X80 heavy-gauge high-strength high-strain pipeline steel, UOE welded pipe, and manufacturing method therefor

Abstract

The present invention relates to an X80 heavy-gauge high-strength high-strain pipeline steel, a UOE welded pipe, and a manufacturing method therefor. In addition to Fe and inevitable impurities, the pipeline steel further comprises the following chemical components in percentage by weight: 0.051-0.09% of C, 0.1-0.4% of Si, 1.5-1.9% of Mn, P ≤ 0.015%, S ≤ 0.002%, Cu ≤ 0.19%, 0.05-0.19% of Ni, 0.11-0.35% of Cr, Mo ≤ 0.13%, 0.02-0.08% of Nb, 0.005-0.035% of Ti, 0.001-0.004% of Ca, 0.010-0.045% of Alt, N ≤ 0.006%, B ≤ 0.0003%, O ≤ 0.005%, and H ≤ 0.0002%, wherein the carbon equivalent CEIIW is 0.41-0.47%, and 0.60% ≤ Ni + 3Cr ≤ 1.10%, each element symbol in the expression being substituted for the mass percentage content of the corresponding element. The UOE welded pipe of the present invention has a wall thickness of 25-40 mm and a caliber of φ 1016 to φ 1422 mm, and has a yield strength of 555-665 MPa, a tensile strength ≥ 625 MPa, a low-temperature impact energy higher than 1600 J at -20ºC, and a full-wall-thickness DWTT shear fracture area percentage greater than 85% at -10ºC, as well as a longitudinal yield strength of 530-640 MPa, a yield ratio ≤0.85, and a uniform elongation ≥7%.

Description

X80 grade thick specification high strength large strain pipeline steel, UOE welded pipe and manufacturing method thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of pipeline steel, and particularly relates to an X80 grade thick specification high strength large strain pipeline steel, a UOE welded pipe and a manufacturing method thereof. BACKGROUND

[0002] The extension of oil and gas exploitation to polar and remote areas has become an important direction of current pipeline construction. Adverse geological environments such as permafrost settlement and earthquake landslides pose great challenges to pipeline safety, thereby putting forward higher performance requirements for pipe materials. In addition to requiring high strength and high toughness, thick-walled pipes are also required to improve structural stability, and high plastic deformation capacity is also required to ensure service safety.

[0003] From the current research on submarine pipeline products, in addition to optimization design in terms of composition design, rolling process control and microstructure control, the key is to improve the strength and toughness of the steel through equipment capacity, thereby laying a foundation for the manufacture of thick specification pipeline steel plate with high internal quality and large reduction ratio, which can effectively improve the strength and toughness of the steel. Alternatively, an on-line heat treatment device is used to apply HOP process to improve the uniformity of the microstructure in the thickness direction of the steel plate, which is beneficial to improve the toughness of the thick specification pipeline steel and obtain uniform mechanical properties, and can also improve the ovality of the steel pipe. At present, the research on submarine pipeline steel mainly focuses on high strength and high toughness, and the research on high deformation performance is less.

[0004] Due to the large plastic deformation of thick-walled steel pipes during pipe forming, the strain capacity is significantly reduced; at the same time, due to the large wall thickness, a large welding heat input welding process is required to meet the welding penetration requirement, so how to ensure high deformation capacity and welding toughness is a major challenge in the development of submarine pipes. At present, dual-phase structure control is the main way to improve the deformation capacity of the steel, and the combination of soft and hard phases can obtain an arch-shaped stress-strain curve, which has good work hardening rate, thereby improving the uniform deformation capacity of the steel. For example, the ferrite + lower bainite dual-phase structure obtained by adopting the delayed relaxation + controlled cooling process, and the MA component + bainite dual-phase structure obtained by adopting the on-line heat treatment HOP process, both of which can obtain high uniform elongation, but due to the existence of dual-phase interface, the low temperature impact toughness of the steel is significantly reduced, further reducing the toughness of the heat affected zone of the steel.

[0005] Chinese patent 1 (publication number CN10175506A) discloses a steel pipe with excellent deformation properties and a production method. The patent proposes a method for manufacturing a longitudinal low yield ratio high deformation capacity straight seam electric resistance welded steel pipe. By controlling the addition of Cu / Ni / Cr / Mo and other alloys, combined with a heat treatment process in the range of Ac1+10°C to Ac1+60°C, a MA component ratio of 2% to 10% is obtained, which can achieve a longitudinal yield ratio of ≤0.90 under the condition of a large thickness-diameter ratio, thereby improving the deformation capacity of the steel pipe.

[0006] Chinese patent 2 (publication number CN102953018A) discloses a high-strength pipeline steel, a steel pipe and a manufacturing method thereof. The patent provides a manufacturing method for an X70 grade strain design pipeline steel and a steel pipe. By adopting a low C niobium Mo alloying composition design and adding an appropriate amount of B, combined with controlled rolling and two-stage cooling process, a microstructure of 50-75% ferrite + bainite dual phase is obtained, and the steel pipe is trial-produced by adopting UOE process and 0.1-0.5% compression rate and 0.05-0.15% expansion rate. The manufactured steel pipe has high uniform elongation and low yield ratio, and can meet the demand of land strain design pipeline.

[0007] Chinese patent 3 (patent number ZL201510125587.3) discloses an X80 pipeline steel with good strain aging resistance, a pipeline pipe and a manufacturing method thereof, and specifically relates to an X80 pipeline steel with low C and higher Nb micro-alloying design. By adopting a composition design of 0.02-0.05% C and 0.06-0.09% Nb, combined with TMCP stage rolling and delayed variable cooling process, an X80 pipeline steel with a microstructure of 25-40% ferrite + bainite dual phase is obtained. The obtained X80 pipeline steel is manufactured into an X80 pipeline pipe by adopting UOE process with a compression rate of 0.15-0.3% and an expansion rate of 0.8-1.2%. The manufactured steel pipe has high uniform elongation and meets the low temperature impact and DWTT toughness at-45°C.

[0008] Chinese patent 4 (patent number ZL200980119540.9) discloses a high-strength UOE steel pipe with excellent seismic performance and low-temperature toughness of the weld heat-affected zone, and specifically relates to a manufacturing method of an X80 UOE welded pipe with longitudinal yield strength of 480 MPa for seismic resistance. A low yield ratio pipeline steel with a bainite structure of more than 80% is obtained by using a low C and low Nb micro-alloying composition design. The obtained pipeline steel is manufactured into a UOE welded pipe with a diameter of 30-56 inches and a wall thickness of 20-28 mm, and the obtained UOE welded pipe has a low yield ratio of 0.85 and below and a low temperature toughness of ≥40 J at-40°C, and can be used for pipeline laying in earthquake zones and permafrost regions.

[0009] The existing UOE welded pipe mainly improves the strain performance of the steel through technical means such as adding B element, low-C high-Nb design, MA hard phase control or more than 80% of the proportion of bainite. SUMMARY

[0010] The present application aims to provide a X80 grade thick specification high-strength large-strain pipeline steel and UOE welded pipe and a manufacturing method thereof. The UOE welded pipe with a wall thickness of 25-40 mm and a caliber of φ1016-φ1422 mm obtained by the present application has a yield strength of 555-665 MPa, a tensile strength of ≥625 MPa, especially a low-temperature impact energy at-20 ℃ higher than 160 J, a full-wall-thickness DWTT shear fracture area percentage at-10 ℃ of ≥85%, a longitudinal yield strength of 530-640 MPa, a yield strength ratio of ≤0.85, and an average elongation of ≥7.0%. The large-strain pipeline steel and the UOE welded pipe can be used in the field of oil and gas pipeline construction in areas with severe geological deformation.

[0011] To achieve the above-mentioned purpose, the first aspect of the present application provides a X80 grade thick specification high-strength large-strain pipeline steel, which, in addition to Fe and inevitable inclusions, contains the following chemical components in the following weight percentage: C: 0.051-0.090%, Si: 0.10-0.40%, Mn: 1.50-1.90%, P: ≤0.015%, S: ≤0.0020%, Cu: ≤0.19%, preferably 0.05-0.19%, Ni: 0.05-0.19%, Cr: 0.11-0.35%, Mo: ≤0.13%, preferably 0.05-0.13%, Nb: 0.020-0.080%, Ti: 0.005-0.035%, Ca: 0.0010-0.0040%, total aluminum content Alt: 0.010-0.045%, N: ≤0.006%, preferably 0.001-0.006%, B: ≤0.0003%, O: ≤0.005%, H: ≤0.00020%, wherein the carbon equivalent CE IIW : 0.41-0.47%, and 0.60%≤Ni+3Cr≤1.10%, wherein the symbol of each element is substituted for the mass percentage content of each element.

[0012] Preferably, the pipeline steel comprises the following chemical components in the following weight percentage: C: 0.051-0.090%, Si: 0.10-0.40%, Mn: 1.50-1.90%, P: ≤0.015%, S: ≤0.0020%, Cu: ≤0.19%, preferably 0.05-0.19%, Ni: 0.05-0.19%, Cr: 0.11-0.35%, Mo: ≤0.13%, preferably 0.05-0.13%, Nb: 0.020-0.080%, Ti: 0.005-0.035%, Ca: 0.0010-0.0040%, total content of aluminum element Alt: 0.010-0.045%, N: ≤0.006%, preferably 0.001-0.006%, B: ≤0.0003%, O ≤0.005%, H ≤0.00020%, the balance being Fe and inevitable inclusions; wherein the carbon equivalent CE IIW : 0.41%-0.47% and 0.60% ≤Ni+3Cr ≤1.10%, in which the element symbols are substituted for the mass percentage content of each element.

[0013] Preferably, the microstructure of the pipeline steel according to the present application is ferrite + bainite, the proportion of the ferrite being 45-80%, and the hardness of the bainite being 350HV0.02-600HV0.02.

[0014] Preferably, the pipeline steel according to the present application satisfies one or more or all of the following properties:

[0015] Transverse tensile properties: yield strength Rt0.5: 555-665 MPa, tensile strength Rm ≥625 MPa, preferably 625-677 MPa, yield ratio ≤0.90, preferably 0.83-0.90, elongation A 50.8 ≥15.0%, preferably ≥24.5%;

[0016] Longitudinal tensile properties: yield strength Rt0.5: 530-640 MPa, tensile strength Rm ≥621 MPa, preferably ≥625 MPa, preferably 625-673 MPa, elongation A 50.8 ≥25%, preferably ≥26.5%, uniform elongation Agt ≥7.0%, preferably ≥7.5%, yield ratio ≤0.85, preferably 0.82-0.85.

[0017] In the component design of the pipeline steel according to the present application:

[0018] C: C is the most basic strengthening element. Carbon dissolves in steel to form interstitial solid solution, which plays a role of solid solution strengthening. Carbon and strong carbide forming elements form carbide precipitation, which plays a role of precipitation strengthening, and can increase the hardness of the hard phase. However, excessive C is not conducive to the ductility, toughness and welding performance of the steel; too low C content can reduce the strength of the steel, and the present application needs to use the solid solution strengthening of C to improve the yield strength of the pipeline steel after light heat treatment. Therefore, the content of C in the pipeline steel of the present application is controlled at 0.051-0.090%.

[0019] Si: Si is a solid solution strengthening element, and also a deoxidizing element in steel. However, too high Si content can deteriorate the welding performance of the steel, and is not conducive to the removal of hot rolled iron scale during rolling. Therefore, the Si content in the pipeline steel of the present application is controlled at 0.10-0.40%.

[0020] Mn: Mn can improve the strength of the steel through solid solution strengthening. Mn is the most important and economical strengthening element in steel to compensate for the loss of strength caused by the reduction of C content. Mn is also an element that expands the γ phase region, which can reduce the γ→α phase transition temperature of the steel, help to obtain fine phase transition products, and improve the toughness of the steel; but Mn is also an easy segregation element. When the Mn content is too high, Mn is easy to segregate in the center of the plate during casting, and after rolling, martensite organization of hard phase is generated, which reduces the low temperature toughness and dynamic tear resistance of the material. Therefore, the Mn content in the pipeline steel of the present application is controlled at 1.50-1.90%.

[0021] Nb: Nb is one of the important elements of low-carbon micro-alloyed steel. The Nb strain-induced precipitation formed by the solid solution of Nb during hot rolling forms Nb(N,C) particles, which pin the grain boundaries to inhibit the growth of deformed austenite, and through controlled rolling and controlled cooling, the deformed austenite is transformed into fine products with high dislocation density; after phase transition, the second phase particles NbC are dispersedly precipitated in the matrix, which plays a role of precipitation strengthening. Too low Nb content has no obvious dispersion precipitation effect, and cannot play the role of grain refinement and matrix strengthening; excessive Nb inhibits recrystallization, and also cannot play the role of grain refinement. Therefore, the Nb content in the pipeline steel of the present application should be controlled at 0.020-0.080%.

[0022] Ti: Ti is a strong carbonitride forming element, which can inhibit the combination of nitrogen and other micro-alloying elements to play the role of carbide precipitation strengthening; in addition, the unsolved carbonitride of Ti can prevent the growth of austenite grains when the steel is heated, and the TiN particles can significantly prevent the grain growth in the heat affected zone during welding, thereby improving the welding performance of the steel plate and having obvious effect on improving the impact toughness of the welding heat affected zone. Therefore, the Ti content in the pipeline steel of the present application is controlled at 0.005-0.035%.

[0023] Cu: Cu is a solid solution strengthening element, which can improve the strength of the steel through solid solution strengthening effect, and can improve the toughness of the steel. However, too much Cu is easy to produce copper brittle crack, which is not conducive to the toughness and welding performance of the steel plate. Therefore, the Cu content in the present application is controlled to be ≤0.19%, preferably 0.05-0.19%.

[0024] Ni: Ni can improve the strength of the steel through solid solution strengthening effect, and Ni is beneficial to improve the toughness by reducing the stacking fault energy; Ni is an element that expands the austenite region, reduces the critical transformation temperature, reduces the diffusion rate of each element in the steel, and improves the hardenability of the steel. Too low Ni cannot play a role, but excessive Ni will damage the weldability, therefore, the addition amount of Ni in the pipeline steel of the present application is controlled to be 0.05-0.19%.

[0025] Cr: Cr is an important element for improving the hardenability and hardenability of the steel, which effectively improves the strength of the steel, and plays a phase change control and improves the uniformity of the microstructure in the thickness direction. However, excessive chromium and manganese are added to the steel at the same time, which will lead to the formation of low melting point Cr-Mn composite oxides, forming surface cracks during hot working, and at the same time, will seriously deteriorate the welding performance. Therefore, the Cr content in the pipeline steel of the present application is controlled to be 0.11-0.35%, and at the same time, in order to ensure the hardness requirement of the second phase structure, 0.6%≤Ni+3Cr≤1.1% is controlled, in which the symbol of each element is substituted into the mass percentage content of each element.

[0026] Mo: Mo is a solid solution strengthening element, and appropriate amount of Mo can expand the γ phase region, reduce the γ→α phase transition temperature of the steel, improve the hardenability of the steel, promote the formation of acicular ferrite, refine the structure and improve the strength of the material. In addition, it should be noted that Mo element can also reduce the diffusion coefficient of C, improve the high temperature stability of the structure, and is beneficial to the material to obtain higher high temperature strength. However, too much Mo element content will promote the formation of M-A island, which is not conducive to the toughness of the material, and will significantly increase the cost of the alloy. Therefore, the content of Mo in the present application is controlled to be ≤0.13%, preferably 0.05-0.13%.

[0027] N: In microalloyed steel, appropriate content of nitrogen can play a role in inhibiting the grain coarsening of the slab during reheating by forming high melting point TiN particles, thereby improving the strength and toughness of the steel. However, when the N content is too high, the high concentration of free N atoms after aging pin the dislocations, which significantly increases the yield strength, and at the same time, damages the toughness. Therefore, the N content in the pipeline steel of the present application is controlled to be ≤0.006%.

[0028] O: For low alloy clean steel smelting, deoxidation treatment is needed at the end of smelting to reduce the bubbles and oxide inclusions generated in the casting process, so as to improve the endoplasm of the steel and increase the low-temperature impact toughness and dynamic tear resistance of the finished steel plate. When the oxygen content is higher than 50ppm, the inclusions, pores and other endoplasmic defects increase significantly, therefore, the O content in the pipeline steel of the present application is controlled to be ≤0.005%.

[0029] H: Hydrogen is the key element that causes delayed cracking in steel. For thin-gauge steel plates, hydrogen can easily diffuse out. For thick-gauge steel plates, hydrogen is difficult to overflow due to the increased diffusion path; since the present application adopts hard+soft dual-phase structure, the stress at the soft-hard phase interface is large, which easily leads to hydrogen enrichment and delayed cracking. Therefore, the H content in the pipeline steel of the present application is controlled to be ≤0.00020%.

[0030] S, P: S and P are inevitable impurity elements in steel, and it is desirable to have lower content. By controlling the sulfide inclusions through ultra-low sulfur (20ppm or below, i.e. 0.0020% or below) and Ca treatment, and controlling the P content to be below 150ppm (i.e. P: ≤0.015%), the pipeline steel of the present application can have good low-temperature impact toughness.

[0031] Ca: The morphology of sulfides can be controlled by Ca treatment, so as to improve the anisotropy of the steel plate and increase the low-temperature toughness. A small amount of Ca cannot play a role in sulfide spheroidization, and excessive Ca is easy to become a new inclusion. In order to ensure the best effect, the Ca content in the pipeline steel of the present application is controlled in the range of 0.0010-0.0040%.

[0032] Total aluminum element content Alt: Al is added to steel for deoxidization, and appropriate amount of Al is beneficial to grain refinement and improvement of the strength and toughness of the steel. Therefore, the Alt content in the pipeline steel of the present application is controlled in the range of 0.010-0.045%.

[0033] B: The main role of B in steel is to increase the hardenability and strength of the steel, but excessive addition of B element will have a significant adverse effect on the low-temperature performance of the material. Therefore, the B content is controlled to be ≤0.0003% in the present application.

[0034] Carbon equivalent CE IIW : CE IIW = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5, where V is 0. If the carbon equivalent is too high, the hardenability of the steel will increase, the strength will increase and the toughness will decrease, and welding cold cracks are easy to occur; if the carbon equivalent is too low, the hardenability of the steel will be insufficient and the strength will decrease significantly. Therefore, the carbon equivalent is controlled to be 0.41-0.47% in the present application, which not only meets the requirements of the pipe body, but also obtains excellent weld performance.

[0035] Therefore, the present disclosure is based on the material theory of grain refinement, precipitation strengthening, phase transformation control, etc., and adopts the composition design of appropriate C, high Mn, Ni / Cr alloying and Nb, Ti micro-alloying, so that the microstructure of the hot-rolled steel plate and the welded pipe for the welded pipe is 45-80% ferrite + bainite with a hardness of 350HV0.02-600HV0.02, which has a transverse yield strength of 555-665 MPa, a longitudinal yield strength of 530-640 MPa, a low yield strength ratio, and a high uniform elongation. The hot-rolled steel plate and the welded pipe obtained by the present disclosure have high strength, high toughness and good deformation characteristics. The C and Mn contents are the core elements that determine the ferrite / bainite ratio and the phase hardness. If the C and Mn contents are lower than the target content, the Ar3 transformation point will rise and the ferrite ratio will decrease. The bainite hardness will decrease, which will eventually increase the yield strength ratio and reduce the uniform elongation. The Ni / Cr elements also need to be controlled within a reasonable range, and the target content is controlled between 0.6%≤Ni+3Cr≤1.1%. When the value is lower than the lower limit of the range, not only the toughness of the steel is reduced, but also the hardenability of the steel is decreased, and the hardness of the core hard phase bainite is also decreased, which will result in an increase in the yield strength ratio and a decrease in the deformation capacity. When the value is higher than the upper limit of the range, the strength of the steel will increase as a whole, the deformation capacity will decrease, and the weldability of the steel will be deteriorated.

[0036] The second aspect of the present disclosure provides an X80 grade thick specification high strength large strain UOE welded pipe, which is made of the above pipeline steel.

[0037] Preferably, the transverse yield strength of the UOE welded pipe is 555-665 MPa, and the longitudinal yield strength is 530-640 MPa. The outer diameter of the UOE welded pipe is the wall thickness is 25-40 mm; in the transverse direction, the pipe body impact energy AKv at-20℃ is ≥160J, preferably ≥216J, the weld and heat affected zone impact energy AKv at-20℃ is ≥50J, preferably the weld impact energy AKv at-20℃ is ≥175J and / or the heat affected zone impact energy AKv at-20℃ is ≥196J, the-10℃ full wall thickness DWTT performance: SA% is ≥85%, preferably 85-92%.

[0038] The third aspect of the present disclosure provides a method for manufacturing an X80 grade thick specification high strength large strain UOE welded pipe, which comprises the following steps performed in sequence:

[0039] 1) smelting and continuous casting: obtaining a 300-450 mm thick specification slab through smelting-LF+RH furnace external refining and continuous casting;

[0040] 2) heating: heating the slab to obtain a heated slab, wherein the heating temperature is 1070-1170℃;

[0041] 3) Rolling: rolling the heated slab to obtain a rolled slab, the rolling being rough rolling + finish rolling, wherein:

[0042] The rough rolling is performed under the following conditions: the finish rolling temperature of the rough rolling is 950-1050℃, and the single pass reduction ratio of rolling is ≥8%; the intermediate blank thickness is 3t-5t, t being the target UOE welded pipe wall thickness, unit: mm;

[0043] The finish rolling is performed under the following conditions: the finish rolling temperature of the finish rolling is 730-820℃;

[0044] 4) Air cooling: waiting for the rolled slab to reach the target temperature on the roller bed to obtain an air-cooled slab, wherein the target temperature is the open cooling temperature of water cooling;

[0045] 5) Water cooling: water cooling the air-cooled slab to obtain a steel plate, wherein the water cooling is performed under the following conditions: the open cooling temperature is 640-690℃, the final cooling temperature is 100-350℃, and the cooling rate is 15-35℃ / s;

[0046] 6) Steel pipe forming:

[0047] 6.1) Arc starting steel plate welding: welding the arc starting steel plate at the four corners of the steel plate obtained in step 5);

[0048] 6.2) Milling, beveling;

[0049] 6.3) Forming by C, U, O forming process to obtain an O-formed split steel pipe; wherein the O-forming compression rate = (π × (pre-welded outer diameter - wall thickness) - width after milling) / width after milling × 100% = 0.18-0.22%;

[0050] 6.4) Pre-welding + welding: pre-welding and welding the O-formed split steel pipe to obtain a welded steel pipe; the welding line energy is: 1.7t≤H≤2.1t, preferably 1.7t≤H≤2.0t, wherein H is the welding line energy, unit: KJ / cm; t is the target UOE welded pipe wall thickness, unit: mm;

[0051] 6.5) Expanding: expanding the entire length of the welded steel pipe to obtain an expanded steel pipe; wherein the expansion rate = (expanded steel pipe outer diameter - unexpanded steel pipe outer diameter) / unexpanded steel pipe outer diameter × 100% = 0.80%-1.20%;

[0052] 6.6) Light heat treatment of the expanded steel pipe to obtain a UOE welded pipe, the light heat treatment of the whole pipe being performed under the following conditions: temperature 200-250℃, time 5-15min.

[0053] Preferably, the step 6) steel pipe forming further comprises the following steps after the step 6.6):

[0054] 6.7) Welding seam ultrasonic detection: adopting the ultrasonic detection method, cracks, delamination, incomplete penetration and other welding defects in the welding seam of the UOE welded pipe are detected;

[0055] 6.8) Welding seam X-ray detection: adopting the X-ray detection method, the point-shaped welding defects such as bubbles and inclusions in the welding seam of the UOE welded pipe are detected;

[0056] 6.9) Chamfering: the flat head and chamfering treatment is carried out on both ends of the UOE welded pipe, and the steel pipe after chamfering is obtained, which can bring convenience for the field welding;

[0057] 6.10) Pipe end delamination ultrasonic detection: the ultrasonic detection is carried out on the end of the steel pipe after chamfering to prevent the delamination defects;

[0058] 6.11) Pipe end magnetic particle detection: the magnetic particle detection is carried out on the end of the steel pipe after chamfering to prevent the delamination defects;

[0059] 6.12) Upper protection ring: the upper protection ring is arranged on the end of the steel pipe after chamfering, which can ensure the welding quality in the field construction process of the steel pipe.

[0060] Preferably, before the step 6.5), the welded steel pipe is subjected to the following: welding seam ultrasonic detection, welding seam X-ray detection;

[0061] The welding seam ultrasonic detection is: adopting the ultrasonic detection method, cracks, delamination, incomplete penetration and other welding defects in the welded steel pipe are detected;

[0062] The welding seam X-ray detection is: adopting the X-ray detection method, the point-shaped welding defects such as bubbles and inclusions in the welded steel pipe are detected.

[0063] In the method for manufacturing the X80 grade thick specification high-strength large-strain UOE welded pipe provided by the application:

[0064] The manufacturing process mainly adopts the two-stage rolling deformation and relaxation cooling process. A relatively low heating temperature is adopted in the heating stage, so as to obtain the initial refined original austenite grain size, and lay a foundation for subsequent organization refinement and phase transition promotion.

[0065] In the rough rolling stage, the key parameters such as the relatively high deformation temperature and single pass reduction rate are controlled, so as to ensure that recrystallization occurs sufficiently in the stage to refine the recrystallized austenite grain size; and the rough rolling termination rolling temperature is controlled to be greater than or equal to 950 DEG C, so as to avoid mixed grains. In the finish rolling stage, the finish rolling temperature is mainly controlled, so as to obtain the deformed austenite organization with high dislocation / density, provide more nucleation points for the subsequent phase, and promote the ferrite phase transition.

[0066] In the cooling stage, firstly, the target proportion of pro-eutectoid ferrite structure is obtained by air cooling; then, the hard phase bainite structure is obtained by reasonable accelerated cooling to the low temperature region, so as to obtain the final target phase proportion, target hardness and type of dual-phase structure morphology, thereby obtaining the final target performance.

[0067] The steel pipe forming welding process adopts C, U, O and E forming processes, wherein,

[0068] Arc guide steel plate welding: arc guide steel plates are welded at four corners of the steel plate, which is mainly used for arc guiding during welding. At the beginning and end of welding, the welding current is unstable and prone to welding defects. Therefore, the arc guide steel plates are used to ensure the stability of the welding process of the steel pipe part and ensure the welding quality.

[0069] Edge milling and groove machining: 30° inner and outer groove size design is adopted, combined with reasonable welding process and welding speed, which is beneficial to ensure the welding stability and improve the welding quality under the condition of ensuring low welding heat input.

[0070] C forming: also known as edge bending forming, the edge of the steel plate is bent into the required shape through the edge bending device on the edge bending forming machine, so as to ensure that the straight edge section of the plate edge is minimized during O forming.

[0071] U forming: the pre-bent steel plate is pressed into a "U" shape on the U forming machine. In actual production, appropriate adjustments are made according to specific needs.

[0072] O forming: the U formed steel plate is pressed into a "O" shape on the O forming machine, during which the pipe body and the die need to be fully lubricated. The O forming compression rate is 0.18-0.22%. Among them, the O forming compression rate = (π × (pre-welded outer diameter-wall thickness)-milled width) / milled width × 100%.

[0073] Preferably, steel pipe high-pressure water flushing and drying: the inner and outer surfaces of the O formed and slit steel pipe are subjected to high-pressure water flushing, which is mainly used for removing iron oxide scale, grease, dust and other pollutants; immediately after the flushing is completed, the drying treatment is carried out in the drying furnace, the temperature of the drying treatment is controlled to be 100-300℃, so as to prevent re-rust pollution and ensure the subsequent welding quality.

[0074] Pre-welding: the slit steel pipe after O forming is accurately aligned and positioned, and continuous pre-welding is carried out by using CO2 or Ar+CO2 shielding welding, so as to ensure the stability of the arc during the subsequent inner welding and outer welding process and ensure the final welding quality.

[0075] Welding, including inner welding and outer welding. In the welding, the heat input control range is 1.7t≤H≤2.1t, preferably 1.7t≤H≤2.0t, wherein H is the welding line energy, unit KJ / cm; t is the wall thickness of the target UOE welded pipe, unit mm; the welding line energy is a key parameter affecting the grain size of the welding coarse grain zone, when the welding energy is higher than the upper limit, the grain of the welding coarse grain zone grows significantly, which deteriorates the low temperature impact toughness of the region and the fusion line; when the welding line energy is lower than the lower limit, the weld penetration of the corresponding specification cannot be guaranteed, and the incomplete penetration defect is generated.

[0076] Expanding (i.e. E forming): the full length of the welded steel pipe is expanded to obtain the expanded steel pipe, so as to meet the final pipe type requirement of the steel pipe, improve the dimensional accuracy of the steel pipe, and improve the uniform distribution state of the internal stress of the steel pipe. The expanding rate is 0.8% to 1.2%, wherein the expanding rate=(expanded steel pipe outer diameter-expanded steel pipe outer diameter before expanding) / steel pipe outer diameter before expanding*100%.

[0077] Light heat treatment of the whole pipe: the whole pipe after expanding is subjected to light heat treatment at a temperature of 200 to 250℃ and a time of 5 to 15min. If the temperature is lower than 200℃ and the time is shorter than 5min, the free C and N atoms in the matrix cannot diffuse freely to the deformation dislocation to play a pinning effect, so that the yield strength cannot meet the lower limit requirement. If the temperature is higher than 250℃ or the time is longer than 15min, the free C and N atoms in the matrix fully pin the dislocation, and there are also Nb C and N compound particles precipitated, so that the yield strength of the steel pipe is significantly increased, and the uniform elongation is lower than the lower limit.

[0078] The application has the following characteristics:

[0079] 1) The application adopts low C micro-alloying component design and ferrite+ bainite dual-phase structure design, so that the ferrite proportion is 45 to 80%, the hardness of the bainite phase is 350HV0.02 to 600HV0.02, and excellent deformation capacity and comprehensive performance are finally obtained.

[0080] 2) In the TMCP cooling process control, weak cooling (air cooling)+strong cooling (DQ) process is adopted to obtain the required phase change organization type, and the plate shape is improved.

[0081] 3) The application adopts C, U, O and E forming processes for forming, adopts large compression rate and large expanding rate for forming, and adopts low heat input for welding, so as to realize the comprehensive matching of excellent mechanical properties, deformation capacity and pipe type precision.

[0082] 4) After pipe making, the whole pipe is subjected to light heat treatment at 200 to 250℃, so as to ensure that the required strength is obtained without losing the uniform elongation.

[0083] Compared with the prior art, the present application has the beneficial effects that:

[0084] Compared with the prior art, the present application has the beneficial effects that:

[0085] Compared with the prior art, the present application has the beneficial effects that:

[0086] Compared with the prior art, the present application has the beneficial effects that:

[0087] Compared with the prior art, the present application has the beneficial effects that:

[0088] Compared with the anti-seismic longitudinal yield strength 480MPa grade UOE welded pipe manufacturing method with good deformation ability disclosed in Chinese patent 4 (patent number ZL200980119540.9), the present application adopts a low-C, appropriate-Nb component design method and a dual-phase structure designed pipeline steel plate, and a high-strain steel pipe with a large diameter and thick wall, a diameter range of 1016mm-1422mm, and a wall thickness range of 30-40mm is made by the UOE process. After forming and welding, low-temperature heat treatment is carried out, the transverse and longitudinal yield strengths reach the level of 555MPa and 530MPa, the longitudinal uniform elongation is high, the yield strength ratio is low, and the strain hardening capacity is high, and the heat-affected zone impact energy at-20℃ is ≥50J, which can be used for thick-walled strain design pipeline laying. BRIEF DESCRIPTION OF DRAWINGS

[0089] Fig. 1 is a typical microstructure photograph of the pipeline steel manufactured by the present application. DETAILED DESCRIPTION

[0090] The technical solutions of the present application will be further described below in combination with examples and drawings. It should be clear that the following examples are only used to describe the specific embodiments of the present application and do not constitute any limitation on the protection scope of the present application.

[0091] Examples 1-8 and Comparative Examples 1-2

[0092] 1) Smelting and continuous casting: based on the component composition of the pipeline steel in Table 1, smelting-LF+RH furnace external refining and continuous casting are carried out to obtain a 300-450mm thick slab;

[0093] 2) Heating: the slab is heated to obtain a heated slab;

[0094] 3) Rolling: the heated slab is rolled to obtain a rolled slab, and the rolling is rough rolling+precision rolling;

[0095] 4) Air cooling: the rolled slab is cooled on a roller bed to a target temperature to obtain an air-cooled slab, wherein the target temperature is the open cooling temperature of water cooling;

[0096] 5) Water cooling: the air-cooled slab is water-cooled to obtain a steel plate (i.e. a pipeline steel plate);

[0097] 6) Steel pipe forming:

[0098] 6.1) Arc starting steel plate welding: arc starting steel plates are welded at the four corners of the steel plate obtained in step 5);

[0099] 6.2) Edge milling and beveling;

[0100] 6.3) Forming by C, U, O forming process to obtain an O-formed split steel pipe;

[0101] 6.4) Pre-welding + welding: pre-welding, inner welding and outer welding are performed on the slit steel pipe after O forming, to obtain a welded steel pipe;

[0102] 6.5) Expanding (E forming): expanding is performed on the whole length of the welded steel pipe, to obtain an expanded steel pipe;

[0103] 6.6) The expanded steel pipe is subjected to light heat treatment for pipe finishing, to obtain a UOE welded pipe.

[0104] The components of the pipeline steel in the embodiments 1-8 of the present application are shown in Table 1, and the balance is Fe and unavoidable inclusions (or impurities).

[0105] Table 2 shows the manufacturing process parameters of the UOE welded pipes manufactured in the embodiments 1-8 of the present application.

[0106] Table 3 shows the performance parameters of the UOE welded pipes obtained in the embodiments 1-8 of the present application.

[0107] The performance parameters are tested in the following manner:

[0108] The transverse tensile properties of the pipeline steel are determined according to the ASTM A370 standard.

[0109] The longitudinal tensile properties of the pipeline steel are determined according to the ASTM A370 standard.

[0110] The transverse yield strength of the UOE welded pipe is determined according to the ASTM A370 standard.

[0111] The longitudinal yield strength of the UOE welded pipe is determined according to the ASTM A370 standard.

[0112] The outer diameter and wall thickness of the UOE welded pipe are determined according to the ASTM A370 standard.

[0113] The -20℃ pipe body impact energy AKv of the UOE welded pipe is determined according to the ASTM A370 standard.

[0114] The -20℃ weld and heat affected zone impact energy Akv of the UOE welded pipe is determined according to the ASTM A370 standard.

[0115] The -10℃ full wall thickness DWTT shear fracture area percentage of the UOE welded pipe is determined according to the ASTM A370 standard.

[0116] After the metallographic preparation is completed, different types of microstructures are determined by manual judgment, and different metallographic microstructures are color-coded using image software. Finally, the area ratio is obtained by the ratio of the pixel number of different metallographic microstructures to the pixel number of the whole metallographic photo. The meaning of ferrite ratio is that the area ratio of ferrite in different microstructures of the base layer under the metallographic microscope.

[0117] The hardness of the bainite of the pipeline steel of the present application is determined by using the ASTM E92 standard.

[0118] Referring to Fig. 1, which shows a microstructure photograph of the pipeline steel manufactured by the present application, it can be seen from the photograph that the pipeline steel of the present application is in a typical ferrite + bainite dual-phase organization form, the ferrite is mainly in the form of fine and uniform quasi-polygonal ferrite and the proportion of the ferrite is higher than that of the bainite; the bainite is mainly in the form of lath or lower bainite and is uniformly distributed on the ferrite matrix.

[0119] The high-strength UOE welded pipe with high uniform deformation capacity of the present application, which has a transverse yield strength of 555-665 MPa and a longitudinal yield strength of 530-640 MPa, can be applied to pipeline construction in earthquake fracture zones and can also be used for construction of other structural members with high deformation resistance. For long-distance long-distance pipeline construction, the pipeline steel and the UOE welded pipe of the present application can be used in the environment of frequent geological movement and are suitable for safe margin pipeline construction. With the continuous extension of pipelines to the ocean, the polar region and other regions, the present application has a good application prospect.

[0120] Table 3:

Claims

1. A pipeline steel, characterized in that, The pipeline steel comprises, in addition to Fe and unavoidable inclusions, the following chemical components in the following weight percentages: C: 0.051-0.090%, Si: 0.10-0.40%, Mn: 1.50-1.90%, P: ≤0.015%, S: ≤0.0020%, Cu: ≤0.19%, preferably 0.05-0.19%, Ni: 0.05-0.19%, Cr: 0.11-0.35%, Mo: ≤0.13%, preferably 0.05-0.13%, Nb: 0.020-0.080%, Ti: 0.005-0.035%, Ca: 0.0010-0.0040%, total content of aluminum element Alt: 0.010-0.045%, N: ≤0.006%, preferably 0.001-0.006%, B: ≤0.0003%, O ≤0.005%, H ≤0.00020%, wherein the carbon equivalent CE IIW : 0.41-0.47% and 0.60% ≤ Ni+3Cr ≤ 1.10%, in which the element symbols are replaced by the mass percentage content of the corresponding element.

2. The pipeline steel according to claim 1, characterized in that, The pipeline steel comprises the following chemical components with the weight percentage content as follows: C: 0.051-0.090%, Si: 0.10-0.40%, Mn: 1.50-1.90%, P: ≤0.015%, S: ≤0.0020%, Cu: ≤0.19%, preferably 0.05-0.19%, Ni: 0.05-0.19%, Cr: 0.11-0.35%, Mo: ≤0.13%, preferably 0.05-0.13%, Nb: 0.020-0.080%, Ti: 0.005-0.035%, Ca: 0.0010-0.0040%, total content of aluminum element Alt: 0.010-0.045%, N: ≤0.006%, preferably 0.001-0.006%, B: ≤0.0003%, O ≤0.005%, H ≤0.00020%, the balance being Fe and inevitable inclusions; wherein the carbon equivalent CE IIW : 0.41%-0.47% and 0.60% ≤Ni+3Cr ≤1.10%, in the formula, each element symbol is substituted into the mass percentage content of each element.

3. A pipeline steel according to claim 1 or 2, characterized in that, The microstructure of the pipeline steel is ferrite + bainite, the proportion of the ferrite is 45-80%, and the hardness of the bainite is 350HV0.02-600HV0.

02.

4. A pipeline steel according to any one of claims 1 to 3, characterized in that, The pipeline steel satisfies one or more or all of the following performances: Transverse tensile properties: yield strength Rt0 5: 555-665 MPa, tensile strength Rm > 625 MPa, preferably 625-677 MPa, yield strength / tensile strength ratio < 0.90, preferably 0.83-0.90, elongation A 50.8 ≥ 15.0 %, preferably > 24.5 %; Longitudinal tensile properties: yield strength Rt0 5: 530 to 640 MPa, tensile strength Rm > 621 MPa, preferably > 625 MPa, more preferably 625 to 673 MPa, elongation A 50.8 > 25 %, preferably > 26.5 %, uniform elongation Agt > 7.0 %, preferably > 7.5 %, yield strength ratio < 0.85, preferably 0.82 to 0.

85.

5. A UOE pipe, characterized by, The UOE welded pipe is made of the pipeline steel according to any one of claims 1-4.

6. The UOE pipe according to claim 5, characterized by The UOE welded pipe has an outer diameter of 1016mm-1422mm and a wall thickness of 25-40mm, a transverse yield strength of 555-665MPa, a longitudinal yield strength of 530-640MPa, in the transverse direction, a pipe body impact energy AKv of-20℃ of ≥160J, preferably ≥216J, a weld and heat affected zone impact energy AKv of-20℃ of ≥50J, preferably a weld impact energy AKv of-20℃ of ≥175J and / or a heat affected zone impact energy AKv of-20℃ of ≥196J, and a-10℃ full wall thickness DWTT performance: SA% of ≥85%, preferably 85-92%.

7. A method of manufacturing the UOE pipe as set forth in claim 5 or 6, characterized by, The method comprises the following steps performed in sequence: 1) smelting and continuous casting: obtaining a 300-450mm-thick slab through smelting-LF+RH secondary refining and continuous casting; 2) heating: heating the slab to obtain a heated slab, wherein the heating temperature is 1070-1170℃; 3) rolling: rolling the heated slab to obtain a rolled slab, wherein the rolling is rough rolling+finish rolling, and wherein: the rough rolling is performed under the following conditions: the finish rolling temperature of the rough rolling is 950-1050℃, and the rolling single pass reduction is ≥8%; the intermediate blank thickness is 3t-5t, t being the target UOE welded pipe wall thickness in mm; the finish rolling is performed under the following conditions: the finish rolling temperature is 730-820℃; 4) air cooling: waiting for the rolled slab to reach a target temperature on a roller bed to obtain an air-cooled slab, wherein the target temperature is the open cooling temperature of water cooling; 5) water cooling: water cooling the air-cooled slab to obtain a steel plate, wherein the water cooling is performed under the following conditions: the open cooling temperature is 640-690℃, the final cooling temperature is 100-350℃, and the cooling rate is 15-35℃ / s; 6) steel pipe forming: 6.1) arc starting plate welding: welding an arc starting plate to the four corners of the steel plate obtained in step 5); 6.2) edge milling and beveling; 6.3) forming using the C, U and O forming process to obtain an O-formed split steel pipe; wherein the O-forming compression rate=(π×(pre-welded outer diameter-wall thickness)-milled width) / milled width×100%=0.18-0.22%; 6.4) pre-welding+ welding: pre-welding and welding the O-formed split steel pipe to obtain a welded steel pipe; the welding line energy is: 1.7t≤H≤2.1t, preferably 1.7t≤H≤2.0t, wherein H is the welding line energy in KJ / cm, and t is the target UOE welded pipe wall thickness in mm; 6.5) Expanding: the whole length of the welded steel pipe is expanded to obtain an expanded steel pipe; wherein the expanding rate = (the outer diameter of the expanded steel pipe - the outer diameter of the steel pipe before expanding) / the outer diameter of the steel pipe before expanding x 100% = 0.80% ~ 1.20%; 6.6) The expanded steel pipe is subjected to a light heat treatment to obtain a UOE welded pipe; the light heat treatment is performed at a temperature of 200 ~ 250℃ for 5 ~ 15 min.

8. The method of claim 7, wherein: Step 6) The steel pipe forming further comprises the following steps after step 6.6): 6.7) Welding seam ultrasonic detection: the welding seam defects such as cracks, delamination and incomplete penetration in the welding seam of the UOE welded pipe are detected by using an ultrasonic detection method; 6.8) Welding seam X-ray detection: the point-like welding seam defects such as bubbles and inclusions in the welding seam of the UOE welded pipe are detected by using an X-ray detection method; 6.9) Chamfering: the ends of the UOE welded pipe are subjected to flat head and chamfering treatment to obtain a chamfered steel pipe; 6.10) Ultrasonic detection of pipe end delamination: the end of the chamfered steel pipe is subjected to ultrasonic detection to prevent delamination defects; 6.11) Magnetic particle detection of pipe end: the end of the chamfered steel pipe is subjected to magnetic particle detection to prevent delamination defects; 6.12) Installing a protective ring: the end of the chamfered steel pipe is installed with a protective ring.

9. The method according to claim 7 or 8, characterized in that, Before step 6.5), the welded steel pipe is subjected to welding seam ultrasonic detection and welding seam X-ray detection; The welding seam ultrasonic detection is to detect the welding seam defects such as cracks, delamination and incomplete penetration in the welded steel pipe by using an ultrasonic detection method; The welding seam X-ray detection is to detect the point-like welding seam defects such as bubbles and inclusions in the welded steel pipe by using an X-ray detection method.

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