High-crack-arrest-toughness carbon-dioxide-corrosion-resistant pipeline steel and manufacturing method thereof

Abstract

The invention relates to manufacturing of a pipeline steel hot-rolled coil plate for a longitudinal welded pipe, in particular to high-crack-arrest-toughness carbon dioxide corrosion-resistant pipeline steel and a manufacturing method thereof. The steel comprises the following chemical components: C, Si, Mn, less than or equal to 0.010% of P, less than or equal to 0.002% of S, less than or equal to 0.008% of Mo, Nb, Ti, Al, Co, less than or equal to 0.008% of N and the balance of Fe and inevitable elements. According to the steel plate, the transverse yield strength is 490 MPa or above, the tensile strength is 600 MPa or above, the yield ratio is smaller than or equal to 0.86, the elongation A50 mm is larger than or equal to 37%, the impact energy at the temperature of-40 DEG C is 350 J or above, the drop weight at the temperature of-20 DEG C is larger than or equal to 95%, and the average corrosion rate in a carbon dioxide environment is smaller than 0.08 mm / a; the longitudinal yield strength is 485MPa or above, the tensile strength is 590MPa or above, the yield ratio is smaller than or equal to 0.85, and the elongation A50mm is larger than or equal to 41%.

Description

Technical Field

[0001] The present invention relates to the manufacture of a hot-rolled coil of pipeline steel for a straight seam welded pipe, and in particular to a pipeline steel with high crack arrest toughness and resistance to carbon dioxide corrosion and a manufacturing method thereof. Background Art

[0002] CCUS (carbon capture, utilization, and storage) is a key technology for addressing global climate change. CO2 transportation is a key link in the CCUS industry chain, connecting CO2 capture with storage and utilization. The efficiency and cost of CO2 transportation directly impact the overall scale and economic benefits of CCUS.

[0003] The critical pressure of pure carbon dioxide is 7.38 MPa, and its critical temperature is 31.1°C. Supercritical transportation refers to a form of transportation in which the transportation pressure is higher than the critical pressure. It has the characteristics of high density and low viscosity. When the entire pipeline transportation process is in a supercritical state, transportation is most efficient and wear is low. However, when free water and impurity gases are present in the supercritical carbon dioxide pipeline, it is extremely corrosive. Existing API carbon steel system pipelines used to transport natural gas are subject to occasional corrosion, which may cause leakage and failure. Pipes are the foundation for ensuring the safe transportation of pipelines. Pipe costs are relatively high in the total investment in pipeline construction. Due to factors such as corrosion and third-party damage, the pipe wall may become thinner or fail, and in severe cases, various safety accidents will occur. Key technical requirements for supercritical pipes include: low-temperature brittleness when the temperature drops sharply to -40°C during carbon dioxide leakage; and corrosion rate in a supercritical carbon dioxide environment.

[0004] Currently, China does not have a large-capacity, long-distance X65M-class carbon dioxide transmission pipeline. The following is a brief introduction to patent documents that are relatively close to the present invention:

[0005] 1) Chinese patent document CN112941422A, a CO2 corrosion-resistant steel plate and its preparation method. The composition contains C: 0.03%-0.07%, Cr: 4.0%-6.0%, Ni: 0.15%-2.50%, Nb: 0.01%-0.06%, P ≤ 0.005%, and S ≤ 0.0050%. This invention is a method for producing CO2 corrosion-resistant steel plate, disclosed by the University of Science and Technology Beijing. The product is produced using a medium and heavy plate rolling mill, and the rolled steel plate requires a quenching and tempering heat treatment process. The Cr content of this invention is relatively high, classifying it as stainless steel, and cannot be produced through conventional smelting or continuous casting. Furthermore, the excessively high Cr content makes the steel plate unable to be subsequently welded to a straight seam. Furthermore, the steel plate has low impact toughness, failing to meet the crack arrest requirements at -40°C during CO2 leakage.

[0006] 2) Chinese patent CN106498279A discloses a low-Cr, economical X65 pipeline steel resistant to CO2 corrosion and its production method. The steel contains 0.04%-0.05% C, 0.18%-0.22% Si, 0.50%-0.60% Mn, 0.1%-0.2% Cr, 0.10%-0.15% Mo, 0.035%-0.050% Nb, 0.020%-0.030% V, 0.010%-0.020% Ti, with P ≤ 0.01% and S ≤ 0.0030%. This invention, disclosed by Wuhan Iron and Steel Co., Ltd., describes a production method for X65 hot-rolled coil resistant to CO2 corrosion. The Mn content of this invention is relatively low, and the hardenability of the subsequent straight seam welding process is poor, which cannot guarantee the low-temperature toughness of the weld and heat-affected zone at -40°C. At the same time, the low-temperature toughness of the base material at -20°C is average, and it cannot meet the crack arrest requirement at -40°C when carbon dioxide leaks. Summary of the Invention

[0007] In response to the technical problems that the currently produced 485MPa grade pipeline steel coils do not have carbon dioxide corrosion resistance, cannot adapt to the service environment of supercritical carbon dioxide transportation, and have poor safety, the present invention provides a high crack arrest toughness carbon dioxide corrosion-resistant pipeline steel and a manufacturing method thereof, the purpose of which is to produce a hot-rolled coil for supercritical carbon dioxide transportation, with a transverse yield strength of not less than 490MPa, a tensile strength of not less than 600MPa, a longitudinal yield strength of not less than 485MPa, a tensile strength of not less than 590MPa, an impact energy of not less than 350J at -40°C, and an average corrosion rate of less than 0.08mm / a in a 14.5MPa supercritical carbon dioxide environment.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A high crack arrest toughness and carbon dioxide corrosion-resistant pipeline steel, wherein the chemical composition of the steel is as follows by weight: C: 0.02%-0.05%, Si: 0.10%-0.35%, Mn: 1.50%-1.70%, P≤0.010%, S≤0.002%, Mo: 0.60%-0.90%, Nb: 0.01%-0.03%, Ti: 0.01%-0.03%, Al: 0.10%-0.20%, Co: 0.05%-0.15%, N≤0.008%, and the remainder is Fe and unavoidable elements.

[0010] Compared with the existing technology, the present invention adopts a low-carbon, medium-manganese, molybdenum-containing alloy design to ensure the low-temperature toughness of the weld and fully refined grains; an appropriate amount of molybdenum element reduces the anisotropy of the transverse and longitudinal properties of the steel plate, improving the corrosion resistance and oxidation resistance of the steel; a small amount of aluminum element significantly improves the low-temperature crack arrest toughness and the material's resistance to carbon dioxide corrosion, and has higher safety in pipeline projects.

[0011] C: A carbide-forming element, it is the most effective element for ensuring strength. It can improve hardenability and ensure material strength and hardness. Its effect is second only to phosphorus and is stronger than elements such as manganese, nickel, chromium, tungsten, molybdenum, and vanadium. Carbon significantly increases strength through solid solution strengthening and phase transformation strengthening. Only with sufficient carbon can sufficient acicular ferrite be formed. If the carbon content is too low, the material's strength and hardness cannot be guaranteed; however, if the content is too high, it can easily cause center segregation in the steel plate, which is detrimental to the steel's corrosion resistance and crack arrest toughness, and will affect the product's weldability. The optimal range is 0.02% to 0.05%.

[0012] Silicon dissolves in ferrite and austenite, providing a degree of solid solution strengthening, significantly increasing the hardness and strength of steel. It also promotes ferrite grain coarsening and reduces the anisotropy of the steel's transverse and longitudinal properties. When steel containing silicon is heated in an oxidizing atmosphere, a thin SiO2 film forms on the surface, protecting the steel from further oxidation. Silicon, combined with elements such as molybdenum and chromium, helps improve the steel's corrosion and oxidation resistance. Silicon exists in steel as silicide, effectively blocking the entry of oxidants and reducing the occurrence of corrosion. However, increasing silicon content can reduce the steel's weldability and significantly reduce its ductility and toughness. The optimal range is 0.10% to 0.35%.

[0013] Mn: Manganese has a solid solution strengthening effect. The solid solution formed by manganese and iron increases the hardness and strength of ferrite and austenite in steel. It is also a carbide-forming element, entering cementite to replace some iron atoms. By lowering the critical transition temperature in steel, manganese also increases austenite stability and significantly enhances the hardenability of the steel, effectively ensuring its strength. Manganese compensates for the strength loss caused by carbon reduction, making it the most important and economical strengthening element. Manganese shifts the C curve to the right, promoting bainite transformation and favoring the formation of acicular ferrite, significantly increasing strength with minimal loss of toughness. A certain amount of manganese ensures weld strength during straight seam welding and low-temperature impact toughness at -40°C. However, excessive manganese content can increase the tendency for central segregation in continuous casting ingots, leading to increased banding in the steel plate, increased brittleness, and decreased ductility. The optimal range is 1.50% to 1.70%.

[0014] P, S, N: are inevitable impurity elements in steel. The lower the better, but too low a requirement will increase production costs. In the present invention, P≤0.01%, S≤0.002%, and N≤0.008%.

[0015] Mo: Molybdenum increases the strength of the base material by improving the hardenability of steel. Mo is an element that expands the y-phase region and can lower the y→a phase transformation temperature of steel. As the Mo content increases, the phase transformation temperature gradually decreases, effectively promoting bainite transformation and playing a role in phase transformation strengthening, resulting in a finer lath bainite structure. Mo can refine the grain size of steel. The effect of molybdenum is stronger than that of tungsten, significantly improving the hardenability and heat resistance of steel, preventing temper brittleness, and increasing the tensile strength and toughness of steel. Experiments have found that when the molybdenum content is less than 0.3%, the corrosion resistance of the steel remains basically unchanged. When the molybdenum content is between 0.3% and 0.9%, the corrosion resistance of the steel is improved to a certain extent. When the molybdenum content exceeds 0.9%, the corrosion resistance of the steel decreases. At the same time, Mo works in conjunction with Al (amounts exceeding 0.10%), with the combined content exceeding 0.70%. The Al compound further refines the lath bainite formed by the Mo element and forms a layer of Al oxide on the bainite surface, resulting in a higher resistance to carbon dioxide corrosion than either element alone. However, excessive Mo content increases alloy cost and compromises plasticity and toughness. The optimal range is 0.60% to 0.90%.

[0016] Nb: Niobium is a key element in low-carbon microalloyed steel. It significantly increases the austenite recrystallization temperature of steel, expands the unrecrystallized zone, and inhibits austenite grain growth, exhibiting significant grain refinement and precipitation strengthening effects. Niobium partially dissolves into solid solution, exerting a solid solution strengthening effect. When dissolved in austenite, it significantly improves the hardenability of steel. However, when present as carbide and oxide particles, it refines the grain size. It increases the tempering stability of steel and has a secondary hardening effect. Trace amounts of niobium can increase the strength of steel without affecting its plasticity or toughness. Niobium can improve yield strength and impact toughness and lower the brittle transition temperature. However, excessive niobium content increases alloy cost and adversely affects the toughness of the weld heat-affected zone. The optimal range is 0.01% to 0.03%.

[0017] Titanium: Titanium is a strong nitrogen-binding element. Adding approximately 0.015% Ti forms high-temperature stable, fine TiN precipitates during slab continuous casting. These fine TiN precipitates effectively prevent austenite grain growth during heating and significantly improve the toughness of the heat-affected zone during steel welding. Small amounts of precipitated TiC produce a strong precipitation strengthening effect, preventing significant grain growth during subsequent normalizing heat treatment, thereby ensuring uniform performance in the steel pipe. However, excessive TiC content has limited effectiveness and can easily form large inclusions. The optimal range is 0.01% to 0.03%.

[0018] Al: Aluminum is a commonly used deoxidizer. The addition of aluminum can significantly improve the strength of steel. By reacting with carbon and other elements in the steel, the generated AlN helps to refine the grain structure, thereby achieving a reinforcement effect and improving strength and low-temperature impact toughness. Aluminum improves toughness by reducing the sensitivity of steel to cracks, especially in low-temperature environments, and can significantly reduce the toughness transition temperature. The solid solution strengthening effect of aluminum is significant, which strongly limits the expansion of the austenite phase region, which is beneficial to improving strength. Adding aluminum to steel can also improve the corrosion resistance of steel, especially when used in combination with molybdenum, the effect is better. The Al content of the present invention is 0.10% to 0.20%.

[0019] Cobalt: As a powerful solid-solution strengthening element, cobalt forms a solid solution with the iron in steel, enhancing the steel's hardness and strength. It also refines the grain size, increasing the steel's strength and toughness, thereby improving its performance. Cobalt reduces the hardenability of steel and shifts the austenite isothermal transformation curve (C-curve) to the left. Its addition alone reduces overall mechanical properties, but its co-addition with molybdenum strengthens ferrite, increasing hardness and strength. Cobalt forms a stable alloy phase with the iron in steel, forming a dense oxide film on the steel surface and improving its resistance to carbon dioxide corrosion. Excessive levels significantly reduce the steel's hardenability and negatively impact its strength. The ideal range is 0.05% to 0.15%.

[0020] The transverse yield strength of the steel plate of the present invention is above 490 MPa, the tensile strength is above 600 MPa, the yield strength ratio is ≤ 0.86, and the elongation A 50mm ≥37%, -40℃ impact energy 350J or more, -20℃ drop hammer ≥95%, according to ASTM-G111 corrosion standard, using NACE-A solution, test temperature 60℃, CO2 pressure 2.0MPa, stirring rate 2m / s, test time 72h, average corrosion rate in carbon dioxide environment <0.08mm / a, higher than the supercritical carbon dioxide transport corrosion standard requirement of ≤0.15mm / a; longitudinal yield strength is above 485MPa, tensile strength is above 590MPa, yield strength ratio ≤0.85, elongation A 50mm ≥41%.

[0021] The steel plate structure is a mixed structure of acicular ferrite and MA components, and the volume ratio of MA components is less than 1%.

[0022] A method for manufacturing high crack arrest toughness carbon dioxide corrosion resistant pipeline steel comprises the following steps:

[0023] 1) The continuous casting slab is heated in a furnace to 1150-1200°C and held for 150-260 minutes. Thermomechanical rolling is then performed. This temperature range and holding time allow for full solid solution of alloys such as Mo and Al, while also facilitating the precipitation of Ti and refining the austenite grain size, which contributes to improved yield and tensile strength.

[0024] 2) The rough rolling and finishing temperatures are 980-1020°C, with a pressure ratio greater than 60%. This temperature helps prevent austenite grain growth, refine grains, and improve strength. The finishing rolling start temperature is 900-950°C, and the final rolling temperature is 750-800°C. This temperature range adequately refines and elongates austenite grains, avoids mixed grains, and ensures excellent low-temperature impact and drop hammer properties. A high reduction ratio can generate a large number of dislocations and twins, which play a dislocation strengthening role and significantly improve yield strength and tensile strength.

[0025] 3) After rolling, laminar water cooling is used, with a coiling temperature of 450-490°C and a cooling rate of 14-19°C / s. This coiling temperature and cooling rate are conducive to obtaining a uniformly sized acicular ferrite structure with good low-temperature crack arrest toughness.

[0026] During the molten steel smelting process, the LF furnace adopts shallow desulfurization and calcium treatment to control the morphology of inclusions and improve the ductility, toughness and cold bending properties of the steel.

[0027] Slab continuous casting uses electromagnetic stirring or dynamic soft reduction.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1) The present invention adopts a low-carbon, medium-manganese, molybdenum-containing alloy design to ensure the low-temperature toughness of the weld and fully refine the grains.

[0030] 2) An appropriate amount of molybdenum reduces the anisotropy of the transverse and longitudinal properties of the steel plate, and improves the corrosion resistance and oxidation resistance of the steel.

[0031] 3) A small amount of aluminum significantly improves the low-temperature crack arrest toughness and the material's resistance to carbon dioxide corrosion, providing higher safety in pipeline projects. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the specific implementation methods of the present invention are further described below in conjunction with examples. The following examples are used to specifically illustrate the contents of the present invention. These examples are only general descriptions of the contents of the present invention and do not limit the contents of the present invention.

[0033] The present invention provides a hot-rolled coil for pipeline steel with high crack arrest toughness and resistance to carbon dioxide corrosion. The production process includes molten steel smelting, continuous casting billet heating, rolling, cooling, and coiling. The chemical compositions of Examples 1-8 are shown in Table 1, the heating, rolling, and cooling process parameters are shown in Table 2, and the mechanical property test results are shown in Table 3.

[0034] Table 1 Chemical composition of the examples wt%

[0035]

[0036] Table 2 Heating, rolling and cooling processes

[0037]

[0038] Table 3 Mechanical properties and tissue proportions

[0039]

[0040] As can be seen from Tables 1-3, the composition design and rolling and coiling processes of the present invention are used to produce high crack arrest toughness hot-rolled coils for 485 MPa grade supercritical carbon dioxide conveying straight seam welded pipes.

[0041] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A high crack arrest toughness carbon dioxide corrosion resistant pipeline steel, characterized in that: The chemical composition of the steel by weight percentage is: C: 0.02%~0.05%, Si: 0.10%~0.35%, Mn: 1.50%~1.70%, P≤0.010%, S≤0.002%, Mo: 0.60%~0.90%, Nb: 0.01%~0.03%, Ti: 0.01%~0.03%, Al: 0.10%~0.20%, Co: 0.05%~0.15%, N≤0.008%, and the rest are Fe and unavoidable elements.

2. The high crack arrest toughness carbon dioxide corrosion resistant pipeline steel according to claim 1, characterized in that: The transverse yield strength of the steel plate is above 490MPa, the tensile strength is above 600MPa, the yield strength ratio is ≤0.86, and the elongation A 50mm ≥37%, -40℃ impact energy 350J or more, -20℃ drop hammer ≥95%, according to ASTM-G111 corrosion standard, average corrosion rate in carbon dioxide environment <0.08mm / a; longitudinal yield strength 485MPa or more, tensile strength 590MPa or more, yield strength ratio ≤0.85, elongation A 50mm ≥41%.

3. The high crack arrest toughness carbon dioxide corrosion resistant pipeline steel according to claim 1, characterized in that: The steel plate structure is a mixed structure of acicular ferrite and MA, and the volume ratio of MA component is less than 1%.

4. A method for manufacturing a high crack arrest toughness carbon dioxide corrosion resistant pipeline steel according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: 1) The continuous casting slab is heated to 1150-1200℃ in a heating furnace and kept warm for 150-260min; 2) The rough rolling and finishing temperature is 980-1020℃, and the reduction rate is greater than 60%; the finishing rolling temperature is 900-950℃, and the finishing temperature is 750-800℃; 3) After rolling, laminar water cooling is adopted, the coiling temperature is 450-490℃, and the cooling rate is 14-19℃ / s.

5. The method for manufacturing a high crack arrest toughness carbon dioxide corrosion resistant pipeline steel according to claim 4, characterized in that: During the molten steel smelting process, the LF furnace adopts shallow desulfurization treatment and calcium treatment.

6. The method for manufacturing a high crack arrest toughness carbon dioxide corrosion resistant pipeline steel according to claim 4, characterized in that: Slab continuous casting uses electromagnetic stirring or dynamic soft reduction.

Images