfate and hydrogen peroxide.
  10. 　前記置換析出金属が銀、パラジウム、金、白金のいずれかであり、前記金属除去処理液が、シアン化カリウムやペルオキソ硫酸アンモニウムのいずれかを含むことを特徴とする請求項８に記載のステンレス鋼の表面加工方法。 The surface treatment of stainless steel according to claim 8, wherein the substitutional deposited metal is one of silver, palladium, gold, and platinum, and the metal removal treatment liquid contains either potassium cyanide or ammonium peroxosulfate. Method.
  11. 　請求項１～１０のいずれかに記載のステンレス鋼の表面加工方法により得られたステンレス鋼材であって、高さ５μｍ以下、且つ、表面積が平滑面の１５倍以上となる微細構造部を表面に有することを特徴とするステンレス鋼材。  A stainless steel material obtained by the surface processing method for stainless steel according to any one of claims 1 to 10, wherein a fine structure having a height of 5 µm or less and a surface area of 15 times or more of a smooth surface is formed on the surface. Stainless steel material characterized by having.
  12. 　気体と接触して熱交換を行う伝熱部を備え、前記気体と接触する伝熱部は、高さ５μｍ以下、且つ、表面積が平滑面に対して１５倍以上となる微細構造部を表面に有するステンレス鋼であることを特徴とする熱交換器。 A heat transfer portion that contacts the gas to perform heat exchange is provided, and the heat transfer portion that contacts the gas has a microstructure portion on the surface having a height of 5 μm or less and a surface area of 15 times or more of a smooth surface. A heat exchanger characterized by comprising stainless steel.
  13. 　前記伝熱部の微細構造部における内部結晶粒径は１μｍ以下であることを特徴とする請求項１２に記載の熱交換器。 The heat exchanger according to claim 12, wherein an internal crystal grain size in the fine structure portion of the heat transfer portion is 1 µm or less.
  14. 　前記伝熱部の微細構造部における表面クロム濃度は、前記伝熱部の微細構造部を形成していない表面に対して１．５倍以上であることを特徴とする請求項１２に記載の熱交換器。 The heat according to claim 12, wherein the surface chromium concentration in the microstructure portion of the heat transfer portion is 1.5 times or more that of the surface of the heat transfer portion where the microstructure portion is not formed. Exchanger.
  15. 　前記伝熱部の表面微細構造が、請求項１～１０のいずれかに記載のステンレス鋼の表面加工方法によって形成されたことを特徴とする請求項１２に記載の熱交換器。 The heat exchanger according to claim 12, wherein the surface microstructure of the heat transfer section is formed by the surface processing method for stainless steel according to any one of claims 1 to 10.
PCT/JP2014/073606 2014-03-25 2014-09-08 Method for processing surface of stainless steel, and heat exchanger obtained using same WO2015145808A1 (en)

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US20220251714A1 (en) 2019-07-30 2022-08-11 Mitsubishi Gas Chemical Company, Inc. Composition, method for roughening stainless steel surface using same, roughened stainless steel, and method for producing said roughened stainless steel
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