WO2022131570A1 - 고온 pwht 저항성이 우수한 압력용기용 강판 및 그 제조방법 - Google Patents
고온 pwht 저항성이 우수한 압력용기용 강판 및 그 제조방법 Download PDFInfo
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- WO2022131570A1 WO2022131570A1 PCT/KR2021/016649 KR2021016649W WO2022131570A1 WO 2022131570 A1 WO2022131570 A1 WO 2022131570A1 KR 2021016649 W KR2021016649 W KR 2021016649W WO 2022131570 A1 WO2022131570 A1 WO 2022131570A1
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- weight
- steel sheet
- heat treatment
- pwht
- pressure vessel
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 122
- 239000010959 steel Substances 0.000 title claims abstract description 122
- 238000000034 method Methods 0.000 title claims description 67
- 238000004519 manufacturing process Methods 0.000 title claims description 24
- 239000012535 impurity Substances 0.000 claims abstract description 9
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 7
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 7
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 7
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 3
- 238000010438 heat treatment Methods 0.000 claims description 57
- 230000008569 process Effects 0.000 claims description 52
- 229910000734 martensite Inorganic materials 0.000 claims description 39
- 238000001816 cooling Methods 0.000 claims description 20
- 229910001563 bainite Inorganic materials 0.000 claims description 17
- 230000009467 reduction Effects 0.000 claims description 10
- 238000003303 reheating Methods 0.000 claims description 8
- 238000005096 rolling process Methods 0.000 claims description 7
- 238000005098 hot rolling Methods 0.000 claims description 5
- 238000003466 welding Methods 0.000 claims description 5
- 229910052758 niobium Inorganic materials 0.000 abstract description 3
- 229910052720 vanadium Inorganic materials 0.000 abstract description 3
- 230000002829 reductive effect Effects 0.000 description 18
- 230000007423 decrease Effects 0.000 description 17
- 230000000052 comparative effect Effects 0.000 description 16
- 239000000203 mixture Substances 0.000 description 10
- 239000000463 material Substances 0.000 description 9
- 230000003247 decreasing effect Effects 0.000 description 6
- 150000001247 metal acetylides Chemical class 0.000 description 6
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- 229910001566 austenite Inorganic materials 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 238000001953 recrystallisation Methods 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 239000013589 supplement Substances 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 208000012868 Overgrowth Diseases 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 230000001502 supplementing effect Effects 0.000 description 1
- 230000008719 thickening Effects 0.000 description 1
- 238000000844 transformation Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Classifications
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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
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/84—Controlled slow cooling
-
- 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
- C21D6/002—Heat treatment of ferrous alloys containing Cr
-
- 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
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- 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
- C21D6/008—Heat treatment of ferrous alloys containing Si
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
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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
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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
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
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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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/06—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
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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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
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Definitions
- the present invention relates to a steel sheet for a pressure vessel having excellent high-temperature PWHT resistance and a method for manufacturing the same, and more preferably, a steel sheet for a pressure vessel having excellent tensile strength and low-temperature impact toughness even when PWHT is performed at a high temperature of 750 to 850°C, and the same It is about the manufacturing method.
- Post-weld heat treatment may be performed to remove residual stress inside the steel sheet.
- the PWHT has a problem in that mechanical properties are deteriorated due to softening of grain boundaries in the steel sheet, growth, and coarsening of carbides during a long heat treatment process.
- the PWHT is 700° C. or higher, there is a problem in that the deterioration of the mechanical properties is further aggravated.
- Patent Document 1 includes C: 0.05 to 0.25%, Mn: 0.1 to 1.0%, Si: 0.1 to 0.8%, Cr: 1 to 3%, Cu: 0.05 to 0.3%, Mo: 0.5 to 1.5%, Ni: 0.05 to 0.5%, Al: 0.005 to 0.1%, containing at least one of Ir: 0.005 to 0.10% and Rh: 0.005 to 0.10%, the remainder being Fe and inevitable
- a medium-to-high temperature steel sheet containing impurities is disclosed, it has a problem in that it is difficult to apply in a state where the PWHT is 700°C.
- Patent Document 0001 Republic of Korea Patent Publication No. 10-2020-0064581
- Patent Document 0002 Japanese Patent Application Laid-Open No. 2015-018868
- the present invention is to solve the above problems, and a steel sheet for pressure vessel with excellent resistance to high temperature post-weld heat treatment (PWHT) that does not deteriorate mechanical properties even after a post-weld heat treatment (PWHT) process at a high temperature and to provide a method for manufacturing the same.
- PWHT high temperature post-weld heat treatment
- One aspect of the present invention for achieving the above object is C: 0.10 to 0.16 wt%, Si: 0.20 to 0.35 wt%, Mn: 0.4 to 0.6 wt%, Cr: 7.5 to 8.5 wt%, Mo: 0.7 to 1.0 wt% %, Al: 0.005 to 0.05% by weight, P: 0.015% by weight or less, S: 0.002% by weight or less, Nb: 0.001 to 0.025% by weight, V: 0.25 to 0.35% by weight, and the remainder consisting of Fe and unavoidable impurities It relates to a steel plate for pressure vessels with excellent resistance to high temperature PWHT.
- the steel sheet structure may be made of a mixed structure of tempered martensite and tempered bainite.
- the tempered martensite may have an area fraction of 50 to 80%, and the remainder may be composed of tempered bainite.
- the steel sheet may have a tensile strength of 650 MPa or more even in post-weld heat treatment (PWHT) for 10 to 50 hours at 750 to 850°C.
- PWHT post-weld heat treatment
- the Charpy impact energy (CVN @ -30 °C) value of the steel sheet for the pressure vessel may be 100J or more.
- a process of reheating a slab comprising a High-temperature PWHT resistance characterized in that it comprises a heat treatment process, a cooling process of cooling the first heat-treated steel sheet at 1 to 30 ° C./sec, and a secondary heat treatment process for maintaining the cooled steel sheet at 820 to 845 ° C. It relates to a method for manufacturing this excellent steel sheet for pressure vessels.
- the first heat treatment time (T1) may be defined by the following relational expression (1).
- T 1 means the time (min) for performing the primary heat treatment
- t means the thickness of the hot-rolled steel sheet.
- the second heat treatment time (T2) may be defined by the following relational expression (2).
- T 2 means the time (min) for performing the secondary heat treatment
- t means the thickness of the hot-rolled steel sheet.
- a post-welding heat treatment (PWHT) process may be performed in which the secondary heat-treated steel sheet is maintained at 750 to 850° C. for 10 to 50 hours.
- PWHT post-welding heat treatment
- the present invention in the steel sheet for a pressure vessel containing 7.5 to 8.5% by weight of Cr, it is possible to provide a steel sheet for a pressure vessel with strong resistance to post-weld heat treatment (PWHT) performed at a high temperature of 700° C. or higher. have.
- PWHT post-weld heat treatment
- the PWHT is a heat treatment process for removing residual stress generated inside the base material during welding or rolling process, and is characterized in that it is performed at high temperature for a long time. For this reason, the PWHT removes the residual stress in the steel sheet, but induces softening, growth, and coarsening of carbides in the grain boundary in the base material, thereby reducing the mechanical properties of the steel sheet.
- the steel sheet for pressure vessel excellent in high temperature PWHT resistance according to an embodiment of the present invention, C: 0.10 to 0.16 wt%, Si: 0.20 to 0.35 wt%, Mn: 0.4 to 0.6 wt%, Cr: 7.5 to 8.5 wt%, Mo: 0.7 to 1.0% by weight, Al: 0.005 to 0.05% by weight, P: 0 to 0.015% by weight S: 0.002% by weight or less, Nb: 0.001 to 0.025% by weight or less, and the remainder may contain Fe and unavoidable impurities have.
- composition range of the present invention will be described in detail.
- unit is % by weight.
- the C is an element that improves strength.
- the content is less than 0.1% by weight, the strength of the matrix itself decreases, and when it exceeds 0.16% by weight, the strength increases excessively, thereby reducing toughness.
- the C is preferably added 0.1 to 0.16% by weight, a more preferable lower limit may be 0.12% by weight, and a more preferable upper limit may be 0.15% by weight.
- Si is added in an amount of 0.2 to 0.35% by weight.
- the Si is an element effective for deoxidation and solid solution strengthening, and is an element accompanied by an increase in the impact transition temperature. If Si is less than 0.2% by weight, it is difficult to expect sufficient mechanical properties due to insufficient strength of the steel sheet for pressure vessels. There is a problem that the impact toughness is lowered. Accordingly, the Si is preferably added in an amount of 0.2 to 0.35% by weight, a more preferable lower limit may be 0.25% by weight, and a more preferable upper limit may be 0.32% by weight.
- Mn is added in an amount of 0.4 to 0.6% by weight.
- the Mn may form MnS, which is a non-metallic inclusion, together with S, which will be described later.
- the non-metallic inclusion MnS has an effect of increasing the strength of the base material by interfering with the movement of dislocations inside the grains, but causes a decrease in room temperature elongation and low temperature toughness.
- the Mn is preferably added in an amount of 0.4 to 0.6% by weight, a more preferable lower limit may be 0.5% by weight, and a more preferable upper limit may be 0.58% by weight.
- the Cr increases the hardenability and forms a low-temperature transformation structure, thereby increasing yield and tensile strength, and has an effect of preventing a decrease in strength by slowing the decomposition rate of cementite during tempering or PWHT after quenching.
- a tempered martensite structure is formed in the center of the steel sheet to enhance low-temperature strength. For this reason, it is preferable to add 7.5 wt% or more of Cr.
- a coarse Cr-Rich M 23 C 6 -type carbide may be precipitated in the tempered martensite structure. This greatly reduces the impact toughness of the steel sheet and causes brittle fracture.
- the Cr is preferably added 7.5 to 8.5% by weight, a more preferable lower limit may be 7.8% by weight, and a more preferable upper limit may be 8.3% by weight.
- Mo is added in an amount of 0.7 to 1.0% by weight.
- the Mo may increase the high-temperature strength of the base material. In addition, it is possible to prevent cracks from occurring in the steel sheet for pressure vessels due to the sulfide. For this reason, it is preferable that Mo is added in an amount of 0.7% by weight or more. However, since Mo has a relatively high unit price compared to other added elements, when the Mo exceeds 1.0 wt %, the production cost may excessively increase, thereby reducing marketability. Accordingly, the Mo is preferably added in an amount of 0.7 to 1.0% by weight, and a more preferable lower limit may be 0.8% by weight.
- Al is added in an amount of 0.005 to 0.05% by weight.
- the Al is one of the strong deoxidizers in the steelmaking process.
- the deoxidizer serves to induce oxygen to be discharged in the form of CO by blowing in oxygen inside the base material.
- oxygen in the base material may increase to deteriorate the quality of the steel sheet.
- the Al content exceeds 0.05% by weight, more than necessary deoxidation effect is realized, and rather, the manufacturing cost may increase, thereby reducing commercial properties.
- the Al is preferably added in an amount of 0.005 to 0.05% by weight, a more preferable lower limit may be 0.02% by weight, and a more preferable upper limit may be 0.04% by weight.
- P is added in an amount of 0.015% by weight or less.
- the P decreases the low-temperature toughness of the steel sheet for pressure vessel, and is segregated at grain boundaries and is a major cause of occurrence of temper brittleness.
- S is added in an amount of 0.002% by weight or less.
- S is an element that reduces the low-temperature toughness like P, and forms MnS inclusions in the steel sheet for pressure vessels, thereby causing the toughness of the steel sheet for pressure vessels to decrease.
- P low-temperature toughness
- the S is preferably managed at 0.002% by weight or less.
- Nb is added in an amount of 0.001 to 0.025% by weight.
- the Nb is an element effective in preventing softening of the matrix forming the steel sheet by forming fine carbides or nitrides in the steel sheet for pressure vessels. For this reason, the Nb is preferably added in an amount of 0.001% by weight or more. However, when the Nb content exceeds 0.025% by weight, the cost of the steel sheet may increase and marketability may decrease. Accordingly, the Nb is preferably added in an amount of 0.001 to 0.025% by weight, a more preferable lower limit may be 0.01% by weight, and a more preferable upper limit may be 0.023% by weight.
- V is added 0.25 to 0.35% by weight.
- V can easily form fine carbides and nitrides, and is an effective element to prevent softening of the matrix. For this reason, it is preferable that V is added in an amount of 0.25% by weight or more. However, if the V exceeds 0.35% by weight, the cost of the steel sheet may be increased and the marketability may be deteriorated. Accordingly, the V is preferably added 0.25 to 0.35% by weight, a more preferable lower limit may be 0.28%, and a more preferable upper limit may be 0.32% by weight.
- composition which is one characteristic of the present invention, has been described above.
- another feature of the present invention will be described with respect to the microstructure.
- the microstructure at the center of the steel sheet may be made of a mixed structure of tempered martensite and tempered bainite, and more preferably, the tempered An area fraction of martensite may be included in 50% or more, and the remaining portion may be composed of a mixed structure of tempered bainite.
- the tempered martensite structure refers to a martensitic structure in which residual stress is relieved in martensite through the secondary heat treatment process described later, and has an effect of supplementing brittleness while maintaining the strength of a typical martensite structure. have For this reason, it is preferable that the area fraction of the tempered martensite structure is 50% or more in order to manufacture a 650 MPa class steel sheet targeted by the present invention.
- the tempered martensite structure when the area fraction of the tempered martensite structure in the steel sheet exceeds 80%, the tempered martensite structure may have a coarse Cr-Rich M 23 C 6 -type carbide precipitated at grain boundaries, resulting in a decrease in toughness. have. For this reason, the tempered martensite structure preferably has an area fraction of 50 to 80%.
- the tempered bainite (Tempered bainite) has a lower strength than the tempered martensite structure, but relatively excellent toughness and high impact absorption energy. Through this, the tempered bainite may supplement the toughness of the steel sheet for the pressure vessel.
- the steel sheet for the pressure vessel is preferably provided in a mixed structure of the tempered martensite structure and the tempered bainite, and more preferably, the area fraction of the tempered martensite is 50 to 80%, the tempered martensite structure It is preferable that the area fraction of de bainite is 20% to 50%.
- the tensile strength can be effectively maintained at 650 MPa or more even by additionally performing heat treatment in a high temperature range of 750 to 850 ° C. for up to 50 hours after welding the steel sheet having the composition and microstructure as described above. .
- the steel sheet having the composition components and microstructure as described above may have excellent low-temperature toughness even after the PWHT, and specifically, the Charpy impact energy value at -30°C may have a value of 100J or more.
- the steel sheet for pressure vessel manufactured according to an embodiment of the present invention can have excellent tensile strength and low-temperature toughness even when PWHT is performed at a high temperature.
- the high-temperature PWHT steel sheet having excellent resistance to the pressure vessel is a step of reheating the slab having the above-described composition at 1,070 to 1,250 °C; hot rolling the reheated slab at a reduction ratio of 2.5 to 35% per rolling pass; a primary heat treatment process for maintaining the hot-rolled steel sheet at 1,020 to 1,070°C; It may include any one or more processes of a cooling process of cooling the first heat-treated steel sheet to 1 to 30°C and a secondary heat treatment process for maintaining the cooled steel sheet at 820 to 845°C.
- a process of reheating the slab having the above composition may be performed.
- the reheating is preferably performed at 1,070 to 1,250 ° C. This is, if the reheating temperature is less than 1,070 ° C, solute atoms are not dissolved as much as intended, so it is difficult to secure strength.
- the overgrowth of the knight phase may reduce the mechanical properties of the steel sheet.
- the reheating temperature is preferably 1,070 to 1,250 °C, more preferably the lower limit may be 1,100 °C, more preferably the upper limit may be 1,170 °C.
- the reheated slab may be hot rolled to manufacture a steel sheet.
- the hot rolling may be performed in a recrystallization region that is a temperature section higher than the recrystallization end temperature.
- the hot rolling is preferably performed at a reduction ratio of 2.5 to 35% for each rolling pass. If the reduction ratio is less than 2.5%, the reduction amount is insufficient, the tempered martensite and tempered bainite structures formed by the cooling process to be described later become coarse, and the strength of the steel sheet may decrease. On the other hand, when the reduction ratio exceeds 35%, the load on the rolling mill becomes heavy and productivity may be reduced. Accordingly, the reduction ratio per each rolling pass is preferably controlled to be 2.5 to 35%, and a more preferable lower limit may be 5%, and a more preferable upper limit may be 25%.
- the hot-rolled steel sheet may be subjected to a primary heat treatment process.
- the primary heat treatment process refers to a heat treatment of maintaining the steel sheet at 1,020 to 1,070° C. for a time (T 1 ) satisfying the following relational expression 1.
- T 1 means the time (min) for performing the primary heat treatment
- t means the thickness of the hot-rolled steel sheet.
- the temperature of the primary heat treatment is less than 1,020° C. or the T 1 is less than 1.3Xt 1 + 10 minutes, homogenization of the structure in the steel sheet may not sufficiently occur. This causes segregation in the steel sheet to occur. In addition, it is difficult to re-dissolve the solute elements that have been dissolved in the steel sheet, which causes a decrease in mechanical properties of the steel sheet.
- the primary heat treatment temperature exceeds 1,070° C. or the T 1 exceeds 13 ⁇ t 1 + 30 minutes, crystal grains in the steel sheet grow and the strength of the steel sheet may be reduced.
- the first heat-treated steel sheet may be cooled to 20 to 40° C. at a rate of 1 to 30° C./sec, and may be cooled through water cooling treatment (DQ treatment).
- DQ treatment water cooling treatment
- the cooling rate is less than 1° C./sec, the ferrite in the steel sheet cannot be transformed into martensite, so that the area fraction of the tempered martensite structure in the steel sheet may decrease.
- the tempered martensite and tempered bainite structures may become coarse. This causes a decrease in the strength of the steel sheet.
- the cooling rate is preferably 1 to 30° C./sec, and a more preferable lower limit may be 1.5° C./sec, and a more preferable upper limit may be 25° C./sec.
- the steel sheet manufactured by performing the primary heat treatment and cooling process has a tensile strength of 650 MPa or more, and at the same time, it is required to secure a Charpy impact energy value of 100 J or more at -30 ° C. In order to achieve these conditions, the secondary heat treatment and a PWHT process.
- the secondary heat treatment process refers to a heat treatment for maintaining the steel sheet at 820 to 845° C. for a time (T 2 ) satisfying the following relation 2, in other words, it can be defined as a tempering heat treatment.
- T 2 means the time (min) for performing the secondary heat treatment
- t means the thickness of the hot-rolled steel sheet.
- the secondary heat treatment process is preferably performed at 820 to 845° C. for 1.6 ⁇ t + 10 to 1.6 ⁇ t + 30 minutes. This is because, when the secondary heat treatment process is performed for less than 820° C. or less than 1.6 ⁇ t + 10, the dislocation recovery effect is reduced, the toughness of the steel sheet is reduced, and it is difficult to obtain a tempered martensitic structure. On the other hand, when the secondary heat treatment process exceeds 845° C. or the heat treatment time exceeds 1.6 ⁇ t + 30 minutes, precipitates overgrow and overaging may occur, resulting in a decrease in strength.
- a PWHT process may be additionally performed.
- the PWHT process is a process of heat treatment over a long period of time in a high-temperature environment to remove residual stress inside the steel sheet as described above, and specifically, the second heat-treated steel sheet is maintained at 750 to 850 ° C. for 10 to 50 hours It means a process do.
- the PWHT process temperature is less than 750° C. or the PHWT process time is less than 10 hours, annealing may not be sufficient and residual stress may remain in the steel sheet. In this case, it causes deformation of the steel plate and a reduction in service life.
- the PWHT process temperature exceeds 850° C.
- the PWHT process is preferably performed at 750 to 850° C. for 10 to 50 hours or less, the lower limit of the more preferable temperature may be 780° C., and the upper limit of the more preferable temperature may be 820° C. Also, a more preferable lower limit of the time may be 20 hours.
- the steel sheet was cooled by air cooling until it reached 25°C of room temperature, and then heated to 1,050°C, and the time was adjusted according to the thickness of each steel sheet to perform a primary heat treatment process. After that, it was cooled with water until it reached 25°C based on the temperature of the center of the steel.
- the thickness, primary heat treatment holding time, and cooling time of each of the steel sheets are shown in Table 2 below.
- the tempered martensite fraction (%) and mechanical properties were measured for the steel sheet prepared according to Table 2, and are shown in Table 3 below.
- yield strength (YS), tensile strength (TS), elongation (EL), and low-temperature toughness (J) were measured.
- the low-temperature toughness was evaluated based on a Charpy impact energy (CVN @ -30°C) value obtained by performing a Charpy impact test on a specimen having a V notch at -30°C.
- tempered martensite has an area fraction of 50% or more, so that the PWHT process was performed for 50 hours. It can be seen that the yield strength is 650 MPa or more, and more preferably has a high strength of 656 MPa or more. At the same time, it can be confirmed that the Charpy impact energy value at -30°C is 100J or more, more preferably 215J or more, and has excellent low-temperature toughness through this.
- the decrease in yield strength (YS) is 0.5 to 3%
- the decrease in tensile strength (TS) is about 1 to 4.5%. This is because, as described above, the tempered martensite structure in the steel sheet is formed by 50% or more based on the area fraction, which compensates for the decrease in strength due to softening of grain boundaries and coarsening of carbides after PWHT.
- Comparative Examples 1 to 6 when the PWHT process is increased from 20 hours to 50 hours, it can be seen that the mechanical properties are significantly reduced. Specifically, Comparative Examples 1 to 3, which were heat-treated in the same manner as in Examples with Comparative Steel A containing 2.29% by weight of Cr, had yield strength (YS) and Both the tensile strength (TS) is reduced by 7 to 10%, and the Charpy impact energy is reduced by 45 to 55%. In Comparative Examples 4 to 6 prepared with Comparative Steel B containing 5.21% by weight of Cr, the yield strength was decreased by 15 to 20%, the tensile strength was decreased by 10 to 15%, and the Charpy impact energy was decreased by 45 to 55%.
- Comparative Examples 1 to 6 the reason for the rapid decrease in mechanical properties in Comparative Examples 1 to 6 is that when the content of Cr in the steel sheet is less than 7.5% by weight, the austenite region increases and the retained austenite is generated. , because the fraction of the tempered martensite and the tempered bainite structure is relatively reduced due to this.
- Example 1 tensile strength of 650 MPa or more and low-temperature toughness of 200 J or more were maintained even when the PWHT process was performed at 800° C. for 50 hours, whereas Comparative Examples 1 to 6 were tempered formed inside the steel sheet Since the area fraction of the martensitic structure is less than 20%, the strength of the base material is relatively low. This is that in Example 1 again 9, the martensitic structure having relatively excellent strength was formed at 50% or more based on the area fraction, and the strength was maintained even after heat treatment, but Comparative Examples 1 to 6 lack the martensitic structure, so after high temperature PWHT This is because it cannot compensate for the decrease in strength caused by softening of grain boundaries and coarsening of carbides.
- Comparative Examples 7 to 9 containing 9.54% by weight of Cr had excellent yield strength of 715 MPa on average, but elongation was very low with an average of 15.3%, and low-temperature toughness was very low with an average of 44J. This is because the tempered bainite structure is too small to supplement the toughness of the steel sheet. In addition, coarse Cr-Rich M 23 C 6 -type carbide was precipitated at the tempered martensite grain boundary, so that the brittleness of the steel sheet was greatly increased. For this reason, in consideration of both the strength and toughness of the steel sheet, the tempered martensite structure is preferably formed in an area fraction of 50 to 80%.
- Comparative Examples 10 to 17 were prepared by changing the heat treatment time with the invention steel A satisfying the alloy composition proposed by the present invention. As a result, it can be confirmed that the mechanical properties are reduced compared to Preparation Examples 1 to 3.
- Comparative Examples 10 to 11 in which the primary heat treatment was performed for less than 50 minutes than the T 1 had an average yield strength (YS) of 427 MPa and the tensile strength (TS) of 512 MPa, 15 to more than those of Examples 1 to 3 A 25% reduction can be seen.
- the Charpy impact energy was also reduced by 35 to 45% compared to Examples 1 to 3. This is because, as described above, the internal stress of the steel was not sufficiently removed due to insufficient time for the primary heat treatment, and unstable martensite and bainite structures were formed.
- Comparative Examples 14 to 15 in which the secondary heat treatment was performed for less than 50 minutes than the T 2 , had an average yield strength (YS) of 4175 MPa and the tensile strength (TS) of an average of 487.5 MPa, 15 than Examples 1 to 3 decreased by 25%.
- the Charpy impact energy was also reduced by 25 to 35% compared to Examples 1 to 3 with an average of 161J.
- YS average yield strength
- TS average tensile strength
- the Charpy impact energy is also reduced by 25 to 35% compared to Examples 1 to 3 with an average of 172.5J.
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Abstract
Description
Claims (9)
- C:0.10 내지 0.16중량%, Si:0.20 내지 0.35중량%, Mn:0.4 내지 0.6중량%, Cr:7.5 내지 8.5중량%, Mo:0.7 내지 1.0중량%, Al: 0.005 내지 0.05중량%, P: 0.015중량%이하, S:0.002중량%이하, Nb: 0.001 내지 0.025중량%, V: 0.25 내지 0.35중량% 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어진 것을 특징으로 하는, 고온 PWHT 저항성이 우수한 압력용기용 강판.
- 제 1항에 있어서,상기 강판 조직이 템퍼드 마르텐사이트와 템퍼드 베이나이트의 혼합조직으로 이루어진 것을 특징으로 하는, 고온 PWHT 저항성이 우수한 압력용기용 강판.
- 제 2항에 있어서,상기 템퍼드 마르텐사이트는 면적분율이 50 내지 80%이며, 나머지는 템퍼드 베이나이트로 구성되는 것을 특징으로 하는, 고온 PWHT 저항성이 우수한 압력용기용 강판.
- 제 1항에 있어서,상기 강판은 750 내지 850℃에서 10 내지 50시간 용접후 열처리(Post Weld Heat Treatment, PWHT)에도 인장강도가 650MPa 이상인 것을 특징으로 하는, 고온PWHT 저항성이 우수한 압력용기용 강판.
- 제 4항에 있어서,상기 강판은 샤르피 충격 에너지(CVN @ -30℃) 값이 100J이상인 것을 특징으로 하는, 고온 PWHT 저항성이 우수한 압력용기용 강판.
- 중량%로, C:0.10 내지 0.16중량%, Si:0.20 내지 0.35중량%, Mn:0.4 내지 0.6중량%, Cr:7.5 내지 8.5중량%, Mo:0.7 내지 1.0중량%, Al: 0.005 내지 0.05중량%, P:0 내지 0.015중량% S:0.002중량%이하, Nb: 0.001 내지 0.025중량%, V: 0.25 내지 0.35중량% 포함하고, 나머지는 Fe 및 불가피한 불순물을 포함하는 슬라브를 1,070 내지 1,250℃에서 재가열하는 공정;상기 재가열된 슬라브를 압연 패스당 2.5 내지 35%의 압하율로 열간 압연하는 공정;상기 열간 압연된 강판을 1,020 내지 1,070℃로 유지하는 1차 열처리 공정;상기 1차 열처리된 강판을 1 내지 30℃/sec로 냉각하는 냉각 공정; 및상기 냉각된 강판을 820 내지 845℃로 유지하는 2차 열처리 공정;을 포함하는 것을 특징으로 하는, 고온 PWHT 저항성이 우수한 압력용기용 강판의 제조방법.
- 제 6항에 있어서,상기 1차 열처리 시간(T1)은 하기 관계식 1로 정의되는 것을 특징으로 하는, 고온 PWHT 저항성이 우수한 압력용기용 강판의 제조방법.[관계식 1]1.3×t +10 ≤ T1 ≤ 1.3×t + 30(상기 관계식 1에서 T1은 1차 열처리를 수행하는 시간(min)을 의미하며, t는상기 열간 압연된 강판의 두께를 의미한다.)
- 제 6항에 있어서,상기 2차 열처리 시간(T2)은 하기 관계식 2으로 정의되는 것을 특징으로 하는, 고온 PWHT 저항성이 우수한 압력용기용 강판의 제조방법.[관계식 2]1.6×t +10 ≤ T2 ≤ 1.6×t + 30(상기 관계식 2에서 T2는 2차 열처리를 수행하는 시간(min)을 의미하며, t는 상기 열간 압연된 강판의 두께를 의미한다.)
- 제 6항에 있어서,상기 2차 열처리 공정 후, 750 내지 850℃에서 10 내지 50시간 동안 용접 후 열처리(PWHT) 공정을 추가로 수행하는 것을 특징으로 하는, 고온 PWHT 저항성이 우수한 압력용기용 강판의 제조방법.
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EP21906875.6A EP4265777A1 (en) | 2020-12-16 | 2021-11-15 | Pressure vessel steel plate having excellent high temperature pwht resistance and method for manufacturing same |
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JP2015522071A (ja) | 2012-07-09 | 2015-08-03 | イーエルシー マネージメント エルエルシー | 架橋シリコーンマトリックス中に封入された固体粒子を含む組成物、及びその作製方法 |
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