CN101541994B - Weld steel pipe with excellent low-temperature toughness for high-strength line pipe and process for producing the same - Google Patents
Weld steel pipe with excellent low-temperature toughness for high-strength line pipe and process for producing the same Download PDFInfo
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Abstract
A weld steel pipe for high-strength line pipes which is inexpensive and has excellent low-temperature toughness; and a process for producing the pipe. A base steel plate which contains, in terms of mass%, 0.010-0.050% carbon, 0.01-0.50% silicon, 0.50-2.00% manganese, 0.0001-0.0050% sulfur, and 0.003-0.030% titanium, has an aluminum content and a molybdenum content reduced to up to 0.020 mass% and less than 0.10 mass%, respectively, has a carbon equivalent (Ceq) of 0.30-0.53 and a cracking parameter (Pcm) of 0.10-0.20, comprises up to 20% polygonal ferrite in terms of areal proportion and bainite as the remainder, and has an effective crystalgrain diameter of 20 [mu]m or smaller is formed into a pipe shape.
Description
Technical field
The present invention relates to be suitable for the effective Welded Steel Pipe of high-strength line-pipe of the low-temperature flexibility excellence of the line pipe that crude oil and natural gas transport use.
Background technology
As the long-distance delivery method of crude oil, Sweet natural gas etc. and the line-pipes steel pipe that in the main line of important pipeline, uses, the line-pipes steel pipe (for example patent documentation 1) of high strength, high tenacity had been proposed once.Up to now, API (API) standard x 70 (more than the tensile strength 564MPa) are above and then up to the line-pipes steel pipe of X80 (more than the tensile strength 620MPa) practicability, but being accompanied by the investigation that turns to the high-pressure trend of pressing in the pipeline of purpose with the efficient of the conveying of crude oil and Sweet natural gas, is more than the X70 more than the 600MPa and then the effective steel pipe of high-strength line-pipe more than the X80 requires further high strength, wall thickening to tensile strength.
About high strength, for example, during the line pipe of the X120 level of the tensile strength more than use has 900MPa, pressing in can making is that the pressure of crude oil or Sweet natural gas is about 2 times of line pipe of X65 level, therefore can carry the crude oil or the Sweet natural gas of about 2 times amount.In addition,, when burst strength is improved, compare, can cut down materials cost, pipage, site welding construction cost, can save the pipeline laying expense significantly with the situation that wall thickness is thickened when the intensity that makes line pipe improves.
In addition, the situation that pipeline is laid at cold district is also more, therefore must the low-temperature flexibility excellence.In addition, line pipe end each other engages during owing to construction, therefore also requires excellent site welding.Once proposed a kind ofly to satisfy such requirement, and the line-pipes steel pipe (for example TOHKEMY 2004-52104 communique) of the X120 level of the intensity higher than the line-pipes steel pipe that in Japanese kokai publication sho 62-4826 communique, proposes.This is that the microstructure of mother metal is based on the effective steel pipe of the high-strength line-pipe of bainite and martensitic mixed structure.In addition, for wall thickening, once having proposed to make metal structure by controlled rolling and controlled chilling is fine bainite, makes the method (for example TOHKEMY 2000-256777 communique, TOHKEMY 2004-76101 communique, TOHKEMY 2004-143509 communique) of the good Plate Steel of intensity and toughness.
Intensity height, the line-pipes steel pipe that wall thickness is thick be by Plate Steel being utilized the UO process forming be tubulose, the end is docked each other, stitches weldering and make.Requiring toughness and productive occasion as the effective steel pipe of high-strength line-pipe, in seam weldering, the submerged arc welding of carrying out from inner face and outside is more suitable.Like this, in the occasion of steel being welded repeatedly, (Heat Affected Zone is called HAZ to the welded heat affecting zone of thickization owing to the heat input of welding in advance.), owing to the heat input of back row welding is reheated the problem that exists toughness to reduce.
Technology for the low-temperature flexibility of the HAZ that makes the effective steel pipe of high-strength line-pipe improves had once proposed to utilize the method for organizing miniaturization (for example Japanese kokai publication hei 8-325635 communique, TOHKEMY 2001-355039 communique, TOHKEMY 2003-138340 communique) of intracrystalline phase transformation with HAZ.The method that proposes in the Japanese kokai publication hei 8-325635 communique, be to be the method that nuclear generates acicular ferrite with the oxide compound, the method that proposes in TOHKEMY 2001-355039 communique and the TOHKEMY 2003-138340 communique is that the complex inclusion with oxide compound and sulfide is the method that nuclear generates the intracrystalline bainite.
The majority of the effective steel pipe of existing high-strength line-pipe like this, contain morely improve hardening capacity, to the effective Mo of high strength, obtain the metal structure that bainite is a main body, seek to improve toughness, require to reduce the content of high price elements Mo but become recently., when reducing Mo, hardening capacity reduces easily, is difficult to obtain the intracrystalline bainite, therefore is difficult to guarantee the low-temperature flexibility of HAZ.In addition, the wall thickness of double-strength pipe spool in the past at the most less than 25mm, can not require to obtain the heavy-walled line pipe that 25mm is above or 30mm is above.
Summary of the invention
Even the present invention provides the content of restriction Mo, also can guarantee HAZ particularly low-temperature flexibility, cheapness and the invention of effective Welded Steel Pipe of the high-strength line-pipe of low-temperature flexibility excellence and manufacture method thereof.
In addition, present inventors to have manufactured experimently thickness of slab be that 25mm is above, tensile strength (TS) is the above above effective Plate Steel of high-strength line-pipe of X70, X80 of 600MPa.Its result knows, results from the problem of increase of thickness of slab of steel plate, great more than anticipation.Particularly at the central part of thickness of slab, controlled rolling depress and the speed of cooling of controlled chilling insufficient, compare with the skin section of steel plate, toughness significantly reduces.In addition, the result of the metal structure of the thickness of slab central part of investigation steel plate obtains following opinion: for the effective Plate Steel of high-strength line-pipe, the central part that makes thickness of slab is that fine bainite structure is extremely difficult.
The present invention is the invention that solves the problem that can not envision according to such prior art, and wall thickness is more than the 25mm and then is the effective Welded Steel Pipe of high-strength line-pipe and the manufacture method thereof that also can limit heavy-walled low-temperature flexibility excellence content, cheap of Mo more than the 30mm even provide particularly.
The present invention reduces C and Al, contain an amount of Ti and promote the intracrystalline phase transformation, and add an amount of B and improve hardening capacity, to be controlled at best scope as the carbon equivalent Ceq of the index of hardening capacity and as the crack sensitivity indices P cm of the index of weldability, even the content of restriction Mo, also making mother metal and HAZ is that bainite is the fine metal tissue of main body, and to utilize the oxide compound with Ti be the intracrystalline bainite that nuclear generates, particularly pass through the miniaturization of effective crystal particle diameter of HAZ, but the effective Welded Steel Pipe of high-strength line-pipe of the wall thickening that the low-temperature flexibility that makes HAZ improves, its main idea is as follows.
(1) the effective Welded Steel Pipe of a kind of high-strength line-pipe of low-temperature flexibility excellence, be to being configured as the steel pipe that piped mother metal steel plate has carried out the seam weldering, it is characterized in that, above-mentioned mother metal steel plate has in quality % and contains C:0.010～0.050%, Si:0.01～0.50%, Mn:0.50～2.00%, S:0.0001～0.0050%, Ti:0.003～0.030%, O:0.0001～0.0080%, B:0.0003～0.0030%, and P, Al, Mo is restricted to below the P:0.050% respectively, below the Al:0.020%, Mo: less than 0.10%, its surplus is grouped into by the one-tenth that iron and unavoidable impurities constitute, the Ceq that is tried to achieve by following formula 1 is 0.30～0.53, the Pcm that is tried to achieve by following formula 2 is 0.10～0.20, it is that polygonal ferrite below 20% and area occupation ratio are the bainite more than 80% that the metal structure of above-mentioned mother metal steel plate comprises area occupation ratio, effectively crystal particle diameter is below the 20 μ m, effective crystal particle diameter of welded heat affecting zone is below the 150 μ m
Ceq＝C+Mn/6+(Ni+Cu)/15
+ (Cr+Mo+V)/5 formula 1
Pcm＝C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B
Wherein, C, Si, Mn, Ni, Cu, Cr, Mo, V, B are the content [quality %] of each element.
According to the high-strength thick line pipe Welded Steel Pipe of above-mentioned (1) described low-temperature flexibility excellence, it is characterized in that (2) wall thickness of above-mentioned mother metal steel plate is 25～40mm.
(3) according to the high-strength thick line pipe Welded Steel Pipe of above-mentioned (1) or (2) described low-temperature flexibility excellence, it is characterized in that, is 600～800MPa with the tensile strength of the above-mentioned mother metal steel plate that circumferentially is made as draw direction of above-mentioned steel pipe.
(4) according to the effective Welded Steel Pipe of high-strength line-pipe of each described low-temperature flexibility excellence of above-mentioned (1)～(3), it is characterized in that above-mentioned mother metal steel plate also contains Cu:0.05～1.50%, the side among Ni:0.05～5.00% or two sides in quality %.
(5) according to the effective Welded Steel Pipe of high-strength line-pipe of each described low-temperature flexibility excellence of above-mentioned (1)～(4), it is characterized in that above-mentioned mother metal steel plate also contains one or more among Cr:0.02～1.50% in quality %, V:0.010～0.100%, Nb:0.001～0.200%, Zr:0.0001～0.0500%, Ta:0.0001～0.0500%.
(6) according to the effective Welded Steel Pipe of each described high-strength line-pipe of above-mentioned (1)～(5), it is characterized in that above-mentioned mother metal steel plate also contains one or more among Mg:0.0001～0.0100% in quality %, Ca:0.0001～0.0050%, REM:0.0001～0.0050%, Y:0.0001～0.0050%, Hf:0.0001～0.0050%, Re:0.0001～0.0050%, W:0.01～0.50%.
(7) according to the effective Welded Steel Pipe of high-strength line-pipe of each described low-temperature flexibility excellence of above-mentioned (1)～(6), it is characterized in that, weld metal contains C:0.010～0.100%, Si:0.01～0.50%, Mn:1.0～2.0%, Al:0.001～0.100%, Ti:0.003～0.050%, O:0.0001～0.0500% in quality %, and P, S are restricted to respectively below the P:0.010%, below the S:0.010%, and its surplus is made of iron and unavoidable impurities.
According to the effective Welded Steel Pipe of high-strength line-pipe of above-mentioned (7) described low-temperature flexibility excellence, it is characterized in that (8) above-mentioned weld metal also contains in side among the Ni:0.2 of quality %～3.2%, Cr+Mo+V:0.2～2.5% or two sides.
(9) a kind of manufacture method of the effective Welded Steel Pipe of high-strength line-pipe of low-temperature flexibility excellence, it is characterized in that, when steel-smelting, after interpolation Si, Mn carry out weak deoxidation, add Ti, cast the steel of the composition described in each that is adjusted into above-mentioned (1), (4)～(6), the steel ingot hot rolling that obtains, with the steel formability that obtains is tubulose, with docking section seam weldering.
(10) according to the manufacture method of the effective Welded Steel Pipe of high-strength line-pipe of above-mentioned (9) described low-temperature flexibility excellence, it is characterized in that, above-mentioned steel ingot is heated to more than 1000 ℃, makes depressing in the non-recrystallization humidity province, stopping water-cooled below 600 ℃ than being to carry out hot rolling more than 2.5.
(11) according to the manufacture method of the effective Welded Steel Pipe of high-strength line-pipe of above-mentioned (9) or (10) described low-temperature flexibility excellence, it is characterized in that, is tubulose with above-mentioned steel plate by the UO process forming, use welding wire and sintered type or fusion solder flux to carry out submerged arc welding from interior outside the docking section, carry out expander then.
(12) according to the manufacture method of the effective Welded Steel Pipe of high-strength line-pipe of above-mentioned (11) described low-temperature flexibility excellence, it is characterized in that the heat input of above-mentioned submerged arc welding is 4.0～10.0kJ/mm.
(13) according to the high-strength thick line pipe of each described low-temperature flexibility excellence of above-mentioned (9)～(12) manufacture method, it is characterized in that butt seam welding portion heat-treats with Welded Steel Pipe.
(14) according to the manufacture method of the effective Welded Steel Pipe of high-strength line-pipe of above-mentioned (13) described low-temperature flexibility excellence, it is characterized in that, in 300～500 ℃ scope, stitch the thermal treatment of weldering portion.
Description of drawings
Fig. 1 is again the mode chart of hot HAZ.
Embodiment
The present invention is to reduce the content of C, making metal structure is low temperature phase change tissue based on bainite, thereby improved the flexible steel and be the basis, replace restriction Mo content, make hardening capacity index Ceq and weldability index Pcm be best scope, and add B and improve hardening capacity, make full use of the intracrystalline bainite, particularly, seek to improve the Welded Steel Pipe of low-temperature flexibility with effective crystal particle diameter miniaturization of HAZ.Promptly, maximum feature of the present invention is, Al content is reduced, the control oxygen level, add an amount of Ti, make as the product nucleus of the intracrystalline phase transformation of mother metal steel plate and the microinclusions that the utmost point acts on effectively disperses, and utilize the product nucleus of this microinclusions, with effective crystal particle diameter miniaturization as the intracrystalline phase transformation.In addition, below the mother metal steel plate also is called steel plate simply, Welded Steel Pipe also is called steel pipe simply.
The intracrystalline bainite of HAZ is that making with above-mentioned microinclusions is product nucleus, and at high temperature phase transformation forms the intracrystalline ferrite that produces by the intracrystalline phase transformation when cooling off.Therefore, in order to generate the intracrystalline bainite among the HAZ that makes the steel pipe that has limited the Mo addition as the present invention, making hardening capacity index Ceq and weldability index Pcm is extremely effective for best scope.By generating this intracrystalline bainite, the low-temperature flexibility of HAZ improves significantly.In addition, has the remollescent possibility that the intracrystalline bainite also helps to suppress HAZ.
For the formation mechanism of intracrystalline bainite, can consider as follows.The oxide compound of positively charged ion cavity type can be organized into Mn ion morely, in addition, and the easy compound MnS that separates out in the oxide compound.Therefore, around oxide compound and sulfide, generate Mn and lack layer.This Mn lacks layer, becomes the high temperature of austenite phase and carries out the refrigerative occasion steel being heated to metal structure, acts on as the nuclear of phase transformation, generates petal-like intracrystalline ferrite usually.This intracrystalline ferrite in the fast occasion of speed of cooling, occasion that hardening capacity is high, because condensate depression is big, becomes bainite when therefore cooling off mutually, becomes the intracrystalline bainite.
The representative of the oxide compound of positively charged ion cavity type is to be the fine oxide of principal constituent with Ti, is nuclear, generates petal-like intracrystalline bainite.In addition, be in the fine oxide of principal constituent with Ti at this, still compound sometimes separating out with Mn is the fine sulfide of principal constituent.In addition, be grouped into, in oxide compound, contain among Al, Si, Mn, Cr, Mg, the Ca one or more sometimes, in sulfide, contain among Ca, Cu, the Mg one or more according to the one-tenth of steel.For these sizes of inclusion that becomes the nuclear of intracrystalline bainite, can (be also referred to as TEM by transmission electron microscope.) measure, preferred diameter is the scope of 0.01～5 μ m.
When generating more intracrystalline bainite among the HAZ, (Martensite-Austenite Constituent is called MA to become the martensite of destructive starting point and austenitic mixture.) miniaturization, low-temperature flexibility improves greatly.When being suppressed at C content below 0.05%, when microinclusions is disperseed, generating the intracrystalline bainite, the tissue of intracrystalline is segmented, and the summer is that effective crystal particle diameter becomes minimum than section unit.In addition, because the intracrystalline bainite is harder than intracrystalline ferrite, therefore, has and to suppress HAZ remollescent possibility by generating the intracrystalline bainite.
The central part of the wall thickness of the effective Welded Steel Pipe of high-strength line-pipe (1/2 part of wall thickness near, be called 1/2t portion.) HAZ, shown in Fig. 1 pattern ground, the thick MA that exists along the original austenite crystal boundary of hot HAZ again becomes the destructive starting point, damages toughness sometimes.In Fig. 1, the hot again HAZ of 1 expression, 2 expression martensite and austenitic mixtures, 3 expression original austenite crystal boundaries.The hot again HAZ of what is called is near weld metal and the HAZ the welded bonds of in advance welding, because the back row welds the position that has been reheated.Usually, HAZ is according to the heat input in when welding and what are different, but be apart from welded bonds 10mm with interior position, for example, be provided with the occasion of otch in the position of distance welded bonds 1mm or 2mm, the ratio absorption of the summer-40 ℃ under can be less than 50J sometimes.
Present inventors are for the low-temperature flexibility of the HAZ that satisfies mother metal steel plate and Welded Steel Pipe and carry out the following situation of having found that of lucubrate.With Ti is fine oxide compound, composite oxides, the complex sulfide of principal constituent, effective to the generation of the intracrystalline bainite of HAZ, and, also effective to the miniaturization of effective crystal particle diameter of mother metal.Thus, can make effective crystal particle diameter of HAZ is that 150 μ m are following, effective crystal particle diameter of mother metal steel plate is below the 20 μ m.
In addition, in the occasion that Mo content is restricted to less than 0.10%, if make the carbon equivalent Ceq as the hardening capacity index is 0.30～0.53, and to make the crack sensitivity indices P cm as the weldability index be 0.10～0.20, then the area occupation ratio of the polygonal ferrite of mother metal steel plate is below 20%, the area occupation ratio of bainite is more than 80%, and the intracrystalline phase-change organization of HAZ is the intracrystalline bainite.Thus, the tensile strength of having carried out the welding joint of seam weldering reaches more than the 600MPa.
Particularly wall thickness is that 25mm is above and then be 30mm when above, sometimes the toughness of the 1/2t portion of mother metal steel plate reduces, but utilizing with Ti is fine oxide compound, composite oxides, the complex sulfide of principal constituent, can be with effective crystal particle diameter miniaturization of mother metal steel plate.About its reason, can consider as follows.At first, in the occasion of depressing that can guarantee in the non-recrystallization humidity province, the common phase transformation that begins from crystal boundary is promoted that it is difficult therefore to carry out the intracrystalline phase transformation from oxide compound, composite oxides, complex sulfide.Can think this be because, when depressing by guaranteeing, when crystal particle diameter diminishes, compare with the intracrystalline phase transformation, carried out the excessive cause of the speed of growth of caryogenic bainite from crystal boundary.Can think that promptly the phase transformation that begins from crystal boundary finishes before the intracrystalline phase transformation generates.
On the other hand, depressing in the non-recrystallization humidity province than inadequate occasion, particularly at the thickness of slab central part, thickization of crystal particle diameter, therefore it is also slack-off to have carried out the growth of caryogenic bainite from crystal boundary.Therefore can think, at intragranular, by by the intracrystalline phase transformation based on the oxide compound of Ti, composite oxides, complex sulfide, effectively crystal particle diameter miniaturization.Can think that in addition fine oxide compound plays a role as pinning (pinning) particle, suppress the growth of crystal grain, this is also effective to the miniaturization of effective crystal particle diameter of mother metal steel plate.
According to the present invention, even particularly wall thickness is more than the 25mm, effective crystal particle diameter that also can make the mother metal steel plate is below 20 μ m.In addition, by the area occupation ratio that makes polygonal ferrite be below 20%, the area occupation ratio of bainite is more than 80%, near the top layer, promptly the summer under-40 ℃ of the test specimen of producing from the position of surperficial about 2～12mm of distance steel can reach more than the 200J than absorbing, can make 1/2t portion, promptly the summer under the situation about producing from the substantial middle of wall thickness can be for more than the 100J than absorbing.
In the present invention, be fine oxide compound, composite oxides, the complex sulfide of principal constituent in order to generate with Ti, the control of the oxygen level in the steel making working procedure is of the utmost importance.Particularly when the one-tenth of adjusting steel is grouped into, be that it was necessary adding Ti after the mode of above-mentioned scope was added Si, Mn and carried out weak deoxidation with content.Oxygen concn when adding Ti is preferably 0.001～0.003%.Thus, can make particle diameter is 0.01～10 μ m, per 1 μ m
2The number of area is 10～1000/mm
2The Ti oxide compound disperse, specifically can make Ti
2O
3Disperse.Thus, can promote the generation of intracrystalline phase transformation, effective crystal particle diameter miniaturization of the HAZ of mother metal steel plate and Welded Steel Pipe.
Utilize such steel making working procedure to be adjusted to and be grouped into, cast, during with the steel ingot hot rolling that obtains, by make from 900 ℃ up to the depressing of rolling end than being more than 2.5, being preferably more than 3.0, effective crystal particle diameter that can make the mother metal steel plate is below the 20 μ m.
Effective size of grain is to adopt EBSP, and the area of the part that will be surrounded by the border with the crystalline orientation difference more than 15 ° is converted into circle quite footpath and the value that obtains.In addition, so-called polygonal ferrite, in the opticmicroscope tissue, do not contain as intragranular thick cementite, MA etc. thick precipitate white blocky tissue and observe.In the opticmicroscope tissue of mother metal steel plate,, contain martensite, residual austenite, MA sometimes as the remaining tissue outside polygonal ferrite and the bainite.
In the present invention, bainite is defined in and separates out the tissue of carbide between bar or granular ferrite or separate out the tissue that carbide is arranged in bar.In addition, martensite is the tissue that does not have carbide precipitate between bar or in the bar.Residual austenite is that the austenite that at high temperature generates residues in the austenite in mother metal steel plate or the Welded Steel Pipe.
In addition, by the thermal treatment of welding zone, the thick MA that generates along the original austenite crystal boundary of HAZ resolves into fine cementite, so low-temperature flexibility improves.Thus, the junction portion of the 1/2t portion under low temperature more or the toughness at junction portion+1mm place improve, for example, when the temperature that the welding zone is heated to 300～500 ℃, can make the V otch summer under-40 ℃ the low temperature than absorb can be for 50J more than.Therefore, when under the utmost point low temperature below-40 ℃, using, preferably heat-treat, form the mixed structure of intracrystalline bainite and cementite having generated organizing further of intracrystalline bainite.
Below the qualification reason of mother metal steel plate of the present invention is narrated.In addition, infusible heat affected zone when being welding owing to HAZ, so the composition of HAZ is identical with mother metal.
C:C is the element that improves the intensity of steel, but in the present invention, the content of restriction C obtains the metal structure based on bainite, seeks to have both high strength and high tenacity.C content is less than at 0.010% o'clock, and intensity is insufficient, and when surpassing 0.050%, toughness reduces.Therefore, in the present invention, best C content is defined as 0.010～0.050% scope.
Si:Si is important deoxidant element in the present invention, in order to obtain effect, need make the Si that contains in the steel more than 0.01%.On the other hand, the content of Si surpasses at 0.50% o'clock, and the toughness of HAZ reduces, so its upper limit is defined as 0.50%.
Mn:Mn uses as reductor, is to guarantee that the intensity of mother metal steel plate and toughness are necessary, and, be to generate as the effective element of MnS sulfides of the product nucleus of intracrystalline phase transformation, of the utmost importance in the present invention.In order to obtain these effects, need contain 0.50% Mn, but the content of Mn surpasses at 2.00% o'clock, can damage the toughness of HAZ.Therefore, the content range of Mn is defined as 0.50～2.00%.In addition, Mn is cheap element, therefore in order to ensure hardening capacity, preferably contains the Mn more than 1.00%, best following being limited to more than 1.50%.
P:P is an impurity, and content surpasses at 0.050% o'clock, and the toughness of mother metal steel plate is significantly reduced.Therefore, the upper limit of the content of P is defined as 0.050%.In order to improve the toughness of HAZ, the content of preferred P is below 0.010%.
S:S is the important element that generates as the effective MnS sulfides of product nucleus of intracrystalline phase transformation in the present invention.The content of S was less than 0.0001% o'clock, and the growing amount of sulfide reduces, and the intracrystalline phase transformation does not take place significantly, therefore need be more than 0.0001%.On the other hand, when in the mother metal steel plate, containing, can generate thick sulfide, toughness is reduced, so the upper limit of S content be defined as below 0.0050% greater than 0.0050% S.In order to improve the toughness of HAZ, be limited to below 0.0030% on the preferred S content.
Al:Al is a reductor, but in the present invention, the oxide compound of Ti is disperseed imperceptibly, therefore with the ceiling restriction of Al content of the utmost importance below 0.020%.In addition, in order to promote the generation of intracrystalline phase transformation, preferred Al content is below 0.010%.Be limited to below 0.008% on preferred.
Ti:Ti in the present invention, make as the product nucleus of intracrystalline phase transformation and effectively the oxide compound of the Ti of effect disperse imperceptibly, be epochmaking element therefore., when containing Ti superfluously, can produce carbonitride and damage toughness.Therefore, in the present invention, the content of Ti is required to be 0.003～0.030%.In addition, Ti is powerful reductor, and therefore the oxygen level when adding Ti can generate thick oxide compound for a long time.Therefore, when steel-making, need utilize Si, Mn to carry out deoxidation in advance, oxygen level is reduced.When thickization of oxide compound of Ti, the intracrystalline phase transformation is difficult to take place, and the effect of crystal boundary pinning is also little, and therefore effective crystal particle diameter of the HAZ of mother metal steel plate and Welded Steel Pipe becomes thick sometimes.
B:B is in steel during solid solution, the element that hardening capacity is increased, but when adding, produces thick BN superfluously, particularly make the toughness reduction of HAZ, so the upper limit of B content is defined as 0.0030%.Welded Steel Pipe of the present invention is the B that adds the raising hardening capacity 0.0003% or more, the index carbon equivalent Ceq of hardening capacity and the index crack sensitivity indices P cm of weldability are controlled at the scope of the best, thereby guarantees intensity and weldability.In addition, the B that adds more than 0.0003% is also effective to suppressing to generate ferrite from crystal boundary.In addition, when the active interpolation by B produces fine BN, be accompanied by the reduction of solid solution N, the toughness of HAZ improves, and therefore preferred B content is greater than 0.0005%.
Mo:Mo improves hardening capacity, promotes to generate the intracrystalline bainite in HAZ, also form carbonitride and useful element that intensity is improved, but by adding more than 0.10%, cost of alloy increases.Therefore, in the present invention, the content of the Mo of high price is restricted to less than 0.10%.Welded Steel Pipe of the present invention is controlled at best scope with the index carbon equivalent Ceq of hardening capacity and the index crack sensitivity indices P cm of weldability, even so that the content of Mo reduces, also can guarantee hardening capacity.
O: oxygen is the element that contains inevitably in the steel, but in the present invention, in order to generate the oxide compound that contains Ti, must restriction O content.Remaining oxygen level in steel during casting, promptly the O content in the mother metal steel plate is required to be 0.0001～0.0080%.This be because, O content was less than 0.0001% o'clock, the number of oxide compound is insufficient, when surpassing 0.0080%, thick oxide compound increases, and can damage the toughness of mother metal and HAZ.In addition, when because the increase of oxygen level, when becoming thick based on the oxide compound of Ti, effective crystal particle diameter of the HAZ of mother metal steel plate and Welded Steel Pipe becomes thick sometimes.
In addition, as improving intensity and flexible element, also can add among Cu, Ni, Cr, V, Nb, Zr, the Ta one or more.In addition, these elements can not cause special detrimentally affect in the occasion of content less than preferred lower limit, therefore can regard impurity as.
Cu, Ni:Cu and Ni can not reduce or damage toughness and effective element that intensity is improved, and in order to obtain effect, the lower limit of Cu content, Ni content is preferably more than 0.05%.On the other hand, the generation of the crackle when suppressing steel ingot when heating and welding, the upper limit of Cu content is preferably 1.50%.The upper limit of Ni content is damaged weldability sometimes owing to ought contain superfluously, therefore is preferably 5.00%.In addition, Cu and Ni in order to suppress the generation of surface imperfection, preferably contain compoundly.In addition, from the viewpoint of cost, the upper limit of Cu and Ni is preferably below 1.00%.
Cr, V, Nb, Zr, Ta:Cr, V, Nb, Zr, Ta are to generate carbide, nitride, by the element that precipitation strength improves the intensity of steel, can contain wherein one or more.For intensity is improved effectively, preferred Cr content following is limited to 0.02%, V content be limited to 0.010% down, Nb content be limited to 0.001% down, the lower limit of Zr content, Ta content is 0.0001%.On the other hand, when adding Cr, because hardening capacity improves, intensity improves, and damage toughness sometimes, so the upper limit of Cr content is preferably 1.50% superfluously.In addition, when adding V, Nb, Zr, Ta, carbide, thickization of nitride are damaged toughness sometimes superfluously, therefore preferred V content on be limited to 0.100%, Nb content on be limited to 0.200%, the upper limit of Zr content, Ta is 0.0500%.
In addition,, seek to improve toughness, also can add among Mg, Ca, REM, Y, Hf, Re, the W one or more in order to control the form of inclusion.In addition, these elements can not cause special detrimentally affect at content down in limited time less than preferred yet, therefore can regard impurity as.
Mg:Mg is the element that manifests effect on the morphology Control of miniaturization, sulfide at oxide compound.The oxide compound of particularly fine Mg plays a role as the product nucleus of intracrystalline phase transformation, in addition, in order to obtain suppressing as the pinning particle effect of thickization of particle diameter, preferably adds more than 0.0001%.On the other hand, when add surpassing the Mg of 0.0100% amount, can generate thick oxide compound, the toughness of the HAZ of mother metal steel plate and Welded Steel Pipe is reduced, so the upper limit of Mg content be preferably 0.0100%.
Ca, REM:Ca and REM, useful to the control of oxide morphology, be to generate granulate, suppress along the generation of the MnS of rolling direction elongation, improve the element of characteristic, particularly anti-lamellar tearing of the thickness of slab direction of steel.In order to obtain this effect, the lower limit of preferred Ca content, REM content is more than 0.0001%.On the other hand, when the upper limit of Ca content, REM content surpassed 0.0050%, oxide compound increased, and the fine Ti oxide compound that contains reduces, and hinders the generation of intracrystalline phase transformation sometimes, therefore is preferably below 0.0050%.
Y, Hf, Re, W:Y, Hf, W, Re also are the elements that presents with the same effect of Ca, REM, when adding, hinder the generation of intracrystalline phase transformation sometimes superfluously.Therefore, the preferable range of Y content, Hf content, Re content is respectively 0.0001～0.0050%, and the preferable range of W content is 0.01～0.50%.
In addition, in the present invention, hardening capacity in order to ensure the HAZ of mother metal steel plate and Welded Steel Pipe, the area occupation ratio that makes the bainite of mother metal is more than 80%, make among the HAZ to generate the intracrystalline bainite, the carbon equivalent Ceq of the following formula of being calculated by the content [quality %] of C, Mn, Ni, Cu, Cr, Mo, V 1 is defined as 0.30～0.53.
Ceq＝C+Mn/6+(Ni+Cu)/15
+ (Cr+Mo+V)/5 formula 1
In addition, in order to ensure the low-temperature flexibility of mother metal and HAZ, the crack sensitivity indices P cm of the following formula of being calculated by the content [quality %] of C, Si, Mn, Cu, Cr, Ni, Mo, V, B 2 is defined as 0.10～0.20.
Pcm＝C+Si/30+(Mn+Cu+Cr)/20+Ni
/60+Mo/15+V/10+5B
In addition, as Ni, Cu, Cr, the V of the element that optionally contains,, in above-mentioned formula 1 and formula 2, calculate as 0 less than above-mentioned preferably prescribing a time limit down.
Become the metal structure of the mother metal steel plate of Welded Steel Pipe, if the area occupation ratio of bainite is more than 80%, the area occupation ratio of polygonal ferrite is below 20%, then the balance of strength and toughness becomes good.In addition, by generating the oxide compound based on Ti, need only effective crystal particle diameter below 20 μ m, then the toughness of mother metal steel plate becomes good.In addition, polygonal ferrite is also effective to the miniaturization of effective crystal particle diameter of mother metal steel plate, and preferably its area occupation ratio is more than 3%.In addition, the wall thickness of preferred mother metal steel plate be 25mm above, be more than the 600MPa with the tensile strength of the circumferential corresponding direction of steel pipe.This is for when using as line pipe, prevents to cause fracture by interior pressure.In addition, the occasion of in needs improve, pressing, the wall thickness of preferred mother metal steel plate is more than the 30mm.On the other hand, the wall thickness of preferred mother metal steel plate be 40mm following, be below the 800MPa with the tensile strength of the circumferential corresponding direction of steel pipe.This be because, because the increase of wall thickness, the rising of tensile strength, the cause that the load with the mother metal steel plate during by the UO process forming increases.In addition, the circumferential corresponding direction of usually so-called and steel pipe is that the plate of mother metal steel plate is horizontal.
Then, manufacture method is described.
In above-mentioned steel making working procedure, after the refining steel, cast, form steel ingot.Casting adopts ordinary method to get final product, but from productive viewpoint, preferred continuous casting.Steel ingot is heated for hot rolling.
The hot rolled Heating temperature is decided to be more than 1000 ℃.This is that the temperature that becomes austenite one phase for the tissue at steel is that hot rolling is carried out in the austenitic area, and makes the crystal particle diameter of mother metal steel plate fine.The upper limit is not stipulated, but in order to suppress thickization of effective crystal particle diameter, preferred reheat temperature is below 1250 ℃.
Owing to can after process furnace is extracted out, begin hot rolling immediately, so hot rolled begins the not special regulation of temperature.For effective crystal particle diameter miniaturization, preferably greater than depressing than being more than 2.0 in 900 ℃ the recrystallization zone with the mother metal steel plate.Depressing ratio in the recrystallization zone, is the thickness of slab of steel ingot and the ratio of thickness of slab under 900 ℃.
Then, if make depressing than being more than 2.5 in the non-recrystallization district below 900 ℃, then after the water-cooled, effective crystal particle diameter of mother metal steel plate becomes below the 20 μ m.For effective crystal particle diameter of making the mother metal steel plate is finer, preferred depressing than being more than 3.0 in the non-recrystallization district below 900 ℃.In addition, in the present invention, so-called non-recrystallization district is rolling depresses ratio, is the ratio of the thickness of slab after the thickness of slab under 900 ℃ is divided by rolling end.In addition, in non-recrystallization district and recrystallization zone depress than the upper limit do not stipulate, but consider the steel ingot before rolling thickness of slab and rolling after the thickness of slab of mother metal steel plate, be generally below 12.0.
About rolling end temp, preferably more than becoming the temperature of austenite one phase, the tissue of mother metal steel plate carries out hot rolling.That is, rolling end temp is preferably Ar
3More than, even but also it doesn't matter owing to generate a spot of polygonal ferrite when rolling, therefore also can be Ar
3More than-50 ℃.Ac
3And Ar
3, can calculate according to the content (quality %) of C, Si, Mn, P, Cr, Mo, W, Ni, Cu, Al, V, Ti.
Ar
3＝910-310C-55Ni-80Mo-80Mn
-15Cr-20Cu
In addition, water-cooled is implemented in rolling end back, is below 600 ℃, then can obtains above-mentioned metal structure that it is good that the toughness of mother metal steel plate becomes if make water-cooled stop temperature.Water-cooled stops the lower limit of temperature not to be stipulated, can be cooled to room temperature yet, but consider productivity, hydrogen defect, is preferably more than 150 ℃.Steel of the present invention is grouped into owing to having the one-tenth that contains B and improve hardening capacity, therefore after the rolling end, even carried out the occasion of air cooling, also generate bainite easily, but according to one-tenth be grouped into, Heating temperature, produce polygonal ferrite sometimes, the area occupation ratio of bainite becomes less than 80%.
After the mother metal steel plate is configured as tubulose, arc welding is carried out in the docking section, make the occasion of Welded Steel Pipe, about being shaped the UOE technology of preferably steel plate being carried out C punching press, U punching press, O punching press.
Arc welding is considered from the toughness and the productive viewpoint of weld metal, preferably adopts submerged arc welding.Particularly when the manufacturing wall thickness was the Welded Steel Pipe of 25～40mm, preferably the heat input from the submerged arc welding of interior outside was 4.0～10.0kJ/mm.If be the heat input of this scope, then have the Welded Steel Pipe of the present invention that above-mentioned one-tenth is grouped into, produce the intracrystalline bainite at HAZ, the effective crystal particle diameter of HAZ becomes below the 150 μ m, can obtain excellent low-temperature flexibility.
Particularly respectively carry out the occasion of together (pass) submerged arc welding from interior outside, if heat input is less than 4.0kJ/mm, the weld metal of the tack welding that before remaining in this welding between inner face metal and the outside metal, carries out sometimes then.In addition, be below the 10.0kJ/mm if make the heat input of submerged arc welding, even the steel pipe of the wall thickness of 25～40mm then, the original austenite particle diameter that also can make HAZ is below the 500 μ m, and flexible is improved effectively.In addition, not needing to make the heat input of heat input when welding from the outside when inner face welds is identical condition, and it is poor to have some heat inputs.
When making when the heat input of interior outside submerged arc welding is 4.0～10.0kJ/mm, be the occasion of 25～40mm at the wall thickness of Welded Steel Pipe, the speed of cooling from 800 ℃ to 500 ℃ the during cooling of HAZ becomes 2～15 ℃/second.Even under the common slow speed of cooling of such ratio, have the Welded Steel Pipe of the present invention that above-mentioned one-tenth is grouped into, in HAZ, also produce the intracrystalline bainite, effective crystal particle diameter of HAZ is below the 150 μ m, can obtain excellent low-temperature flexibility.
In addition, the welding wire that uses in welding is considered the dilution of the composition that is caused by the mother metal steel plate, for the composition that makes weld metal consists of scope described later, is preferably following composition.Promptly, be in quality %, contain C:0.010～0.120%, Si:0.05～0.50%, Mn:1.0～2.5%, Ni:2.0～8.5%, also contain below the Al:0.100%, below the Ti:0.050%, its surplus is grouped into by the one-tenth that Fe and unavoidable impurities constitute.Can contain B:0.0001～0.0050%, also can contain among Cr, Mo, the V one or more in the scope of Cr+Mo+V:1.0～5.0%.
In addition, butt welded seam metal components composition is narrated.
C improves utmost point effective elements to intensity, preferably contains more than 0.010%., when C content was too much, the low temperature crackle was welded in easy generation, and particularly harden with the HAZ that seam welds crossing so-called T cross part in the site welding district sometimes, infringement toughness.Therefore, preferred C content on be limited to 0.100%.For the toughness that makes weld metal improves, be limited to below 0.050% on more preferably.
Si is in order to prevent preferably to contain more than 0.01% as the generation of the pore of welding flaw.On the other hand, contain sometimes superfluously, can make the remarkable deterioration of low-temperature flexibility, so preferred upper limit is below 0.50%.Particularly in the occasion of carrying out welding repeatedly, therefore the low-temperature flexibility deterioration of hot weld seam metal more sometimes is limited to below 0.40% on more preferably.
Mn is that preferred lower limit is more than 1.0% to the balance effective elements of the strength and toughness of guaranteeing excellence., when containing Mn in large quantities, can encourage segregation, not only make the low-temperature flexibility deterioration, and the manufacturing of the welding employed welding wire difficulty that also becomes, so preferred upper limit is below 2.0%.
P and S are impurity, for the deterioration of the low-temperature flexibility that reduces weld metal, reduce the low temperature crack sensitivity, preferably they on be limited to below 0.020% and 0.010%.In addition, consider, be limited to 0.010% on P preferred from the viewpoint of low-temperature flexibility.
Al is to be to make refining and solidify to carry out the element that adds well when making welding wire, for the oxide compound that makes full use of fine Ti system suppresses thickization of the particle diameter of weld metal, preferably contains the Al more than 0.001%., Al is the element that promotes that MA generates, so the preferred upper limit of content is below 0.100%.
Ti is the fine oxide that produces the product nucleus that becomes the intracrystalline phase transformation, helps the element of the particle diameter miniaturization of weld metal, preferably contains more than 0.003%.On the other hand, when containing Ti in large quantities, can generate the carbide of Ti morely, make the low-temperature flexibility deterioration sometimes, so preferred upper limit be below 0.050%.
O is an impurity, and the oxygen amount in the weld metal of finally remaining in is that the situation more than 0.0001% is more., remaining O measures the occasion greater than 0.0500%, and it is many that thick oxide compound becomes, and the toughness of weld metal reduces sometimes, so preferred upper limit is below 0.0500%.
Preferred weld metal also optionally contains Ni, Cr, Mo, V.
Ni is raising hardening capacity, guarantees intensity that the element that low-temperature flexibility is improved preferably contains more than 0.2%.On the other hand, when the content of Ni is too much, produce heat cracking sometimes, so the upper limit is defined as below 3.2%.
Cr, Mo, V all are the elements that improve hardening capacity, for the high strength of weld metal, can contain add up to more than 0.2%, among them one or more.On the other hand, the total amount of one or more among Cr, Mo, the V surpasses at 2.5% o'clock, and low-temperature flexibility deterioration, so preferred upper limit sometimes is below 2.5%.
Weld metal also can also contain B.
B is the element that makes the hardening capacity increase of weld metal, in order to improve intensity, preferably contains more than 0.0001%.On the other hand, the content of B surpasses at 0.0050% o'clock, damage toughness sometimes, so preferred upper limit is below 0.0050%.
In weld metal, because dilution from the mother metal steel plate, sometimes contain element beyond above-mentioned, for example, contain the Cu, the Nb that add to selectively in the mother metal, Zr, Ta, Mg, Ca, REM, Y, Hf, Re, W etc., for the refining that makes welding wire and solidify well and carry out, contain elements such as the Zr, the Nb that add as required, Mg sometimes.They make the impurity that contains inevitably.
The seam postwelding in order to improve the circularity of steel pipe, also can carry out expander.In the occasion that improves the circularity of steel pipe by expander, must make it be deformed to the plastic zone, therefore preferred pipe expanding rate is more than 0.7%.Pipe expanding rate is the outer perimeter of the difference of the outer perimeter steel pipe before divided by expander of representing the outer perimeter of the steel pipe behind the expander and the steel pipe before the expander with percentage and the value that obtains.When pipe expanding rate greater than 2% the time, mother metal, welding zone all reduce owing to viscous deformation causes toughness sometimes.Therefore, pipe expanding rate is preferably 0.7～2.0%.
In addition, preferably thermal treatment is implemented in the welding zone of steel pipe and HAZ, particularly when the temperature that is heated to 300～500 ℃, the thick MA that generates along the original austenite crystal boundary resolves into bainite and fine cementite, and toughness improves.When Heating temperature during less than 300 ℃, the decomposition of thick MA sometimes is insufficient, and it is insufficient that flexible improves effect, so preferred lower limit is more than 300 ℃.On the other hand, when the welding zone being heated to, produce precipitate sometimes greater than 500 ℃, the toughness deterioration of weld metal, so preferred upper limit is below 500 ℃.When the MA that generates among the hot HAZ again resolves into bainite and cementite, in SEM observes,, contain the tissue of fine white precipitate for inside though shape and MA are same, can distinguish with MA.
The thermal treatment of welding zone and HAZ is adopted burner to heat from the outside and is got final product, and also can carry out ratio-frequency heating.Outside surface arrives after the thermal treatment temp, can cool off immediately, but in order to promote the decomposition of MA, preferably keep for 1～600 second., consider cost, the productivity of equipment, the hold-time was preferably below 300 seconds.
Embodiment
Then, embodiments of the invention are narrated.
Oxygen concn when adding Ti is adjusted in 0.001～0.003% the scope, and melting has the steel of the chemical ingredients of table 1, makes the steel ingot of the 240mm thickness of the chemical ingredients with table 1.These steel ingots are heated to the Heating temperature shown in the table 2, carry out hot rollings to 45～160mm in the recrystallization temperature district more than 950 ℃.In addition, in non-recrystallization district, with depressing than hot rolling shown in the table 2 to the thickness of slab shown in the table 2 from 880 ℃ to 800 ℃ temperature range.The hot rolled end temp is defined as beginning water-cooled more than Ar3-50 ℃ under 750 ℃, stops water-cooled under various temperature.
By the steel plate that obtains, according to JIS Z 2242, making is horizontal as vertical with plate, the v-notch test specimen that otch and thickness of slab direction are provided with abreast.The produce position of summer than test specimen is that skin section is the substantial middle of wall thickness apart from position and the 1/2t portion of the about 2～12mm in surface promptly.Charpy test is carried out under-40 ℃, obtains the absorption energy.Tensile properties adopts the test specimen of API standard to estimate.In addition, when the mother metal steel plate that with thickness of slab is 25～40mm is configured as Welded Steel Pipe,, confirmed at the thickness of slab central part by the parsing of finite elements method, little by the strained influence that shaping imports.In addition, in fact,, make Welded Steel Pipe with the steel plate cold shaping, the result who confirms for the influence of work hardening, TS rises about 20～30MPa sometimes, about toughness, no matter is the central part at thickness of slab, still in skin section, influence all for a short time, be the degree of error at measurment.
The microstructure of the thickness of slab central part by observation by light microscope mother metal steel plate is measured the area occupation ratio of polygonal ferrite, bainite, confirms remaining tissue.Effective crystal particle diameter of mother metal steel plate is measured by EBSP.
Table 2
| Make No. | Heating temperature ℃ | Depress ratio | Water-cooled stops temperature ℃ | Thermal treatment temp ℃ | Thickness of |
| 1 | 1025 | 3.4 | 290 | 450 | 30 |
| 2 | 1030 | 3.4 | 550 | 380 | 29 |
| 3 | 1060 | 3.7 | 560 | ? | 34 |
| 4 | 1045 | 2.8 | 450 | 420 | 38 |
| 5 | 1035 | 3.4 | 300 | ? | 35 |
| 6 | 1010 | 3.5 | 290 | 350 | 29 |
| 7 | 1025 | 3.9 | 100 | ? | 34 |
| 8 | 1035 | 4.5 | 320 | ? | 32 |
| 9 | 1040 | 4.1 | 350 | 300 | 31 |
| 10 | 1080 | 3.5 | 520 | ? | 32 |
| 11 | 1030 | 4.5 | 550 | ? | 35 |
| 12 | 1040 | 1.5 | 300 | 460 | 32 |
| 13 | 1060 | 3.3 | Air cooling | ? | 38 |
| 14 | 1030 | 3.5 | 450 | ? | 34 |
| 15 | 1050 | 3.3 | 500 | ? | 33 |
* depress than being below 900 ℃, up to the ratio of depressing of rolling end
* heat treated empty hurdle means does not have thermal treatment
* the underscore in the table means beyond the scope of the invention
Then, the dilution that consideration is caused by the mother metal steel plate, employing has the welding wire that following compositions is formed, it is in quality % that described one-tenth is grouped into, contain C:0.010～0.120%, Si:0.05～0.5%, Mn:1.0～2.5%, below the Al:0.100%, below the Ti:0.050%, and contain Ni:2.0～8.5% as required, Cr in the scope of Cr+Mo+V:1.0～5.0%, Mo, among the V one or more, contain B:0.0001～0.0050%, its surplus is made of Fe and unavoidable impurities, making weld heat input is 4.0～10.0kJ/mm, respectively carry out one submerged arc welding from interior outside, made welding joint.In addition, the joint of a part has been implemented thermal treatment under the temperature shown in the table 2.In addition, produce sample, carried out composition analysis from weld metal.The tensile strength of weld metal is measured according to JIS Z 3111.The chemical ingredients and the tensile strength of weld metal are shown in table 3.
Produce small pieces from welding joint, measure effective crystal particle diameter of HAZ by EBSP.In addition, will be that the petal-like bainite of being generated as of starting point is defined as the intracrystalline bainite with the inclusion, measured area occupation ratio.In addition, the summer of HAZ according to JIS Z 2242, adopts the v-notch test specimen to measure down at-40 ℃ than absorbing energy.V-notch is arranged at from the position of welded bonds to mother metal side 1mm, is determined under-40 ℃ to carry out.In addition, will with weld metal vertical laterally be made as test specimen vertically, make the substantial middle of weld metal in parallel portion, produce the test specimen of API standard, carry out tension test, carry out the judgement of fracture position.The results are shown in table 4.About the intracrystalline phase-change organization of table 4, be the area occupation ratio of intracrystalline bainite.
In addition, one one mother metal steel plate is made steel pipe by UO technology, submerged arc welding, expander, and investigation microstructure and mechanical characteristics have confirmed that the microstructure of HAZ of the mother metal of steel plate and joint and mechanical characteristics are for equal.
Making No.1～9 is example of the present invention, and effective crystal particle diameter of mother metal steel plate is below the 20 μ m, and effective crystal particle diameter of HAZ is below the 150 μ m.In addition, the summer under-40 ℃ of mother metal and HAZ can be greater than 50J than absorbing, and low-temperature flexibility is good.In these examples of the present invention, the fracture position of the tension test of joint is the mother metal steel plate, and the softening of HAZ also is out of question.In addition, making No.9, is that its thermal treatment temp is low, and is carrying out heat treated situation relatively under preferred temperature, the slightly little example of raising effect of low-temperature flexibility.
On the other hand, make No.10,11,14 and 15, the composition of its mother metal steel plate is made No.12 and 13 beyond the scope of the invention, and it is created conditions beyond the scope of the invention, and they all are comparative examples.Wherein, the Al content of making No.10 is many, and the Ti content of making No.11 is few, therefore is that the intracrystalline bainite reduces, and the example that also reduces of the low-temperature flexibility of HAZ.
Making No.12, is depressing than little below 900 ℃, and effective crystal particle diameter of mother metal steel plate becomes big, the example that the low-temperature flexibility of mother metal steel plate reduces.In addition, making No.13, is to have carried out air cooling owing to after rolling, so the example that the area occupation ratio of the polygonal ferrite of mother metal increases, intensity reduces.Making No.14 is because Ceq and Pcm are low, so the example of intensity reduction.Make No.15 and be because Ceq and Pcm height, so the example that reduces of the toughness of intensity height, mother metal steel plate.In addition, because the intensity height of mother metal steel plate, so the result of the tension test of joint, rupture at HAZ.
Utilize possibility on the industry
According to the present invention, even reduce Mo content, also can guarantee the low-temperature flexibility of the HAZ of line-pipes welded still pipe, the effective welded still pipe of high-strength line-pipe and the manufacture method thereof of the excellent in low temperature toughness of cheapness can be provided, and, according to the present invention, can also guarantee that wall thickness is more than the 25mm and then is the low-temperature flexibility of the effective welded still pipe of high-strength line-pipe of the above heavy wall of 30mm that contribution industrially is remarkable.
Among the present invention the expression number range " more than " and " following " include given figure.
Claims (13)
1. the effective Welded Steel Pipe of the high-strength line-pipe of a low-temperature flexibility excellence, be to being configured as the steel pipe that piped mother metal steel plate has carried out the seam weldering, it is characterized in that, described mother metal steel plate has in quality % and contains C:0.010～0.050%, Si:0.01～0.50%, Mn:0.50～2.00%, S:0.0001～0.0050%, Ti:0.003～0.030%, O:0.0001～0.0080%, B:0.0003～0.0030%, and P, Al, Mo is restricted to below the P:0.050% respectively, below the Al:0.020%, Mo: less than 0.10%, its surplus is grouped into by the one-tenth that iron and unavoidable impurities constitute, the Ceq that is tried to achieve by following formula 1 is 0.30～0.53, the Pcm that is tried to achieve by following formula 2 is 0.10～0.20, it is that polygonal ferrite below 20% and area occupation ratio are the bainite more than 80% that the metal structure of described mother metal steel plate comprises area occupation ratio, adopt the area of the part that EBSP will surround by the border with the crystalline orientation difference more than 15 ° to be converted into quite footpath and effective crystal particle diameter of obtaining is below the 20 μ m of circle, effective crystal particle diameter of welded heat affecting zone is below the 150 μ m
Ceq＝C+Mn/6+(Ni+Cu)/15
+ (Cr+Mo+V)/5 formula 1,
Pcm＝C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B
Formula 2,
Wherein, C, Si, Mn, Ni, Cu, Cr, Mo, V, B are the content (quality %) of each element.
2. the effective Welded Steel Pipe of the high-strength line-pipe of low-temperature flexibility excellence according to claim 1 is characterized in that, the wall thickness of described mother metal steel plate is 25～40mm.
3. the effective Welded Steel Pipe of the high-strength line-pipe of low-temperature flexibility excellence according to claim 1 and 2 is characterized in that, is 600～800MPa with the tensile strength of the described mother metal steel plate that circumferentially is made as draw direction of described steel pipe.
4. the effective Welded Steel Pipe of the high-strength line-pipe of low-temperature flexibility excellence according to claim 1 and 2 is characterized in that, described mother metal steel plate also contains Cu:0.05～1.50% in quality %, among Ni:0.05～5.00% one or both.
5. the effective Welded Steel Pipe of the high-strength line-pipe of low-temperature flexibility excellence according to claim 1 and 2, it is characterized in that described mother metal steel plate also contains one or more among Cr:0.02～1.50% in quality %, V:0.010～0.100%, Nb:0.001～0.200%, Zr:0.0001～0.0500%, Ta:0.0001～0.0500%.
6. the effective Welded Steel Pipe of high-strength line-pipe according to claim 1 and 2, it is characterized in that described mother metal steel plate also contains one or more among Mg:0.0001～0.0100% in quality %, Ca:0.0001～0.0050%, REM:0.0001～0.0050%, Hf:0.0001～0.0050%, Re:0.0001～0.0050%, W:0.01～0.50%.
7. the effective Welded Steel Pipe of the high-strength line-pipe of low-temperature flexibility excellence according to claim 1 and 2, it is characterized in that, weld metal contains C:0.010～0.100%, Si:0.01～0.50%, Mn:1.0～2.0%, Al:0.001～0.100%, Ti:0.003～0.050%, O:0.0001～0.0500% in quality %, and P, S are restricted to respectively below the P:0.010%, below the S:0.010%, and its surplus is made of iron and unavoidable impurities.
8. the effective Welded Steel Pipe of the high-strength line-pipe of low-temperature flexibility excellence according to claim 7, it is characterized in that described weld metal also contains Ni:0.2～3.2% or Cr+Mo+V:0.2～2.5% or Ni:0.2～3.2% and Cr+Mo+V:0.2～2.5% in quality %.
9. the manufacture method of the effective Welded Steel Pipe of high-strength line-pipe of a low-temperature flexibility excellence, it is characterized in that, when steel-smelting, interpolation Si, Mn add Ti after carrying out weak deoxidation, cast the steel of the composition described in each that is adjusted into claim 1 and 4～6, the steel ingot that obtains is heated to more than 1000 ℃, makes depressing than being to carry out hot rolling more than 2.5 in the non-recrystallization humidity province, stopping water-cooled below 600 ℃, and then be tubulose, with docking section seam weldering the steel formability that obtains.
10. the manufacture method of the effective Welded Steel Pipe of high-strength line-pipe of low-temperature flexibility excellence according to claim 9, it is characterized in that, is tubulose with described steel plate by the UO process forming, use welding wire and sintered type or fusion solder flux to carry out submerged arc welding from interior outside the docking section, carry out expander then.
11. the manufacture method of the effective Welded Steel Pipe of high-strength line-pipe of low-temperature flexibility excellence according to claim 10 is characterized in that, the heat input of described submerged arc welding is 4.0～10.0kJ/mm.
12. the manufacture method according to the effective Welded Steel Pipe of high-strength line-pipe of each described low-temperature flexibility excellence of claim 9～11 is characterized in that butt seam welding portion heat-treats.
13. the manufacture method of the effective Welded Steel Pipe of high-strength line-pipe of low-temperature flexibility excellence according to claim 12 is characterized in that, stitches the thermal treatment of weldering portion in 300～500 ℃ scope.
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| JP2006324176 | 2006-11-30 | ||
| JP324176/2006 | 2006-11-30 | ||
| JP309280/2007 | 2007-11-29 | ||
| JP2007309280 | 2007-11-29 | ||
| JP2007310457A JP5251092B2 (en) | 2006-11-30 | 2007-11-30 | Welded steel pipe for high-strength line pipe excellent in low temperature toughness and method for producing the same |
| JP310457/2007 | 2007-11-30 | ||
| PCT/JP2007/073622 WO2008069289A1 (en) | 2006-11-30 | 2007-11-30 | Weld steel pipe with excellent low-temperature toughness for high-strength line pipe and process for producing the same |
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| CN101541994B true CN101541994B (en) | 2011-08-03 |
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