KR101797319B1 - Hot rolled steel sheet having excellent weldability and ductility for pipe and method for manufacturing the same - Google Patents
Hot rolled steel sheet having excellent weldability and ductility for pipe and method for manufacturing the same Download PDFInfo
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- KR101797319B1 KR101797319B1 KR1020150184493A KR20150184493A KR101797319B1 KR 101797319 B1 KR101797319 B1 KR 101797319B1 KR 1020150184493 A KR1020150184493 A KR 1020150184493A KR 20150184493 A KR20150184493 A KR 20150184493A KR 101797319 B1 KR101797319 B1 KR 101797319B1
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- rolled steel
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- pipe
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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
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
- B21C37/06—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of tubes or metal hoses; Combined procedures for making tubes, e.g. for making multi-wall tubes
- B21C37/08—Making tubes with welded or soldered seams
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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
- 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
- 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
- C21D2211/001—Austenite
Abstract
An aspect of the present invention is a steel sheet comprising, by weight, 0.4 to 0.6% of C, 0.1 to 0.5% of Si, 14 to 26% of Mn, 0.01 to 5.0% of Cr, 0.001 to 0.03% of P, , The balance Fe and other unavoidable impurities,
The present invention relates to a hot-rolled steel sheet for pipes having excellent weldability and elongation, including austenite of 95% or more by area.
Description
The present invention relates to a hot-rolled steel sheet for pipes excellent in weldability and elongation, and a method for producing the same.
In general, seamless pipes have been used for mining pipes used for crude oil and gas development.
In recent years, oil majors have attempted to use simpler and less costly drilling methods to reduce the cost of crude oil and gas development by applying the expansion technique of pipe for mining. The mining pipe is partially applied up to 5km from the upper part of the oil field to the lower part.
It is known that excellent dewaxing ability can be obtained by high uniform elongation and work hardening index, and usually seamless pipes are mainly used. However, the seamless pipe is very expensive compared to electric resistance welding (ERW) pipe, has a large thickness deviation and roundness, and recently there is a movement to replace steel pipe for expansion with ERW pipe.
Accordingly, oil major companies are looking for suitable materials to replace steel pipes for distribution with electrical resistance welded (ERW) pipes, and have a high uniform elongation and work hardening index at the center. In addition, several km of pipe should exhibit uniform overall ductility.
As a method for obtaining a high uniform elongation and a work hardening index, by increasing the dislocation density of the steel itself, the driving elongation is increased by tensile deformation and the uniform elongation is increased. Ordinary carbon steel forms ferrite and perlite, ferrite and bainite Thereby causing a large amount of work hardening in the light pearlite and bainite to induce a high work hardening index. However, the conventional techniques have a problem in that it is difficult to simultaneously satisfy a high uniform elongation and a high work hardening index.
One aspect of the present invention is to provide a hot-rolled steel sheet for pipes having excellent weldability and elongation, and a method for producing the same. The hot-rolled steel sheet according to one aspect of the present invention can be preferably applied to a simple and low-cost drilling method in oil and gas mining environments.
On the other hand, the object of the present invention is not limited to the above description. It will be understood by those of ordinary skill in the art that there is no difficulty in understanding the additional problems of the present invention.
An aspect of the present invention is a steel sheet comprising, by weight, 0.4 to 0.6% of C, 0.1 to 0.5% of Si, 14 to 26% of Mn, 0.01 to 5.0% of Cr, 0.001 to 0.03% of P, , The balance Fe and other unavoidable impurities,
The present invention relates to a hot-rolled steel sheet for pipes having excellent weldability and elongation, including austenite of 95% or more by area.
In another aspect of the present invention, there is provided a method for manufacturing a semiconductor device, comprising the steps of: 0.4 to 0.6% of C, 0.1 to 0.5% of Si, 14 to 26% of Mn, 0.01 to 5.0% of Cr, 0.001 to 0.03% 0.02% or less, the balance Fe and other unavoidable impurities at 900 to 1200 占 폚;
Hot rolling the heated slab to a finish rolling temperature of 750 to 1050 占 폚 to obtain a hot rolled steel sheet; And
Cooling the hot-rolled steel sheet at a temperature of 500 to 600 ° C; And a method of producing a hot-rolled steel sheet for pipes having excellent weldability and elongation.
In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof can be understood in more detail with reference to the following specific embodiments.
INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a hot-rolled steel sheet excellent in electrical resistance weldability and uniform elongation, which is advantageously applicable to a simple and low-cost drilling method in oil and gas mining environments.
1 is a photograph showing the microstructure of Inventive Example 1. Fig.
2 is a photograph showing the microstructure of Comparative Example 1. Fig.
3 is a graph showing XRD results of Inventive Example 1. FIG.
4 is a graph showing a tensile curve of Inventive Example 1. Fig.
Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.
The present inventors have recognized that electrical resistance weldability and uniform elongation should be improved in order to apply an electric resistance welded pipe rather than a seamless pipe to oil and gas mining environments.
As a result, it has been confirmed that the aforementioned problems can be solved by appropriately controlling the alloy composition, and the present invention has been accomplished.
Hereinafter, a hot-rolled steel sheet for pipes having excellent weldability and elongation according to one aspect of the present invention will be described in detail.
According to one aspect of the present invention, there is provided a hot-rolled steel sheet for pipes having excellent weldability and elongation, comprising 0.4 to 0.6% of C, 0.1 to 0.5% of Si, 14 to 26% of Mn, 0.01 to 5.0% : 0.001 to 0.03%, S: 0.02% or less, the balance Fe and other unavoidable impurities, and the microstructure contains austenite of 95% or more by area.
First, the alloy composition of the hot-dip galvanized steel sheet for superior rolling resistance and uniform elongation according to one aspect of the present invention will be described in detail. Hereinafter, the unit of each alloy element is% by weight.
C: 0.4 to 0.6%
Carbon (C) is an element that stabilizes austenite and increases the strength of a steel sheet. Carbon can serve to lower Ms and Md, which are transformations of austenite, epsilon-martensite or alpha -martensite by cooling or processing.
When the C content is less than 0.4% by weight, the austenite is not stable enough to obtain stable austenite at a cryogenic temperature, and it is easily transformed into ε-martensite or α-martensite by external stress to cause organic transformation, There is a problem that it can be reduced. On the other hand, when the C content exceeds 0.6% by weight, the toughness of the steel sheet may be deteriorated rapidly due to the precipitation of carbide, and the strength of the steel sheet may become excessively high and the workability of the steel sheet may be reduced. Therefore, the C content is preferably 0.4 to 0.6%.
Si: 0.1 to 0.5%
Silicon (Si) forms a low melting point oxide such as Mn2SiO4 during electric resistance welding, so that the oxide is easily discharged at the time of welding.
If the Si content is less than 0.1%, there is a cost problem in steelmaking. On the other hand, when the Si content exceeds 0.5%, the amount of SiO2, which is a high melting point oxide other than Mn2SiO4, increases, . Therefore, the Si content is preferably 0.1 to 0.5%.
Mn: 14 to 26%
Manganese (Mn) is an element that stabilizes austenite. Manganese may be included in an amount of 14 wt% or more to stabilize the austenite phase at a cryogenic temperature.
When the content of manganese is less than 14%, 竜 -martensite, which is a metastable phase, is formed in the case of a steel sheet having a small carbon content, and can be transformed into? -Martensite easily by the processing organic transformation at an extremely low temperature. . Further, in the case of a steel sheet in which the content of carbon is increased in order to secure the toughness of the steel sheet, the physical properties of the steel sheet can be drastically reduced owing to the precipitation of carbide.
If the content of manganese exceeds 26% by weight, the economical efficiency of the steel sheet may be reduced due to an increase in production cost.
Cr: 0.01 to 5.0%
Chromium (Cr) stabilizes austenite up to the appropriate amount of added amount, improves impact toughness at low temperature, and increases the strength of steel by solidification in austenite. Chromium is also an element that improves the corrosion resistance of steel. However, chromium is a carbide element, and it is also an element that reduces carbothermic transition at austenitic grain boundaries to reduce cold shock. Therefore, the content of chromium added in the present invention is preferably determined in consideration of the relationship with carbon and other elements to be added together.
When the Cr content is less than 0.01%, the above-mentioned effect is not sufficient. When the Cr content exceeds 5%, it is difficult to effectively inhibit carbide formation at the austenite grain boundary due to excessive chromium content. Is reduced.
P: 0.001 to 0.03%
Phosphorus (P) is an element favorable for improving the strength and corrosion resistance of steel.
If the P content is less than 0.001%, the above-mentioned effect is not sufficient and a load of the steelmaking process may occur. On the other hand, when the P content exceeds 0.03 wt%, the impact toughness of the steel sheet can be greatly reduced.
S: not more than 0.02%
Sulfur (S) is an element which is present in the steel sheet as a trace element and is likely to form coarse inclusions. It is preferably added as low as possible because it promotes toughness and crack propagation due to internal defects due to stress concentration around the inclusions. However, since the austenite phase has high toughness, internal defects due to MnS inclusions can be suppressed. Therefore, it is preferable that the content of S is determined depending on the content of Mn. If the content of S exceeds 0.02% by weight, it may be difficult to suppress hydrogen embrittlement due to excessive MnS inclusions.
The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.
As the steel sheet having the above-mentioned component system, it is necessary to further restrict the kind and shape of the internal structure as a preferable condition for exhibiting excellent uniform elongation after shrinkage and excellent drivability.
The main structure of the steel sheet of the present invention is preferably an austenite structure and contains 95% or more of the area fraction. Austenite, which is a representative soft structure showing soft fracture at low temperatures, is an essential microstructure for ensuring low-temperature toughness, and preferably contains 95% or more of an area fraction. When the austenite is less than 95% The lower limit is preferably limited to 95%.
By satisfying the above-mentioned component system and microstructure, it is excellent in electric resistance weldability, excellent in uniform elongation and work hardening index, and can be substituted for existing pipe for diffusing.
At this time, the hot-rolled steel sheet of the present invention may have a yield strength of 400 MPa or more, a uniform elongation of 50% or more, and a work hardening index of 0.2 or more. By ensuring high uniform elongation and work hardening index, a high expansion ratio can be secured.
Further, the hot rolled steel sheet of the present invention may have a expansion ratio of 10% or more after electric resistance welding.
Hereinafter, a method for manufacturing a hot-rolled steel sheet for pipes having excellent weldability and elongation, which is another aspect of the present invention, will be described.
In another aspect of the present invention, there is provided a method of manufacturing a hot-rolled steel sheet for pipes having excellent weldability and elongation, comprising the steps of: heating a slab satisfying the above-described alloy composition at 900 to 1200 ° C; Hot rolling the heated slab to a finish rolling temperature of 750 to 1050 占 폚 to obtain a hot rolled steel sheet; And cooling the hot-rolled steel sheet at a temperature of 500 to 600 ° C; .
Slab heating step
The slab satisfying the above alloy composition is heated at 900 to 1200 占 폚. The heating process of the slab is a process of heating the steel so as to smoothly perform the subsequent rolling process and sufficiently obtain the physical properties of the target steel sheet, so that the heating process should be performed within an appropriate temperature range in accordance with the purpose. Further, in the step of heating the slab, it is preferable to uniformly heat the precipitation-type elements in the steel sheet so that the precipitation-type elements are sufficiently dissolved, and prevent coarse grains from being excessively heated.
If the heating temperature is lower than 900 캜, various carbides generated during casting may not be sufficiently solidified, and brittleness due to intergranular carbides may be generated. On the other hand, if the heating temperature exceeds 1200 ° C, the austenite grains may be coarsened and the strength may be lowered.
Rolling step
The hot slab is hot-rolled to obtain a hot-rolled steel sheet at a finishing rolling temperature of 750 to 1050 ° C. Thereby effectively securing low-temperature toughness by refining the crystal grains effectively.
If the finish rolling temperature is less than 750 캜, the uniform elongation of the steel sheet at room temperature may be reduced due to the grain boundary precipitation of a large amount of carbides, and the microstructure may be pancaked to cause non-uniform stretching due to tissue anisotropy. In addition, finishing mill equipment load problems may occur.
On the other hand, when the finish rolling temperature exceeds 1050 DEG C, crystal grains are vigorously grown and crystal grains are easily coarsened, whereby the strength of the steel sheet can be reduced.
Cooling and Coiling step
The hot-rolled steel sheet is cooled and then rolled at a temperature of 500 to 600 ° C.
At this time, the cooling can be performed at a cooling rate of 10 ° C / s or higher to a cooling termination temperature of 600 ° C or lower.
If the cooling rate is less than 10 占 폚 / s or the cooling termination temperature is 600 占 폚 or more, carbon is not solidified and excess carbides are precipitated, thereby reducing the uniform elongation of the steel sheet.
The cooling rate may be more preferably 20 ° C / s or higher, and the upper limit may be limited to 50 ° C / s in consideration of facility load. It is preferable that the hot-rolled steel sheet is rolled in a temperature range of 500 to 600 ° C.
The hot-rolled steel sheet produced by the above-described production method can contain austenite in an area fraction of 95% or more, has a yield strength of 400 MPa or more, a uniform elongation of 50% or more and a work hardening rate of 0.2 or more.
Meanwhile, the manufacturing method of the present invention may further include a step of welding the rolled hot-rolled steel sheet by electrical resistance welding.
For example, the rolled hot-rolled steel sheet is planarized by leveling the rounded coil, and both ends are cut out. Then, when the pipe is formed into a round shape using a roller, Can be manufactured. The pipe thus produced may have a ductility rate of 10% or more.
Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.
( Example )
The slab having the composition shown in the following Table 1 was heated at 1160 占 폚, followed by finish rolling at 900 占 폚. Thereafter, the hot-rolled steel sheet was cooled to a temperature of 600 ° C at a cooling rate of 20 ° C / s and wound at 550 ° C. Thereafter, a hot-rolled steel sheet having a thickness of 3 mm and an outer diameter of 89.1 mm was prepared by means of an electric resistance welding method. The yield strength, the uniform elongation, the work hardening index and the pipe expansion ratio were measured for each manufactured steel pipe, and the results are shown in Table 2 below.
The yield strength, the uniform elongation and the work hardening index of each steel tube were measured at room temperature using a tensile tester. The test was carried out in accordance with the conventional ASTM A370. In addition, the Full Body Flaring Test was performed to measure the expansion rate.
As shown in Tables 1 and 2, in the case of Inventive Examples 1 and 2, it was confirmed that after heat treatment, a yield strength of 400 MPa or more, a work hardening index of 0.2 or more, a uniform elongation of 50% or more and a pipe expansion rate of 10% have.
On the other hand, in the case of Comparative Examples 1 and 2, the yield strength and the pipe expansion ratio were similar to those of inventive examples 1 and 2, but the uniform elongation was very low compared to Examples 1 and 2 and the work hardening index Can be confirmed.
Fig. 1 shows a tissue photograph of Inventive Example 1, wherein the microstructure is a 100% austenite structure, which can be confirmed by the XRD results of Fig. This is in contrast to Comparative Example 1 shown in Fig. 2, which is a typical ferrite-bainite structure. 4 is a graph showing the tensile curve of Inventive Example 1. Fig. In the case of Inventive Example 1, it can be seen that because of austenitic structure, a very high uniform elongation and work hardenability are obtained in spite of yield strength and expansion ratio similar to those of Comparative Example.
It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.
Claims (7)
The microstructure contains more than 95% area percent austenite,
Hot-rolled steel for pipes with excellent weldability and elongation with a ductility rate of 10% or more after electric resistance welding.
Wherein the hot-rolled steel sheet has a yield strength of 400 MPa or more.
Wherein the hot-rolled steel sheet has a uniform elongation of 50% or more and a work hardening index of 0.2 or more.
Hot rolling the heated slab to a finish rolling temperature of 750 to 1050 占 폚 to obtain a hot rolled steel sheet; And
Cooling the hot-rolled steel sheet at a temperature of 500 to 600 ° C; Wherein the hot-rolled steel sheet has excellent weldability and elongation.
Wherein the cooling is carried out at a cooling rate of 10 占 폚 / s or more to a cooling end temperature of 600 占 폚 or less.
Winding the hot rolled steel sheet by electrical resistance welding to form a pipe; Wherein the hot-rolled steel sheet has an excellent weldability and elongation.
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| Application Number | Priority Date | Filing Date | Title |
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| KR1020150184493A KR101797319B1 (en) | 2015-12-23 | 2015-12-23 | Hot rolled steel sheet having excellent weldability and ductility for pipe and method for manufacturing the same |
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| KR1020150184493A KR101797319B1 (en) | 2015-12-23 | 2015-12-23 | Hot rolled steel sheet having excellent weldability and ductility for pipe and method for manufacturing the same |
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| KR20170075822A KR20170075822A (en) | 2017-07-04 |
| KR101797319B1 true KR101797319B1 (en) | 2017-11-14 |
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| EP3677700B1 (en) * | 2017-09-01 | 2023-05-10 | JFE Steel Corporation | High-mn steel and production method therefor |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2015012357A1 (en) | 2013-07-26 | 2015-01-29 | 新日鐵住金株式会社 | High-strength steel material for oil well use, and oil well pipe |
| JP7017949B2 (en) * | 2018-03-02 | 2022-02-09 | 株式会社ディスコ | Processing equipment |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2015012357A1 (en) | 2013-07-26 | 2015-01-29 | 新日鐵住金株式会社 | High-strength steel material for oil well use, and oil well pipe |
| JP7017949B2 (en) * | 2018-03-02 | 2022-02-09 | 株式会社ディスコ | Processing equipment |
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