CN114107800B - Longitudinal variable-thickness steel plate for upper deck of crude oil cargo oil tank and production method - Google Patents
Longitudinal variable-thickness steel plate for upper deck of crude oil cargo oil tank and production method Download PDFInfo
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Abstract
The invention relates to a longitudinal variable-thickness steel plate for an upper deck of a crude oil cargo oil tank, which is characterized by comprising the following chemical components in percentage by weight: 0.020-0.080% of C, 0.10-0.50% of Si, 0.90-1.50% of Mn, 0.015-0.045% of Nb, 0.020-0.060% of V, 0.005-0.018% of Ti, 0.18-0.34% of Cu, 0.10-0.33% of Ni, 0.08-0.19% of Cr, 0.15-0.25% of Sn, 0.06-0.20% of Sb, 0.0120-0.0160% of N, 0.008-0.015% of P, less than or equal to 0.005% of S, 0.015-0.030% of Als, and the balance of Fe and inevitable impurities. The steel plate has excellent mechanical property and corrosion resistance.
Description
Technical Field
The invention relates to the technical field of metal material production, in particular to a longitudinal variable-thickness steel plate for an upper deck of a crude oil cargo oil tank and a production method thereof.
Background
In recent years, the crude oil consumption and import quantity of China are gradually increased year by year and are the second largest petroleum consumption country in the world, and the crude oil in China has high external dependence degree which is more than 65%, so the transportation safety of the crude oil is vital to the energy strategy of China, more than 90% of the imported crude oil is transported by means of large oil tankers (VLCC), and the crude oil contains H, for example 2 S、Cl - And the corrosive media can corrode oil tankers, oil storage tanks and the like, which is the biggest potential safety hazard in the crude oil storage and transportation process. Aiming at the problem of the operation safety of oil tankers, the international maritime affairs association (IMO) has increasingly strict requirements on corrosion resistance of cargo oil tanks of offshore crude oil tankers, the standard of a protective coating is promoted, and meanwhile, corrosion-resistant steel is provided as a substitute measure for further promoting the corrosion resistance. The corrosion-resistant steel replaces a protective coating, has the remarkable advantages of economy, environmental protection and energy conservation, and is a great hotspot of the current research.
The longitudinal variable thickness (LP) steel plate is a steel plate having a thickness varying in a length direction, and the longitudinal thickness thereof is varied by continuously changing the opening degree of a roll during rolling, and may be divided into 10 different shapes according to the thickness variation manner. The LP steel plate has unique advantages in optimizing the design of structural sections of a ship body and the like because the thickness of the LP steel plate can be changed according to the load bearing condition. Depending on the design, LP steel plates of at least 8 shapes may be used in the hull structure. The LP steel plate is applied to reduce the amount of steel used and the number of welding operations, and also to improve the workability by making the joints thicker, such as omitting a backing plate and taper processing. Therefore, the LP steel plate is a reduced and economical steel plate, and is favored by manufacturers and users at home and abroad.
At present, corrosion-resistant steel and LP steel plate have been applied, but the production and application of longitudinally-thickened ship plates having corrosion resistance properties have not been reported. The name is "a corrosion-resistant steel for cargo oil tank bottom plate of crude oil carrier", application number: 201210562247.3 discloses corrosion-resistant steel for a cargo oil tank bottom plate of a crude oil tanker, which comprises the following chemical components: 0.04 to 0.12 percent of C, 0.10 to 0.50 percent of Si, 0.70 to 1.60 percent of Mn, 0.003 to 0.03 percent of P, less than 0.005 percent of S, 0.10 to 0.50 percent of Ni, 0.10 to 0.50 percent of Cu, 0.005 to 0.05 percent of Nb, 0.005 to 0.05 percent of Ti, 0.01 to 0.05 percent of Al, 0.001 to 0.003 percent of Ca, 0.05 to 0.12 percent of Sn and 0.02 to 0.15 percent of Mo, wherein Sn and Mo are main corrosion-resistant elements, and the corrosion-resistant steel plate has good corrosion resistance through smelting-rolling and other processes, but has slightly poor strength and toughness, the strength is only 36Kg grade, the toughness is only-20 ℃, the use requirement is far not met, and the shape of the steel plate has the same thickness. The name is 'a corrosion-resistant steel plate of a base plate of a cargo oil tank of a crude oil tanker and a manufacturing method thereof', application numbers are as follows: patent 201611077373.4 discloses a corrosion-resistant steel plate of a base plate of a crude oil cargo oil tank, which comprises the following chemical components: 0.015 to 0.085 percent of C, 0.10 to 0.50 percent of Si, 0.05 to 2.5 percent of Mn, 0.003 to 0.030 percent of P, less than or equal to 0.008 percent of S, 0.005 to 0.30 percent of Cr, 0.005 to 0.5 percent of Mo, 0.005 to 0.50 percent of Cu, 0.005 to 0.50 percent of Ni and 0.01 to 0.12 percent of Al. The corrosion-resistant steel plate is obtained by adopting processes such as high pressure and the like, the yield strength of the steel plate is more than or equal to 235MPa, the tensile strength is 400-660 MPa, and the impact energy at minus 60 ℃ is more than or equal to 120J. However, the steel of this patent contains a high Mn content of at most 2.5%, and tends to suffer from core segregation, which affects the properties of the steel sheet, and is also a steel sheet of an equal thickness. The name is 'manufacturing method of corrosion-resistant steel plate for upper deck of cargo oil tank of crude oil tanker and steel plate', application number: 201310235149.3, which discloses a corrosion-resistant steel plate for the upper deck of a crude oil cargo tank, comprises the following chemical components: 0.02 to 0.25 percent of C, 0.05 to 0.5 percent of Si, 0.1 to 2.0 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.01 percent of S, 0.05 to 0.20 percent of Cu, 0.05 to 2 percent of Ni, 0.01 to 5 percent of Cr, 0.001 to 1 percent of W, 0.001 to 0.1 percent of Zr, 0.0002 to 0.01 percent of Ca, 0.005 to 0.1 percent of Ti, 0.001 to 0.008 percent of N, and 0.020 to 0.1 percent of Als. The corrosion-resistant steel plate is obtained by adopting the technological means of high pressure, TMCP and the like, the yield strength of the steel plate is 430MPa, the tensile strength of the steel plate is 506MPa, the content of each element is higher, the production cost of the steel plate is increased, the highest content of C is 0.25%, the corrosion resistance of the steel plate is greatly reduced, and the steel plate is also the steel plate with the same thickness. The name is 'wedge-shaped weather-proof bridge steel with uniform thin and thick end performance and production method thereof', application number: 201811329589.4, which discloses a wedge-shaped atmospheric corrosion resistant steel plate, comprising the following chemical components: 0.07 to 0.09 percent of C, 0.15 to 0.35 percent of Si, 1.15 to 1.5 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, 0.3 to 0.42 percent of Cu, 0.3 to 0.48 percent of Ni, 0.06 to 0.10 percent of Mo, 0.38 to 0.52 percent of Cr, 0.06 to 0.08 percent of Nb, 0.01 to 0.03 percent of V and 0.012 to 0.025 percent of Ti. The strength grade of the steel plate is 355-395 MPa, the transverse elongation is more than or equal to 23 percent, the average value of longitudinal impact energy at minus 20 ℃ is more than or equal to 150J, and the steel plate has high strength and low toughness. However, this patent contains a high Nb content, resulting in an increase in the cost of the steel sheet. The name is 345 MPa-level LP steel plate and a production method thereof, and the application number is as follows: 201710068867.4, a 390 MPa-level LP steel plate and a production method thereof, and application numbers: 201710068896.0, a 420 MPa-grade LP steel plate and a production method thereof, wherein the application number is as follows: 201710068882.9, which discloses a wedge-shaped steel plate with different strength levels and a thin end and a thick end, wherein the steel plate is cast into a continuous casting blank with chemical components changing along the length by adopting molten steel with different components of two tanks and then is rolled, so that the mechanical property of the rolled wedge-shaped steel plate tends to be uniform, but the process is complex, the wedge-shaped steel plate is only suitable for the wedge-shaped steel plate with the thin end and the thick end, and the steel plate produced by the above patent has no corrosion resistance. And the production of the corrosion-resistant ship plate with the variable longitudinal thickness is not reported at present.
In summary, the following problems mainly exist in the production of the steel plate for the cargo oil tank at present.
1) Higher alloying elements, high production cost and deteriorated steel plate performance.
2) The steel plate has low strength and toughness grade and can not meet the use requirement.
2) The steel plate is a steel plate with equal thickness, which is not beneficial to the optimization of the hull structure.
Disclosure of Invention
The invention aims to solve the technical problem of providing a longitudinal variable-thickness steel plate for an upper deck of a crude oil cargo oil tank and a production method thereof, wherein the steel plate has excellent mechanical property and corrosion resistance.
In order to realize the purpose, the invention adopts the following technical scheme:
a longitudinal variable-thickness steel plate for an upper deck of a crude oil cargo tank comprises the following chemical components: 0.020-0.080% of C, 0.10-0.50% of Si, 0.90-1.50% of Mn, 0.015-0.045% of Nb, 0.020-0.060% of V, 0.005-0.018% of Ti, 0.18-0.34% of Cu, 0.10-0.33% of Ni, 0.08-0.19% of Cr, 0.15-0.25% of Sn, 0.06-0.20% of Sb, 0.0120-0.0160% of N, 0.008-0.015% of P, less than or equal to 0.005% of S, 0.015-0.030% of Als, and the balance of Fe and inevitable impurities.
The components have the functions:
c: the main strengthening elements in the steel are main elements for improving the hardenability of the steel; if the content is too low, the amount of carbide and the like produced is reduced, and the effect of refining grains during rolling is impaired. When the content is too high, the content of cementite in the steel increases, which is detrimental to the low-temperature toughness, weldability, and corrosion resistance of the steel sheet. Therefore, the cost, the performance and other factors are comprehensively considered, and the range of C is controlled to be 0.020-0.080%.
Si: the necessary elements for steelmaking deoxidation have strong solid solution capacity in steel and can play a certain strengthening role, but the low-temperature toughness and the welding performance of the steel are seriously damaged due to too high content. The range of Si is controlled to be 0.10-0.50%.
Mn: can delay the transformation of ferrite and pearlite in steel, greatly increase the hardenability of the steel, reduce the brittle transformation temperature of the steel and improve the impact toughness, but the Mn content is too high, so that segregation is easily formed in the steel, the plasticity and the toughness of the steel are adversely affected, and the corrosion resistance of the steel is also easily reduced. Comprehensively considering, the range of Mn is controlled to be 0.90-1.50%.
Nb: grain refining elements, wherein carbon and nitride particles of the Nb which is not dissolved during heating are distributed on austenite grain boundaries, so that the austenite grains of the steel can be prevented from growing during heating; the invention can effectively delay the recrystallization of the deformed austenite, prevent the austenite grains from growing large, refine ferrite grains and improve the strength and toughness of the steel. The range of Nb is controlled to be 0.012 percent to 0.045 percent.
V: the strong carbide forming element has small influence on austenite recrystallization, and the large precipitation of V carbon and nitride can play the roles of refining and strengthening crystal grains at low temperature, so that the strength of the steel plate is improved, and simultaneously, the precipitation amount of the longitudinal variable-thickness steel plate at the thin and thick positions is controlled by utilizing the matching effect of the strong carbide forming element and another element N, so that the non-uniform mechanical property caused by the thickness difference in the length direction is compensated, and the property uniformity in the length direction is realized. The range of V is controlled to be 0.020-0.060%.
Cu: the corrosion resistance of the steel can be effectively improved, and the steel and P can form various composite salts together, so that the corrosion resistance of the steel is further improved; meanwhile, the strength and low-temperature toughness of the steel can be improved; cu and Ni are coupled and gathered and distributed in a thickening way at a corrosion interface, so that the corrosion resistance of the steel in an acid environment can be improved. However, if the content is too high, the hot brittleness of the steel deteriorates and hot cracks are easily generated. The Cu content is controlled to be 0.18-0.34%.
Ni: the corrosion resistance of the steel is obviously improved, the Ni element is enriched in the rust layer near the surface of the steel, and the rust layer enriched with the alloy element has ion selective permeability and can prevent Cl < - > from permeating, so that the metal in the rust layer is protected. Meanwhile, nickel can improve the low-temperature toughness of the steel. However, the addition of a large amount of nickel causes a considerable increase in the cost of steel due to its high price. Controlling the range of Ni to be 0.10-0.33%.
Cr: cr is mainly segregated at the grain boundary in the steel, so that the hardenability of the steel is improved, and the strength and toughness of the steel are improved. The addition of a small amount of Cr can effectively delay the initial corrosion of the steel plate, but when the Cr content is too high, the corrosion resistance of the steel can be reduced along with the prolonging of the corrosion time of an acid environment. The range of Cr is controlled to be 0.08-0.19 percent.
Sn: when a small amount of tin is added into the steel, the corrosion resistance of the steel can be improved, and the self-corrosion potential of the steel in an acid environment is obviously improved, so that the electrochemical corrosion performance of the steel in the acid corrosion environment is effectively improved. The strength of the steel can be improved without greatly affecting the plasticity. The range of Sn is controlled to be 0.15-0.25%.
Sb: the mechanical properties of the steel are adversely affected, the strength of the steel is generally reduced, the brittleness of the steel is generally increased, but if a certain amount of antimony is added into the steel, the corrosion resistance and the wear resistance of the steel are improved to different degrees, and when the antimony is compounded with Sn, the corrosion resistance of the steel is further improved. The range of Sb production is 0.06% -0.20%.
N: the important toughening element of the invention is that N exists mainly in two states of a free state and a compound state in the steel, wherein the existence of the former is unfavorable for the toughness of the steel plate, and the existence of the latter has good influence on the comprehensive performance of the steel plate. In the case of a steel containing V, most of V does not sufficiently exhibit its precipitation strengthening action when nitrogen is deficient in the steel. In addition, the nitrogen-containing steel not only eliminates the cost increase caused by degassing and refining denitrogenation in the steel-making process, but also can fully play the role of microalloy elements by increasing nitrogen in the steel, saves the using amount of alloying elements and greatly reduces the production cost. The range of N is controlled to be 0.0120% -0.0160%.
P: improve the corrosion resistance of steel, can form various composite salts when being coexisted with Cu element, ensures that the crystal grains of the inner rust layer are fine and compact, and can resist Cl - The corrosion rate of the steel is reduced, but too high a content is detrimental to the low temperature toughness and weldability of the steel. The range of the control P is 0.010 percent to 0.030 percent.
Al: the strong deoxidizer produces highly fine and ultra-microscopic oxide in steel, and plays a role in refining grains. The range of Als is controlled to be 0.015-0.030%.
A production method of a longitudinal variable-thickness steel plate for an upper deck of a crude oil cargo oil tank comprises the following steps of smelting, continuous casting, heating by a heating furnace and rolling, and comprises the following specific steps:
(1) Smelting
a. Adjusting components during converter smelting;
b. refining the molten steel, and feeding Ca-Si wires at the later stage of refining, wherein the quantity of the Ca-Si wires is not less than 500m;
c. RH processing is carried out on the refined molten steel for 20-60min, nitrogen is blown in the whole process of RH processing, and the final N content range of steel is ensured; 0.0120 to 0.0160 percent of N;
(2) Continuously casting molten steel to obtain a required casting blank, and controlling the superheat degree of a tundish to be 25-35 ℃;
(3) Stacking and slowly cooling the casting blanks, wherein the slow cooling time is not less than 36 hours;
(4) Heating the casting blank to 1110-1180 ℃, wherein the heating rate is 10-20 ℃/min, and the heat preservation time is 40-240 min;
(5) Rolling of
a. A rough rolling stage: rolling the heated casting blank to the thickness which is 1.5 to 2.5 times of the maximum thickness of the final LP steel plate, wherein the starting rolling temperature of the casting blank is 1000 to 1100 ℃, and obtaining an intermediate blank after rolling;
b. a finish rolling stage: the intermediate blank obtained in the step a) is heated to 840-880 ℃, then is rolled with variable thickness, and is rolled according to the shape and the inclination required by the steel plate, and the final rolling temperature of the steel plate meets the LP steel plate
The temperature at the thickness is 780-830 ℃;
(6) Cooling down
a. The rolled steel plate is subjected to accelerated cooling, and the starting cooling temperature meets the LP steel plate
The temperature of the thick part is 720-800 ℃, and the temperature of the red returning meets the LP steel plate
The thickness is 520-650 ℃;
b. and cooling the steel plates after the re-reddening is finished to room temperature, wherein the steel plates with the maximum thickness of more than or equal to 40mm are stacked and slowly cooled, the stacking temperature is more than 350 ℃, and the stacking time is more than 12h.
In the steps (5) and (6), t is max Maximum thickness of LP steel plate, t min Is the minimum thickness of the LP steel plate.
Compared with the prior art, the invention has the beneficial effects that:
by designing the chemical components and the rolling process of the longitudinal variable-thickness steel plate, the steel plate has excellent mechanical property and corrosion resistance. The yield strength of the alloy reaches more than 380MPa, the elongation after fracture is more than 26.0, the impact absorption energy at minus 40 ℃ is more than 250J, the impact absorption energy at minus 60 ℃ is more than 200J, and the annual average corrosion rate CR is less than or equal to 0.50 mm/year. The invention is suitable for the LP steel plate used on the upper deck of the cargo oil tank, fully exerts the strengthening effect of elements in the steel, and makes up the uneven mechanical property caused by the thickness difference in the length direction of the steel plate, thereby realizing the uniformity of the mechanical property in the length direction of the steel plate, and finally the uniformity of the mechanical property of the steel plate in the length direction is good, and the strength difference of thick and thin positions is within 25 MPa.
Drawings
FIG. 1 is a metallographic structure diagram of a thin end of a steel plate according to example 3.
FIG. 2 is a metallographic structure drawing of a thick end of a steel plate in example 3.
FIG. 3 distribution diagram of precipitated phases at the thin end of the steel sheet of example 3.
FIG. 4 is a distribution diagram of precipitated phases at the thick end of the steel sheet of example 3.
Detailed Description
The following further illustrates embodiments of the invention:
a method for producing a longitudinal variable-thickness steel plate for an upper deck of a crude oil cargo tank,
1) The steel sheet was smelted according to the designed chemical composition, as shown in table 1.
Table 1: chemical composition of example Steel (wt%)
2) The obtained molten steel was subjected to continuous casting, heating, rolling, and cooling to obtain a longitudinally thickened steel sheet, the heating process being shown in Table 2, the rolling process being shown in Table 3, and the cooling process being shown in Table 4.
Table 2: example heating Process
| Numbering | Degree of superheat/. Degree.C | Slow cooling time/h | Heating temperature/. Degree.C | Temperature rise rate/° C/min | Holding time/min |
| 1 | 27 | 38 | 1125 | 13 | 60 |
| 2 | 29 | 42 | 1115 | 14 | 100 |
| 3 | 32 | 50 | 1145 | 16 | 150 |
| 4 | 33 | 54 | 1175 | 19 | 200 |
| 5 | 28 | 45 | 1155 | 18 | 180 |
| 6 | 30 | 52 | 1135 | 17 | 120 |
Table 3: rolling Process of examples
Table 4: example Cooling Process of Steel
| Number of | Cold start temperature/. Degree C | Temperature of re-reddening/. Degree.C | Stacking temperature/. Degree.C | Stacking time/h |
| 1 | 747 | 540 | 360 | 15 |
| 2 | 735 | 610 | 372 | 20 |
| 3 | 754 | 630 | - | - |
| 4 | 776 | 550 | 381 | 36 |
| 5 | 795 | 640 | 413 | 24 |
| 6 | 765 | 570 | 392 | 18 |
The mechanical properties and corrosion properties of the steels according to the examples are shown in table 5, and corrosion properties were evaluated by the corrosion resistance test method for the upper deck specified in "guidelines for testing corrosion resistant steel for cargo oil tanks of crude oil tanker" of classification of ships, china.
Table 5: mechanical Properties of examples
It will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the principles of the invention, and these modifications and variations also fall within the scope of the claims of the present invention. The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered as the technical solutions and their concepts of the present invention within the technical scope of the present invention.
Claims (1)
1. A production method of a longitudinal variable-thickness steel plate for an upper deck of a crude oil cargo oil tank is characterized in that the longitudinal variable-thickness steel plate for the upper deck of the crude oil cargo oil tank comprises the following chemical components: 0.020-0.080% of C, 0.10-0.50% of Si, 0.90-1.50% of Mn, 0.015-0.045% of Nb, 0.020-0.060% of V, 0.005-0.018% of Ti, 0.18-0.34% of Cu, 0.10-0.33% of Ni, 0.08-0.19% of Cr, 0.15-0.25% of Sn, 0.06-0.20% of Sb, 0.0120-0.0160% of N, 0.008-0.015% of P, less than or equal to 0.005% of S, 0.015-0.030% of Als, and the balance of Fe and unavoidable impurities; the production method comprises the following steps of smelting, continuous casting, heating by a heating furnace and rolling, and comprises the following specific steps:
(1) Smelting
a. Adjusting components during converter smelting;
b. refining the molten steel, and feeding Ca-Si wires at the later stage of refining, wherein the amount of the Ca-Si wires is not less than 500m;
c. RH processing is carried out on the refined molten steel for 20-60min, nitrogen is blown in the whole process of RH processing, and the final N content of steel is ensured; the content of N is 0.0120 to 0.0160 percent;
(2) Continuously casting molten steel to obtain a required casting blank, and controlling the superheat degree of a tundish to be 25-35 ℃;
(3) Stacking and slowly cooling the casting blanks for not less than 36 hours;
(4) Heating the casting blank to 1110-1180 ℃, wherein the heating rate is 10-20 ℃/min, and the heat preservation time is 40-240 min;
(5) Rolling of
a. A rough rolling stage: rolling the heated casting blank to the thickness which is 1.5 to 2.5 times of the maximum thickness of the final LP steel plate, wherein the starting rolling temperature of the casting blank is 1000 to 1100 ℃, and obtaining an intermediate blank after rolling;
b. and (3) finish rolling stage: the intermediate blank obtained in the step a) is heated to 840-880 ℃, then is rolled with variable thickness, and is rolled according to the shape and the inclination required by the steel plate, and the final rolling temperature of the steel plate meets the LP steel plate
The temperature at the thickness is 780-830 ℃; wherein: t is t max Maximum thickness of LP steel plate, t min Is the most excellent of LP steel plateSmall thickness;
(6) Cooling
a. Accelerated cooling is carried out on the rolled LP steel plate, and the starting cooling temperature meets the LP steel plate
The temperature of the thick part is 720-800 ℃, and the temperature of the red returning meets the LP steel plate
The thickness is 520-650 ℃;
b. and cooling the steel plates after the re-reddening to room temperature, wherein the steel plates with the maximum thickness of more than or equal to 40mm are stacked and slowly cooled, the stacking temperature is more than 350 ℃, and the stacking time is more than 12 hours.
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