KR20140042108A - Hot-rolled steel sheet and method of manufacturing the same - Google Patents
Hot-rolled steel sheet and method of manufacturing the same Download PDFInfo
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- KR20140042108A KR20140042108A KR1020120108424A KR20120108424A KR20140042108A KR 20140042108 A KR20140042108 A KR 20140042108A KR 1020120108424 A KR1020120108424 A KR 1020120108424A KR 20120108424 A KR20120108424 A KR 20120108424A KR 20140042108 A KR20140042108 A KR 20140042108A
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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
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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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
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
Abstract
Disclosed is a hot rolled steel sheet having excellent heat treatment characteristics and corrosion resistance and satisfying API (American Petroleum Institute) 5CT J55 standard and controlling a method thereof by controlling alloy components and controlling process conditions.
Hot-rolled steel sheet according to the present invention by weight, carbon (C): 0.02 ~ 0.03%, manganese (Mn): 1.1 ~ 1.3%, silicon (Si): 0.15 ~ 0.25%, titanium (Ti): 0.01 ~ 0.03% , Nickel (Ni): 0.1 to 0.3%, chromium (Cr): 0.05 to 0.25%, calcium (Ca): 0.001 to 0.004%, boron (B): 0.001 to 0.003%, phosphorus (P): 0.01% or less, Sulfur (S): 0.001% or less, Nitrogen (N): 0.01% or less and the remaining iron (Fe) and inevitable impurities, CLR (Crack Length Ratio): 10% or less, CTR (Crack Thickness Ratio): 4% And CSR (Crack Sensitivity Ratio): characterized by having 2% or less.
Description
The present invention relates to a hot-rolled steel sheet and a method for manufacturing the same, and more particularly, to a hot-rolled steel sheet that satisfies the API (American Petroleum Institute) 5CT J55 standard having excellent heat treatment properties and corrosion resistance through controlling alloy components, and a method of manufacturing the same. will be.
API (American Petroleum Institute) steel pipes used for drilling oil and gas are variously used after heat-combusted material and heat treatment depending on the purpose of use, and API 5CT J55, API 5CT K55, API 5CT L80, It may be classified into API 5CT N80, API 5CT P110, and the like.
Among them, API 5CT J55 steel pipe is most used as 380MPa based on yield strength, and is a steel grade that can improve the material to API 5CT P110 after quenching and tempering (QT) heat treatment. Accordingly, there is an increasing demand for API 5CT J55 steel pipe that can be used as an oil well pipe even in a corrosive environment.
In general, API 5CT J55 is a hot rolled steel containing 0.2 ~ 0.25% by weight of the total weight of steel to add titanium (Ti), boron (B), etc. to improve the heat treatment hardenability, thereby guaranteeing strength after heat treatment. I could do it. However, better corrosion resistance is required for use as an oil well tube even in a corrosive environment.
Related prior art documents include Korean Patent Laid-Open Publication No. 10-0770572 (August 26, 2007), which discloses a high carbon steel sheet having excellent hardening heat treatment characteristics and a method of manufacturing the same.
An object of the present invention is to provide a method for producing a hot rolled steel sheet that satisfies API (American Petroleum Institute) 5CT J55 standard, and has excellent heat treatment characteristics and corrosion resistance characteristics through alloy component control and process condition control.
Another object of the present invention is manufactured by the above method, while satisfying the API 5CT J55 standard having a tensile strength (TS): 655MPa or more and yield strength (YS): 552 ~ 655MPa CLR (Crack Length Ratio): 10% or less, It is to provide a hot rolled steel sheet having a crack thickness ratio (CTR) of 4% or less and a crack sensitivity ratio (CSR) of 2% or less.
In addition, another object of the present invention is to prepare the API 5CT J55 standard that can improve the tensile strength (TS) to 862MPa or more through heat treatment with a material having a carbon content of 0.2% by weight or more of the total weight of the steel sheet It is to provide a satisfactory hot rolled steel sheet.
Hot rolled steel sheet manufacturing method according to an embodiment of the present invention for achieving the above object by weight, carbon (C): 0.02 ~ 0.03%, manganese (Mn): 1.1 ~ 1.3%, silicon (Si): 0.15 ~ 0.25 %, Ti: 0.01 ~ 0.03%, Nickel (Ni): 0.1 ~ 0.3%, Chromium (Cr): 0.05 ~ 0.25%, Calcium (Ca): 0.001 ~ 0.004%, Boron (B): 0.001 ~ 0.003 %, Phosphorus (P): 0.01% or less, sulfur (S): 0.001% or less, nitrogen (N): 0.01% or less, and slab plate material consisting of the remaining iron (Fe) and unavoidable impurities; Slab Reheating Temperature; SRT) reheating to 1150 ~ 1250 ℃ condition; Hot rolling the reheated plate to a finish rolling temperature (FDT) of 750 to 850 ° C .; and cooling the hot rolled plate to a coiling temperature of 550 to 650 ° C. Taking; characterized in that it comprises a.
Here, the cooling is characterized in that carried out at a cooling rate of 10 ~ 100 ℃ / sec.
Hot-rolled steel sheet according to an embodiment of the present invention for achieving the other object by weight, carbon (C): 0.02 ~ 0.03%, manganese (Mn): 1.1 ~ 1.3%, silicon (Si): 0.15 ~ 0.25% , Ti: 0.01 ~ 0.03%, Nickel (Ni): 0.1 ~ 0.3%, Chromium (Cr): 0.05 ~ 0.25%, Calcium (Ca): 0.001 ~ 0.004%, Boron (B): 0.001 ~ 0.003% , Phosphorus (P): 0.01% or less, sulfur (S): 0.001% or less, nitrogen (N): 0.01% or less, and the remaining iron (Fe) and inevitable impurities, CLR (Crack Length Ratio): 10% or less , CTR (Crack Thickness Ratio): 4% or less and CSR (Crack Sensitivity Ratio): characterized in that it has 2% or less.
Here, the hot rolled steel sheet is characterized in that it has a tensile strength (TS): 655MPa or more and yield strength (YS): 552 ~ 655MPa.
Hot rolled steel sheet and a method of manufacturing the same according to the present invention through the adjustment of the alloy composition and process conditions control, CLR (Crack Length Ratio): 10% or less, CTR (Crack Thickness Ratio): 4% or less and CSR (Crack Sensitivity Ratio): It exhibits 2% or less and excellent corrosion resistance, and satisfies API (American Petroleum Institute) 5CT J55 standard having a tensile strength (TS) of 655 MPa or more and a yield strength (YS) of 552 to 655 MPa.
Accordingly, the hot rolled steel sheet according to the present invention is excellent in heat treatment characteristics and corrosion resistance is suitable for use as an oil well for heat treatment by suppressing the occurrence of cracks after heat treatment.
1 is a process flowchart showing a method for manufacturing a hot rolled steel sheet according to an embodiment of the present invention.
FIG. 2 is a photograph of UT flaw detection of a HIC test specimen in a welded specimen prepared according to Example 1 of the present invention. FIG.
BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.
Hereinafter, a hot rolled steel sheet for an oil well and a manufacturing method thereof according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
Hot-rolled steel sheet
Hot rolled steel sheet according to the present invention has a tensile strength (TS): 655 MPa or more while having a crack length ratio (CLR) of 10% or less, a crack thickness ratio (CTR) of 4% or less and a crack sensitivity ratio (CSR) of 2% or less And yield strength (YS): aims to satisfy the API (American Petroleum Institute) 5CT J55 standard having a 552 ~ 655MPa.
To this end, the hot rolled steel sheet according to the present invention by weight%, carbon (C): 0.02 ~ 0.03%, manganese (Mn): 1.1 ~ 1.3%, silicon (Si): 0.15 ~ 0.25%, titanium (Ti): 0.01 ~ 0.03%, Nickel (Ni): 0.1-0.3%, Chromium (Cr): 0.05-0.25%, Calcium (Ca): 0.001-0.004%, Boron (B): 0.001-0.003%, Phosphorus (P): 0.01 % Or less, sulfur (S): 0.001% or less, nitrogen (N): 0.01% or less, and the remaining iron (Fe) and inevitable impurities.
Hereinafter, the role and content of each component included in the hot-rolled steel sheet according to the present invention will be described.
Carbon (C)
Carbon (C) is added for strength and microstructure control.
In the present invention, it is preferable to design with a low carbon-based alloy component in order to derive excellent weldability. To this end, carbon (C) is preferably added in an amount ratio of 0.20 to 0.30% by weight of the total weight of the hot rolled steel sheet according to the present invention. If the content of carbon (C) is less than 0.20% by weight of the total weight of the hot rolled steel sheet, it may be difficult to secure sufficient strength. On the contrary, when the content of carbon (C) exceeds 0.30% by weight of the total weight of the hot-rolled steel sheet, corrosion resistance may decrease due to pearlite formation by carbon (C).
silicon( Si )
Silicon (Si) is a ferrite stabilizing element that improves the ductility of the steel and is added to improve the strength.
Silicon (Si) is preferably added in a content ratio of 0.15 to 0.25% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the content of silicon (Si) is less than 0.15% by weight of the total weight of the hot-rolled steel sheet, the effect of adding silicon can not be exhibited properly. On the contrary, when the content of silicon (Si) exceeds 0.25 wt% of the total weight of the hot rolled steel sheet, the weldability of the steel is reduced due to the generation of oxide, and the red scale is reduced during the reheating process and hot rolling during the hot rolling process. This can cause problems with surface quality.
manganese( Mn )
Manganese (Mn) is a solid solution strengthening element, which improves the hardenability of steel and contributes to securing strength. In addition, as an austenite stabilizing element, retarding pearlite transformation contributes to grain refinement of ferrite.
Manganese (Mn) is preferably added in a content ratio of 1.1 to 1.3% by weight of the total weight of the hot rolled steel sheet according to the present invention. If the content of manganese (Mn) is less than 1.1% by weight of the total weight of the hot-rolled steel sheet may not exhibit a solid solution strengthening effect. On the contrary, when the content of manganese (Mn) exceeds 1.3% by weight of the total weight of the hot-rolled steel sheet, not only the weldability is greatly reduced, but also the corrosion resistance of the steel sheet is greatly reduced by the generation of MnS inclusions and the occurrence of center segregation. There is a problem.
titanium( Ti )
Titanium (Ti) prevents austenite grain growth during welding by producing Ti (C, N) precipitates having high temperature stability, thereby minimizing the weld structure and improving the toughness and strength of the hot rolled product. In particular, titanium (Ti) is combined with nitrogen (N) to increase the solubility of boron (B).
Titanium (Ti) is preferably added in an amount of 0.01 to 0.03% by weight of the total weight of the hot rolled steel sheet according to the present invention. If the content of titanium (Ti) is less than 0.01% by weight of the total weight of the hot rolled steel sheet, the addition effect may not be properly exhibited. On the contrary, when a large amount of titanium (Ti) exceeds 0.03% by weight of the total weight of the hot rolled steel sheet, coarse precipitates may be generated to reduce toughness and corrosion resistance of the steel.
nickel( Ni )
Nickel (Ni) is a corrosion resistant element to improve the corrosion resistance of the hot rolled steel sheet, and also to improve the hardenability of the steel.
Nickel (Ni) is preferably added in a content ratio of 0.1 to 0.3% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the content of nickel (Ni) is less than 0.1% by weight of the total weight of the hot rolled steel sheet, the addition effect may not be properly exhibited. On the contrary, when a large amount of nickel (Ni) exceeds 0.3 wt% of the total weight of the hot rolled steel sheet, there is a problem in that the manufacturing cost is increased without any further effect.
chrome( Cr )
Chromium (Cr) contributes to improving corrosion resistance and hardenability at a relatively low price compared to other elements. In addition, chromium (Cr) serves to suppress the central segregation by increasing the diffusion of manganese (Mn) in the slab manufacturing.
Chromium (Cr) is preferably added in an amount of 0.05 to 0.25% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the content of chromium (Cr) is less than 0.05% by weight of the total weight of the hot rolled steel sheet, the addition effect may not be properly exhibited. On the contrary, when the content of chromium (Cr) exceeds 0.25% by weight of the total weight of the hot rolled steel sheet, there is a problem of decreasing the ductility of the steel by coarse carbide formation.
calcium( Ca )
Calcium (Ca) is added for the purpose of improving the electrical resistance weldability by forming CaS inclusions and hindering the production of MnS inclusions. That is, since Ca (Ca) has a higher affinity with sulfur (S) than manganese (Mn), CaS inclusions are generated when calcium is added, and MnS inclusions are reduced. 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.
Calcium (Ca) is preferably added in an amount ratio of 0.001 to 0.004% by weight of the total weight of the oil-treated hot rolled steel sheet according to the present invention. When the calcium (Ca) content is less than 0.001% by weight of the total weight of the hot rolled steel sheet, the MnS control effect may not be properly exhibited. On the contrary, when the content of calcium (Ca) exceeds 0.004% by weight of the total weight of the hot-rolled steel sheet, generation of CaO inclusions is excessively generated, which deteriorates performance and electrical resistance weldability.
Boron (B)
Boron (B), instead of niobium (Nb) serves to improve the heat treatment hardenability like titanium (Ti).
Boron (B) is preferably added in an amount of 0.001 to 0.003% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the content of boron (B) is less than 0.001% by weight of the total weight of the hot rolled steel sheet, the heat treatment hardenability improvement effect may not be properly exhibited. On the contrary, when a large amount of boron (B) exceeds 0.003% by weight of the total weight of the hot rolled steel sheet, there is a problem of lowering the toughness of the steel due to segregation at grain boundaries.
In (P)
Phosphorus (P) is generally present in molten steel as an impurity, but may also be added to increase its strength.
However, phosphorus (P) has a problem of deteriorating weldability and deteriorating corrosion resistance by slab center segregation. Therefore, in the present invention, the content of phosphorus (P) was limited to 0.01% by weight or less of the total weight of the hot rolled steel sheet.
Sulfur (S)
Sulfur (S) inhibits the toughness and weldability of steel. In particular, the sulfur (S) may increase the MnS non-metal inclusions to deteriorate the resistance to stress corrosion cracking to generate cracks during processing of the steel, as a result can reduce the corrosion resistance of the steel.
Accordingly, in the present invention, the content of sulfur (S) is limited to 0.001% by weight or less based on the total weight of the hot-rolled steel sheet.
Nitrogen (N)
Nitrogen (N) is combined with titanium (Ti) to increase the solid solution of boron (B) through TiN precipitation and is added to secure hardenability.
When the nitrogen (N) is contained in a large amount of steel, there is a problem in that the solid solution nitrogen is increased to reduce the impact characteristics and elongation of the steel sheet and greatly reduce the toughness of the weld. Therefore, in the present invention, the content of nitrogen (N) is limited to not more than 0.01 wt% of the total weight of the hot-rolled steel sheet.
Hot-rolled steel sheet manufacturing method
1 is a process flowchart showing a method for manufacturing a hot rolled steel sheet according to an embodiment of the present invention.
Referring to FIG. 1, the method for manufacturing a hot rolled steel sheet according to an exemplary embodiment of the present invention includes a slab reheating step S110, a hot rolling step S120, and a cooling / winding step S130. 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 method for manufacturing a hot rolled steel sheet according to the present invention, the slab sheet in the semi-finished state, which is the target of the hot rolling process, is% by weight, carbon (C): 0.02 to 0.03%, manganese (Mn): 1.1 to 1.3%, and silicon (Si): 0.15 to 0.25%, Titanium (Ti): 0.01 to 0.03%, Nickel (Ni): 0.1 to 0.3%, Chromium (Cr): 0.05 to 0.25%, Calcium (Ca): 0.001 to 0.004%, Boron (B): 0.001 ~ 0.003%, phosphorus (P): 0.01% or less, sulfur (S): 0.001% or less, nitrogen (N): 0.01% or less and the remaining iron (Fe) and inevitable impurities.
At this time, the slab plate having the above composition can be obtained through a continuous casting process after obtaining a molten steel having a desired composition through a steelmaking process.
Reheating slabs
In the slab reheating step S110, the slab plate having the above composition is reheated to a slab reheating temperature (SRT) of 1150 to 1250 ° C. Through the reheating of the slab plate, re-use of the segregated components and re-use of precipitates may occur during casting.
If the slab reheating temperature (SRT) is less than 1150 DEG C in this step, the segregated components in casting may not be sufficiently reused. On the other hand, when the SRT exceeds 1250 ° C, the austenite grain size increases and the ferrite of the final microstructure is coarsened, which may make it difficult to secure strength. In addition, can do.
Hot rolling
In the hot rolling step (S120), the reheated sheet is finished hot rolled in a finishing rolling temperature (FDT): 750 to 850 ° C. corresponding to the austenite uncrystallized region.
In this step, when the finish rolling temperature (FDT) is less than 750 ° C., abnormal reverse rolling occurs to form a mixed structure, thereby greatly reducing low-temperature impact toughness. On the contrary, when the finish rolling temperature (FDT) exceeds 850 ° C., the ductility and toughness are excellent, but there is a problem that the strength is sharply lowered.
In this case, the hot rolling may be performed so that the cumulative rolling reduction in the non-recrystallized region is 40 to 60%. If the cumulative rolling reduction of the hot rolling is less than 40%, it is difficult to obtain a uniform and fine structure, which may cause a significant variation in strength and impact toughness. On the other hand, when the cumulative rolling reduction of the hot rolling exceeds 60%, there is a problem that the rolling process time is prolonged and the fishy property is deteriorated.
Cooling/ Coiling
In the cooling / winding step (S130), the hot rolled sheet is wound while cooling. If winding is performed simultaneously with cooling, the cooling end temperature may be a coiling temperature (CT).
In this step, the winding may be carried out at a coiling temperature (CT) 550 ~ 650 ℃. In this case, the strength of the steel sheet can be maintained by forming the appropriate precipitated phase.
If the coiling temperature CT is less than 550 ° C., the strength may be insufficient due to the coarsening of the crystal grains. On the other hand, when the coiling temperature (CT) exceeds 650 ° C low temperature impact toughness can be greatly reduced.
On the other hand, the cooling is preferably carried out at a cooling rate of 10 ~ 100 ℃ / sec. If the cooling rate is less than 10 ℃ / sec, it may be difficult to secure the strength due to the coarsening of precipitates. On the contrary, when the cooling rate exceeds 100 ° C / sec, the structure is hardened, the low-temperature toughness can be lowered, and only the steel sheet manufacturing cost can be increased by excessive cooling without any further effect.
The hot rolled steel sheet manufactured by the above process (S110 ~ S130) is added to the carbon content of 0.2 ~ 0.3% by weight of the total weight of the steel sheet in order to secure the heat treatment characteristics, chromium (Cr) and nickel as the corrosion resistance elements to improve the corrosion resistance (Ni) was added and the amount of manganese (Mn), an element that causes segregation in the hot rolled steel sheet, was reduced compared to the existing API 5CT J55 standard.
Accordingly, the hot rolled steel sheet according to the present invention has an API 5CT having a tensile strength (TS) of at least 655 MPa and a yield strength (YS) of 552 to 655 MPa, although the carbon content is 0.2 to 0.3 wt% of low carbon based on the total weight of the steel sheet. It satisfies the J55 standard, and has a crack length ratio (CLR) of 10% or less, a crack thickness ratio (CTR) of 4% or less, and a crack sensitivity ratio (CSR) of 2% or less. . In addition, the hot rolled steel sheet according to the present invention has a characteristic that the tensile strength (TS) after the heat treatment is improved to 862MPa or more.
As such, the hot rolled steel sheet according to the present invention has excellent heat treatment characteristics and corrosion resistance, and thus is suitable for use as an oil well tube for heat treatment because crack generation is suppressed after heat treatment.
Example
Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. 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
Specimens according to Examples 1 to 3 and Comparative Examples 1 to 2 were prepared under the compositions shown in Table 1 and the process conditions described in Table 2. Then, after reheating, hot rolling, cooling, and winding the hot rolled specimens according to Examples 1 to 3 and Comparative Examples 1 to 2, HIC (Hydrogen induced cracking) tests were performed.
[Table 1]
[Table 2]
Then, the specimens according to Examples 1 to 3 and Comparative Examples 1 to 2 were heat-treated at the tube and 800 ℃, and the strength of the steel grade was improved by the API 5CT L80 standard, and the tensile test was carried out for each, Example In the specimen prepared according to 1, the UT flaw of the HIC test specimen of the weld portion was observed and shown in FIG. 2.
2. Evaluation of mechanical properties
Table 3 shows the mechanical property results for the specimens prepared in Examples 1-3 and Comparative Examples 1-2.
[Table 3]
Referring to Tables 1 to 3, in the case of specimens prepared according to Examples 1 to 3 after engraving and heat treatment, tensile strength (TS) corresponding to the target value of API 5CT L80 standard: TS 862 MPa or more and yield strength (YS) ): It can be seen that all of 552 ~ 655MPa is satisfied.
In addition, in the case of specimens prepared according to Examples 1 to 3, a crack length ratio (CLR): 10% or less, a crack thickness ratio (CTR): 4% or less, and a crack sensitivity ratio (CSR): 2 corresponding to a target value It can be seen that all values below% are satisfied and these values are close to zero.
FIG. 2 is a photograph of UT flaw detection of a HIC test specimen in a welded specimen prepared according to Example 1 of the present invention. FIG.
Referring to FIG. 2, in the case of the specimen prepared according to Example 1, it was confirmed that no crack was generated inside the welded part as a result of the UT inspection, and thus, the corrosion resistance was excellent.
On the other hand, in the case of the specimens prepared according to Comparative Examples 1 and 2, the tensile strength (TS) and the yield strength (YS) satisfied all the API (American Petroleum Institute) 5CT J55 standard, but did not meet the target value after heat treatment.
In addition, CLR, CTR, and CSR did not all meet the target value, and showed a significant difference from the target value.
As can be seen from the above experimental results, the specimens prepared according to Examples 1 to 3 satisfying the conditions presented in the present invention compared to Comparative Examples 1 to 2, which is not, the content of carbon (C) is the total weight of the steel sheet By taking 0.2 to 0.3% by weight of the chromium (Cr) and nickel (Ni) by adding a relatively large amount, while satisfying the API 5CT J55 standard while improving the heat treatment characteristics and corrosion resistance characteristics. Through this, while satisfying the API 5CT L80 standard after the tubing and heat treatment can have excellent corrosion resistance characteristics.
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: cooling / winding step
Claims (4)
Hot rolling the reheated sheet to a finish rolling temperature (FDT) of 750 to 850 ° C .; And
And cooling and hot rolling the hot rolled plate to a coiling temperature (CT) of 550 to 650 占 폚.
The cooling
Method for producing a hot rolled steel sheet, characterized in that carried out at a cooling rate of 10 ~ 100 ℃ / sec.
CLR (Crack Length Ratio): 10% or less, CTR (Crack Thickness Ratio): 4% or less, and CSR (Crack Sensitivity Ratio): Hot rolled steel sheet characterized in that it has 2% or less.
The hot-
Tensile strength (TS): 655MPa or more and Yield strength (YS): 552 ~ 655MPa Hot rolled steel sheet characterized in that it has.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020120108424A KR20140042108A (en) | 2012-09-27 | 2012-09-27 | Hot-rolled steel sheet and method of manufacturing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020120108424A KR20140042108A (en) | 2012-09-27 | 2012-09-27 | Hot-rolled steel sheet and method of manufacturing the same |
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| KR20140042108A true KR20140042108A (en) | 2014-04-07 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104831175A (en) * | 2014-11-25 | 2015-08-12 | 宝鸡石油钢管有限责任公司 | J55-steel-grade SEW expandable casing tube and manufacturing method thereof |
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2012
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104831175A (en) * | 2014-11-25 | 2015-08-12 | 宝鸡石油钢管有限责任公司 | J55-steel-grade SEW expandable casing tube and manufacturing method thereof |
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