KR20130013547A - Steel sheet for oil tubular country goods and method of manufacturing the steel sheet - Google Patents
Steel sheet for oil tubular country goods and method of manufacturing the steel sheet Download PDFInfo
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- KR20130013547A KR20130013547A KR1020110075258A KR20110075258A KR20130013547A KR 20130013547 A KR20130013547 A KR 20130013547A KR 1020110075258 A KR1020110075258 A KR 1020110075258A KR 20110075258 A KR20110075258 A KR 20110075258A KR 20130013547 A KR20130013547 A KR 20130013547A
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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Abstract
Prior to QT heat treatment, the steel sheet for oil wells having excellent impact characteristics and its manufacturing method having an impact value of 140 J or more while having a tensile strength (TS) of 517 MPa or more and a yield strength (YS) of 379 to 552 MPa. It starts with.
Method for producing a steel sheet for oil wells according to the present invention is carbon (C): 0.22 ~ 0.27% by weight, silicon (Si): 0.15 ~ 0.35% by weight, manganese (Mn): 1.2 ~ 1.6% by weight, aluminum (Al): 0.01 ~ 0.03 % By weight, titanium (Ti): 0.01 to 0.03% by weight, boron (B): 0.0015 to 0.003% by weight, calcium (Ca): 0.001 to 0.004% by weight, and the reheating slab plate consisting of the remaining iron (Fe) and unavoidable impurities Making; Finishing hot-rolling the reheated plate to Finishing Delivery Temperature (FDT): 800 ~ 850 ℃; And coiling the hot rolled plate to a CT (Coiling Temperature): cooling to 550 to 600 ° C.
Description
The present invention relates to a steel sheet for oil wells and a method of manufacturing the same, and more specifically, API-5CT J55 standard (tensile strength) widely used as steel pipe material for oil well before QT (Quenching & Tempering) heat treatment through alloy composition control and process condition control. : 517 MPa or more, yield strength: 379 ~ 552 MPa) relates to a steel sheet for oil wells and a method of manufacturing the same, which satisfies the mechanical properties and at the same time have excellent impact characteristics.
Oil well steel pipes are steel pipes used for drilling oil or gas in deep sea and oil sands. Such oil well steel pipes are usually upgraded by hot-rolled steel sheets and then subjected to QT (Quenching & Tempering) heat treatment according to the purpose of use.
Related prior art is Korean Patent Publication No. 2001-0062875 (2001.07.09 publication).
An object of the present invention is API-5CT J55 standard (tensile strength: 517 MPa or more, yield strength: 379 ~ 552 MPa) widely used as a steel pipe material for oil wells before QT (Quenching & Tempering) heat treatment through alloy composition control and process condition control It is to provide a method of manufacturing a steel sheet for oil wells that satisfies the mechanical properties of the () and at the same time has excellent impact characteristics.
Another object of the present invention is manufactured by the above method, while having a tensile strength (TS): 517 MPa or more and a yield strength (YS): 379 ~ 552 MPa before QT heat treatment to ensure an impact value at 0 ℃: 140 J or more It is providing a steel plate for oil wells which has the outstanding impact characteristic by this.
In order to achieve the above object, a steel sheet manufacturing method for an oil well according to an embodiment of the present invention is carbon (C): 0.22 to 0.27 wt%, silicon (Si): 0.15 to 0.35 wt%, manganese (Mn): 1.2 to 1.6 wt% , Aluminum (Al): 0.01 ~ 0.03% by weight, titanium (Ti): 0.01 ~ 0.03% by weight, boron (B): 0.0015 ~ 0.003% by weight, calcium (Ca): 0.001 ~ 0.004% by weight and the remaining iron (Fe) Reheating the slab plate made of and unavoidable impurities; Finishing hot-rolling the reheated plate to Finishing Delivery Temperature (FDT): 800 ~ 850 ℃; And coiling the hot rolled plate to a CT (Coiling Temperature): cooling to 550 to 600 ° C.
At this time, the slab plate may include phosphorus (P): 0.018 wt% or less, sulfur (S): 0.003 wt% or less, and nitrogen 0.006 wt% or less.
Oil well steel sheet according to an embodiment of the present invention for achieving the other object is carbon (C): 0.22 ~ 0.27% by weight, silicon (Si): 0.15 ~ 0.35% by weight, manganese (Mn): 1.2 ~ 1.6% by weight, Aluminum (Al): 0.01 to 0.03% by weight, Titanium (Ti): 0.01 to 0.03% by weight, boron (B): 0.0015 to 0.003% by weight, calcium (Ca): 0.001 to 0.004% by weight and the remaining iron (Fe) It consists of inevitable impurities and is characterized by having a complex structure comprising acicular ferrite and bainite.
In this case, the steel sheet may include phosphorus (P): 0.018% by weight or less, sulfur (S): 0.003% by weight or less, and nitrogen, 0.006% by weight or less.
Oil well steel sheet according to the present invention and its manufacturing method contains at least 0.2% by weight of carbon (C), and the elements such as titanium (Ti), boron (B), which is a hardenability element is added to the steel pipe material for oil well before QT heat treatment It satisfies the mechanical properties of the widely used API-5CT J55 standard (tensile strength: 517 MPa and yield strength: 379 ~ 552 MPa) and at the same time secures excellent impact characteristics.
1 is a flow chart showing a method for manufacturing a steel sheet for oil wells according to an embodiment of the present invention.
2 is a photograph showing the microstructure of a specimen produced according to Comparative Example 1. Fig.
3 is a photograph showing the microstructure of a specimen produced according to Example 1. Fig.
Advantages and features of the present invention, and methods of achieving the same will become apparent with reference to the embodiments described below in detail in conjunction with 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 steel plate for an oil well and a method for manufacturing the same according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
Oil well steel plate
Oil well steel sheet according to the present invention is the mechanical strength of the API5CT J55 specified by the American Petroleum Institute (API), before the QT (Quenching and Tempering) heat treatment tensile strength (TS): 517 MPa or more and yield strength 379 ~ 552 It aims to ensure the shock value at 0 degreeC: 140 J or more, having MPa.
To this end, the steel sheet for oil wells according to the present invention is carbon (C): 0.22 ~ 0.27% by weight, silicon (Si): 0.15 ~ 0.35% by weight, manganese (Mn): 1.2 ~ 1.6% by weight, aluminum (Al): 0.01 ~ 0.03% by weight, titanium (Ti): 0.01 ~ 0.03% by weight, boron (B): 0.0015 ~ 0.003% by weight, calcium (Ca): 0.001 to 0.004% by weight and the rest of iron (Fe) and inevitable impurities, needle It is characterized by having a complex structure containing a type ferrite and bainite.
At this time, the steel sheet may include phosphorus (P): 0.018% by weight or less, sulfur (S): 0.003% by weight or less and nitrogen, 0.006% by weight or less.
Hereinafter, the role and content of each component included in the oil well steel plate according to the present invention will be described.
Carbon (C)
Carbon (C) is added to secure the strength, it is preferable to be added to less than heavy carbon to secure the strength after QT (Quenching & Tempering) heat treatment.
The carbon is preferably added in 0.22 ~ 0.27% by weight of the total weight of the steel sheet according to the present invention, more preferably 0.25% by weight can be presented. If the carbon content is less than 0.22% by weight, it is difficult to secure sufficient strength. On the contrary, when the content of carbon exceeds 0.27% by weight, there is a problem of deterioration of toughness and deterioration of weldability in electric resistance welding (ERW).
Silicon (Si)
In the case of silicon (Si), the weldability of the steel may be degraded when it is added in excess of 0.35% by weight, and re-heating during the hot rolling process and red scale during the hot rolling may cause problems on the surface quality. After the plating can be inhibited.
On the other hand, Al-Si complex deoxidation is required to control the properties of Mn-oxide and Si-oxide due to the characteristics of the steel sheet according to the present invention, in which manganese (Mn) is added in an amount of 1.2% by weight or more. do. This is because when the resistance resistance welding (ERW) for manufacturing steel pipes within the range of 6 ~ 9 Mn / Si ratio within a certain range will significantly reduce the occurrence of weld cracks.
Therefore, the silicon is preferably added in a content ratio of 0.15 to 0.35% by weight of the total weight of the steel sheet according to the present invention.
Manganese (Mn)
Manganese (Mn) is a solid solution strengthening element that is effective in securing strength by improving the hardenability of steel. In addition, manganese is an austenite stabilizing element, which contributes to the grain refinement of ferrite by delaying the transformation of ferrite and pearlite.
The manganese is preferably added in an amount ratio of 1.2 to 1.6% by weight of the total weight of the steel sheet according to the present invention in consideration of the strength improving effect and the center segregation. If the content of manganese is less than 1.2% by weight, the effect of strengthening solid solution is insufficient. On the contrary, when the content of manganese exceeds 1.6% by weight, the weldability is greatly reduced, and there is a problem in that the ductility of the steel is greatly reduced by the generation of MnS inclusions and the generation of center segregation.
On the other hand, the steel sheet for oil wells according to the present invention is more preferably added to the manganese (Mn) and silicon (Si) in the content range of the following equation (1).
Equation 1: 6? [Mn] / [Si]? 9
(Where [] is the weight percentage of each element)
This is because when the resistance resistance welding (ERW) for manufacturing steel pipes within the range of 6 ~ 9 Mn / Si ratio within a certain range will significantly reduce the occurrence of weld cracks. If the Mn / Si ratio is less than 6 or more than 9, the MnO and SiO 2 oxides are stable at high temperatures, thereby causing a hook crack during electric resistance welding, thereby greatly deteriorating weld quality. .
Aluminum (Al)
Aluminum (Al) is an element that reacts with nitrogen (N) to form fine AlN precipitates and contributes to strength enhancement by grain refinement and precipitation strengthening.
The aluminum is preferably added in an amount ratio of 0.01 to 0.03% by weight of the total weight of the steel sheet according to the present invention. If the content of aluminum is less than 0.01% by weight, it may be difficult to secure sufficient strength because the amount of AlN precipitates is reduced. On the contrary, when the content of aluminum exceeds 0.03% by weight, difficulty occurs in the playing process, thereby lowering the productivity and excessively increasing the yield strength.
Titanium (Ti)
Titanium (Ti) is a strong carbonitride-forming element, and precipitates solid carbon and solid solution nitrogen to improve inaging and workability. In particular, titanium (Ti) prevents the boron (B) from being precipitated as a nitride precipitate, so that boron remains in solid solution in the steel, and boron plays a role in improving the hardenability of the steel.
The titanium is preferably added in 0.01 to 0.03% by weight of the total weight of the steel sheet according to the present invention. If the content of titanium is less than 0.01% by weight, there is a problem that age hardening occurs due to the solid solution carbon and the solid solution nitrogen remaining without precipitation. On the contrary, when the content of titanium exceeds 0.03% by weight, the playability is lowered and there is a problem of increasing the manufacturing cost without any additional effect.
Boron (B)
Boron (B) is a strong hardenable element, and serves to prevent the segregation of phosphorus to improve strength. If segregation of phosphorus occurs, secondary processing brittleness may occur, and thus, boron is added to prevent segregation of phosphorus, thereby increasing resistance to processing brittleness.
The boron is preferably added in 0.0015 ~ 0.003% by weight of the total weight of the steel sheet according to the present invention. If the boron content is less than 0.0015% by weight, the added amount is insignificant and the above effects cannot be properly exhibited. On the contrary, when the boron content is added in excess of 0.003% by weight, the formation of boron oxide may cause a problem of inhibiting the surface quality of the steel sheet.
Calcium (Ca)
Calcium (Ca) forms CaS to lower the sulfur content in the steel, and also reduces MnS segregation, thereby reducing steel cleanliness and grain boundary segregation of sulfur, thereby increasing resistance to reheat cracking.
The calcium is preferably added in 0.001 to 0.004% by weight of the total weight of the steel sheet according to the present invention. If the calcium content is less than 0.001% by weight, the above effects cannot be exerted properly. On the contrary, when the content of calcium exceeds 0.004% by weight, there is a problem of forming inclusions such as CaO.
Phosphorus (P)
Phosphorous (P) is added to inhibit cementite formation and increase strength.
However, phosphorus deteriorates the weldability and causes the final material deviation by slab center segregation. Therefore, in the present invention, the content of phosphorus (P) was limited to 0.018% by weight or less of the total weight of the steel sheet.
Sulfur (S)
Sulfur (S) inhibits the toughness and weldability of steel, and forms an MnS non-metallic inclusion by binding with manganese, thereby generating cracks during steel processing.
Therefore, in the present invention, the content of sulfur (S) was limited to 0.003% by weight or less of the total weight of the steel sheet.
Nitrogen (N)
Nitrogen (N) is an unavoidable impurity, and there is a problem in that solid solution nitrogen increases when a large amount is added, thereby reducing elongation and formability of steel. Therefore, in the present invention, the nitrogen content is limited to 0.006% by weight or less of the total weight of the steel sheet.
Manufacturing method of steel sheet for oil well
1 is a flow chart showing a method for manufacturing a steel sheet for oil wells according to an embodiment of the present invention.
Referring to FIG. 1, the method for manufacturing a steel sheet for an oil well according to 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 to be performed, it is more preferable to perform the slab reheating step (S110) in order to derive the effect, such as re-use of the precipitate.
In the method for manufacturing a steel sheet for oil wells according to the present invention, the slab sheet material of the semi-finished state, which is the target of the hot rolling process, includes carbon (C): 0.22 to 0.27 wt%, silicon (Si): 0.15 to 0.35 wt%, and manganese (Mn): 1.2 to 1.6% by weight, aluminum (Al): 0.01-0.03% by weight, titanium (Ti): 0.01-0.03% by weight, boron (B): 0.0015-0.003% by weight, calcium (Ca): 0.001-0.004% by weight and the remaining iron (Fe) and inevitable impurities.
At this time, the slab plate may include phosphorus (P): 0.018% by weight or less, sulfur (S): 0.003% by weight or less and nitrogen up to 0.006% by weight.
Meanwhile, as described above, the slab plate may include silicon (Si) and manganese (Mn) in a range satisfying Equation 1 below.
Equation 1: 6? [Mn] / [Si]? 9
(Where [] is the weight percentage of each element)
The slab plate having the composition can be obtained through a continuous casting process after obtaining a molten steel of the desired composition through a steelmaking process.
Reheat slab
In the slab reheating step (S110), the slab plate having the composition is reheated to SRT (Slab Reheating Temperature): 1150-1250 ° C. At this time, through the reheating of the slab plate, inventory of segregated components and inventory of precipitates may be generated during casting.
If the slab reheating temperature (SRT) is less than 1150 ° C., the segregated components during casting may not be sufficiently reused, and precipitates such as titanium (Ti) may not be sufficiently dissolved. On the contrary, when the slab reheating temperature (SRT) exceeds 1250 ° C, the austenite grain size may increase, resulting in coarsening of the final microstructure, and it may be difficult to secure the strength. have.
Hot rolling
In the hot rolling step (S120), the reheated plate is hot rolled. Hot rolling step (S120) in the present invention may be carried out by primary rolling and secondary rolling.
In the first rolling process, the reheated sheet is first roughly rolled. At this time, the rough rolling temperature (RDT) of the primary rolling may present 950 ~ 1050 ℃, but is not limited thereto. If the rough rolling temperature (FDT) exceeds 1050 ° C, it may be difficult to secure a sufficient reduction ratio.
In the secondary rolling process, the first rolled sheet is secondary rolled in the austenite uncrystallized region. At this time, the secondary rolling can use a plurality of rolling passes.
Finishing rolling temperature (FDT) of secondary rolling is preferably carried out at 800 ~ 850 ℃. If the finishing rolling temperature of the secondary rolling is less than 8000 ° C., abnormal reverse rolling occurs to form a non-uniform structure, which can greatly reduce low-temperature impact toughness. On the contrary, when the finishing rolling temperature of secondary rolling exceeds 850 ° C., the ductility and toughness are excellent, but there is a problem that the strength is sharply lowered.
At this time, the secondary rolling may be performed so that the cumulative rolling reduction in the non-recrystallized region is 40 to 60%. If the cumulative reduction ratio of the secondary rolling is less than 40%, it is difficult to secure a uniform and fine structure, which may result in severe variations in strength and impact toughness. On the other hand, when the cumulative reduction rate of the secondary rolling exceeds 60%, there is a problem that the rolling process time is prolonged and the fishy property is deteriorated.
Cooling / Winding
In the cooling / winding step (S130), the hot rolled sheet is cooled by winding to CT (Coiling Temperature): 550 ° C to 600 ° C.
In the present invention, the cooling process by cooling the rolled plate to 550 ℃ ~ 600 ℃ by forced cooling method such as water cooling, to suppress the grain growth of the steel sheet to form a matrix having fine grains to secure high strength and high toughness Is carried out. Cooling rate may be about 1 ~ 100 ℃ / sec, but is not limited thereto.
If the winding temperature CT is less than 550 ° C., the manufacturing cost of the steel increases, and sufficient strength can be secured, but it is difficult to secure high toughness. On the contrary, when the winding temperature CT exceeds 600 ° C., it may be difficult to secure sufficient strength.
Oil well steel sheet produced by the above process may have a complex structure including acicular ferrite and bainite.
In addition, the hot rolled steel sheet produced by the above method may have mechanical properties of API 5CT J55 standard (tensile strength: 517 MPa or more, yield strength: 379 ~ 552 MPa) widely used as a steel pipe material for oil wells.
In addition, the steel sheet for oil wells according to the present invention can be upgraded to various oil grade steel grades through heat treatment, QT (Quenching and Tempering).
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.
Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.
1. Preparation of specimens
Specimens according to Examples 1 to 3 and Comparative Examples 1 to 3 were prepared under the compositions shown in Table 1 and the hot rolling process conditions described in Table 2.
[Table 1] (unit:% by weight)
[Table 2]
2. Evaluation of mechanical properties
Table 3 shows the mechanical property evaluation results for the specimen prepared according to Examples 1 to 3 and Comparative Examples 1 to 3. At this time, the impact value at 0 ° C was measured by using the specimens according to Examples 1 to 3 and Comparative Examples 1 to 3 with a thickness of 10 mm.
[Table 3]
Referring to Tables 1 to 3, in the case of specimens prepared according to Examples 1 to 3, the tensile strength (TS) corresponding to the target API 5CT J55 standard (TS): 517 MPa or more and the yield strength (YS): 379 ~ While satisfying 552 MPa, the impact value at 0 ° C .: 140 J or more was shown, indicating that the low-temperature impact toughness was excellent.
On the other hand, compared with the specimen prepared according to Example 1, most of the alloying components are added in a similar content, but titanium (Ti) and boron (B) are not added, niobium (Nb) is further added, and finish rolling temperature ( FDT) and the winding temperature (CT) of the specimen prepared according to Comparative Example 1 outside the temperature range proposed in the present invention, the target tensile strength (TS) and yield strength (YS) was satisfied, but at 0 ℃ It can be seen that the impact value of represents 88 J that falls short of the target value.
In addition, compared to the specimen prepared according to Example 1, most of the alloying components are added in a similar content, but titanium (Ti) is not added, niobium (Nb) is further added, finish rolling temperature (FDT) and winding temperature In the case of specimens prepared according to Comparative Example 2 (CT) outside the temperature range suggested by the present invention, the target tensile strength (TS) and the yield strength (YS) were satisfied, but the impact value at 0 ° C was the target. It can be seen that 130 J is below the value.
In addition, compared to the specimen prepared according to Example 1, most of the alloying components are added in a similar content, but boron (B) is not added, niobium (Nb) is further added, which is outside the winding temperature suggested by the present invention. In the case of the specimen prepared according to Comparative Example 3, the target tensile strength (TS) was satisfied, but it can be seen that the yield strength (YS) and the impact value at 0 ° C have 589 MPa and 93J, which deviate from the target value. .
2 is a photograph showing the microstructure of the specimen prepared according to Comparative Example 1, Figure 3 is a photograph showing the microstructure of the specimen prepared according to Example 1.
Referring to FIG. 2, it can be seen that the microstructure of the specimen prepared according to Comparative Example 1 is composed of a composite structure including ferrite and pearlite.
On the other hand, referring to Figure 3, it can be seen that the microstructure of the specimen prepared according to Example 1 consists of a complex structure including acicular ferrite and bainite.
At this time, the microstructure of the specimen prepared according to Example 1 could be made of a composite structure containing acicular ferrite and bainite, instead of adding a precipitation enhancing element such as niobium (Nb), titanium (Ti) and In addition to adding hardenable elements, such as boron (B), it is understood that this is due to strict control of the finish rolling temperature (FDT) and the winding temperature (CT). Through this, it was confirmed that the specimen prepared according to Example 1 satisfied the API 5CT J55 standard and at the same time excellent impact properties.
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 (10)
Finishing hot-rolling the reheated plate to Finishing Delivery Temperature (FDT): 800 ~ 850 ℃; And
The hot rolled sheet material CT (Coiling Temperature): cooling step up to 550 ~ 600 ℃; winding steel sheet manufacturing method comprising a.
The slab plate is
A method for manufacturing a steel sheet for oil wells, comprising silicon (Si) and manganese (Mn) in a range satisfying Equation 1 below.
Equation 1: 6? [Mn] / [Si]? 9
(Where [] is the weight percentage of each element)
The slab plate
Phosphorus (P): 0.018% by weight or less, sulfur (S): 0.003% by weight or less and 0.006% by weight or less of a method for producing a steel sheet for an oil well.
The step of reheating the slab
Slab Reheating Temperature (SRT): 1150 ~ 1250 ℃ characterized in that the steel sheet manufacturing method for oil wells.
The hot rolling step
Roughly rolling the reheated sheet at RDT (Roughing Delivery Temperature): 950 to 1050 ° C.,
And rolling the roughly rolled sheet material in an austenite uncrystallized region secondarily.
A steel plate for oil wells, characterized by having a composite structure containing acicular ferrite and bainite.
The steel sheet
A steel sheet for oil wells comprising silicon (Si) and manganese (Mn) in a range satisfying Equation 1 below.
Equation 1: 6? [Mn] / [Si]? 9
(Where [] is the weight percentage of each element)
The steel sheet
Phosphorus (P): 0.018% by weight or less, sulfur (S): 0.003% by weight or less, characterized in that it contains less than 0.006% by weight of nitrogen.
The steel sheet
Tensile strength (TS): 517 MPa or more and Yield strength (YS): 379 ~ 552 MPa characterized in that the steel sheet having a.
The steel sheet
Impact value at 0 ° C: Oil well steel plate, characterized in that it has a 140 J or more.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103045944A (en) * | 2012-12-27 | 2013-04-17 | 江苏长强钢铁有限公司 | High-toughness steel for petroleum casing and manufacturing method of petroleum casing |
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2011
- 2011-07-28 KR KR1020110075258A patent/KR20130013547A/en active Search and Examination
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103045944A (en) * | 2012-12-27 | 2013-04-17 | 江苏长强钢铁有限公司 | High-toughness steel for petroleum casing and manufacturing method of petroleum casing |
| CN103045944B (en) * | 2012-12-27 | 2015-11-18 | 江苏长强钢铁有限公司 | High toughness petroleum casing pipe steel and petroleum casing pipe manufacture method |
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