A bimodal high-strain marine pipeline steel, pipeline pipe and manufacturing method thereof

Abstract

The present invention discloses a bimodal high-strain marine pipeline steel, a pipeline pipe and a manufacturing method thereof, and belongs to the technical field of steel. The shape of inclusions is controlled by Ca treatment, and harmful elements such as P and S and harmful gases such as oxygen, hydrogen and nitrogen in the steel are strictly controlled; through controlled rolling of the austenite + ferrite dual-phase region and medium-temperature relaxation treatment in the critical region, accelerated cooling when the relaxation temperature is lower than the starting temperature of bainite transformation, a two-phase structure of fine-grained / ultra-fine-grained polygonal ferrite + granular bainite is obtained, and a typical bimodal structure is formed, which effectively improves plasticity. Finally, a small amount of diffusely distributed MA structure is obtained by low-temperature tempering treatment, and the strength of the pipeline pipe is further improved, thereby obtaining comprehensive mechanical properties of high strength, high plasticity and high toughness. The obtained pipeline pipe has excellent performance, especially good plastic deformation capacity and good weldability, which can meet the use requirements of such pipeline steel and pipeline pipe in deep-sea areas.

Description

Technical Field

[0001] The invention belongs to the technical field of steel materials, and in particular relates to a bimodal structure high-strain marine pipeline steel, a pipeline pipe and a manufacturing method thereof. Background Art

[0002] With the completion of the development of near-shore and offshore oil and gas fields, the development of new oil and gas fields has gradually moved to remote areas such as the ocean. In recent years, the focus of world oil exploration has shifted from land to ocean, from shallow sea to deep sea, and the exploration and development of deepwater and ultra-deepwater oil and gas resources has become a key area of ​​world oil and gas production.

[0003] During the laying and construction of submarine pipelines (J-Lay, S-Lay, coiling, towing, etc.), pipelines are inevitably deformed, and the deformation often exceeds 0.5%. Therefore, high strength and high plasticity of pipeline pipes are necessary guarantees for deepwater oil and gas development. At the same time, the harsh deep-sea service environment has prompted deep-sea pipeline steel to develop in the direction of high steel grade and high toughness (low temperature). Generally speaking, when the strength of pipeline steel is low, the uniform plastic deformation capacity is large, and it is difficult to obtain a large plastic deformation capacity for high-grade pipeline steel. In addition, in the subsequent anti-corrosion process, high-grade pipeline steel and pipeline pipes will produce an increase in strength and hardness, and a decrease in plasticity and toughness due to the effect of temperature, that is, strain aging phenomenon. Pipeline pipes will also produce strain aging phenomenon during long-term use.

[0004] In recent years, with the development of controlled rolling and controlled cooling technology, the yield strength ratio of pipeline steel has increased from 0.80-0.85 in the past to 0.90-0.95. The excessively high yield strength ratio limits the deformation capacity of pipeline steel and pipeline pipes, thus affecting the safety of use. Although high-grade marine pipeline steel with high strain performance has been developed internationally and applied in engineering, it cannot well balance the matching of high strength, high plasticity and high toughness. Summary of the invention

[0005] In order to overcome the defects of the above-mentioned prior art, the present invention discloses a bimodal high-strain marine pipeline steel, a pipeline pipe and a manufacturing method thereof, which can obtain high strength, high plasticity, high toughness and good weldability.

[0006] The present invention is achieved through the following technical solutions:

[0007] The invention discloses a bimodal high-strain marine pipeline steel, which has a dual-phase structure of bimodal polygonal ferrite + granular bainite supplemented by a M / A structure, and has the following composition by mass percentage: C: 0.04% to 0.06%, Mn: 1.50% to 1.90%, Si: 0.15% to 0.25%, P≤0.005%, S≤0.003%, Al: 0.005% to 0.03%, N≤0.005%, a first strengthening component and a second strengthening component, and the balance is Fe; the first The strengthening components are one or more of Nb: 0.004% to 0.008%, V: 0.01% to 0.03% and Ti: 0.001% to 0.025%, and 0.05%≤Nb+V+Ti≤0.10%; the second strengthening component is one or more of Cr: 0.10% to 0.30%, Mo: 0.08% to 0.30%, Ni: 0.10% to 0.30%, Cu: 0.10% to 0.30% and B: 0.0001% to 0.0005%; the carbon equivalent is ≤0.17.

[0008] The present invention discloses a method for manufacturing a bimodal structure high strain marine pipeline steel, comprising the following steps:

[0009] S1: The raw materials containing the above components are subjected to oxygen-blown converter smelting, Ca treatment, external refining and vacuum degassing, and then continuously cast into thick slabs;

[0010] S2: heating the thick slab to 1180-1200°C and keeping the temperature; performing relaxation treatment after rough rolling and finish rolling;

[0011] S3: Low temperature tempering is performed at 450-550°C, and pipeline steel is obtained after cooling.

[0012] Preferably, in S2, the insulation time is 8 to 15 minutes.

[0013] Preferably, in S2, the rough rolling temperature is 1050-1120°C, and multiple rolling passes are used.

[0014] Preferably, in S2, the start temperature of the finishing rolling is 810°C to 850°C, the end temperature of the finishing rolling is 700°C to 750°C, and multiple rolling passes are adopted.

[0015] Preferably, in S2, the relaxation start temperature is 700-750°C, the relaxation time is 80-150s, and then the reaction mixture is water-cooled to 150-250°C at a cooling rate of 20-35°C / s.

[0016] Preferably, in S3, the low-temperature tempering time is 15 to 30 minutes.

[0017] Preferably, in S3, the cooling method is air cooling.

[0018] The method for preparing a pipeline pipe using the above-mentioned bimodal high-strain marine pipeline steel comprises: forming a steel plate by JCO or UOE, performing straight seam submerged arc welding, using a fine-grained acicular ferrite low-oxygen content material containing Ti-B as welding material, and expanding the diameter by 0.6% to 1.2% to obtain a pipeline pipe.

[0019] The pipeline pipe prepared by the method of preparing a pipeline pipe with a bimodal structure high strain marine pipeline steel has a transverse yield strength of 529-598 MPa, a tensile strength of 666-694 MPa, a total elongation of 26-38%, a Charpy impact toughness of 219-295 J at -20°C, a DWTT shear area of ​​85-93% at -10°C, a hardness of 202-236 HV10, a longitudinal yield strength of 536-553 MPa, a tensile strength of 663-680 MPa, a total elongation of 29-43%, a uniform elongation of 7.2-11.3%, and a work hardening rate n value of 0.101-0.126.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] The bimodal structure high strain marine pipeline steel disclosed in the present invention adopts low carbon or ultra-low carbon components, adds Mn to increase the stability of austenite, adds first strengthening components Nb, V, and Ti for micro-alloying, and adds a small amount of second strengthening components Mo, Ni, Cu, Cr, and B to promote the formation of MA island structure, strictly controls harmful elements such as P and S in the steel, and improves the strain aging phenomenon caused by the interaction between C and N elements in the steel and dislocations in the steel by strictly controlling the content of N element.

[0022] The manufacturing method of the bimodal high-strain marine pipeline steel disclosed in the present invention adopts Al and Si fully deoxidized calm steel, Ca treatment to control the shape of inclusions, and strictly controls harmful elements such as P and S and harmful gases such as oxygen, hydrogen, and nitrogen in the steel; through controlled rolling in the austenite + ferrite dual-phase region and medium-temperature relaxation treatment in the critical region, accelerated cooling when the relaxation temperature is lower than the bainite transformation start temperature, a fine-grained / ultra-fine-grained polygonal ferrite + granular bainite dual-phase structure is obtained, and a typical bimodal structure is formed, which effectively improves the plasticity of the pipeline. Finally, a low-temperature tempering treatment is used to obtain a small amount of diffusely distributed MA structure, further improve the strength of the pipeline, and thus obtain comprehensive mechanical properties of high strength, high plasticity, and high toughness.

[0023] The bimodal structure high-strain marine pipeline pipe produced by the present invention has excellent performance, especially good plastic deformation capacity and good weldability, and can meet the use requirements of such pipeline steel and pipeline pipe in deep sea areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The metallographic diagram of the bimodal high-strain marine line pipe of the present invention;

[0025] Figure 2 This is a transmission image of the MA island of the bimodal high-strain marine line pipe of the present invention;

[0026] Figure 3 It is a tensile stress-strain curve diagram of the metallographic diagram of the bimodal high-strain marine pipeline of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0028] Example 1

[0029] Alloy composition: C: 0.05%; Mn: 1.69%; Si: 0.21%; P: 0.0059%; S: 0.0026%; Al: 0.023%; N: 0.0038%; Nb: 0.065%; Ti: 0.015%; Mo: 0.17%; Ni: 0.23%; Cu: 0.014%; the balance is Fe and unavoidable impurities; carbon equivalent 0.17%.

[0030] Manufacturing process: The above materials are melted in an oxygen-blown converter, treated with Ca, refined outside the furnace and vacuum degassed, and continuously cast into slabs, heated to about 1200°C, kept warm for 8 minutes, rough rolled at 1050°C, rolled in two passes, with a reduction rate of 51%, then cooled to 830°C and rolled in two passes, with a reduction rate of 72%, a rolling end temperature of 750°C, a relaxation time of 80s, a water cooling temperature of 650°C, cooled to 250°C, a cooling rate of 20°C to 30°C / s, and then tempered at 520°C at a medium and low temperature for 20 minutes to make a hot-rolled steel plate with a thickness of about 29.6mm. The steel plate is then formed by JCOE, and multi-pass straight seam submerged arc welding is adopted. The welding material is a fine-grained acicular ferrite with low oxygen content containing Ti-B, and then expanded by 0.6 to 0.8% to make a straight seam submerged arc welded line pipe.

[0031] Performance characteristics: The high-strain line pipe produced in this embodiment has a thickness of about 29.6 mm and a diameter of 1016 mm, and has a multiphase structure of ultrafine grain / fine grain polygonal ferrite + granular bainite + M / A, and has high strength, high plasticity, high toughness and good weldability, and has good plastic deformation capacity. The transverse yield strength of the pipe body is 555-598 MPa, the tensile strength is 684-690 MPa, the total elongation is 27-35%, the Charpy impact toughness at -20°C reaches 285-293 J, the DWTT shear area at -10°C is 85-92%, and the hardness is 215-236 HV 10The longitudinal yield strength of the pipe body is 536~550MPa, the tensile strength is 663~674MPa, the total elongation is 29~42%, the uniform elongation is 7.2~9.3%, and the work hardening rate n value is 0.101~0.113.

[0032] Example 2

[0033] Alloy composition: C: 0.06%; Mn: 1.62%; Si: 0.22%; P: 0.009%; S: 0.002%; Al: 0.028; N: 0.003%; V: 0.04%; Ti: 0.014%; Mo: 0.099%; Ni: 0.11%; Cr: 0.022%; the balance is Fe and unavoidable impurities; carbon equivalent 0.17%.

[0034] Manufacturing process: The above materials are melted in an oxygen-blown converter, treated with Ca, refined outside the furnace and vacuum degassed, and continuously cast into slabs, heated to about 1200°C, kept warm for 10 minutes, rough rolled at 1100°C, rolled in two passes, with a reduction rate of 60%, then cooled to 810°C and rolled in two passes, with a reduction rate of 65%, the end temperature of rolling is 730°C, the relaxation time is 100s, the water cooling temperature is 620°C, cooled to 150°C, the cooling rate is 20°C~30°C / s, and then tempered at 550°C at a medium and low temperature for 15 minutes to make a hot-rolled steel plate with a thickness of about 31.8mm. The steel plate is then formed by JCOE, and multi-pass straight seam submerged arc welding is adopted. The welding material is a fine-grained acicular ferrite with low oxygen content containing Ti-B, and then expanded by 0.6~0.9% to make a straight seam submerged arc welded line pipe.

[0035] Performance characteristics: The high-strain line pipe produced in this embodiment has a thickness of about 31.8mm and a diameter of 559mm. It has a multiphase structure of ultrafine grain / fine grain polygonal ferrite + granular bainite + M / A, which has high strength, high plasticity, high flexibility and good weldability, and has good plastic deformation capacity and low strain aging sensitivity. The transverse yield strength of the pipe body is 549-580MPa, the tensile strength is 685-692MPa, the total elongation is 28-37%, the Charpy impact toughness at -20℃ reaches 219-248J, the DWTT shear area at -10℃ is 87-93%, and the hardness is 206-233HV 10 The longitudinal yield strength of the pipe body is 538~553MPa, the tensile strength is 671~680MPa, the total elongation is 30~41%, the uniform elongation is 9.8~11.3%, and the work hardening rate n value is 0.103~1.126.

[0036] Embodiment 3:

[0037] Alloy composition: C: 0.05%; Mn: 1.67%; Si: 0.20%; P: 0.008%; S: 0.0024%; Al: 0.019%; N: 0.003%; Nb: 0.055%; Ti: 0.015%; Mo: 0.14%; Ni: 0.15%; Cu: 0.022%; Cr: 0.2%; B: 0.0002%, the balance is Fe and unavoidable impurities; carbon equivalent 0.17%.

[0038] Manufacturing process: The above materials are melted in an oxygen-blown converter, treated with Ca, refined outside the furnace and vacuum degassed, and continuously cast into slabs, heated to about 1180°C, kept warm for 15 minutes, rough rolled at 1120°C, rolled in two passes, with a reduction rate of 60%, then cooled to 850°C and rolled in three passes, with a reduction rate of 75%, a rolling end temperature of 700°C, a relaxation time of 150s, a water cooling temperature of 640°C, cooled to 200°C, a cooling rate of 35°C / s, and then tempered at 450°C at low temperature for 30 minutes to make a hot-rolled steel plate with a thickness of about 24.1mm. The steel plate is then formed by UOE, and multi-pass straight seam submerged arc welding is adopted. The welding material is a fine-grained acicular ferrite with low oxygen content containing Ti-B, and then expanded by 0.8-1.2% to make a straight seam submerged arc welded line pipe.

[0039] Performance characteristics: The X70 high-strain line pipe produced in this embodiment has a thickness of about 24.1 mm and a diameter of 610 mm, and has a multiphase structure of polygonal ferrite + granular bainite + M / A, and has high strength, high plasticity, high toughness and good weldability, and has good plastic deformation capacity and low strain aging sensitivity. The transverse yield strength of the pipe body is 529-541 MPa, the tensile strength is 666-671 MPa, the total elongation is 26-38%, the Charpy impact toughness at -20°C reaches 243-295 J, the DWTT shear area at -20°C is 85-92%, and the hardness is 202-229 HV 10 The longitudinal yield strength of the pipe body is 536~546MPa, the tensile strength is 663~668MPa, the total elongation is 31~43%, the uniform elongation is 8.3~9.8%, and the work hardening rate n value is 0.106~0.123.

[0040] like Figure 1 , is a metallographic diagram of the bimodal high strain marine pipeline of the present invention. It can be seen from the figure that the structure consists of a bimodal structure of ultrafine ferrite and fine ferrite and a granular bainite structure.

[0041] like Figure 2 , which is a transmission image of the MA island of the bimodal structure high strain marine pipeline of the present invention. It can be seen from the figure that a typical MA island structure exists between the ferrite grains and the bainite grains.

[0042] like Figure 3 , which is a longitudinal tensile stress-strain curve of the bimodal high-strain marine pipeline pipe of the present invention. It can be seen from the figure that the longitudinal yield strength of the high-strain marine pipeline pipe is 536MPa, the tensile strength is 668MPa, and the uniform elongation is 9.8%.

Claims

1. A method for preparing a line pipe, characterized in that: The specific steps include: The raw materials are subjected to oxygen-blown converter smelting, Ca treatment, external refining and vacuum degassing, and continuously cast into slabs, which are heated to 1200°C, kept warm for 8 minutes, and rough rolled at 1050°C, rolled in two passes, with a reduction rate of 51%, then cooled to 830°C and rolled in two passes, with a reduction rate of 72%, a rolling end temperature of 750°C, a relaxation time of 80s, a water cooling temperature of 650°C, cooled to 250°C, a cooling rate of 20°C to 30°C / s, and then tempered at 520°C at a medium and low temperature for 20 minutes to form a hot-rolled steel plate with a thickness of 29.6mm; the steel plate is then formed by JCOE, and multi-pass straight seam submerged arc welding is adopted, and the welding material is a fine-grained acicular ferrite low-oxygen content material containing Ti-B, and then expanded by 0.6 to 0.8% to form a straight seam submerged arc welded line pipe; The raw materials include C: 0.05%; Mn: 1.69%; Si: 0.21%; P：0.0059％； S: 0.0026%; Al: 0.023%; N: 0.0038%; Nb: 0.065%; Ti: 0.015%; Mo: 0.17%; Ni: 0.23%; Cu: 0.014%; the balance is Fe and unavoidable impurities; carbon equivalent 0.17%; The thickness of the pipeline pipe is 29.6 mm; the pipe diameter is 1016 mm; the transverse yield strength of the pipe body is 555-598 MPa, the tensile strength is 684-690 MPa, the total elongation is 27-35%, the Charpy impact toughness at -20°C reaches 285-293 J, the DWTT shear area at -10°C is 85-92%, the hardness is 215-236 HV10, the longitudinal yield strength of the pipe body is 536-550 MPa, the tensile strength is 663-674 MPa, the total elongation is 29-42%, the uniform elongation is 7.2-9.3%, and the work hardening rate n value is 0.101-0.

113.

2. A method for preparing a line pipe, characterized in that: The specific steps include: The raw materials are subjected to oxygen-blown converter smelting, Ca treatment, external refining and vacuum degassing, and continuously cast into slabs, heated to 1200°C, kept warm for 10 minutes, rough rolled at 1100°C, rolled in two passes, with a reduction rate of 60%, then cooled to 810°C and rolled in two passes, with a reduction rate of 65%, a rolling end temperature of 730°C, a relaxation time of 100s, a water cooling temperature of 620°C, cooled to 150°C, a cooling rate of 20°C to 30°C / s, and then tempered at 550°C at a medium and low temperature for 15 minutes to form a hot-rolled steel plate with a thickness of 31.8mm; the steel plate is then formed by JCOE, and multi-pass straight seam submerged arc welding is adopted, and the welding material is a fine-grained acicular ferrite low-oxygen content material containing Ti-B, and then expanded by 0.6 to 0.9% to form a straight seam submerged arc welded line pipe; The raw materials include C: 0.06%; Mn: 1.62%; Si: 0.22%; P：0.009％； S: 0.002%; Al: 0.028; N：0.003％； V：0.04％； Ti: 0.014%; Mo: 0.099%; Ni: 0.11%; Cr: 0.022%; the balance is Fe and unavoidable impurities; carbon equivalent 0.17%; The thickness of the pipeline is 31.8 mm; the diameter is 559 mm; the transverse yield strength of the pipe body is 549-580 MPa, the tensile strength is 685-692 MPa, the total elongation is 28-37%, the Charpy impact toughness at -20°C reaches 219-248 J, the DWTT shear area at -10°C is 87-93%, and the hardness is 206-233 HV 10 The longitudinal yield strength of the pipe body is 538~553MPa, the tensile strength is 671~680MPa, the total elongation is 30~41%, the uniform elongation is 9.8~11.3%, and the work hardening rate n value is 0.103~1.

126.

3. A method for preparing a line pipe, characterized in that: The specific steps include: The raw materials are subjected to oxygen-blown converter smelting, Ca treatment, external refining and vacuum degassing, and continuously cast into slabs, which are heated to 1180°C, kept warm for 15 minutes, and rough rolled at 1120°C, two passes of rolling, with a reduction rate of 60%, and then cooled to 850°C and rolled, three passes of rolling, with a reduction rate of 75%, a rolling end temperature of 700°C, a relaxation time of 150s, a water cooling temperature of 640°C, cooled to 200°C, a cooling rate of 35°C / s, and then subjected to low-temperature tempering at 450°C for 30 minutes to form a hot-rolled steel plate with a thickness of 24.1 mm; the steel plate is then formed by UOE, and multi-pass straight seam submerged arc welding is adopted, and the welding material is a fine-grained acicular ferrite low-oxygen content material containing Ti-B, and then expanded by 0.8-1.2% to form a straight seam submerged arc welded line pipe; The raw materials include C: 0.05%; Mn: 1.67%; Si: 0.20%; P：0.008％； S：0.0024％； Al：0.019％； N: 0.003%; Nb: 0.055%; Ti: 0.015%; Mo: 0.14%; Ni: 0.15%; Cu: 0.022%; Cr: 0.2%; B: 0.0002%, the balance is Fe and unavoidable impurities; carbon equivalent 0.17%; The thickness of the pipeline is 24.1 mm; the diameter is 610 mm; the transverse yield strength of the pipe body is 529-541 MPa, the tensile strength is 666-671 MPa, the total elongation is 26-38%, the Charpy impact toughness at -20°C reaches 243-295 J, the DWTT shear area at -20°C is 85-92%, and the hardness is 202-229 HV 10 The longitudinal yield strength of the pipe body is 536~546MPa, the tensile strength is 663~668MPa, the total elongation is 31~43%, the uniform elongation is 8.3~9.8%, and the work hardening rate n value is 0.106~0.123.

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