A 450mpa-grade carbon dioxide corrosion resistant steel and a manufacturing method thereof

Abstract

The present application relates to a kind of manufacture of pipeline steel hot-rolled coil for straight seam welded pipe, especially 450MPa grade carbon dioxide corrosion resistant steel and its manufacturing method.The chemical composition in steel contains:C, Si, Mn, P≤0.020%, S≤0.002%, Cr, Cu, V, Ti, Al, N≤0.008%, the rest is Fe and inevitable element.The transverse yield strength of steel plate is 470MPa or more, tensile strength is 580MPa or more, yield ratio≤0.87, elongation A 50mm ≥39%, impact energy at-40 ℃ is 280J or more, drop hammer at-20 ℃≥95%, according to ASTM-G111 corrosion standard, average corrosion rate in carbon dioxide environment is less than 0.10mm / a;Longitudinal yield strength is 460MPa or more, tensile strength is 570MPa or more, yield ratio≤0.86, elongation A 50mm ≥38%.

Description

TECHNICAL FIELD

[0001] The present application relates to the manufacture of a pipeline steel hot-rolled coil for straight seam welded pipes, in particular to a 450MPa-grade steel resistant to carbon dioxide corrosion and a manufacturing method thereof. BACKGROUND

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

[0003] The critical pressure of pure carbon dioxide is 7.38MPa, and the critical temperature is 31.1℃. Supercritical state transportation refers to a 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 lower. 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 materials are the basis for ensuring the safe transportation of pipelines. In the total investment of pipeline construction, the cost of pipe materials is relatively high, and affected by factors such as corrosion and third-party damage, the pipe wall may be thinned or fail, and in severe cases, various safety accidents may occur. Key technical requirements for supercritical pipe materials include low-temperature brittleness when carbon dioxide leaks and the temperature drops sharply to -40℃, and 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 patents and documents similar to the present application:

[0005] 1) Chinese patent 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, and the steel plate after rolling needs to be quenched and tempered for quenching and tempering heat treatment process. The Cr content of the present application is relatively high, which belongs to stainless steel, and cannot be implemented by ordinary smelting and continuous casting. Moreover, the steel plate cannot be directly welded after the Cr content is too high, and the impact toughness of the steel plate is not high, which cannot meet the requirements of stopping cracks at -40℃ when carbon dioxide leaks.

[0006] 2) Chinese patent 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 Mn content of the invention is low, the subsequent straight seam welding process has poor hardenability, and the weld and heat-affected zone cannot guarantee the low-temperature toughness at-40℃, at the same time, the base material has general low-temperature toughness at-20℃, and cannot meet the crack arrest requirement at-40℃ when carbon dioxide leaks. SUMMARY

[0007] The present application provides a 450MPa grade steel resistant to carbon dioxide corrosion and a manufacturing method thereof, aiming to produce a supercritical carbon dioxide conveying hot-rolled coil resistant to carbon dioxide corrosion, the steel plate of the coil has a transverse yield strength of 470MPa or more, a tensile strength of 580MPa or more, a yield strength ratio of ≤0.87, an elongation A 50mm ≥39%, an impact energy at-40℃ of 280J or more, a drop hammer at-20℃ of ≥95%, according to the ASTM-G111 corrosion standard, using NACE-A solution, test temperature 60℃, CO2 pressure 2.0MPa, stirring rate 2m / s, experimental time 72h, average corrosion rate in carbon dioxide environment <0.10mm / a, higher than the 0.15mm / a required by the supercritical carbon dioxide conveying corrosion standard; longitudinal yield strength of 460MPa or more, tensile strength of 570MPa or more, yield strength ratio of ≤0.86, elongation A 50mm ≥38%.

[0008] In order to achieve the above-mentioned purpose, the following technical scheme is adopted in the present application:

[0009] A 450MPa grade steel resistant to carbon dioxide corrosion, the chemical composition in the steel is as follows in terms of weight percentage: C: 0.02%-0.05%, Si: 0.10%-0.35%, Mn: 0.50%-0.80%, P≤0.020%, S≤0.002%, Cr: 0.75%-1.00%, Cu: 0.75%-1.00%, V: 0.03%-0.06%, Ti: 0.01%-0.03%, Al: 0.10%-0.20%, N≤0.008%, and Cu / P>40, Cr / Al≥5; the rest is Fe and inevitable elements.

[0010] Compared with the prior art, the application adopts low-carbon and low-manganese design, the low-temperature toughness of the material is better, and the corrosion resistance is better; chromium and copper are combined to strengthen, to ensure high yield strength and tensile strength of the steel plate, and to significantly improve the carbon dioxide corrosion resistance; 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 the pipeline engineering.

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

[0012] Si: can dissolve into 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 to coarsen, reduce the effect of anisotropy of the steel plate in the transverse and longitudinal directions. When the steel containing silicon is heated in an oxidizing atmosphere, a thin layer of SiO2 film will be formed on the surface, thereby protecting the steel from further oxidation. Silicon combined with molybdenum, tungsten, 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% to 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 replaces a part of iron atoms in cementite. Manganese can increase the stability of austenite and significantly improve the hardenability of steel, effectively ensuring the strength of 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 transformation of bainite, and is beneficial to the formation of acicular ferrite, which can significantly improve the strength and toughness. Reducing the content of manganese can reduce the segregation of continuous casting billet, which is beneficial to the carbon dioxide corrosion resistance of the product. However, too much manganese can increase the tendency of center segregation 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 0.50% to 0.80%.

[0014] P, S, N: are inevitable impurity elements in steel, the lower the better, but too low will increase the production cost, the P≤0.020%, S≤0.002%, N≤0.008% of the application.

[0015] Cr: chromium can improve the strength by solid solution strengthening.Cr can be dissolved in the solid solution as Mn, improve the hardenability of steel, play a role in improving the strength.Cr element dissolved in austenite increases the stability of supercooled austenite, makes C curve right shift, promotes the formation of supercooled structure low carbon bainite, improves the strength and hardness of steel.Cr has excellent corrosion resistance, tests show that with the increase of Cr content, the corrosion rate is reduced.Cr in CO2 corrosion system can generate FeCO3 and Cr(OH)3 mixed phase multilayer film structure, complete and dense corrosion product film Cr(OH)3 not only hinders the electrode activation reaction, but also inhibits the ion diffusion process, effectively reduces the corrosion rate;Cr can also combine with oxygen to form a dense chromium oxide layer (Cr203), this layer of passivation layer can prevent oxygen, water and other corrosive media from further corrosion, thereby providing protection against carbon dioxide corrosion.Cr element can also form Cr7C3, Cr2S3 and other stable compounds, the existence of these compounds can form a hard film on the surface of steel, thereby improving the carbon dioxide corrosion resistance of steel.Cr mainly improves the tensile strength, can reduce the effect of copper element on the yield ratio, to ensure a lower yield ratio.Cr and copper composite addition can improve the yield strength and tensile strength, and the effect of carbon dioxide corrosion is much greater than that of each single addition, and can also avoid the copper brittleness phenomenon caused by copper element.But too high chromium content will significantly increase the brittle transition temperature of steel, reduce the elongation, easy to form coarse carbide, lead to the deterioration of toughness.The appropriate range is 0.75% to 1.00%.

[0016] Cu: copper can improve the hardenability, improve the strength of steel in hot rolling and quenching heat treatment.Copper can also improve the tensile strength of steel by means of precipitation strengthening, and has the effect of improving corrosion resistance, especially copper can form a passivation film on the surface of steel, improve the ability of carbon dioxide corrosion.The addition of appropriate amount of copper can enhance the yield strength and yield ratio of steel, and does not affect the welding performance.When the copper content is more than 0.75%, after solid solution treatment and aging, the aging strengthening effect can be produced, in order to avoid copper brittleness, add chromium element in equal proportion.Cu and P can also improve the carbon dioxide corrosion resistance of ordinary low alloy steel when used together, and has no adverse effect on the welding performance.But when the copper content is high, it is difficult to smelt and continuous cast, the cost of alloy is high, the best range is 0.75% to 1.00%.

[0017] V: Vanadium forms stable compounds with carbon, nitrogen and oxygen, mainly in the form of carbides, which refine the structure and grain, reduce the overheating sensitivity, and improve the strength and toughness. The vanadium carbonitride uniformly precipitates in the ferrite in the form of fine dispersion, which can significantly improve the strength of the material. When dissolved in the solid solution at high temperature, it increases the quenching property, and also improves the tempering stability and secondary hardening effect of the coil after coiling. Vanadium refines the grain and improves the welding performance. However, too high content does not significantly improve the strength, and increases the alloy cost. The appropriate range is 0.03% to 0.06%.

[0018] Al: Aluminum is a common deoxidizer. The addition of aluminum can significantly improve the strength of the steel, and the generated AlN helps to refine the grain structure, thereby achieving the strengthening effect and improving the strength and low temperature impact toughness. Aluminum reduces the sensitivity of steel to cracks, improves toughness, especially in low temperature environment, which can significantly reduce the toughness transition temperature. The solid solution strengthening effect of aluminum is significant, which effectively limits the expansion of austenite phase area, which is beneficial to improve the strength. The addition of aluminum in steel can also improve the corrosion resistance of the steel, especially in combination with Cr element, and the effect is better when the ratio of Cr to Al is more than 5. The Al content of the present application is 0.10% to 0.20%.

[0019] Ti: Titanium is a strong nitrogen-fixing element. When about 0.015% Ti is added, high-temperature stable fine TiN precipitates can be formed during slab continuous casting. This fine TiN precipitate can effectively prevent the growth of austenite grains during the heating process, and also has a significant effect on improving the toughness of the heat-affected zone during steel welding. A small amount of TiC precipitates produces strong precipitation strengthening effect, 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 content has no obvious effect, and large particle inclusions are easily formed. The best range is 0.01% to 0.03%.

[0020] The transverse yield strength of the steel plate of the present application is 470 MPa or more, the tensile strength is 580 MPa or more, the yield strength ratio is ≤0.87, the elongation A 50mm ≥39%, the-40℃ impact energy is 280 J or more, the-20℃ drop hammer 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 <0.10 mm / a, which is higher than the requirement of 0.15 mm / a of the supercritical carbon dioxide transportation corrosion standard; the longitudinal yield strength is 460 MPa or more, the tensile strength is 570 MPa or more, the yield strength ratio is ≤0.86, and the elongation A 50mm ≥38%.

[0021] The steel plate has a mixed structure of acicular ferrite and M-A, and the volume ratio of M-A component is less than 3%.

[0022] A manufacturing method of a 450MPa-grade steel plate for resisting carbon dioxide corrosion comprises the following steps:

[0023] 1) The continuous casting slab is heated to 1150-1250℃ in a heating furnace and kept for 150-250min, and then hot mechanical rolling is adopted. The temperature range and the holding time make Cr, Cu and other alloys fully solid-solute, and at the same time, Ti is precipitated in a large amount, and the austenite grain size is refined, which is beneficial to the increase of yield strength and tensile strength. When heated at a high temperature, a thin SiO2 film is formed on the surface, so as to protect the steel from further oxidation and improve the corrosion resistance.

[0024] 2) The rough rolling final rolling temperature is 970-1030℃, which is beneficial to preventing the growth of austenite grains, refining the grains and improving the strength; the rough rolling starting rolling temperature is 900-950℃, and the final rolling temperature is 740-790℃; the temperature range is suitable for fully refining the elongated austenite grains and avoiding mixed grains, so as to ensure the low-temperature impact and drop hammer performance.

[0025] 3) After rolling, laminar flow water cooling is adopted, and the coiling temperature is 400-470℃, and the cooling speed is 25-35℃ / s. The coiling temperature and the cooling speed are beneficial to obtaining acicular ferrite structure with uniform size, high strength and good low-temperature toughness.

[0026] During the smelting of the molten steel, the LF furnace is treated by shallow desulfurization and calcium treatment, so as to control the inclusion shape and improve the ductility, toughness and cold bending performance of the steel.

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

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

[0029] 1) The present application adopts low-carbon and low-manganese design, and the low-temperature toughness of the material is better, and the corrosion resistance is better.

[0030] 2) Chromium and copper are combined to strengthen, so as to ensure high yield strength and tensile strength of the steel plate, and at the same time, the carbon dioxide corrosion resistance can be significantly improved.

[0031] 3) 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. 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 in combination with examples. 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 present application provides a 450MPa supercritical carbon dioxide conveying anti-carbon dioxide corrosion hot-rolled coil, the production process includes molten steel smelting, continuous casting billet heating, rolling, cooling, coiling. The chemical composition of examples 1-8 is shown in table 1, the heating, rolling, cooling process parameters are shown in table 2, and the mechanical property test results are shown in table 3.

[0034] Table 1 example chemical composition wt%

[0035]

[0036] Table 2 heating, rolling, cooling process

[0037]

[0038] Table 3 mechanical properties

[0039]

[0040] As can be seen from tables 1-3, by using the component design and rolling, coiling process of the present application, a 450MPa supercritical carbon dioxide conveying anti-carbon dioxide corrosion hot-rolled coil is produced.

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

Claims

1. A 450MPa grade steel resistant to carbon dioxide corrosion, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.02%–0.05%, Si: 0.10%–0.35%, Mn: 0.50%–0.80%, P≤0.020%, S≤0.002%, Cr: 0.75%–1.00%, Cu: 0.75%–1.00%, V: 0.03%–0.06%, Ti: 0.01%–0.03%, Al: 0.10%–0.20%, N≤0.008%, with Cu / P > 40 and Cr / Al ≥ 5; the remainder is Fe and unavoidable elements. The steel plate has a transverse yield strength of ≥470MPa, a tensile strength of ≥580MPa, a yield strength ratio ≤0.87, and an elongation A. 50mm ≥39%, impact energy above 280J at -40℃, drop weight strength above 95% at -20℃, average corrosion rate <0.10mm / a in a carbon dioxide environment according to ASTM-G111 corrosion standard; longitudinal yield strength above 460MPa, tensile strength above 570MPa, yield ratio ≤0.86, elongation A 50mm ≥38%.

2. The 450MPa grade carbon dioxide corrosion resistant steel according to claim 1, characterized in that, The microstructure of the steel plate is a mixture of acicular ferrite and MA, with the volume ratio of MA component being less than 3%.

3. A method for manufacturing 450MPa grade carbon dioxide corrosion resistant steel as described in claim 1 or 2, characterized in that, The methods and steps include the following: 1) The continuously cast slab is heated in a heating furnace to 1150-1250℃ and held for 150-250 minutes; 2) Roughing rolling temperature: 970-1030℃; Finishing rolling temperature: 900-950℃; Finishing rolling temperature: 740-790℃. 3) After rolling, laminar flow water cooling is adopted, the coiling temperature is 400~470℃, and the cooling rate is 25~35℃ / s.

4. The method for manufacturing a 450MPa grade carbon dioxide corrosion resistant steel according to claim 3, characterized in that, During the steelmaking process, the LF furnace undergoes shallow desulfurization and calcium treatment.

5. The method for manufacturing a 450MPa grade carbon dioxide corrosion resistant steel according to claim 3, characterized in that, Slab continuous casting employs electromagnetic stirring or dynamic light reduction.

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