WO2024096109A1 - Tôle d'acier inoxydable à base de ferrite ainsi que procédé de fabrication de celle-ci, et composant - Google Patents

Tôle d'acier inoxydable à base de ferrite ainsi que procédé de fabrication de celle-ci, et composant Download PDF

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WO2024096109A1
WO2024096109A1 PCT/JP2023/039683 JP2023039683W WO2024096109A1 WO 2024096109 A1 WO2024096109 A1 WO 2024096109A1 JP 2023039683 W JP2023039683 W JP 2023039683W WO 2024096109 A1 WO2024096109 A1 WO 2024096109A1
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steel sheet
less
stainless steel
ferritic stainless
oxide layer
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PCT/JP2023/039683
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English (en)
Japanese (ja)
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佳幸 藤村
純一 濱田
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日鉄ステンレス株式会社
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Publication of WO2024096109A1 publication Critical patent/WO2024096109A1/fr

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    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • 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
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
    • C23G1/08—Iron or steel

Definitions

  • the present invention relates to ferritic stainless steel, its manufacturing method, and parts made from said ferritic stainless steel sheet.
  • ammonia is attracting attention as a fuel to replace carbon fuels.
  • the combustion reaction of ammonia is 4NH 3 + 3O 2 ⁇ 2N 2 + 6H 2 O, and it is expected to be a circulable fuel because it produces water and nitrogen and has a small environmental impact.
  • the combustion temperature of ammonia is 1750°C in adiabatic flame temperature, which is lower than the 2120°C of hydrogen, the 1970°C of methane, and the approximately 2000°C of gasoline, and the combustion temperature in actual engines and gas turbines is also lower than these existing fuels.
  • the exhaust gas temperature is about 500 to 700°C, which is lower than that of existing fuels.
  • This temperature range of 500 to 700°C is a temperature range at which steel materials used in exhaust pipes, etc. are easily oxidized, and is a temperature range at which so-called red scale is easily generated.
  • Patent Document 1 proposes a ferritic stainless steel for fuel cell reformers that is resistant to oxidation and red scale even at high temperatures of around 600°C.
  • Patent Document 2 proposes a ferritic stainless steel for use in the exhaust pipes of internal combustion engines equipped with a pollution control system that contains urea or ammonia to reduce nitrogen oxides.
  • ammonia which has a lower combustion temperature than existing fuels, is added and burned, so the combustion exhaust gas temperature is lower than that of existing fuels, at around 500 to 700°C.
  • ammonia combustion gas contains a large amount of nitrogen and water vapor. The inclusion of water vapor makes it easy for steam oxidation and red scale to occur.
  • the combustion gas temperature is about 500 to 700°C, which is also a temperature range in which red scale is likely to occur. For this reason, oxidation resistance (red scale resistance) is required for steel materials used in ammonia combustion gas systems, etc.
  • Patent Document 1 has high-temperature oxidation resistance and red scale resistance as a steel material for exhaust gas system parts, but does not take into consideration measures against grain boundary cracking caused by surface nitriding in gases that contain large amounts of nitrogen, such as ammonia combustion gas.
  • Patent Document 2 does have the effect of suppressing surface grain boundary cracking caused by urea and ammonia, but it cannot be said to have sufficient nitriding resistance against gases containing large amounts of nitrogen, such as the exhaust gas from ammonia combustion.
  • the present invention aims to provide a ferritic stainless steel that has red scale resistance (oxidation resistance) and intergranular cracking resistance (nitridation resistance) even when exposed to gases containing large amounts of nitrogen and water (water vapor), such as ammonia combustion exhaust gas, at temperatures of about 500 to 700°C.
  • Nitriding tendency index 10Al + 2Mo + 3Ti + 0.5Cu - 1.5Si ⁇ 5.0 .... (Equation 1)
  • the ferritic stainless steel of the present invention makes it possible to obtain stainless steel with good corrosion resistance and wear resistance, even when it comes into contact with gases containing large amounts of nitrogen and water (water vapor) at temperatures of about 500 to 700°C, such as ammonia combustion exhaust gas.
  • % indicates mass% in the steel. When no lower limit is specified or the lower limit is 0%, this also includes cases where the component is not contained (0%).
  • ⁇ Steel composition> C 0 to 0.030%
  • C is an element that reduces formability (r value), so the less C the better, with the upper limit set at 0.030%. From the viewpoint of formability, 0.020% or less, or 0.010% or less is preferred. There is no particular lower limit, but an excessive reduction leads to an increase in refining costs, so 0.001% or more is preferred, and 0.002% or more is even more preferred.
  • Si 0.05 to 3.00% Si is an element that is effective in suppressing oxidation, particularly steam oxidation, and is also effective in suppressing nitridation. Furthermore, from the viewpoint of generating an SiO 2 internal oxidation layer just below the steel sheet surface, the content is 0.05% or more.
  • the lower limit of Si is preferably 0.10%, 0.20%, 0.30%, 0.50%, 0.80%, 1.00%, 1.25%, 1.50%, 1.70%, 1.90%, 2.00%, 2.20%, 2.40%, 2.50%, or 2.60%.
  • the upper limit is set to 3.00%.
  • the upper limit of Si is preferably 2.95% or 2.90%.
  • Mn 0.05 to 1.20% Mn, like Si, is an element effective for oxidation resistance, so it is preferable to contain 0.05% or more.
  • the lower limit of Mn is preferably 0.07%, 0.09%, 0.11%, 0.13%, or 0.15%.
  • the upper limit of Mn is preferably 1.10%, 1.00%, 0.90%, or 0.80%.
  • P 0.050% or less P is harmful to stainless steels, as it reduces toughness, hot workability, and corrosion resistance, so the less the better, and it is better to keep it at 0.050% or less, and preferably at 0.040% or less.
  • an excessive decrease in P content increases the load during refining or requires the use of expensive raw materials, so in reality it may contain 0.001% or more.
  • S 0.005% or less S is harmful to stainless steels, as it reduces toughness, hot workability, and corrosion resistance, so the less the better, and the upper limit should be 0.005% or less, preferably 0.003% or less.
  • an excessive reduction in S content increases the load during refining or requires the use of expensive raw materials, so in reality, a content of 0.0001% or more is acceptable.
  • Ni 0 to 1.00% or less
  • Ni has the effect of further enhancing the high corrosion resistance of stainless steel by adding it.
  • Ni is an expensive element, even if it is contained in a large amount, the effect is not commensurate with the increase in alloy cost, so it is good to make it 1.00% or less, and preferably 0.80% or less, 0.60% or less, or 0.50% or less.
  • Cr 12.0 to 31.0% Cr is an important element that provides corrosion resistance to stainless steel, and should be contained at 12.0% or more, preferably 12.5% or more, 13.0% or more, 14.0% or more, 15.0% or more, 18.0% or more, or 20.0% or more. On the other hand, since a large content of Cr leads to a decrease in workability, it should be contained at 31.0% or less, preferably 30.0% or less, 29.0% or less, 28.0% or less, 26.0% or less, or 24.0% or less.
  • N 0 to 0.030%
  • the N content in the steel material is small.
  • N reduces workability and reduces corrosion resistance by combining with Cr, it is preferable that the content is small, and it is good to set it to 0.030% or less, preferably 0.025% or less, 0.020% or less, 0.015% or less, or 0.010% or less.
  • excessive reduction places a large load on the refining process, it may be contained at 0.001% or more.
  • Nb 0 to 1.00% Nb has the effect of improving formability and corrosion resistance. On the other hand, if it is added in excess of 1.00%, recrystallization becomes difficult and the structure becomes coarse, so it is preferable to set the content at 1.00% or less, and preferably at 0.90% or less, 0.80% or less, or 0.70% or less. There is no particular lower limit for the Nb content, but it is preferable to include 0.01% or more in order to ensure the effect.
  • Mo 0 to 2.50%
  • Mo is not only an element that promotes nitriding, but also forms a brittle sigma phase with high Cr, which leads to embrittlement and a decrease in corrosion resistance, so it is recommended that the content be 2.50% or less, preferably 2.20% or less, or 2.00% or less.
  • Mo content is no particular lower limit for the Mo content, but it is preferable to contain 0.01% or more in order to reliably obtain the effect of corrosion resistance.
  • Cu 0 to 3.00%
  • the addition of Cu has the effect of further enhancing the high corrosion resistance of stainless steel.
  • excessive addition does not improve performance to justify the manufacturing cost, so it is preferable to set it to 3.00% or less, and preferably to 2.50% or less, 2.20% or less, or 1.90% or less.
  • Al 0.002 to 0.500%
  • Al is an element that combines with N to form AlN and promotes nitriding, and since excessive addition reduces workability, the Al content should be 0.500% or less, and preferably 0.450% or less, 0.400% or less, 0.350% or less, 0.300% or less, 0.250% or less, or 0.200% or less.
  • the Al content should be 0.002% or more, and preferably 0.004% or more, 0.007% or more, or 0.010% or more.
  • Ti 0 to 0.600% Ti ensures corrosion resistance by stabilizing C and N.
  • Ti is an element that promotes nitriding, and if added in excess, TiN is significantly generated, causing nozzle blockage during production and surface defects in the product, so it is preferable to make the content 0.600% or less, and preferably 0.500% or less, 0.400% or less, or 0.300% or less. There is no particular lower limit for the Ti content, but it is preferable to contain 0.001% or more to ensure the effect.
  • V 0 to 1.00%
  • the addition of V has the effect of further enhancing the high corrosion resistance of stainless steel.
  • the upper limit of V should be set to 1.00%, and preferably 0.90% or less, 0.70% or less, or 0.50% or less.
  • B 0 to 0.0100% B is an element that enhances the strength of grain boundaries and contributes to improving workability.
  • the content should be 0.0100% or less, preferably 0.0090% or less, 0.0070% or less, or 0.0050% or less.
  • the B content it is preferable to contain 0.0001% or more, or 0.0005% or more.
  • Ca 0 to 0.0150% If Ca is contained in a large amount, the concentration in the oxide for promoting TiN generation increases and the ability to do so is lost, so it is good to contain 0.0150% or less, and preferably 0.0120% or less, 0.0090% or less, 0.0070% or less, or 0.0050% or less. There is no particular lower limit, but Ca is the main component of slag, and some inclusion is unavoidable. In addition, it is difficult to completely remove it, and excessive reduction increases the load during refining, so it may be contained in an amount of 0.0001% or more, or 0.0002% or more in practical operation.
  • Sn 0 to 1.00%
  • the addition of Sn has the effect of further enhancing the high corrosion resistance of stainless steel.
  • the content should be 1.00% or less, preferably 0.70% or less, 0.50% or less, or 0.30% or less.
  • impurities refer to components that are mixed in during the industrial production of steel due to various factors in the manufacturing process, including raw materials such as ores and scraps, and are acceptable within the scope of not adversely affecting the present invention.
  • ⁇ Nitriding tendency index> In optimizing the steel components from the viewpoint of suppressing nitridation of steel, the relationship of the content of elements that affect nitridation was considered. Cr, Mo, Ti, and Al are known as elements that promote nitridation, but a certain amount of them may be contained in order to ensure the functions of stainless steel, such as corrosion resistance. Furthermore, the inventors have found that Si, an important element contained in the steel according to the present invention, not only has an effect of suppressing red scale caused by steam oxidation, but also has an effect of suppressing nitridation, although the reason is unclear. In addition, as will be described later, it is also effective to form a Si oxide film (SiO 2 film) on the steel surface.
  • SiO 2 film Si oxide film
  • Nitriding tendency index 10Al + 2Mo + 3Ti + 0.5Cu - 1.5Si ⁇ 5.0 ....
  • Equation 1 In the formula 1, the symbol of an element indicates the content (mass%) of the element, and 0 is substituted when the element is not contained.
  • the nitriding tendency index is, in short, an index of the ease of nitriding, and a smaller value is preferable. Therefore, the upper limit of the nitriding tendency index is preferably 4.8, 4.6, 4.4, 4.2, 4.0, 3.9, 3.8, 3.7, 3.6, or 3.5.
  • SiO2 film ⁇ Area ratio of surface Si oxide film ( SiO2 film)> It is preferable that a Si oxide film (SiO 2 film) is present on the steel sheet surface. This is because the portion where the Si oxide film is present does not penetrate into the steel even if nitrogen (N) comes into contact with the portion, and nitridation of the portion is suppressed. Therefore, it is preferable that the Si oxide film is present at an area ratio of 5.0% or more on the steel sheet surface. Preferably, it is 6.0% or more, 7.0% or more, 8.0% or more, 9.0% or more, 10.0% or more, 11.0% or more, 12.0% or more, 13.0% or more, 14.0% or more, or 15.0% or more. There is no particular upper limit to the area ratio of the Si oxide film.
  • the Si oxide film inhibits the luster and design of stainless steel, and also deteriorates workability and weldability. Therefore, it is preferable that the Si oxide film is present at an area ratio of 50.0% or less on the steel sheet surface. Preferably, it may be 45.0% or less, 40.0% or less, 35.0% or less, 30.0% or less, 25.0% or less, or 20.0% or less.
  • the Si oxide film of the present invention is a Si oxide that is internally oxidized during the manufacturing process and is exposed on the steel sheet surface by removing the Fe-based and Cr-based oxides on the surface. Therefore, it is different from the Si oxide with an amorphous structure in the FeCr-based oxide layer (passive film).
  • the area ratio of the Si oxide film on the steel plate surface can be measured as follows.
  • the observation field is a 30 ⁇ m square on the stainless steel plate surface to be measured, and the observation surface is analyzed by EPMA.
  • the area of the oxide formed on the surface that has an Si content of 5 wt% or more is measured as the Si oxide film, and the area ratio in the observation field is calculated.
  • three or more observation fields can be arbitrarily selected, and the area ratio of the Si oxide film obtained in each can be calculated as an arithmetic average.
  • photo editing software e.g., ImageJ
  • Si oxide (SiO 2 ) is also present in the surface layer of the steel sheet.
  • the surface layer of the steel sheet refers to a region from the surface of the steel sheet to 10 ⁇ m in the sheet thickness direction.
  • the presence of Si-based oxides in the surface layer of the steel sheet prevents the intrusion of nitrogen (N) into the steel and suppresses nitriding. Therefore, it is preferable that Si oxides having a grain size of 1 ⁇ m or more are present in an area ratio of 3.0% or more in an observation surface of 30 ⁇ m in width in the surface layer of the steel sheet.
  • the Si oxide in the steel sheet surface layer is an Si oxide that is internally oxidized during the manufacturing process. Therefore, it is different from the Si oxide with an amorphous structure in the FeCr-based oxide layer (passive film).
  • the area ratio of the Si oxide on the surface of the steel plate can be measured as follows. In the vertical cross section of the steel plate surface of the stainless steel plate to be measured, a rectangular observation surface 30 ⁇ m wide and 10 ⁇ m from the steel plate surface in the plate thickness direction is arbitrarily selected, and the observation surface is analyzed by EPMA. Among the oxides observed, the parts with a Si content of 5 wt% or more are regarded as Si oxides, and their shapes (particularly the major and minor axes) are measured, and Si oxides with an average particle size of 1 ⁇ m or more are identified, and the area ratio on the observation surface is calculated.
  • the average particle size is the diameter of a circle equivalent to the area (diameter of a circle equivalent to the area).
  • Intergranular crack length As a result of suppressing nitridation of the steel sheet surface, intergranular cracking due to the intrusion of nitrogen (N) is suppressed. Intergranular cracking can be measured by observing the crystal grain boundaries, and three arbitrary 100 ⁇ m square ranges are selected from the surface layer portion (at least the portion including the nitrided portion) of the steel sheet cross section, and the total intergranular crack length in these areas is preferably 20 ⁇ m or less. If the total intergranular crack length in the three observation surfaces is 20 ⁇ m or less, embrittlement of the steel sheet surface can be suppressed, and the steel sheet strength in the temperature range of 500 to 700 ° C. can be ensured. The shorter the total intergranular crack length, the more preferable it is, and it is more preferable that it is 18 ⁇ m or less, 16 ⁇ m or less, 14 ⁇ m or less, 12 ⁇ m or less, or 10 ⁇ m or less.
  • the intergranular crack length in the surface layer of the steel plate can be measured as follows.
  • the cross section of the sample steel plate is observed under an optical microscope with a square observation field of 100 ⁇ m on each side, and the intergranular crack length is measured.
  • the observation field is set to the area directly below the steel plate surface.
  • the intergranular crack area can be marked on the measurement image, and its length can be measured using image processing.
  • the steel plate according to the present invention has a shallow nitriding depth on average because the components are adjusted to suppress nitriding and the surface has a silicon oxide film.
  • the nitriding depth varies slightly depending on the nitrogen (N) content of the contacting gas, but it has been confirmed that surface embrittlement is suppressed if the nitriding depth is generally 220 ⁇ m or less.
  • the nitriding depth is preferably 210 ⁇ m or less, 200 ⁇ m or less, 190 ⁇ m or less, or 180 ⁇ m or less.
  • the manufacturing method described below is one embodiment for obtaining the steel plate according to the present invention, and the manufacturing method is not limited to this. As long as the steel plate according to the present invention can be obtained, the manufacturing method is not limited.
  • a steel plate is manufactured by a conventional method, and then a Si oxide layer is formed under the surface of the steel plate by internal oxidation during final annealing, and a Cr oxide layer and an Fe oxide layer are formed on top of that (on the surface side of the steel plate). After final annealing, the Cr oxide layer and the Fe oxide layer are etched away by acid washing, whereby the Si oxide layer appears on the surface and becomes a Si oxide film, thereby obtaining the steel plate according to the present invention.
  • Steel sheets before final annealing can be manufactured using standard manufacturing methods. For example, they can be manufactured using the process of steelmaking-hot rolling, steelmaking-hot rolling-annealing, or steelmaking-hot rolling-pickling-cold rolling.
  • a suitable method is to melt steel containing the components adjusted to the composition described above in a converter or electric furnace, followed by secondary refining.
  • the molten steel thus adjusted to the desired composition is made into slabs using a known casting method (e.g., continuous casting).
  • the slabs are heated to a desired temperature and hot rolled to a desired thickness.
  • the steel may be cold rolled (cold rolling) if necessary. Cold rolling may also be performed using conventional methods.
  • the slab thickness and hot-rolled sheet thickness may be set as appropriate. After coiling the hot-rolled sheet, it may be immersed in a water-cooled pool.
  • the mechanical descaling method such as shot blasting, bending, or brushing, may be selected as appropriate.
  • the pickling solution after hot rolling either, so existing conditions such as sulfuric acid, nitric hydrofluoric acid, etc. may be used.
  • the coil surface may be ground after this.
  • the hot-rolled steel sheet, hot-rolled annealed steel sheet, and cold-rolled steel sheet thus obtained are then subjected to final annealing.
  • the annealing atmosphere is not particularly limited, and may be an air atmosphere. Annealing is preferably performed in a temperature range of 900 to 1100°C.
  • the holding time is not particularly limited, but is preferably 30 seconds to 5 minutes.
  • a silicon oxide layer is formed under the surface of the steel sheet (internal oxidation).
  • a Cr oxide layer is formed above the silicon oxide layer (on the surface side of the steel sheet) due to the diffusion of Cr in the steel sheet, and an Fe oxide layer is formed due to the Fe in the steel sheet.
  • the steel sheet after final annealing is cooled to 60°C or less and pickled to etch away the upper Cr oxide layer and Fe oxide layer.
  • the pickling solution should contain 2.0% or less hydrofluoric acid (HF) and 6-15% nitric acid, and should be adjusted to a temperature of 50-60°C and an immersion time of 40-60 seconds. This removes the upper Fe oxide and Cr oxide layers, and the internally oxidized Si oxide layer appears on the surface, forming a Si oxide film with an appropriate area ratio. Hydrofluoric acid is not necessary, but if excessive Si oxide remains, it will not only deteriorate the design due to surface coloring, but also deteriorate workability and weldability.
  • hydrofluoric acid in the pickling solution at a concentration of preferably 0.1% or more, preferably 0.2% or more, 0.3% or more, 0.4% or more, or 0.5% or more to dissolve part of the Si oxide and leave an appropriate Si oxide film. If there is too much HF, excessive silicon oxide will be removed, so it should be 2.0% or less, preferably 1.5% or less, or 1.0% or less.
  • a brushing step of brushing the steel sheet surface may be added after pickling.
  • the Fe oxide and Cr oxide in the upper layer can be reliably removed, and the amount of removal can be adjusted, so that the Si oxide film can be exposed on the steel sheet surface so as to have a desired area ratio.
  • Brushing is sufficient if at least a part of the steel sheet surface is brushed, and the entire steel sheet surface may also be brushed.
  • brushing may be performed on either the front or back surface of the steel sheet, or both.
  • the type of brush for brushing is not particularly limited. It is advisable to select a brush based on the difference in hardness between the Fe oxide and Cr oxide to be removed and the Si oxide to be left behind. This is because it is possible to selectively remove the Fe oxide and Cr oxide without removing the surface Si oxide. For example, it is advisable to use an abrasive brush with abrasive grains having adjusted roughness.
  • the steel sheet according to the present invention is used in a gas environment with a high nitrogen (N) content, the good nitriding resistance reduces nitrogen penetration into the surface layer of the steel sheet, suppressing grain boundary cracking. Furthermore, the steel sheet according to the present invention has oxidation resistance, and is effective against the generation of red scale, which is a problem with conventional stainless steels, particularly in the medium to high temperature range of about 500 to 700°C. For this reason, the steel sheet according to the present invention can be used, for example, for ammonia combustion equipment with a high nitrogen content and a medium to high gas temperature range of 500 to 700°C. In particular, the steel sheet can be used for exhaust parts of ammonia combustion equipment.
  • the nitrogen ions in the solution and the nitrogen in the evaporated gases of ammonia and urea are prevented from penetrating into the steel sheet surface, thereby suppressing grain boundary cracking.
  • the steel sheet according to the present invention can be used to obtain the same effects when applied to parts that require resistance to nitridation and oxidation.
  • the liquid temperature conditions and immersion time of the final pickling are shown in Table 2.
  • the surface was finished by brushing using a SiC abrasive brush at a load current of 80 to 120 A, a rotation speed of 1000 rpm, and a reduction of 0.5 to 1.0 mm.
  • test pieces measuring 20 mm x 25 mm were cut from the obtained test material, one of which was used to measure the area ratio of the surface silicon oxide film, and the remaining three were subjected to nitriding and oxidation treatment to simulate ammonia combustion gas.
  • the area ratio of the Si oxide film on the steel sheet surface was measured using an EPMA under the following conditions: acceleration voltage: 15 kV, irradiation current: 2.0 ⁇ 10 ⁇ 7 A, analysis area: 30 ⁇ m ⁇ 30 ⁇ m, measurement time: 50 ms.
  • the Si oxide film (SiO 2 ) was identified from the obtained image, and the image was binarized using photo editing software (ImageJ), and the area ratio relative to the observation field area was calculated using image processing software.
  • the nitriding and oxidation treatment involved introducing 10 vol% ammonia, 10 vol% water vapor, and the balance nitrogen (N) into the atmospheric gas of an annealing furnace, placing the remaining test pieces in the furnace, heating them to a temperature of 600°C and holding them there for 50 hours, then cooling and removing them, and measuring the intergranular crack length and nitriding depth.
  • the intergranular crack length was measured by cutting the test piece after nitriding and oxidation treatment so that the cross section in the thickness direction could be observed, and observing the cross section of the test piece using an optical microscope. The observation was performed with a field of view of 100 ⁇ m x 100 ⁇ m just below the steel plate surface, and three randomly selected points on the sample cross section were observed to measure the intergranular crack length. A satisfactory result was obtained if the total intergranular crack length on the three observation surfaces was 20 ⁇ m or less.
  • the nitriding depth was measured by cutting the test piece after the nitriding and oxidation treatment, electrolytically etching it with a 10% oxalic acid aqueous solution at a voltage of 6 V for 5 seconds, and observing it with an optical microscope. The nitriding depth was measured using a photograph. The red scale was visually confirmed, and samples in which no red scale was found were rated as pass ( ⁇ ), and samples in which even a small amount of red scale was found were rated as fail ( ⁇ ). The results of these measurements are shown in Table 2. The data in Table 2 show that the steel plate according to the present invention has a reduced intergranular crack length.
  • This invention can be used in all industries, including the automotive and general machinery industries.

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Abstract

L'invention fournit une tôle d'acier inoxydable à base de ferrite dans laquelle la rupture intergranulaire est inhibée (résistance à la nitruration) et l'apparition d'une calamine rouge est également inhibée (résistance à l'oxydation), y compris dans une atmosphère de gaz comprenant un azote et une vapeur d'eau telle qu'un gaz de combustion d'ammoniac, dans une plage de températures moyennes ou élevées de ５００ à ７００℃.　La tôle d'acier inoxydable à base de ferrite de l'invention présente une composition prédéfinie d'indice de tendance de nitruration inférieur ou égal à 5, et est telle qu'un film d'oxyde Si est présent à raison de 5% ou plus en rapport surfacique à sa surface. Cette tôle d'acier est obtenue de la manière suivante : une tôle d'acier est soumise à un recuit final et une couche d'oxydation interne (couche d'oxyde Si) est formée, puis une couche d'oxyde Cr et une couche d'oxyde Fe superficielles sont éliminées par décapage chimique, et une couche d'oxyde Si est formée en surface.　Indice de tendance de nitruration = １０Ａｌ＋２Ｍｏ＋３Ｔｉ＋０,５Ｃｕ－１,５Ｓｉ
PCT/JP2023/039683 2022-11-04 2023-11-02 Tôle d'acier inoxydable à base de ferrite ainsi que procédé de fabrication de celle-ci, et composant WO2024096109A1 (fr)

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JP2022-177115 2022-11-04
JP2022177115 2022-11-04

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2018181257A1 (fr) * 2017-03-30 2018-10-04 新日鐵住金ステンレス株式会社 Tôle d'acier inoxydable à base de ferrite ayant un faible poids spécifique et son procédé de production
WO2022085788A1 (fr) * 2020-10-23 2022-04-28 日鉄ステンレス株式会社 Acier inoxydable à base de ferrite et composant pour gaz d'échappement

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2018181257A1 (fr) * 2017-03-30 2018-10-04 新日鐵住金ステンレス株式会社 Tôle d'acier inoxydable à base de ferrite ayant un faible poids spécifique et son procédé de production
WO2022085788A1 (fr) * 2020-10-23 2022-04-28 日鉄ステンレス株式会社 Acier inoxydable à base de ferrite et composant pour gaz d'échappement

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