KR101758527B1 - Steel sheet for pipe having excellent weldability, method for manufacturing the same, and method for manufacturing welded steel pipe using the same - Google Patents
Steel sheet for pipe having excellent weldability, method for manufacturing the same, and method for manufacturing welded steel pipe using the same Download PDFInfo
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- KR101758527B1 KR101758527B1 KR1020150185474A KR20150185474A KR101758527B1 KR 101758527 B1 KR101758527 B1 KR 101758527B1 KR 1020150185474 A KR1020150185474 A KR 1020150185474A KR 20150185474 A KR20150185474 A KR 20150185474A KR 101758527 B1 KR101758527 B1 KR 101758527B1
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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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- 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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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
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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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
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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Abstract
The present invention relates to a steel material for pipes used for mining or transporting oil or gas, and more particularly, to a steel material for pipes excellent in weldability, a method for manufacturing the same, and a method for manufacturing a welded steel pipe using the steel material for a pipe .
Description
The present invention relates to a steel material for pipes used for mining or transporting oil or gas, and more particularly, to a steel material for pipes excellent in weldability, a method for manufacturing the same, and a method for manufacturing a welded steel pipe using the steel material for a pipe .
Recently, the environment for mining or transporting oil, gas and the like is becoming increasingly severe, and demands for improving the weldability and toughness of steel pipes used for mining and transportation in such environments are increasing rapidly.
Particularly, regardless of whether or not the welded material is used in the welded steel pipe obtained by welding, the property of the heat affected part is always inferior to the base material, so that the quality improvement of the edge part that directly affects the welding becomes an important issue.
Generally, when the edge quality is degraded after manufacturing a slab, the quality is improved through hand scarfing, but there is a problem that additional cost is incurred.
Further, in order to heat the slab toughness, it is necessary to perform the rolling through the reheat treatment or the CEM process in which the thin slab is produced by continuous casting and then rolled. In this case, the edge quality is checked in advance to improve the weldability There is no room for it.
Accordingly, along with the development of a technique capable of improving the weldability of the welded steel pipe, there has been a demand for development of a steel material for a pipe suitable for the welded steel pipe.
An aspect of the present invention is to provide a steel material for a pipe having excellent weldability while securing a certain strength or more, a method for manufacturing the same, and a method for manufacturing a welded steel pipe using the same.
An aspect of the present invention is a method of manufacturing a semiconductor device, comprising: 0.03 to 0.10% of carbon (C), 0.10 to 0.50% of silicon (Si), 0.5 to 2.0% of manganese (Mn) 0.001 to 0.005% of sulfur (S), 0.01 to 0.1% of niobium (Nb), 0.01 to 0.05% of titanium (Ti), 0.001 to 0.006% of calcium (Ca) And other inevitable impurities, and satisfies the following relational expression (1).
[Relation 1]
89.0 - (58.5 x Cu) - (100 x Nb) - (4825 x N)? 50
(Cu, Nb, N in the above relational expression 1 means the weight content of each element, and Cu may be 0).
According to another aspect of the present invention, there is provided a method of manufacturing a steel slab, comprising the steps of: reheating a steel slab satisfying the alloy composition and the above-described formula 1 at 1100 to 1300 占 폚; Subjecting the reheated steel slab to rough rolling; After the rough rolling, finishing hot-rolling at 750 to 900 ° C to produce a hot-rolled steel sheet; And cooling the hot-rolled steel sheet to a temperature of 450 to 650 ° C at a cooling rate of 10 ° C / s or higher, and winding the hot-rolled steel sheet with excellent weldability.
Another aspect of the present invention provides a method of manufacturing a welded steel pipe excellent in weldability, which is formed into a steel pipe by forming and welding a steel material for a pipe manufactured by the above-described manufacturing method.
INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a steel for pipes excellent in weldability while having strength of 5 L X 60 or more in API standard.
The steel pipe obtained by molding and welding the steel material for a pipe of the present invention is advantageously applicable in a harsh environment.
The inventors of the present invention have conducted intensive studies to provide a steel material having excellent weldability, having a strength suitable for mining or transporting oil, gas and the like, in particular, a strength equivalent to API standard 5L X60 (yield strength 415 MPa or more and tensile strength 520 MPa or more) Respectively.
As a result, it has been confirmed that steel steels for pipes having the intended properties can be provided by optimizing the steel alloy composition, component relationship and manufacturing conditions, and have completed the present invention.
Hereinafter, the present invention will be described in detail.
According to one aspect of the present invention, there is provided a steel material for a pipe excellent in weldability, wherein the alloy composition contains 0.03 to 0.10% carbon (C), 0.10 to 0.50% silicon (Si), 0.5 to 2.0% manganese (Mn) P): 0.020% or less, sulfur (S): 0.005% or less, niobium (Nb): 0.01 to 0.1%, titanium (Ti): 0.01 to 0.05%, calcium (Ca): 0.001 to 0.006% : 0.01% or less.
Hereinafter, the reason why the alloy composition of the steel for pipes provided in the present invention is limited as described above will be described in detail. Here, the content of each component means weight% unless otherwise specified.
C: 0.03 to 0.10%
Carbon (C) is an element which increases the hardenability of the steel. If the content is less than 0.03%, the hardenability is insufficient and the intended strength in the present invention can not be secured. On the other hand, if the content exceeds 0.10%, the quality of the performance may deteriorate due to entering the apical region, which is not preferable.
Therefore, in the present invention, the content of C is preferably limited to 0.03 to 0.10%.
Si: 0.10 to 0.50%
Silicon (Si) increases the activity of C in the ferrite phase, promotes the stabilization of the ferrite, and contributes to securing strength by solid solution strengthening. Further, by forming a low-melting-point oxides such as Mn 2 SiO 4 in electrical resistance welding of the steel material, so that the oxide is easily discharged at the time of welding.
In order to sufficiently obtain the above-mentioned effect, it is preferable to add Si at 0.10% or more. However, when the content exceeds 0.50%, the formation of SiO 2 , which is a high melting point oxide other than Mn 2 SiO 4 , The toughness of the welded portion can be lowered.
Therefore, in the present invention, the content of Si is preferably limited to 0.10 to 0.50%.
Mn: 0.5 to 2.0%
Manganese (Mn) is an effective element for strengthening the strength of the steel. If the content of Mn is more than 0.5%, the desired strength of the present invention can be secured in addition to the effect of increasing the incombustibility. On the other hand, if the content exceeds 2.0%, a large amount of segregation occurs at the center of the thickness during casting of the slab in the steelmaking process, which is undesirable because of the problem of reducing the weldability of the final product.
Therefore, in the present invention, the content of Mn is preferably limited to 0.5 to 2.0%.
P: not more than 0.020%
Phosphorus (P) is an impurity which is inevitably added in the steel, and is an element which deteriorates toughness. Therefore, it is preferable to reduce the content of P as much as possible.
However, the upper limit can be limited to 0.020% in consideration of the cost in the steelmaking process, and 0% is excluded.
S: not more than 0.005%
Sulfur (S) is an impurity which is inevitably added in the steel, like P, and is an element which is likely to form coarse inclusions. Such S is preferably contained as low as possible because it lowers the toughness of steel or promotes the progress of cracks.
However, considering the cost in the steel making process, the upper limit may be limited to 0.005%, more preferably 0.003% or less, and 0% is excluded.
Nb: 0.01 to 0.1%
Niobium (Nb) is an element that forms precipitates and greatly affects the strength of steel. It enhances the strength of steel by precipitating carbonitrides in the steel or strengthening the solid solution in Fe.
Particularly, the Nb-based precipitates are solidified during hot rolling of the slab and finely precipitated during hot rolling, effectively increasing the strength of the steel.
If the content of Nb is less than 0.01%, a sufficient amount of fine precipitates can not be formed and the desired strength can not be secured in the present invention. On the other hand, when the content exceeds 0.1%, excessive precipitation causes performance, It is undesirable because sacredness can be degraded.
Therefore, in the present invention, the content of Nb is preferably limited to 0.01 to 0.1%.
Ti: 0.01 to 0.05%
Titanium (Ti) reacts with nitrogen (N) to form TiN, which not only inhibits the growth of austenite grains during reheating of the slab but also increases the strength by inhibiting the growth of austenite grains in the weld heat affected zone (HAZ) .
Further, solid solution N can be removed through formation of TiN, and solid solution B contributing to enhancement of hardenability can be secured by inhibiting BN generation.
In order to sufficiently obtain the above-mentioned effect, it is preferable to add it in an amount exceeding [3.4 x N (wt%)]. However, if the content thereof is excessively excessive, coarse TiN may be formed and the toughness may be lowered. Therefore, it is preferable that the content is limited to 0.05% or less.
Ca: 0.001 to 0.006%
Calcium (Ca) is an element added for controlling the shape of the emulsion. If the content of Ca is less than 0.001%, MnS may be generated and the toughness may be lowered. On the other hand, when the content exceeds 0.006%, there is a problem that CaS clusters are generated due to excessive addition to the S content in the steel.
Therefore, in the present invention, the content of Ca is preferably limited to 0.001 to 0.006%.
N: not more than 0.01%
Nitrogen (N) is an element that forms a nitride by binding with Ti or Al in a steel. If the content of N exceeds 0.01%, it is inevitable to increase the addition amount of Ti, Al or the like in order to fix the N. Therefore, the content thereof is preferably limited to 0.01% or less. However, 0% is excluded considering the load during the steelmaking process.
The steel for pipes of the present invention may further contain Cr, Cu, Ni, V, Mo, B, etc. in addition to the alloy composition described above. These components may be added alone or in combination of two or more.
Cr: 0.01 to 0.5%
Cr (Cr) is an element which improves the hardenability of the steel. If the content of Cr is less than 0.01%, there is a problem that the effect of improving the hardenability by the addition of Cr is insufficient. On the other hand, if the content exceeds 0.5%, the toughness may be rapidly lowered, which is not preferable.
Therefore, in the present invention, the content of Cr is preferably limited to 0.01 to 0.5%.
Cu: 0.01 to 0.5%
Copper (Cu) is an element effective for improving hardenability and corrosion resistance of a base material or a welded portion. For this purpose, it is preferable to add Cu at 0.01% or more, but if the content exceeds 0.5%, the toughness and weldability of the weld heat affected zone may be deteriorated.
Therefore, in the present invention, the content of Cu is preferably limited to 0.01 to 0.5%.
Ni: 0.01 to 0.5%
Nickel (Ni) is an element effective for improving the hardenability and corrosion resistance, and when added together with the above-described Cu, reacts with Cu to inhibit generation of a Cu phase having a low melting point, thereby suppressing the problem of cracking during hot working have. Further, the Ni is an effective element for improving the toughness of the base material.
In order to sufficiently secure the above-mentioned effect, it is preferable to add Ni at 0.01% or more, but it is not preferable because the above-mentioned Ni has a problem that the production cost increases greatly when added in excess of 0.5% as an expensive element.
Therefore, in the present invention, the content of Ni is preferably limited to 0.01 to 0.5%.
V: 0.01 to 0.5%
Vanadium (V) has the same effect as Nb, and has an effect of suppressing softening of the welded portion.
In order to sufficiently secure the above-mentioned effect, it is preferable to add V to not less than 0.01%. However, if the content of V is more than 0.5% as the expensive element, the manufacturing cost increases greatly, which is disadvantageous from the economical point of view.
Therefore, in the present invention, the content of V is preferably limited to 0.01 to 0.5%.
Mo: 0.01 to 0.5%
Molybdenum (Mo) is an effective element for improving hardenability, corrosion resistance, and toughness of a base material. For this purpose, it is preferable to add Mo at a content of 0.01% or more. However, since Mo is a high-priced element, there is a problem that the cost increases greatly when added in a large amount, and therefore the upper limit is preferably limited to 0.5%.
Therefore, in the present invention, the content of Mo is preferably limited to 0.01 to 0.5%.
B: 0.0005 to 0.003%
Boron (B) stabilizes austenite by segregating into the austenite grains to lower the grain boundary energy, and is an element that slows ferrite nucleation of grain boundaries and improves the hardenability of steel. For this purpose, it is preferable to add B at 0.0005% or more. However, if the content exceeds 0.003%, the material deviation may be increased by locally biased B, so that the upper limit is preferably limited to 0.003%.
Therefore, in the present invention, the content of B is preferably limited to 0.0005 to 0.003%.
The remainder of the present invention is iron (Fe). However, in the ordinary steel 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 steel making.
In the steel material for a pipe of the present invention, it is preferable that the compositional relationship of Cu, Nb and N satisfies the following relational expression 1 in the above-mentioned alloy composition.
[Relation 1]
89.0 - (58.5 x Cu) - (100 x Nb) - (4825 x N)? 50
(Cu, Nb, N in the above relational expression 1 means the weight content of each element, and Cu may be 0).
The Cu, Nb and N contributes to the quality (quality) of the steel material. If the content of Cu is excessive, the possibility of surface cracking increases.
The Nb is an element which forms NbC system precipitates and N is an element which influences formation of TiN precipitates. In the present invention, when a large amount of precipitates are formed by Nb and N during rolling, edge quality Resulting in a problem that the high temperature ductility (indicated by the reduction ratio at 800 deg. C), which is intended in the present invention, can not be ensured.
Therefore, it is preferable to control the content relationship of Cu, Nb and N, and more preferably, the value of the above-mentioned relational expression 1 is controlled to be 50 or more.
If the value of the above relational expression 1 is less than 50, surface cracking by Cu may occur, or even if Cu is not contained, a large amount of Nb and N precipitates may be formed during the rolling process, .
It is preferable that the steel material for a pipe of the present invention satisfying the above-described alloy composition and component relationship (relational expression 1) includes a ferrite and a pearlite composite structure as a microstructure.
In other words, the steel material for pipes of the present invention can provide a steel for pipes having a yield strength of 415 MPa or more and a tensile strength of 520 MPa or more by complexly including ferrite and pearlite in an appropriate proportion.
On the other hand, the steel material for pipes of the present invention satisfying the above-described alloy composition and microstructure has a technical feature that the high temperature ductility represented by a reduction ratio at 800 캜 exceeds 50%.
Specifically, a high temperature ductility index is an index for evaluating ductility. A Gleeble specimen is prepared and heated to a temperature of 1200 ° C. or higher, and then the specimen is tensioned at a specific temperature while cooling from the temperature, ) Calculate the area at the point where the fracture occurs, and represent the reduced ratio to the area of the original specimen.
The larger the reduction ratio of the specimen is, the more ductility can be interpreted. If the reduction ratio of the temperature is higher when the specimen is deformed at a certain temperature, it is easily deformed and does not cause cracks or the like internally. Can be predicted.
The 800 ° C temperature is a temperature for the most heat of the high temperature ductility. The pipe steel of the present invention has a reduction ratio of more than 50% at 800 ° C, so that not only the conventional hot rolled steel sheet but also the edge sensitivity Good quality can be secured even in high CEM (compact endless casting and rolling mill) process. This is advantageous in securing the desired weldability in the present invention.
Hereinafter, a method for manufacturing a steel for pipes having excellent weldability according to another aspect of the present invention will be described in detail.
The steel material for a pipe according to the present invention can be prepared by preparing a steel slab satisfying the alloy composition proposed in the present invention and subjecting it to a reheating-hot rolling-cooling-winding process. Hereinafter, Will be described in detail.
[Reheating Process]
It is preferable to prepare a steel slab satisfying the alloy composition which is limited in the present invention and reheat it.
The reheating step is a step of heating the steel so as to smoothly perform the subsequent rolling process and sufficiently obtain the physical properties of the target steel sheet, and therefore, the reheating step should be performed within an appropriate temperature range according to the purpose.
In the present invention, it is preferable to perform the reheating process in the temperature range of 1100 to 1300 ° C. If the reheating temperature is less than 1100 ° C, Nb is hardly completely solidified and it becomes difficult to secure sufficient strength. On the other hand, There is a problem in that it becomes difficult to make the grain size finer.
[Hot rolling process]
It is preferable that the reheated steel slab is subjected to rough rolling and finish hot rolling to produce a hot-rolled steel sheet.
At this time, the rough rolling is preferably performed at 900 to 1100 DEG C, and if the rough rolling is finished at a temperature lower than 900 DEG C, there is a problem that the risk of load problem of the mill equipment is increased.
The finish hot rolling performed subsequent to the rough rolling is preferably performed at 750 to 900 DEG C, which is the non-recrystallization temperature region. If the final hot rolling temperature is less than 750 ° C, there is a problem that the possibility of occurrence of blast-furnace structure increases. On the other hand, if the final hot rolling temperature exceeds 900 ° C, the final structure becomes too large and the desired strength can not be secured.
Therefore, in the present invention, it is preferable to restrict the temperature range of rough rolling at the time of hot rolling to 900 to 1100 캜, and to restrict the temperature range of finish hot rolling to 750 to 900 캜.
[Cooling and Winding Process]
It is preferable that the hot rolled steel sheet produced as described above is cooled and then wound.
The cooling is an element for improving the strength and toughness of the steel. As the cooling rate is higher, the crystal grains of the internal structure of the steel sheet become finer and the toughness is improved.
Therefore, in the present invention, it is preferable that cooling is performed at a cooling rate of 10 DEG C / s or more. If the cooling rate is less than 10 DEG C / s, it is difficult to secure the intended microstructure in the present invention, and the desired strength can not be secured. At this time, the upper limit of the cooling rate is not particularly limited, and may be set in consideration of the load of the cooling equipment.
The cooling is preferably terminated at 450 to 650 ° C. When the cooling end temperature exceeds 650 ° C, sufficient strength can not be ensured. On the other hand, when the cooling is terminated at less than 450 ° C, the martensite fraction excessively increases, have.
Therefore, in the present invention, it is preferable that the cooling is performed at a cooling rate of 10 ° C / s or more, and the cooling is finished in the temperature range of 450 to 650 ° C, and then the winding is performed within the temperature range.
The hot-rolled steel sheet of the present invention (i.e., steel for pipes) manufactured through the above-described processes can be used to produce steel pipes.
At this time, the method of producing the steel pipe is not particularly limited, but it is preferable that the steel pipe is formed and welded by using electric resistance welding which has the highest economical efficiency. Since any welding method can be used in the electrical resistance welding, the welding method is not particularly limited.
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 steel slab having the alloy composition shown in the following Table 1 (the remainder being Fe and unavoidable impurities) was heated to 1260 DEG C or higher and subjected to rough rolling, then subjected to finish hot rolling and cooling under the conditions shown in Table 2, Hot-rolled steel sheets were produced. At this time, winding was performed at the temperature at which the cooling was completed, and cooling was performed at a cooling rate of 20 to 40 ° C / s.
The yield strength and tensile strength of each of the above hot-rolled steel sheets were measured using a tensile tester, and the tests were carried out according to the conventional ASTM A370. Also, the high temperature ductility value at 800 ° C was measured for each specimen using a Gleeble high temperature tensile tester.
Then, each hot-rolled steel sheet was ground using electric resistance welding, and the defect rate was checked by ultrasonic testing, which is a non-destructive testing method, UT (Ultrasonic Test).
The results of the above measurements are shown in Table 2 below.
07
10
04
06
(Ca * and N * in Table 1 are in ppm by weight.)
division
Termination temperature
(° C)
Hot rolling
Temperature (℃)
Temperature
(° C)
(MPa)
(MPa)
UT defect rate
(%)
As shown in Tables 1 and 2, Examples 1 and 2, which satisfy both the steel alloy composition and the manufacturing conditions, have weld strength of 1% with a UT defect ratio of at least 1% It is expected to be excellent.
On the other hand, in the case of the comparative steels 1 and 2 in which the steel composition or composition relationship (relational expression 1) did not satisfy the present invention, the UT defect rate was as high as 26% and 11%, respectively, and the high temperature ductility value Was less than 50%.
The comparative steels 1 and 2 are intended to heat edge quality and are expected to have poor weldability during welding.
Claims (9)
A steel material for pipes excellent in weldability, which satisfies the following relational expression 1 and whose high temperature ductility ratio at 800 占 폚 exceeds 50%.
[Relation 1]
89.0 - (58.5 x Cu) - (100 x Nb) - (4825 x N)? 50
(Cu, Nb, and N in the relational expression 1 means the weight content of each element, and Cu may be 0.)
Wherein the steel material contains 0.01 to 0.5% of chromium (Cr), 0.01 to 0.5% of copper (Cu), 0.01 to 0.5% of nickel (Ni), 0.01 to 0.5% of vanadium (V) ) Of 0.01 to 0.5% and boron (B): 0.0005 to 0.003%.
The steel material is a microstructure and contains ferrite and pearlite composite structure, and is excellent in weldability.
The steel material has excellent yield strength with a yield strength of 415 MPa or more and a tensile strength of 520 MPa or more.
Subjecting the reheated steel slab to rough rolling;
After the rough rolling, finishing hot-rolling at 750 to 900 ° C to produce a hot-rolled steel sheet; And
Cooling the hot-rolled steel sheet to a temperature of 450 to 650 ° C at a cooling rate of 10 ° C / s or more,
A method of producing a steel for pipes excellent in weldability.
[Relation 1]
89.0 - (58.5 x Cu) - (100 x Nb) - (4825 x N)? 50
(Cu, Nb, and N in the relational expression 1 means the weight content of each element, and Cu may be 0.)
Wherein the rough rolling is performed at 900 to 1100 占 폚.
Wherein the steel slab comprises 0.01 to 0.5% of chromium (Cr), 0.01 to 0.5% of copper (Cu), 0.01 to 0.5% of nickel (Ni), 0.01 to 0.5% of vanadium (V) Mo in an amount of 0.01 to 0.5% and boron (B) in an amount of 0.0005 to 0.003%.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020150185474A KR101758527B1 (en) | 2015-12-23 | 2015-12-23 | Steel sheet for pipe having excellent weldability, method for manufacturing the same, and method for manufacturing welded steel pipe using the same |
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| KR1020150185474A KR101758527B1 (en) | 2015-12-23 | 2015-12-23 | Steel sheet for pipe having excellent weldability, method for manufacturing the same, and method for manufacturing welded steel pipe using the same |
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| KR20170075925A KR20170075925A (en) | 2017-07-04 |
| KR101758527B1 true KR101758527B1 (en) | 2017-07-17 |
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| KR102443927B1 (en) * | 2020-08-26 | 2022-09-19 | 주식회사 포스코 | Hot-rolled steel plate having excellent impact toughness of welded zone and method for manufacturing thereof |
| KR20220087189A (en) * | 2020-12-17 | 2022-06-24 | 주식회사 포스코 | Steel sheet for pipe having excellent hydrogen induced crack resistance and method of manufacturing the same |
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