CN116043130B - Economical 700 MPa-level storage tank steel plate with excellent die-welding performance and manufacturing method thereof - Google Patents
Economical 700 MPa-level storage tank steel plate with excellent die-welding performance and manufacturing method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 103
- 239000010959 steel Substances 0.000 title claims abstract description 103
- 238000003466 welding Methods 0.000 title claims abstract description 31
- 238000003860 storage Methods 0.000 title claims abstract description 17
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 15
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 15
- FBPFZTCFMRRESA-JGWLITMVSA-N D-glucitol Chemical compound OC[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO FBPFZTCFMRRESA-JGWLITMVSA-N 0.000 claims abstract description 8
- 239000000463 material Substances 0.000 claims abstract description 8
- 239000012535 impurity Substances 0.000 claims abstract description 7
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 5
- 239000000126 substance Substances 0.000 claims abstract description 5
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 3
- 238000005096 rolling process Methods 0.000 claims description 47
- 238000001816 cooling Methods 0.000 claims description 33
- 238000005266 casting Methods 0.000 claims description 26
- 238000000034 method Methods 0.000 claims description 24
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 21
- 238000005496 tempering Methods 0.000 claims description 18
- 230000008569 process Effects 0.000 claims description 16
- 238000003723 Smelting Methods 0.000 claims description 15
- 238000009749 continuous casting Methods 0.000 claims description 13
- 238000010438 heat treatment Methods 0.000 claims description 12
- 229910052742 iron Inorganic materials 0.000 claims description 9
- 230000009467 reduction Effects 0.000 claims description 9
- 238000007670 refining Methods 0.000 claims description 8
- 229910000734 martensite Inorganic materials 0.000 claims description 7
- 238000007599 discharging Methods 0.000 claims description 5
- 238000009489 vacuum treatment Methods 0.000 claims description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 5
- 238000007664 blowing Methods 0.000 claims description 4
- 238000013461 design Methods 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 4
- 229910052758 niobium Inorganic materials 0.000 claims description 4
- 238000002791 soaking Methods 0.000 claims description 4
- 230000000630 rising effect Effects 0.000 claims description 2
- 230000008901 benefit Effects 0.000 abstract description 5
- 229910052750 molybdenum Inorganic materials 0.000 abstract description 2
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- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 239000013078 crystal Substances 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
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- 229910000990 Ni alloy Inorganic materials 0.000 description 2
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- 238000011161 development Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000009847 ladle furnace Methods 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
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- 238000001556 precipitation Methods 0.000 description 2
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- 230000000171 quenching effect Effects 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
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- 229910052802 copper Inorganic materials 0.000 description 1
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- 238000005098 hot rolling Methods 0.000 description 1
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- 239000003345 natural gas Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- JMANVNJQNLATNU-UHFFFAOYSA-N oxalonitrile Chemical compound N#CC#N JMANVNJQNLATNU-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
-
- 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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
The invention relates to an economic 700 MPa-level storage tank steel plate with excellent die-welding performance and a manufacturing method thereof, wherein the steel plate comprises the following chemical components in percentage by mass: 0.10 to 0.20 percent, si:0.30 to 0.50 percent, mn:1.40 to 2.00 percent, P is less than or equal to 0.007 percent, S is less than or equal to 0.002 percent, and Nb+Ti:0.010 to 0.050%, wherein Nb:0 to 0.030 percent, ti:0 to 0.020 percent, cr:0.15 to 0.30 percent, and the balance of Fe and unavoidable impurity elements, and simultaneously satisfies the following conditions: the carbon equivalent CEV=C+Mn/6+ (Mo+V+Cr)/5+ (Ni+Cu)/15 is less than or equal to 0.47%, wherein the element symbol represents the mass percent of the corresponding element, and Mo, V, ni, cu is the residual element, and the weight ratio of w (Cr)/w (Nb+Ti) is less than or equal to 5 and less than or equal to 10. The structure is tempered sorbite and tempered bainite, and the grain size reaches more than 8 grades. Transverse impact energy at the position of 1/4 of the plate thickness is-70 ℃, and KV 2 is more than or equal to 100J; the performance requirement after the die welding treatment is the same as that of the base material. The steel plate has the characteristics of high strength, excellent low-temperature impact toughness after die welding, easy welding and the like, and has the advantages of short production flow, low cost and obvious market competitive advantage.
Description
Technical Field
The invention relates to a steel plate with excellent die-welding performance for a storage tank and a manufacturing method thereof, belonging to the field of iron-based alloy and smelting methods thereof.
Background
In recent years, a large amount of petrochemical and natural gas projects are carried out at home and abroad successively, the demand of large-scale steel storage tanks is remarkably increased, and quenched and tempered steel plates are increasingly favored in the industry because of good toughness matching. Meanwhile, along with the continuous development of large-scale, light-weight and high-parametrization of equipment, the equipment is ensured to run safely and stably, and the good low-temperature impact toughness and weldability are particularly critical. At present, the strength of the steel plate for the large storage tank is generally 600MPa, and the steel plate for the storage tank, which is applicable to 700MPa in the environment of-70 ℃, is not involved, so that the development of the high-strength steel plate for the storage tank, which can be stably produced in batches and has low cost and low service temperature, has very broad market prospect.
Patent document (publication No. CN 111621723A) discloses a 700MPa low-temperature quenched and tempered steel plate with excellent weldability and fatigue resistance, the tensile strength is controlled to 790-830 MPa, the yield strength is controlled to 640-690 MPa, and the low-temperature impact energy at-60 ℃ is more than 200J, but noble metals such as Cu, ni, mo and the like are added, the cost of element components is higher, and the mechanical property after die welding is not mentioned.
Patent document (publication No. CN 108660383A) applies for a nickel-free economical low-temperature steel plate suitable for-100 ℃ and a manufacturing method thereof, which adopts hot rolling state or normalizing and tempering state delivery, and the impact energy at-100 ℃ reaches more than 60J, but the strength is only 400-500 MPa, which is obviously lower for industrial use, thus leading to the increase of the wall thickness of equipment and being unfavorable for the processing and manufacturing and the large-scale use requirement of a storage tank.
Patent literature (publication number CN 107974625A) discloses a production method of a high-toughness low-temperature steel plate for an LPG ship storage tank, which adopts a normalizing and tempering heat treatment process to produce the steel plate, the yield ratio is low, the low-temperature impact energy of-80 ℃ reaches more than 100J, the produced steel plate has stable performance and good toughness matching, but the Ni alloy elements are excessively added, and the production cost is greatly improved.
In summary, the existing high-strength low-temperature steel plates are mostly produced by adding precious Ni alloy to reduce the ductile-brittle transition temperature of materials or adopting a low-carbon and controlled rolling process, so that the strength of the steel plates for the storage tanks obtained in the mode is low or the alloy cost is high, and meanwhile, the low-temperature impact toughness of the steel plates after die welding cannot be ensured, so that the comprehensive market competitiveness of products is not improved.
Disclosure of Invention
The invention aims to provide an economic 700 MPa-grade storage tank steel plate with excellent die-welding performance and a manufacturing method thereof, and the steel plate not only has the characteristics of high strength of 700MPa grade, excellent low-temperature impact toughness after die-welding, easy welding and the like, but also has short production flow, low cost and obvious market competition advantage, and does not need to obviously improve the production cost of products.
The invention solves the problems by adopting the following technical scheme: an economic 700 MPa-level storage tank steel plate with excellent die-welding performance comprises the following chemical components in percentage by mass: 0.10 to 0.20 percent, si:0.30 to 0.50 percent, mn:1.40 to 2.00 percent, P is less than or equal to 0.007 percent, S is less than or equal to 0.002 percent, and Nb+Ti:0.010 to 0.050%, wherein Nb:0 to 0.030 percent, ti:0 to 0.020 percent, cr:0.15 to 0.30 percent, and the balance of Fe and unavoidable impurity elements, and simultaneously satisfies the following conditions: the carbon equivalent CEV=C+Mn/6+ (Mo+V+Cr)/5+ (Ni+Cu)/15 is less than or equal to 0.47%, wherein the element symbol represents the mass percent of the corresponding element, and Mo, V, ni, cu is the residual element, and the weight ratio of w (Cr)/w (Nb+Ti) is less than or equal to 5 and less than or equal to 10.
Further, the structure of the steel plate is tempered sorbite and tempered bainite, and the grain size reaches more than 8 grades. The yield strength of the steel plate is more than or equal to 600MPa, the tensile strength Rm is more than or equal to 700MPa, the elongation A after fracture is more than or equal to 16 percent, and the transverse impact energy at the plate thickness of 1/4 part is more than or equal to 100J at-70 ℃ KV 2; the performance requirement after the die welding treatment is the same as that of the base material, wherein the die welding process comprises the following steps: heating to 560 ℃, preserving heat for 3 hours, controlling the temperature rising and falling rate to be less than or equal to 100 ℃/h at the temperature of more than 300 ℃, discharging from a furnace below 300 ℃, cooling by air, and circulating for 3 times.
The arrangement principle of C, si, mn, P, S, nb, ti, cr and other elements in the invention is described as follows:
C is the most economical element for improving the strength of the steel plate, the main idea of improving the strength is to increase the content of C, but the excessive content can lead to the reduction of plasticity and impact toughness, and simultaneously the sensitivity of welding cracks is increased, so that the cracks are easy to generate in the welding process. In order to ensure that the base material has good toughness matching, weldability and the like, the content of the steel C is 0.10-0.20%.
Si can improve the strength of the steel plate and the welded joint through solid solution strengthening, when the content of Si is more than 0.50%, the toughness of the steel plate and the welded joint can be obviously reduced, meanwhile, the formed hard silicate inclusion is easy to cause the surface defect of the steel plate, and the content of Si is 0.30-0.50%.
Mn is a common element for improving the strength of the steel plate, and a proper amount of Mn can replace C element to improve the strength of the steel plate and the welded joint and improve the toughness. With the increase of Mn content, the method can improve the stability of austenite in steel, reduce critical cooling speed, strengthen ferrite, obviously improve hardenability, simultaneously slow down the tissue decomposition and transformation speed in the tempering process after quenching, and improve the tempering tissue stability, but too high content can coarsen crystal grains of steel at high temperature and reduce the toughness and weldability of steel plates and welded joints, so that the Mn content of the steel is 1.40-2.00%.
P, S is unavoidable as an impurity element in steel, but is detrimental to workability of steel sheet, particularly low-temperature impact toughness after die-welding, and the lower the content is, the better the content is, so that the content of P is 0.007% or less and the content of S is 0.002% or less in the steel of the present invention.
Nb can introduce a large number of high-density dislocations and distortion regions during non-recrystallization region rolling, promoting the formation of more transformation cores, thereby refining the austenitic structure. And meanwhile, carbon nitride is formed, precipitation and precipitation are carried out in ferrite of an austenite grain boundary, and the recrystallization of austenite can be restrained and the growth of crystal grains can be prevented in the rolling process, so that the effect of refining ferrite crystal grains is achieved, and the strength and toughness of steel are improved. Ti can form high-temperature oxide, is used as nucleation points of acicular ferrite in a welded joint, promotes the formation of the acicular ferrite, and remarkably improves the low-temperature impact toughness of a welding heat affected zone. In addition, in the tempering process, due to the pinning effect of precipitates of Nb and Ti on dislocation, dislocation movement can be effectively prevented, the recovery of a matrix is delayed, the reduction of dislocation density is reduced, and the strength is not obviously reduced while the toughness of the steel plate is greatly improved. If added too much, not only the cost increases but also the number and size of precipitates increases, resulting in a decrease in toughness of steel, particularly thin gauge steel sheet. Therefore, the Nb+Ti content of the steel is less than or equal to 0.05 percent, and the weight ratio of the steel to the steel is more than or equal to 5 percent and less than or equal to w (Cr)/w (Nb+Ti) content is less than or equal to 10 percent, and in the application, cr ensures the strength of the steel plate mainly by promoting the formation of martensite and lath bainite; nb+Ti ensures the toughness (limited strength contribution) of the steel plate mainly through the grain size in the refining rolling process, and the steel plate can be reasonably toughness-matched through the arrangement of the formula, so that the alloy cost is reduced, and the economical efficiency of the element cost of the product is improved.
Cr can promote the formation of hard phase structures such as martensite, lath bainite and the like in steel, form continuous solid solution with iron, strengthen a matrix by solid solution, and improve the strength and the hardness of the steel plate. Meanwhile, the tempering stability and refined grains of the steel can be improved, and particularly, the mechanical property of the steel plate after die welding is improved, and the strength is prevented from being greatly reduced. Therefore, the Cr content of the steel of the present invention is 0.15-0.30%.
The method for manufacturing the steel plate comprises the following steps: molten iron pretreatment, converter smelting (primary smelting), ladle furnace refining, vacuum treatment (soft blowing), continuous casting, casting blank heating, controlled rolling, controlled cooling, slow-stacking cooling, tempering, flaw detection and performance inspection, and the method is specifically described as follows:
Step one, molten steel smelting and casting blank casting: and smelting molten steel according to the element composition design of the steel plate, casting the molten steel into a casting blank, and slowly cooling the casting blank (preferably stacking).
Step two, rolling is controlled: heating the continuous casting blank to 1180-1240 ℃, and soaking for at least 90min at a high temperature section to enable Nb and Ti to be fully dissolved, and dispersing and separating out in the subsequent rolling process to refine initial austenite grains, thereby laying a foundation for obtaining good toughness of the final steel plate. Removing surface iron scales from the cast blank after discharging the cast blank from the furnace by high-pressure water, and adopting two-stage rolling: the initial rolling adopts small-pass large reduction, the initial rolling temperature is 1000-1080 ℃, the final rolling temperature is 980-1040 ℃, the reduction rate of at least 2 passes is more than or equal to 12%, the finish rolling is performed until Wen Houdu is more than or equal to 3.0H, H is the thickness of the finished steel plate, the rolling deformation is increased, austenite grains can be refined effectively through deformation, dislocation density in a tissue is greatly increased, and the matrix strength is further improved. The final rolling temperature is controlled above Ac3, so that the steel plate structure is in complete austenitization before controlled cooling, and is converted into martensite and lath bainite structure in the subsequent cooling process. Finally rolling the steel plate into a finished steel plate with the thickness of 12-36 mm.
Step three, cooling control: cooling is controlled after rolling, the cooling speed is controlled to be 15-30 ℃/s, and the cooling speed is cooled to be below 200 ℃ to obtain the martensite and lath bainite structure.
Step four, tempering heat treatment: tempering at 500-600 deg.c to convert the controlled cooled structure to obtain tempered sorbite and tempered bainite structure, eliminating stress and eliminating stress, and has structure granularity over 8 level.
Preferably, in the first step, molten steel smelting involves molten iron pretreatment, primary smelting, refining and vacuum treatment, and soft blowing is performed for more than 15 minutes after the vacuum treatment; the casting adopts a continuous casting process, the pulling speed is controlled to be 0.45-0.55 m/min during continuous casting, the superheat degree is controlled to be 10-30 ℃, a continuous casting slab with the thickness of more than 300mm is cast, and the casting blanks are stacked and slowly cooled.
Preferably, in the second step, the final rolling temperature of the rolling is controlled to be 900-940 ℃.
The invention adopts a simpler C-Mn-Cr chemical composition design and controlled rolling, controlled cooling and tempering process to produce the steel. Ensuring the purity of molten steel during smelting, for example, adopting high-quality scrap steel and KR molten iron pretreatment, strictly controlling the content of harmful elements and impurity elements, controlling [ P ] to be less than or equal to 0.005% after slag skimming of a converter, and carrying out argon blowing treatment from the bottom of the converter; during refining, the Al wires are used for deoxidizing and the argon flow for stirring molten steel is properly regulated, so that flocculent large particles such as alumina are promoted to be mixed and float upwards. Adding desulfurizing agent to further desulfurizing, controlling S less than or equal to 0.002%, and strictly controlling impurity element and harmful element content in alloy and auxiliary material. In the preparation method, grain refinement is emphasized, and finally tempering treatment is carried out at 500-600 ℃ to ensure that the yield strength of the steel plate of the product is more than or equal to 600MPa, the tensile strength Rm is more than or equal to 700MPa, the elongation after fracture A is more than or equal to 16 percent, and the transverse impact energy at the plate thickness of 1/4 is more than or equal to 100J at-70 ℃ KV 2. The performance requirement after the die welding treatment is the same as that of the base material (the die welding process is that the temperature is raised to 560 ℃, the temperature is kept for 3 hours, the temperature raising and lowering rate is controlled to be less than or equal to 100 ℃/h at the temperature of more than 300 ℃, the base material is discharged from a furnace for air cooling at the temperature of less than 300 ℃, and the cycle is carried out for 3 times). The microstructure of the product is tempered sorbite and tempered bainite.
Compared with the prior art, the invention has the advantages that:
(1) On one hand, the economic Cr element is added, the hardenability of the matrix is improved, and on the other hand, the cooling speed is increased by depending on the cooling capacity of equipment, and the martensite and lath bainite structure is obtained by air cooling after rolling, so that the strength of the matrix is improved. Reduces the use of noble alloys such as Ni, mo, V and the like, and realizes the replacement of the alloy with water.
(2) Compared with the traditional off-line quenching process, the method has the advantages that the thick continuous casting billet with the thickness of more than 300mm is adopted, the thickness to be heated in finish rolling is controlled to be more than or equal to 3.0H, the deformation of rolling in the second stage is increased, a large amount of dislocation is introduced into a matrix, and the strength of the steel plate before tempering is further improved.
(3) The application has low cost, short production flow and good mechanical property after die welding, can replace the existing steel grade with service temperature of-40 ℃ to-70 ℃, and has wide application prospect.
Drawings
FIG. 1 is a schematic diagram of tempered sorbite and tempered bainite in a metallographic structure at 1/4 of a plate thickness of a 32mm thick steel plate according to example 2 of the present invention.
Detailed Description
The invention is described in further detail below in connection with the following examples, which are exemplary and intended to illustrate the invention, but are not to be construed as limiting the invention.
The smelting chemistry of this example and comparative example is shown in Table 1 (wt%), with the remainder being Fe and unavoidable impurity elements.
TABLE 1
| Element(s) | C | Si | Mn | P | S | Nb+Ti | Cr | Ni | B | Cr/(Nb+Ti) | CEV |
| Example 1 | 0.16 | 0.35 | 1.52 | 0.005 | 0.001 | 0.034 | 0.20 | / | 0.0005 | 5.88 | 0.46 |
| Example 2 | 0.15 | 0.34 | 1.51 | 0.006 | 0.002 | 0.030 | 0.28 | / | 0.0004 | 9.33 | 0.47 |
| Comparative example | 0.08 | 0.25 | 1.45 | 0.012 | 0.006 | 0.050 | 0.05 | 0.32 | 0.0013 | 1.00 | 0.41 |
The above examples and comparative examples are all smelted in a converter, then subjected to deep desulfurization and refining treatment by a ladle furnace, finally subjected to degassing by a vacuum furnace, and soft-blown for more than 15 minutes, so that large-particle inclusions are sufficiently removed in a floating manner, components and temperature uniformity are ensured, and then subjected to soft-reduction and overall process protection casting to form continuous casting slabs with the thickness of more than 300 mm.
Heating the continuous casting slab to 1180-1240 ℃, wherein the total furnace time is more than or equal to 240min, the soaking time in a high-temperature section is more than or equal to 90min, and removing scales on the surface of the casting blank through high-pressure water after discharging; then two-stage rolling is carried out, the initial rolling temperature is 1000-1080 ℃, the final rolling temperature is 980-1040 ℃, and the reduction rate of 2 passes is ensured to be more than or equal to 12%; the finish rolling is carried out until the temperature thickness is more than or equal to 3.0H (H is the thickness of a finished steel plate), the finish rolling temperature is controlled to 900-940 ℃, the finished steel plate with the thickness of 12-36 mm is rolled, controlled cooling is carried out after rolling, the cooling speed is controlled to 15-30 ℃/s, the steel plate is slowly cooled after being taken off line, and finally tempering treatment is carried out at 500-600 ℃.
Table 2 shows the main rolling, controlled cooling and tempering process parameters for each example and comparative example.
TABLE 2
The heat-treated steel sheet was subjected to mechanical property testing by taking a transverse sample at 1/4 of the sheet thickness and processing into a tensile sample and an impact sample, and the detection results are shown in Table 3.
TABLE 3 Table 3
The steel plate was subjected to die-welding treatment (die-welding process: heating to 560 ℃ C., maintaining the temperature for 2 hours, controlling the temperature rise and fall rate to be less than or equal to 100 ℃/h at 300 ℃ C., discharging from the furnace for air cooling at 300 ℃ C., and circulating for 3 times), and then subjected to tensile and impact property detection, and the results are shown in Table 4.
Table 4 comparison of mechanical properties after die-welding of the example and comparative steel sheets
As can be seen from tables 3 and 4, the strength of the test steel plate of the embodiment of the invention is obviously higher than that of the comparative example, the impact energy level at the low temperature of-70 ℃ is similar, but after the die welding treatment, the impact energy of the comparative example is unstable, the single value is only 19J at the lowest, and the impact energy of the embodiment of the invention is reduced to some extent, but still is maintained above 100J.
The invention not only ensures the high strength of the steel plate, but also has stable low-temperature impact toughness after die welding. The invention can be implemented in medium and thick plate factories of metallurgical enterprises, has simple process flow, strong operability and low cost, and can be applied to the construction of large-scale storage tanks in industries such as petroleum, chemical industry and the like.
In addition to the above embodiments, the present invention also includes other embodiments, and all technical solutions that are formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.
Claims (5)
1. An economical 700 MPa-level storage tank steel plate with excellent die-welding performance is characterized in that: the steel plate comprises the following chemical components in percentage by mass: 0.10 to 0.20 percent, si:0.30 to 0.50 percent, mn:1.40 to 2.00 percent, P is less than or equal to 0.007 percent, S is less than or equal to 0.002 percent, and Nb+Ti:0.010 to 0.050%, wherein Nb:0 to 0.030 percent, ti:0 to 0.020 percent, cr:0.15 to 0.30 percent, and the balance of Fe and unavoidable impurity elements, and simultaneously satisfies the following conditions: the carbon equivalent CEV=C+Mn/6+ (Mo+V+Cr)/5+ (Ni+Cu)/15 is less than or equal to 0.47%, wherein element symbols represent mass percent of corresponding elements, mo, V, ni, cu is residual elements, w (Cr)/w (Nb+Ti) is less than or equal to 5 and less than or equal to 10, the structure is tempered sorbite and tempered bainite, and the grain size reaches more than 8 grades;
The steel plate is manufactured by the following steps:
Step one, molten steel smelting and casting blank casting: smelting molten steel according to the element composition design of the steel plate, casting the molten steel into a casting blank, and slowly cooling the casting blank;
Step two, rolling is controlled: heating the continuous casting blank to 1180-1240 ℃, soaking for at least 90min at a high temperature section to enable Nb and Ti to be fully dissolved, removing surface iron scales from the casting blank by high-pressure water after the casting blank is discharged from a furnace, and adopting two-stage rolling: the initial rolling adopts small-pass large reduction, the initial rolling temperature is 1000-1080 ℃, the final rolling temperature is controlled to 980-1040 ℃, the reduction rate of at least 2 passes is more than or equal to 12%, the finish rolling is carried out until Wen Houdu is more than or equal to 3.0H, H is the thickness of the finished steel plate, the final rolling temperature is controlled to be more than Ac3, the steel plate structure is in complete austenitization before controlled cooling, and finally the steel plate with the thickness of 12-36 mm is rolled into the finished steel plate;
Step three, cooling control: cooling after rolling, wherein the cooling speed is controlled to be 15-30 ℃/s, and cooling to below 200 ℃ to obtain a martensite and lath bainite structure;
Step four, tempering heat treatment: tempering at 500-600 deg.c to convert the controlled cooled structure to obtain tempered sorbite and tempered bainite structure, eliminating stress and eliminating stress, and has structure granularity over 8 level.
2. The economical 700 MPa-level storage tank steel sheet excellent in die-bonding performance according to claim 1, characterized in that: the yield strength of the steel plate is more than or equal to 600MPa, the tensile strength Rm is more than or equal to 700MPa, the elongation A after fracture is more than or equal to 16 percent, and the transverse impact energy at the plate thickness of 1/4 part is more than or equal to 100J at-70 ℃ KV 2; the performance requirement after the die welding treatment is the same as that of the base material, wherein the die welding process comprises the following steps: heating to 560 ℃, preserving heat for 3 hours, controlling the temperature rising and falling rate to be less than or equal to 100 ℃/h at the temperature of more than 300 ℃, discharging from a furnace below 300 ℃, cooling by air, and circulating for 3 times.
3. A method for manufacturing the economical 700 MPa-level storage tank steel sheet excellent in die-bonding performance according to claim 1, characterized in that:
Step one, molten steel smelting and casting blank casting: smelting molten steel according to the element composition design of the steel plate, casting the molten steel into a casting blank, and slowly cooling the casting blank;
Step two, rolling is controlled: heating the continuous casting blank to 1180-1240 ℃, soaking for at least 90min at a high temperature section to enable Nb and Ti to be fully dissolved, removing surface iron scales from the casting blank by high-pressure water after the casting blank is discharged from a furnace, and adopting two-stage rolling: the initial rolling adopts small-pass large reduction, the initial rolling temperature is 1000-1080 ℃, the final rolling temperature is controlled to 980-1040 ℃, the reduction rate of at least 2 passes is more than or equal to 12%, the finish rolling is carried out until Wen Houdu is more than or equal to 3.0H, H is the thickness of the finished steel plate, the final rolling temperature is controlled to be more than Ac3, the steel plate structure is in complete austenitization before controlled cooling, and finally the steel plate with the thickness of 12-36 mm is rolled into the finished steel plate;
Step three, cooling control: cooling after rolling, wherein the cooling speed is controlled to be 15-30 ℃/s, and cooling to below 200 ℃ to obtain a martensite and lath bainite structure;
Step four, tempering heat treatment: tempering at 500-600 deg.c to convert the controlled cooled structure to obtain tempered sorbite and tempered bainite structure, eliminating stress and eliminating stress, and has structure granularity over 8 level.
4. A method according to claim 3, characterized in that: in the first step, molten steel smelting involves molten iron pretreatment, primary smelting, refining, vacuum treatment, and soft blowing for more than 15 minutes after the vacuum treatment; the casting adopts a continuous casting process, the pulling speed is controlled to be 0.45-0.55 m/min during continuous casting, the superheat degree is controlled to be 10-30 ℃, a continuous casting slab with the thickness of more than 300mm is cast, and the casting blanks are stacked and slowly cooled.
5. A method according to claim 3, characterized in that: in the second step, the final rolling temperature of the rolling is controlled to be 900-940 ℃.
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