CN117626116A - Thick high-strength high-toughness low-temperature-resistant rolled H-shaped steel for low-cost ship structure and preparation method thereof - Google Patents
Thick high-strength high-toughness low-temperature-resistant rolled H-shaped steel for low-cost ship structure and preparation method thereof Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
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Abstract
The invention belongs to the technical field of metallurgy, and particularly relates to thick high-strength and high-toughness low-temperature-resistant rolled H-shaped steel for a low-cost ship structure and a preparation method thereof, wherein the H-shaped steel comprises the following chemical components in percentage by weight: c:0.05 to 0.07 percent, si: less than or equal to 0.25 percent, mn:1.20 to 1.50 percent, V:0.11 to 0.15 percent, A1t:0.035 to 0.055%, cr:0.3 to 0.5 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.005 percent, and N:0.010 to 0.015 percent, O is less than or equal to 0.004 percent, and the balance is Fe and unavoidable impurities. The preparation method comprises the following steps: molten iron pretreatment, 120 ton converter smelting, ladle argon blowing, LF refining, special-shaped continuous casting blank casting, slow cooling of a continuous casting blank slow cooling pit, heating by a heating furnace, BD rough rolling, intermediate blank turning operation, finish rolling TM reversible rolling, inter-frame cooling, water cooling of a flange phase change area after rolling, intensive slow cooling of a cooling bed, straightening by a straightener and finishing treatment of finished products. The high-strength high-toughness hot-rolled H-shaped steel with stable performance above 420MPa grade is obtained on a general hot-rolled H-shaped steel rolling mill.
Description
Technical Field
The invention belongs to the technical field of metallurgy, and particularly relates to thick high-strength high-toughness low-temperature-resistant rolled H-shaped steel for a low-cost ship structure and a preparation method thereof.
Background
Steel is an important raw material for building shipbuilding structures, and occupies 20-30% of the ship building cost. The steel consumption for hull construction is about 60% of the total mass of the ship, wherein the section bar accounts for more than 10%. With the rise of the manufacturing process and the technical level of ships, various special-purpose ships are gradually increased, including various bulk carriers, ultra-large tankers, floating production oil storage ships, container ships, LNG ships, jack-up drilling platforms and the like. As the demands for enlargement, weight reduction and speed increase of ships increase, the strength and toughness of the hot rolled H-section steel for ships in special use are gradually improved. On one hand, the yield strength is gradually increased from 355MPa to 390/420MPa, and meanwhile, the toughness is also improved from the normal-temperature impact toughness under the common working condition to the level of-40 ℃ or even-60 ℃ to reach the F level, thereby meeting the requirement of rapid environmental adaptability when reaching a designated place and being convenient for the development and operation of ships in all sea areas worldwide.
Therefore, different enterprises develop high-grade high-strength and high-toughness H-shaped steel successively, and upgrading of products are realized. Particularly for the preparation of large-size thick-flange hot rolled H-section steel, the preparation differences of different enterprises and production lines can be found in the published patent.
The patent of application No. CN201510498771.2 designs a 420MPa grade hot rolled H-shaped steel with excellent low temperature toughness and a production method thereof, wherein the chemical components comprise 0.06-0.12% of C, 0.20-0.40% of Si, 1.20-1.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.050-0.070% of V, 0.10-0.20% of Ni, 0.0050-0.0100% of N, and the balance of Fe and unavoidable impurities. According to the invention, through reasonable design of V, ni and N components and a controlled rolling and cooling process, 420MPa hot rolled H-shaped steel with excellent comprehensive performance is developed; yield strength ReH is 440-520 MPa; the tensile strength Rm is 550-650 MPa, the elongation A is more than or equal to 22 percent, and the low-temperature impact toughness KV2 at minus 40 ℃ is more than or equal to 100J. The patent control cooling adopts two-section type, the first stage is quick to cool and the second stage is air-cooled, a special cooling device is needed to meet the preparation requirements, and meanwhile, abnormal tissues are easy to generate in the later stage of cooling, so that the stability of the toughness is influenced.
The application number CN201610096590.1 relates to a hot rolled H-shaped steel with super-thick low ductile-brittle transition temperature and a production method thereof, and the hot rolled H-shaped steel comprises the following chemical components in percentage by mass: 0.08 to 0.15 percent of C, 0.10 to 0.40 percent of Si, 1.0 to 1.5 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.008 percent of S, 0.020 to 0.070 percent of V, 0.005 to 0.025 percent of Ti, 0.006 to 0.015 percent of N, 0.10 to 0.50 percent of Ni, and the balance of iron and residual trace impurities. The flange thickness of the H-shaped steel is between 25mm and 36mm, the web height is between 700mm and 1000mm, the rolling compression ratio is less than 3.5, and the H-shaped steel is produced by adopting a hot rolling process (processes such as water cooling, ultra-fast cooling, heat treatment and the like are not adopted). The yield strength of the final product is more than 420Mpa, the tensile strength is more than 500Mpa, the ductile-brittle transition temperature is lower than-65 ℃, and the product has good resistance to low-temperature Charpy impact energy of-45 to-65 ℃. The finishing temperature of the patent is controlled between 860 ℃ and 900 ℃, stable control is difficult to realize by simply relying on natural cooling, and meanwhile, the strength deviation of the upper flange and the lower flange of the H-shaped steel is larger. Meanwhile, the carbon content in the embodiment is 0.11-0.14%, and the excessively high carbon content has adverse effect on the toughness and stability.
The invention patent of application number CN201510788520.8 discloses 420 MPa-grade high-strength low-yield-ratio H-shaped steel and a preparation method thereof, wherein the H-shaped steel comprises the following chemical components in percentage by weight: 0.11 to 0.15 percent of C, 0.20 to 0.35 percent of Si, 1.35 to 1.50 percent of Mn, less than or equal to 0.035 percent of P, less than or equal to 0.025 percent of S, 0.25 to 0.30 percent of Cu, 0.40 to 0.45 percent of Cr, 0.20 to 0.30 percent of Ni, 0.20 to 0.30 percent of Nb, and the balance of iron and trace impurities. The invention realizes that the yield strength of the low yield ratio H-shaped steel is more than 427MPa, the tensile strength is more than 641MPa, and the yield ratio is 0.64-0.67. The patent adds Ni, cr and Cu corrosion resistant elements; the probability of cracking of the legs of the H-shaped steel, which is added with a certain Cu element casting blank and a finished product, is obviously improved, and the surface grinding is required to be carried out, so that the finished product rate is lower; the lack of effective cooling control means, the addition of Cr and Cu elements easily causes abnormal tissues.
The patent relates to thick 420MPa grade H-shaped steel and the preparation technology does not provide effective control means for equipment and cooling conditions; meanwhile, ni element is added in component design, so that the manufacturing cost is increased remarkably. As the yield strength of the marine low-temperature-resistant H-shaped steel is integrally improved to a level above 420MPa, the uniformity and stability of upper and lower flanges and head and tail tissues need to be improved; meanwhile, the requirement that the ship structural steel has lower ductile-brittle transition temperature is met, so that good low-temperature impact toughness is guaranteed, fatigue failure of ship steel structural parts due to low-temperature brittle fracture is avoided, and the service life and the period are shortened.
In order to improve the high consistency and uniformity of upper and lower flanges of the structural performance of the marine hot rolled H-shaped steel, the invention is specifically designed in the process aspect, meets the requirement of integral improvement of the structural performance, and simultaneously obviously reduces the cost.
Therefore, in order to meet the preparation requirement of the marine low-temperature-resistant H-shaped steel, on a domestic general-purpose X-H rolling mill for the shaped steel, the ductile-brittle transition temperature is further reduced while the yield strength of the thick H-shaped steel reaches 420MPa level through fine grain strengthening and precipitation strengthening by designing special steel turning equipment between rough rolling and finish rolling and matching with corresponding low-cost chemical component design and tissue design.
Disclosure of Invention
In order to meet the preparation requirements of high-toughness low-temperature-resistant toughness steel for ship structures in complex and changeable environments, the invention provides a low-cost high-toughness low-temperature-resistant rolled H-shaped steel for ship structures and a preparation method thereof, which are specially used for preparing structural members on the upper parts of the ship bodies.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
the thick high-strength and high-toughness low-temperature-resistant H-shaped steel for the low-cost ship structure comprises the following chemical components in percentage by weight: c:0.05 to 0.07 percent, si: less than or equal to 0.25 percent, mn:1.20 to 1.50 percent, V:0.11 to 0.15 percent, A1t:0.035 to 0.055%, cr:0.3 to 0.5 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.005 percent, and N:0.010 to 0.015 percent, O is less than or equal to 0.004 percent, and the balance is Fe and unavoidable impurities. The H-shaped steel prepared by meeting the component requirements can better meet the impact toughness requirements at different environmental temperatures.
The invention is especially suitable for preparing the flange thickness of 20-40mm thick specification steel products, but is not limited to the specification products, and other related products are also suitable for the same.
The design principle of main chemical elements in the high-strength hot-rolled H-shaped steel is as follows:
carbon: in order to meet the 420MPa strength level of the marine hot rolled H-shaped steel and simultaneously ensure the low-temperature impact toughness performance requirement of minus 60 ℃, the superfine ferrite and a small amount of pearlite structure are obtained, and the grain size is more than 9 levels. For thick H-shaped steel, the compression ratio is small, the carbon content is high, abnormal structures are easy to generate, the pearlite structure is easy to be coarse due to carbon segregation, and the carbon content is controlled within the range of 0.05-0.07% according to the comprehensive index requirement of toughness.
Manganese: mn can stabilize austenite structure in steel, increase hardenability of steel, and improve strength of steel by solid solution strengthening. The deformation and the tissue transformation of different parts of the H-shaped steel are different, and too much Mn belongs to segregation elements, so that larger performance difference is easy to cause. In order to ensure the strength of the marine steel and reduce segregation, the upper limit of Mn content is not more than 1.5 percent, and the Mn content is controlled to be 1.20 to 1.50 percent by comprehensively considering the invention.
Aluminum: al is used as a strong deoxidizing element, so that the cleanliness of steel is easy to be improved; and simultaneously forms a large amount of AlN with N to play a role of refining grains. On the one hand, in order to ensure that the oxygen content in the steel is as low as possible, the generation probability of large-particle oxide inclusion is reduced; in addition, the AlN precipitates formed by the aluminum element and the nitrogen element in the steel can refine grains, thereby improving the strength of the steel. Therefore, the content of aluminum is controlled to be 0.035 to 0.055% in the present invention.
Chromium: cr can obviously improve the hardenability of steel in the steel, and is beneficial to stabilizing the austenitic structure and improving the transformation of the pearlite structure. Too high or too low Cr content is detrimental to hardenability and delayed fracture properties of the steel, and is liable to cause local defects. The Cr element added into the steel cannot be too high, so that local tissue segregation caused by high hardenability is avoided, and a large number of abnormal tissues such as Wittig bodies, variant pearlite and the like are avoided. The comprehensive consideration is that Cr is controlled to be 0.30% -0.50%.
Vanadium: v is taken as a strong carbonitride forming element, and V (C, N) plays a role in precipitation strengthening; in addition, the V (C, N) nano precipitated particles can be used as nucleation points of ferrite and pearlite structures, which is beneficial to the grain refinement of the structures and refines the austenite structures. Because the invention has lower C content and higher N content and less VC precipitation amount, the VC mainly exists in the form of VN in the rolling process and the cooling process after rolling, thereby playing a role in increasing precipitation strengthening. In order to meet the low temperature resistant section steel with the yield strength of 420MPa, the V content is controlled to be 0.11-0.15%.
Nitrogen: n element and V element with certain concentration in steel are combined to form VN second phase particle precipitate, so that the precipitation strengthening effect is achieved, and the strength can be remarkably improved. However, the N content is too high, so that the surface quality defect of the casting blank is easy to induce, and transverse cracks, corner cracks and the like are generated on the surface of the special-shaped blank; the nitrogen content is low, the formed VN particles are less in precipitation, and the precipitation strengthening effect is poor, so that the nitrogen content is required to be 0.011-0.015%.
Oxygen: the high oxygen content is easy to form large-particle oxide inclusion with elements such as Al, mg, ca and the like, and the low oxygen content is controlled to cause cost increase, so that the strength is ensured, and the oxygen content is required to be less than or equal to 0.004 percent in order to improve the toughness and the plasticity of the marine hot rolled steel.
The yield strength of the marine hot rolled H-shaped steel is more than or equal to 430MPa, the tensile strength is more than or equal to 530MPa, the elongation is more than or equal to 19%, and the impact energy at minus 60 ℃ is more than or equal to 180J.
The invention provides a preparation method of the hot rolled H-shaped steel for ships with the yield strength of 420MPa, which comprises the following steps: molten iron pretreatment, 120 ton converter smelting, ladle argon blowing, LF refining, special-shaped continuous casting blank casting, slow cooling of a continuous casting blank slow cooling pit, heating by a heating furnace, BD rough rolling, intermediate blank turning operation, finish rolling TM reversible rolling, inter-frame cooling, water cooling of a flange phase change area after rolling, intensive slow cooling of a cooling bed, straightening by a straightener and finishing treatment of finished products.
The soaking temperature of a heating furnace in the rolling process is 1230-1250 ℃, and the casting blank is in the furnace for 210-300 min; and in the rolling process BD rough rolling, reversible rolling is adopted to form 7-9 passes, the integral compression ratio of rough rolling is controlled to be more than 40%, the large compression ratio is ensured in the rough rolling stage, and the intermediate billet is fully recrystallized to increase the austenite nucleation rate and refine the austenite structure. The finish rolling adopts reciprocal reversible rolling for 5-7 times, the initial rolling temperature of the finish rolling is 960-980 ℃, the cooling water between the finishing mill frames is fully opened, and the final rolling temperature of the finish rolling is 760-830 ℃. Because the steel billet used by the thick-gauge section steel has large weight, in order to reduce the temperature difference between the upper flange and the lower flange, a special steel tilting machine is used for tilting steel between rough rolling and finish rolling. In order to ensure the control of the final rolling temperature, the final pass compression ratio of the finish rolling is 8-12%, and simultaneously, the rolling mill is controlled to be below 2m/s for reducing the speed; and the final pass of the finish rolling TM is fully cooled, so that the vanadium-containing carbonitride which is precipitated later can play a role in precipitation strengthening.
In order to realize the steel turning process operation after BD rough rolling, an automatic steel turning device is adopted, and particularly as shown in fig. 1, the turning operation of the upper flange and the lower flange is realized. The specific implementation process is as follows: after BD rolling, the intermediate blank is quickly moved to the middle position of the tilting gear, and after the tilting gear is stopped, the tilting gear starts to operate, and the rotation mechanism 4 is driven by the three driving gears 1-3 to realize rotation. The upper roller 6 and the lower roller 8 are driven, the upper roller and the lower roller clamp the billet 7 under the action of the upper hydraulic cylinder 5 and the lower hydraulic cylinder 9, and the rotating mechanism drives the billet to rotate under the drive of the driving gear. The upper roller and the lower roller of the device adopt driven rollers, so that sliding friction is formed between the steel billet and the rollers, and the steel billet is prevented from being scratched. The device can realize the rotation of the billet at any angle, including 45 degrees, 90 degrees and 180 degrees turning. Because of the special H-shaped shape of the H-shaped steel, the phenomenon that the cooling speed of the upper flange is faster than that of the lower flange naturally exists when the H-shaped steel is rolled, the upper flange temperature of an intermediate blank after rough rolling is lower than that of the lower flange, after the steel is turned over by using the device, the upper flange and the lower flange realize position turning, the original lower flange with high temperature is turned over and then becomes the upper flange with high temperature, the upper flange temperature of the intermediate blank after turning over is higher than that of the lower flange, the cooling speed of the upper flange is faster than that of the lower flange during subsequent finish rolling, and the upper flange temperature and the lower flange temperature gradually become the same, so that the temperature difference of the upper flange and the lower flange detection of a rolled material after final rolling is reduced to below 20 ℃. The device can also be arranged at the rolling inlet side to clamp the billet entering the rolling mill, and the clamping and feeding of the steel are realized under the cooperation of the driving roller way. The device can also be arranged at the rolling outlet side to hold the billet out of the rolling mill, so that the unstable phenomena of torsion, tilting of the buckling head and the like of the billet out of the rolling mill are avoided. Along the length direction of the billet, three devices can be arranged at the head, the middle and the tail of the conveying roller way, and when the billet is rotated, the three devices carry out linkage control to cooperatively realize the rotation of the billet. The device can produce the above quadruple effect.
According to the invention, through microalloying process design and combining the reciprocating rolling characteristic of thick-specification steel, the industrial production of the thick-specification 420 MPa-level high-strength H-shaped steel product for ships is realized.
The technical scheme of the invention has the advantages that:
1. adopting a low carbon +VN alloying +recrystalization zone to control rolling, and realizing refinement of the grain size of a matrix structure to a level above 9 levels; compared with other patents, the method removes Ni element in component design, meets the design requirement of low-cost components, adopts the mixture ratio of vanadium-nitrogen alloy and ferrovanadium to be added, and meets the cost control requirement according to the change of the adding quantity of the two alloy prices on the basis of ensuring the nitrogen content to meet the requirement.
2. By combining the characteristics of rolling H-shaped steel with different compression ratios of 20-40mm thick specification by the special-shaped blank, adopting the design of low C content matched with VN microalloying components suitable for temperature control rolling, and simultaneously improving the precipitation quantity and size of VN by adopting a mode of controlling N content in an LF refining process, the high-strength and toughness requirement of products with different specifications at minus 60 ℃ is met, so that high-strength and toughness hot-rolled H-shaped steel with stable performance above 420MPa level is obtained on a general hot-rolled H-shaped steel rolling mill.
3. The VN alloy is added in the refining process, and the N content is obviously improved while V is increased. In order to control the N content within a reasonable range and control the crack defect of a casting blank, VN alloy and ferrovanadium are required to be added according to a certain proportion, a certain manganese nitride cored wire is added in a refining process according to the N yield condition, the nitrogen content in steel is ensured to be kept within a range of 0.011-0.015%, and cracks at flange corners and web plates caused by the excessively high N content are avoided.
4. In the rolling process, steel turning operation is carried out between rough rolling and finish rolling by adopting specially designed steel turning equipment, so that the temperature difference of upper and lower flanges is obviously reduced, and the detection temperature difference of the upper and lower flanges is reduced to below 15 ℃; before the rolled piece enters the TM finishing mill, the automatic steel turning equipment is utilized to turn steel, then a roller way is properly adopted for waiting for the temperature operation, the casting blank can be turned steel for multiple times according to the stable condition, the temperature of the rolled piece is controlled to be in the range of 960-980 ℃ after 60-120 seconds, and the rolled piece enters the finishing mill for multipass reciprocating rolling, so that the effect of refining the structure is achieved.
5. The cooling water between frames and after rolling is fully opened, wherein the cooling water after rolling mainly cools the lower flange, the gap between the upper flange and the lower flange is reduced to below 20 ℃, the final rolling temperature is controlled between 760 ℃ and 830 ℃, the yield strength difference between the upper leg and the lower leg is controlled within a range of less than 15MPa, and the requirement of uniform performance is met.
6. The H-shaped steel matrix structure after rolling is fine flake pearlite and superfine proeutectoid ferrite, and the grain size is controlled within the range of 9-11 grades; the second phase particles which are stably precipitated in the steel are mainly VN, the size of the precipitated particles is less than 50nm, the proportion exceeds more than 60%, the structure uniformity is high, and the toughness is improved.
7. The profile steel has low carbon equivalent and excellent welding performance, and the carbon equivalent index is controlled below 0.42.
Drawings
FIG. 1 is a schematic view of a steel turning apparatus according to the present invention;
FIG. 2 is a microstructure chart (100) of 420 MPa-grade hot-rolled low-temperature-resistant H-steel according to example 2 of the present invention;
FIG. 3 is a microstructure of 420MPa grade hot rolled low temperature resistant H-steel (x 200) according to example 2 of the present invention.
Reference numerals:
1-3, a driving gear; 4. a rotation mechanism; 5. a hydraulic cylinder is arranged; 6. an upper roller; 7. a special-shaped steel billet; 8. a lower roller; 9. and a lower hydraulic cylinder.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings and examples.
The special-shaped continuous casting blanks in the following examples are prepared according to the following process flow: according to the set chemical composition range, adding a certain amount of scrap steel into the blast furnace molten iron serving as a raw material, smelting by a converter, LF refining, adjusting the content of C, si, mn, S, P and the like, performing V microalloying, and performing continuous casting, direct heating of a casting blank or soaking after the composition reaches a target value.
The preparation steps for examples 1-5 are as follows:
molten iron pretreatment, 150t converter smelting, ladle argon blowing, LF refining, special-shaped continuous casting blanks, slow cooling of continuous casting blank slow cooling pits, heating by a heating furnace, BD multi-pass rough rolling, automatic steel turning of intermediate blanks, reversible rolling of a profile steel line TM, inter-frame cooling and finish rolling, lower flange water cooling after finish rolling, and intensive slow cooling of a cooling bed. Wherein, the section steel line rolling comprises rough rolling and finish rolling. The hot rolling process mainly controls the temperature, and rolled materials are naturally stacked and cooled in a cooling bed after rolling.
Example 1:
the chemical components of the structural steel for the selected ship are as follows by weight percent: c:0.05%, si:0.20%, mn:1.25%, V:0.11%, A1t:0.05%, cr:0.35%, P:0.013%, S:0.005%, N:0.011%, O:0.003% of Fe and the balance of Fe; cev:0.35. smelting the prepared raw materials in a 150-ton converter process, wherein the proportion of vanadium-nitrogen alloy to vanadium-iron is 2:1, specifically: 1.1 kg/ton of vanadium-nitrogen alloy with the vanadium grade of 77% and 0.55 kg/ton of vanadium-iron alloy with the vanadium grade of 50% are added, then continuously cast into a special-shaped continuous casting blank, and a 100-meter manganese nitride cored wire is properly added for fine adjustment according to the nitrogen content detection condition in the later stage of LF refining, and then continuously cast into the special-shaped continuous casting blank. And heating the continuous casting blank to 1230 ℃ in the rolling process, preserving heat for 280min, performing upward and downward steel turning operation by using a turning device after BD is discharged, rolling on a finishing continuous rolling mill after the temperature is 70s, controlling the initial rolling temperature of finish rolling to 980 ℃, controlling the temperature difference between finishing rolling mill frames by adopting water cooling, controlling the final rolling temperature of the finish rolling to 790 ℃, controlling the lower flange to 803 ℃, and straightening by using a straightening machine according to the rolling specification of national standard H700 x 300 x 17 x 24 mm.
The grain size rating of the product organization is 9.5, and the mechanical property test data result is that: reH: 4576 MPa, rm:551MPa, δ:23% >, akv at-50 ℃): average 233J.
Example 2:
the chemical components of the structural steel for the selected ship are as follows by weight percent: c:0.06%, si:0.18%, mn:1.35%, V:0.13%, A1t:0.04%, cr:0.3%, P:0.013%, S:0.003%, N:0.012%, O:0.003% of Fe and the balance of Fe; cev:0.39. smelting the prepared raw materials in a 150-ton converter process, wherein the proportion of vanadium-nitrogen alloy to vanadium-iron is 2:1, specifically: 1.32 kg/ton of vanadium-nitrogen alloy with the vanadium grade of 77% and 0.66 kg/ton of vanadium-iron alloy with the vanadium grade of 50% are added, 80m of manganese nitride cored wire is added for fine adjustment according to the detection condition in the later stage of LF refining, and then the special-shaped continuous casting blank is formed by continuous casting. And heating the continuous casting blank to 1240 ℃ in the rolling process, preserving heat for 300min, performing upward and downward turning steel operation by using a turning device after the BD is discharged, rolling on a finishing continuous rolling mill after the BD is heated for 80s, controlling the finish rolling start temperature to 990 ℃, adopting water cooling control temperature difference between finishing rolling mill frames, controlling the finish rolling temperature upper flange to 800 ℃, controlling the lower flange to 814 ℃, and straightening in a straightening machine, wherein the rolling specification is 900 x 300 x 16 x 28 mm.
The grain size of the product organization is rated as 10 grades, and the mechanical property test result is as follows: reH: 4476 MPa, rm:542MPa, delta: 22%, akv impact energy at-60 ℃): average 224J.
Example 3:
the chemical components of the structural steel for the selected ship are as follows by weight percent: c:0.065%, si:0.21%, mn:1.42%, V:0.14%, A1t:0.035%, cr:0.38%, P:0.014%, S:0.004%, N:0.013%, O:0.003% of Fe and the balance of Fe; cev:0.40. smelting the prepared raw materials in a 150-ton converter process, wherein the proportion of vanadium-nitrogen alloy to vanadium-iron is 2:1, specifically: 1.4 kg/ton of vanadium-nitrogen alloy with the vanadium grade of 77% and 0.7 kg/ton of vanadium-iron alloy with the vanadium grade of 50% are added, and 50m of manganese nitride cored wire is added for fine adjustment according to the detection condition in the later stage of LF refining, and then the special-shaped continuous casting blank is formed by continuous casting. And heating the continuous casting blank to 1230 ℃ in the rolling process, preserving heat for 300min, performing upward and downward turning steel operation by using a turning device after BD is discharged, rolling on a finishing continuous rolling mill after the temperature is 100s, controlling the initial rolling temperature of finish rolling to 980 ℃, controlling the temperature difference between finishing rolling mill frames by adopting water cooling, controlling the final rolling temperature of the finish rolling to 810 ℃ on the upper flange, controlling the lower flange to 823 ℃, and straightening by using a straightening machine, wherein the rolling specification is national standard specification H1000 x 300 x 19 x 36 mm.
The grain size of the product organization is rated as 9 grades, and the mechanical property test result is as follows: reH:436MPa, rm:539MPa, delta: 21% >, akv impact energy at-60 ℃: average 205J.
Example 4:
the chemical components of the structural steel for the selected ship are as follows by weight percent: c:0.07%, si:0.18%, mn:1.41%, V:0.13%, A1t:0.04%, cr:0.40%, P:0.012%, S:0.003%, N:0.012%, O:0.004%, the balance being Fe; cev:0.41. smelting the prepared raw materials in a 150-ton converter process, wherein the proportion of vanadium-nitrogen alloy to vanadium-iron is 2:1, specifically: 1.32 kg/ton of vanadium-nitrogen alloy with the vanadium grade of 77% and 0.66 kg/ton of vanadium-iron alloy with the vanadium grade of 50% are added, 80m of manganese nitride cored wire is added for fine adjustment according to the detection condition in the later stage of LF refining, and then the special-shaped continuous casting blank is formed by continuous casting. And heating the continuous casting blank to 1245 ℃ in the rolling process, preserving heat for 270min, performing upward and downward steel turning operation by using a steel turning device after the BD is discharged, rolling on a finishing continuous rolling mill after the BD is heated for 90s, controlling the finish rolling start temperature to 1000 ℃, controlling the temperature difference between finishing rolling mill frames by adopting water cooling, controlling the finish rolling temperature upper flange to 820 ℃, controlling the lower flange to 835 ℃, controlling the rolling specification to national standard H-shaped steel H850 x 300 x 16 x 27 sub mm, and straightening in a straightening machine.
The product organization grain size rating is 10.5 grade; the mechanical property test result is as follows: reH: 4572 MPa, rm:549MPa, delta: 25%, akv impact energy at-60 ℃): average 245J.
Example 5:
the chemical components of the structural steel for the selected ship are as follows in percentage by weight: c:0.07%, si:0.21%, mn:1.25%, V:0.11%, A1t:0.05%, cr:0.35%, P:0.013%, S:0.005%, N:0.011%, O:0.003% of Fe and the balance of Fe; cev:0.40. smelting the prepared raw materials in a 150-ton converter process, wherein the proportion of vanadium-nitrogen alloy to vanadium-iron is 3:1, specifically: 1.1 kg/ton of vanadium-nitrogen alloy with the vanadium grade of 77% and 0.55 kg/ton of vanadium-iron alloy with the vanadium grade of 50% are added, then continuously cast into a special-shaped continuous casting blank, and a 100-meter manganese nitride cored wire is properly added for fine adjustment according to the nitrogen content detection condition in the later stage of LF refining, and then continuously cast into the special-shaped continuous casting blank. And heating the continuous casting blank to 1235 ℃ in the rolling process, preserving heat for 300min, performing upward and downward steel turning operation by using a steel turning device after the BD is discharged, rolling on a finishing continuous rolling mill after the BD is heated for 95s, controlling the initial rolling temperature of finish rolling to 980 ℃, controlling the temperature difference between finishing rolling mill frames by adopting water cooling, controlling the final rolling temperature upper flange to 815 ℃, controlling the lower flange to 825 ℃, and straightening in a straightening machine, wherein the rolling specification is national standard specification H1000 x 300 x 19 x 36 mm.
Sampling according to GB/T2975-2018 'test sampling position of mechanical properties of steel and steel products and sample preparation', wherein a test method of yield strength, tensile strength and elongation is referred to a test method of room temperature tensile test of metal materials of GB/T228-2021; the impact power test method is referred to the standard GB/T229-2020 Charpy pendulum impact test method for metallic materials. The yield strength of the embodiment 1-5 of the invention is maintained at the level of more than 440MPa, the extension performance is good, the impact energy at the temperature of minus 60 ℃ is higher, the whole reaches the level of F, the ductile-brittle transition temperature is extremely low, and the floating ship is suitable for operation in different sea environments. The method can meet the use conditions of the prepared ship and ocean engineering components in extremely low environments, and is suitable for manufacturing support structural members with high low-temperature toughness requirements, such as floating oil storage ships, ocean oil platforms in extremely cold areas and the like.
As can be seen from fig. 2 and 3, the structure of the present invention is an ultrafine pearlite+ferrite structure. Meanwhile, the temperature difference of the upper flange and the lower flange is controlled within 15 ℃, so that the strength of the upper leg and the lower leg is controlled below 15 MPa. The superfine crystal structure meets the requirement of preparing the H-shaped steel with the strength of 420MPa, and the low-temperature toughness is improved while the strength index is met.
The method can be realized by the upper and lower limit values of the interval and the interval value of the process parameters (such as temperature, time and the like), and the examples are not necessarily listed here.
The invention may be practiced without these specific details, using any knowledge known in the art.
Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention and are not limiting. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is intended to be covered by the appended claims.
Claims (10)
1. The thick high-strength high-toughness low-temperature-resistant rolled H-shaped steel for the low-cost ship structure is characterized by comprising the following chemical components in percentage by weight: c:0.05 to 0.07 percent, si: less than or equal to 0.25 percent, mn:1.20 to 1.50 percent, V:0.11 to 0.15 percent, A1t:0.035 to 0.055%, cr:0.3 to 0.5 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.005 percent, and N:0.010 to 0.015 percent, O is less than or equal to 0.004 percent, and the balance is Fe and unavoidable impurities.
2. The thick high-strength and high-toughness low-temperature-resistant rolled H-shaped steel for a low-cost ship structure according to claim 1, wherein the flange thickness of the H-shaped steel is 20-40mm, and the carbon equivalent index is controlled below 0.42.
3. The thick high-strength and high-toughness low-temperature-resistant H-shaped steel for low-cost ship structures according to claim 1, wherein the yield strength of the H-shaped steel is more than or equal to 430MPa, the tensile strength is more than or equal to 530MPa, the elongation is more than or equal to 19%, and the impact energy at minus 60 ℃ is more than or equal to 180J.
4. The thick high-strength high-toughness low-temperature-resistant rolled H-shaped steel for a low-cost ship structure according to claim 1, wherein the structure of the rolled H-shaped steel matrix is fine-piece pearlite and superfine proeutectoid ferrite, and the grain size is controlled within the range of 9-11 grades; the second phase particles stably precipitated in steel mainly contain VN, and the fraction of precipitated particles having a size of 50nm or less exceeds 60%.
5. A preparation method of thick-specification high-strength high-toughness low-temperature-resistant rolled H-shaped steel for a low-cost ship structure comprises the following steps:
molten iron pretreatment, 120 ton converter smelting, ladle argon blowing, LF refining, special-shaped continuous casting blank casting, slow cooling of a continuous casting blank slow cooling pit, heating by a heating furnace, BD rough rolling, intermediate blank turning operation, finish rolling TM reversible rolling, inter-frame cooling, water cooling of a flange phase change area after rolling, intensive slow cooling of a cooling bed, straightening by a straightener and finishing treatment of finished products.
6. The method for preparing the thick high-strength high-toughness low-temperature-resistant rolled H-shaped steel for the low-cost ship structure, which is disclosed in claim 5, is characterized in that the soaking temperature of a heating furnace in the rolling process is 1230-1250 ℃, and the casting blank is in the furnace for 210-300 min.
7. The method for manufacturing thick high-strength and high-toughness low-temperature resistant rolled H-shaped steel for a low-cost ship structure according to claim 5, wherein the BD rough rolling is performed in a reversible rolling process for 7-9 times, the integral compression ratio of rough rolling is controlled to be more than 40%, the large compression ratio is ensured in the rough rolling stage, and the intermediate billet is fully recrystallized to increase the austenite nucleation rate and refine the austenite structure.
8. The method for producing thick high strength and toughness low temperature heat resistant rolled H-shaped steel for low cost marine structure according to claim 5, wherein the finish rolling is performed by reciprocal reversible rolling for 5-7 passes, the finish rolling start temperature is 960-980 ℃, the cooling water between the finishing mill frames is all opened, and the finish rolling temperature is 760-830 ℃.
9. The method for manufacturing thick high-strength and high-toughness low-temperature-resistant rolled H-shaped steel for a low-cost ship structure, according to claim 5, wherein the thick-gauge shaped steel uses a steel billet with large weight, and in order to reduce the temperature difference between an upper flange and a lower flange, a steel turning machine is used for turning steel between rough rolling and finish rolling, specifically:
after BD rolling, rapidly moving the intermediate blank to the middle position of the tilting gear, stopping the tilting gear, and starting to operate the tilting gear, and driving a rotating mechanism (4) to rotate by using three driving gears (1), (2) and (3); the upper roller (6) and the lower roller (8) are driven, the upper roller and the lower roller clamp the billet (7) under the action of the upper hydraulic cylinder (5) and the lower hydraulic cylinder (9), and the rotating mechanism drives the billet to rotate under the drive of the driving gear.
10. The method for producing a thick high strength and high toughness low temperature resistant rolled H-shaped steel for a low cost marine structure according to claim 5, wherein, to ensure the control of the finish rolling temperature, the final pass reduction ratio of the finish rolling is 8% -12%, and simultaneously the rolling mill is controlled to be under 2m/s for the reduction rolling; and the final pass of the finish rolling TM is fully cooled, so that the vanadium-containing carbonitride which is precipitated later can play a role in precipitation strengthening.
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