KR20120132835A - Hot-rolled steel sheet and method of manufacturing the hot-rolled steel sheet - Google Patents
Hot-rolled steel sheet and method of manufacturing the hot-rolled steel sheet Download PDFInfo
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- KR20120132835A KR20120132835A KR1020110051195A KR20110051195A KR20120132835A KR 20120132835 A KR20120132835 A KR 20120132835A KR 1020110051195 A KR1020110051195 A KR 1020110051195A KR 20110051195 A KR20110051195 A KR 20110051195A KR 20120132835 A KR20120132835 A KR 20120132835A
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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
- 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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- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
The present invention relates to a hot-rolled steel sheet and a method for manufacturing the same, more specifically, excellent heat treatment characteristics by controlling the alloy components, and has a low yield ratio before heat treatment by growing the grain size to a certain level through high temperature rolling and winding After the heat treatment relates to a hot rolled steel sheet satisfying the API 5CT P110 (tensile strength: 862MPa or more and yield strength: 758 ~ 965MPa) and its manufacturing method.
Oil well steel pipes are steel pipes used for drilling oil or gas. Such oil well steel pipes are usually manufactured by piping hot rolled steel sheets.
In general, hot rolled steel sheet is manufactured through a slab reheating process, hot-rolling process, cooling / coiling process, and the like.
In the slab reheating process, the semi-finished slab plate is reheated.
In the hot rolling process, the slab sheet is hot rolled to a final thickness at a high temperature using a rolling roll.
In the cooling / winding process, the hot rolled plate is cooled and wound to a coiling temperature (CT).
An object of the present invention is to meet the API 5CT J55 (tensile strength: 517MPa or more and yield strength: 379 ~ 552 MPa) before QT (Quenching & Tempering) heat treatment through alloy composition control and hot rolling process condition control, and after heat treatment, the API It is to provide a method for manufacturing a hot rolled steel sheet that satisfies the 5CT P110 (tensile strength: 862MPa or more and yield strength: 758 ~ 965MPa).
Another object of the present invention is to provide a hot rolled steel sheet produced by the above production method.
Hot rolled steel sheet manufacturing method according to an embodiment of the present invention for achieving the above 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 ~ 0.04% 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 slab plate made of inevitable impurities FDT (Finishing Delivery Temperature): hot rolling step of finishing rolling to 850 ℃ ~ 910 ℃; And a cooling / winding step of winding the hot rolled sheet to a coil temperature (CT): 640 to 720 ° C.
In this case, the slab plate may further include phosphorus (P): 0.018% by weight or less, sulfur (S): 0.003% by weight or less, and nitrogen (N): 0.006% by weight or less.
Hot-rolled 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 0.04 wt%, Titanium (Ti): 0.01 to 0.03 wt%, Boron (B): 0.0015 to 0.003 wt%, Calcium (Ca): 0.001 to 0.004 wt% and the rest of iron (Fe) It is composed of inevitable impurities, and characterized in that the microstructure has a complex structure of ferrite and pearlite.
In this case, the steel sheet may further include phosphorus (P): 0.018% by weight or less, sulfur (S): 0.003% by weight or less, and nitrogen (N): 0.006% by weight or less.
The hot rolled steel sheet according to the present invention and a method for manufacturing the same are tensile properties that are mechanical properties of API 5CT J55 defined by the American Petroleum Institute (API) before QT (Quenching & Tempering) heat treatment through alloy composition control and hot rolling process condition control. Strength: 517 MPa or more and yield strength: 379 ~ 552 MPa. After heat treatment, the mechanical properties of API 5CT P110 are tensile strength: 862 MPa or more and yield strength: 758 ~ 965 MPa.
1 is a flowchart schematically showing a method for manufacturing a hot rolled steel sheet according to an embodiment of the present invention.
2 is a schematic diagram showing a cooling process applied to Example 1. FIG.
3 is a microstructure photograph of a hot rolled specimen prepared by the method according to Example 2, showing the microstructure before QT heat treatment.
4 is a microstructure photograph of a hot rolled specimen prepared by the method according to Example 2, showing the microstructure after QT heat treatment.
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.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a hot-rolled steel sheet according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
Hot rolled steel
Hot rolled steel sheet according to the present invention is a mechanical property of the API 5CT J55 specified by the American Petroleum Institute (API) before the QT (Quenching & Tempering) heat treatment through the control of alloy components and hot rolling process conditions: tensile strength of at least 517MPa And yield strength: 379 ~ 552 MPa, and after heat treatment, the tensile strength of the mechanical properties of API 5CT P110: 862 MPa or more and yield strength: 758 ~ 965 MPa.
To this end, the hot rolled steel sheet 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 ~ 0.04% 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 remaining iron (Fe) and inevitable impurities, fine The tissue is characterized by having a complex structure of ferrite and pearlite.
In this case, the steel sheet may further include phosphorus (P): 0.018% by weight or less, sulfur (S): 0.003% by weight or less, and nitrogen (N): 0.006% by weight or less.
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 to secure the strength.
The carbon is preferably added in 0.22 ~ 0.27% by weight of the total weight of the hot rolled steel sheet according to the present invention. If the carbon content is less than 0.22% by weight, it may be difficult to secure sufficient strength. On the contrary, when the content of carbon exceeds 0.27% by weight, it may cause a decrease in toughness, and there is a problem in that weldability is reduced during electric resistance welding (ERW).
Silicon (Si)
Silicon (Si) is added to enhance the function and solid solution of the deoxidizer to remove oxygen in the steel.
The silicon is preferably added in an amount of 0.15 to 0.35% by weight of the total weight of the hot rolled steel sheet according to the present invention. If the silicon content is less than 0.15% by weight, the deoxidation effect due to the addition of silicon is insufficient and the solid solution strengthening effect may be insignificant. On the contrary, when the silicon content exceeds 0.35% by weight, the weldability is degraded, and a red scale is generated during reheating and hot rolling, which may cause a problem on the surface quality and may inhibit the plating property after welding. .
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 delays ferrite and pearlite transformation and contributes to grain refinement of ferrite.
The manganese is preferably added in an amount ratio of 1.2 to 1.6% by weight of the total weight of the hot-rolled 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 solid solution strengthening may be insignificant. On the contrary, when the content of manganese exceeds 1.6% by weight, not only the weldability is greatly lowered, but also the ductility of the steel sheet is greatly reduced by the generation of MnS inclusions and the generation of center segregation.
On the other hand, the hot rolled steel sheet according to the present invention is more preferably added to the manganese (Mn) and silicon (Si) in the content range of the following formula (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 added for deoxidation during steelmaking.
The aluminum is preferably added in 0.01 ~ 0.04% by weight of the total weight of the hot rolled steel sheet according to the present invention, more preferably 0.03% by weight can be presented. When the content of aluminum is less than 0.01% by weight, sufficient deoxidation effect cannot be obtained. On the contrary, when the content of aluminum exceeds 0.04% by weight, there is a problem of inhibiting weldability.
Titanium (Ti)
Titanium (Ti) is added for the purpose of depositing solid solution carbon and solid solution nitrogen to improve processability. In particular, titanium (Ti) is added in order to deposit solid solution carbon and solid solution nitrogen with TiC and TiN to secure inferiority and processability.
The titanium is preferably added in 0.01 ~ 0.03% by weight of the total weight of the hot rolled steel sheet according to the present invention, more preferably can present 0.02% by weight.
If the titanium content is less than 0.01% by weight, the solid solution strengthening effect of titanium addition may not be properly exhibited. On the contrary, when the content of titanium exceeds 0.03% by weight, TiN precipitates are coarsened, thereby reducing the effect of inhibiting grain growth, and may cause surface defects of the steel sheet to be manufactured.
Boron (B)
Boron (B) is an element that segregates in austenite grains and stabilizes austenite by lowering grain boundary energy, thereby improving hardenability of steel.
The boron is preferably added in 0.0015 ~ 0.003% by weight of the total weight of the hot rolled steel sheet according to the present invention, more preferably 0.002% by weight can be presented.
If the content of boron is less than 0.0015% by weight, it is not possible to properly exhibit the effect of improving the hardenability according to the addition of boron. On the contrary, when a large amount of boron exceeds 0.003% by weight, there is a problem of rapidly increasing brittleness of steel.
Calcium (Ca)
Calcium lowers the sulfur content in the steel by forming CaS, 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 hot rolled steel sheet according to the present invention, more preferably 0.003% by weight can be presented.
If the calcium content is less than 0.001% by weight, the control effect of the MnS inclusions may be insignificant. On the contrary, when the content of calcium exceeds 0.004% by weight, inclusions such as CaO are formed and there is a problem of inhibiting playability.
Phosphorus (P)
Phosphorous (P) is added to inhibit cementite formation and increase strength.
However, since phosphorus deteriorates weldability and causes final material variation by slab center segregation, the phosphorus (P) is limited to 0.018% by weight or less of the total weight of the hot rolled steel sheet according to the present invention. It is desirable to.
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, the content of sulfur (S) is preferably limited to 0.003% by weight or less of the total weight of the hot rolled steel sheet according to the present invention.
Nitrogen (N)
Nitrogen (N) is an unavoidable impurity. When a large amount is added, solid solution nitrogen increases, which degrades the impact property and elongation of the steel sheet and greatly reduces the toughness of the welded part. Therefore, nitrogen is preferably limited to 60 ppm or less of the total weight of the hot rolled steel sheet according to the present invention.
Hot-rolled steel sheet manufacturing method
1 is a flowchart schematically showing a method of 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 includes a slab reheating step S110, a hot rolling step S120, a cooling / winding step S130, and a QT (Quenching & Tempering) heat treatment step S140. In this case, the slab reheating step S110 may be omitted as necessary.
In the method for manufacturing a hot rolled steel sheet 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): 0.01-0.04% 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.
In this case, the slab plate may further include phosphorus (P): 0.018% by weight or less, sulfur (S): 0.003% by weight or less, and nitrogen (N): 0.006% by weight or less.
On the other hand, the slab sheet material preferably contains silicon (Si) and manganese (Mn) in a range satisfying the following equation (1).
Equation 1: 6? [Mn] / [Si]? 9
(Where [] is the weight percentage of each element)
Reheat slab
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.
The slab plate may be obtained through a continuous casting process after obtaining molten steel of a desired composition through a steelmaking process. At this time, in the slab reheating step (S110) through the reheating of the slab plate obtained through the continuous casting process, re-use segregated components during casting.
If the slab reheating temperature (SRT) is less than 1150 ° C., there is a problem in that the segregated components are not reusable sufficiently during casting. On the other hand, if the SRT reheating temperature (SRT) exceeds 1250 ° C, the austenite crystal grain size may increase and the strength of the steel sheet may be difficult to secure, and the manufacturing cost of the steel sheet may be increased due to the excessive heating process.
Hot rolling
In the hot rolling step (S120), the slab plate is finished rolled to FDT (Finishing Delivery Temperature): 850 ~ 910 ℃.
If the finish rolling temperature (FDT) exceeds 910 ° C, the austenite grains are coarsened, thereby making it difficult to secure the strength. On the contrary, when the finishing rolling temperature is too low below 850 ° C, problems such as generation of a mixed structure due to abnormal reverse rolling may occur.
Cooling / Winding
In the cooling / winding step (S130), the hot rolled sheet is wound up by cooling to CT (Coiling Temperature): 640 ° C to 720 ° C.
In the cooling process of the present invention, the hot rolled sheet is cooled to 640 ° C to 720 ° C through water cooling or the like, thereby suppressing grain growth of the steel sheet to form a matrix structure having fine ferrite grains, and also forming a pearlite structure. High strength and high toughness can be ensured. At this time, the cooling rate may be about 1 ~ 100 ℃ / sec, but is not limited thereto.
If the winding temperature CT exceeds 720 ° C., it may be difficult to secure sufficient strength. On the contrary, when the coiling temperature CT is less than 640 ° C., the manufacturing cost of the steel increases, and sufficient strength may be secured, but difficulty in securing high toughness occurs.
The hot rolled steel sheet manufactured through the above process may have a composite structure of ferrite and pearlite.
In addition, the hot rolled steel sheet according to the present invention manufactured through the above process can secure the mechanical properties of tensile strength (TS): 517 MPa or more and yield strength (YS): 379 ~ 552 MPa.
On the other hand, the hot rolled steel sheet according to the present invention may further include a cooling and winding step (S130), QT (Quenching and Tempering) heat treatment step (S140), the hot-rolled steel sheet by the QT heat treatment step (S140) Can be upgraded to oil grade steel grade.
QT heat treatment
In the QT heat treatment step (S140), the steel sheet is soaked at 900 to 1000 ° C. to form austenite, and then quenched to transform into bainite and martensite. Then, the tempering (Tempering) is carried out at 450 ~ 550 ℃ to improve the toughness.
The QT heat treatment step S140 may be performed after the wound steel sheet is piped.
By the QT (Quenching & Tempering) heat treatment process, the hot rolled steel sheet according to the present invention is upgraded to a steel grade that satisfies the mechanical properties of tensile strength (TS): 862 MPa or more and yield strength (YS): 758 ~ 965 MPa -grade)
At this time, the recrystallization at a low temperature of the austenitic single-phase zone decreases the grain size, but at a low temperature above a certain level, the effect is gradually reduced, so the soaking temperature is preferably carried out at 900 ℃ or more. In addition, when the soaking temperature is less than 900 ℃ may cause a problem that the segregated components are not reusable. On the contrary, when the soaking temperature exceeds 1000 ° C., it may be difficult to secure desired strength due to coarsening of austenite.
At this time, when the tempering temperature is less than 450 ℃ because the tempering time should be performed for a long time, there is a problem that the process efficiency is lowered. On the contrary, when the tempering temperature exceeds 550 ° C., an excessive tempering process may be performed to deteriorate the mechanical properties of the heat-treated steel sheet. Therefore, the tempering temperature is preferably carried out at 450 ~ 550 ℃.
The hot rolled steel sheet manufactured by the above process has resistance yield ratio characteristics before QT heat treatment, and after QT heat treatment, tensile strength, which is the mechanical property of API 5CT P110, defined by the American Petroleum Institute (API): 862 MPa or more and yield strength : Upgraded to steel grade that satisfies 758 ~ 965MPa.
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 Hot Rolled Specimens
Hot rolled specimens according to Comparative Examples 1 to 2 and Examples 1 to 3 were prepared using the compositions shown in Table 1 and the process conditions described in Table 2. Thereafter, the hot rolled specimens prepared according to Comparative Examples 1 and 2 and Examples 1 to 3 were annealed at 920 ° C., then quenched, and tempered at 480 ° C. for 200 seconds.
In this case, in the case of hot rolled specimens according to Comparative Examples 1 and 2 and Examples 1 to 3, an ingot having a respective composition was prepared, and this was simulated using a rolling simulation tester to simulate the hot rolling process of heating, hot rolling and cooling Charged in.
[Table 1] (unit:% by weight)
[Table 2]
[Table 3]
2. Evaluation of mechanical properties
Table 3 shows the evaluation results for the mechanical properties of the hot-rolled specimen prepared according to Comparative Examples 1 and 2 and Examples 1 to 3.
Referring to Tables 1 to 3, the hot rolled specimens prepared according to Examples 1 to 3 were tensile strength (TS): 590 to 600 MPa, yield strength (YS): 385 to 400 MPa, elongation (EL): 33 before QT heat treatment. ~ 34 and yield ratio (YR): 65 ~ 67.5% can confirm that all the target values are satisfied.
On the other hand, the hot-rolled specimen prepared according to Examples 1 to 3, after QT heat treatment, tensile strength (TS): 975 ~ 983 MPa, yield strength (YS): 859 ~ 870 MPa, elongation (EL): 14 to 16% and yield Ratio (YR): 87.6 ~ 88.5%, it can be confirmed that all the target values are satisfied.
On the other hand, in comparison with Examples 1 to 3, instead of niobium (Nb), titanium (Ti) and boron (B) were not added, and the finish hot rolling temperature (FDT) and the winding temperature (CT) were approximately respectively. The hot-rolled specimens prepared according to Comparative Examples 1 to 2, which are about 50 to 100 ° C. low, have tensile strength (TS): 610 to 615 MPa, yield strength (YS): 480 to 483 MPa and elongation (EL): 29 ~ before QT heat treatment. Although the target value was satisfied at 30%, the yield ratio (YR) was lower than the target value at 78.5 to 78.7%.
On the other hand, the hot-rolled specimens prepared according to Comparative Examples 1 and 2, after the QT heat treatment, the elongation (EL): 17 ~ 18% satisfied the target value, but the tensile strength (TS) and yield strength (YS) to the target value It can be seen that it has less than 763 ~ 765MPa and 649 ~ 652MPa.
2 is a schematic diagram showing a cooling process applied to Example 1. FIG.
Referring to FIG. 2, in the case of the hot-rolled specimen manufactured by the method according to Example 1, it can be seen that the bainite transformation region and martensite transformation region are widely distributed in comparison with the ferrite transformation region and the pearlite transformation region. In the case of Example 1, it is due to the removal of niobium (Nb) and the addition of titanium (Ti) and boron (B) of the alloy components in order to secure a higher tensile strength (TS) compared to the yield strength (YS), this It can be seen that through the hardenability can be greatly improved.
On the other hand, Figure 3 is a microstructure picture of the hot rolled specimen prepared by the method according to Example 2, showing the microstructure before the QT heat treatment, Figure 4 is a microstructure picture of the hot rolled specimen prepared by the method according to Example 2 , Shows the microstructure after QT heat treatment.
As shown in Figure 3, in the case of hot-rolled specimen prepared by the method according to Example 2, before the QT heat treatment, the final microstructure is wound by winding at 700 ℃ relatively high temperature compared to Comparative Examples 1 and 2 It can be seen that it consists of a complex structure of coarse ferrite and pearlite.
On the other hand, as shown in Figure 4, in the case of hot-rolled specimen prepared by the method according to Example 2, after the QT heat treatment, considering the capacity of the tube heat treatment equipment, the final microstructure is not a harsh condition It can be seen that it consists of a complex structure of dense bainite and martensite.
As described above, the hot rolled steel sheet according to the present invention has a resistive ratio property before QT heat treatment, and after QT heat treatment, tensile strength which is a mechanical property of API 5CT P110 defined by the American Petroleum Institute (API): 862 MPa Abnormal and yield strength: can be upgraded to steel grades satisfying 758 ~ 965MPa.
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
S140: QT Heat Treatment Step
Claims (13)
The hot rolled sheet material CT (Coiling Temperature): cooling / winding step of winding by cooling to 640 ~ 720 ℃; hot rolled steel sheet manufacturing method comprising a.
Prior to the hot rolling step,
Slab reheating temperature (SRT): a slab reheating step of reheating to 1150 ~ 1250 ℃; hot rolled steel sheet manufacturing method further comprising.
The slab plate is
Method for producing a hot rolled steel sheet comprising silicon (Si) and manganese (Mn) in a range satisfying the following equation (1).
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 nitrogen (N): 0.006% by weight or less are further included.
After the cooling / winding step,
After the soaking (soaking) the steel sheet at 900 ~ 1000 ℃, quenching and tempering at 450 ~ 550 ℃ tempered at QT (Quenching & Tempering) heat treatment step; further comprising a hot rolled steel sheet manufacturing method.
By the QT heat treatment step,
The final microstructure of the hot rolled steel sheet is characterized in that it has a composite structure of bainite and martensite.
Hot rolled steel sheet, characterized in that the microstructure has a complex structure of ferrite and pearlite.
The steel sheet
A hot rolled steel sheet 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): 0.03% or less, sulfur (S): 0.003% or less and nitrogen (N): 0.006% or less by weight.
The steel sheet
Tensile strength (TS): 517 MPa or more and yield strength (YS): 379 ~ 552 MPa having a hot rolled steel sheet characterized in that it has.
The steel sheet
Elongation: 20% or more and yield ratio: 70% or less hot rolled steel sheet characterized in that it has.
The steel sheet is subjected to QT (Quenching & Tempering) heat treatment,
The hot rolled steel sheet, characterized in that the complex structure of the ferrite and pearlite is transformed into a complex structure of bainite and martensite.
The steel sheet
By the QT (Quenching & Tempering) heat treatment,
Tensile strength (TS): 862 MPa or more and yield strength (YS): Hot rolled steel sheet, characterized in that upgraded to 758 ~ 965 MPa.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020110051195A KR20120132835A (en) | 2011-05-30 | 2011-05-30 | Hot-rolled steel sheet and method of manufacturing the hot-rolled steel sheet |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020110051195A KR20120132835A (en) | 2011-05-30 | 2011-05-30 | Hot-rolled steel sheet and method of manufacturing the hot-rolled steel sheet |
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| KR20120132835A true KR20120132835A (en) | 2012-12-10 |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20180072493A (en) * | 2016-12-21 | 2018-06-29 | 주식회사 포스코 | Hot rolled steel sheet for use in oil well pipe, steel pipe using the same and method for manufacturing thereof |
| WO2019124765A1 (en) * | 2017-12-22 | 2019-06-27 | 주식회사 포스코 | High-strength steel sheet having excellent impact resistance, and method for manufacturing same |
-
2011
- 2011-05-30 KR KR1020110051195A patent/KR20120132835A/en not_active Application Discontinuation
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20180072493A (en) * | 2016-12-21 | 2018-06-29 | 주식회사 포스코 | Hot rolled steel sheet for use in oil well pipe, steel pipe using the same and method for manufacturing thereof |
| CN108265222A (en) * | 2016-12-21 | 2018-07-10 | Posco公司 | Hot rolled steel plate for oil well pipe, steel pipe and its manufacturing method using the steel plate |
| WO2019124765A1 (en) * | 2017-12-22 | 2019-06-27 | 주식회사 포스코 | High-strength steel sheet having excellent impact resistance, and method for manufacturing same |
| US11708623B2 (en) | 2017-12-22 | 2023-07-25 | Posco Co., Ltd | High-strength steel sheet having excellent impact resistance, and method for manufacturing same |
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