KR20140056760A - Steel for pressure vessel and method of manufacturing the same - Google Patents
Steel for pressure vessel and method of manufacturing the same Download PDFInfo
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- KR20140056760A KR20140056760A KR1020120122410A KR20120122410A KR20140056760A KR 20140056760 A KR20140056760 A KR 20140056760A KR 1020120122410 A KR1020120122410 A KR 1020120122410A KR 20120122410 A KR20120122410 A KR 20120122410A KR 20140056760 A KR20140056760 A KR 20140056760A
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 100
- 239000010959 steel Substances 0.000 title claims abstract description 100
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 17
- 239000011651 chromium Substances 0.000 claims description 34
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 31
- 238000001816 cooling Methods 0.000 claims description 29
- 239000011572 manganese Substances 0.000 claims description 28
- 238000010438 heat treatment Methods 0.000 claims description 20
- 238000005098 hot rolling Methods 0.000 claims description 14
- 238000003303 reheating Methods 0.000 claims description 14
- 239000010949 copper Substances 0.000 claims description 11
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 11
- PWHULOQIROXLJO-UHFFFAOYSA-N manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 10
- 229910052748 manganese Inorganic materials 0.000 claims description 10
- 229910052750 molybdenum Inorganic materials 0.000 claims description 10
- 229910052759 nickel Inorganic materials 0.000 claims description 10
- 229910052804 chromium Inorganic materials 0.000 claims description 9
- ZOKXTWBITQBERF-UHFFFAOYSA-N molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 9
- 239000011733 molybdenum Substances 0.000 claims description 9
- 238000005096 rolling process Methods 0.000 claims description 9
- 238000010521 absorption reaction Methods 0.000 claims description 8
- VYZAMTAEIAYCRO-UHFFFAOYSA-N chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 8
- 229910000529 magnetic ferrite Inorganic materials 0.000 claims description 8
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 8
- 229910052710 silicon Inorganic materials 0.000 claims description 8
- 239000010703 silicon Substances 0.000 claims description 8
- 229910000859 α-Fe Inorganic materials 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 6
- DIMMBYOINZRKMD-UHFFFAOYSA-N vanadium(5+) Chemical compound [V+5] DIMMBYOINZRKMD-UHFFFAOYSA-N 0.000 claims description 6
- 239000002131 composite material Substances 0.000 claims description 4
- 229910001562 pearlite Inorganic materials 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 206010057190 Respiratory tract infection Diseases 0.000 claims 2
- 230000002427 irreversible Effects 0.000 claims 1
- 239000000463 material Substances 0.000 abstract description 26
- 238000000034 method Methods 0.000 abstract description 8
- 229910045601 alloy Inorganic materials 0.000 abstract description 6
- 239000000956 alloy Substances 0.000 abstract description 6
- REDXJYDRNCIFBQ-UHFFFAOYSA-N aluminium(3+) Chemical class [Al+3] REDXJYDRNCIFBQ-UHFFFAOYSA-N 0.000 abstract description 6
- 239000010955 niobium Substances 0.000 description 19
- 239000011575 calcium Substances 0.000 description 16
- 230000000694 effects Effects 0.000 description 15
- OKTJSMMVPCPJKN-UHFFFAOYSA-N carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 14
- 229910052799 carbon Inorganic materials 0.000 description 14
- 229910052758 niobium Inorganic materials 0.000 description 10
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 9
- 229910052791 calcium Inorganic materials 0.000 description 8
- OYPRJOBELJOOCE-UHFFFAOYSA-N calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 6
- 229910052802 copper Inorganic materials 0.000 description 6
- NINIDFKCEFEMDL-UHFFFAOYSA-N sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 6
- 229910052717 sulfur Inorganic materials 0.000 description 6
- 239000011593 sulfur Substances 0.000 description 6
- 229910052782 aluminium Inorganic materials 0.000 description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminum Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 5
- 229910001566 austenite Inorganic materials 0.000 description 5
- RYGMFSIKBFXOCR-UHFFFAOYSA-N copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 5
- 239000002244 precipitate Substances 0.000 description 5
- 238000005728 strengthening Methods 0.000 description 4
- 238000003466 welding Methods 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000005755 formation reaction Methods 0.000 description 3
- 230000001965 increased Effects 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 230000002829 reduced Effects 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 229910052720 vanadium Inorganic materials 0.000 description 3
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium(0) Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 3
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium monoxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 239000011574 phosphorus Substances 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 230000035939 shock Effects 0.000 description 2
- 230000001629 suppression Effects 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 206010017577 Gait disturbance Diseases 0.000 description 1
- 229910019802 NbC Inorganic materials 0.000 description 1
- 229910019794 NbN Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000000875 corresponding Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000002542 deteriorative Effects 0.000 description 1
- 230000002708 enhancing Effects 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000000670 limiting Effects 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000006011 modification reaction Methods 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N oxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- ABLZXFCXXLZCGV-UHFFFAOYSA-N phosphorous acid Chemical compound OP(O)=O ABLZXFCXXLZCGV-UHFFFAOYSA-N 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000000087 stabilizing Effects 0.000 description 1
- 230000001131 transforming Effects 0.000 description 1
Images
Classifications
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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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/28—Normalising
-
- 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
- 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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- 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
-
- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- 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
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- 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
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
Abstract
A pressure vessel steel material capable of securing excellent low-temperature impact properties through control of alloy components and process conditions, and a method for manufacturing the same.
The pressure vessel steel according to the present invention comprises 0.14 to 0.18% of C, 0.3 to 0.4% of Si, 1.0 to 1.2% of Mn, 0.02% or less of P, 0.005% or less of S, 0.1 to 0.2% of Cr, 0.1 to 0.25% of Cr, 0.01 to 0.08% of Mo, 0.02 to 0.03% of V, 0.0001 to 0.0020% of Ca, 0.01 to 0.02% of Nb, 0.05 to 0.15% (YS): 260 MPa or higher and an elongation (EL) of 60 to 60 MPa, a tensile strength (TS) of 485 to 620 MPa, a yield strength ): 21% or more.
Description
TECHNICAL FIELD The present invention relates to a pressure vessel steel material and a method for manufacturing the same, and more particularly, to a pressure vessel steel material having a tensile strength (TS) of 485 to 620 MPa and capable of securing excellent low temperature toughness through control of alloy components and process conditions, .
In recent years, pressure vessel steels have been in a state of extreme poverty with high strength and high toughness in keeping with the trend of increasing size.
In addition, for pressure vessel steels, customers are required to have excellent low-temperature toughness even after long-term post-weld heat treatment (PWHT). However, there is a tendency for the microstructure to vary in the thickness direction As a result, it is a stumbling block to satisfy the shock guarantee at low temperature after long-time PWHT heat treatment.
A related prior art document is Korean Patent Registration No. 10-0928796 (published on Nov. 19, 2009), which discloses a method for producing a steel for a pressure vessel having a tensile strength of 600 MPa and excellent toughness.
It is an object of the present invention to provide a method of manufacturing a pressure vessel steel material capable of ensuring excellent low-temperature impact properties through control of alloy components and process conditions.
Another object of the present invention is to provide a pressure vessel steel produced by the above method and having a tensile strength (TS) of 485 to 620 MPa, a yield strength (YS) of not less than 260 MPa and an elongation (EL) of not less than 21%.
(A) 0.14 to 0.18% of C, 0.3 to 0.4% of Si, 1.0 to 1.2% of Mn, and 0.02 to 1.2% of Cr in terms of weight%, based on the weight of the steel. 0.1 to 0.2% of Cr, 0.15 to 0.25% of Cr, 0.01 to 0.08% of Mo, 0.1 to 0.2% of Cr, 0.01 to 0.02% of S, 0.01 to 0.02% of Nb, , A steel slab consisting of 0.02 to 0.03% of V, 0.0001 to 0.0020% of Ca, and the balance of Fe and unavoidable impurities to a slab reheating temperature (SRT) of 1010 to 1050 캜; (b) subjecting the reheated steel slab to finishing hot rolling at a finishing rolling temperature (FRT) of 860 to 900 캜; (c) first cooling the hot-rolled steel; (d) performing a normalizing heat treatment on the primary cooled steel at a temperature of 870 to 910 占 폚; And (e) secondarily cooling the normalized heat-treated steel.
According to another aspect of the present invention, there is provided a pressure vessel steel according to the present invention comprising 0.14 to 0.18% of C, 0.3 to 0.4% of Si, 1.0 to 1.2% of Mn, : 0.005% or less, S_Al: 0.015-0.050%, Nb: 0.01-0.02%, Cu: 0.05-0.15%, Ni: 0.1-0.2%, Cr: 0.15-0.25%, Mo: 0.01-0.08% (TS): 485 to 620 MPa, and a yield strength (TS) of 0.03 to 0.03%, Ca: 0.0001 to 0.0020%, and the balance of Fe and unavoidable impurities. The final microstructure has a composite structure including ferrite and pearlite. (YS) of 260 MPa or more and elongation (EL) of 21% or more.
According to the present invention, a pressure vessel steel material excellent in low-temperature impact properties can be produced by satisfying the impact absorption energy at -50 ° C of 70 J or more through control of alloy components and process conditions.
Therefore, the pressure vessel steel produced by the above method can form a fine and uniform structure in the thickness direction, so that the impact absorption energy at -50 ° C: 40 J or more can be satisfied even after PWHT (post-weld heat treatment).
The pressure vessel steel according to the present invention is characterized in that the final microstructure has a composite structure including ferrite and pearlite and has a tensile strength (TS) of 485 to 620 MPa, a yield strength (YS) of 260 MPa or more, and an elongation %.
FIG. 1 is a process flow chart showing a method of manufacturing a pressure vessel steel material according to an embodiment of the present invention.
The features of the present invention and the method for achieving the same will be apparent from the accompanying drawings and the embodiments described below. However, the present invention is not limited to the embodiments described below, but may be embodied in various forms. The present embodiments are provided so that the disclosure of the present invention is complete and that those skilled in the art will fully understand the scope of the present invention. The invention is only defined by the description of the claims.
Hereinafter, a pressure vessel steel according to a preferred embodiment of the present invention and a method of manufacturing the same will be described in detail with reference to the accompanying drawings.
Pressure vessel steel
The pressure vessel steel according to the present invention is characterized in that it has a tensile strength (TS) of 485 to 620 MPa, a yield strength (YS) of not less than 260 MPa, an elongation (EL) of not less than 21% Shock absorption energy of 70 J or more.
For this, the pressure vessel steel according to the present invention comprises 0.14 to 0.18% of C, 0.3 to 0.4% of Si, 1.0 to 1.2% of Mn, 0.02% of P or less, 0.005% or less of S, 0.1 to 0.25% of Cr, 0.15 to 0.25% of Cr, 0.01 to 0.08% of Mo, 0.02 to 0.03% of V, 0.02 to 0.03% of V, 0.0001 to 0.03% of Cr, 0.05 to 0.15% To 0.0020% and the balance of iron (Fe) and unavoidable impurities.
Hereinafter, the role and content of each component included in the pressure vessel steel according to the present invention will be described.
Carbon (C)
Carbon (C) is added to secure strength and is the most influential element in weldability. At this time, the influence of the alloying element other than carbon may be expressed as equivalent carbon (carbon equivalent: Ceq).
The carbon (C) is preferably added at a content ratio of 0.14 to 0.18% by weight based on the total weight of the steel material according to the present invention. When the content of carbon (C) is less than 0.14% by weight of the total weight of the steel, it may be difficult to secure sufficient strength. On the contrary, when the content of carbon (C) exceeds 0.18% by weight of the total weight of the steel, carbide is formed to inhibit grain boundary growth, and weldability is reduced during electrical resistance welding (ERW).
Meanwhile, the steel material according to the present invention may contain carbon (C), manganese (Mn), silicon (Si), nickel (Ni), chromium (Cr), molybdenum (Mo), and vanadium ) Is more preferable.
In the case of electrical resistance welding (ERW) for steel pipe manufacturing,
Cr / 5] + [Mo / 4] + [V / 14]? 0.43 [C] + [Mn / 6] + [Si / 24] + [Ni /
(Where [] is the weight percentage of each element), the occurrence of cracks in welds is significantly reduced if the carbon content is within a certain range.
Silicon (Si)
Silicon (Si) acts as a deoxidizer in the steel and contributes to securing strength.
The silicon (Si) is preferably added in an amount of 0.3 to 0.4% by weight based on the total weight of the steel according to the present invention. When the content of silicon (Si) is less than 0.3 wt% of the total weight of the steel, the effect of the addition is insufficient. On the contrary, when the content of silicon (Si) exceeds 0.4% by weight of the total weight of the steel material, the toughness and weldability of the steel material deteriorate.
Manganese (Mn)
Manganese (Mn) is an element useful for improving strength without deteriorating toughness.
The manganese is preferably added at a content ratio of 1.0 to 1.2% by weight based on the total weight of the steel material according to the present invention. When the content of manganese (Mn) is less than 1.0% by weight of the total weight of the steel, the effect of addition thereof can not be exhibited properly. On the contrary, when the content of manganese (Mn) exceeds 1.2% by weight of the total weight of the steel, there is a problem that the sensitivity to temper embrittlement is increased.
In (P)
Phosphorous (P) is added to inhibit cementite formation and increase strength.
However, when the content of phosphorus (P) exceeds 0.02% by weight of the total weight of the steel according to the present invention, the weldability is deteriorated and the slab center segregation may cause the final material deviation have. Therefore, in the present invention, the content of phosphorus (P) is limited to 0.02% by weight or less based on the total weight of the steel material.
Sulfur (S)
Sulfur (S) reacts with manganese (Mn) to form precipitates of fine MnS to improve processability.
However, when the content of sulfur (S) exceeds 0.005% by weight of the total weight of the steel material according to the present invention, the content of sulfur (S) is too large, so that ductility and formability may be significantly lowered, . Therefore, it is preferable that the content of sulfur (S) is limited to 0.005% by weight or less based on the total weight of the steel material according to the present invention.
Soluble Aluminum (S_Al)
Soluble aluminum (S_Al) acts as a deoxidizer to remove oxygen in the steel.
The soluble aluminum (S_Al) is preferably added in an amount of 0.015 to 0.050 wt% of the total weight of the steel according to the present invention. If the content of soluble aluminum (S_Al) is less than 0.015% by weight of the total weight of the steel material, the deoxidizing effect described above can not be exhibited properly. On the contrary, when the content of soluble aluminum (S_Al) exceeds 0.050 wt% of the total weight of the steel material, it is difficult to perform, resulting in a decrease in productivity and a compound which causes a pinning effect such as Al 2 O 3 to form austenite crystal grains Which is a factor that causes microfabrication.
Niobium (Nb)
Niobium (Nb) combines with carbon (C) at high temperature to form carbide. Niobium carbide improves the strength and low temperature toughness of steel by refining crystal grains by suppressing grain growth during hot rolling.
The niobium (Nb) is preferably added in an amount of 0.01 to 0.02% by weight based on the total weight of the steel according to the present invention. When the content of niobium (Nb) is less than 0.01% by weight of the total weight of the steel, the effect of adding niobium can not be exhibited properly. On the other hand, when the content of niobium (Nb) exceeds 0.02% by weight of the total weight of the steel material, excessive addition thereof decreases the weldability of the steel material. If the content of niobium (Nb) exceeds 0.02% by weight, the strength and low temperature toughness due to the increase of the niobium content are not further improved but exist in a solid state in the ferrite, and there is a risk of lowering the impact toughness.
Copper (Cu)
Copper (Cu) contributes to solid solution strengthening and enhances strength.
The copper (Cu) is preferably added in an amount of 0.05 to 0.15% by weight based on the total weight of the steel according to the present invention. When the content of copper (Cu) is less than 0.05 wt% of the total weight of the steel, the effect of the addition can not be exhibited properly. On the other hand, when the content of copper exceeds 0.15% by weight of the total weight of the steel, the hot workability of the steel is lowered and the susceptibility to stress relief cracking after welding is increased.
Nickel (Ni)
Nickel (Ni) is effective for improvement in toughness while improving incineration.
The nickel (Ni) is preferably added in an amount of 0.1 to 0.2% by weight based on the total weight of the steel according to the present invention. When the content of nickel (Ni) is less than 0.1% by weight of the total weight of the steel, the effect of addition thereof can not be exhibited properly. On the contrary, when the content of nickel (Ni) exceeds 0.2 wt% of the total weight of the steel, the cold workability of the steel is deteriorated. Also, the addition of excessive nickel (Ni) greatly increases the manufacturing cost of the steel.
Chromium (Cr)
Chromium (Cr) is a ferrite stabilizing element and contributes to strength improvement. Chromium (Cr) also plays a role in enlarging the delta ferrite region and shifting the hypo-peritectic region to the high carbon side to improve the slab surface quality.
The chromium (Cr) is preferably added in a content ratio of 0.15 to 0.25% by weight based on the total weight of the steel according to the present invention. If the content of chromium (Cr) is less than 0.15% by weight of the total weight of the steel, the addition effect can not be exhibited properly. On the contrary, if the content of Cr exceeds 0.25% by weight of the total weight of the steel, excessive toughness of the weld heat affected zone (HAZ) may occur during steel pipe manufacturing.
Molybdenum (Mo)
Molybdenum (Mo) is a substitutional element and improves the strength of steel by solid solution strengthening effect. In addition, molybdenum (Mo) serves to improve the hardenability of the steel.
The molybdenum (Mo) is preferably added in an amount of 0.01 to 0.08% by weight based on the total weight of the steel according to the present invention. If the content of molybdenum (Mo) is less than 0.01% by weight of the total weight of the steel, the above effects can not be exhibited properly. On the other hand, when the content of molybdenum (Mo) exceeds 0.08% by weight of the total weight of the steel material, there is a problem of raising the manufacturing cost without any further effect.
Vanadium (V)
Vanadium (V) plays a role in improving the strength of steel through precipitation strengthening effect by precipitate formation.
The vanadium (V) is preferably limited to a content ratio of 0.02 to 0.03% by weight of the total weight of the steel according to the present invention. When the content of vanadium (V) is less than 0.02% by weight of the total weight of the steel, precipitation strengthening effect due to vanadium addition is insufficient. On the contrary, when the content of vanadium (V) exceeds 0.03% by weight of the total weight of the steel material, the low-temperature impact toughness is deteriorated.
Calcium (Ca)
Calcium (Ca) is added for the purpose of improving electrical resistance weldability by inhibiting the formation of MnS inclusions by forming CaS inclusions. That is, calcium (Ca) has a higher affinity with sulfur than manganese (Mn), so CaS inclusions are formed and CaS inclusions are reduced when calcium is added. Such MnS is stretched during hot rolling to cause hook defects and the like in electrical resistance welding (ERW), so that electrical resistance weldability can be improved.
The calcium (Ca) is preferably added in an amount of 0.0001 to 0.0020 wt% of the total weight of the steel material according to the present invention. When the content of calcium (Ca) is less than 0.0001 wt% of the total weight of the steel sheet, the MnS control effect can not be exerted properly. On the contrary, when the content of calcium (Ca) exceeds 0.0020% by weight of the total weight of the steel sheet, generation of CaO inclusions is excessive, which deteriorates performance and electrical resistance weldability.
Pressure vessel steel manufacturing method
FIG. 1 is a process flow chart showing a method of manufacturing a pressure vessel steel material according to an embodiment of the present invention.
Referring to FIG. 1, a method of manufacturing a pressure vessel steel according to an embodiment of the present invention includes a slab reheating step S110, a hot rolling step S120, a first cooling step S130, a normalizing heat treatment step S140, And a secondary cooling step (S150). At this time, the slab reheating step (S110) is not necessarily performed, but it is more preferable to carry out the step to derive effects such as reuse of precipitates.
In the pressure vessel steel material manufacturing method according to the present invention, the semi-finished slab plate to be subjected to the hot rolling is composed of 0.14 to 0.18% of C, 0.3 to 0.4% of Si, 1.0 to 1.2% of Mn, 0.02 0.1 to 0.2% of Cr, 0.15 to 0.25% of Cr, 0.01 to 0.08% of Mo, 0.1 to 0.2% of Cr, 0.01 to 0.02% of S, 0.01 to 0.02% of Nb, 0.02 to 0.03% of V, 0.0001 to 0.0020% of Ca, and the balance of iron (Fe) and unavoidable impurities.
Reheating slabs
In the slab reheating step S110, the steel slab having the above composition is reheated. In this step, the slab reheating temperature (SRT) is preferably 1010 to 1050 占 폚, and more preferably 1020 to 1040 占 폚. The reason why the slab is reheated in the relatively low temperature region as in the above temperature range is to improve the low temperature impact characteristic through microstructure.
In this slab reheating step S110, the segregated components are reused through reheating of the steel slab.
At this time, when the slab reheating temperature (SRT) is less than 1010 DEG C, there is a problem that the reheating temperature is too low to increase the rolling load. In addition, since the Nb-based precipitates NbC and NbN can not reach the solid solution temperature, they can not be precipitated as fine precipitates upon hot rolling, and the austenite grain growth can not be suppressed, resulting in a rapid coarsening of the austenite grains. On the other hand, when the slab reheating temperature exceeds 1050 DEG C, the austenite grains are rapidly coarsened and it is difficult to secure the strength and low temperature toughness of the steel to be produced.
Hot rolling
In the hot rolling step (S120), the reheated steel slab is hot-rolled under FRT (Finish Rolling Temperature): 860 to 900 ° C.
At this time, when the final hot rolling temperature (FRT) is lower than 860 ° C, problems such as the occurrence of blistering due to abnormal reverse rolling may occur. On the other hand, when the final hot rolling temperature (FRT) exceeds 900 ° C, the austenite grains are coarsened and the ferrite grain refinement after the transformation is not sufficiently performed, which may make it difficult to secure the strength.
At this time, in the present invention, the average rolling reduction per pass is preferably 5 to 15% so that sufficient rolling can be performed for each pass. If the average rolling reduction per pass is less than 5%, strain can not be sufficiently applied to the center of the thickness, so that it may be difficult to secure fine crystal grains after cooling. On the other hand, when the average reduction rate per pass is more than 15%, there is a problem that the production becomes impossible due to the load of the rolling mill.
Primary cooling
In the primary cooling step (S130), the hot-rolled steel is first cooled to room temperature. Here, the primary cooling may be air cooling which is carried out in a natural cooling manner up to room temperature. At this time, the normal temperature may be 1 to 40 ° C, but is not limited thereto.
In this step, the primary cooling rate may be 1 to 50 DEG C / sec, but is not limited thereto. When the primary cooling rate is less than 1 캜 / sec, it is difficult to secure sufficient strength and toughness. On the other hand, when the primary cooling rate exceeds 50 DEG C / sec, cooling control is difficult, and excessive cooling may lower the economical efficiency.
Normalizing heat treatment
In the normalizing heat treatment step (S140), the primary cooled steel is subjected to a normalizing heat treatment.
At this time, the normalizing heat treatment temperature is preferably 870 to 910 ° C. In this step, when the normalizing heat treatment temperature is less than 870 ° C, it is difficult to reuse the solute elements, so that it may be difficult to secure sufficient strength. On the other hand, when the normalizing heat treatment temperature exceeds 910 ° C, crystal grains are grown to deteriorate low-temperature toughness.
On the other hand, the normalizing heat treatment time is preferably 120 to 240 minutes, because if the normalizing heat treatment time is out of the above range, the residual stress can not be easily removed.
Secondary cooling
In the second cooling step (S150), the normalized heat-treated steel is secondarily cooled.
The secondary cooling may be air cooling, which is conducted in a natural cooling manner. At this time, the normal temperature may be 1 to 40 ° C, but is not limited thereto.
The pressure vessel steels manufactured in the above-described processes (S110 to S150) have a fine and uniform structure in the thickness direction, so that the impact absorption energy at -50 ° C satisfies 70 J or more, -weld heat treatment), the impact absorption energy at -50 ° C: 40 J or more can be satisfied.
Therefore, the pressure vessel steel material according to the present invention has a composite structure including ferrite and pearlite and has a final tensile strength (TS) of 485 to 620 MPa, a yield strength (YS) of 260 MPa or more and an elongation (EL) of 21 %.
Example
Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.
The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.
1. Preparation of specimens
The specimens according to Examples 1 to 4 and Comparative Examples 1 and 2 were prepared with the compositions of Tables 1 and 2 and the process conditions of Table 3. At this time, in the case of the hot-rolled samples according to Examples 1 to 4 and Comparative Examples 1 and 2, ingots having the respective compositions were prepared and subjected to heating, hot rolling, primary cooling, normalizing heat treatment and secondary Cooling was performed. At this time, the primary cooling and the secondary cooling were performed by a natural cooling method. Thereafter, tensile tests and low-temperature impact tests were conducted on the specimens prepared according to Examples 1 to 4 and Comparative Examples 1 and 2.
[Table 1] (unit:% by weight)
[Table 2] (unit:% by weight)
[Table 3]
2. Evaluation of mechanical properties
Table 4 shows evaluation results of mechanical properties and low-temperature impact properties for the specimens prepared according to Examples 1 to 4 and Comparative Examples 1 and 2.
[Table 4]
Tensile Strength (TS): 485 to 620 MPa, Yielding Strength (YS): 260 MPa or more, elongation (EL) corresponding to the target value in the specimens prepared according to Examples 1 to 4, : 21% or more, and the impact absorption energy at -50 캜: 70 J or more. Further, in the case of the specimens produced according to Examples 1 to 4, it can be seen that the carbon content (Ceq) satisfies all 0.43 or less.
On the other hand, most of the alloy components are added in a similar amount, except that some of the alloy components are not added as compared to Example 1, but the slab reheating temperature (SRT) and the finish hot rolling temperature (FRT) (TS), yield strength (YS), and elongation (EL) of the specimens prepared according to Comparative Examples 1 and 2 were all within the target values, but the impact absorption energy at -50 ° C: 61J and 52J, respectively. Further, in the case of the specimens produced according to Comparative Examples 1 and 2, it can be seen that the carbon content (Ceq) deviates from the range suggested by the present invention.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.
S110: Slab reheating step
S120: Hot rolling step
S130: primary cooling step
S140: Normalizing heat treatment step
S150: Secondary cooling step
Claims (6)
(b) subjecting the reheated steel slab to finishing hot rolling at a finishing rolling temperature (FRT) of 860 to 900 캜;
(c) first cooling the hot-rolled steel;
(d) performing a normalizing heat treatment on the primary cooled steel at a temperature of 870 to 910 占 폚; And
(e) secondarily cooling the normalized heat treated steel. < RTI ID = 0.0 > 8. < / RTI >
The slab plate
(C), manganese (Mn), silicon (Si), nickel (Ni), chromium (Cr), molybdenum (Mo) and vanadium (V) in the range satisfying the following formula Method of manufacturing a pressure vessel steel.
Cr / 5] + [Mo / 4] + [V / 14]? 0.43 [C] + [Mn / 6] + [Si / 24] + [Ni /
(Where [] is the weight percentage of each element)
In the step (d)
The normalizing heat treatment
Wherein the heating is performed for 120 to 240 minutes.
Wherein the final microstructure has a composite structure including ferrite and pearlite and has a tensile strength (TS) of 485 to 620 MPa, a yield strength (YS) of 260 MPa or more and an elongation (EL) of 21% Steel.
The steel
(C), manganese (Mn), silicon (Si), nickel (Ni), chromium (Cr), molybdenum (Mo) and vanadium (V) in the range satisfying the following formula Pressure vessel steel.
Cr / 5] + [Mo / 4] + [V / 14]? 0.43 [C] + [Mn / 6] + [Si / 24] + [Ni /
(Where [] is the weight percentage of each element)
The steel
And an impact absorption energy at -50 DEG C of 70 J or more.
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| KR1020120122410A KR20140056760A (en) | 2012-10-31 | 2012-10-31 | Steel for pressure vessel and method of manufacturing the same |
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| WO2016104975A1 (en) * | 2014-12-24 | 2016-06-30 | 주식회사 포스코 | High-strength steel material for pressure container having outstanding toughness after pwht, and production method therefor |
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| KR20190077830A (en) * | 2017-12-26 | 2019-07-04 | 주식회사 포스코 | Steel plate having excellent HIC resistance and manufacturing method for the same |
| WO2019132465A1 (en) * | 2017-12-26 | 2019-07-04 | 주식회사 포스코 | Steel material showing excellent hydrogen-induced cracking resistance and method for preparing same |
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