Economical high-strength pipeline steel with excellent low-temperature toughness and preparation method thereof

Abstract

The economical high-strength pipeline steel with excellent low-temperature toughness comprises the following components in percentage by weight: 0.03-0.06% of C, 0.15-0.25% of Si, 1.50-1.75% of Mn, less than or equal to 0.15% of Ni, 0.15-0.30% of Cr, 0.03-0.06% of Nb, 0.010-0.015% of Ti, less than or equal to 0.010% of impurity elements P needing to be controlled, less than or equal to 0.0015% of S, less than or equal to 0.0004% of B, less than or equal to 0.005% of N and the balance of Fe and inevitable impurities, and the formula 1 is more than or equal to 0.40. According to the formula 1 = {(T * W) / w-delta p-a * t} / {(T * W) / w-delta p} + {(0.06-C) + (Nb-0. 03)} * 3 + Ni / 2, on the premise that more elements such as Cu and Ni with higher cost do not need to be added, higher strength and low-temperature toughness are matched.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal materials and its manufacturing technology, and particularly relates to an economic high-strength pipeline steel with excellent low-temperature toughness and a preparation method thereof. BACKGROUND

[0002] Improving the long-distance pipeline transportation capacity and safety has become two major themes faced by contemporary pipeline engineering. In recent years, China's clean energy supply capacity and coverage area have gradually increased, and the construction of oil transportation pipelines has been growing. The key problem to be solved is the contradiction between pipeline capacity, construction cost and operation safety, so that large-diameter, high-strength and thick-specification pipeline steels are increasingly widely used. In recent years, the application proportion of high-strength pipeline steel exceeds 50%.

[0003] For high-strength pipeline steel, DWTT performance is one of the core indicators for measuring its service safety. Since the fracture morphology of DWTT drop hammer tearing test has good consistency with the full-size burst test of the pipeline, DWTT SA% ≥ 85% can ensure that the pipeline conveying compressible fluid (especially natural gas) operates above the ductile-brittle transition temperature, avoiding the propagation of pipeline brittle cracks.

[0004] Chinese patent CN113166905B discloses a steel material for high-strength thick pipeline with excellent low-temperature toughness and elongation and small yield ratio, and a manufacturing method thereof. The yield strength is above 550 MPa, the tensile strength is above 660 MPa, the yield ratio is below 0.83, and the total elongation is above 42%, meeting the requirements of DWTT at -30℃. However, the patent adds a large amount of noble metals such as Mo, Ni, Nb, etc., and the alloy design is not economical, which is obviously different from the present patent.

[0005] Chinese patent CN107406951B discloses a high-strength and high-toughness steel plate and a manufacturing method thereof. The tensile strength (TS) is above 625 MPa, the Charpy impact absorbed energy at -40℃ (vE-40℃) is above 375 J, and the plastic fracture rate (SA-40℃) obtained in the DWTT test at -40℃ is above 85%, which is a high-strength and high-toughness steel plate. However, the composition of the patent includes REM, Mg, Zr and other elements, which is obviously different from the present patent.

[0006] Chinese patent CN107532254A discloses a high-strength pipeline steel plate with excellent low-temperature toughness. The CTOD value at -10℃ meets 0.25 mm above, 85% SATT is below -10℃, and the DWTT characteristics are excellent. However, the composition of the patent includes REM, Zr and other elements, which is obviously different from the present patent.

[0007] Chinese patent CN102409224B discloses a thick specification hot-rolled steel plate for submarine pipeline with excellent low-temperature toughness, the transverse and longitudinal yield strength can reach 480 MPa or above 510 MPa, the transverse and longitudinal tensile strength reaches 560 MPa or above 600 MPa, the impact toughness at-60℃ is greater than or equal to 400 J, and the DWTT shear area at-25℃ is greater than or equal to 85%. But the composition of the patent is wide, and the controlled rolling and controlled cooling process design is obviously different from the patent.

[0008] Chinese patent CN103834874B discloses a thick-wall high-DWTT performance X65-70 submarine pipeline steel and a manufacturing method, and the strength and toughness are excellent. The patent adds more noble metals such as Cu, Ni, etc., and the alloy design is not economical, which is obviously different from the patent.

[0009] At present, how to balance the strength and toughness matching of high-strength pipeline steel, and at the same time combine with the actual situation of industrial production, reduce the production cost and improve the product performance stability is a technical problem to be solved by those skilled in the art. SUMMARY

[0010] The purpose of the present application is to provide an economical high-strength pipeline steel with excellent low-temperature toughness and a preparation method thereof. Without adding more cost-high Cu, Ni and other elements, the pipeline steel obtains high strength while ensuring the low-temperature toughness of the steel, the yield strength R t0.5 of the pipeline steel is 450-550 MPa, the tensile strength R m is 535-655 MPa, the yield strength ratio R t0.50 / Rm≤0.90; the low-temperature toughness: at-20℃, using V-shaped notch specimen, impact test is carried out on the test steel plate according to ASTM E23, the Charpy impact energy at-20℃ is≥250 J; at-20℃, using full-thickness V-shaped notch specimen, drop weight tear test is carried out on the test steel plate according to API RP 5L3, the DWTT test SA% at-20℃ is≥85%.

[0011] To achieve the above purpose, the technical scheme of the present application is as follows:

[0012] An economical high-strength pipeline steel with excellent low-temperature toughness, the composition includes, by weight percentage: C: 0.03-0.06%, Si: 0.15-0.25%, Mn: 1.50-1.75%, Ni≤0.15%, Cr: 0.15-0.30%, Nb: 0.03-0.06%, Ti: 0.010-0.015%, the impurity elements P≤0.010%, S≤0.0015%, B≤0.0004%, N≤0.005% need to be controlled, the balance includes Fe and unavoidable impurities, and the calculated value of formula 1 needs to be≥0.40;

[0013] Formula 1 = {(T x W) ÷ w - δ p -a x t) / {(T x W) ÷ w - δ p} + {(0.06 - C) + (Nb - 0.03)} x 3 + Ni / 2

[0014] Wherein:

[0015] T is the slab thickness after casting, unit mm;

[0016] W is the slab width after casting, unit mm;

[0017] w is the finished steel plate width, unit mm;

[0018] δ p is the total reduction in the rough rolling forming stage, unit mm;

[0019] a is the multiple of the intermediate slab after rough rolling relative to the thickness of the finished steel plate;

[0020] t is the thickness of the finished steel plate, unit mm;

[0021] C, Nb, Ni are the weight percentage of the corresponding elements, unit wt%.

[0022] Further, the balance is Fe and inevitable impurities.

[0023] The microstructure of the high-strength pipeline steel described in the application is bainite or bainite + ferrite, and the average grain size is ≤15um.

[0024] The high-strength pipeline steel described in the application has the following transverse tensile properties: yield strength R t0.5 : 450-550 MPa, tensile strength R m : 535-655 MPa, yield strength ratio R t0.50 / Rm ≤ 0.90; low temperature toughness: impact test of the test steel plate according to ASTM E23 using V-notch specimen at -20℃, Charpy impact energy at -20℃ ≥ 250J; DWTT test of the test steel plate according to API RP 5L3 using full-thickness V-notch specimen at -20℃, SA% at -20℃ DWTT test ≥ 85%.

[0025] In the component design of the economic high-strength pipeline steel with excellent low-temperature toughness described in the application:

[0026] Carbon C: the most basic strengthening element, carbon dissolved in steel forms interstitial solid solution, plays the role of solid solution strengthening, and forms carbide precipitation with strong carbide forming elements, which plays the role of precipitation strengthening; but with the increase of C content, the ductility, toughness and welding performance of steel are significantly reduced, and the center segregation of continuous casting billet is caused, which is not conducive to the low temperature toughness of steel plate. Therefore, the C content in the application is controlled at 0.03-0.06%.

[0027] Manganese Mn: a solid solution strengthening element, which is the most important and economic strengthening element to compensate for the loss of strength caused by the reduction of C content in steel. Mn is also an element that expands the gamma phase region, which can improve the hardenability of steel and reduce the gamma to alpha phase transition temperature, which helps to obtain fine phase transition products and improve the toughness of steel. However, Mn is also an easy segregation element, and excessive content can easily cause center segregation in continuous casting billet, and hard phase structure is easily generated during cooling after rolling, which reduces the low temperature toughness of the material. Therefore, the Mn content in the application is controlled at 1.50-1.75%.

[0028] Silicon Si: a solid solution strengthening element, which is also a deoxidizing element in steel, but excessive content will deteriorate the welding performance of steel, especially the deterioration of the toughness of the welding heat affected zone, and is not conducive to the removal of iron oxide scale during hot rolling. Therefore, the Si content in the application is controlled at 0.15-0.25%.

[0029] Nickel Ni: a solid solution strengthening element, which can also improve the toughness of steel, and has the effect of improving the hardenability of steel and delaying pearlite transformation during cooling of steel plate, but excessive addition is not conducive to the toughness and welding performance of steel plate. Therefore, the Ni content in the application is ≤0.15%.

[0030] Chromium Cr: a solid solution strengthening element, an important element for improving the hardenability of steel, promoting the formation of acicular ferrite, improving the toughness of steel, and being conducive to ensuring the uniformity of the microstructure and properties of the whole thickness of the steel plate; but excessive content will promote the formation of low temperature phase transition structure, which is not conducive to low temperature toughness. Therefore, the Cr content in the application is controlled at 0.15-0.30%.

[0031] Nb: one of the important elements of low carbon micro-alloyed steel, Nb strain-induced precipitation of solid solution in hot rolling process forms Nb(C, N) particles, which can delay austenite recrystallization, improve the austenite recrystallization temperature of the steel, make two-stage controlled rolling possible, avoid the formation of mixed crystals, and be beneficial to obtain uniform and fine structure, improve the strength and toughness of the material, and ensure the isotropy of the steel plate performance. In addition, the solid solution of Nb is precipitated as second phase particles NbC in the matrix during cooling, which plays a role in precipitation strengthening. However, too high content of Nb cannot be completely solid-solved, which not only cannot play a role, but also increases the production cost, and makes NbC precipitate too early at high temperature, which is easy to form larger size NbC precipitates at the center segregation, which is not conducive to toughness. Therefore, the content of Nb in the application is controlled at 0.03-0.06%.

[0032] Titanium Ti: is a strong carbonitride forming element, which can play a role in nitrogen fixation, and can form fine high-temperature stable TiN precipitates during slab continuous casting, thereby improving the toughness of the material. In addition, the unsolved carbonitride of Ti can prevent the growth of austenite grains during steel heating, and the TiN and TiC precipitated during high-temperature austenite zone rough rolling can effectively inhibit the growth of austenite grains. In addition, during the welding process, the TiN and TiC particles in the steel can significantly prevent the grain growth in the heat-affected zone, thereby improving the welding performance of the steel plate. Therefore, the content of Ti in the application is controlled at 0.010-0.015%.

[0033] Sulfur, phosphorus, boron and nitrogen (S, P, B, N): inevitable impurity elements in steel, P is an easily segregated element in steel, S is easy to form sulfides in steel, which will seriously reduce the low temperature toughness of the steel; B is easy to precipitate at the grain boundary, resulting in the decrease of material plasticity and toughness; too high N content is easy to form cracks in the continuous casting billet. Therefore, the application controls P≤0.01%, S≤0.0015%, B≤0.0004%, N≤0.005%.

[0034] The above composition design also needs to meet the formula 1 calculation value≥0.40,

[0035] Formula 1={(T×W)÷w-δ p -a×t} / {(T×W)÷w-δ p}+{(0.06-C)+(Nb-0.03)}×3+Ni / 2

[0036] Wherein: T is the thickness of the slab after casting, unit mm; W is the width of the slab after casting, unit mm; w is the width of the steel plate, unit mm; δ pis the total reduction of the rough rolling forming stage, unit: mm; a is the multiple of the thickness of the intermediate billet obtained after rough rolling relative to the thickness of the finished steel plate; t is the thickness of the finished steel plate, unit: mm; C, Nb, Ni are the weight percentages of the corresponding elements, unit: wt%, only the numerical value before the percentage sign of the corresponding element is substituted when calculating.

[0037] The design of formula 1 mainly considers the following factors: the present application controls the carbon content at a low level, and adds an appropriate amount of niobium to refine the grain, which is one of the prerequisites for the pipeline steel to have good toughness at low temperature. At the same time, sufficient reduction can improve the uniformity of the material and the degree of grain refinement, thereby optimizing its low temperature toughness, but the reduction at different stages has different effects on the improvement of low temperature toughness, among them, the reduction at the rough rolling extension stage is particularly important for the deformation penetration, especially the grain refinement at the center of the plate thickness, and the reduction at the rough rolling forming stage is not obvious for improving the low temperature toughness effect because the slab thickness is large and the single pass reduction is small, the deformation penetration ability to the center is insufficient, therefore, to ensure good low temperature toughness, it is necessary to ensure a higher reduction at the rough rolling extension stage by ensuring a lower reduction at the rough rolling forming stage. In addition, the actual reduction that the steel plate can obtain and the slab size used and the size of the final steel plate are also closely related. Through regression analysis of a large number of experimental and production data, in order to obtain excellent low temperature toughness, the slab size, steel plate size need to be considered to ensure the proportion of the reduction at the rough rolling extension stage, and the content of alloying elements (C, Nb) is adjusted in combination with the actual conditions of the reduction, when other conditions are not conducive to the guarantee of low temperature toughness, a certain amount of Ni needs to be added to improve the stability of low temperature toughness, to ensure that their mutual relationship meets the requirement of formula 1≥0.40, so as to ensure that the final product has good low temperature toughness.

[0038] The method for manufacturing the economic high-strength pipeline steel with excellent low-temperature toughness comprises the following steps:

[0039] 1) Smelting and casting

[0040] Smelting and casting are performed according to the above-mentioned components to obtain a slab.

[0041] 2) Heating and rough rolling

[0042] The heating temperature is 1130-1180℃; the rough rolling final rolling temperature is ≥950℃, and the average single pass reduction rate at the rough rolling extension stage is ≥10%; an intermediate billet is obtained after rough rolling, and the thickness of the intermediate billet is 3.5-4.5 times the thickness of the finished steel plate.

[0043] 3) Finish rolling

[0044] When the calculated value of formula 2 is ≥0.40, the finish rolling final rolling temperature is 810-830℃, the cooling speed is 25-30℃ / s, and the final cooling temperature is 420-480℃.

[0045] When the value calculated by formula 2 is <0.40, the finish rolling temperature of the finishing mill is 770-800℃, the cooling speed is 15-20℃ / s, and the final cooling temperature is 350-400℃;

[0046] Formula 2={(T×W)÷w-δ p -a×t} / {(T×W)÷w-δ p}+(Ti / N-3) / 50;

[0047] Wherein,

[0048] T is the thickness of the slab after casting, in mm;

[0049] W is the width of the slab after casting, in mm;

[0050] w is the width of the finished steel plate, in mm,

[0051] δ p is the reduction in the rough rolling forming stage, in mm;

[0052] a is the multiple of the thickness of the intermediate slab obtained after rough rolling relative to the thickness of the finished steel plate;

[0053] t is the thickness of the finished steel plate, in mm;

[0054] Ti, N are the contents of corresponding chemical components, in wt%;

[0055] The slab heating temperature is controlled at 1130-1180℃, if the slab heating temperature is too low, the alloy carbide cannot be dissolved sufficiently, the effects of solid solution strengthening and precipitation strengthening cannot be fully played, and the control of center segregation is not good; if the heating temperature is too high, the grains are coarsened, which is not good for the low temperature toughness of the steel plate.

[0056] The finish rolling temperature of the rough rolling is ≥950℃, the average single pass reduction rate in the rough rolling extension stage is ≥10%, the rough rolling is performed in the complete recrystallization region of austenite, so that the mixed grains are avoided, and the sufficient reduction in the rough rolling can sufficiently refine the original austenite grains, which is good for the strength and toughness of the steel plate.

[0057] The intermediate slab is obtained after the rough rolling, the thickness of the intermediate slab is 3.5-4.5 times the thickness of the finished steel plate, the finish rolling is performed in the non-recrystallization region of austenite, the sufficient reduction in the finish rolling can sufficiently flatten the austenite grains, so that more nucleation sites are provided for the subsequent phase change, thereby refining the final structure and improving the strength and toughness of the steel plate.

[0058] Two schemes are designed for the combination of the finish rolling temperature of the finishing mill, the cooling speed and the final cooling temperature, and the selection is made according to the value calculated by formula 2, so that the stable low temperature toughness of the steel plate can be realized under various different actual conditions.

[0059] Formula 2={(T×W)÷w-δp -a×t} / {(T×W)÷w-δ p}+(Ti / N-3) / 50;

[0060] Where T is the thickness of the cast slab in mm; W is the width of the cast slab in mm; w is the width of the finished steel plate in mm; δ p t represents the total reduction in the rough rolling stage, in mm; a represents the multiple of the intermediate billet thickness obtained after rough rolling relative to the finished steel plate thickness; t represents the thickness of the finished steel plate, in mm; Ti and N represent the weight percentage of the corresponding elements, in wt%, and only the values ​​before the percentage sign of the corresponding elements are substituted in the calculation.

[0061] When the calculated value of Formula 2 is ≥0.40, Scheme 1 is adopted: finishing rolling temperature 810~830℃, cooling rate 25~30℃ / s, and final cooling temperature 420~480℃;

[0062] When the calculated value of Formula 2 is less than 0.40, Scheme 2 is adopted: finishing rolling temperature 770-800℃, cooling rate 15-20℃ / s, and final cooling temperature 350-400℃.

[0063] Formula 2 is designed with the following main considerations: Ti is a strong carbonitride forming element that can fix nitrogen. During slab continuous casting, it can form fine, high-temperature stable TiN precipitates, thereby improving the toughness of the material. However, when the N content is too high and the Ti / N ratio decreases, the TiN phase tends to aggregate and coarsen, weakening its grain-refining effect. In actual production, due to fluctuations in process and composition, if these fluctuations all move in a direction unfavorable to low-temperature toughness, it will cause a lack of low-temperature toughness. Therefore, it is necessary to adjust the final rolling temperature, cooling rate, and final cooling temperature according to the actual process and composition fluctuations to compensate for the toughness loss caused by the above fluctuations. When the calculated value of Formula 2 is ≥0.40, the process of Scheme 1 can be used for production; otherwise, Scheme 2 needs to be activated to compensate for the loss of low-temperature toughness. This mainly relies on lowering the final rolling temperature to promote the precipitation of proeutectoid ferrite, using a lower cooling rate and final cooling temperature to make the microstructure more uniform throughout the thickness during cooling, and to promote the precipitation of fine ferrite on the coarse microstructure in the center of the plate thickness, thereby increasing the resistance to crack propagation in the low-temperature toughness test and improving the low-temperature toughness.

[0064] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0065] The present application adopts a low-C and low-Ni component design, combines the addition of alloy elements Mn, Cr and trace Nb-Ti elements, uses solid solution strengthening to improve the strength and toughness of the steel plate, at the same time, the calculated value of formula 1 is greater than or equal to 0.40, the slab size and the steel plate size need to be comprehensively considered to ensure the proportion of the reduction amount in the rough rolling extension stage, and the content of the alloy elements (C, Nb, Ni) is adjusted in combination with the actual conditions of the reduction amount, so as to ensure that the final product has higher strength and better low-temperature toughness. In the prior art, in order to make the steel plate have such high strength and high low-temperature toughness, more cost-higher Cu, Ni and other elements need to be added in the composition, resulting in higher overall cost.

[0066] On the basis of the component design, the present application controls rolling by using two-stage controlled rolling technology in the austenite recrystallization zone and the non-recrystallization zone, ensures sufficient compression ratio in the two-stage rolling process, fully refines the grains, avoids mixed crystal structure, improves the strength and toughness of the steel plate, and creatively designs different matching modes of the slab size, the steel plate size, the chemical composition and the rolling and cooling process path, and selects the finish rolling final rolling temperature, the cooling speed and the final cooling temperature according to the calculated value of formula 2, so as to ensure the stable controllability of the low-temperature toughness of the high-strength pipeline steel in industrial batch production.

[0067] The high-strength pipeline steel obtained by the present application has the following properties: transverse tensile yield strength R t0.5 : 450-550 MPa, tensile strength R m : 535-655 MPa, yield strength ratio R t0.50 / Rm≤0.90; low-temperature toughness: the impact test of the test steel plate is carried out according to ASTM E23 using a V-shaped notch specimen at-20℃, the Charpy impact energy at-20℃ is greater than or equal to 250J; the drop weight tear test of the test steel plate is carried out according to API RP 5L3 using a full-thickness V-shaped notch specimen, and the DWTT test SA% at-20℃ is greater than or equal to 85%. BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1 It is a microstructure photo of the high-strength pipeline steel obtained by the present application.

[0069] Figure 2 It is a microstructure photo of the high-strength pipeline steel obtained by the present application. DETAILED DESCRIPTION

[0070] The present application will be further described below in combination with the embodiments and the drawings.

[0071] The specific components of the steel in the embodiments and the comparative examples of the present application are shown in Table 1, and the balance is Fe and inevitable impurities. The parameters of the steel billets and finished steel plates in the embodiments and the comparative examples of the present application are shown in Table 2, the process parameters for preparing the steel in the embodiments and the comparative examples of the present application are shown in Table 3, and the performance parameters of the steel in the embodiments and the comparative examples of the present application are shown in Table 4.

[0072] Figure 1 and Figure 2 The microstructure photographs of the high-strength pipeline steel obtained in Example 1 and Example 2 of the present application are shown in the drawings, and it can be seen from the drawings that the typical microstructure is bainite or bainite + ferrite, and the average grain size is ≤15 um.

[0073] As can be seen from the results in Table 4, the yield strength R t0.5 of the pipeline steel of the present application is 450-550 MPa, the tensile strength R m is 535-655 MPa, the yield strength R t0.50 / Rm is ≤0.90, the low-temperature toughness is that the Charpy impact energy at -20 ℃ is ≥250 J using a V-notch specimen according to ASTM E23, and the DWTT test SA% at -20 ℃ is ≥85% using a full-thickness V-notch specimen according to API RP 5L3, and the low-temperature toughness is excellent, which very well meets the strength and toughness matching of the pipeline steel and the performance is stable.

[0074] In Comparative Example 1, the C content in the component design is relatively high, which does not meet the design requirements.

[0075] In Comparative Example 2, the formula 1 = 0.23, which does not meet the requirements of the present application.

[0076] In Comparative Example 3, although the formula 1 meets the requirements of the present application, the formula 2 = 0.30, but in the process, the finishing rolling stage should use scheme 2: the finishing rolling final rolling temperature is 770-800 ℃, the cooling speed is 15-20 ℃ / s, and the final cooling temperature is 350-400 ℃, and the finishing rolling final rolling temperature, the cooling speed and the final cooling temperature all do not meet the requirements of the present application.

[0077] In Comparative Example 4, the average single-pass reduction rate in the rough rolling extension stage is relatively low, which does not meet the requirement of sufficient rough rolling reduction rate.

[0078] Therefore, although the strengths of Comparative Examples 1-4 can also meet the requirements, the low-temperature toughness is obviously reduced, and especially the DWTT performance cannot meet the requirement of SA% ≥85%.

[0079]

[0080]

[0081]

[0082]

Claims

1. An economical, high-strength pipeline steel with excellent low-temperature toughness, characterized in that, The components include, in percentage by weight: C: 0.03-0.06%, Si: 0.15-0.25%, Mn: 1.50-1.75%, Ni≤0.15%, Cr: 0.15-0.30%, Nb: 0.03-0.06%, Ti: 0.010-0.015%, and impurities P≤0.010%, S≤0.0015%, B≤0.0004%, N≤0.005% need to be controlled, the balance including Fe and inevitable impurities, and the calculated value of formula 1 needs to be ≥0.40: Formula 1 = {(T x W) ÷ w - δ p - a x t) / {(T x W) ÷ w - δ p} + {(0.06 - C) + (Nb - 0.03)} x 3 + Ni / 2 where: T is the slab thickness after casting, unit: mm; W is the slab width after casting, unit: mm; w is the finished steel plate width, unit: mm; delta p δ total reduction for the roughing forming stage, in mm; a is the multiple of the intermediate slab after rough rolling relative to the thickness of the finished steel plate; t is the thickness of the finished steel plate, unit: mm; C, Nb, Ni are the weight percentages of the corresponding elements, unit: wt%.

2. The economical high-strength pipeline steel having excellent low-temperature toughness according to claim 1, wherein the steel contains 0.0005 to 0.0030% of phosphorus. The balance is Fe and inevitable impurities.

3. The economical high-strength pipeline steel having excellent low-temperature toughness according to claim 1, wherein the steel contains 0.0005 to 0.0030% of phosphorus. The microstructure of the high-strength pipeline steel is bainite or bainite + ferrite, and the average grain size is ≤15 um.

4. The economical high-strength pipeline steel having excellent low-temperature toughness according to claim 1, wherein the steel contains 0.0005 to 0.0030% of phosphorus. Said high strength pipeline steel has a transversal tensile yield strength R t0.5 : 450-550 MPa, a tensile strength R m : 535-655 MPa, a yield strength to tensile strength ratio R t0.50 / Rm < 0.

90. Low-temperature toughness: impact test of the test steel plate is carried out according to ASTM E23 using V-notch test specimens at -20℃, and the Charpy impact energy at -20℃ is ≥250J; the drop weight tear test of the test steel plate is carried out according to API RP 5L3 using full-thickness V-notch test specimens, and the DWTT test SA% at -20℃ is ≥85%.

5. The method of producing a high-strength pipeline steel excellent in economy and low-temperature toughness according to any one of claims 1 to 4, characterized by, The method comprises the following steps: 1) smelting and casting The components according to claim 1 or 2 are smelted and cast to obtain a slab; 2) heating and rough rolling The heating temperature is 1130-1180℃, the rough rolling final rolling temperature is ≥950℃, the average single pass reduction rate of the rough rolling extension stage is ≥10%, and the intermediate slab is obtained after rough rolling, and the thickness of the intermediate slab is 3.5-4.5 times the thickness of the finished steel plate; 3) finish rolling When the calculated value of formula 2 is ≥0.40, the finish rolling final rolling temperature is 810-830℃, the cooling speed is 25-30℃ / s, and the final cooling temperature is 420-480℃; When the calculated value of formula 2 is <0.40, the finish rolling final rolling temperature is 770-800℃, the cooling speed is 15-20℃ / s, and the final cooling temperature is 350-400℃; Equation 2 = {(T x W) ÷ w - δ p - a x t) / {(T x W) ÷ w - δ p} + (Ti / N - 3) / 50; Wherein, T is the slab thickness after casting, unit: mm; W is the slab width after casting, unit: mm; w is the finished steel plate width, unit: mm, delta p Ptotal is the total reduction for the roughing forming stage, in mm; a is the multiple of the intermediate slab after rough rolling relative to the thickness of the finished steel plate; t is the thickness of the finished steel plate, unit: mm; Ti, N are the contents of the corresponding chemical components, unit: wt%. The components include, in percentage by weight: C: 0.03-0.06%, Si: 0.15-0.25%, Mn: 1.50-1.75%, Ni≤0.15%, Cr: 0.15-0.30%, Nb: 0.03-0.06%, Ti: 0.010-0.015%, and impurities P≤0.010%, S≤0.0015%, B≤0.0004%, N≤0.005% need to be controlled, the balance including Fe and inevitable impurities, and the calculated value of formula 1 needs to be ≥0.40: T is the slab thickness after casting, unit: mm; W is the slab width after casting, unit: mm; w is the finished steel plate width, unit: mm; a is the multiple of the intermediate slab after rough rolling relative to the thickness of the finished steel plate; t is the thickness of the finished steel plate, unit: mm; C, Nb, Ni are the weight percentages of the corresponding elements, unit: wt%. The balance is Fe and inevitable impurities. The microstructure of the high-strength pipeline steel is bainite or bainite + ferrite, and the average grain size is ≤15 um. Low-temperature toughness: impact test of the test steel plate is carried out according to ASTM E23 using V-notch test specimens at -20℃, and the Charpy impact energy at -20℃ is ≥250J; the drop weight tear test of the test steel plate is carried out according to API RP 5L3 using full-thickness V-notch test specimens, and the DWTT test SA% at -20℃ is ≥85%.

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