JP4171169B2 - Ultra-high-strength steel pipe with seam welds with excellent cold cracking resistance and manufacturing method thereof - Google Patents

Ultra-high-strength steel pipe with seam welds with excellent cold cracking resistance and manufacturing method thereof Download PDF

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JP4171169B2
JP4171169B2 JP2000310935A JP2000310935A JP4171169B2 JP 4171169 B2 JP4171169 B2 JP 4171169B2 JP 2000310935 A JP2000310935 A JP 2000310935A JP 2000310935 A JP2000310935 A JP 2000310935A JP 4171169 B2 JP4171169 B2 JP 4171169B2
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welding
weld metal
steel pipe
seam
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JP2002115032A (en
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卓也 原
均 朝日
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新日本製鐵株式会社
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[0001]
BACKGROUND OF THE INVENTION
The present invention is an ultra-high-strength steel pipe that can be used widely as a line pipe for transporting natural gas and crude oil, and that enables high-pressure, high-efficiency transport, and high-efficiency local construction with a small outer diameter and low weight, and a method for manufacturing the same In particular, the present invention relates to an ultra-high strength steel pipe having a seam welded portion excellent in cold cracking resistance and having a tensile strength (TS) of 900 MPa or more and a method for producing the same.
[0002]
[Prior art]
In recent years, pipelines have become increasingly important as long-distance transportation methods for crude oil and natural gas. Currently, the American Petroleum Institute (API) standard X65 is the basic design for trunk line pipes for long-distance transportation, and the actual usage is overwhelmingly large.
[0003]
However, in order to (1) improve transportation efficiency by increasing pressure and (2) improve local construction efficiency by reducing the outer diameter and weight of the line pipe, a higher strength line pipe is required. Up to now, line pipes up to X80 (tensile strength of 620 MPa or more) have been put into practical use, but the need for higher-strength line pipes has become stronger. Currently, research on ultra-high-strength line pipe manufacturing methods is based on conventional X80 line pipe manufacturing techniques (eg NKK Technical Report No. 138 (1992), pp24-31 and The 7th Offshore Mechanics and Arctic Engineering (1988), Volume V , pp. 179-185), but it is considered that the production of X100 (tensile strength of 760 MPa or more) line pipe is the limit. For ultra-high-strength line pipes exceeding X100, steel plate production has already been studied (PCT / JP96 / 00155, 00157), but the balance between strength and low-temperature toughness, welding heat affected zone (HAZ) and welding We have many problems such as metal toughness, on-site weldability, joint softening, weld properties that can break the pipe by burst test, etc. Early development is desired.
[0004]
On the other hand, in order to improve the seam welding efficiency of HT80 and HT100 class high-tensile steel pipes, a method of performing seam welding by double-sided one-pass welding with large heat input from conventional multi-layer welding with small heat input has been studied. However, when seam welding of such an ultra-high strength steel pipe is performed with one pass of high heat input, cold cracking of the weld metal is likely to occur. Conventionally, in order to prevent such cold cracking, It was necessary to preheat or postheat the steel (Journal of the Japan Welding Society 49 (1980) p.572).
[0005]
If such preheating or post heat treatment is applied during seam welding in an actual ultra high strength line pipe production line, it will not only cost a lot for the equipment, but also considering the processing time for preheating and postheating. It was not necessarily a fundamental solution for improving productivity.
[0006]
[Problems to be solved by the invention]
In view of the problems of the above prior art, the present invention provides a method for producing an ultra-high-strength line pipe having a tensile strength of 900 MPa or more (API standard X100 or more) when performing double-sided one-pass seam welding with large heat input. It is an object of the present invention to provide an ultra-high strength steel pipe free from cold cracking of weld metal and a method for producing an ultra-high strength steel pipe capable of preventing cold cracking of weld metal.
[0007]
[Means for Solving the Problems]
  This invention solves said subject and the place made into the summary is as follows.
(1) In the weld metal of the seam welded portion, the components of the inner and outer surfaces of the weld metal formed by the seam welding are mass%, C: 0.04 to 0.14%, Si: 0.05 to 1. %, Mn: 1.2-2.2%, P: ≦ 0.01%, S: ≦ 0.01%, Ni: 1.3-6%, Ti:0.018~ 0.05%, Al: ≦0.010%, B: ≦ 0.005%In addition, 2 types of Cr and Mo are contained in a total amount of 1 to 2.5%, or 3 types of Cr, Mo and V are contained in a total amount of 1 to 2.5%, with the balance being iron. And a seam weld having excellent low-temperature cracking resistance, comprising at least 1% of the retained austenite phase in the structure of at least the inner surface of the inner and outer surface of the weld metal, the inevitable impurities. Having ultra high strength steel pipe.
(2The above-mentioned (1), wherein the weld metal has a bainite martensite fraction of 50% or more.)An ultra-high-strength steel pipe having a seam welded portion having excellent cold cracking resistance as described.
(3(1) The tensile strength of the weld metal is 900 MPa or more.Or(2)Ultra high strength steel with seam welds with excellent cold crack resistance
tube.
(4)% By mass, C: 0.03-0.1%, Si: ≦ 0.6%, Mn: 1.7-2.5%, P: ≦ 0.015%, S: ≦ 0.003% Ni: 0.1-1%, Mo: 0.15-0.6%, Nb: 0.01-0.1%, Ti: 0.005-0.03%, Al: ≦0.0134%N: 0.001 to 0.006%, Mg: ≦ 0.006%, B: ≦ 0.005%, V: ≦ 0.1%, Cu: ≦ 1%, Cr: ≦ A steel plate containing one or more of 0.8%, Ca: ≦ 0.01%, and REM: ≦ 0.02%, the balance being iron and unavoidable impurities is formed into a tubular shape in the UO process After shaping | molding and butting | matching the steel plate edge part to which the groove processing was given, after performing the tack welding of the butted groove part, C: 0.01-0.12%, Si: ≦ 0.3%, Mn: 1.2 to 2.4%, Ni: 4 to 8.5%, total amount of one or more of Cr, Mo and V: 3 to 5%, Ti :0.060Containing ~ 0.15%,Al: ≦ 0.033%,Low temperature resistance characterized in that main welding is performed by submerged arc welding from the inner surface and outer surface using a welding wire consisting of iron and inevitable impurities and the firing-type flux or fusion-type flux, and then tube expansion is performed. A method for producing an ultra-high-strength steel pipe having a seam welded portion with excellent crackability.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the contents of the present invention will be described in detail.
The ultra-high strength steel pipe having a seam welded portion having a tensile strength (TS) of 900 MPa or more and excellent in low-temperature cracking resistance, which is an object of the present invention. Because it withstands about twice the pressure compared to X65, it can transport about twice as much gas at the same size. On the other hand, when using X65 to achieve the same gas transport efficiency as the above ultra-high-strength line pipe, it is necessary to increase the wall thickness in order to increase the pressure, resulting in high material costs, transport costs, and local welding costs. As a result, the pipeline laying costs will rise significantly. This is the reason why an ultra-high-strength line pipe having a tensile strength (TS) of 900 MPa or more is required, but with such an ultra-high-strength line pipe, it is extremely difficult to manufacture a steel pipe.
[0009]
In particular, the low-temperature cracking of weld metal that occurs in seam welding during the manufacture of steel pipes tends to occur more frequently depending on the strength of the weld metal and the amount of heat input during seam welding. The decrease in the strength of the weld metal has a limit in order to ensure the strength balance with the base metal, and the decrease in the heat input during seam welding (small heat input multi-layer welding) has the problem of a decrease in productivity. Therefore, conventionally, when performing seam welding of an ultra-high strength steel pipe by high heat input double-sided one-pass welding, cold cracking of the weld metal has been prevented by preheating and post heat treatment of the welded portion.
[0010]
The present inventors prevent cold cracking of weld metal without performing preheating and post heat treatment of conventional welds in large heat input double pass 1-pass seam welding when manufacturing ultra-high strength steel pipes with a tensile strength of 900 MPa or more. The production method of the super high strength steel pipe with excellent productivity was studied by experiments.
FIG. 1 shows a seam weld of an ultra high strength steel pipe. In seam welding at the time of normal steel pipe manufacturing, after attaching both ends of a steel plate formed into a tubular shape, the attachment portion is first tack welded from the outer surface by MAG arc welding or the like, and then the tack welded portion is attached. Further, main welding is performed from the inner surface and then from the outer surface by submerged arc welding or the like. Usually, as shown in FIG. 1, the inner surface main weld metal part 2 is formed by performing main welding from the inner surface so as to overlap with the tack weld metal part 4 formed at the time of tack welding. The outer surface weld metal portion 1 is formed by performing main welding from the outer surface so as to overlap with 2 and melt the tack weld metal portion 4.
[0011]
The inventors conducted seam welding under various welding conditions and examined in detail the relationship between the structure of the weld metal and the cold cracking resistance. As a result, the low-temperature cracking of the ultra-high-strength weld metal occurs in the inner surface main weld metal 2 after the main welding from the outer surface shown in FIG. 1, and there are many residual austenite phases in the structure of the inner surface main welding metal 2. When present, it has been found that the low temperature cracking resistance is good, and that the effect is remarkably exhibited especially when the content of the retained austenite phase is 1% or more.
[0012]
This is because if there is a lot of retained austenite in the inner surface of the main weld metal 2, hydrogen in the weld metal is trapped, the apparent hydrogen diffusion constant decreases, and the allowable limit hydrogen amount that does not cause cold cracking of the weld metal increases. It is thought to do.
The present invention has been made based on these findings, and remains in the structure of at least the inner surface main weld metal and the inner surface main weld metal formed during the main welding in the seam weld. An ultrahigh strength steel pipe having a seam welded portion excellent in cold cracking resistance, characterized by containing 1% or more of an austenite phase.
[0013]
In the present invention, it is necessary that at least 1% of the retained austenite phase is contained in the structure of at least the inner surface main weld metal of the inner surface main weld metal and the outer surface main weld metal. This means that the residual austenite phase is less than 1%. Then, the effect of increasing the allowable limit hydrogen amount that does not cause low temperature cracking due to hydrogen trap in the weld metal is not sufficiently exerted, and the tensile strength (TS): preventing low temperature cracking of the super high strength weld metal of 900 MPa or more. It is because it becomes impossible.
[0014]
In order to make the tensile strength of the weld metal 900 MPa or more, the bainite / martensite fraction needs to be 50% or more in the bainite / martensite structure of the weld metal.
Moreover, in this invention, the component of a weld metal is prescribed | regulated as follows.
In addition,% shown below means the mass% unless there is particular description.
[0015]
The amount of C is limited to 0.04 to 0.14%. C is extremely effective for improving the strength of steel, and at least 0.04% is necessary to obtain the target strength in the martensite structure. However, if the amount of C is too large, cold cracking is likely to occur, leading to an increase in the HAZ maximum hardness of the so-called T-cross portion where the on-site weld and seam welding intersect, so the upper limit was made 0.14%. Furthermore, the upper limit is preferably 0.1%.
[0016]
Si needs to be 0.05% or more in order to form retained austenite to suppress low temperature cracking, but if the content is large, the low temperature toughness will be significantly deteriorated, and the low temperature toughness of inner and outer surface main welding will be ensured. The upper limit was 1%.
Mn is an indispensable element for ensuring an excellent balance between strength and low-temperature toughness. In addition, Mn-containing sulfide inclusions are generated and intragranular bainite is generated as a core to produce low-temperature toughness of weld metals. To improve. In particular, when a cation vacancy type Ti-containing oxide is present in the grain, Mn-containing sulfide is precipitated around the Ti-containing oxide, and the generation of Mn-containing sulfide in the grain is promoted. Generation is promoted. Further, Mn is a component necessary for forming retained austenite for suppressing the low-temperature cracking that is the object of the present invention. In order to obtain these effects, the lower limit of the addition amount is set to 1.2%. However, too much Mn not only promotes segregation and deteriorates low-temperature toughness, but also makes it difficult to produce a welding material, so the upper limit was made 2.2%.
[0017]
The content of P and S is preferably low in order to reduce the low temperature toughness of the weld metal and reduce the low temperature cracking susceptibility, and the upper limit of each is defined as 0.010%.
Ni is necessary for increasing the hardenability to ensure strength, further improving low-temperature toughness and forming retained austenite for suppressing low-temperature cracking. Since it is difficult to obtain the target strength and low temperature toughness at 1.3% or less, the lower limit is set to 1.3%. On the other hand, if the content is too high, there is a risk of hot cracking, so the upper limit was made 6%.
[0018]
  Cr, Mo, and V are all elements that are necessary for improving the hardenability and obtaining high strength.Add 2 types of Cr and Mo in the range of 1 to 2.5% in total amount, or 3 types of Cr, Mo and V in total amountAdd in the range of 1-2.5%. If the total content is less than 1%, the effect is not sufficient. On the other hand, if excessively added, the risk of cold cracking increases, so the upper limit was made 2.5%. B is an element that enhances the hardenability in a small amount and is effective for improving the low temperature toughness of the weld metal. However, if the content is too large, the low temperature toughness is lowered, so the content range is set to 0.005% or less.
[0019]
  Al is known as a deoxidizing component and Al2OThreeThe oxide is an anion vacancy type oxide and has poor bonding with Mn-containing sulfides such as MnS. In order not to inhibit, it is preferable to make it as low as possible. Therefore, in this invention, the upper limit of the content is prescribed | regulated to 0.02%.In addition, the upper limit of the amount of Al of the weld metal is the implementation No. in Table 4 of the examples of the present invention. Based on 0.010% of the Al content of 1, the content is made 0.010% or less.
[0020]
  Ti is an essential component for generating inclusions of Ti-containing oxides that generate intragranular bainite and composite particles of this oxide and Mn-containing sulfide, and these inclusions serve as nuclei in the grains. Inner bainite is generated to improve the low temperature toughness of the weld metal. In order to obtain these effects, the lower limit of the content is 0.003%. Further, if the Ti content is excessively large, a large amount of Ti carbide is generated and the low temperature toughness is deteriorated, so the upper limit was made 0.05%.In addition, the lower limit of the amount of Ti of the weld metal is the implementation No. in Table 4 of the examples of the present invention. Based on 0.018% of the Ti content of 2, it is set to 0.018% or more.
[0021]
Further, in the present invention, in addition to the above components, elements such as Zr, Nb, and Mg may be further contained in the weld metal as necessary in order to improve refining and solidification during welding. . In addition, it is preferable that the oxygen amount contained in a weld metal is 20 ppm or more.
Next, the manufacturing method of the ultra high strength steel pipe of this invention is demonstrated below.
[0022]
The ultra high strength steel pipe of the present invention is formed into a tubular shape in the UO process in which the steel sheet is formed into a U shape and then into an O shape. This seam welding is performed by submerged arc welding of a pass, and thereafter, it can be efficiently manufactured by a method of manufacturing a steel pipe that is expanded to increase the roundness. This seam welding by submerged arc welding is excellent in welding efficiency, but since the dilution rate of the base metal is large, in order to obtain the desired weld metal composition and characteristics, dilution of the component from the base material is considered. It is necessary to select a welding material. Further, the tack seam welding performed before the seam welding has a smaller welding area and less influence on the quality of the weld metal part than the seam welding. Therefore, in this invention, although the component of the welding wire used for this seam welding needs to be prescribed | regulated, the component of the welding wire used for temporary seam welding does not need to prescribe | regulate in particular.
[0023]
The reason for limiting the chemical composition of the welding wire used for the present seam welding at the time of manufacturing the steel pipe of the present invention is described below. In addition, unless otherwise indicated,% shown below shall show the mass%.
C was set to 0.01 to 0.12% in consideration of dilution with the base material component and mixing of C from the atmosphere in order to obtain a range of C amount required for the weld metal.
[0024]
In order to obtain a range of Si amount required for the weld metal, Si is set to 0.3% or less in consideration of dilution by the base material component.
Mn is set to 1.2% to 2.4% in consideration of dilution by a base material component in order to obtain a range of Mn amount required for the weld metal.
In order to obtain a range of Ni amount required for the weld metal, Ni is set to 4% to 8.5% in consideration of dilution by the base material component.
[0025]
  In order to obtain a range of contents in which the total amount of one or more of these components is required for the weld metal, Cr, Mo, and V are 3 to 3 in consideration of dilution by the base material components. 5%. In order to obtain a range of Ti amount required for the weld metal, Ti takes into account 0.005 to 0.005 in consideration of dilution by the base material component.0.15%It was.In addition, the lower limit of the Ti amount of the welding wire is the implementation No. in Table 3 of the examples of the present invention. Based on 0.060% of the Ti amount of 2, it is made 0.060% or more.
[0026]
  P, S, and Al are unavoidable impurity components. In the present invention, P, S, and Al are desirably as small as possible in order to suppress deterioration of the low temperature toughness of the weld metal. P and S are each 0.01% or less. , Al is preferably regulated to 0.02% or less.Note that the Al amount of the welding wire is the same as that in Table 3 of the embodiment of the present invention. Based on 0.033% of the Al content of 1, the content is regulated to 0.033% or less.Further, in the present invention, the B content in the welding wire is not particularly required to be specified, but may be added as a hardenability component according to the necessity of adjusting the strength.
[0027]
Moreover, you may add Zr, Nb, Mg, etc. as a deoxidizer in a welding wire. In the present invention, the temporary seam welding and the main seam welding can be welded using not only a single electrode but also a plurality of electrodes. In consideration of welding efficiency, the seam welding is particularly preferably gas shielded arc welding or submerged arc welding with a plurality of electrodes. In the case of welding with a plurality of electrodes, it is possible to combine various wires, and it is not necessary for each wire to be in the above component range, and it is sufficient that the average composition from each wire component and consumption is in the above component range.
[0028]
Moreover, the filling flux used for this seam welding by the submerged arc welding at the time of manufacturing the steel pipe of the present invention is roughly classified into a firing type flux and a melting type flux. Firing-type fluxes have the advantage that alloy materials can be added and the amount of diffusible hydrogen is low, but they have the disadvantage of being easily pulverized and difficult to use repeatedly. On the other hand, the melt-type flux is in the form of glass powder, has the advantages of high grain strength and is difficult to absorb moisture, and has the disadvantage that diffusible hydrogen is slightly high. From the viewpoint of reducing the low temperature cracking of the ultra-high strength weld metal, which is the object of the present invention, a calcined flux is more desirable, but there is a problem of high cost. On the other hand, molten flux can be recovered and used repeatedly, and it is suitable for mass production and has a low cost. However, there is a problem in that strict quality control is required although it can be handled industrially. Therefore, in the present invention, it is not particularly necessary to limit the type of flux, and either can be used.
[0029]
Next, the reasons for limiting the steel plate components used in manufacturing the steel pipe of the present invention will be described.
The amount of C is limited to 0.03 to 0.1%. C is extremely effective for improving the strength of steel, and at least 0.03% is necessary to obtain the target strength in the martensite structure. However, if the amount of C is too large, the base metal, HAZ low temperature toughness and on-site weldability are significantly deteriorated, so the upper limit was made 0.1%. Furthermore, the upper limit is preferably 0.07%.
[0030]
Si is an element added for deoxidation and strength improvement, but if added in a large amount, the HAZ toughness and on-site weldability are remarkably deteriorated, so the upper limit was made 0.6%. Steel can be deoxidized with either Al or Ti, and Si does not necessarily have to be added.
Mn is a martensite-based microstructure of the steel of the present invention, and is an indispensable element for ensuring an excellent balance between strength and low temperature toughness, and its lower limit is 1.7%. However, if Mn is too much, not only the hardenability of the steel will increase and the HAZ toughness and on-site weldability will deteriorate, but also the center segregation of the continuously cast steel slab will be promoted and the low temperature toughness of the base metal will also deteriorate, so the upper limit is set. 2.5%.
[0031]
The purpose of adding Ni is to improve the low carbon steel of the present invention without deteriorating the low temperature toughness and on-site weldability. Compared with the addition of Mn, Cr and Mo, the addition of Ni is less likely to form a hardened structure harmful to low temperature toughness in the rolled structure (especially the central segregation zone of the continuous cast steel slab). It has been found that the addition of a trace amount of Ni is also effective for improving the HAZ toughness (in particular, the effective Ni addition amount is 0.3% or more in terms of HAZ toughness). However, if the addition amount is too large, not only the economy but also the HAZ toughness and on-site weldability are deteriorated, so the upper limit was made 1%. Ni addition is also effective for preventing Cu cracking during continuous casting and hot rolling. In this case, Ni needs to be added by 1/3 or more of the amount of Cu.
[0032]
Mo is added in an amount of 0.15% or more in order to improve the hardenability of the steel sheet and to obtain a target martensite-based structure. In particular, in the B-added steel, the effect of improving the hardenability of Mo is enhanced, and when Mo coexists with Nb, recrystallization of austenite during controlled rolling is suppressed, and the austenite structure is refined. However, if added in excess, the upper limit is made 0.6% in order to degrade the HAZ toughness and field weldability and further reduce the effect of improving the hardenability of B.
[0033]
By coexisting with the Mo described above, Nb not only suppresses austenite recrystallization during controlled rolling and refines the structure, but also contributes to precipitation hardening and hardenability, thereby strengthening the steel. In particular, when Nb and B coexist, the effect of improving hardenability increases synergistically. In order to obtain these effects, 0.01% or more of Nb is added in the present invention. However, if the amount of Nb added is too large, the HAZ toughness and on-site weldability are adversely affected, so the upper limit was made 0.1%.
[0034]
Ti forms fine TiN in the steel, suppresses coarsening of austenite grains during slab reheating and HAZ, refines the microstructure, and improves the low temperature toughness of the base material and HAZ. Moreover, it has a role which fixes solid solution N harmful to the hardenability improvement effect of B as TiN. For this purpose, it is desirable to add Ti in an amount of 3.4 N (each by weight%) or more. Further, when the amount of Al is small (for example, 0.005% or less), Ti forms an oxide, acts as an intragranular ferrite formation nucleus in the HAZ, and has an effect of refining the HAZ structure. In order to exhibit such an effect of TiN, it is necessary to add at least 0.005% Ti. However, if the amount of Ti is too large, TiN coarsening and precipitation hardening due to TiC occur and the low temperature toughness is deteriorated, so the upper limit was limited to 0.030%.
[0035]
  P and S are unavoidable impurity elements. In the present invention, in order to further improve the low temperature toughness of the base material and the HAZ, the contents of P and S are respectively 0.015% and 0.003% or less. regulate. The reduction of the P content reduces the center segregation of the continuously cast slab, prevents the grain boundary fracture and improves the low temperature toughness. Moreover, the reduction of the S content has an effect of improving the ductility by reducing MnS that is stretched by hot rolling.
  Al is an element usually contained in steel as a deoxidizing material, and has an effect on refinement of the structure. However, if the amount of Al exceeds 0.06%, Al-based non-metallic inclusions increase to impair the cleanliness of the steel, so the upper limit was made 0.06%.In addition, the upper limit of the amount of Al of the steel plate is the implementation No. Based on 0.0134% of the Al content of 9, the content is made 0.0134% or less.
  N forms TiN and suppresses coarsening of the austenite grains of HAZ during reheating of the slab and improves the low temperature toughness of the base material and HAZ. The minimum amount required for this is 0.001%. However, if the amount of N is too large, it will cause deterioration of the HAZ toughness due to slab surface defects and solute N, and decrease in the effect of improving the hardenability of B, so the upper limit must be limited to 0.006%.
  Mg forms finely dispersed oxide and suppresses the coarsening of the weld heat-affected zone to improve the low temperature toughness. If over 0.006% is added, a coarse oxide is formed and, on the contrary, the toughness is deteriorated, so the upper limit of the content is made 0.006%.
[0036]
  The above are the basic components of the steel sheet used in the present invention, and the following components are selectively added in the following ranges.
[0037]
B is an extremely effective element for dramatically increasing the hardenability of steel in a very small amount and obtaining the target martensite-based structure. Further, B enhances the hardenability improvement effect of Mo, and synergistically increases the hardenability by coexisting with Nb. On the other hand, if added excessively, not only the low temperature toughness is deteriorated, but also the effect of improving the hardenability of B may be lost, so the upper limit was made 0.005%.
[0039]
  V, Cu, Cr, Ca, REM isIn order to further improve the strength and toughness and expand the size of the steel material that can be manufactured without impairing the excellent characteristics of the steel of the present invention, it is possible to add an appropriate amount as follows.
  V has almost the same effect as Nb, but the effect is weaker than Nb. However, the effect of V addition in the ultra high strength steel is great, and the combined addition of Nb and V makes the excellent characteristics of the steel of the present invention even more remarkable. The upper limit is acceptable up to 0.1% in terms of HAZ toughness and on-site weldability, but 0.03 to 0.08% is particularly desirable.
[0040]
Cu increases the strength of the base metal and the welded portion, but if too much, the HAZ toughness and on-site weldability deteriorate significantly. For this reason, the upper limit of the amount of Cu is 1%.
Cr increases the strength of the base metal and the weld, but if too much, the HAZ toughness and on-site weldability deteriorate significantly. For this reason, the upper limit of the Cr content is 0.8%.
Ca and REM control the form of sulfide (MnS) and improve low-temperature toughness (such as an increase in absorbed energy in the Charpy test). If the Ca content exceeds 0.01% and the REM content exceeds 0.02%, a large amount of CaO-CaS or REM-CaS is generated, resulting in large clusters and large inclusions, which only harms the cleanliness of the steel. In addition, it adversely affects on-site weldability. For this reason, the upper limit of the Ca addition amount is limited to 0.01% or the condition of the REM addition amount is limited to 0.02%.
[0041]
In the ultra-high-strength line pipe, the amount of S and O is reduced to 0.001% and 0.002% or less, respectively, and ESSP (Effective Sulphide Shape) is an index for controlling the shape of the MnS cluster shown below. It is particularly effective to adjust Ca, S, and O so that Controlling Parameter) satisfies 0.5 ≦ ESSP ≦ 10.0.
ESSP = (Ca) [1-124 (O)] / 1.25S (1)
When the above ESSP is less than 0.5, a large amount of CaO-CaS is formed, resulting in coarse clusters and coarse inclusions, which deteriorate weldability such as weld cracks. When the ESSP exceeds 10.0, the shape of MnS Since the effect of control is lost, ESSP is specified to be 0.5 to 10.0.
[0042]
  Less thanIn addition to the limitations of the individual additive elements above, it is desirable to further limit the P value, which is a hardenability index shown below, to 1.9 ≦ P ≦ 4.0 in order to achieve a strength / toughness balance. . In addition, intensity | strength becomes large, so that P value becomes high, and it shows that a metal structure tends to become a bainite martensite structure.
P = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + (1 + β) Mo-1 + β (2)
However, β = 1 when B ≧ 3 ppm, and β = 0 when B <3 ppm.
[0043]
The reason for limiting the P value as described above is to achieve the desired balance between strength and low temperature toughness. The lower limit of the P value is set to 1.9 in order to obtain a strength of 900 MPa or more and excellent low temperature toughness. The upper limit of the P value is set to 4.0 in order to maintain excellent HAZ toughness and on-site weldability.
In addition, the steel sheet (base material) for the ultra-high-strength steel pipe of the present invention needs to have a steel sheet structure of a microstructure mainly composed of a low-temperature transformation structure such as martensite and bainite in order to set the tensile strength to 900 MPa or more. . For this purpose, the steel having the above-mentioned components is cast, then hot worked, and then rapidly cooled, or in some cases, tempered and manufactured, and the steel sheet structure suppresses the ferrite structure, such as martensite and bainite. It is necessary to make the microstructure mainly composed of low-temperature transformation structures.
[0044]
【Example】
Next, examples of the present invention will be described.
After the ultra high strength steel pipe steel having the chemical composition shown in Table 1 is melted in a 300 ton converter, it is made into a continuous cast steel piece, and then heated at 1100 ° C. and then subjected to finish rolling with a cumulative reduction of 80% at 800-900 ° C. After that, a 16 mm steel plate having a tensile strength of 900 MPa or more was produced by water cooling from 800 ° C. to 200 ° C. Using this steel plate, it is formed into a tube at a UO factory, and 80% Ar + 20% CO2After tentative welding using MAG arc welding with various shielding gases, welding with 3 electrodes, 1.75 m / min, heat input 2.2 KJ / mm using welding wires and fluxes of various components shown in Table 2 Under conditions, submerged arc welding was performed for each pass from the inner and outer surfaces, and then 1% pipe expansion was performed. Table 3 shows the chemical composition, structure and characteristics of the weld metal of the welded portion of the steel pipe obtained. In Table 3, Comparative Example No. 15-22, the chemical composition of the wire used in the seam welding, the structure and chemical composition of the weld metal are outside the scope of the present invention, and the low temperature toughness of the weld metal of the present invention (Charpy absorbed energy at −20 ° C. is 80 J). This is an example that does not satisfy the above) or that cold cracking occurs during welding.
[0045]
No. 15, 17, 19 and 21, the wire component is outside the scope of the present invention, so the contents of C, Mn, Si and Ni in the weld metal are lower than the scope of the present invention, respectively, and the weld metal strength is TS. Although 900 MPa or more was satisfied, since the retained austenite in the inner surface main weld metal was too low, less than 1%, cold cracking of the weld metal occurred.
[0046]
  No. Nos. 16, 18, 20, and 22 show that the content of C, Mn, Si, and Ni in the weld metal is significantly higher than the range of the present invention because the wire component is out of the range of the present invention. The toughness was significantly reduced and cold cracking or hot cracking occurred in the weld metal. On the other hand, No. which is an example of the invention. 1 to9, 11, 13,No. 14, the steel plate and wire components are within the scope of the present invention, and the components and structures in the weld metal are also within the scope of the present invention. Therefore, the tensile strength and low temperature toughness of the weld metal are good, and the weld metal Cold cracking did not occur.
[0047]
[Table 1]
[0048]
[Table 2]
[0049]
[Table 3]
[0050]
[Table 4]
[0051]
[Table 5]
[0052]
【The invention's effect】
According to the present invention, when performing one-pass seam welding on the inner and outer surfaces with high heat input when manufacturing an ultra-high strength steel pipe having a tensile strength of 900 MPa or more (API standard X100 or more), Cold cracking of the weld metal can be prevented without heat treatment, and an ultra-high strength steel pipe excellent in strength and low temperature toughness can be produced at high productivity and at low cost.
[Brief description of the drawings]
FIG. 1 is a diagram showing a weld metal in a steel pipe seam weld.
[Explanation of symbols]
1 ... Outside real weld metal
2 ... Inner main weld metal
3. Steel pipe base material
4 ... Temporary weld metal

Claims (4)

  1. In the weld metal of the seam weld portion, the components of the inner and outer surfaces of the weld metal formed by the present seam welding are mass%, C: 0.04 to 0.14%, Si: 0.05 to 1%, Mn : 1.2 to 2.2%, P: ≤ 0.01%, S: ≤ 0.01%, Ni: 1.3 to 6%, Ti: 0.018 to 0.05%, Al: ≤ 0 0.010%, B: ≦ 0.005% , and further, 2 types of Cr and Mo are contained in a total amount of 1 to 2.5%, or 3 types of Cr, Mo and V are 1 in a total amount. -2.5%, the balance is made of iron and inevitable impurities, and at least 1% of the retained austenite phase is contained in the structure of at least the inner surface of the inner and outer surface weld metals. Super high strength steel pipe with seam welds with excellent cold cracking resistance.
  2. The ultrahigh strength steel pipe having a seam welded portion having excellent cold crack resistance according to claim 1, wherein the weld metal has a bainite-martensite fraction of 50% or more.
  3. The tensile strength of the weld metal is 900 MPa or more, and the ultra high strength steel pipe having a seam welded portion having excellent cold crack resistance according to claim 1 or 2 .
  4. In mass%, C: 0.03-0.1%, Si: ≦ 0.6%, Mn: 1.7-2.5%, P: ≦ 0.015%, S: ≦ 0.003%, Ni: 0.1-1%, Mo: 0.15-0.6%, Nb: 0.01-0.1%, Ti: 0.005-0.03% , Al: ≦ 0.0134% N: 0.001 to 0.006%, Mg: ≦ 0.006%, B: ≦ 0.005%, V: ≦ 0.1%, Cu: ≦ 1%, Cr: ≦ 0 .8%, Ca: ≦ 0.01%, and REM: ≦ 0.02% containing one or more of them, the balance being iron and inevitable impurities formed into a steel sheet in the UO process Then, after the end portions of the steel sheets subjected to the groove processing are butted, the butted groove portions are subjected to tack welding, and then in mass%, C: 0.01 to 0.12%, Si: ≦ 0.3 , Mn: 1.2~2.4%, Ni: 4~8.5%, Cr, 1 or two or more of the total amount of Mo and V: 3~5%, Ti: 0.060 ~ Containing 0.15%, Al: ≦ 0.033%, the balance is submerged arc from the inner and outer surfaces using a welding wire consisting of iron and unavoidable impurities and a calcined or molten flux A method for producing an ultra-high-strength steel pipe having a seam welded portion excellent in cold cracking resistance, characterized in that main welding is performed by welding and then pipe expansion is performed.
JP2000310935A 2000-10-11 2000-10-11 Ultra-high-strength steel pipe with seam welds with excellent cold cracking resistance and manufacturing method thereof Active JP4171169B2 (en)

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JP4564245B2 (en) 2003-07-25 2010-10-20 新日本製鐵株式会社 Super high strength welded joint with excellent low temperature cracking property of weld metal and method for producing high strength welded steel pipe
JP4482355B2 (en) * 2004-03-17 2010-06-16 新日本製鐵株式会社 Seam welding method for high strength UO steel pipe with excellent transverse cracking resistance
JP4566146B2 (en) * 2006-02-28 2010-10-20 住友金属工業株式会社 High tensile welded joint with excellent joint toughness and method for producing the same
JP4969915B2 (en) * 2006-05-24 2012-07-04 新日本製鐵株式会社 Steel tube for high-strength line pipe excellent in strain aging resistance, steel plate for high-strength line pipe, and production method thereof
JP5202862B2 (en) * 2007-03-28 2013-06-05 Jfeスチール株式会社 High-strength welded steel pipe with weld metal having excellent cold cracking resistance and method for producing the same
JP4860722B2 (en) * 2009-06-08 2012-01-25 新日本製鐵株式会社 Seam welding method for high strength UO steel pipe with excellent transverse cracking resistance
JP5321493B2 (en) * 2010-02-12 2013-10-23 新日鐵住金株式会社 Spiral steel pipe manufacturing method and spiral steel pipe
CN101733584B (en) 2010-02-13 2012-02-01 宝鸡石油钢管有限责任公司 Pipeline submerged arc welding wire of high strength
JP5607002B2 (en) 2011-02-02 2014-10-15 株式会社神戸製鋼所 Weld metal with excellent resistance to hydrogen embrittlement
JP5606985B2 (en) * 2011-04-08 2014-10-15 株式会社神戸製鋼所 Weld metal with excellent resistance to hydrogen embrittlement
KR101351267B1 (en) 2011-10-21 2014-02-13 한양대학교 산학협력단 1GPa HIGH STRENGTH WELDING JOINT HAVING EXCELLENT LOW TEMPERATURE TOUGHNESS
JP5894463B2 (en) 2012-02-27 2016-03-30 株式会社神戸製鋼所 Method for forming weld metal with excellent resistance to hydrogen embrittlement
US10065272B2 (en) 2012-12-27 2018-09-04 Posco Super high-strength flux cored arc welded joint having excellent impact toughness, and welding wire for manufacturing same
CA3023415A1 (en) 2013-01-11 2014-10-01 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Weld metal with excellent resistance to hydrogen embrittlement, and solid wire for submerged arc welding
CN105848820B (en) 2013-12-24 2019-01-22 Posco公司 The excellent superhigh intensity gas metal arc welding connector of impact flexibility and the welding wire for making it
CN107803574A (en) * 2017-10-31 2018-03-16 中国石油天然气集团公司 A kind of X100 levels pipe line steel large-caliber spiral submerged-arc welded (SAW) pipe manufacture method

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