Large-deformation-resistant pipeline steel hot-rolled coiled plate and manufacturing method thereof

Abstract

The invention relates to the technical field of hot-rolled steel strip production, in particular to a large-deformation-resistant pipeline steel hot-rolled coiled plate and a manufacturing method thereof. The large-deformation-resistant pipeline steel hot-rolled coil plate comprises the following chemical components in percentage by mass: 0.04%-0.06% of C, 0.20%-0.30% of Si, 1.45%-1.55% of Mn, less than or equal to 0.015% of P, less than or equal to 0.002% of S, 0.02%-0.03% of Nb, less than or equal to 0.0005% of B, 0.24%-0.35% of Cr, 0.01%-0.02% of Ti, 0.02%-0.05% of Al and the balance of Fe and inevitable impurity elements. On the basis of component design, a unique three-section type continuous cooling and low-temperature coiling process is adopted on the basis of the characteristics of a hot continuous rolling production line, the large-deformation-resistant pipeline steel hot-rolled coil plate is produced, and on the basis that the requirement for high toughness is met, the low yield ratio and the high uniform deformation elongation are achieved at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of hot-rolled strip steel production, and in particular to a hot-rolled coil of pipeline steel resistant to large deformation and a manufacturing method thereof. Background Art

[0002] With the continuous development of oil and gas resources, new resources are gradually extending to areas with harsh geological conditions such as frozen soil, oceans, and seismic zones. The complex and changeable geological disaster environment will seriously affect the safe operation of pipelines. In order to ensure the safety of pipelines in special service environments such as earthquake fault zones, in addition to requiring pipelines to have large wall thickness, high strength, and high toughness, they are also required to have excellent resistance to large deformation, that is, they can withstand greater deformation than conventional pipeline steels when subjected to tensile, compressive, and bending loads in harsh environments without breaking. This puts forward the demand for the development of pipeline steel based on strain design. Large deformation-resistant pipeline steel should have characteristics such as dual-phase structure, low yield strength ratio, high uniform deformation elongation, and dome-shaped stress-strain curve, so that it has good plasticity and adaptability in large deformation areas. In the process of pipe making, the strength of steel coils, especially the yield strength, will increase due to work hardening, which has a great influence on the yield strength ratio and uniform deformation elongation. In the subsequent anti-corrosion process of the steel pipe, due to the effect of temperature, the strength may also increase and the plastic toughness may decrease, that is, the aging phenomenon will occur. Therefore, pipeline steel development based on strain design is one of the most challenging areas in pipeline steel development.

[0003] Patent CN102534377A announced "X70 grade large deformation resistant pipeline steel plate with excellent toughness and its preparation method". The composition design adopted by this patent adds precious alloy elements such as Mo and Ni, which is beneficial to the organizational transformation and performance improvement, but the alloy cost is relatively high and it is produced based on medium and thick plate production lines.

[0004] Patent CN101962733A announced "a low-cost, high-strength and tough X80 large deformation resistant pipeline steel and production method". The alloy design uses Mo 0.10% to 0.30%. The alloy cost is relatively high, the ferrite content in the structure is only 20%-40%, and the Charpy impact toughness at -20℃ is low, only about 250J.

[0005] Patent CN109234623A announced "A X80M deep-sea strain-resistant pipeline steel plate and rolling process". The patented composition design uses a high content of Ni and Mo elements, which has a high alloy cost. At the same time, the final rolling temperature is low and the roll speed is set to 1.0m / s. The process is not suitable for hot rolling production lines and has low production efficiency.

[0006] Patent CN103627980A announced "Low-temperature, large-wall thickness X80HD large deformation pipeline steel and its production method". This patent adopts a composite component design of Cu, Ni, and Mo, and the alloy cost is high. At the same time, it is based on the production line of medium and thick plates and adopts a relaxation phase change control process. The steel plate needs to be kept at temperature for 30-100s, and the production efficiency is low.

[0007] At present, large deformation resistant pipeline steel based on strain design has been developed and applied, but it is limited to medium and thick plate production lines, and there are still problems such as high production cost and low production efficiency. For the production of large deformation resistant pipeline steel based on hot rolling production lines, no research and development work has been carried out at home and abroad. Summary of the invention

[0008] In view of the deficiencies in the prior art, the technical problem solved by the present invention is to provide a hot-rolled coil of pipeline steel resistant to large deformation and a manufacturing method thereof. The invention adopts low-cost component design and reasonable element ratio, designs a unique three-stage continuous cooling and low-temperature coiling process based on the hot rolling production line and precisely controls it, and develops a hot-rolled coil of pipeline steel resistant to large deformation on the hot rolling production line. The hot-rolled coil has an ultra-low yield strength ratio and high uniform deformation elongation. After the coil is rolled and the UOE process is used to make the pipe, the performance fully meets the acceptance requirements of the straight seam submerged arc welded pipe for service in the earthquake fault zone. The invention not only has low production cost and high production efficiency but also has stable and excellent performance, but can also well meet the construction needs of oil and natural gas transmission pipelines in special and complex service environments such as earthquake fault zones.

[0009] In a first aspect, the present invention provides a hot-rolled coil of pipeline steel resistant to large deformation, wherein the chemical composition and mass percentage of the hot-rolled coil of pipeline steel resistant to large deformation are: C 0.04%-0.06%, Si 0.20%-0.30%, Mn 1.45%-1.55%, P ≤0.015%, S ≤0.002%, Nb 0.02%-0.03%, B ≤0.0005%, Cr 0.24%-0.35%, Ti 0.01%-0.02%, Al0.02%-0.05%, and the balance is Fe and unavoidable impurity elements; The thickness of the hot-rolled coil of the large deformation resistant pipeline steel is 12-20mm, and the microstructure is a dual-phase structure of ferrite + bainite, with ferrite accounting for 65%-75%, bainite accounting for 25%-35%, and the grain size is 11.0-11.5; Transverse tensile properties meet: yield strength Rt 0.5 460-505MPa, tensile strength 580-640MPa, elongation ≥40%, yield strength ratio ≤0.80; Longitudinal tensile properties meet: yield strength Rt 0.5 420-460MPa, tensile strength 580-630MPa, elongation ≥40%, yield strength ratio ≤0.75, uniform deformation elongation ≥12%; After aging at 200℃ for 5 minutes, the longitudinal tensile properties meet the following requirements: yield strength Rt 0.5 425-475MPa, tensile strength 585-635MPa, elongation ≥40%, yield strength ratio ≤0.76, uniform deformation elongation ≥11%; -30℃ lateral impact energy ≥300J, -20℃ drop hammer shear area ≥95%.

[0010] In a second aspect, the present invention provides a method for manufacturing hot-rolled coil of pipeline steel resistant to large deformation, comprising adopting a three-stage continuous cooling mode: front ultra-fast cooling low-pressure sparse water cooling + air cooling + rear ultra-fast cooling high-pressure dense water cooling.

[0011] Furthermore, the cooling rate of the front ultra-fast cooling low-pressure sparse water cooling is 10-20℃ / s, cooled to the intermediate temperature MT1 of 670-730℃, air-cooled for 20-25s, and then the rear ultra-fast cooling high-pressure intensive cooling is carried out at a cooling rate of 25-40℃ / s. After cooling, low-temperature coiling is carried out, and the coiling temperature CT is 250-330℃.

[0012] Furthermore, the pressure of the front ultra-fast cooling equipment is 0.30-0.40MPa, and the pressure of the rear ultra-fast cooling equipment is 0.80-1.00MPa.

[0013] Furthermore, the ingot is heated and rolled before cooling.

[0014] Furthermore, when the ingot is heated, the thickness of the ingot is 230 mm, the heating period of the ingot in the furnace is 180-260 min, the soaking period is 30-60 min, and the furnace discharge temperature is 1180-1220°C.

[0015] Furthermore, during rolling, the rough rolling outlet temperature R2DT is 970-1020°C, the rolling intermediate billet thickness is 60-65mm, the finishing rolling inlet temperature FET is 940-980°C, the finishing rolling final rolling temperature FDT is 790-830°C, and the rolling speed is 2.0-4.0m / s.

[0016] Furthermore, the first 2 meters of the strip are not water-cooled or weakly water-cooled, and the temperature is controlled at 500-600℃ to ensure the safety of coiling.

[0017] The beneficial effects of the present invention are: The large deformation resistant pipeline steel hot-rolled coil provided by the present invention adopts an optimized composition design, which is not only conducive to the stable control of product structure and performance during the production process, but also has a relatively economical alloy cost. Low C content is adopted, and the content of P and S elements is controlled in a low range to ensure the low temperature toughness and welding performance of thick specification pipeline steel; an appropriate amount of Mn is adopted, and appropriate Nb, Ti microalloying elements and a certain amount of Cr elements are combined to exert their solid solution strengthening, fine grain strengthening and phase transformation strengthening effects to ensure that the product has a high strength and toughness match, a low yield strength ratio and a high uniform deformation elongation; based on the analysis of the solid solution and precipitation temperature of the precipitated phase under the above-mentioned composition system and the influence on the austenite recrystallization temperature, a reasonable heating and rolling process is formulated to achieve uniform refinement control of austenite grains; especially based on the influence of this component on the phase transformation temperature, combined with the characteristics and production rhythm of the hot rolling production line, a unique three-stage continuous cooling process is formulated, firstly, through the medium-speed water cooling of the pre-rolling ultra-fast cooling low-pressure sparse water cooling to prevent phase transformation in the high temperature section, and then by setting the appropriate air cooling time, a ferrite structure of appropriate proportion and size is obtained, and finally, post-ultra-fast cooling high-pressure intensive cooling is performed to a lower temperature to obtain a bainite structure of appropriate proportion. Through the combined control of ingredients and processes, hot-rolled coils of pipeline steel with excellent performance are finally obtained. On the basis of high strength and toughness, they have low yield strength ratio and high uniform deformation elongation. After pipe making, the performance can also meet the service requirements of pipelines in earthquake fault zones. The present invention has achieved the successful development of hot-rolled coils of pipeline steel with high deformation resistance, which not only promotes the development of high-performance hot-rolled strip steel, but also creates conditions for expanding user groups and engineering application scenarios. It has created a precedent for the production of hot-rolled coils of pipeline steel with high deformation resistance based on hot continuous rolling production lines, filling the gap in the supply of hot-rolled coils of pipeline steel with high deformation resistance in the industry, and has good economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is the microstructure of the hot-rolled coil of large deformation resistant pipeline steel in Example 1.

[0020] Figure 2 This is the microstructure of the hot-rolled coil of large deformation resistant pipeline steel of Example 3.

[0021] Figure 3 This is the microstructure of the hot-rolled coil of large deformation resistant pipeline steel in Example 1.

[0022] Figure 4This is the microstructure of the hot-rolled coil of large deformation resistant pipeline steel in Example 2. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0024] The embodiment of the present invention adopts the following steps: molten iron pretreatment → converter steelmaking → LF furnace refining → RH furnace refining → continuous casting → heating in the ingot heating furnace → R1 rough rolling → E2R2 rough rolling → finishing rolling 7-stand continuous rolling → ultra-fast cooling low-pressure sparse water cooling → air cooling → post-ultra-fast cooling high-pressure intensive water cooling → coiling.

[0025] The chemical composition and mass percentage of the steel are C 0.04%-0.06%, Si 0.21%-0.24%, Mn1.49%-1.51%, P ≤0.014%, S ≤0.0012%, Nb 0.02%-0.03%, Cr 0.24%-0.29%, Ti 0.01%-0.02%, Al 0.027%-0.037%, and the balance is Fe and unavoidable impurity elements; Refining adopts LF+RH double refining, continuous casting adopts full-process argon protection casting, and the continuous casting billet thickness is 230mm. The billet is then heated, the billet heating section in the furnace time is 192-243min, the soaking section time is 34-51min, and the furnace temperature is 1196-1212℃, to ensure that the billet is fully austenitized and the micro-alloying elements are completely dissolved; after being taken out of the furnace, rough rolling is carried out in the austenite recrystallization zone, the rough rolling outlet temperature R2DT is 979-1008℃, the rolling intermediate billet thickness is 60-65mm, and after rough rolling, fine rolling is carried out, the fine rolling inlet temperature FET is 943-977℃, and it is continuously rolled through 7 stands, the rolling speed is 2.1-3.9m / s, the fine rolling final rolling temperature FDT is 798-823℃, and the thickness of the rolled product is 12-20mm.

[0026] After rolling, a three-stage continuous cooling mode is adopted. First, the front ultra-fast cooling low-pressure sparse water cooling is carried out. The pressure of the front ultra-fast cooling equipment is 0.30-0.40MPa, the cooling rate is 10-19℃ / s, and the intermediate temperature MT1 is 693-718℃, then air cooling is carried out for 21-24s, and finally the rear ultra-fast cooling high-pressure intensive water cooling is carried out. The pressure of the rear ultra-fast cooling equipment is 0.80-1.0MPa, the cooling rate is 26-33℃ / s, and the coiling is cooled to 253-321℃, that is, the coiling temperature CT is 253-321℃; Among them, when the front ultra-fast cooling low-pressure sparse water cooling, air cooling and rear ultra-fast cooling high-pressure intensive water cooling are carried out, the head 2m of the steel coil is not water-cooled and the temperature is controlled at 500-600℃ to ensure the safety of coiling. After coiling, the steel coil is air-cooled to room temperature.

[0027] The microstructure of the hot-rolled coil of large deformation resistant pipeline steel is a dual-phase structure of ferrite + bainite, with ferrite accounting for 67%-73%, bainite accounting for 27%-33%, and grain size 11.0-11.5.

[0028] Transverse tensile properties meet: yield strength Rt 0.5 466-488MPa, tensile strength 597-630MPa, elongation ≥40.5%, yield strength ratio ≤0.80; longitudinal tensile properties meet: yield strength Rt 0.5 425-447MPa, tensile strength 588-609MPa, elongation ≥43%, yield strength ratio ≤0.73, uniform deformation elongation ≥12.97%; after aging at 200℃ for 5min, the longitudinal tensile properties meet the following requirements: yield strength Rt 0.5 422-438MPa, tensile strength 590-617MPa, elongation ≥44%, yield strength ratio ≤0.74, uniform deformation elongation ≥13.72%; -30℃ transverse impact energy ≥303J, -20℃ drop hammer shear area 100%.

[0029] The chemical composition designs of the embodiments of the present invention and the comparative examples are shown in Table 1, the main hot rolling process parameters of the embodiments of the present invention and the comparative examples are shown in Table 2, the mechanical property test data of the steel coils produced by the embodiments of the present invention and the comparative examples are shown in Table 3, and the metallographic test data of the steel coils produced by the embodiments of the present invention and the comparative examples are shown in Table 4. The mechanical property test data of the steel pipes (pipes made by UOE process after the coils are flattened) produced by the embodiments of the present invention and the comparative examples are shown in Table 5.

[0030] Table 1 Chemical composition of various embodiments of the present invention and comparative examples (wt%)

[0031] Table 2 Main process parameters of hot rolling of various embodiments of the present invention and comparative examples

[0032] Note: The front-end cooling rate in the table refers to the cooling rate of the front ultra-fast cooling low-pressure sparse water cooling, and the rear-end cooling rate refers to the cooling rate of the rear ultra-fast cooling high-pressure dense water cooling.

[0033] Table 3 Mechanical properties of various embodiments of the present invention and comparative examples

[0034] Note: R stands for aging treatment at 200℃ for 5 minutes.

[0035] Table 4 Metallographic structure analysis of various embodiments of the present invention and comparative examples

[0036] Table 5 Mechanical properties of pipes made from various embodiments of the present invention and comparative examples

[0037] Note: The mechanical properties of Comparative Example 2 before and after pipe making did not change much and were not ideal, so only Comparative Example 1 is listed in Table 5 for comparison.

[0038] It can be seen from the above embodiments that the hot-rolled coil of pipeline steel produced in the hot rolling production line according to the composition and process of the present invention has a typical ferrite + bainite dual-phase structure, excellent comprehensive performance, ultra-low yield ratio and high uniform deformation elongation while meeting high strength and toughness requirements, especially after pipe making, the performance can also fully meet the owner's acceptance standards for straight seam submerged arc welded pipes for service in earthquake fault zones. It not only has low production cost, high production efficiency and stable performance, but can also well meet the construction needs of oil and natural gas pipelines in special and complex service environments such as earthquake fault zones. However, due to differences in composition, process and organization, the mechanical properties of the comparative example, especially the yield ratio and uniform deformation elongation, are not ideal and difficult to meet the requirements.

[0039] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A hot-rolled coil of pipeline steel resistant to large deformation, characterized in that: The chemical composition and mass percentage of the hot-rolled coil of the large deformation resistant pipeline steel are: C 0.04%-0.06%, Si 0.20%-0.30%, Mn 1.45%-1.55%, P ≤0.015%, S ≤0.002%, Nb 0.02%-0.03%, B ≤0.0005%, Cr 0.24%-0.35%, Ti 0.01%-0.02%, Al 0.02%-0.05%, and the balance is Fe and unavoidable impurity elements; The thickness of the hot-rolled coil of the large deformation resistant pipeline steel is 12-20mm, and the microstructure is a dual-phase structure of ferrite + bainite, with ferrite accounting for 65%-75%, bainite accounting for 25%-35%, and the grain size is 11.0-11.5; Transverse tensile properties meet: yield strength Rt 0.5 460-505MPa, tensile strength 580-640MPa, elongation ≥40%, yield strength ratio ≤0.80; Longitudinal tensile properties meet: yield strength Rt 0.5 420-460MPa, tensile strength 580-630MPa, elongation ≥40%, yield strength ratio ≤0.75, uniform deformation elongation ≥12%; After aging at 200℃ for 5 minutes, the longitudinal tensile properties meet the following requirements: yield strength Rt 0.5 425-475MPa, tensile strength 585-635MPa, elongation ≥40%, yield strength ratio ≤0.76, uniform deformation elongation ≥11%; -30℃ lateral impact energy ≥300J, -20℃ drop hammer shear area ≥95%.

2. A method for manufacturing a hot-rolled coil of pipeline steel resistant to large deformation according to claim 1, characterized in that: It includes a three-stage continuous cooling mode: front ultra-fast cooling low-pressure sparse water cooling + air cooling + rear ultra-fast cooling high-pressure dense water cooling.

3. The method for manufacturing a hot-rolled coil of pipeline steel resistant to large deformation according to claim 2, characterized in that: The cooling rate of the front ultra-fast cooling low-pressure sparse water cooling is 10-20℃ / s, cooled to the intermediate temperature MT1 of 670-730℃, air cooled for 20-25s, and then the rear ultra-fast cooling high-pressure intensive cooling is carried out with a cooling rate of 25-40℃ / s. After cooling, low-temperature coiling is carried out, and the coiling temperature CT is 250-330℃.

4. The method for manufacturing a hot-rolled coil of pipeline steel resistant to large deformation according to claim 2, characterized in that: The pressure of the front ultra-fast cooling equipment is 0.30-0.40MPa, and the pressure of the rear ultra-fast cooling equipment is 0.80-1.00MPa.

5. The method for manufacturing a hot-rolled coil of pipeline steel resistant to large deformation according to claim 2, characterized in that: The ingot is heated and rolled before cooling.

6. The method for manufacturing a hot-rolled coil of pipeline steel resistant to large deformation according to claim 5, characterized in that: When the ingot is heated, the thickness of the ingot is 230 mm, the heating period in the furnace is 180-260 min, the soaking period is 30-60 min, and the furnace outlet temperature is 1180-1220°C.

7. The method for manufacturing a hot-rolled coil of pipeline steel resistant to large deformation according to claim 5, characterized in that: During rolling, the rough rolling outlet temperature R2DT is 970-1020°C, the rolling intermediate billet thickness is 60-65mm, the finishing rolling inlet temperature FET is 940-980°C, the finishing rolling final temperature FDT is 790-830°C, and the rolling speed is 2.0-4.0m / s.

8. The method for manufacturing a hot-rolled coil of pipeline steel resistant to large deformation according to claim 2, characterized in that: When performing front ultra-fast cooling low-pressure sparse water cooling, air cooling and rear ultra-fast cooling high-pressure dense water cooling, the first 2 meters of the strip are not water-cooled or weakly water-cooled, and the temperature is controlled at 500-600℃.

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