CN114058975A - High heat input welded low temperature resistant corrosion resistant steel for cargo oil tank and manufacturing method thereof - Google Patents

High heat input welded low temperature resistant corrosion resistant steel for cargo oil tank and manufacturing method thereof Download PDF

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Publication number
CN114058975A
CN114058975A CN202111401895.6A CN202111401895A CN114058975A CN 114058975 A CN114058975 A CN 114058975A CN 202111401895 A CN202111401895 A CN 202111401895A CN 114058975 A CN114058975 A CN 114058975A
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steel
corrosion
resistant
rolling
heat input
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严玲
王�华
王长顺
张鹏
王晓航
李广龙
王东旭
齐祥羽
李博雍
韩鹏
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Angang Steel Co Ltd
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Angang Steel Co Ltd
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Priority to CN202111401895.6A priority Critical patent/CN114058975A/en
Priority to EP21945363.6A priority patent/EP4227432A1/en
Priority to KR1020227044900A priority patent/KR20230074416A/en
Priority to PCT/CN2021/132953 priority patent/WO2023087350A1/en
Priority to US18/013,134 priority patent/US20240018616A1/en
Publication of CN114058975A publication Critical patent/CN114058975A/en
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Abstract

The invention provides a high heat input welded low temperature resistant corrosion resistant steel for cargo oil tank and a manufacturing method thereof, wherein the steel comprises the following chemical components in percentage by weight: c: 0.04-0.13%, Si: 0.10 to 0.40%, Mn: 0.60-1.30%, P: 0.005-0.012%, S is less than or equal to 0.006%, Al: 0.01 to 0.05%, Sn: 0.03 to 0.15%, Nb: 0.005-0.020%, Ti: 0.005-0.025%, Ni: 0.15-0.40%, Cu: 0.15 to 0.50%, Cr: 0.10 to 0.25%, Ca: 0.007 to 0.024 percent, and the balance of Fe and inevitable impurities. The invention mainly aims at the corrosion-resistant steel designed for the upper deck and the inner bottom plate of the storage and transportation tank of the polar region ship, and the steel has excellent low-temperature toughness and can be welded with large heat input.

Description

High heat input welded low temperature resistant corrosion resistant steel for cargo oil tank and manufacturing method thereof
Technical Field
The invention relates to the technical field of low-alloy ship steel, in particular to low-temperature-resistant and corrosion-resistant steel for a cargo oil tank welded at high heat input and a manufacturing method thereof.
Background
With the development of economy and society, the demand and consumption of crude oil are continuously increased, and the rapid increase of crude oil transportation is also promoted. At the same time, the climate warming makes possible the transport of arctic routes, with a significant increase in the number of tankers passing through the arctic northeast channel. During crude oil storage and transportation, the bottom plate of a Cargo Oil Tank (COT) as a main storage and transportation container is covered with a layer containing oil sludge and high-concentration Cl-Brine and H2The deposited oil film of S causes the bottom plate in the oil tank to generate serious local punctiform corrosion, the deepest corrosion pit can reach 10mm, and the corrosion becomes a great potential safety hazard in the operation of the crude oil tanker. The oil tanker sailing the arctic channel needs to bear the low-temperature environment, and the steel for the cargo oil tank structure needs to have good weldability, low-temperature toughness and corrosion resistanceExcellent comprehensive mechanical properties such as performance and the like.
In 2012, the International Maritime Organization (IMO) requires a cargo oil tank coating protection mode or a corrosion-resistant steel construction mode to ensure that the cargo oil tank structural steel resists the corrosion of high chloride ions, temperature alternation and acid gas-phase media, and the problems of marine environment pollution, oil tanker safety danger and the like caused by crude oil leakage generated by oil tanker corrosion are prevented. However, the coating protection can only be maintained for 5-7 years, and 3-4 times of repair and re-spraying are needed in the 25-year life cycle of the oil tanker, so that the maintenance labor hour is increased, and the operation environment is severe; and the oil tanker is stopped due to the restoration of the docking, so that the operation cost of the oil tanker is greatly increased. Meanwhile, with the trend of large-scale and high-efficiency oil tanker construction, 80% of workload of a ship enterprise is from a welding process in the oil tanker construction process, so that the willingness of high-heat-input welding on the corrosion-resistant steel for the cargo oil tank body is stronger, the corrosion-resistant steel which is currently suitable for the oil tanker can only meet the conventional low-heat-input welding requirement of 50KJ/cm or less, and the corrosion-resistant steel which is suitable for high-heat-input welding is not reported yet. In order to improve shipbuilding efficiency, high-heat input welding equipment such as multi-wire submerged arc welding, FCB (flux cored welding), electrogas welding and the like is generally introduced into large shipyards, so that the high efficiency of oil tanker construction is realized. Therefore, there is an urgent need for corrosion resistant steel for oil tankers suitable for high heat input welding.
At present, some researches on corrosion-resistant steel for cargo oil tanks at home and abroad find partial patents and documents through retrieval, but the recorded contents of the corrosion-resistant steel and the aspects of components, production methods, weldability, corrosion resistance, low-temperature toughness and the like in the technical scheme of the invention have obvious defects.
Related patent 1: CN103290337A corrosion-resistant steel for the upper deck of the cargo oil tank of a crude oil tanker provides common strength and high strength corrosion-resistant steel only used for the upper deck of the cargo oil tank, ECL is 1.95mm, low temperature toughness only meets-20 ℃, no weldability evaluation index is given, and no mention is made about whether the steel has high heat input welding characteristics.
Related patent 2: CN103305761A corrosion-resistant steel for base plate in cargo oil tank of crude oil tanker provides common strength and high strength corrosion-resistant steel only used for upper deck of cargo oil tank, the low temperature toughness only meets-20 ℃, similarly, no evaluation index of weldability is given, and no mention is made about whether high heat input welding characteristic is provided.
Related patent No. 3: CN103469101A corrosion-resistant steel for cargo ship cabin bottom plates of high Nb crude oil ships provides steel for bottom plates in cargo oil cabins with 32Kg strength level containing a high Nb component system, the quality level is only A level (normal temperature), and the application under the condition of 0 ℃ and lower temperature cannot be met.
Related patent 4: JP 4935578 corrosion resistant steel for ships and related patent 5: JP 5130828 "method for manufacturing high-strength corrosion-resistant steel material for ships" provides corrosion-resistant steel having good low-temperature toughness (quality grade E, -40 ℃), but its weld heat input is only 60kJ/cm, and does not provide an evaluation effect of corrosion properties of the upper deck and the inner bottom plate based on the IMO standard.
Related patent 6: CN102974661A straightening process of a corrosion-resistant steel plate of a crude oil cargo oil bin, relating to a straightening process of a steel plate for the crude oil cargo oil bin with the thickness of 30-50mm, and key technologies such as material components, manufacturing process and the like are not mentioned.
In conclusion, the prior art is insufficient in product development of the steel for the cargo oil tank of the oil tanker, which has comprehensive properties such as corrosion resistance, low temperature resistance, high toughness, suitability for high-heat input welding and the like, and cannot meet the requirements of efficient construction of shipyards and the requirements of the cargo oil tank of the crude oil tanker for material comprehensive properties of low temperature resistance and high-sulfur and high-acid oil gas corrosion resistance in polar region navigation.
Disclosure of Invention
In view of the above problems, there is provided a low temperature resistant and corrosion resistant steel for cargo oil tanks welded at high heat input and a method for manufacturing the same.
The technical means adopted by the invention are as follows:
the low-temperature-resistant corrosion-resistant steel for the cargo oil tank welded at high heat input comprises the following chemical components in percentage by weight:
c: 0.04-0.13%, Si: 0.10 to 0.40%, Mn: 0.60-1.30%, P: 0.005-0.012%, S is less than or equal to 0.006%, Al: 0.01 to 0.05%, Sn: 0.03 to 0.15%, Nb: 0.005-0.020%, Ti: 0.005-0.025%, Ni: 0.15 to 0.40%, Cu: 0.15 to 0.50%, Cr: 0.10 to 0.25%, Ca: 0.007 to 0.024%, and the balance of Fe and inevitable impurities.
Preferably, the weight percentage of the material is as follows: sb: 0.02-0.15%, W: 0.03 to 0.10%, Mo: 0.05-0.15%, RE: 0.05-0.10% of one or more of the following components.
Preferably, the unavoidable impurities comprise N, H, O, wherein the weight percentage of N is 0.0020-0.0060%, the weight percentage of H is less than or equal to 0.00015%, and the weight percentage of O is less than or equal to 0.0020%.
Preferably, the ratio of Ti to N is 2.43 to 3.56.
Preferably, Ni + Cu is more than or equal to 0.35 percent, and Ni/Cu is more than or equal to 0.70; Ca/S is 1.8 to 4.
Preferably, the thickness of the steel plate made of the corrosion-resistant steel for the cargo oil tank suitable for high-heat input welding is 8-50 mm, the volume fraction of pearlite in a microstructure of the corrosion-resistant steel with the yield strength requirement of being larger than or equal to 355MPa (36Kg) is smaller than or equal to 30%, and the volume fractions of bainite of the corrosion-resistant steel with the yield strength requirement of being larger than or equal to 370MPa (40Kg) and larger than or equal to 420MPa are smaller than or equal to 35%.
The action mechanism of each alloy component in the corrosion-resistant steel for the acid crude oil storage and transportation tank is explained in detail as follows, wherein the percentage symbol% represents the weight percentage:
c: is an essential element for securing the strength of steel, and the content is 0.04% or more, but when the content exceeds a certain amount, the weld crack sensitivity is increased, resulting in deterioration of the welding performance. In addition, an increase in the C content increases the pearlite phase content of the sheet-layer cementite in the steel, pearlite becomes a cathode in an acidic environment and can promote corrosion, MA is likely to occur at the HAZ (heat affected zone) position near the remelted line of the steel sheet after welding, and the low-temperature toughness of the material is significantly reduced, so the upper limit is 0.13%.
Si: is a main deoxidizing component in the steel making process, and must be contained by more than 0.10% in order to obtain a sufficient deoxidizing effect. However, if the content exceeds the upper limit, the toughness of the base material and the weld zone is lowered, and Si in the form of solid solution increases the toughness and the brittle transition temperature, so that the Si content is 0.10 to 0.40%.
Mn: the Mn and S are combined to form MnS, thereby avoiding hot cracks caused by FeS formed at the grain boundary, and the Mn is also a good deoxidizer. Manganese is used as a low-cost toughening element, the content of manganese is too low, the strength of the material cannot be ensured, but when the content of manganese is higher than 1.30%, the segregation of a casting blank is increased, and the low-temperature toughness of a Coarse Grain Heat Affected Zone (CGHAZ) is deteriorated, so that the content of manganese is controlled to be 0.60-1.30%.
P: are inevitable impurity elements in steel and deteriorate toughness and weldability of steel. Studies have shown that when the P content is higher than 0.012%, its corrosivity under the acidic gas phase medium conditions of the upper deck is significantly reduced, so the upper limit is 0.012%.
S: MnS inclusions are easily formed in the steel, and the MnS inclusion sites are the origin of pitting corrosion to lower the corrosion resistance of the steel, and therefore measures are taken to reduce the S content in the steel as much as possible. Therefore, in the present invention, the upper limit of the S content is determined to be 0.006%.
Al: the content of the deoxidation and grain refinement elements is generally 0.01% or more, but if the content is too high, the ingot is liable to generate hot cracks, and a large amount of Al is formed2O3And inclusion, which significantly reduces the toughness of the steel, so that the upper limit of the Al content is 0.05%.
Sn: the component which is necessary to be added in the invention and used for improving the corrosion resistance exists in the steel in a solid solution form, and can obviously improve the electrochemical corrosion self potential of the steel, thereby inhibiting the corrosion of the steel in an acid corrosion environment. However, when the content is less than 0.03%, the corrosion resistance cannot be effectively improved, and when the content exceeds 0.15%, austenite grain boundaries are enriched in the hot working process such as continuous casting and rolling, so that the high-temperature plasticity is reduced, so that the content of Sn is in the range of 0.03-0.15%.
Ni: the addition of a proper amount of Ni element is beneficial to forming a compact rust layer on the surface of steel, can inhibit the corrosion reaction of the steel, has better effect particularly under the coexistence of Cu, Cr and the like, and is beneficial to microstructure control and grain refinement and improvement of low-temperature toughness because the nickel can improve the strength, reduce the critical cooling speed and delay the pearlite transformation; however, under the S-containing atmosphere, the formation of nickel sulfide causes red hot brittleness of the steel, so the content of nickel is not suitable to be too high, and therefore, the content of Ni is controlled to be 0.15-0.40%.
Cu: the corrosion resistance, especially the seawater corrosion resistance, of the steel plate can be obviously improved, and the effect of ensuring the corrosion resistance of the steel plate is obvious. However, the toughness is unfavorable due to the excessively high Cu content, the steel plate is easy to embrittle, and the Cu content is controlled to be 0.15-0.50%.
Cu/Ni composite addition: its main mechanism of action in steel is represented in the following two aspects: on one hand, the addition of Cu and Ni promotes the formation of alpha-FeOOH in steel, and Ni can promote the formation of spinel oxides and improve the density of a rust layer in a dry-wet alternating environment; cu can be used as a core of oxide crystals in the rust layer to promote the formation of alpha-FeOOH, and the alpha-FeOOH is a relatively stable phase in the rust layer and is difficult to convert into other phases once formed, so that cracks and defects caused by volume change due to phase conversion cannot be generated. On the other hand, under the condition that a certain potential is satisfied in an etching medium, the dissolution of Cu may form Cu2+And form a sparingly soluble protective film with certain anions, e.g. Cu2S effectively protects the matrix, and the insoluble salts of Cu have repairing and protecting effects on cracks and holes, so that the compactness of the continuous rust layer is improved. Therefore, the addition amount of Ni + Cu in the steel is determined to be more than or equal to 0.35 percent, and simultaneously, the Ni/Cu is more than or equal to 0.70 percent so as to inhibit the adverse effect of Cu on the low-temperature toughness.
Sb: the effect of improving the corrosion resistance of the steel is similar to that of Sn, the corrosion resistance of the steel under the acidic corrosion environment can be effectively improved, and if the Sn is added together, the corrosion resistance of the steel can be further improved, so that the Sn-doped stainless steel is an optional addition element. If the Sb content exceeds 0.15%, the corrosion resistance effect is saturated and the thermoplasticity of the steel is reduced. Therefore, the Sb content is in the range of 0.02 to 0.15% when adding.
W: are optional additional elements for improving corrosion resistance in the present invention. W can form WO in acidic corrosive environment4 2-Ionic inhibition of Cl-Attack by anions such as ions can also form FeWO4The dense layer inhibits corrosion. WWhen the content exceeds 0.10%, the effect of suppressing corrosion is saturated and the weldability is not favorable, so that the upper limit is 0.10%.
Cr: formation of dense Cr on the surface of steel as oxidation proceeds2O3Layer for inhibiting the invasion of anions in acidic corrosive environment, thereby reducing Cl-The enrichment of plasma on the surface of the steel has good pitting corrosion resistance effect on the steel plate in the environment of the inner bottom plate. However, if the Cr content is too high, the weld crack sensitivity increases. The preferable range of the content of Cr added is 0.10 to 0.25% in view of the comprehensive weldability and corrosion resistance.
Mo: the effect of improving the corrosion resistance of the steel is similar to that of W, Cr, the formation of a compact rust layer on the surface can be promoted, the further development of corrosion can be prevented, and the preferable content range of the additive is 0.05-0.15% from the aspects of cost and corrosion resistance.
RE: the steel purification effect is achieved, and the crystal boundary can be effectively purified, so that the corrosion resistance of the crystal boundary is improved, and the overall corrosion rate is reduced; simultaneously, the composite material is a good desulfurization and deoxidant, and can improve the low-temperature toughness and the easy weldability; the RE is used as a modifier, so that the form, size and distribution of inclusions can be improved, the comprehensive mechanical property of the material is further improved, but when the content is too high, the smelting continuous casting difficulty is increased, and the manufacturing cost of the product is increased, so that the RE content is controlled to be 0.05-0.10%.
Nb: the element is added to improve the strength and toughness of the steel, and can effectively reduce the grain size of the steel. When the Nb content is less than 0.005%, the effect on the strength and toughness of the steel is small, and when the Nb content exceeds 0.020%, MA brittle components are easily generated during high-heat input welding, so that the welding performance and low-temperature toughness of the steel are reduced, and therefore, the Nb content ranges from 0.005% to 0.020%.
Ti: the TiN-based composite material is added as a component for improving the toughness of steel and a welding part, is used as a strong N-fixing element, is easy to form TiN to improve the N-pore resistance of weld metal, has little effect when the content is less than 0.005 percent, and is easy to form large-particle TiN when the content is more than 0.021 percent to lose the effect. Steel sheet to obtain low temperature toughness at high heat input, it is necessary to control Ti: the ratio of N is 2.43-3.56, so the content of Ti added is 0.005-0.021%.
Ca: the Ca and the S are combined to form CaS which can coat inclusions such as alumina and the like, so that the denaturation and spheroidization of the inclusions are realized, and the corrosion resistance, the toughness and the fatigue resistance are improved; meanwhile, the early formed finely dispersed CaS can reduce the formation ratio of MnS, and the CaS and H2O to dissociate basic OH-Ions can reduce the acidification degree of the corrosion pit and reduce the pitting corrosion sensitivity. And the CaO with small size formed in the steel can also play the roles of refining grains and improving the toughness of the material. In the present invention, Ca: 0.007-0.024%, and Ca/S is between 1.8-4.
N can form fine precipitates with Nb, Ti and V to play a role of strengthening and fine grains and improve the toughness, but the toughness is deteriorated due to excessively high content, and the content is preferably controlled to be 0.0020-0.0060%.
H. O is a harmful impurity element in the present invention; the content of the additive is increased, so that the hydrogen induced cracking tendency is increased, the inclusion content is increased, and the corrosion resistance and the fatigue resistance are reduced, therefore, the invention controls H to be less than or equal to 0.00015 percent and O to be less than or equal to 0.0020 percent.
The invention also discloses a manufacturing method of the steel for the high-heat input welded low-temperature-resistant corrosion-resistant cargo oil tank, which comprises the following steps:
smelting: adopting deep desulfurization molten iron, wherein the weight percentage of sulfur in the deep desulfurization molten iron is less than or equal to 0.002 percent, smelting the molten iron after the molten iron reaches a converter, and adjusting and adding the chemical components in the converter to ensure that the chemical components in the converter meet the weight percentage of the low-temperature-resistant and corrosion-resistant steel for the cargo oil tank welded by high heat input;
refining: carrying out secondary refining on the molten steel carried out of the converter;
continuous casting: continuously casting the molten steel after the secondary refining to obtain a steel plate blank;
heating: heating the steel plate blank to 1100-1150 ℃ for 3-5 hours;
rolling: rolling the heated steel plate blank, performing first-stage rolling to obtain an intermediate blank, and performing second-stage rolling on the intermediate blank, wherein the initial rolling temperature of the first-stage rolling is 950-1100 ℃, the initial rolling temperature of the second-stage rolling is 850-900 ℃, and the final rolling temperature of the second-stage rolling is 800-860 ℃;
online cooling: and cooling the rolled steel plate to 500-600 ℃, wherein the cooling rate is 5-20 ℃/s, and obtaining the steel plate.
Wherein the initial rolling temperature of the second-stage rolling is 850-900 ℃, and the final rolling temperature of the second-stage rolling is 840-860 ℃; in the on-line cooling process, the rolled steel plate is cooled to 550-600 ℃, and the cooling rate is 5-15 ℃/s. Or in the rolling process, the initial rolling temperature of the second-stage rolling is 850-890 ℃, and the final rolling temperature of the second-stage rolling is 800-840 ℃; in the on-line cooling process, the rolled steel plate is cooled to 500-560 ℃, and the cooling rate is 7-20 ℃/s.
Preferably, further comprising offline cooling: shearing the steel plate with the thickness of less than 40mm of the finished steel plate, and carrying out offline transportation to a finished product stacking area; and (3) for the steel plate with the thickness of more than or equal to 40mm of the finished steel plate, stacking and slow cooling are carried out after straightening, the slow cooling starting temperature is 250-400 ℃, the stacking time is not less than 24 hours, and then shearing and unloading are carried out to a finished product stacking area.
Preferably, in the smelting process, the smelting production is carried out by adopting a high-tensile carbon one-time point blowing mode.
Preferably, in the smelting process, the alkalinity of the smelted final slag is 3.2-4.1, and the steel discharging time is not less than 5 min;
preferably, aluminum particles, silicon carbide and calcium carbide are adopted for slag adjustment in the refining process, the alkalinity of refined final slag is more than or equal to 2.4, Ca treatment is carried out after refining is finished, and the wire feeding of molten steel in each furnace is 200-300 meters.
Preferably, in the continuous casting process, the superheat degree is less than or equal to 25 ℃, in the continuous casting process, weak cooling is adopted for secondary cooling, the continuous casting blank drawing speed is 0.8-1.2 m/min, and the thickness of the cast steel plate blank is 200-360 mm;
preferably, during rolling, the ratio of the thickness of the intermediate billet to the thickness of the finished steel plate is not less than 2.5: 1, the cumulative reduction rate of the first-stage rolling and the second-stage rolling is not less than 50%.
The steel plate formed by the steel has Charpy impact toughness of not less than 198J at-60 ℃, ECL corrosion rate (25-year extrapolated corrosion rate) of not more than 2.0mm and fracture toughness of not less than 0.8mm, wherein the fracture toughness satisfies the characteristic value delta c of CTOD at-10 ℃. And after 240KJ/cm welding, the Charpy impact toughness (AKv) of the welded joint is ≧ 170J at-40 ℃.
The corrosion-resistant steel is designed mainly aiming at the comprehensive uniform corrosion of the upper deck and the local pitting corrosion of the inner bottom plate of the storage and transportation tank of the oil tanker in the polar region, and the material has excellent low-temperature toughness (meeting-60 ℃) and can be used for large heat input welding (the linear energy reaches 240 KJ/cm). The base metal and the high heat input welding joint prepared by the invention are subjected to mechanical property evaluation and simulation to obtain the mixed gas (O) at the top of the cargo oil tank of the actual oil tanker2-CO2-SO2-H2S) corrosion performance evaluation under alternate dry and wet corrosive environments and bottom highly acidic solution (10% NaCl solution with pH 0.85) corrosive environments. The result shows that the comprehensive mechanical property and the corrosion resistance of the alloy meet the requirements of IACS and IMO standard evaluation indexes.
Compared with the prior art, the invention has the following advantages:
(1) the invention is based on the chemical component system specified by classification society, and adopts low C and low Mn elements, thereby reducing the corrosion sensitivity; a proper amount of Ni, Cu and Mo is added, so that the corrosion resistance is improved while the strength is compensated; fine carbonitride precipitation is formed by Nb, Ti and V, so that the strengthening and fine grain effects are exerted, and the excellent low-temperature toughness of the steel plate at minus 60 ℃ is ensured; by reducing the P, S, H, O content, strictly controlling the N content, the size and the form of inclusions, segregation and the like, the corrosion resistance is ensured, and the low-temperature toughness and the weldability are improved; the segregation of the continuous casting billet is not more than 0.5 grade, the grade sum of A, B, C, D four types of inclusions is not more than 2.0 grade, and the strength, toughness, corrosion resistance and weldability of the steel are ensured by controlling the cleanliness of the steel and the weight, size and number of the inclusions.
(2) The invention adopts the component design and the manufacturing method to obtain the microstructure of the polygonal ferrite + pearlite and the polygonal ferrite + bainite, and meanwhile, the unicity of the microstructure has good effects on reducing the potential difference and realizing high corrosion resistance.
(3) The corrosion-resistant steel plate suitable for high-heat input welding has the maximum thickness of 50mm, can cover 355MPa (36kg), 390MPa (40kg) and 420MPa levels on the strength grade of the steel plate through regulation and control of components and a rolling process, and has low-temperature toughness which can meet F-level toughness indexes, particularly has excellent fracture toughness (CTOD) at low temperature and reaches more than 0.8 mm; when the welding heat input reaches 240KJ/cm, the material still has good toughness, and meets the application technical requirements of the materials required by the construction of cargo oil tanks of oil ships in polar region air routes.
(4) The invention provides the environment-friendly and long-life high-performance steel for building the cargo oil tank of the oil tanker in the polar region, can realize that the oil tanker does not need maintenance in the whole life cycle, and can save a large amount of coating and maintenance operation costs.
For the reasons described above, the present invention can be widely applied to the fields of low alloy ship steels and the like.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a 355MPa grade microstructure of corrosion-resistant steel for cargo tanks suitable for high heat input welding in an embodiment of the steel of the present invention.
FIG. 2 is a microstructure diagram of a 420MPa grade corrosion resistant steel for cargo tanks suitable for high heat input welding in an embodiment of the steel of the present invention.
FIG. 3 is a corrosion microstructure of a lower plate according to an embodiment of the present invention.
FIG. 4 is a three-dimensional profile analysis diagram of the corrosion auto-focus of the lower plate according to the embodiment of the present invention.
FIG. 5 is a microstructure view of corrosion of the upper deck of an embodiment of the present invention.
FIG. 6 is an analysis diagram of the upper deck corrosion auto-focus three-dimensional topography in accordance with the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective portions shown in the drawings are not drawn in an actual proportional relationship for the convenience of description. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate. Any specific values in all examples shown and discussed herein are to be construed as exemplary only and not as limiting. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.
As shown in figures 1-6, the invention discloses a high heat input welded low temperature resistant and corrosion resistant steel for cargo oil tanks, which comprises the following chemical components in percentage by weight:
c: 0.04-0.13%, Si: 0.10 to 0.40%, Mn: 0.60-1.30%, P: 0.005-0.012%, S is less than or equal to 0.006%, Al: 0.01 to 0.05%, Sn: 0.03 to 0.15%, Nb: 0.005-0.020%, Ti: 0.005-0.025%, Ni: 0.15-0.40%, Cu: 0.15 to 0.50%, Cr: 0.10 to 0.25%, Ca: 0.007 to 0.024 percent, and the balance of Fe and inevitable impurities.
Also comprises the following components in percentage by weight: sb: 0.02-0.15%, W: 0.03 to 0.10%, Mo: 0.05-0.15%, RE: 0.05-0.10% of one or more of the following components.
The unavoidable impurities comprise N, H, O, wherein the weight percentage of N is 0.0020-0.0060%, the weight percentage of H is less than or equal to 0.00015%, and the weight percentage of O is less than or equal to 0.0020%.
Wherein, Ni + Cu is more than or equal to 0.35 percent, and Ni/Cu is more than or equal to 0.70 percent; Ti/N is 2.43-3.56; Ca/S is 1.8 to 4.
The thickness of a steel plate made of the corrosion-resistant steel for the cargo oil tank suitable for high-heat input welding is 8-50 mm, the volume fraction of pearlite in a microstructure of the corrosion-resistant steel with the yield strength requirement of being larger than or equal to 355MPa (36Kg level) is smaller than or equal to 30% (see figure 1), and the volume fractions of bainite of the corrosion-resistant steel with the yield strength requirement of being larger than or equal to 390MPa (40Kg) and 420MPa are smaller than or equal to 35% (see figure 2).
By adopting the component design and the manufacturing method, the microstructure composition and the phase proportion are regulated and controlled aiming at the corrosion-resistant steels with different strength grades, the microstructure of polygonal ferrite and a small amount of pearlite (shown in figure 1) is obtained aiming at the 355KPa (36Kg) grade high-strength steel, the volume fraction of the pearlite is less than or equal to 30 percent, the microstructure of acicular ferrite and a small amount of bainite (shown in figure 2) is adopted aiming at the super-strength steels with 390MPa (40Kg) grade and 420MPa grade, the volume fraction of the bainite is less than or equal to 35 percent, and simultaneously, the grain size of steel plates with various steel grades and various thicknesses is effectively controlled. This is because the relative singleness of the microstructure is effective for reducing the difference in corrosion potential between different phases and achieving high corrosion resistance of the material.
The element components and weight percentages of the embodiments 1-10 are shown in table 1:
TABLE 1
Figure BDA0003365352070000111
The embodiment also discloses a manufacturing method of the steel for the low-temperature-resistant and corrosion-resistant cargo oil tank with high heat input welding, which comprises the following steps:
smelting: the method comprises the steps of adopting deep desulfurization molten iron, wherein the weight percentage of sulfur in the deep desulfurization molten iron is less than or equal to 0.002%, adjusting the content of each element in a converter after the molten iron reaches the converter to meet the chemical components and the weight percentage thereof, adopting a process of combining double-slag dephosphorization with slag skimming of molten steel after the converter for smelting, and adopting a high-carbon-drawing one-time point blowing mode for smelting production; the alkalinity of the smelted final slag is 3.2-4.1, a large amount of slag is prevented from being discharged through effective slag blocking operation, and the time for discharging steel is not less than 5 min;
refining: the molten steel carried out of the converter is subjected to secondary refining to further reduce the content of harmful impurities such as O, S and nonmetallic inclusions. Aluminum particles, silicon carbide and calcium carbide are adopted for slag adjustment in the refining process, the alkalinity of refined final slag is more than or equal to 2.4 (the term "double slag" refers to smelted final slag and refined final slag), Ca treatment is carried out after refining is finished, and the wire feeding of molten steel in each furnace is 200-300 meters.
Continuous casting: continuously casting the molten steel after the secondary refining to obtain a steel plate blank; the superheat degree in the continuous casting process is less than or equal to 25 ℃, the secondary cooling in the continuous casting process adopts weak cooling, the continuous casting blank drawing speed is 0.8-1.2 m/min, and the thickness of the cast steel plate blank is 200-360 mm;
heating: heating the steel plate blank to 1100-1150 ℃ for 3-5 hours; the reason for this heating temperature is that the temperature below 1100 ℃ is not sufficient to completely dissolve the alloying elements into the austenite, and the finishing temperature required for hot rolling cannot be ensured. And higher than 1150 ℃, so that the coarsening of original austenite grains is obvious, and the low-temperature toughness of the steel plate can be obviously reduced.
Rolling: rolling the heated steel plate blank, performing first-stage rolling to obtain an intermediate blank, and performing second-stage rolling on the intermediate blank, wherein the initial rolling temperature of the first-stage rolling is 950-1100 ℃, the initial rolling temperature of the second-stage rolling is 850-900 ℃, and the final rolling temperature of the second-stage rolling is 800-860 ℃; the rolling temperature is selected to meet the mechanical property requirement of the corrosion-resistant steel, the temperature of 950-1100 ℃ is an austenite recrystallization region, the temperature of 850-900 ℃ is an austenite non-recrystallization region, and the ratio of the thickness of the intermediate blank to the thickness of the steel plate obtained after the two-stage rolling is not less than 2.5: 1, the cumulative reduction rate of the first-stage rolling and the second-stage rolling is not less than 50%.
Online cooling: and cooling the rolled steel plate to 500-600 ℃, wherein the cooling rate is 5-20 ℃/s, and obtaining the steel plate.
According to the mechanical property requirement of the steel plate, different rolling temperatures and cooling rates of non-recrystallization regions can be selected. For high-strength steel with yield strength requirement ≧ 355MPa level (36kg level) and meeting the requirement of impact temperature of-60 ℃, the initial rolling temperature of two-stage rolling is preferably 850-900 ℃, the final rolling temperature range is 840-860 ℃, the cooling mode is multi-stage laminar cooling, the cooling rate is controlled at 5-15 ℃/s, and the rolled steel plate is cooled to 550-600 ℃. The volume fraction of pearlite in the microstructure of the obtained steel plate is less than or equal to 30 percent.
For high-strength steel with yield strength requirements of 390MPa or more (40kg grade) and 420MPa grade and meeting the requirements of strength and impact temperature of-60 ℃, the initial rolling temperature of the two-stage rolling is preferably 850-890 ℃, the final rolling temperature is preferably 800-840 ℃, and then the steel plate is cooled to 500-560 ℃ at a cooling rate of 7-20 ℃/s. The volume fraction of bainite in the microstructure of the obtained steel plate is less than or equal to 35 percent.
Cooling under the line: shearing the steel plate with the thickness of less than 40mm of the finished steel plate, and carrying out offline transportation to a finished product stacking area; and (3) for the steel plate with the thickness of more than or equal to 40mm of the finished steel plate, stacking and slow cooling are carried out after straightening, the slow cooling starting temperature is 250-400 ℃, the stacking time is not less than 24 hours, and then shearing and unloading are carried out to a finished product stacking area.
The corrosion-resistant steel plate manufactured by the method has the thickness of 8-50 mm, has excellent comprehensive mechanical property, is suitable for high-heat input welding, has excellent corrosion resistance through the corrosion evaluation method specified by IMO, and can be used under the condition of no coating protection.
The parameters of the heating-rolling-cooling control process in examples 1 to 10 are shown in Table 2:
TABLE 2
Figure BDA0003365352070000131
In Table 2, examples 1 to 3 are steels requiring a yield strength of 355MPa or more; examples 4 to 6 are steels requiring 390MPa of yield strength. Examples 6 to 10 are steels requiring 420MPa of yield strength. The difference between the finishing temperature and the starting water cooling temperature is because the temperature naturally decreases during transportation.
The mechanical properties of examples 1 to 10 are shown in Table 3:
TABLE 3
Figure BDA0003365352070000141
As can be seen from Table 3, the 355MPa steel provided by the invention has the yield strength of 367-402 MPa, the tensile strength of 512-526 MPa and the elongation after fracture of more than 25.5%; the impact toughness is between 244J and 329J under the condition of-60 ℃; fracture toughness satisfies CTOD-10℃Not less than 0.82mm, higher than the standard of ship gauge not less than 0.40 mm.
The 390MPa steel provided by the invention has the yield strength of 395-435 MPa, the tensile strength of 518-572 MPa and the elongation after fracture of more than 24.5%; under the condition of-60 ℃, the impact toughness is between 254J and 332J; fracture toughness satisfies CTOD-10℃Not less than 0.90mm and not less than 0.40mm higher than the ship gauge.
The yield strength of the 420MPa steel provided by the invention is 435-475 MPa, the tensile strength is 565-602 MPa, and the elongation after fracture is 22.5%The above; the impact toughness is between 198J and 232J at the temperature of minus 60 ℃; fracture toughness satisfies CTOD-10℃Not less than 0.80mm, far higher than the standard of ship gauge not less than 0.40 mm.
In conclusion, the corrosion-resistant steel of each steel grade has good mechanical property stability and a margin of strength and toughness indexes. Can fully meet the material design requirements of high-strength and high-toughness easy-welding corrosion-resistant steel for oil ships.
The mechanical properties of the joints of examples 1-10 after 240KJ/cm welding are shown in table 4:
TABLE 4
Figure BDA0003365352070000151
As can be seen from Table 4, after the steel provided by the invention is welded at 240KJ/cm, the tensile strength, the elongation and the hardness parameters still conform to the ship gauge, and the impact toughness of a welded joint at-40 ℃ is not less than 170J, which is far higher than the ship gauge.
Examples 1-10 corrosion rate measurements for corrosion resistant steels for upper deck based on the IMO289(87) standard are shown in table 5:
TABLE 5
Figure BDA0003365352070000152
Figure BDA0003365352070000161
It is apparent from Table 5 that the ECL corrosion rate (25-year extrapolated corrosion rate) of the steel provided by the present invention is less than or equal to 2.0mm, which meets the standard. Moreover, the height of the corrosion step in the embodiment 4 is 12 μm, which is far from meeting the standard, can be visually seen through the graphs in FIGS. 5 to 6.
Examples 1 to 10 corrosion rates of corrosion-resistant steels for inner base plates based on the IMO289(87) standard are shown in Table 6:
TABLE 6
Figure BDA0003365352070000162
It is apparent from table 6 that the average annual corrosion rate of the steel provided by the present invention is not more than 0.72mm, which meets the IMO standard, and the height of the corrosion step also meets the IMO standard. From fig. 3 to 4, it can be seen that the height of the etching step in the embodiment 7 is 4 μm, which is better than the value required by the IMO standard.
In conclusion, the high-heat input welded low-temperature-resistant corrosion-resistant steel for the cargo oil tank meets the requirements of the ship gauge, has the performance far exceeding the requirements of the ship gauge, has good corrosion resistance, has excellent low-temperature toughness at the temperature of minus 60 ℃, and still has good obdurability when the welding heat input reaches 240KJ/cm, thereby meeting the application technical requirements of materials required for constructing the cargo oil tank of the oil tanker in the airlines in the extreme regions.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. The low-temperature-resistant corrosion-resistant steel for the cargo oil tank welded at high heat input is characterized by comprising the following chemical components in percentage by weight:
c: 0.04-0.13%, Si: 0.10 to 0.40%, Mn: 0.60-1.30%, P: 0.005-0.012%, S is less than or equal to 0.006%, Al: 0.01 to 0.05%, Sn: 0.03 to 0.15%, Nb: 0.005-0.020%, Ti: 0.005-0.025%, Ni: 0.15 to 0.40%, Cu: 0.15 to 0.50%, Cr: 0.10 to 0.25%, Ca: 0.007 to 0.024%, and the balance of Fe and inevitable impurities.
2. A high heat input welded, low temperature resistant, corrosion resistant cargo tank steel as claimed in claim 1 further comprising in weight percent: sb: 0.02-0.15%, W: 0.03 to 0.10%, Mo: 0.05-0.15%, RE: 0.05-0.10% of one or more of the following components.
3. The high heat input welded, low temperature resistant, corrosion resistant cargo oil tank steel of claim 1 wherein the unavoidable impurities include N, H, O, and the weight percent of N is 0.0020 to 0.0060%, the weight percent of H is 0.00015% or less, and the weight percent of O is 0.0020% or less.
4. A high heat input welded, low temperature resistant, corrosion resistant cargo oil tank steel according to claim 3, wherein Ti/N is 2.43 to 3.56.
5. The high heat input welded, low temperature resistant, corrosion resistant cargo oil tank steel of claim 1, wherein Ni + Cu is 0.35% or more, and Ni/Cu is 0.70 or more; Ca/S is 1.8 to 4.
6. A method for manufacturing low-temperature-resistant and corrosion-resistant steel for a cargo oil tank by high heat input welding is characterized by comprising the following steps:
heating: heating a steel slab having the composition of any one of claims 1 to 5 to 1100 ℃ to 1150 ℃ for 3 to 5 hours;
rolling: rolling the heated steel plate blank, performing first-stage rolling to obtain an intermediate blank, and performing second-stage rolling on the intermediate blank, wherein the initial rolling temperature of the first-stage rolling is 950-1100 ℃, the initial rolling temperature of the second-stage rolling is 850-900 ℃, and the final rolling temperature of the second-stage rolling is 800-860 ℃;
online cooling: and cooling the rolled steel plate to 500-600 ℃, wherein the cooling rate is 5-20 ℃/s, and obtaining the steel plate.
7. The method of manufacturing a high heat input welded, low temperature resistant, corrosion resistant steel for cargo oil tanks according to claim 6 wherein: in the rolling process, the finishing temperature of the two-stage rolling is 840-860 ℃; in the on-line cooling process, the rolled steel plate is cooled to 550-600 ℃, the cooling rate is 5-15 ℃/s, and the volume fraction of pearlite of the cooled steel plate is less than or equal to 30%.
8. The method of manufacturing a high heat input welded, low temperature resistant, corrosion resistant steel for cargo oil tanks according to claim 6 wherein: in the rolling process, the initial rolling temperature of the second-stage rolling is 850-890 ℃, and the final rolling temperature of the second-stage rolling is 800 ℃/s-840 ℃; in the on-line cooling process, the rolled steel plate is cooled to 500-560 ℃, the cooling rate is 7-20 ℃/s, and the volume fraction of bainite of the cooled steel plate is less than or equal to 35%.
9. The method of manufacturing a high heat input welded, low temperature resistant, corrosion resistant steel for cargo oil tanks according to claim 6 wherein:
also includes the offline cooling: and (3) straightening a steel plate with the thickness of more than or equal to 40mm of a finished steel plate, stacking and slowly cooling the steel plate, wherein the slow cooling starting temperature is 250-400 ℃, the stacking time is not less than 24 hours, and then shearing the steel plate, and transporting the steel plate to a finished product stacking area.
10. The method of manufacturing a high heat input welded, low temperature resistant, corrosion resistant steel for cargo oil tanks according to claim 6 wherein:
in the rolling process, the ratio of the thickness of the intermediate blank to the thickness of the finished steel plate is not less than 2.5, and the cumulative reduction rate of the first-stage rolling and the second-stage rolling is not less than 50%.
CN202111401895.6A 2021-11-19 2021-11-19 High heat input welded low temperature resistant corrosion resistant steel for cargo oil tank and manufacturing method thereof Pending CN114058975A (en)

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