CN117026093A - Steel for low-surface-hardness spherical tank and production method thereof - Google Patents
Steel for low-surface-hardness spherical tank and production method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 97
- 239000010959 steel Substances 0.000 title claims abstract description 97
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 11
- 238000010438 heat treatment Methods 0.000 claims abstract description 45
- 238000005096 rolling process Methods 0.000 claims abstract description 39
- 238000000034 method Methods 0.000 claims abstract description 38
- 230000008569 process Effects 0.000 claims abstract description 34
- 238000009749 continuous casting Methods 0.000 claims abstract description 18
- 238000005496 tempering Methods 0.000 claims abstract description 15
- 238000010791 quenching Methods 0.000 claims abstract description 13
- 230000000171 quenching effect Effects 0.000 claims abstract description 13
- 238000007670 refining Methods 0.000 claims abstract description 12
- 238000003723 Smelting Methods 0.000 claims abstract description 10
- 230000007704 transition Effects 0.000 claims abstract description 6
- 238000009489 vacuum treatment Methods 0.000 claims abstract description 6
- 238000010521 absorption reaction Methods 0.000 claims abstract description 5
- 239000000126 substance Substances 0.000 claims abstract description 4
- 239000012535 impurity Substances 0.000 claims abstract description 3
- 238000010079 rubber tapping Methods 0.000 claims description 23
- 238000004321 preservation Methods 0.000 claims description 12
- 239000002893 slag Substances 0.000 claims description 9
- 238000005266 casting Methods 0.000 claims description 8
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 6
- 230000009467 reduction Effects 0.000 claims description 6
- 229910001563 bainite Inorganic materials 0.000 claims description 4
- 208000004434 Calcinosis Diseases 0.000 claims description 3
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 3
- 229910052786 argon Inorganic materials 0.000 claims description 3
- 238000007664 blowing Methods 0.000 claims description 3
- 230000002308 calcification Effects 0.000 claims description 3
- 239000011575 calcium Substances 0.000 claims description 3
- 229910052791 calcium Inorganic materials 0.000 claims description 3
- 238000003466 welding Methods 0.000 abstract description 7
- 230000000630 rising effect Effects 0.000 abstract description 2
- 238000001514 detection method Methods 0.000 abstract 1
- 239000000203 mixture Substances 0.000 description 8
- 230000009286 beneficial effect Effects 0.000 description 5
- 229910001566 austenite Inorganic materials 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000010955 niobium Substances 0.000 description 4
- 238000009628 steelmaking Methods 0.000 description 4
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 239000011572 manganese Substances 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 229910052698 phosphorus Inorganic materials 0.000 description 3
- 239000011574 phosphorus Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 2
- 239000003921 oil Substances 0.000 description 2
- 238000011056 performance test Methods 0.000 description 2
- 229910052711 selenium Inorganic materials 0.000 description 2
- 239000011669 selenium Substances 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 238000009849 vacuum degassing Methods 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Classifications
-
- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/18—Controlling or regulating processes or operations for pouring
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/18—Controlling or regulating processes or operations for pouring
- B22D11/181—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level
- B22D11/182—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level by measuring temperature
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0056—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
-
- 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
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
-
- 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
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
-
- 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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- 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
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
-
- 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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
-
- 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
Abstract
The steel for the spherical tank with low surface hardness and the production method thereof comprise the following chemical components in percentage by mass: c=0.05 to 0.07, si=0.15 to 0.30, mn=1.40 to 1.60, p is not more than 0.008, s is not more than 0.003, alt=0.020 to 0.050, nb=0.020 to 0.030, v=0.040 to 0.060, ni=0.30 to 0.50, mo=0.20 to 0.30, sn is not more than 0.008, pcm is not more than 0.20%; the balance of Fe, indispensable impurities; the process route is as follows: converter smelting, LF refining, VD vacuum treatment, continuous casting, slab heating, controlled rolling, quenching and tempering. The steel plate delivery state and the simulated post-welding heat treatment state are the die-welding heat treatment process: the temperature is kept at 580+/-20 ℃ for 540 minutes, the temperature rising and falling speed is less than or equal to 100 ℃/h at more than 400 ℃, the performance simultaneously meets the requirements of surface hardness less than or equal to 220HBW, impact absorption energy at the positions of 1/4 and 1/2 and 50 ℃ below zero, the temperature without plastic transition (NDT) is less than-50 ℃, the product surface quality is excellent, and the ultrasonic detection meets the requirements of NB/T47013.3 standard grade I.
Description
Technical Field
The invention belongs to the technical field of metallurgy, and relates to steel for a spherical tank with low surface hardness and a production method thereof.
Background
The spherical tank is widely applied to the fields of oil refining, petrochemical industry and the like, is mainly used for storing and transporting liquid or gaseous materials, and is generally operated at the temperature of-50 to 50 ℃ and the operating pressure of below 3 MPa. Compared with a cylindrical storage tank, the spherical tank has the main advantages that: the bearing capacity of the spherical tank is highest under the condition of the same wall thickness, and the required wall thickness of the spherical container is only 1/2 of the wall thickness of a cylindrical container with the same diameter and the same material under the condition of the same internal pressure (without considering corrosion margin); under the same volume condition, the surface area of the spherical container is minimum, and the steel is saved by 30-40% compared with the cylindrical container due to the reasons of small wall thickness, small surface area and the like. Its main disadvantages are complex manufacturing and construction and high requirements for various properties of the material.
The main technical requirements of the 600 MPa-grade steel for spherical tanks widely used at present are as follows: (1) pcm is less than or equal to 0.20 percent; (2) delivery and die-weld tensile properties: reL is more than or equal to 490MPa, 610MPa is more than or equal to Rm is less than or equal to 730MPa, and elongation A is more than or equal to 17%; (3) delivery and die-weld impact properties: impact absorption energy at the temperature of 50 ℃ below zero at the positions of 1/4 and 1/2 of the thickness is respectively more than or equal to 100J and 80J; (4) the non-plastic transition (NDT) temperature is not higher than-50 ℃. Considering that part of liquefied hydrocarbon (such as ethylene) contains a small amount of wet H2S, in order to improve the corrosion resistance of the material, the surface hardness of steel for spherical tanks is required to be less than or equal to 220HBW. The prior art 600MPa grade steel for spherical tanks, such as 07MnNiMoDR, is difficult to meet the requirements at the same time, and development of new steel for spherical tanks is urgently needed to meet all the performance requirements.
Disclosure of Invention
The invention aims to provide steel for a spherical tank with low surface hardness and a production method thereof, wherein the delivery state and the simulated post-welding heat treatment state of a steel plate meet the requirements of performance requirements, namely a die-welding heat treatment process of 580+/-20 ℃ and heat preservation of 540 minutes, and the temperature rising speed of more than 400 ℃ is less than or equal to 100 ℃/h.
The technical scheme of the invention is as follows:
a steel for a low surface hardness spherical tank, characterized in that: the steel comprises the following chemical components in percentage by mass: c=0.05 to 0.07, si=0.15 to 0.30, mn=1.40 to 1.60, p is not more than 0.008, s is not more than 0.003, alt=0.020 to 0.050, nb=0.020 to 0.030, v=0.040 to 0.060, ni=0.30 to 0.50, mo=0.20 to 0.30, sn is not more than 0.008, pcm is not more than 0.20%; the balance of Fe, indispensable impurities; the structure of the steel is bainite, and simultaneously, the indexes that the surface hardness is less than or equal to 220HBW, the impact absorption energy at the positions of 1/4 and 1/2 of the steel is more than or equal to 100J and the plastic-free transition temperature NDT is less than-50 ℃ are satisfied.
The production method of the steel for the spherical tank with low surface hardness adopts the following process route: converter smelting, LF refining, VD vacuum treatment, continuous casting, slab heating, controlled rolling, quenching and tempering, wherein the key process steps comprise:
(1) Smelting in a converter: and tapping P is less than or equal to 0.010%, and after tapping, carrying out slag skimming operation after the tapping to further remove P.
(2) LF refining: after molten steel enters an LF refining furnace, performing white slag making and heating operation, wherein the rapid slag forming is required, the total standing time is more than or equal to 50min, and argon is blown from bottom in the whole process; and when the LF furnace is out of the station, calcification treatment is carried out, and the feeding quantity of calcium wires is more than or equal to 200m.
(3) And (3) VD vacuum treatment: the vacuum degree of the VD is below 0.5 torr (67 Pa), the vacuum holding time is more than or equal to 15min, and the soft blowing time before the VD is discharged is more than or equal to 12min.
(4) Continuous casting: the thickness of the continuous casting billet is 260mm, the continuous casting is performed with full-process protection casting, low superheat degree steel casting is adopted, and the superheat degree of the tundish is: the temperature of the casting furnace is less than or equal to 25 ℃ and the temperature of the continuous casting furnace is less than or equal to 18 ℃.
(5) And (3) heating a plate blank: the slab is heated in a stepping furnace, the temperature of a hearth is limited to be less than or equal to 1220 ℃, and the tapping temperature is controlled to be 1170-1210 ℃.
(6) And (3) rolling control: the initial rolling temperature at one stage is 1050-1150 ℃, the final rolling temperature is more than or equal to 950 ℃, and low-speed large-reduction rolling is adopted, so that the reduction rate of at least one pass is ensured to be more than 20%; the initial rolling temperature of the two stages is 800-960 ℃ (different initial rolling temperatures according to the thickness of the finished steel plate), and the final rolling temperature is more than or equal to 760 ℃.
(7) Quenching and tempering:
in the step (7), the heat treatment process of the steel plate with the thickness of 10mm to 20mm comprises the following steps: the quenching process comprises the following steps: heating temperature 890+/-10 ℃, holding time 15-30 min, tempering process: heating temperature 670+/-10 ℃ and heat preservation time 20-35 min.
In the step (7), the heat treatment process of the steel plate with the thickness of 20mm to 50mm comprises the following steps: the quenching process comprises the following steps: heating temperature 920+/-10 ℃, heat preservation time 30-50 min, tempering process: and (3) setting the temperature of a hearth to 700 ℃ and the surface temperature of the steel plate to 670-675 ℃ by adopting a high-temperature rapid heating process, and tapping.
The reason for designing the chemical composition of the steel of the present invention is as follows:
c: carbon element exists in the form of solid solution and carbide in steel, so that the strength and hardness of the steel are improved, and the plasticity and toughness of the steel are reduced, and therefore, the content of C is required to be as low as possible on the premise of ensuring the strength. The C content of the steel is controlled to be 0.05-0.07% by comprehensively considering the performance requirement and the alloy cost of the steel.
Si: the silicon element is dissolved in ferrite in the steel to increase the strength and hardness of the steel, reduce the plasticity and toughness, and simultaneously, the silicon improves the fluidity of molten steel to be beneficial to the casting performance. The Si content of the steel is controlled to be 0.15-0.30% by comprehensively considering the Si content of the steel.
Mn: manganese element is advantageous for improving the strength and toughness of the steel sheet, but Mn is an easily segregated element and is disadvantageous for controlling center segregation. The Mn of the steel is controlled to be 1.50-1.60%.
P: the phosphorus element is a cold brittle element, and the low-temperature toughness of the steel is greatly reduced, so that the content of phosphorus in the steel is strictly controlled, and the P in the steel is controlled below 0.008% by comprehensively considering the performance requirement and the cost factor.
S: the sulfur element is a hot brittle element, sulfide inclusion is easy to form, and the plasticity and toughness of the steel are reduced, so that the S content in the steel is reduced as much as possible. S in the steel is controlled within 0.003%.
Nb: the niobium element has extremely strong affinity with nitrogen and carbon in steel, can form extremely stable Nb (C, N) compound with the niobium element, and Nb (C, N) particles dispersed along an austenite grain boundary can greatly improve the coarsening temperature of original austenite grains, thereby achieving the purpose of refining the grains and being beneficial to improving the low-temperature toughness of the steel. The Nb content of the steel is controlled to be 0.020-0.030%.
V: the vanadium element has stronger precipitation strengthening and fine grain strengthening effects, can improve the strength and toughness of steel, reduce overheat sensitivity and improve heat stability. The V of the steel is controlled to be 0.040-0.060 percent.
Mo: the molybdenum element can obviously improve the hardenability of steel in the steel, reduce the tempering brittleness of the steel, and is beneficial to the low-temperature toughness of quenched and tempered steel. The steel of the invention controls Mo to be 0.20-0.30%.
Sn: the influence of selenium element on the steel performance is similar to that of phosphorus element, the low-temperature toughness of the steel is reduced strongly, and the content of the selenium element is controlled strictly. The Sn in the steel of the present invention is controlled to be 0.008% or less.
The invention has the beneficial effects and advantages that: by reasonable component design, the influence rule of each alloy element on the performance is fully utilized, the content of each element is reasonably allocated, and the steel plate delivery state and the simulated post-welding heat treatment state performance are ensured to meet the requirements on the basis of meeting Pcm less than or equal to 0.20% and good welding performance; adopting a furnace postslag skimming process and LF refining and VD vacuum degassing treatment to ensure the cleanliness of steel; the continuous casting billet heating strictly limits the hearth temperature to inhibit the growth of austenite grains, particularly to inhibit the abnormal growth of surface austenite grains, which is very beneficial to reducing the non-plastic transformation (NDT) temperature of steel; the rolling adopts a mode of combining one-stage high-temperature low-speed large-pressure and two-stage control rolling, fully refines the crystal grains of the rolled structure, and provides fine and uniform original structure for subsequent heat treatment; aiming at a thick steel plate with the thickness of more than 20mm and 50mm, a tempering process of high-temperature rapid heating is adopted to greatly reduce the surface hardness of the steel plate and the thickness of 1/4 and 1/2 of the strength of the steel plate, and finally the obtained product has excellent physical quality and various performances. The steel delivery state and the simulated post-welding heat treatment state performances of the spherical tank with the thickness of 10-50 mm produced by the invention both meet the following conditions: (1) tensile properties: reL is more than or equal to 490MPa, 610MPa is more than or equal to Rm is less than or equal to 730MPa, and elongation A is more than or equal to 17%; (2) impact properties: the impact absorption energy at the temperature of 50 ℃ below zero at the positions of 1/4 and 1/2 of the thickness is more than or equal to 100J; (3) the non-plastic transition (NDT) temperature is below-50 ℃; (4) the surface hardness is less than or equal to 220HBW. The structure of the steel is bainite.
Drawings
FIG. 1 is a metallographic structure diagram of example 1; FIG. 2 is a metallographic structure diagram of example 2;
FIG. 3 is a metallographic structure diagram of example 3; FIG. 4 is a metallographic structure of example 4.
Detailed Description
The invention is further illustrated below with reference to examples.
Example 1:
the implementation process of the steelmaking technology comprises the following steps: the steel tapping of the converter is P=0.009%, the slag removing operation is carried out after the steel tapping, the P is further removed, and the P=0.006% after the slag removing is finished. After molten steel enters an LF refining furnace, carrying out alloying, white slag making and heating operations, wherein the total standing time is 70min, argon is blown from the bottom in the whole process, calcification treatment is carried out when the molten steel leaves a station, the feeding amount of calcium wires is more than or equal to 200m, and S=0.0015% when the molten steel leaves the station; vacuum degree of VD vacuum treatment is 0.4 torr, vacuum time is 17min, soft blowing time before the VD furnace is 15min, and hydrogen is fixed to be 1.1ppm. The thickness of the casting section of continuous casting is 260mm, the superheat degree of the continuous casting tundish is 10-16 ℃, and the smelting compositions are shown in table 1.
The implementation process of the steel rolling process comprises the following steps: the continuous casting billet is heated to limit the hearth temperature to 1220 ℃, the actual tapping temperature to 1186 ℃, the initial rolling temperature of the first stage to 1078 ℃, the reduction rate of the last three passes to 16%,19%,21%, the final rolling temperature to 1010 ℃, the thickness of the rolled intermediate billet to 125mm, the initial rolling temperature of the second stage to 800 ℃, the final rolling temperature to 771 ℃ and the thickness of the rolled finished product to 50mm.
The implementation process of the heat treatment process comprises the following steps: the quenching heating furnace chamber is set at 920 ℃, the actual tapping temperature is 918 ℃, the heat preservation time is 46 minutes, the tempering heating furnace chamber is set at 700 ℃, and the actual tapping temperature is 672 ℃. Finally, the steel plate is obtained, the performance of the steel plate is shown in table 2, and the metallographic structure of the steel plate is shown in figure 1.
Example 2:
the steelmaking process and the smelting composition were the same as in example 1.
The implementation process of the steel rolling process comprises the following steps: the continuous casting billet is heated to limit the hearth temperature to 1220 ℃, the actual tapping temperature to 1192 ℃, the initial rolling temperature in the first stage to 1105 ℃, the reduction rates of the last three passes to 18%,20% and 23%, the final rolling temperature to 1006 ℃, the thickness of the rolled intermediate billet to 80mm, the initial rolling temperature in the second stage to 860 ℃, the final rolling temperature to 803 ℃ and the thickness of the rolled finished product to 25mm.
The implementation process of the heat treatment process comprises the following steps: the quenching heating furnace chamber is set at 920 ℃, the actual tapping temperature is 921 ℃, the heat preservation time is 30 minutes, the tempering heating furnace chamber is set at 700 ℃, and the actual tapping temperature is 674 ℃. Finally, the steel plate is obtained, the performance of the steel plate is shown in table 2, and the metallographic structure of the steel plate is shown in fig. 2.
Example 3:
the steelmaking process and the smelting composition were the same as in example 1.
The implementation process of the steel rolling process comprises the following steps: the continuous casting billet is heated to limit the hearth temperature to 1220 ℃, the actual tapping temperature to 1181 ℃, the initial rolling temperature of the first stage to 1101 ℃, the reduction rates of the last three passes to 18%,21%,22%, the final rolling temperature to 1000 ℃, the thickness of the rolled intermediate billet to 70mm, the initial rolling temperature of the second stage to 910 ℃, the final rolling temperature to 819 ℃ and the thickness of the rolled finished product to 18mm.
The implementation process of the heat treatment process comprises the following steps: the quenching heating furnace chamber setting temperature 890 ℃, the actual tapping temperature 890 ℃, the heat preservation time 18 minutes, the tempering heating furnace chamber setting temperature 670 ℃, the actual tapping temperature 668 ℃ and the heat preservation time 22 minutes. Finally, the steel plate is obtained, the performance of the steel plate is shown in table 2, and the metallographic structure of the steel plate is shown in fig. 3.
Example 4:
the steelmaking process and the smelting composition were the same as in example 1.
The implementation process of the steel rolling process comprises the following steps: the continuous casting billet is heated to limit the hearth temperature to 1220 ℃, the actual tapping temperature to 1195 ℃, the initial rolling temperature in the first stage to 1115 ℃, the reduction rates of the last three passes to 18%,21% and 23% respectively, the final rolling temperature to 1017 ℃, the thickness of a rolled intermediate billet to 70mm, the initial rolling temperature in the second stage to 960 ℃, the final rolling temperature to 804 ℃ and the thickness of a rolled finished product to 10mm.
The implementation process of the heat treatment process comprises the following steps: the quenching heating furnace chamber is set at 890 ℃, the actual tapping temperature is 889 ℃, the heat preservation time is 15 minutes, the tempering heating furnace chamber is set at 670 ℃, the actual tapping temperature is 671 ℃, and the heat preservation time is 25 minutes. Finally, the steel plate is obtained, the performance of the steel plate is shown in table 2, and the metallographic structure of the steel plate is shown in fig. 4.
Table 1 example 1 smelting chemistry composition (wt.%)
Table 2-1 results of the Performance test of each example (1)
Tables 2-2 results of the performance test of each example (2)
As can be seen from table 1 above, the example composition meets the design composition requirements. As can be seen from the above tables 2-1 and 2-2, the steel of the invention has good toughness, low surface hardness, good bending process performance, no plastic transition (NDT) temperature lower than-50 ℃, and all performances completely meet the technical requirements, and can be used for manufacturing low-temperature spherical tanks in oil refining and petrochemical industries. As can be seen from fig. 1 to 4, the structure is bainite, and the structure is fine and uniform.
Claims (4)
1. A steel for a low surface hardness spherical tank, characterized in that: the steel comprises the following chemical components in percentage by mass of C=0.05-0.07, si=0.15-0.30, mn=1.40-1.60, P is less than or equal to 0.008, S is less than or equal to 0.003, alt=0.020-0.050, nb=0.020-0.030, V=0.040-0.060, ni=0.30-0.50, mo=0.20-0.30, sn is less than or equal to 0.008, and pcm is less than or equal to 0.20%; the balance of Fe, indispensable impurities; the structure of the steel is bainite, and simultaneously, the surface hardness is less than or equal to 220HBW, the impact absorption energy at the positions of 1/4 and 1/2 and 50 ℃ below zero is more than or equal to 100J, and the performance index of the non-plastic transition temperature NDT is less than-50 ℃.
2. The production method of the steel for the spherical tank with low surface hardness adopts the process route of converter smelting, LF refining, VD vacuum treatment, continuous casting, slab heating, controlled rolling, quenching and tempering, and is characterized by comprising the following key process steps:
(1) Smelting in a converter: the tapping P is less than or equal to 0.010 percent, and the slag skimming operation after tapping is carried out to further remove P;
(2) LF refining: after molten steel enters an LF refining furnace, performing white slag making and heating operation, wherein the rapid slag forming is required, the total standing time is more than or equal to 50min, and argon is blown from bottom in the whole process; calcification treatment is carried out when the LF furnace is out of the station, and the feeding quantity of calcium wires is more than or equal to 200m;
(3) And (3) VD vacuum treatment: the vacuum degree of the VD is below 0.5 torr (67 Pa), the vacuum holding time is more than or equal to 15min, and the soft blowing time before the VD is discharged is more than or equal to 12min;
(4) Continuous casting: the thickness of the continuous casting billet is 260mm, the continuous casting is performed with full-process protection casting, low superheat degree steel casting is adopted, and the superheat degree of the tundish is: the temperature of the casting furnace is less than or equal to 25 ℃ and the temperature of the continuous casting furnace is less than or equal to 18 ℃;
(5) And (3) heating a plate blank: heating the slab in a stepping furnace, limiting the temperature of a hearth to be less than or equal to 1220 ℃, and controlling the tapping temperature to be 1170-1210 ℃;
(6) And (3) rolling control: the initial rolling temperature at one stage is 1050-1150 ℃, the final rolling temperature is more than or equal to 950 ℃, and low-speed large-reduction rolling is adopted, so that the reduction rate of at least one pass is ensured to be more than 20%; the initial rolling temperature of the two stages is 800-960 ℃ (different initial rolling temperatures according to the thickness of the finished steel plate), and the final rolling temperature is more than or equal to 760 ℃;
(7) And (3) heat treatment: quenching and tempering.
3. The method for producing a steel for a low surface hardness spherical tank according to claim 2, characterized in that: and (7) heat treatment: the heat treatment process of the steel plate with the thickness of 10mm to 20mm comprises the following steps: quenching process, heating temperature 890+/-10 ℃ and heat preservation time 15-30 min; tempering: heating temperature 670+/-10 ℃ and heat preservation time 20-35 min.
4. The method for producing a steel for a low surface hardness spherical tank according to claim 2, characterized in that: and (7) heat treatment: the heat treatment process of the steel plate with the thickness of more than 20mm to 50mm comprises the following steps: quenching process, heating temperature 920+/-10 ℃ and heat preservation time 30-50 min; and tempering, namely setting the temperature of a hearth to 700 ℃ and the surface temperature of the steel plate to 670-675 ℃ by adopting a high-temperature rapid heating process, and tapping.
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