WO2010016378A1 - Acier inoxydable austénitique et procédé pour son hydrogénation - Google Patents

Acier inoxydable austénitique et procédé pour son hydrogénation Download PDF

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Publication number
WO2010016378A1
WO2010016378A1 PCT/JP2009/062970 JP2009062970W WO2010016378A1 WO 2010016378 A1 WO2010016378 A1 WO 2010016378A1 JP 2009062970 W JP2009062970 W JP 2009062970W WO 2010016378 A1 WO2010016378 A1 WO 2010016378A1
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stainless steel
austenitic stainless
hydrogen
mass
concentration
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PCT/JP2009/062970
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English (en)
Japanese (ja)
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村上　敬宜
峯　洋二
俊彦 金▲崎▼
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独立行政法人産業技術総合研究所
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Priority to EP09804865A priority Critical patent/EP2312006A1/fr
Priority to US13/057,578 priority patent/US20110139321A1/en
Priority to CA2733658A priority patent/CA2733658A1/fr
Publication of WO2010016378A1 publication Critical patent/WO2010016378A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite

Definitions

  • the present invention relates to austenitic stainless steel and its hydrogenation method. Specifically, the present invention relates to an austenitic stainless steel having high fatigue properties with reduced hydrogen embrittlement, and a hydrogenation method thereof. In particular, the present invention relates to an austenitic stainless steel that suppresses the generation of fatigue cracks in the austenitic stainless steel and the growth of the fatigue cracks by occluding hydrogen at 30 ppm by mass or more on the surface or the entire surface of the austenitic stainless steel.
  • Table 1 illustrates typical austenitic stainless steel components.
  • the first column of Table 1 is the names of stainless steel and heat resistant steel defined by the Japanese Industrial Standard (hereinafter referred to as JIS (Japan Industrial Standard) standard).
  • JIS Japanese Industrial Standard
  • HV Vickers hardness of stainless steel
  • the other columns are chemical components contained in the stainless steel, and the unit of the component is expressed by mass%.
  • the amount of hydrogen (H) contained in the stainless steel described in the last column of Table 1 is expressed in ppm by mass.
  • Non-Patent Documents 1 and 2 It is known that hydrogen penetrates into a metal material and reduces the static strength and fatigue strength of the material.
  • Non-Patent Documents 1 and 2 Various methods for removing this hydrogen or predicting the influence of hydrogen have been proposed.
  • austenitic stainless steel is subjected to heat treatment at a temperature of 270 to 400 ° C. for 10 minutes or more after the plating treatment to remove hydrogen to prevent hydrogen embrittlement.
  • Patent Document 3 discloses a method for predicting and determining the degree of hydrogen embrittlement of austenitic stainless steel using chemical components.
  • Non-Patent Document 1 discloses fatigue test results for austenitic stainless steels compliant with SUS304, SUS316, and SUS316L. This fatigue test was carried out by comparing these austenitic stainless steels charged with hydrogen with austenitic stainless steels not charged with hydrogen. As a result of this comparison, the fatigue crack growth rate of hydrogen-charged SUS304 and SUS316 is faster than that of the uncharged case. In the case of SUS316L, there is no clear difference.
  • the hydrogen-charged SUS304 has a fatigue crack growth rate 10 times faster than that in the case of no charge. In the case of SUS316L, the fatigue crack growth rate is accelerated twice.
  • Non-Patent Document 1 shows a result that overturns this common sense. In this experiment, the above results were obtained by applying a repeated load at a low frequency of 5 Hz or less, which is very significant.
  • Non-Patent Document 2 states that “(3) The martensite phase generated by transformation in austenitic stainless steel becomes a passage for hydrogen diffusing in the material and increases the diffusion coefficient of hydrogen (see page 130). ) ”.
  • Non-Patent Document 3 shows that the development of fatigue cracks in austenitic stainless steels SUS304 and SUS316L can be suppressed by removing non-diffusible hydrogen contained in a normal steelmaking process.
  • stainless steel when stainless steel is used in equipment and devices related to the use of hydrogen fuel, it is affected by various environments depending on the usage environment. For example, when stainless steel is used for a high-pressure hydrogen container or piping for a fuel cell vehicle, filling with hydrogen gas in the container and release by consumption of the hydrogen gas are repeated. In other words, the high-pressure hydrogen container and piping for a fuel cell vehicle are repeatedly loaded and released by hydrogen gas. It is considered that the accompanying temperature change occurs in a high-pressure hydrogen container or piping for a fuel cell vehicle, and hydrogen above the equilibrium level at room temperature enters and diffuses into the material.
  • low frequency repetitive loads occur due to temperature changes due to outside air temperature.
  • the cyclic load due to changes in the outside air temperature may be due to compression and expansion of the stainless steel itself due to temperature difference between day and night, and thermal stress due to compression and expansion of the parts connected to the stainless steel parts.
  • the frequency for example, the temperature difference between day and night is from several degrees to 10 ° C. or more, and becomes one cycle for 24 hours.
  • the high-pressure hydrogen tank, the fuel supply equipment for the fuel cell, etc. have a period of one day as described above and the hydrogen filling time is long.
  • An object of the present invention is to provide an austenitic stainless steel for suppressing the occurrence of fatigue cracks in an austenitic stainless steel and the progress of fatigue cracks, and a method for hydrogenation thereof.
  • Another object of the present invention is to pay attention to the amount of diffusible hydrogen and non-diffusible hydrogen that cause hydrogen embrittlement of austenitic stainless steel, and by adding hydrogen to 30 mass ppm or more, fatigue cracks
  • An object of the present invention is to provide an austenitic stainless steel in which generation and / or fatigue crack growth is delayed, and a method for hydrogenation thereof.
  • Still another object of the present invention is to provide an austenitic stainless steel capable of suppressing the fatigue crack growth rate under low frequency cyclic loading and a method for hydrogenation thereof.
  • Hydrogen charging means that hydrogen penetrates into the material.
  • a method of hydrogen charging a method of exposing a material in a high-pressure hydrogen chamber, a method of applying a cathodic hydrogen charge, and a method of immersing in a chemical solution or the like are used.
  • Fatigue crack growth means that a fatigue crack in a material becomes larger under repeated loading. This fatigue crack is a defect or a crack generated in a material during a manufacturing process or a processing process. The repeated load is applied to a hole or the like artificially introduced into the material.
  • the austenitic stainless steel is a Cr—Ni-based steel material, which is a stainless steel having an austenitic phase in which Cr and Ni are added to Fe to increase corrosion resistance against a corrosive environment. Examples of this stainless steel are shown in Table 1.
  • the austenite phase is an iron phase in a temperature range of 911 to 1392 ° C. in 100% pure iron (Fe) and has a face-centered cubic lattice structure (hereinafter referred to as an FCC (Face Centered Cubic Lattice) structure). .
  • FIG. 9A shows a face-centered cubic lattice.
  • an austenite phase can exist even at room temperature.
  • the martensite phase is a structure obtained by rapidly cooling steel from a high-temperature stable austenite phase, and has a body-centered cubic lattice structure (hereinafter referred to as a BCC (Body Centered Cubic Lattice) structure).
  • FIG. 9B shows a body-centered cubic lattice. Further, when cold working such as stress is applied to stainless steel in an austenite phase state at room temperature, a martensite phase may be generated.
  • Diffusible hydrogen refers to hydrogen present in a material that exits the material over time at room temperature.
  • Non-diffusible hydrogen refers to hydrogen that exists in a material and cannot escape from the material with time even at temperatures from room temperature to about 200 ° C.
  • the present invention employs the following means.
  • the inventors of the present invention have found that the fatigue strength characteristics of austenitic stainless steel can be remarkably improved when diffusible hydrogen and non-diffusible hydrogen in the austenitic stainless steel are present in an amount of 30 mass ppm or more.
  • the present invention relates to an austenitic stainless steel having an austenitic phase whose crystal structure is a face-centered cubic lattice structure, and a hydrogenation method thereof.
  • the austenitic stainless steel of the present invention is an austenitic stainless steel having an austenitic phase whose crystal structure is a face-centered cubic lattice structure, and comprises diffusible hydrogen and non-diffusible hydrogen contained in the austenitic stainless steel.
  • the concentration of hydrogen (H) is locally 0.0030% by mass (30 ppm by mass) or more in a thickness of 100 ⁇ m or more from the surface of the austenitic stainless steel to the inside of the austenitic stainless steel.
  • the manufacturing process is followed, and the occurrence of fatigue cracks in the austenitic stainless steel is slowed and / or the progress of the fatigue cracks is slowed.
  • the method for adding hydrogen to austenitic stainless steel according to the present invention comprises adding hydrogen to the austenitic stainless steel in order to increase the concentration of hydrogen present in the austenitic stainless steel having an austenitic phase having a face-centered cubic lattice structure.
  • a method of hydrogenating austenitic stainless steel for adding wherein the austenitic stainless steel is heated in a hydrogen environment at a heating temperature of 80 ° C. or more, and contained in the austenitic stainless steel The region where the local concentration of hydrogen is 0.0030 mass% (30 mass ppm) or more is formed from the surface of the austenitic stainless steel to the inside of the austenitic stainless steel with a thickness of 100 ⁇ m or more. To do.
  • the concentration of hydrogen (H) contained in the austenitic stainless steel is preferably 0.0030% by mass (30 ppm by mass) or more in the entire austenitic stainless steel.
  • concentration of hydrogen (H) contained in the austenitic stainless steel is 0.0030 mass% (30 mass ppm) or more throughout the austenitic stainless steel, the fatigue strength characteristics of the austenitic stainless steel are remarkably improved. .
  • this concentration of hydrogen throughout the austenitic stainless steel is referred to as the total concentration.
  • the concentration of hydrogen (H) contained in the region of the thickness of at least 100 ⁇ m or more from the surface of the austenitic stainless steel having a minimum cross-sectional dimension of 200 ⁇ m or more is 0.0030 mass% (30 mass ppm) or more.
  • the concentration of hydrogen from the surface of the austenitic stainless steel over a region having a predetermined thickness is referred to as a local concentration.
  • the minimum dimension of the cross section refers to the minimum length among the height, length, and thickness of the austenitic stainless steel material.
  • the minimum dimension of the cross section indicates the diameter.
  • the minimum cross-sectional dimension indicates the plate thickness.
  • the local concentration or total concentration of hydrogen (H) contained in the austenitic stainless steel is 0.0050 mass% (50 mass ppm) or more.
  • the Vickers hardness of austenitic stainless steel containing 0.0005 mass% (5 mass ppm) or less of hydrogen is defined as 1.
  • the austenitic stainless steel produced in the conventional process contains 5 mass ppm or less of hydrogen.
  • the Vickers hardness is a state in which hydrogen inevitably mixed in the conventional manufacturing process is contained, and hydrogen is in an uncharged state.
  • the Vickers hardness of the austenitic stainless steel in the region containing 30 mass ppm or more of hydrogen is 1.05 or more.
  • the addition of diffusible hydrogen and non-diffusible hydrogen is preferably performed by heating austenitic stainless steel in a hydrogen environment at a heating temperature of 80 ° C. or higher. Further, it is efficient that the heating temperature range is 200 ° C. to 500 ° C. The heating temperature is preferably lower than the sensitization temperature at which chromium (Cr) carbide of the austenitic stainless steel is precipitated by heating. Further, the heat treatment is preferably held for 460 hours or less at the above-described heating temperature in a hydrogen environment.
  • Addition of diffusible hydrogen and non-diffusible hydrogen to the austenitic stainless steel may be performed by exposure in a high-pressure hydrogen chamber, cathodic hydrogen charging, or immersion in a chemical solution.
  • the hydrogen environment is preferably a chamber filled with hydrogen gas of 1 MPa or more.
  • the present invention is a heat treatment of austenitic stainless steel in a hydrogen environment at a temperature of 80 ° C. or higher, and the non-diffusible hydrogen and diffusible hydrogen in the austenitic stainless steel are adjusted to a concentration of 30 mass ppm or more.
  • An austenitic stainless steel with slow fatigue crack initiation and fatigue crack growth was realized.
  • FIG. 1 shows the hydrogen concentration distribution of a round bar with a diameter of 7 mm charged with cathodic hydrogen as a function of depth from the surface.
  • FIGS. 2A to 2D are diagrams schematically showing a method for evaluating the hydrogen concentration distribution.
  • 3 (a) to 3 (c) are diagrams illustrating an outline of a fatigue test piece
  • FIG. 3 (a) is a diagram illustrating the shape of Example 1 of a fatigue test piece
  • FIG. 3 (b) is a diagram illustrating fatigue.
  • FIG. 3C is a diagram illustrating the shape of Example 2 of the test piece
  • FIG. 3C is a diagram illustrating the shape of the artificial microhole formed in the fatigue test piece.
  • FIG. 4 shows the outline of the test part of the fatigue test piece, the shape of the introduced artificial microhole, and the fatigue crack generated and propagated from the artificial microhole.
  • FIG. 5 is a photograph of a fatigue crack generated from an artificial microhole after a fatigue test.
  • FIG. 6 is a graph showing the relationship between the crack length of the fatigue crack and the number of repetitions in the fatigue test of Example 1 of the fatigue test piece, FIG. 6 (a) is SUS304, and FIG. 6 (b) is SUS316L. Is the case.
  • FIG. 7 is a graph showing the relationship between the crack length of the fatigue crack and the number of repetitions in the fatigue test of Example 1 of the fatigue test piece.
  • FIG. 7 (a) is SUS304
  • FIG. 7 (b) is SUS316L.
  • FIG. 8 is a graph showing the relationship between the fatigue life N f the test stress amplitude ⁇ and the fatigue test piece in the material of the artificial microhole of SUS304 is broken.
  • FIG. 9 is a conceptual diagram showing the lattice of the crystal structure of the austenite phase and the martensite phase.
  • FIG. 9A is a face-centered cubic lattice structure (FCC) of the austenite phase
  • FIG. 9B is the martensite phase.
  • FCC face-centered cubic lattice structure
  • BCC body centered cubic lattice structure
  • FIG. 10 is a graph that predicts the hydrogen concentration distribution from the surface to the inside when SUS316L is exposed to a hydrogen gas environment at a temperature of 25 ° C. at a pressure of 35 MPa or 70 MPa for 5 years.
  • FIG. 11 is a diagram showing the Vickers hardness ratio with respect to the hydrogen concentration of austenitic stainless steel.
  • Austenitic stainless steels such as SUS304, SUS316, and SUS316L shown in Table 1 above contain 1 to 4.7 ppm by mass of non-diffusible hydrogen even after a normal heat treatment such as a solution treatment.
  • a normal heat treatment such as a solution treatment.
  • FIG. 1 A measurement example in which the distribution of the hydrogen concentration of the material is measured is shown in FIG.
  • Cathodic hydrogen charging was performed on a round bar of SUS304, SUS316, and SUS316L (A) shown in Table 1 having a diameter of 7 mm and a length of about 30 mm. Thereafter, the hydrogen concentration distribution of these round bars was measured and shown in the graph of FIG.
  • the vertical axis of the graph in FIG. 1 indicates the hydrogen concentration.
  • the unit of hydrogen concentration is mass ppm.
  • the horizontal axis of the graph in FIG. 1 is the distance from the surface of the measurement sample. The unit of distance from this surface is ⁇ m.
  • Cathodic hydrogen charging was performed as follows.
  • the anode and cathode were placed in a sulfuric acid aqueous solution, and the anode and cathode were connected to a power source. At this time, the sulfuric acid aqueous solution was kept at a liquid temperature of 50 ° C., and the pH of the sulfuric acid aqueous solution was 3.5. Current density was 27A / m 2. A platinum electrode was used as the anode. An austenitic stainless steel round bar was used as the cathode. Cathodic hydrogen charging was done for 672 hours. After the round bar was charged with hydrogen, the hydrogen concentration distribution of the round bar was measured by the following procedure. The broken line in the figure indicates the hydrogen concentration of a round bar that is not charged with hydrogen.
  • FIG. 2 (a) shows a round bar of austenitic stainless steel subjected to cathodic hydrogen charging. This is a round bar before measurement.
  • a disk-shaped measurement sample having a thickness of about 0.8 mm was cut out from a round bar of austenitic stainless steel subjected to cathodic hydrogen charging. The amount of hydrogen contained in this sample was measured by temperature programmed desorption analysis. Thereafter, the round bar was polished with emery polishing paper. The round bar after emery polishing is shown by a solid line in FIG.
  • the broken line in FIG. 2B is the round bar in FIG. 2A, and the surface is removed by emery polishing.
  • a disk-shaped sample was again cut out from the round bar, and the hydrogen content of this sample was measured.
  • FIG. 2 (b) The round bar in FIG. 2 (b) was again polished with emery polishing paper. This emery-polished round bar is shown by a solid line in FIG.
  • the broken line in FIG. 2 (c) is the round bar shown in FIG. 2 (b).
  • a disk-shaped sample was again cut out from the round bar, and the hydrogen content of this sample was measured. In this way, polishing with emery polishing paper, cutting of the sample, and measurement of the amount of hydrogen were repeated.
  • FIG. 2B and FIG. 2C show the annular portion removed by polishing with emery polishing paper. The annular portion is a portion between a round bar drawn with a solid line and a portion drawn with a broken line.
  • the hydrogen concentration of the annular portion was determined by dividing the difference between the hydrogen amount of the sample before emery polishing and the hydrogen amount of the sample after emery polishing by the mass of the annular portion. As shown in FIG. 2D, this annular portion can be calculated by subtracting the volume of the sample after polishing from the volume of the sample before polishing. Therefore, the mass of the annular portion can be obtained from the polished sample volume, and the hydrogen concentration of the annular portion can be obtained. By repeating this operation, the relationship between the depth of the round bar from the surface of the test piece and the local concentration of hydrogen could be obtained.
  • the region where the local concentration of hydrogen is 0.0030% (30 ppm by mass) or more is in the range of 5 ⁇ m to 60 ⁇ m from the surface.
  • hydrogen enters the austenitic stainless steel placed in a hydrogen environment from its surface, diffuses, and the hydrogen concentration has a gradient.
  • the hydrogen concentration gradient gradually decreases from the surface toward the inside.
  • the local hydrogen concentration on the surface is about 0.0031 mass% (31 mass ppm).
  • the local hydrogen concentration on the surface is expected to exhibit a hydrogen concentration gradient gradually decreasing toward the inside in a range of about 400 ⁇ m from the surface. Note that the region where the local hydrogen concentration is 30 mass ppm or more is expected to be in the range of about 5 ⁇ m from the surface.
  • the local hydrogen concentration on the surface is about 0.0049 mass% (49 mass ppm), and in the range of about 400 ⁇ m from the surface, It is expected that a local hydrogen concentration gradually decreases toward the inside, exhibiting a hydrogen concentration gradient.
  • the region where the local hydrogen concentration is 30 mass ppm or more is expected to be about 80 ⁇ m from the surface.
  • the materials used for the test are austenitic stainless steel SUS304 and SUS316L (A) (hereinafter simply referred to as SUS316L) shown in Table 1 above. As SUS304 and SUS316L, those subjected to solution treatment were used. 3 (a) and 3 (b) show the shape of a fatigue test piece made of this material. The surface of the fatigue test piece was polished to # 2000 with emery polishing paper and then finished by buffing.
  • an artificial microhole having a diameter of 100 ⁇ m and a depth of 100 ⁇ m as shown in FIG. 3C is formed at the center in the length direction of the fatigue test piece, and the fatigue test piece. Drilled in the radial direction. This drill has a tip angle of 120 degrees. The bottom of this artificial microhole matched the shape (conical shape) of the tip angle of the drill. The artificial microhole was introduced in the center of the test part of the fatigue test piece.
  • the test part is a central cylindrical part of the fatigue test piece.
  • the length of the cylindrical portion of the test portion is, in short, the length of the portion having a uniform outer diameter is about 20 mm for the fatigue test piece of FIG. 3A and about 14 mm for the fatigue test piece of FIG. .
  • FIG. 4 illustrates the outline of the test section and the shape of the introduced artificial microhole. In the case of a fatigue test piece charged with hydrogen, immediately after the completion of hydrogen charge, buffing was performed again to open an artificial microhole.
  • the amount of martensite before the fatigue test contained in the hydrogen-charged test part was about 3% when the material was SUS304 or SUS316L.
  • the amount of martensite was measured at two locations before introducing artificial microholes.
  • the first area of this measurement is a circular area having a diameter of 1 mm centered on the position where the artificial microhole is to be introduced.
  • the second area of this measurement is a circle area having a diameter of 1 mm centered on a position obtained by rotating the axis in the length direction of the fatigue test piece by 180 degrees from the position where the artificial microhole is to be introduced. That is, the second measurement region is located on the opposite side of the cylindrical portion from the first measurement region on the cylindrical portion.
  • Hydrogen charging was performed by a cathodic hydrogen charging method or a high-pressure hydrogen exposure method.
  • the temperature of the aqueous sulfuric acid solution was 50 ° C. (323 K), and cathodic hydrogen charging was performed for 672 hours (4 weeks).
  • the aqueous sulfuric acid solution was changed every week in order to reduce the change in sulfuric acid concentration due to evaporation.
  • a fatigue test piece in a high-pressure hydrogen gas environment having a pressure of 10 MPa, 25 MPa, 48 MPa, 74 MPa, or 94 MPa, or a temperature of 235 ° C., 242 ° C., 250 ° C., or 280 ° C. And the fatigue test piece was charged with hydrogen.
  • the fatigue test piece of FIG. 3 (a) is held for 400 hours, 414 hours, 416 hours, 419 hours, or the fatigue test piece of FIG. Charged with hydrogen.
  • the fatigue test was performed using a hydraulic servo tension / compression fatigue tester Servo Pulser EHF-ED30KN manufactured by Shimadzu Corporation (Kyoto, Japan) and a hydraulic servo tension / compression fatigue tester 8500 manufactured by Instron. It was.
  • the fatigue crack was observed and the length of the fatigue crack was measured by a replica method or a scanning electron microscope S-2500CX manufactured by Hitachi, Ltd. (location: Chiyoda-ku, Tokyo, Japan).
  • the observation of fatigue cracks by the replica method is as follows.
  • An acetylcellulose film having a thickness of about 0.034 mm (hereinafter referred to as a replica film) was immersed in a methyl acetate solution for a while and then attached to a place where a fatigue test piece was observed. After applying the replica film, wait for 2 to 3 minutes. When the replica film dries, the replica film is removed from the fatigue test piece and collected. Gold was vapor-deposited on the collected replica film and observed with a metal microscope to observe a fatigue crack in the test part.
  • the target fatigue crack location could be observed without directly observing the fatigue test piece.
  • a sample having a diameter of 7 mm and a thickness of 0.8 mm was cut out from the test part, and this sample was placed in a vacuum chamber and heated at a constant temperature increase rate.
  • the pressure in the vacuum chamber was 1 ⁇ 10 ⁇ 7 to 3 ⁇ 10 ⁇ 7 Pa before heating the sample.
  • the temperature increase rate of the vacuum chamber was 0.33 ° C./s or 0.5 ° C./s.
  • TDS quadrupole mass spectrometry temperature programmed desorption analyzer
  • FIG. 5 is a photograph of a fatigue crack generated from an artificial microhole introduced into hydrogen-uncharged SUS304 after a fatigue test. From the photograph, fatigue cracks generated from artificial microholes can be confirmed. It can be seen that this fatigue crack originates from both sides of the artificial microhole and propagates almost symmetrically.
  • FIGS. 6A and 6B are graphs showing the relationship between the fatigue crack length of a fatigue test piece by a fatigue test and the number of repetitions of the fatigue test. The vertical axis of the graphs shown in FIGS. 6A and 6B indicates the length of the crack.
  • FIGS. 6A and 6B show a case where a fatigue test piece having a diameter of 7 mm of the test portion shown in FIG. 3A is used.
  • FIG. 6A shows the case where the material is SUS304.
  • FIG. 6B shows the case where the material is SUS316L.
  • the graphs shown in FIGS. 6A and 6B show the measurement results of the fatigue test pieces of the materials SUS304 and SUS316L that are charged with hydrogen and those that are not charged with hydrogen.
  • the repetition rate was 1 Hz or 1.2 Hz for SUS304 and 1 Hz for SUS316L. There is almost no influence of the repetition rate due to the difference between 1 Hz and 1.2 Hz.
  • the fatigue test piece charged with cathodic hydrogen having the same hydrogen concentration gradient as that in FIG. This indicates that the fatigue crack growth rate is increasing.
  • the number of repetitions N until the crack length 2a reaches 400 ⁇ m is smaller when the cathode hydrogen is charged than when the hydrogen is not charged.
  • the growth rate of the fatigue crack is about twice as fast as when the cathode hydrogen is charged.
  • this result does not depend on the hydrogen charging method called the cathodic hydrogen charging method.
  • SUS304 having a total hydrogen concentration of 89.2 mass ppm had a Vickers hardness of 192, which was 1.09 times that of Vickers hardness 176 when no hydrogen was charged.
  • the Vickers hardness mentioned here is measured at a test load of 9.8 N in room temperature and air.
  • the fatigue crack growth rate is remarkable when the test is performed in the atmosphere and in hydrogen gas at 0.68 MPa. It has been confirmed that there is no difference, and a sufficient effect of improving fatigue strength characteristics can be obtained even when used in a hydrogen environment.
  • FIG.6 (b) the measurement result of SUS316L which carried out the fatigue test in air
  • the fatigue crack growth rate is slower than that of the specimen not charged with hydrogen.
  • the number of repetitions N until the crack length 2a reaches 400 ⁇ m is larger when hydrogen is charged to 30 mass ppm or more than when hydrogen is not charged.
  • the growth rate of the fatigue crack is about 8 times slower when hydrogen is charged to 30 mass ppm or more.
  • FIG. 7 (a) and 7 (b) are graphs showing the relationship between the crack length of the fatigue test piece and the number of repetitions of the fatigue test.
  • This fatigue test piece is a test piece having a test portion diameter of 4 mm shown in FIG.
  • the fatigue test of the fatigue test piece was performed in the atmosphere.
  • the graph of Fig.7 (a) has shown the measurement result of the fatigue test when the test piece in case the material is SUS304 is hydrogen-charged, and when it is not hydrogen-charged. At this time, the repetition rate of the fatigue test was 0.3 Hz.
  • FIG. 7B shows measurement results of the fatigue test when the material is SUS316L when the fatigue test piece is charged with hydrogen and when the material is not charged with hydrogen.
  • the repetition rate of the fatigue test was 0.3 Hz until the crack length 2a reached about 400 ⁇ m, and thereafter 0.05 Hz.
  • the crack length 2a is 1000 ⁇ m.
  • the number of repetitions N until reaching N is about 4/5 shorter than that in the case of no hydrogen charging (SUS304), and the fatigue crack growth rate is increased.
  • Figure 8 is a graph showing the relationship between the fatigue life N f the test stress amplitude ⁇ and the fatigue test piece in the material of the artificial microhole of SUS304 is broken.
  • the vertical axis of this graph indicates the stress amplitude, and the horizontal axis indicates the fatigue life. Comparing the fatigue life at a stress amplitude of 280 MPa, the test piece containing 89.2 mass ppm of the total hydrogen concentration is about eight times longer than the test piece not charged with hydrogen. With respect to the fatigue test piece containing 109 mass ppm of the total hydrogen concentration, fatigue cracks do not occur even when the fatigue test piece not charged with hydrogen is repeated about 27 times the fatigue life.
  • the fatigue test piece with a total hydrogen concentration of 109 mass ppm has a Vickers hardness of 193, which is 1.10 times the Vickers hardness 176 of a fatigue test piece not charged with hydrogen.
  • the austenitic stainless steel of the present invention is characterized by being charged with hydrogen and containing 30 ppm by mass or more. By containing 30 mass ppm or more of hydrogen in the austenitic stainless steel, fatigue cracks generated in the austenitic stainless steel were dramatically reduced. Further, by containing 30 mass ppm or more of hydrogen in the austenitic stainless steel, the progress of fatigue cracks generated in the austenitic stainless steel could be remarkably slowed.
  • the fatigue life of the austenitic stainless steel can be increased by reducing the occurrence of fatigue cracks and / or resistance to fatigue crack growth.
  • the region where the local hydrogen concentration is 30 mass ppm or more is about several tens of ⁇ m from the surface, and the local hydrogen concentration spreading inside the region is less than 30 mass ppm, the fatigue crack As a result, the progress of development is accelerated.
  • Austenitic stainless steel Austenitic stainless steel is also called Cr-Ni stainless steel, which is obtained by adding Cr and Ni to Fe.
  • the main component of austenitic stainless steel is composed of Fe, Cr, Ni, and there are various additives shown in Table 2 below.
  • Table 2 shows a preferable example of the austenitic stainless steel of the present invention, and the embodiment of the present invention is not limited to this example.
  • Ni is added to Fe in order to improve the corrosion resistance.
  • Ni is added to Fe in combination with Cr in order to increase corrosion resistance.
  • Ni and Mn are elements for ensuring non-magnetism after cold rolling. In order to maintain non-magnetism after cold rolling, it is necessary to contain 10.0% by mass or more of Ni. Furthermore, it is necessary to adjust the amount of Ni according to the contents of Si and Mn so that the work-induced martensite phase is not generated by 1% by volume or more. Mn also has an effect of increasing the solid solubility of N.
  • C is a strong austenite-forming element. Furthermore, C is an element effective for improving the strength of stainless steel. When C is added excessively, coarse Cr-based carbides precipitate during the recrystallization process, causing intergranular corrosion resistance and deterioration of fatigue characteristics. Si is added for the purpose of deoxidation and solid solution strengthening. If the Si content is high, the formation of a martensite phase is promoted during cold working, and therefore a small amount is preferably added. N brings about solid solution hardening.
  • Mo is added for the purpose of improving corrosion resistance. Furthermore, it also has an effect of finely dispersing carbonitride by aging treatment.
  • Ti is an element effective for precipitation hardening, and is added to increase the strength by aging treatment.
  • B is an alloy component effective in preventing the occurrence of edge cracks in the hot-rolled steel strip caused by the difference in deformation resistance between the ⁇ ferrite phase and the austenite phase in the hot working temperature range.
  • Al is an element added for the purpose of deoxidation at the time of steelmaking, and acts effectively on precipitation hardening in the same manner as Ti.
  • the embodiment of the present invention can be used by adding elements such as Nb and Cu as required in addition to the elements described in Table 2 above.
  • Nb can be an alternative element for Ti.
  • About the austenitic phase As for austenitic stainless steel, it is desirable that the austenitic phase is almost 100% of the total volume. It is desirable that there is no martensite phase in the austenitic stainless steel. For example, as shown in Non-Patent Document 2, when the martensite phase is larger than the austenite phase, it does not fall within the range of the austenitic stainless steel defined in the present invention.
  • the average crystal grain size is preferably about 50 ⁇ m or less.
  • the average crystal grain size is about 50 ⁇ m in the current material, and an average crystal grain size smaller than that is desirable.
  • Hydrogenation treatment by heating The hydrogenation treatment by heating of austenitic stainless steel will be described. It is effective to contain 30 ppm by mass or more of hydrogen in the austenitic stainless steel for the generation of fatigue cracks and their progress, or for improving the resistance of either.
  • the inventors of the present invention have first ascertained the effect of this hydrogen. In order to obtain this effect, hydrogen of 30 mass ppm or more is added to the austenitic stainless steel by performing a heat treatment as follows.
  • Addition of diffusible hydrogen and non-diffusible hydrogen involves heat treatment of austenitic stainless steel at a heating temperature of 80 ° C. or higher.
  • the heat treatment is performed in a hydrogen environment.
  • the hydrogen environment includes a high-pressure and low-pressure hydrogen gas environment, a cathodic hydrogen charge environment, an immersion hydrogen charge environment, and a gas phase or liquid phase environment with a high hydrogen partial pressure.
  • the time for holding the austenitic stainless steel at the heating temperature in a hydrogen environment is 460 hours or less.
  • the heating temperature is preferably lower than the sensitization temperature at which the chromium (Cr) carbide of the austenitic stainless steel is precipitated by heating.
  • the upper limit of the heating temperature is 500 ° C.
  • diffusible hydrogen and non-diffusible hydrogen causing hydrogen embrittlement of austenitic stainless steel are added to austenitic stainless steel to 30 ppm by mass or more, and hydrogen contained in austenitic stainless steel (H) is made 0.0030 mass% (30 mass ppm) or more.
  • the amount of hydrogen (H) contained in the austenitic stainless steel after this heat treatment is preferably 0.0050 mass% (50 mass ppm) or more. As described above, the amount of hydrogen contained in the austenitic stainless steel is increased from the conventional amount to suppress the generation of fatigue cracks and / or their growth, and the austenitic stainless steel excellent in fatigue strength characteristics. Can provide.
  • test piece made of SUS316 (A), SUS316L (B), SUS310S (A) and SUH660 (A).
  • the test piece is a round bar having a diameter of 7 mm.
  • a test piece was put in a hydrogen gas at a pressure of 94 MPa at a temperature of 280 ° C. and heat-treated for 200 hours. After the heat treatment, the total hydrogen concentration and Vickers hardness of the test piece were measured.
  • the TDS measurement was performed by cutting into a disk shape having a diameter of 7 mm and a thickness of 0.8 mm.
  • the measurement was performed with a temperature programmed desorption analyzer EMD-WA1000S / H manufactured by Electronic Science Co., Ltd. (Location: Musashino City, Tokyo). The measurement results are shown in Table 3.
  • the hydrogen concentration of the test piece not subjected to hydrogenation treatment was 1.5 to 3.4 mass ppm.
  • the hydrogen concentration of the test piece was 69.9 to 129.1 mass ppm.
  • the change in Vickers hardness before the hydrogenation treatment and Vickers hardness after the hydrogenation treatment was 1.08 to 1.11 times.
  • FIG. 11 shows the relationship between the hydrogen concentration of the entire fatigue test piece and the Vickers hardness ratio.
  • the Vickers hardness ratio refers to the austenitic stainless steel subjected to the hydrogen charge treatment of the present invention when the Vickers hardness of the austenitic stainless steel containing only inevitable hydrogen mixed in the conventional manufacturing process is 1. It refers to the ratio of Vickers hardness.
  • the austenitic stainless steel produced by the conventional manufacturing method usually contains 1 to 5 ppm by mass of hydrogen.
  • the stainless steel was heat-treated in its hydrogen environment, and the hydrogen concentration contained therein could be increased to 30 ppm by mass or more.
  • the hydrogen environment of the present invention is not limited to a high-pressure hydrogen gas environment.
  • the hydrogen charging process may be performed by controlling the environment in the manufacturing process such as the solution treatment to make the environment suitable for hydrogen charging.
  • the saturation concentration of hydrogen in a metal material such as stainless steel is theoretically and experimentally determined by the material of the metal, the hydrogen charge treatment method, the temperature and pressure during the hydrogen charge treatment, and the like.
  • SUS316 and SUS316L have a hydrogen saturation concentration of about 100 ppm when subjected to hydrogen charging in an environment of 100 Mpa and 280 ° C.
  • SUS310S has a hydrogen saturation concentration of about 120 ppm when charged with hydrogen in an environment of 280 ° C. Accordingly, the charge above the hydrogen saturation concentration is technically meaningless, and the hydrogen charge treatment of the present invention means below the hydrogen saturation concentration.
  • the present invention is preferably used in a field that utilizes high-pressure hydrogen as well as corrosion resistance.

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Abstract

L'invention porte sur un acier inoxydable austénitique dans lequel l'apparition d'une fissure de fatigue et la propagation d'une fissure de fatigue sont inhibées par le chargement d'hydrogène ; et sur un procédé pour l'hydrogénation de l'acier inoxydable austénitique. En faisant attention à la quantité d'hydrogène diffusible et d'hydrogène non diffusible qui peut provoquer la fragilisation par l'hydrogène dans de l'acier inoxydable austénitique, on parvient à réaliser une amélioration des caractéristiques de résistance à la fatigue d'un acier inoxydable austénitique en augmentant la quantité d'hydrogène diffusible et d'hydrogène non diffusible contenus dans l'acier inoxydable austénitique à 0,0030 % en masse (30 ppm en masse) ou au-dessus. Un acier inoxydable austénitique est traité thermiquement dans une atmosphère d'hydrogène à une température de 200 à 500°C pendant au maximum 460 heures, la quantité d'hydrogène (H) contenu dans l'acier inoxydable austénitique peut ainsi être accrue à 0,0030 % en masse (30 ppm en masse) ou au-dessus.
PCT/JP2009/062970 2008-08-06 2009-07-17 Acier inoxydable austénitique et procédé pour son hydrogénation WO2010016378A1 (fr)

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US13/057,578 US20110139321A1 (en) 2008-08-06 2009-07-17 Austenitic stainless steel, and hydrogenation method thereof
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