High strength austenitic stainless steel having excellent resistance to hydrogen embrittlement, method for manufacturing the same, and hydrogen equipment used for high-pressure hydrogen gas and liquid hydrogen environment

Abstract

This high strength austenitic stainless steel having excellent resistance to hydrogen embrittlement includes, in terms of mass %, C: 0.2% or less, Si: 0.2% to 1.5%, Mn: 0.5% to 2.5%, P: 0.06% or less, S: 0.008% or less, Ni: 10.0% to 20.0%, Cr: 16.0% to 25.0%, Mo: 3.5% or less, Cu: 3.5% or less, N: 0.01% to 0.50%; and O: 0.015% or less, with the balance being Fe and unavoidable impurities, in which an average size of precipitates is 100 nm or less and an amount of the precipitates is 0.001% to 1.0% in terms of mass %.

Claims

1. An austenitic stainless steel having resistance to hydrogen embrittlement comprising, in terms of mass %: C: 0.2% or less; Si: 0.2% to 1.5%; Mn: 0.5% to 2.5%; P: 0.042% or less; S: 0.008% or less; Ni: 10.0% to 20.0%; Cr: 16.0% to 19.1%; Mo: 3.5% or less; Cu: 1.52% or less; N: 0.01% to 0.50%; and O: 0.015% or less, with a balance being Fe and unavoidable impurities, wherein an average size of precipitates is 100 nm or less and an amount of the precipitates is 0.001% to 1.0% in terms of mass %.

2. The austenitic stainless steel having resistance to hydrogen embrittlement according to claim 1, further comprising one or more selected from the group consisting of, in terms of mass %, Al: 0.3% or less, Mg: 0.01% or less, Ca: 0.01% or less, REM: 0.10% or less, and B: 0.008% or less.

3. The austenitic stainless steel having resistance to hydrogen embrittlement according to claim 1, further comprising one or more selected from the group consisting of, in terms of mass %, Ti: 0.5% or less, Nb: 0.5% or less, and V: 0.5% or less.

4. The austenitic stainless steel having resistance to hydrogen embrittlement according to claim 1, which is used for a high-pressure hydrogen gas and liquid hydrogen environment.

5. A method for manufacturing the austenitic stainless steel having resistance to hydrogen embrittlement according to claim 1, the method comprising: subjecting a semi-finished product having a component composition comprising, in terms of mass %: C: 0.2% or less; Si: 0.2% to 1.5%; Mn: 0.5% to 2.5%; P: 0.042% or less; S: 0.008% or less; Ni: 10.0% to 20.0%; Cr: 16.0% to 19.1%; Mo: 3.5% or less; Cu: 1.52% or less; N: 0.01% to 0.50%; and O: 0.015% or less, with a balance being Fe and unavoidable impurities, to hot working; performing a final heat treatment at a temperature of 1000° C. to 1200° C.; and performing cooling after the final heat treatment, wherein, in the cooling, an average cooling rate until a temperature reaches 750° C. is controlled to be less than 2.0° C./s.

6. The austenitic stainless steel having resistance to hydrogen embrittlement according to claim 2, further comprising one or more selected from the group consisting of, in terms of mass %, Ti: 0.5% or less, Nb: 0.5% or less, and V: 0.5% or less.

7. The austenitic stainless steel having resistance to hydrogen embrittlement according to claim 2, which is used for a high-pressure hydrogen gas and liquid hydrogen environment.

8. The austenitic stainless steel having resistance to hydrogen embrittlement according to claim 3, which is used for a high-pressure hydrogen gas and liquid hydrogen environment.

9. A method for manufacturing the austenitic stainless steel having resistance to hydrogen embrittlement according to claim 2, the method comprising: subjecting a semi-finished product having a component composition comprising, in terms of mass %: C: 0.2% or less; Si: 0.2% to 1.5%; Mn: 0.5% to 2.5%; P: 0.042% or less; S: 0.008% or less; Ni: 10.0% to 20.0%; Cr: 16.0% to 19.1%; Mo: 3.5% or less; Cu: 1.52% or less; N: 0.01% to 0.50%; O: 0.015% or less; and one or more selected from the group consisting of, in terms of mass %, Al: 0.3% or less, Mg: 0.01% or less, Ca: 0.01% or less, REM: 0.10% or less, and B: 0.008% or less; with a balance being Fe and unavoidable impurities, to hot working; performing a final heat treatment at a temperature of 1000° C. to 1200° C.; and performing cooling after the final heat treatment, wherein, in the cooling, an average cooling rate until a temperature reaches 750° C. is controlled to be less than 2.0° C./s.

10. A method for manufacturing the austenitic stainless steel having resistance to hydrogen embrittlement according to claim 3, the method comprising: subjecting a semi-finished product having a component composition comprising, in terms of mass %: C: 0.2% or less; Si: 0.2% to 1.5%; Mn: 0.5% to 2.5%; P: 0.042% or less; S: 0.008% or less; Ni: 10.0% to 20.0%; Cr: 16.0% to 19.1%; Mo: 3.5% or less; Cu: 1.52% or less; N: 0.01% to 0.50%; O: 0.015% or less; and one or more selected from the group consisting of, in terms of mass %, Ti: 0.5% or less, Nb: 0.5% or less, and V: 0.5% or less; with a balance being Fe and unavoidable impurities, to hot working; performing a final heat treatment at a temperature of 1000° C. to 1200° C.; and performing cooling after the final heat treatment, wherein, in the cooling, an average cooling rate until a temperature reaches 750° C. is controlled to be less than 2.0° C./s.

Description

EXAMPLES

(1) Examples of the invention will be described in detail, but the invention is not limited to conditions used in the following Examples.

(2) In addition, the underlined values in Tables indicate that they are out of the ranges of the embodiment.

(3) A stainless steel test material having a component composition shown in Table 1 was melted, and a semi-finished product having a thickness of 120 mm was manufactured. Next, the semi-finished product was heated at a temperature of 1200° C., and then the semi-finished product was subjected to hot forging and hot rolling to obtain a hot-rolled sheet having a thickness of 20 mm. Next, the hot-rolled sheet was subjected to a final heat treatment and cooling under conditions shown in Table 2 to obtain a hot-rolled and annealed sheet. The retention time for the final heat treatment was 3 minutes to 20 minutes. The “heat treatment temperature (° C.)” in Table 2 indicates the temperature of the final heat treatment, and the “cooling rate (° C./s)” indicates the average cooling rate until the temperature reached 750° C.

(4) The average size of the precipitates and the amount of the precipitates of each test material are shown in Table 2.

(5) A sample was formed from the obtained hot-rolled and annealed sheet by an extraction replica method, and then the precipitates were observed by a TEM. The size of one precipitate was determined as the average value of the major axis and the minor axis ((major axis+minor axis)/2). The sizes of 30 precipitates were measured, and the average value of the sizes of the 30 precipitates was determined to be the average size of the precipitates in the test material.

(6) An analysis sample was collected from the test material in the same manner, and the amount of the precipitates was measured according to the electroextraction residual method. A filter having a mesh size of 0.2 μm was used as the filter for filtering out a residue.

(7) Next, with regard to each hot-rolled and annealed sheet of the test material, the resistance to hydrogen gas embrittlement was evaluated according to the method shown below.

(8) A round bar tensile specimen which included a parallel part having an outer diameter of 3 mm and a length of 20 mm was collected from a longitudinal direction of the hot-rolled and annealed sheet having a thickness of 20 mm and a central part of the sheet thickness. (1) A tensile test in the atmosphere and (2) a tensile test in the high-pressure hydrogen gas were performed using this round bar tensile specimen.

(9) The tensile test (1) in the atmosphere was conducted under conditions in which the test temperatures were 25° C. and −40° C. and the strain rate was 5×10.sup.−5/s. A specimen of which the tensile strength measured by the tensile test at 25° C. was higher than 650 MPa was evaluated as “Pass” (acceptable quality).

(10) The tensile test (2) in the high-pressure hydrogen gas was conducted under conditions in which the test temperature was −40° C., the test environment was a hydrogen gas of 70 MPa, and the strain rate was 5×10.sup.−5/s. The specimen Nos. A3, A4, and A6 were also subjected to the tensile test under conditions in which the test environment was a hydrogen gas of 103 MPa in the same manner as described above except for test environment.

(11) Then, the value (relative reduction of area) of “(reduction of the area in the high-pressure hydrogen gas/reduction of the area in the atmosphere)×100(%)” at −40° C. was calculated. A test material having the value of 80% or more was evaluated such that the resistance to hydrogen embrittlement in the high-pressure hydrogen gas was “Pass” (acceptable quality). In particular, a specimen in which the tensile strength at 25° C. was higher than 650 MPa and the reduction of area was 80% or more and less than 85% was evaluated as “0”, and a specimen in which the tensile strength at 25° C. was higher than 650 MPa and the reduction of area was 85% or more was evaluated as “@”.

(12) The results are shown in Table 3 and Table 4.

(13) The specimens A1a, A1c, and A2 to A18 are test materials (Invention Examples) which were subjected to the final heat treatment and the cooling under preferable conditions.

(14) With regard to these specimens, the tensile strengths at 25° C. in the atmosphere were 650 MPa or higher, while the relative reduction of area values (the values of the relative reduction of area) were 80% or more. In particular, with regard to the specimens A1a, A2 to A6, and A8 to A17 in which the amounts of Ni and Cu having great influences on enhancing the resistance to hydrogen embrittlement and the average cooling rate were within the preferable ranges of the embodiment, the relative reduction of area values were 85% or more, and the resistances to hydrogen embrittlement were excellent.

(15) In addition, the specimens A3, A4, and A6 were also subjected to the tensile test in the hydrogen gas of 103 MPa, and the relative reductions of area were 90% or more which were more than the target value of 80%.

(16) With regard to the specimen A1b, the cooling rate after the final heat treatment was out of the range of the invention. As a result, the precipitates were not precipitated in the test material during the cooling after the final heat treatment and the effect of precipitation strengthening could not be obtained. Thus, the tensile strength in the atmosphere at room temperature was lower than 650 MPa.

(17) With regard to the specimen B1, the amount of Ni was less than the range of the invention. As a result, the resistance to hydrogen embrittlement was insufficient and the relative reduction of area value was 59%.

(18) With regard to the specimen B2, the amount of Cu was more than the range of the invention. As a result, the strength of the austenite phase was decreased and the tensile strength at 25° C. in the atmosphere was lower than the target value of 650 MPa.

(19) With regard to the specimen B3, the amount of Si was more than the range of the invention. As a result, the resistance to hydrogen embrittlement was insufficient and the relative reduction of area value was 68.8%.

(20) With regard to the specimen B4, the amount of Cr was more than the range of the invention. As a result, the precipitates were precipitated at an amount of more than the range of the invention. Consequently, the hydrogen gas embrittlement sensitivity was increased, the resistance to hydrogen embrittlement was insufficient, and the relative reduction of area value was 61.5%.

(21) With regard to the specimen B5, the amount of Mn was more than the range of the invention. As a result, the resistance to hydrogen embrittlement was insufficient and the relative reduction of area value was 71.3%.

(22) With regard to the specimen B6, the amount of Cr was less than the range of the invention. As a result, the stability of the austenite phase was decreased; and thereby, the resistance to hydrogen embrittlement was insufficient and the relative reduction of area value was 77.5%.

(23) With regard to the specimen B7, the amount of N was less than the range of the invention. As a result, the strength of the austenite phase was decreased and the tensile strength at 25° C. in the atmosphere was lower than the target value of 650 MPa.

(24) TABLE-US-00001 TABLE 1 Steel Component Composition (mass %) No. C Si Mn P S Ni Cr Mo Cu N O Others Remarks  A1 0.09 0.49 0.66 0.037 0.005 12.9 18.4 2.2 0.22 0.22 0.009 Invention  A2 0.08 0.49 0.81 0.030 0.004 12.8 18.4 2.2 0.31 0.13 0.008 steel  A3 0.15 0.48 0.79 0.034 0.004 13.1 17.9 2.1 0.25 0.26 0.009  A4 0.10 0.50 0.93 0.036 0.005 14.4 18.8 2.2 0.22 0.23 0.011  A5 0.11 1.11 0.50 0.036 0.004 15.0 19.0 2.4 0.23 0.23 0.007  A6 0.06 0.49 2.10 0.035 0.003 18.3 23.8 1.9 1.52 0.44 0.009  A7 0.09 0.51 0.64 0.037 0.003 10.9 19.1 2.1 2.93 0.25 0.009  A8 0.08 0.49 0.72 0.042 0.005 12.6 16.9 2.3 0.24 0.19 0.008  A9 0.09 0.49 0.92 0.037 0.004 12.6 18.3 3.3 0.22 0.22 0.008 A10 0.11 0.55 0.82 0.025 0.005 13.0 18.1 0.8 0.25 0.05 0.007 Al: 0.067, Ca: 0.0031, B: 0.0019 A11 0.10 0.51 1.11 0.034 0.004 12.9 18.0 1.8 0.29 0.22 0.009 Mg: 0.0042, Ca: 0.0021 A12 0.11 0.49 1.14 0.033 0.005 12.8 18.4 1.9 0.22 0.24 0.009 REM: 0.008 A13 0.09 0.51 0.87 0.037 0.005 13.0 18.1 2.0 0.23 0.21 0.007 Ti: 0.12, Nb: 0.09, V: 0.11 A14 0.09 0.49 0.96 0.031 0.004 12.9 17.8 2.0 0.23 0.28 0.007 Ti: 0.21 A15 0.14 0.32 0.68 0.033 0.003 13.1 17.6 2.1 0.28 0.25 0.009 Nb: 0.18 A16 0.10 0.51 0.82 0.033 0.005 13.0 18.0 2.4 0.20 0.25 0.012 V: 0.22 A17 0.06 0.40 1.09 0.016 0.003 14.1 18.7 2.2 0.23 0.39 0.008 Al: 0.059, Ca: 0.0033, Ti: 0.14, Nb: 0.15 A18 0.03 0.41 1.0  0.031 0.004 12.3 17.8 1.7 0.09 0.13 0.004  B1 0.11 0.45 0.65 0.037 0.004  8.5 18.1 1.9 0.22 0.23 0.009 Comparative  B2 0.12 0.49 0.65 0.039 0.005 12.5 18.0 1.9 4.11 0.25 0.006 Al: 0.055, Ca: 0.0038, B: 0.0011 steel  B3 0.10 3.10 0.6  0.034 0.005 12.6 18.7 2.0 0.21 0.24 0.009  B4 0.09 0.50 0.61 0.029 0.005 13.1 27.4 1.9 0.24 0.31 0.009  B5 0.12 0.49 3.2  0.051 0.004 12.9 18.2 2.1 0.28 0.63 0.010  B6 0.11 0.44 0.87 0.035 0.003 12.0 14.2 1.8 0.29 0.14 0.009  B7 0.01 0.49 0.81 0.032 0.004 12.5 17.6 2.4 0.22  0.008 0.006 Ti: 0.10, Nb: 0.08, V: 0.08

(25) TABLE-US-00002 TABLE 2 Heat Size of Amount of treatment Cooling precip- precip- Specimen temperature rate itates itates No. (° C.) (° C./s) (nm) (mass %) Remarks A1 A1a 1080 1.5 15 0.170 Invention Example A1b 1080 7.0 Precipitates were Compar- not detected ative Example A1c 1080 0.3 85 0.205 Invention  A2 1080 1.5 10 0.023 Example  A3 1080 1.5 15 0.217  A4 1100 1.5 20 0.470  A5 1100 1.5 20 0.122  A6 1080 1.8 30 0.571  A7 1080 1.8 30 0.142  A8 1150 1.5 20 0.277  A9 1150 1.5 20 0.660 A10 1150 1.5 20 0.131 A11 1080 1.5 20 0.188 A12 1080 1.5 15 0.158 A13 1080 1.5 20 0.113 A14 1100 1.8 25 0.136 A15 1100 1.8 25 0.141 A16 1100 1.8 20 0.151 A17 1100 1.8 35 0.440 A18 1100 1.8 20 0.143  B1 1080 1.8 20 0.177 Compar-  B2 1080 1.8 30 0.258 ative  B3 1100 1.5 30 0.336 Example  B4 1100 1.5 20 1.328  B5 1100 1.5 25 1.584  B6 1080 1.5 20 0.110  B7 1080 1.8 15 0.020

(26) TABLE-US-00003 TABLE 3 Reduction of Relative Tensile area, −40° C. reduc- strength Atmo- Hydrogen tion Specimen 25° C. sphere of 70 MPa of area Evalu- No. (MPa) (%) (%) (%) ation Remarks A1 A1a 712 79 73 92.4 @ Invention Example A1b 590 82 70 85.4 x Compar- ative Example A1c 660 76 61 80.3 ∘ Invention  A2 681 84 81 96.4 @ Example  A3 709 80 74 92.5 @  A4 776 74 77 104.1 @  A5 701 79 77 97.5 @  A6 710 84 86 102.4 @  A7 664 79 65 82.3 ∘  A8 706 77 75 97.4 @  A9 729 80 72 90.0 @ A10 701 82 73 89.0 @ A11 707 79 76 96.2 @ A12 720 78 70 89.7 @ A13 703 75 68 90.7 @ A14 706 77 71 92.2 @ A15 721 81 75 92.6 @ A16 702 79 68 86.1 @ A17 711 78 77 98.7 @ A18 725 77 62 80.5 ∘  B1 711 78 46 59.0 x Compar-  B2 616 83 68 81.9 x ative  B3 713 77 53 68.8 x Example  B4 755 78 48 61.5 x  B5 749 80 57 71.3 x  B6 716 80 62 77.5 x  B7 619 77 63 81.8 x

(27) TABLE-US-00004 TABLE 4 Reduction of area, −40° C. Specimen Atmosphere Hydrogen of Relative reduction No. (%) 103 MPa (%) of area (%) Remarks A3 81 79 97.5 Invention A4 77 73 94.8 Example A6 72 75 104.2

INDUSTRIAL APPLICABILITY

(28) The austenitic stainless steel of the invention has extremely excellent resistance to hydrogen embrittlement in a high-pressure hydrogen gas having a pressure of higher than 40 MPa, and a tensile strength of higher than 650 MPa. Therefore, the austenitic stainless steel of the present invention can be applied as materials of a high-pressure hydrogen gas tank for storing a hydrogen gas having a pressure of higher than 40 MPa, a high-pressure hydrogen gas tank liner, a high-pressure hydrogen gas heat exchanger, and a piping for a high-pressure hydrogen gas and liquid hydrogen.