KR20160078600A - Hot rolled steel sheet for pipe having expending property and method for manufacturing the same - Google Patents

Hot rolled steel sheet for pipe having expending property and method for manufacturing the same Download PDF

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Publication number
KR20160078600A
KR20160078600A KR1020140188047A KR20140188047A KR20160078600A KR 20160078600 A KR20160078600 A KR 20160078600A KR 1020140188047 A KR1020140188047 A KR 1020140188047A KR 20140188047 A KR20140188047 A KR 20140188047A KR 20160078600 A KR20160078600 A KR 20160078600A
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Prior art keywords
steel sheet
hot
pipe
less
steel
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KR1020140188047A
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Korean (ko)
Inventor
배진호
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주식회사 포스코
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Priority to KR1020140188047A priority Critical patent/KR20160078600A/en
Publication of KR20160078600A publication Critical patent/KR20160078600A/en

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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
    • C21D8/0221—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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled steel sheet for steel pipes used for applications such as construction, line pipes, and offshore structures, and a method for manufacturing the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a hot rolled steel sheet for pipes having excellent ductility,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled steel sheet for pipes, which is used for construction, a line pipe, a fluid pipe, and the like.

As the drilling depth of the oil well becomes deeper and the mining environment becomes more severe, a steel material having high strength, low temperature toughness and excellent ductility is required. In particular, pipes (steel pipes) used in oil tubing and the like are required to have high strength, internal and external pressure tensile strength, toughness and delayed fracture resistance. Particularly, if the pipe is expanded by using a pipe expander after inserting the pipe into the oil well, it is possible to reduce the construction cost of the oil well by reducing the type and diameter of the pipe compared to the existing oil well.

In addition, when the pipe is expanded, the low temperature toughness characteristic of the pipe deteriorates due to plastic deformation, and a hot rolled steel sheet having a high impact energy is required after piping to compensate the deterioration.

Generally used seamless steel pipe is seamless steel pipe, and its manufacturing method is to drill a billet heated to high temperature with a drilling mill, and then, a plug mill, a mandrel mill ), And then subjected to a reduction process or a thickness process using a reducer or a sizer, followed by quenching and tempering heat treatment. It is necessary to install a heating furnace and a crack furnace in order to carry out the quenching and tempering heat treatment, and it can not be expensive.

Therefore, in recent years, it has been attempted to replace low-cost welded steel pipes with seamless pipes, but welded steel pipes are subjected to deformation of 4% or more in the circumferential direction and longitudinal direction during the pipe making process. The ratio is increased. The work hardening increases as the ratio of the thickness and the diameter of the steel pipe increases, and increases as the second phase of the steel becomes larger.

In addition, the impact energy of the steel pipe is reduced due to processing defects such as dislocations accumulated in the steel pipe and minute cracks in the steel pipe. In order to remove the work hardening and machining defects in the pipe, heat treatment such as quenching and tempering is performed to ensure impact toughness and durability. However, if such a heat treatment is carried out, the cost of the tube is increased, and an alloy element is further added to compensate the strength after the heat treatment, which increases the manufacturing cost of the hot-rolled steel sheet.

Therefore, even if such a heat treatment is not performed, a hot-rolled steel sheet for pipes which has excellent strength and toughness and can secure a high heat-shrinkability is in desperate need.

An aspect of the present invention is to provide a hot-rolled steel sheet for pipes capable of securing a high strength and a low temperature toughness and capable of producing a pipe having excellent de-mobility, and a method of manufacturing the same.

An embodiment of the present invention is a steel sheet comprising, by weight%, 0.010 to 0.060% of C, 0.20 to 0.50% of Si, 0.7 to 1.5% of Mn, 0.02% or less of P, 0.01% or less of S, 0.001 to 0.006% 0.001 to 0.06% of Al, 0.008% or less of N, 0.01 to 0.30% of Cr, 0.005 to 0.04% of V, 0.005 to 0.08% of Ti, 0.005 to 0.05% of Nb and Fe and unavoidable impurities ,

Wherein Ca and S satisfy 1? Ca / S? 4,

Wherein Ti, Nb and V satisfy 0.005? 2Ti + Nb + V? 0.1.

Another aspect of the present invention is a method for manufacturing a steel slab, comprising: reheating a steel slab satisfying the composition and component relationship;

Hot-rolling the reheated steel slab and hot rolling at a finish rolling temperature of 750 to 900 占 폚; And

And cooling the hot rolled steel sheet and cooling the hot rolled steel sheet at a temperature of 520 to 610 占 폚.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a hot-rolled steel sheet capable of producing a pipe (steel pipe) having not only high strength and low temperature toughness but also excellent weldability of the welded steel pipe. This makes it possible to manufacture high-strength and high-strength pipes that can be used in extreme environments, thereby providing opportunities for new market preemption.

The inventors of the present invention have been studying hot rolled steel sheets for oil well tubes having high strength and high toughness for high expansion and toughness, and have found that, even when expensive alloying elements such as Mo are not added, the amount, composition and rolling process of crude inclusions It is possible to secure a high-strength, high-strength, high-performance, high-performance retention tube for a hot-rolled steel sheet having a thickness of 14 mm or less by controlling the base structure.

That is, according to the present invention, when Si, Mn, Cr, Nb, V, Ti, Nb, or the like is added except an expensive alloy element such as Mo, a proper amount of ferrite and a proper amount of pearlite necessary for strength are generated, It is possible to secure the abundance and impact toughness.

Hereinafter, the present invention will be described in detail. First, the composition of the hot-rolled steel sheet of the present invention will be described in detail (hereinafter, wt%).

The hot-rolled steel sheet of the present invention contains 0.010 to 0.060% of C, 0.20 to 0.50% of Si, 0.7 to 1.5% of Mn, 0.02% or less of P, 0.01% or less of S, 0.001 to 0.006% 0.001 to 0.06% of N, 0.001 to 0.30% of Cr, 0.01 to 0.30% of Cr, 0.005 to 0.04% of V, 0.005 to 0.08% of Ti, 0.005 to 0.05% of Nb and the balance of Fe and unavoidable impurities.

Carbon (C): 0.01 to 0.06%

C is an element that affects the strength, toughness and toughness of a circumferential weld during pipeline construction. C is an element that increases the hardenability of the steel, and increases the yield strength and the tensile strength by increasing the pearlite fraction by retarding the ferrite transformation upon cooling after the hot finish rolling, but decreases the ductility. When the content of C is less than 0.01%, the effect of strengthening the steel by binding with Nb, V, and Ti is very small, and the strength required for the present invention can not be secured due to a decrease in solid solution strength and the like. , The ductility is deteriorated and the weldability at the time of electric resistance welding is lowered. Therefore, the content of C is preferably 0.01 to 0.06%.

Silicon (Si): 0.2 to 0.5%

The Si increases the C activity in the ferrite phase and promotes ferrite stabilization and contributes to securing strength by solid solution strengthening. In addition, the Si forms a low melting point oxide such as Mn 2 SiO 4 at the time of electric resistance welding (ERW), and allows the oxide to be easily discharged. If the content is less than 0.2%, a cost problem in steelmaking will arise. On the other hand, if the content exceeds 0.5%, the amount of SiO 2 oxide formed in a high melting point in addition to Mn 2 SiO 4 increases and the toughness of the welded portion . Therefore, the Si content is preferably 0.2 to 0.5%.

Manganese (Mn): 0.7 to 1.5%

Mn has a great influence on the osteine / ferrite transformation start temperature and as an element for lowering the transformation starting temperature, affects the toughness of the pipe base material portion and the welded portion and contributes to an increase in strength as a solid solution strengthening element. If the content is less than 0.7%, it is difficult to expect the above effect. If the content is more than 1.5%, the segregation zone is likely to occur. Therefore, the content of Mn is preferably 0.7 to 1.5%.

Phosphorus (P): not more than 0.02%

P is a solid solution strengthening element, which functions to significantly increase the austenite / ferrite transformation start temperature and is useful for forming coarse ferrite particles. When the content is more than 0.02%, it is difficult to secure the above effect. Therefore, the content thereof is preferably not more than 0.02%. More preferably, it is 0.015% or less.

Sulfur (S): not more than 0.01%

The S is an element which is easy to form coarse inclusions and promotes toughness and crack propagation, so that it is preferable to limit the S as low as possible, and therefore, the content of S is preferably limited to 0.01% or less. More preferably, it is 0.005% or less.

Calcium (Ca): 0.001 to 0.006%

Ca is added to control the morphology of the emulsion. When the content exceeds 0.006%, CaS in the CaO cluster is generated in excess of the amount of S in the low-temperature steel, whereas when the content is less than 0.001%, MnS is generated and toughness may be lowered. If the amount of S is large, it is preferable to control the amount of S at the same time in order to prevent the occurrence of CaS clusters. That is, it is preferable to control the Ca amount according to the S amount and O amount of iron. Therefore, the content of Ca is preferably 0.001 to 0.006%.

Aluminum (Al): 0.01 to 0.06%

Al is added for deoxidation at the time of steel making. If the content is less than 0.01%, such action is insufficient. On the other hand, if the content is more than 0.06%, the composite oxide containing alumina or alumina oxide is promoted in the welded portion during the electric resistance welding, and the toughness of the welded portion may be damaged. Therefore, the content of Al is preferably 0.01 to 0.06%. More preferably, it is 0.015 to 0.05%.

Nitrogen (N): Not more than 0.008%

N is fixed as a nitride such as Ti or Al because it causes aging deterioration in a solid state. When the content exceeds 0.008%, the addition amount of Ti, Al or the like is inevitably increased. Therefore, the content of N is preferably 0.008% or less. More preferably, it is 0.005% or less.

Cr (Cr): 0.01 to 0.3%

The Cr has the effect of lowering the austenite / ferrite transformation start temperature similarly to Mn. For this purpose, it is preferable to include 0.01% or more. Further, Cr is harder to be segregated than Mn, but affinity with oxygen is stronger than that of Mn. Therefore, when Cr exceeds 0.3%, oxide can be left in the welded portion. Therefore, the content of Cr is preferably 0.01 to 0.3%.

Vanadium (V): 0.005 to 0.04%

V is similar to Nb, but has a less pronounced precipitation strengthening effect. However, when V is added with Nb, it produces a remarkable effect, further increasing the strength of the steel according to the present invention. It is necessary to add at least 0.005%. If it exceeds 0.05%, excessive V carbides precipitate and are harmful to the toughness of the steel. In particular, from the viewpoint of toughness of the weld heat affected zone (HAZ) 0.04%.

Titanium (Ti): 0.005 to 0.08%

The Ti is an element which is very useful for refining the crystal grains. It exists as TiN in the steel and has an effect of suppressing the growth of crystal grains in the heating process for hot rolling. Ti remaining in the steel reacts with nitrogen, TiC precipitates are formed and the TiC is very fine, which greatly improves the strength of the steel. Therefore, in order to obtain an austenite grain growth growth inhibition effect by TiN precipitation and an effect of increasing the strength by TiC formation, at least 0.005% of Ti should be contained. When the steel is added by more than 0.08% As the TiN is reused due to the heat up to the melting point, the toughness of the weld heat affected zone deteriorates, so the upper limit of Ti is 0.08%.

Niobium (Nb): 0.005 to 0.05%

Nb is a very useful element for refining the crystal grains and at the same time, at least 0.005% should be added because it plays a role of enhancing the strength of the steel. If it exceeds 0.05%, excess Nb carbonitride precipitates, It is preferably 0.01 to 0.15%.

In addition to the above composition, the balance includes Fe and unavoidable impurities. However, the addition of other alloying elements is not excluded from the scope of the present invention.

In the present invention, it is preferable that the content of Ca and S satisfies the relationship (relational expression 1) of 1? Ca / S? 4.

The above relational expression 1 is for suppressing the formation of cracks during formation of the impact test and the expansion of the steel pipe, and the formation of non-metallic inclusions acting as a path of propagation. 1, MnS formation is easy, and it is stretched during rolling to act as a propagation path of cracks. If it is more than 4, Ca nonmetallic inclusions increase to lower the impact toughness of steel and steel pipes and serve as a crack- do.

In the present invention, the contents of Ti, Nb and V preferably satisfy the relationship (relational expression 2): 0.005? 2Ti + Nb + V? 0.14.

The relationship (2) is for forming Ti, Nb and V composite precipitates in order to prevent crystal grain coarsening of the HAZ part which is the heat affected part of the welded part in manufacturing the electric resistance welded steel pipe. If it is less than 0.005, the amount of precipitate is too small to suppress the growth of grain growth, and if it is more than 0.14, the amount of precipitation formed becomes too large and the size of the precipitate becomes large, .

Hereinafter, the microstructure of the hot-rolled steel sheet of the present invention will be described in detail. The hot-rolled steel sheet microstructure of the present invention preferably has an area fraction of 95 to 99% of ferrite. If the fraction of the ferrite is less than 95%, it is difficult to ensure the workability and post-grinding durability required in the present invention. On the other hand, when 99% of ferrite is contained, it is difficult to secure sufficient strength required in the present invention.

On the other hand, the hot-rolled steel sheet preferably has an area percentage of pearlite of 1 to 5%. The pearlite serves to secure strength, and it is preferable that the pearlite is contained in an amount of 1% or more. When the pearlite is formed in an amount exceeding 5%, the pearlite and ferrite interface may be a source of cracking, There is a problem that the low-temperature impact toughness is undermined.

Hereinafter, a method of manufacturing the hot-rolled steel sheet of the present invention will be described in detail.

The manufacturing method of the present invention comprises: preparing a steel slab satisfying the above composition and relational expression, and reheating the steel slab; Hot-rolling the reheated steel slab; And cooling and winding after the hot rolling.

The reheating is determined according to the solid solution temperature of the precipitate. In the component range of the present invention, the reheating is preferably performed at a temperature of 1150 ° C or higher. When the temperature exceeds 1300 ° C, .

The hot rolling at the time of the hot rolling is preferably performed at a temperature of 750 to 900 캜. If the finishing rolling temperature is too high, the strength and impact toughness are lowered. On the other hand, if the finishing rolling temperature is too low, the toughness may be improved. However, since productivity and shape may be problematic, .

The cooling is preferably performed at a cooling rate of 10 to 20 DEG C / s to 520 to 610 DEG C, and it is preferable that the cooling is performed at a temperature of 560 to 610 DEG C. When cooled to a low temperature of less than 520 ° C, the structure becomes finer and toughness is increased. However, the yield strength increases greatly after the piping, resulting in an increase in yield ratio. Further, if the temperature is cooled to a temperature higher than 610 DEG C, there is a problem that the yield ratio is reduced due to the formation of coarseness, but the toughness is lowered. When the cooling rate is lower than 10 ° C / s, coarse ferrite is formed and the strength is decreased, and pearlite is formed and the dispersibility is decreased. On the other hand, when the cooling rate is higher than 30 DEG C / s, bainite or martensite, which is a low-temperature transformation structure, is formed, and thus the deodorizing ability can not be secured.

On the other hand, using the hot-rolled steel sheet of the present invention, a pipe that has been gouged has the following characteristics. For example, it is preferable that the steel pipe is formed by performing electrical resistance welding from 4 to 11 inches, and the steel pipe is heat-treated at 700 ° C. or less, Use

The pipe had a yield strength of 400 MPa or more, an impact energy at -20 ° C of 380 J or more, and a flaring expansion amount of the electric resistance welded steel pipe (the cone was inserted into the pipe end, ) Is preferably 50% or more.

Hereinafter, embodiments of the present invention will be described in detail. The following examples are for the purpose of understanding the present invention and are not intended to limit the present invention.

(Example)

A steel slab having the composition shown in Table 1 (weight%, the balance being Fe and unavoidable impurities) was subjected to hot rolling at 1200 to 1250 캜. Then, hot-rolled steel sheets were produced by the conditions of finish rolling temperature, cooling rate and coiling temperature shown in Table 2 below. The structure of the thus-prepared hot-rolled steel sheet was observed, and the results are shown in Table 2.

The hot-rolled steel sheet was subjected to electric resistance welding to form a pipe of 4 to 11 inches. After the pipe was hot-rolled, the heat treatment was performed at the heat treatment temperature of Table 3 below. The physical properties of the pipes thus manufactured were evaluated, and the results are shown in Table 3. < tb >< TABLE > The physical properties were measured using a tensile tester and the yield strength was tested according to the generally accepted ASTM A370. The impact energy was measured by Charpy impact test at -20 캜. Flaring tests were conducted according to ASTM A513 to evaluate the ductility of steel pipes.

Steel grade C Si Mn Cr Nb Ti V Mo P Ca S Ca / S 2Ti + Nb + V Inventive Steel 1 0.038 0.2 1.2 0.1 0.023 0.015 0.01 - 0.015 0.0011 0.0007 1.6 0.063 Invention river 2 0.046 0.25 1.1 0.11 0.027 0.011 0.01 - 0.017 0.0021 0.0009 2.3 0.059 Comparative River 1 0.065 0.25 1.3 0.12 0.07 0.015 0.04 0.1 0.015 0.0035 0.0015 2.3 0.14 Comparative River 2 0.048 0.2 1.4 0.17 0.08 0.02 0.02 - 0.018 0.0045 0.001 4.5 0.14

(In Table 1, N is not described, but is controlled to be 50 ppm or less, which is a range added in normal operation.)

division Steel grade Finishing rolling temperature (캜) Cooling rate (° C / s) Coiling temperature (캜) Microstructure (area%) ferrite Pearlite Inventory 1 Inventive Steel 1 801 15 560 97 3 Inventory 2 Invention river 2 778 14 570 98 2 Inventory 3 Inventive Steel 1 760 17 520 96 4 Honorable 4 Invention river 2 788 12 530 97 3 Inventory 5 Invention river 2 798 11 601 95 5 Inventory 6 Inventive Steel 1 754 14 586 96 4 Honorable 7 Invention river 2 817 18 548 96 4 Honors 8 Invention river 2 835 20 561 95 5 Comparative Example 1 Inventive Steel 1 811 9 640 92 8 Comparative Example 2 Comparative River 1 795 15 580 94 6 Comparative Example 3 Comparative River 2 820 18 605 88 12 Comparative Example 4 Comparative River 2 814 12 603 87 13 Comparative Example 5 Comparative River 2 799 18 605 88 11 Comparative Example 6 Comparative River 1 813 20 589 92 8 Comparative Example 7 Comparative River 1 825 16 615 86 14 Comparative Example 8 Comparative River 1 791 18 618 88 12 Comparative Example 9 Comparative River 1 812 21 593 90 10 Comparative Example 10 Comparative River 1 821 22 580 92 8

division Steel grade Heat treatment temperature of welding part (℃) Yield strength (MPa) Impact toughness (-20 ° C, J) Flaring (%) HAZ Hardness (Hv) Inventory 1 Inventive Steel 1 500 492 450 68 230 Inventory 2 Invention river 2 650 502 428 71 180 Inventory 3 Inventive Steel 1 550 503 468 66 194 Honorable 4 Invention river 2 600 510 453 69 215 Inventory 5 Invention river 2 600 523 441 91 220 Inventory 6 Inventive Steel 1 580 534 437 64 223 Honorable 7 Invention river 2 620 546 468 68 212 Honors 8 Invention river 2 530 537 462 70 227 Comparative Example 1 Inventive Steel 1 900 632 461 44 170 Comparative Example 2 Comparative River 1 900 502 268 35 160 Comparative Example 3 Comparative River 2 900 498 186 17 165 Comparative Example 4 Comparative River 2 950 456 248 24 154 Comparative Example 5 Comparative River 2 940 463 236 22 162 Comparative Example 6 Comparative River 1 960 473 278 20 149 Comparative Example 7 Comparative River 1 950 451 234 24 152 Comparative Example 8 Comparative River 1 950 439 239 18 157 Comparative Example 9 Comparative River 1 970 471 284 27 141 Comparative Example 10 Comparative River 1 970 480 297 31 132

As shown in Table 3, in Inventive Examples, which were produced according to the production method of the present invention using inventive steels 1 and 2 satisfying the composition of the present invention, pearlite formation was minimized and crystal grain coarsening of ferrite was suppressed, The yield strength of the after-pipe can be secured to 420 MPa or more, and the mechanical properties of the Charpy impact energy at -20 ° C of 380 J or more can be ensured. The heat treatment temperature of the welded portion after the pipe making is 700 ° C. or less, it was possible to secure flaring.

However, it can be confirmed that, in the comparative examples which do not satisfy the composition and the production method of the present invention, it is difficult to secure both excellent yield strength, low temperature toughness and dextrinability as in the present invention.

Claims (5)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.010 to 0.060% of C, 0.20 to 0.50% of Si, 0.7 to 1.5% of Mn, 0.02% or less of P, 0.01 or less of S, 0.001 to 0.006% of Ca, 0.005 to 0.08% of N, 0.005 to 0.05% of Nb, and the balance of Fe and unavoidable impurities, wherein the content of N is 0.008% or less, the content of Cr is 0.01 to 0.30%, the content of V is 0.005 to 0.04%
Wherein Ca and S satisfy 1? Ca / S? 4,
Wherein said Ti, Nb and V satisfy 0.005? 2Ti + Nb + V? 0.1.
The method according to claim 1,
Wherein the microstructure of the hot-rolled steel sheet has an area fraction of not less than 95% of ferrite.
The method according to claim 1,
The hot-rolled steel sheet for pipe according to claim 1, wherein said pipe has a yield strength of 450 MPa or more, an impact energy at -20 ° C of 380 J or more, and a flaring expansion amount of 50% or more.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.010 to 0.060% of C, 0.20 to 0.50% of Si, 0.7 to 1.5% of Mn, 0.02% or less of P, 0.01 or less of S, 0.001 to 0.006% of Ca, 0.005 to 0.08% of N, 0.005 to 0.05% of Nb, and the balance of Fe and unavoidable impurities, wherein Ca and S are selected from the group consisting of 1? Ca / S? 4, and Ti, Nb and V satisfy 0.005? 2Ti + Nb + V? 0.1;
Hot-rolling the reheated steel slab and hot rolling at a finish rolling temperature of 750 to 900 占 폚; And
Cooling after hot rolling and winding at a temperature of 520 to 610 캜
Wherein the steel sheet has excellent ductility.
The method of claim 4,
Wherein the cooling rate during cooling is 10 to 20 占 폚 / s.
KR1020140188047A 2014-12-24 2014-12-24 Hot rolled steel sheet for pipe having expending property and method for manufacturing the same KR20160078600A (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109280859A (en) * 2018-10-19 2019-01-29 北京科技大学 A kind of preparation method of the easy expansion sleeve tubing of petroleum drilling and mining
JPWO2018042522A1 (en) * 2016-08-30 2019-03-28 新日鐵住金株式会社 Oil well pipe for expandable tubular
KR20190076797A (en) * 2017-12-22 2019-07-02 주식회사 포스코 Hot rodled steel sheet and method for manufacturing the same
JP6885524B1 (en) * 2020-08-28 2021-06-16 日本製鉄株式会社 Electric resistance steel pipe

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPWO2018042522A1 (en) * 2016-08-30 2019-03-28 新日鐵住金株式会社 Oil well pipe for expandable tubular
KR20190076797A (en) * 2017-12-22 2019-07-02 주식회사 포스코 Hot rodled steel sheet and method for manufacturing the same
CN109280859A (en) * 2018-10-19 2019-01-29 北京科技大学 A kind of preparation method of the easy expansion sleeve tubing of petroleum drilling and mining
JP6885524B1 (en) * 2020-08-28 2021-06-16 日本製鉄株式会社 Electric resistance steel pipe
WO2022044271A1 (en) * 2020-08-28 2022-03-03 日本製鉄株式会社 Electric resistance welded steel pipe

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