KR101778406B1 - Thick Plate for Linepipes Having High Strength and Excellent Excessive Low Temperature Toughness And Method For Manufacturing The Same - Google Patents
Thick Plate for Linepipes Having High Strength and Excellent Excessive Low Temperature Toughness And Method For Manufacturing The Same Download PDFInfo
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- KR101778406B1 KR101778406B1 KR1020150185503A KR20150185503A KR101778406B1 KR 101778406 B1 KR101778406 B1 KR 101778406B1 KR 1020150185503 A KR1020150185503 A KR 1020150185503A KR 20150185503 A KR20150185503 A KR 20150185503A KR 101778406 B1 KR101778406 B1 KR 101778406B1
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- 238000000034 method Methods 0.000 title claims description 10
- 238000004519 manufacturing process Methods 0.000 title description 12
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 79
- 239000010959 steel Substances 0.000 claims abstract description 79
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 21
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 10
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 8
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 8
- 239000012535 impurity Substances 0.000 claims abstract description 7
- 229910001568 polygonal ferrite Inorganic materials 0.000 claims abstract description 7
- 238000005275 alloying Methods 0.000 claims abstract description 6
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 6
- 238000005096 rolling process Methods 0.000 claims description 38
- 238000001816 cooling Methods 0.000 claims description 30
- 239000000463 material Substances 0.000 claims description 20
- 229910052759 nickel Inorganic materials 0.000 claims description 7
- 238000010438 heat treatment Methods 0.000 claims description 3
- 229910045601 alloy Inorganic materials 0.000 claims description 2
- 239000000956 alloy Substances 0.000 claims description 2
- 230000014509 gene expression Effects 0.000 abstract description 12
- 229910052791 calcium Inorganic materials 0.000 abstract description 6
- 229910052804 chromium Inorganic materials 0.000 abstract description 6
- 229910052802 copper Inorganic materials 0.000 abstract description 5
- 239000011572 manganese Substances 0.000 description 18
- 238000005204 segregation Methods 0.000 description 14
- 239000010936 titanium Substances 0.000 description 14
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 13
- 239000002244 precipitate Substances 0.000 description 13
- 230000000694 effects Effects 0.000 description 11
- 229910052698 phosphorus Inorganic materials 0.000 description 11
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 10
- 230000015572 biosynthetic process Effects 0.000 description 10
- 239000011575 calcium Substances 0.000 description 9
- 230000001965 increasing effect Effects 0.000 description 9
- 229910052799 carbon Inorganic materials 0.000 description 8
- 239000010955 niobium Substances 0.000 description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 6
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 6
- 229910001566 austenite Inorganic materials 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 6
- 239000010949 copper Substances 0.000 description 6
- 239000011574 phosphorus Substances 0.000 description 6
- 229910052717 sulfur Inorganic materials 0.000 description 6
- 229910052719 titanium Inorganic materials 0.000 description 6
- 238000005098 hot rolling Methods 0.000 description 5
- 229910001562 pearlite Inorganic materials 0.000 description 5
- 239000012071 phase Substances 0.000 description 5
- 238000003303 reheating Methods 0.000 description 5
- 238000005728 strengthening Methods 0.000 description 5
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 4
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 229910052748 manganese Inorganic materials 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 3
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- 238000005260 corrosion Methods 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 229910052758 niobium Inorganic materials 0.000 description 3
- 239000010703 silicon Substances 0.000 description 3
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 239000008186 active pharmaceutical agent Substances 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 230000001627 detrimental effect Effects 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 230000002829 reductive effect Effects 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 241000219307 Atriplex rosea Species 0.000 description 1
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 238000005345 coagulation Methods 0.000 description 1
- 230000015271 coagulation Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000010779 crude oil Substances 0.000 description 1
- 230000001186 cumulative effect Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000005194 fractionation Methods 0.000 description 1
- 230000009036 growth inhibition Effects 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 239000011253 protective coating Substances 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 238000004781 supercooling Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/16—Control of thickness, width, diameter or other transverse dimensions
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
-
- 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
- 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
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
(Inclusive of 0%), P: 0.03% or less (inclusive of 0%), Ti: 0.01% or less (inclusive), C: 0.03-0.13%, Si: 0.01-0.80% , Ni: 0.1-0.8%, Mo: 0.1-0.7%, Cr: 0.01-0.8%, Cu: 0.03-1.0%, N: 0.011% or less (excluding 0%), Nb: 0.01-0.15% Ca: 0.001 to 0.004%, the balance Fe and other unavoidable impurities, the alloying elements satisfy the following relational expressions 1 to 4,
[Relation 1]
1? Cr + 3 * Mo + Ni? 2
[Relation 2]
10? 2 * (Mo / 93) / (P / 31)? 18
[Relation 3]
{3 * C / 12 + Mn / 55} * 100? 4
[Relation 4]
P + 10 * S? 0.024
The present invention relates to a low-temperature high-strength line pipe steel excellent in cryogenic toughness, which comprises acicular ferrite: 70 to 90%, polygonal ferrite: 10 to 20%, and bainite: 4% .
Description
The present invention relates to a high strength steel material for steel pipes used for applications such as construction, line pipes, and offshore structures, and more particularly, to a high strength steel pipe material having excellent low temperature toughness and a manufacturing method thereof.
As the mining and transportation environment becomes more severe, there is an increasing demand for API steels having high strength and low temperature toughness.
In addition, when using steel pipes for crude oil or gas transportation, the transport pressure is increased to increase the transport efficiency. Recently, the transport pressure reaches 120 atm.
In addition, projects are being actively carried out to transport rich gas resources in the oilfield to the consuming area through the line pipe as the oilfield development centering on the cold regions such as Siberia and Alaska have poor weather conditions.
This line pipe project is mainly applied to steel materials which have both low-temperature fracture toughness and yield ratio characteristics as well as high-temperature materials and durability in consideration of cryogenic temperature and ground deformation as well as high transport gas pressure.
Particularly, in the case of superfine steel having a thickness of 30 mm or more, it is very important to guarantee the fracture propagation resistance at the center of the thickness. When the thickness of the steel material increases, the absolute reduction amount during rolling is insufficient and it is difficult to secure a sufficient cooling rate, so that the ferrite grains become coarse and the low-temperature toughness deteriorates due to impurities segregated in the center cracks and in internal cracks during performance.
Japanese Patent Application Laid-Open No. 2003-328080 (Patent Document 1) discloses an example of a method for manufacturing a steel pipe having excellent strength, HAZ toughness and deformability of a steel material.
However, the technique disclosed in Patent Document 1 has a problem that Mg and the like are contained and the cost is increased and low-temperature toughness is deteriorated.
A preferred aspect of the present invention is to provide an after-treatment high-strength line pipe steel excellent in cryogenic toughness.
Another desirable aspect of the present invention is to optimize the composition of the steel and the rolling process to optimize the texture, optimize the volume fraction of the mild texture, suppress the center segregation, and minimize segregation of P and S segregated in the internal cracks during performance It is an object of the present invention to provide a method for manufacturing a high-strength line pipe steel excellent in cryogenic toughness.
A preferred aspect of the present invention is a steel sheet comprising, by weight%, 0.03-0.13% of C, 0.01-0.80% of Si, 0.9-2.5% of Mn, 0.012% or less of S (including 0% Ti: 0.01-0.15%, N: 0.011% or less (excluding 0%), Nb: 0.01-0.15%, Ni: 0.1-0.8%, Mo: 0.1-0.7 0.01 to 0.06% of Ca, 0.001 to 0.004% of Ca, and the balance of Fe and other unavoidable impurities, wherein the alloying elements are represented by the following relational expressions 1 to 4 Lt; / RTI >
[Relation 1]
1? Cr + 3 * Mo + Ni? 2
[Relation 2]
10? 2 * (Mo / 93) / (P / 31)? 18
[Relation 3]
{3 * C / 12 + Mn / 55} * 100? 4
[Relation 4]
P + 10 * S? 0.024
High-strength line pipe steels excellent in cryogenic toughness including microstructure as area%, acicular ferrite: 70 to 90%, polygonal ferrite: 10 to 30%, and bainite: 4%
Another preferred aspect of the present invention is a steel sheet comprising, by weight%, 0.03-0.13% of C, 0.01-0.80% of Si, 0.9-2.5% of Mn, 0.012% or less of S (including 0% Ti: 0.01-0.15%, N: 0.011% or less (excluding 0%), Nb: 0.01-0.15%, Ni: 0.1-0.8%, Mo: 0.1- Wherein the alloy contains at least one element selected from the group consisting of Fe, Cr, Fe and Cr in an amount of 0.01 to 0.7%, Cr of 0.01 to 0.8%, Cu of 0.03 to 1.0%, V of 0.01 to 0.06%, Ca of 0.001 to 0.004% Heating the steel slab at a temperature of 1000 to 1350 캜;
[Relation 1]
1? Cr + 3 * Mo + Ni? 2
[Relation 2]
10? 2 * (Mo / 93) / (P / 31)? 18
[Relation 3]
{3 * C / 12 + Mn / 55} * 100? 4
[Relation 4]
P + 10 * S? 0.024
A primary rolling step of extracting the heated steel slab at 950 to 1160 占 폚, primary rolling and terminating primary rolling at 940 to 1050 占 폚;
After the primary rolling as described above, a primary cooling step of cooling at a cooling rate of 20 to 60 DEG C / s;
A secondary rolling step of performing secondary rolling at 750 to 945 占 폚, rolling at a reduction ratio of 65% or more at the non-recrystallized zone and then secondary rolling at 750 to 890 占 폚; And
After secondary rolling, cooling at a speed of 10 to 50 占 폚 / s at an accelerated cooling starting temperature of 700 to 800 占 폚 and a secondary cooling step of finishing at 400 to 500 占 폚. And a manufacturing method thereof.
According to a preferred aspect of the present invention, a post-high-strength line pipe steel excellent in cryogenic toughness can be provided.
A preferred example of the present invention is to optimize the content of Nb, Mo, Cr, Ni and Ti and optimize the rolling process conditions to optimize the texture and optimize the volume fraction of the hardened structure, The present invention provides an API steel for a high toughness and high strength line pipe which suppresses center segregation by controlling Mn content and minimizes segregation of P and S segregated in an internal crack at the time of playing to improve low temperature toughness.
The present invention relates to a method for forming a needle-shaped ferrite having excellent strength and toughness in a matrix structure to simultaneously secure strength and toughness of a post-material.
In the present invention, solid hardening elements such as Mo, Cr, and Ni are utilized to secure the strength and the content thereof is appropriately controlled.
In order to secure toughness, the grain boundary segregation of P which promotes grain boundary fracture at low temperature is suppressed by using the minimum amount of Mo.
By controlling the content of C and Mn, the center segregation is suppressed and the toughness is improved by minimizing segregation of P and S segregated in the internal cracks during performance.
It is believed that it is important to optimize the ratio of each component because the rate of precipitation of precipitates differs depending on the rolling temperature and the amount of rolling when these alloying elements are used. From this point of view, the inventors of the present invention have been able to draw up the following measures for simultaneously securing the strength of the post material and the low temperature toughness.
[1] By controlling the ferrite of steel by control rolling and securing strength in material after using precipitate
[2] 1? Cr + 3 * Mo + Ni? 2
[3] 10 ≤ 2 * (Mo / 93) / (P / 31)
[4] {3 * C / 12 + Mn / 55} * 100 ≤ 4 to suppress slab center segregation
[5] P + 10 * S ≤ 0.024 is satisfied to suppress segregation in cracks in the slab
[6] The steel sheet according to any one of [1] to [6], wherein the non-recrystallization zone sub-mass reduction ratio is 65% or more and the structure thereof is 70-90% in acicular type ferrite fraction, 10-30% in polygonal ferrite fraction and 4% secure
Hereinafter, the present invention will be described in detail.
0.03 to 0.13% by weight (hereinafter also referred to as "%") of carbon (C)
C is the most economical and effective element for strengthening the steel, but when added in large amounts, the weldability, formability and toughness are lowered. Therefore, it is limited to 0.03-0.13%.
If the content of carbon (C) is less than 0.03%, it is difficult to secure sufficient strength. Therefore, it is not economical because a relatively large amount of other alloying elements must be added in order to secure strength. When the content exceeds 0.13%, weldability, formability and toughness Which is undesirable. Therefore, the content of carbon (C) is preferably limited to 0.03 to 0.13%.
Silicon (Si): 0.01 to 0.80 wt%
Si is a component that acts as a deoxidizing agent and solid solution strengthening element of molten steel.
If the content of silicon is less than 0.01%, the deoxidation effect of molten steel can not be sufficiently achieved, and it is difficult to obtain a clean steel. When the content exceeds 0.8%, a red scale is formed by Si during hot rolling, And the ductility is lowered. Therefore, the content of silicon (Si) is preferably limited to 0.01 to 0.8%.
Manganese (Mn): 0.9 to 2.5 wt%
Mn is an effective element for strengthening the solid solution of steel and should be added in an amount of 0.9% or more so that it can exhibit a high strength in addition to the effect of increasing the incombustibility. However, when it is added in an amount exceeding 2.5%, it is not preferable because the segregation portion is developed at the center of the thickness of the slab during continuous casting in the steelmaking process and weldability of the final product is impaired. Therefore, the content of manganese (Mn) is preferably limited to 0.9 to 2.5%.
Sulfur (S): 0.012 wt% or less (including 0%)
S is an impurity element present in the steel, which is combined with Mn or the like to form a nonmetallic inclusive material, thereby greatly impairing the toughness and strength of the steel. Therefore, it is preferable to reduce it as much as possible, and the upper limit is preferably limited to 0.012%.
Phosphorus (P): 0.03% by weight or less (including 0%)
Phosphorus is an element that is inevitably contained in the production of steel, and the content of phosphorus should be controlled as low as possible. When phosphorus is added, it segregates at the center of the steel sheet and can be used as crack initiation or propagation path. Theoretically, it is advantageous to limit the phosphorus content to 0%, but it is inevitably added as an impurity inevitably to the manufacturing process. Therefore, it is important to manage the upper limit, and the upper limit of the phosphorus content is preferably limited to 0.03%.
0.01 to 0.05% of T_Al,
When Al is added in an amount of less than 0.01% by weight, it is difficult to obtain a deoxidizing effect. When Al is added in an amount of more than 0.05% by weight, the alumina aggregate is increased to decrease toughness. %. ≪ / RTI >
V: 0.01 to 0.06%
V is a component showing a precipitation strengthening effect by the addition of a small amount, and when it is added in an amount of less than 0.01% by weight, the effect of addition can not be sufficiently secured. In the carbon range of the present invention, the strength increase due to precipitation strengthening is not large when the content is more than 0.06% by weight. Therefore, the content thereof is preferably limited to 0.01 to 0.06% by weight.
Titanium (Ti): 0.01 to 0.15 wt%
Ti is an element which is very useful for refining the crystal grains and exists as TiN in the steel and has an effect of inhibiting the growth of grains during the heating process for hot rolling. Also, Ti reacted with nitrogen and solidified in the steel, Precipitates are formed and the formation of TiC is very fine, which greatly improves the strength of the steel.
Therefore, at least 0.01% of Ti should be added in order to obtain an austenite grain growth growth inhibition effect by TiN precipitation and an increase in strength by TiC formation. When the steel is added by more than 0.15% The toughness of the weld heat affected zone deteriorates as the TiN is reused. Therefore, the content of titanium (Ti) is preferably limited to 0.01 to 0.15%.
Nitrogen (N): 0.011 wt% or less (excluding 0%)
The component limitation of N is due to the addition of Ti described above. In general, N is dissolved in the steel and precipitates to increase the strength of the steel, which is much greater than carbon. On the other hand, it is known that the presence of nitrogen in the steel significantly degrades the toughness, and it is a general tendency to reduce the nitrogen content as much as possible.
However, in the present invention, an appropriate amount of nitrogen is allowed to exist and react with Ti to form TiN, thereby suppressing crystal growth during reheating.
However, since a part of Ti reacts with carbon in the subsequent steps without reacting with N, it is preferable that the upper limit of N content is limited to 0.011%. The lower limit of the N content is not particularly limited, and a preferable lower limit may be 0.001%.
Niobium (Nb): 0.01 to 0.15 wt%
Nb is a very useful element for refining the crystal grains, and at the same time, it is necessary to add at least 0.01%, because it is a mechanism that greatly improves the strength of the steel. If it exceeds 0.15%, excessive Nb carbonitride precipitates and is detrimental to the toughness of the steel The content thereof is preferably limited to 0.01-0.15%.
Nickel (Ni): 0.1 to 0.8 wt%
Ni is an austenite stabilizing element that inhibits pearlite formation and is an element that facilitates the formation of acicular ferrite which is a low temperature transformed structure. It is added in an amount of 0.1% or more in order to sufficiently obtain such effect and is an expensive element. The upper limit of the content is preferably limited to 0.8%.
Molybdenum (Mo): 0.1 to 0.7 wt%
Mo is very effective in increasing the strength of the material and serves to lower the yield ratio by promoting the formation of acicular ferrite, which is a low-temperature transformed structure. In addition, since the cementite and carbide are integrated, the impact properties are deteriorated and the generation of pearlite structure contributing to decrease in the yield strength after the cementation is suppressed, so that the impact toughness and the decrease in the yield strength after the cementation can be reduced.
For this, Mo should be added in an amount of 0.1% or more, but it is an expensive element. When the Mo is added in an excessive amount, a low temperature transformation phase may be generated in the base material, and toughness may be lowered. Therefore, the upper limit of the Mo content is preferably limited to 0.7%.
Cr (Cr): 0.1 to 0.8 wt%
Cr generally increases the hardenability of steel during direct quenching and improves corrosion resistance and hydrogen cracking resistance. Similarly to Mo, generation of pearlite structure is suppressed, and good impact toughness can be obtained. For this, Cr should be added in an amount of 0.1% or more, but it tends to cause cracking after field welding in the case of excessive addition, and tends to deteriorate the steel and its HAZ toughness.
Copper (Cu): 0.03 to 1.0% by weight or less
Copper is an element added to improve strength and toughness of a steel and to improve corrosion resistance. Cu should be added in an amount of 0.03% or more as it is dissolved in steel to improve strength and to form a protective coating on the surface in an atmosphere containing hydrogen sulfide to lower the corrosion rate of steel and reduce the amount of hydrogen diffused into the steel. However, when the content of copper exceeds 1.0%, cracks are generated on the surface during hot rolling and the surface quality is lowered. Therefore, the upper limit is preferably limited to 1.0%.
Calcium (Ca): 0.001 to 0.004%
Calcium is an element useful for spheroidizing MnS non-metallic inclusions and can inhibit cracking around the MnS inclusions. When the calcium content is less than 0.001% by weight, the effect of spheroidizing the MnS inclusions can not be sufficiently obtained. However, when the content exceeds 0.004%, a large amount of CaO-based inclusions is produced to lower impact toughness.
Therefore, the content of calcium (Ca) is preferably limited to 0.001 to 0.004%.
The following relational formula 1 is for obtaining fine acicular type ferrite. When the value of the relational expression 1 is less than 1, it becomes difficult to secure the strength. When the value exceeds 2, separation which is detrimental to the impact toughness occurs.
[Relation 1]
1? Cr + 3 * Mo + Ni? 2
The following relational expression (2) is for preventing P segregation. When the value of the relational expression 2 is less than 10, the effect of the P-type segregation due to formation of the Fe-Mo-P compound is insufficient. When the value of the relational expression 2 exceeds 18, the impact energy decreases due to the formation of the low- do.
[Relation 2]
10? 2 * (Mo / 93) / (P / 31)? 18
The following relational expression 3 is intended to inhibit the formation of mild secondary phase phases such as pearlite, bainite and MA (martensite and / or austenite).
The increase of C and Mn lowers the coagulation temperature of the slab to promote the segregation of the center of the slab, and narrows the interval of the delta ferrite, making it difficult to homogenize the slab during the performance. In addition, Mn is a typical element segregated in the center of the slab, which promotes the formation of the second phase which deteriorates the ductility of the pipe, and the increase of C widens the coexistence zone of the solid phase and the liquid phase during performance,
Therefore, when the value of the relational expression 3 is larger than 4, the strength is increased but the non-homogeneity of the slab is increased due to the above-mentioned reason, so that the light phase 2 is formed in the slab and the low temperature toughness of the steel and the pipe is lowered. Therefore, in order to ensure the impact toughness of the steel material, the value of the relational expression 3 is preferably less than 4.
[Relation 3]
{3 * C / 12 + Mn / 55} * 100? 4
The following relational expression 4 is intended to prevent segregation of P and S in the internal cracks of the slab during playing. When the value of the relational expression 4 exceeds 0.024, P and S are segregated in the internal crack of the slab, and it is preferable that the value of the relational expression 4 is less than 0.024 in order to secure the toughness and toughness of cracks in the impact test.
[Relation 4]
P + 10 * S? 0.024
The steel material of the present invention has a microstructure in area percentage of 70% to 90% of needle-shaped ferrite, 10% to 30% of polygonal ferrite, and 4% or less of bainite.
When the acicular type ferrite content is less than 70%, sufficient strength is not ensured. When the acicular type ferrite content is more than 90%, it is difficult to secure an excellent low temperature toughness.
When the content of the polygonal ferrite is less than 10%, it is difficult to ensure excellent low-temperature toughness. When the content exceeds 30%, it becomes difficult to secure sufficient strength.
When the content of bainite exceeds 4%, it becomes difficult to secure excellent low-temperature toughness.
A preferred example of the steel of the present invention may have a thickness of 10 mm or more.
More preferably, the thickness of the steel is 20 to 40 mm.
A preferable example of the steel of the present invention is that the minimum temperature at which the yield strength is 500 MPa or more, the tensile strength is 580 MPa or more, the impact energy is 300 J or more at -30 캜, and the DWTT ductile waveguide ratio is 85% or more can be -20 캜 or less.
Hereinafter, the production method of the present invention will be described.
The temperature at which the slab is reheated is important in the present invention. If the reheating temperature is lower than a temperature at which the added alloying elements precipitated during the performance process such as the temperature lower than 1000 ° C are sufficiently reusable, precipitates such as (Ti, Nb) C and NbC are reduced in the process after hot rolling . Therefore, by maintaining the reheating temperature at 1000 ° C or higher, it is possible to obtain a uniform microstructure in the longitudinal direction of the coil while enhancing the strength level of the material by promoting the reuse of precipitates and maintaining an appropriate austenite grain size. At this time, if the reheating temperature is too high, the strength is lowered due to abnormal grain growth of the austenite grains. Therefore, the upper limit of the slab reheating temperature is preferably limited to 1350 ° C.
After the heated slab is extracted at 950 to 1160 ° C, the primary rolling of the slab is finished at 940 to 1050 ° C, water-cooled at a cooling rate of 20 to 60 ° C / s, and secondary rolling is performed at 750 to 945 ° C It is important to finish rolling at a temperature of 750 to 890 캜 after rolling at 65% or more at the non-recrystallized zone. This is because, if the rolling finishing temperature is too high or the underexcited reverse descending load is too small, the desired strength and impact toughness can not be obtained when the final structure is coarsened, and if it is too low, load problems occur in the finishing mill equipment. Also, if the cooling rate after the primary rolling is too low, the P segregates in the austenite grains during the rolling atmosphere and the impact toughness deteriorates, and if it is too fast, the shape will deteriorate due to supercooling.
The thickness of the hot-rolled steel as described above may be 10 mm or more.
More preferably, the thickness of the steel is 20 to 40 mm.
After completion of the hot rolling, water-cooling is performed at a rate of 10 to 50 ° C / sec to form fine needle-like ferrite and precipitates, thereby ensuring sufficient strength. According to the present invention, even if the composition ratio is controlled to obtain a fine precipitate, the average size of the precipitate may exceed 0.2 탆 when the cooling rate is less than 10 캜 / sec. That is, as the cooling rate increases, a large number of nuclei are generated and the precipitates become finer. As the cooling rate increases, the size of the precipitate becomes finer. Therefore, there is no need to limit the upper limit of the cooling rate. However, even if the cooling rate is faster than 50 ° C / sec, Is more preferable.
Accelerated cooling start temperature: 700 to 800 ° C
It is preferable to start cooling the non-recrystallized back-rolled steel sheet at 700 to 800 ° C. Controlling the cooling start temperature is an important factor for suppressing the formation of equiaxed ferrite. When the cooling start temperature is less than 700 캜 or exceeds 800 캜, the suitable ferrite fraction is not satisfied.
Therefore, the accelerated cooling start temperature is preferably limited to 700 to 800 ° C.
When the temperature is higher than 500 ° C, the microstructure is formed of coarse ferrite and pearlite, and the precipitate grows too large to secure strength. When the temperature is lower than 400 ° C, The fraction is increased and the impact characteristics are deteriorated.
According to the preferred method for producing a steel material of the present invention, it is possible to produce a steel material having a microstructure including an acicular ferrite of 70 to 90%, a polygonal ferrite of 10 to 30%, and a bainite of 4% have.
According to the preferred steel material producing method of the present invention, a steel material having a minimum yield temperature of -20 占 폚 or less which satisfies a yield strength of 500 MPa or more, a tensile strength of 580 MPa or more, an impact energy of 300 J or more at -30 캜, and a DWTT ductile wave- Can be produced.
Hereinafter, the present invention will be described in more detail with reference to examples.
(Example)
Molten steel having chemical compositions as shown in Tables 1 and 2 below was prepared as a slab by the continuous casting method and then hot rolled under the conditions shown in Table 3 to produce a steel having a thickness shown in Table 4.
The minimum temperature (캜) satisfying at least 85% of the microstructure, yield strength (MPa), tensile strength (MPa), direction of rolling direction at 90 degrees-impact energy and DWTT ductility percentage was investigated. The results are shown in Table 4 below.
Steel grade
Temperature
(° C)
Cooling start
Temperature (℃)
speed
(° C / s)
persons
Yes
School
Yes
ferrite
Fractionation (area%)
(area%)
Direction - Impact Energy
(mm)
As shown in Table 4, in the case of Inventive Example (1-5) satisfying the composition range and manufacturing conditions of the present invention, the yield strength is 500 MPa or more, the tensile strength is 580 MPa or more, the impact energy is 300 J or more at- It can be seen that the minimum temperature satisfying the DWTT ductile waveguide ratio of 85% or more is -20 占 폚 or less.
On the other hand, in the case of Comparative Example (6-13) which does not satisfy at least one of the component range and the manufacturing conditions of the present invention, at least one of the properties of yield strength, tensile strength, impact energy and DWTT characteristics is lowered have.
The present invention is not limited to the above embodiments, but is merely an example. Anything having substantially the same constitution as the technical idea described in the claims of the present invention and achieving the same operational effect is included in the technical scope of the present invention.
Claims (5)
[Relation 1]
1? Cr + 3 * Mo + Ni? 2
[Relation 2]
10? 2 * (Mo / 93) / (P / 31)? 18
[Relation 3]
{3 * C / 12 + Mn / 55} * 100? 4
[Relation 4]
P + 10 * S? 0.024
A high strength and low temperature toughness line pipe steel excellent in cryogenic toughness, comprising acicular ferrite: 70 to 90%, polygonal ferrite: 11 to 30%, and bainite: 4%
[Relation 1]
1? Cr + 3 * Mo + Ni? 2
[Relation 2]
10? 2 * (Mo / 93) / (P / 31)? 18
[Relation 3]
{3 * C / 12 + Mn / 55} * 100? 4
[Relation 4]
P + 10 * S? 0.024
A primary rolling step of extracting the heated steel slab at 950 to 1160 占 폚, primary rolling and terminating primary rolling at 940 to 1050 占 폚;
After the primary rolling as described above, a primary cooling step of cooling at a cooling rate of 20 to 60 DEG C / s;
A secondary rolling step of performing secondary rolling at 750 to 945 占 폚, rolling at a reduction ratio of 65% or more at the non-recrystallized zone and then secondary rolling at 750 to 890 占 폚; And
After secondary rolling, cooling at a speed of 10 to 50 占 폚 / s at an accelerated cooling starting temperature of 700 to 800 占 폚 and a secondary cooling step of finishing at 400 to 500 占 폚. Gt;
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| KR101858857B1 (en) | 2016-12-21 | 2018-05-17 | 주식회사 포스코 | High-strength hot-rolled steel plate having high dwtt toughness at low temperature, and method for manufacturing the same |
| CN111492085A (en) * | 2017-12-22 | 2020-08-04 | 株式会社Posco | High-strength steel material for polar environment having excellent fracture resistance at low temperature and method for producing same |
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| KR101988771B1 (en) | 2017-12-22 | 2019-09-30 | 주식회사 포스코 | Steel having excellent hydrogen induced cracking resistance and longitudinal strength unifomity and method for manufacturing the same |
| KR102057765B1 (en) | 2017-12-29 | 2019-12-19 | 현대제철 주식회사 | Steel reinforcement and method of manufacturing the same |
| KR102119975B1 (en) * | 2018-11-29 | 2020-06-08 | 주식회사 포스코 | High strength thick steel plate for linepipe having excellent low temperature toughness and ductility as well as low yield ratio |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| KR101858857B1 (en) | 2016-12-21 | 2018-05-17 | 주식회사 포스코 | High-strength hot-rolled steel plate having high dwtt toughness at low temperature, and method for manufacturing the same |
| CN111492085A (en) * | 2017-12-22 | 2020-08-04 | 株式会社Posco | High-strength steel material for polar environment having excellent fracture resistance at low temperature and method for producing same |
| CN111492085B (en) * | 2017-12-22 | 2021-10-29 | 株式会社Posco | High-strength steel material for polar environment having excellent fracture resistance at low temperature and method for producing same |
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