A high crack arrest toughness carbon dioxide corrosion resistant pipeline steel and a method of manufacturing the same

Abstract

The present application relates to a kind of pipeline steel hot-rolled coil for straight seam welded pipe, especially to a kind of high crack arrest toughness carbon dioxide corrosion resistant pipeline steel and its manufacturing method.The chemical composition in steel contains:C, Si, Mn, P≤0.010%, S≤0.002%, Mo, Nb, Ti, Al, Co, N≤0.008%, the rest is Fe and inevitable element.The transverse yield strength of the steel plate of the present application is 490MPa or more, the tensile strength is 600MPa or more, the yield ratio is ≤0.86, the elongation A 50mm ≥37%, the impact energy at-40 ℃ is 350J or more, the drop hammer at-20 ℃ is ≥95%, the average corrosion rate in carbon dioxide environment is <0.08mm / a;The longitudinal yield strength is 485MPa or more, the tensile strength is 590MPa or more, the yield ratio is ≤0.85, the elongation A 50mm ≥41%.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of pipeline steel hot-rolled plate for straight seam welded pipe, especially to a kind of high crack arrest toughness carbon dioxide corrosion resistant pipeline steel and its manufacturing method. BACKGROUND

[0002] CCUS technology (carbon capture, utilization and storage) is a key technology to cope with global climate change. Carbon dioxide transportation is a key link between carbon dioxide capture and storage utilization in the CCUS industry chain, and the efficiency and cost of carbon dioxide transportation will directly affect the overall scale and economic benefit of CCUS.

[0003] The critical pressure of pure carbon dioxide is 7.38 MPa, and the critical temperature is 31.1℃. Supercritical state transportation refers to the transportation form with a pressure 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 the most efficient, and wear is also low. However, when there is free water and impurity gas in the supercritical carbon dioxide pipeline, it has strong corrosiveness, and the existing API carbon steel system pipeline for transporting natural gas may have occasional corrosion, which may cause leakage failure. Pipe material is the basis for ensuring the safe transportation of the pipeline. In the total investment of pipeline construction, the cost of pipe material is relatively high, and affected by factors such as corrosion and third-party damage, the pipe wall may be thinned or failed, and serious accidents may occur. Key technical requirements for supercritical pipe material include low-temperature brittleness when carbon dioxide leaks and the temperature drops sharply to -40℃; corrosion rate in a supercritical carbon dioxide environment.

[0004] At present, China has no large-capacity, long-distance X65M grade carbon dioxide transportation pipeline. The following briefly introduces the patent documents close to the present application:

[0005] 1) Chinese patent document CN112941422A, a steel plate resistant to CO2 corrosion and a 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%, S≤0.0050%. The present application is a production method for a steel plate resistant to carbon dioxide corrosion disclosed by Beijing University of Science and Technology. The product is produced by a medium plate rolling mill. The steel plate after rolling needs to be quenched and tempered for quenching and tempering heat treatment process. The present application has a high Cr content, belongs to stainless steel, cannot be implemented by ordinary smelting and continuous casting, and the steel plate cannot be straight seam welded after the Cr content is too high. At the same time, the impact toughness of the steel plate is not high, and it cannot meet the crack arrest requirement of -40℃ when carbon dioxide leaks.

[0006] 2) Chinese patent document CN106498279A, a low-Cr economic X65 pipeline steel resistant to CO2 corrosion and a production method thereof. The composition contains C: 0.04%-0.05%, Si: 0.18%-0.22%, Mn: 0.50%-0.60%, Cr: 0.1%-0.2%, Mo: 0.10%-0.15%, Nb: 0.035%-0.050%, V: 0.020%-0.030%, Ti: 0.010%-0.020%, P≤0.01%, S≤0.0030%. The invention is a production method for X65 hot-rolled coil resistant to carbon dioxide corrosion disclosed by Wuhan Iron and Steel Co., Ltd. The invention has a low Mn content, poor hardenability during subsequent straight seam welding, and cannot guarantee the low-temperature toughness of the weld and the heat-affected zone at-40℃. At the same time, the base material has general low-temperature toughness at-20℃, and cannot meet the crack arrest requirements at-40℃ when carbon dioxide leaks. SUMMARY

[0007] In view of the technical problems that the 485MPa grade pipeline steel coil produced at present does not have carbon dioxide corrosion resistance, cannot adapt to supercritical carbon dioxide transportation service environment, and has poor safety, the present application provides a high crack arrest toughness carbon dioxide corrosion resistant pipeline steel and a manufacturing method thereof, aiming to produce a supercritical carbon dioxide transportation hot-rolled coil, which has a transverse yield strength of 490MPa or more, a tensile strength of 600MPa or more, a longitudinal yield strength of 485MPa or more, a tensile strength of 590MPa or more, an impact energy at-40℃ of 350J or more, and an average corrosion rate in a 14.5MPa supercritical carbon dioxide environment of <0.08mm / a.

[0008] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] A high crack arrest toughness carbon dioxide corrosion resistant pipeline steel, the chemical composition of the steel is as follows in terms of weight percentage: 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 is Fe and inevitable elements.

[0010] Compared with the prior art, the present application adopts a low-carbon medium-manganese molybdenum-containing alloy design to ensure the low-temperature toughness of the weld, and fully refine the grains; the appropriate amount of molybdenum element reduces the anisotropy effect of the transverse and longitudinal properties of the steel plate, improves 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 carbon dioxide corrosion resistance of the material, and has higher safety in pipeline engineering.

[0011] C: is a carbide forming element, is the most effective element to ensure strength, can improve the hardenability, ensure the strength and hardness of the material, its role is second only to phosphorus, manganese, nickel, chromium, tungsten, molybdenum, vanadium and other elements. Carbon significantly improves strength through solid solution strengthening and phase transformation strengthening. Only enough carbon, will form enough acicular ferrite. If the carbon content is too low, it is difficult to ensure the strength and hardness of the material; but the content is too high, it is easy to make the center segregation of the steel plate, which is not conducive to the corrosion resistance and crack toughness of the steel plate, and will affect the weldability of the product, and the best range is 0.02%~0.05%.

[0012] Si: can be dissolved in ferrite and austenite, play a certain solid solution strengthening effect, can significantly improve the hardness and strength of the steel, and promote the ferrite grain coarsening, reduce the effect of anisotropy of the steel plate in the transverse and longitudinal performance. The surface of the steel containing silicon will form a thin film of SiO2 when heated in an oxidizing atmosphere, thereby protecting the steel from further oxidation. Silicon combined with molybdenum, chromium and other elements, helps to improve the corrosion resistance and oxidation resistance of the steel. The form of silicon existing in the steel is silicide, which can effectively prevent the entry of oxidizing agents, thereby reducing corrosion. However, the increase of silicon content will reduce the welding performance of the steel, and significantly reduce the plasticity and toughness of the steel, and the best range is 0.10%~0.35%.

[0013] Mn: manganese has solid solution strengthening effect, the solid solution of manganese and iron improves the hardness and strength of ferrite and austenite in steel. At the same time, it is a carbide forming element, which enters the cementite to replace a part of iron atoms. Manganese can increase the stability of austenite by reducing the critical transformation temperature, and also strongly increase the hardenability of the steel, effectively ensuring the strength of the steel. Manganese can compensate for the strength reduction caused by carbon element, and is the most important and economical strengthening element. Manganese can make the C curve move to the right, promote the bainite transformation, and is beneficial to the formation of acicular ferrite, which can significantly improve the strength and reduce the toughness. A certain amount of manganese element can ensure the strength of the weld and the low temperature impact toughness at-40℃ during the straight seam welding process. However, too much manganese can increase the center segregation tendency of continuous casting billet, increase the banded structure in the steel plate, increase the brittleness of the steel plate and reduce the plasticity. The best range is 1.50%~1.70%.

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

[0015] Mo: Molybdenum improves the strength of the base material by increasing the hardenability of the steel. Mo is an element that expands the y-phase region, which can reduce the y→a phase transition temperature of the steel, and as the Mo content rises, the phase transition temperature gradually decreases, effectively promoting the bainite transformation to play the role of phase transition strengthening, and obtaining more fine lath bainite structure. Mo can refine the grains of the steel, and the effect of molybdenum is stronger than that of tungsten, which can significantly improve the hardenability and thermal strength of the steel, and prevent temper brittleness, and can improve the tensile strength and toughness of the steel. It was found that when the molybdenum content was less than 0.3%, the corrosion resistance of the steel was basically unchanged, when the molybdenum content was between 0.3% and 0.9%, the corrosion resistance of the steel was improved to a certain extent, and when the molybdenum content was greater than 0.9%, the corrosion resistance of the steel decreased. At the same time, Mo and Al with a content of 0.10% or more work together, and the sum of the two contents reaches 0.70% or more, the Al compound further refines the lath bainite generated by Mo elements, and a layer of Al oxide is attached to the surface of the bainite, which has a higher effect on carbon dioxide corrosion than single element. However, too high Mo content increases the cost of the alloy, and damages the plasticity and toughness, and the best range is 0.60% to 0.90%.

[0016] Nb: Niobium is one of the important elements of low-carbon micro-alloyed steel. Niobium can significantly improve the austenite recrystallization temperature of the steel, expand the range of unrecrystallized zone, and also can inhibit the growth of austenite grains, which has significant grain refinement strengthening and precipitation strengthening effect. Niobium partially dissolves into the solid solution, which has solid solution strengthening effect. When dissolved in austenite, it significantly improves the hardenability of the steel. But in the form of carbide and oxide particles, it refines the grains. It can increase the tempering stability of the steel, and has the effect of secondary hardening. Trace niobium can improve the strength of the steel without affecting the plasticity or toughness of the steel. Niobium can improve the yield strength and impact toughness, and reduce the brittle transition temperature. Too high niobium content will increase the cost of the alloy, and have adverse effects on the toughness of the heat affected zone of welding, and the best range is 0.01% to 0.03%.

[0017] Ti: Titanium is a strong nitrogen-fixing element. When about 0.015% Ti is added, fine TiN precipitates can be formed at high temperatures during slab continuous casting. These fine TiN precipitates can effectively prevent the growth of austenite grains during the heating process, and also have a significant effect on improving the toughness of the heat affected zone during welding. A small amount of TiC precipitation produces strong precipitation strengthening, which can ensure that the grains do not grow significantly after pipe normalizing heat treatment, thereby ensuring the uniformity of the steel pipe performance. However, too high a content has no obvious effect, and is easy to form large particle inclusions, and the best range is 0.01% to 0.03%.

[0018] Al: Aluminum is a common deoxidizer. The addition of aluminum can significantly improve the strength of steel, and the generated AlN helps to refine the grain structure, thereby achieving the effect of strengthening, improving the strength and low temperature impact toughness. Aluminum can significantly reduce the toughness transition temperature by reducing the sensitivity of steel to cracks and improving toughness, especially in low temperature environment. The solid solution strengthening effect of aluminum is significant, which strongly limits the expansion of austenite phase area and is beneficial to improve the strength. The addition of aluminum in steel can also improve the corrosion resistance of steel, especially when used with molybdenum element, the effect is better. The Al content of the present application is 0.10% to 0.20%.

[0019] Co: Cobalt is a strong solid solution strengthening element, which can form a solid solution with iron in steel to enhance the hardness and strength of steel. It also has the effect of refining the grain, improving the strength and toughness of steel, thereby improving the performance of the steel. Cobalt reduces the hardenability of steel and promotes the left shift of the austenite isothermal transformation curve (C-curve) in steel. The separate addition will reduce the comprehensive mechanical properties, and the addition of cobalt together with molybdenum can strengthen ferrite and improve hardness and strength. Cobalt can form a stable alloy phase with iron in steel, and a dense oxide film is formed on the surface of the steel, thereby improving its carbon dioxide corrosion resistance. When the content is too high, the hardenability of the steel is significantly reduced, which is not conducive to the strength of the steel. The appropriate range is 0.05% to 0.15%.

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

[0021] The microstructure of the steel plate is acicular ferrite and M-A group element mixed structure, and the volume ratio of M-A group element is less than 1%.

[0022] A manufacturing method of a high crack arrest toughness carbon dioxide corrosion resistant pipeline steel, comprising the following method steps:

[0023] 1) The continuous casting slab is heated to 1150-1200℃ by a heating furnace, and is kept for 150-260 minutes; then hot mechanical rolling is adopted. The temperature range and the keeping time make Mo, Al and other alloys fully solid solution, and is beneficial to the precipitation of a large amount of Ti and the refinement of austenite grain size, which is beneficial to the increase of yield and tensile strength.

[0024] 2) The rough rolling final rolling temperature is 980-1020℃, and the pressure rate is greater than 60%, which is beneficial to the prevention of austenite grain growth, the refinement of grains and the increase of strength; the finish rolling starting temperature is 900-950℃, and the final rolling temperature is 750-800℃; the temperature range is suitable for the full refinement of elongated austenite grains and the avoidance of mixed grains, so that the excellent low-temperature impact and drop hammer performance is ensured. The large reduction rate can produce a large number of dislocations and twins, which plays a role of dislocation strengthening and significantly improves the yield strength and tensile strength.

[0025] 3) After rolling, laminar flow water cooling is adopted, and the coiling temperature is 450-490℃, and the cooling speed is 14-19℃ / s. The coiling temperature and the cooling speed are beneficial to the obtaining of needle-shaped ferrite structure with uniform size, and the good low-temperature crack arrest toughness is obtained.

[0026] During the smelting of molten steel, the LF furnace is treated by shallow desulfurization and calcium treatment, so that the inclusion shape is controlled and the ductility, toughness and cold bending performance of the steel are improved.

[0027] The slab continuous casting adopts electromagnetic stirring or dynamic soft reduction.

[0028] Compared with the prior art, the beneficial effects of the present application are:

[0029] 1) The present application adopts a low-carbon medium-manganese Mo-containing alloy design, which ensures the low-temperature toughness of the weld and fully refines the grains.

[0030] 2) The appropriate amount of Mo element reduces the anisotropy effect of the transverse and longitudinal performance of the steel plate, and improves the corrosion resistance and oxidation resistance of the steel.

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

[0032] In order to make the purpose, technical scheme and advantages of the present application more clear, the specific embodiments of the present application are further described below, and the following examples are used to specifically describe the present application, which are only general description of the present application and do not limit the present application.

[0033] The application provides a high crack arrest toughness pipeline steel hot-rolled coil for resisting carbon dioxide corrosion, and a production process thereof comprises the following steps: smelting of molten steel, continuous casting blank heating, rolling, cooling and coiling. The chemical components 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 detection results are shown in table 3.

[0034] Table 1 chemical components of examples wt%

[0035]

[0036] Table 2 heating, rolling and cooling process

[0037]

[0038] Table 3 mechanical properties and structure proportion

[0039]

[0040] As shown in tables 1-3, by adopting the component design and the rolling and coiling process of the application, the high crack arrest toughness hot-rolled coil for 485MPa supercritical carbon dioxide conveying straight seam welded pipe is produced.

[0041] The above examples are only for illustrating the technical concept and characteristics of the application, and the purpose is to enable the person skilled in the art to understand the content of the application and implement it, and cannot limit the protection scope of the application. Any equivalent changes or modifications made according to the spirit and principle of the application shall be covered within the protection scope of the application.

Claims

1. A high crack arrest toughness carbon dioxide corrosion resistant line steel characterized in that, Chemical composition of the steel is as follows in percentage 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 rest is Fe and inevitable elements; The steel sheet has a transverse yield strength of 490 MPa or more, a tensile strength of 600 MPa or more, a yield ratio of 0.86 or less, and an elongation A 50mm ≥ 37%, an impact energy at -40°C of 350 J or more, a drop weight at -20°C of 95% or more, an average corrosion rate in a carbon dioxide environment of <0.08 mm / a according to ASTM-G111 corrosion standards, a longitudinal yield strength of 485 MPa or more, a tensile strength of 590 MPa or more, a yield ratio of 0.85 or less, and an elongation A 50mm ≥ 41%. The microstructure of the steel plate is acicular ferrite and M-A mixed structure, and the volume ratio of M-A component is less than 1%; The manufacturing method of the high crack arrest toughness carbon dioxide corrosion resistant pipeline steel comprises the following method steps: 1) continuously cast slab is heated to 1150~1200℃ by a heating furnace and is kept for 150~260min; 2) the rough rolling final rolling temperature is 980~1020℃, and the reduction is greater than 60%; the opening rolling temperature of the finish rolling is 900~950℃, and the final rolling temperature is 750~800℃; 3) after rolling, laminar flow water cooling mode is adopted, and the coiling temperature is 450~490℃, and the cooling speed is 14~19℃ / s.

2. A method of manufacturing a high crack resistance carbon dioxide corrosion resistant pipeline steel as claimed in claim 1, characterized in that, The manufacturing method comprises the following method steps: 1) continuously cast slab is heated to 1150~1200℃ by a heating furnace and is kept for 150~260min; 2) the rough rolling final rolling temperature is 980~1020℃, and the reduction is greater than 60%; the opening rolling temperature of the finish rolling is 900~950℃, and the final rolling temperature is 750~800℃; 3) after rolling, laminar flow water cooling mode is adopted, and the coiling temperature is 450~490℃, and the cooling speed is 14~19℃ / s.

3. The method of manufacturing a high crack-toughness carbon dioxide corrosion resistant pipeline steel according to claim 2, characterized in that, During the smelting process of the molten steel, the LF furnace is treated by shallow desulfurization and calcium treatment.

4. The method of producing a high crack-toughness carbon dioxide corrosion resistant pipeline steel according to claim 2, characterized by, The slab continuous casting adopts electromagnetic stirring or dynamic soft reduction.

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