CN114657322A - Large-caliber duplex stainless steel seamless steel pipe and preparation method and application thereof - Google Patents
Large-caliber duplex stainless steel seamless steel pipe and preparation method and application thereof Download PDFInfo
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- CN114657322A CN114657322A CN202210418511.XA CN202210418511A CN114657322A CN 114657322 A CN114657322 A CN 114657322A CN 202210418511 A CN202210418511 A CN 202210418511A CN 114657322 A CN114657322 A CN 114657322A
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 91
- 239000010959 steel Substances 0.000 title claims abstract description 91
- 229910001039 duplex stainless steel Inorganic materials 0.000 title claims abstract description 88
- 238000002360 preparation method Methods 0.000 title abstract description 17
- 238000000034 method Methods 0.000 claims abstract description 32
- 238000010622 cold drawing Methods 0.000 claims abstract description 28
- 238000007670 refining Methods 0.000 claims abstract description 28
- 238000005098 hot rolling Methods 0.000 claims abstract description 21
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 18
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 15
- 238000005261 decarburization Methods 0.000 claims abstract description 13
- 238000003723 Smelting Methods 0.000 claims abstract description 12
- 238000010438 heat treatment Methods 0.000 claims description 158
- 238000005242 forging Methods 0.000 claims description 145
- 238000001816 cooling Methods 0.000 claims description 65
- 238000000137 annealing Methods 0.000 claims description 32
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 24
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 20
- 238000009749 continuous casting Methods 0.000 claims description 19
- 230000006698 induction Effects 0.000 claims description 17
- 239000000314 lubricant Substances 0.000 claims description 17
- 238000004519 manufacturing process Methods 0.000 claims description 15
- 239000013535 sea water Substances 0.000 claims description 13
- 238000004513 sizing Methods 0.000 claims description 12
- 229910052786 argon Inorganic materials 0.000 claims description 10
- 238000005096 rolling process Methods 0.000 claims description 10
- 230000006835 compression Effects 0.000 claims description 9
- 238000007906 compression Methods 0.000 claims description 9
- 230000001681 protective effect Effects 0.000 claims description 8
- 238000004080 punching Methods 0.000 claims description 6
- 230000003746 surface roughness Effects 0.000 claims description 6
- 230000007547 defect Effects 0.000 claims description 5
- 239000002245 particle Substances 0.000 claims description 4
- 238000005266 casting Methods 0.000 claims description 3
- 238000004140 cleaning Methods 0.000 claims description 2
- 239000004576 sand Substances 0.000 claims description 2
- 238000007599 discharging Methods 0.000 claims 1
- 238000005260 corrosion Methods 0.000 abstract description 27
- 230000007797 corrosion Effects 0.000 abstract description 27
- 229910000765 intermetallic Inorganic materials 0.000 abstract description 8
- 239000000126 substance Substances 0.000 abstract description 7
- 239000013078 crystal Substances 0.000 abstract description 5
- 238000001556 precipitation Methods 0.000 abstract description 5
- 239000012535 impurity Substances 0.000 abstract description 4
- 230000000007 visual effect Effects 0.000 abstract description 2
- 238000012360 testing method Methods 0.000 description 24
- 229910001220 stainless steel Inorganic materials 0.000 description 7
- 239000010935 stainless steel Substances 0.000 description 7
- 239000011248 coating agent Substances 0.000 description 6
- 238000000576 coating method Methods 0.000 description 6
- 238000005482 strain hardening Methods 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 4
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000002480 mineral oil Substances 0.000 description 4
- 235000010446 mineral oil Nutrition 0.000 description 4
- 238000005336 cracking Methods 0.000 description 3
- 239000004033 plastic Substances 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 2
- 238000009835 boiling Methods 0.000 description 2
- 238000005090 crystal field Methods 0.000 description 2
- 238000004321 preservation Methods 0.000 description 2
- 229910000604 Ferrochrome Inorganic materials 0.000 description 1
- 229910000593 SAF 2205 Inorganic materials 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000006399 behavior Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000003628 erosive effect Effects 0.000 description 1
- 238000001192 hot extrusion Methods 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 239000013067 intermediate product Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 description 1
- 229910001629 magnesium chloride Inorganic materials 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
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- 239000000047 product Substances 0.000 description 1
- 238000010926 purge Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
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- 238000002791 soaking Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 229920001169 thermoplastic Polymers 0.000 description 1
- 239000004416 thermosoftening plastic Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000011179 visual inspection Methods 0.000 description 1
Classifications
-
- 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
- C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
- C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B19/00—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work
- B21B19/02—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work the axes of the rollers being arranged essentially diagonally to the axis of the work, e.g. "cross" tube-rolling ; Diescher mills, Stiefel disc piercers or Stiefel rotary piercers
- B21B19/04—Rolling basic material of solid, i.e. non-hollow, structure; Piercing, e.g. rotary piercing mills
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B19/00—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work
- B21B19/02—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work the axes of the rollers being arranged essentially diagonally to the axis of the work, e.g. "cross" tube-rolling ; Diescher mills, Stiefel disc piercers or Stiefel rotary piercers
- B21B19/06—Rolling hollow basic material, e.g. Assel mills
- B21B19/10—Finishing, e.g. smoothing, sizing, reeling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
- B21C37/06—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of tubes or metal hoses; Combined procedures for making tubes, e.g. for making multi-wall tubes
-
- 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
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/52—Manufacture of steel in electric furnaces
-
- 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
-
- 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
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/068—Decarburising
- C21C7/0685—Decarburising of stainless steel
-
- 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
- C21D2211/001—Austenite
-
- 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
- C21D2211/005—Ferrite
-
- 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
- Y02P10/25—Process efficiency
Abstract
The invention provides a large-caliber duplex stainless steel seamless steel tube and a preparation method and application thereof, wherein the outer diameter of the large-caliber duplex stainless steel seamless steel tube is 610-914mm, the radial-wall ratio is more than 60, the grain size is more than 7 grade, and the range of the grain size is less than or equal to 2 grade; the ferrite content is 48-53%; the chemical components are accurately controlled through primary smelting, LF refining and VOD decarburization refining, the contents of non-metallic inclusions, impurity elements, residual elements and harmful elements are reduced, and the proportion and the purity of two phases of austenite and ferrite in the duplex stainless steel seamless steel pipe are ensured; the large-caliber duplex stainless steel seamless steel tube which has the advantages of wide size range, high size precision, good inner and outer surface quality, high purity, low inclusion content, no precipitation of brittle phases and intermetallic compounds, no mixed crystal visual field, excellent corrosion resistance and excellent mechanical property is obtained by organically combining hot rolling, hot expanding and cold drawing processes.
Description
Technical Field
The invention belongs to the field of stainless steel seamless pipe preparation, and particularly relates to a large-caliber duplex stainless steel seamless pipe and a preparation method and application thereof.
Background
The pipeline for conveying seawater and the water pipeline in the marine environment are contacted with seawater for a long time, and the phenomena of local point corrosion perforation, crevice corrosion and chloride stress corrosion cracking are easy to occur. In order to solve the problems of seawater corrosion and erosion, austenitic stainless steel represented by nuclear grade Z2CN1810, super austenitic stainless steel represented by UNSN08367 and duplex stainless steel represented by SAF2205 are sequentially adopted as the pipeline materials, wherein the duplex stainless steel is superior to the austenitic stainless steel in seawater corrosion resistance and lower in cost than the super austenitic stainless steel, so that the duplex stainless steel gradually becomes the first material of a seawater pipeline system, a seabed water pipeline and a seabed water pipeline of a nuclear power plant. Nowadays, with the increasing installed capacity and seabed water delivery capacity of nuclear power plants, pipeline systems develop towards large caliber and light weight, for example, in the current nuclear power plant seawater pipeline system, the thickness of a steel pipe with the diameter of 711mm is only 11mm, the thickness of a steel pipe with the diameter of 914mm is only 15mm, the radial-to-wall ratio exceeds 60, and the pipeline has high requirements on the size precision, the surface quality, the strength and the toughness of the pipeline. The deformation behaviors of an austenite phase and a ferrite phase in the duplex stainless steel are different, so that the thermoplastic property of the duplex stainless steel is poor, the stress and strain distribution between the two phases are uneven during hot processing, the crack nucleation and expansion of a phase boundary are easily induced, and the brittle fracture occurs in a deformation area during hot piercing, rolling or hot extrusion of a steel pipe. Meanwhile, the yield strength of the duplex stainless steel is high, the cold working deformation resistance is large, the cold working deformation is strictly limited, and the problems of cracking, galling and the like can occur in the cold working deformation of the steel pipe. Therefore, in order to adapt to the development trend of nuclear power units and submarine water pipelines, a plurality of problems in manufacturing large-caliber thin-wall duplex stainless steel seamless pipes are urgently needed to be solved.
CN104368623B discloses a method for producing a large-diameter stainless steel seamless pipe by using a 508 machine set perforation, hole expansion and wall reduction method, wherein the outer diameter of the stainless steel seamless pipe is 380-650 mm, the wall thickness is 20-60 mm, and the length is 3000-8000 mm. The manufacturing capability of the 508 hot rolling mill is limited, the size specification of the seamless pipe produced by the method can not meet the requirement of a seawater pipeline system of a nuclear power plant, and the selected process parameters are not suitable for manufacturing the duplex stainless steel pipe.
CN102189187A discloses a method for manufacturing a large-diameter stainless seamless pipe by hot-expanding a mother pipe. However, duplex stainless steel has a sensitive temperature range in which a σ phase and intermetallic compounds are precipitated and a temperature range in which brittle transition at 475 ℃ occurs, and this method does not specifically limit how quickly the temperature range passes through in the heating process before hot expansion and the cooling process after hot expansion.
CN103710637A discloses a method for manufacturing thin-wall super duplex stainless steel seamless tube by hot rolling perforation, cold drawing and cold rolling. However, this method does not describe how to avoid the problems of precipitation of harmful phases and intermetallic compounds and generation of cracks in the inner surface of the pierced pipe during piercing-rolling, and does not involve intermediate annealing and solution heat treatment during cold working, and the quality of cold working cannot be guaranteed.
Therefore, in order to meet the requirements of the seawater pipeline system and the seabed water pipeline of the nuclear power plant on the large-diameter duplex stainless steel seamless pipe, a production process of the large-diameter duplex stainless steel seamless pipe, which is economic, flexible, practical, efficient, high in yield and high in manufacturing precision, is urgently needed.
Disclosure of Invention
The invention aims to provide a large-caliber duplex stainless steel seamless steel tube and a preparation method and application thereof, wherein the outer diameter of the large-caliber duplex stainless steel seamless steel tube is 610-914mm, the radial-wall ratio is more than 60, the grain size is more than 7 grade, and the range of the grain size is less than or equal to 2 grade; the ferrite content is 48-53%; the chemical components are accurately controlled through primary smelting, LF refining and VOD decarburization refining, the contents of non-metallic inclusions, impurity elements, residual elements and harmful elements are reduced, and the purity of stainless steel and the proportion of two phases of austenite and ferrite in a duplex stainless steel seamless steel pipe are ensured; the large-caliber duplex stainless steel seamless steel tube which has the advantages of wide size range, high size precision, good inner and outer surface quality, high purity, low inclusion content, no precipitation of brittle phases and intermetallic compounds, no mixed crystal visual field, excellent corrosion resistance and excellent mechanical property is obtained by organically combining hot rolling, hot expanding and cold drawing processes.
In order to achieve the purpose, the invention adopts the following technical scheme:
one of the purposes of the invention is to provide a large-caliber duplex stainless steel seamless steel pipe, wherein the outer diameter of the large-caliber duplex stainless steel seamless steel pipe is 610-914mm, the radial-wall ratio is more than 60, the grain size is more than 7 grade, and the range of the grain size is less than or equal to 2 grade; the ferrite content of the large-caliber duplex stainless steel seamless steel pipe is 48-53%, and the balance is austenite.
The large-caliber duplex stainless steel seamless steel pipe has the advantages of wide size range, high size precision and good quality of the inner surface and the outer surface; the purity is high, and the inclusion content is low; the metallographic structure is a two-phase structure with balanced ratio of austenite and ferrite, no brittle phase and intermetallic compound are separated out, and no mixed crystal field of view exists; the corrosion resistance and the mechanical property are excellent, and the requirements of technical protocols of duplex stainless steel seamless steel pipes for seawater pipeline systems and seabed water pipelines of nuclear power plants are met.
It is worth to be noted that the outer diameter of the large-caliber duplex stainless steel seamless steel tube is 610-914mm, for example, 610mm, 630mm, 660mm, 680mm, 700mm, 710mm, 725mm, 750mm, 768mm, 800mm, 833mm, 850mm, 887mm, 900mm, 910mm and the like; the ratio of the radial walls is > 60, and can be, for example, 61, 62, 65, 68, 70, 73, 77, 80, 85, 90, etc.; the grain size is 7 or more, for example, 7, 8, 9, etc.; the range of the grain size is less than or equal to 2 grades, for example, the range can be 1 grade or 2 grades, and the range of the grain size is the grade of the difference between the maximum grade and the minimum grade of the grain size; the large-caliber duplex stainless steel seamless steel pipe has a ferrite content of 48 to 53%, for example, 48%, 49%, 50%, 51%, 52%, 53%, etc., and the balance is austenite.
As a preferable embodiment of the present invention, the large-diameter duplex stainless steel seamless steel pipe may have a straightness of < 1.5mm/m, for example, 0.1mm/m, 0.2mm/m, 0.3mm/m, 0.4mm/m, 0.5mm/m, 0.6mm/m, 0.7mm/m, 0.8mm/m, 0.9mm/m, 1.0mm/m, 1.1mm/m, 1.2mm/m, 1.3mm/m, 1.4mm/m, 1.49mm/m, or the like.
Preferably, the surface roughness of the large-caliber duplex stainless steel seamless steel pipe is less than 12.5 μm, and can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 12.4 μm and the like.
The second purpose of the invention is to provide a preparation method of the large-caliber duplex stainless steel seamless steel pipe, which comprises the following steps:
(1) carrying out electric furnace primary smelting, LF refining and VOD decarburization refining on the molten steel in sequence, and pouring to obtain a continuous casting billet;
(2) sequentially carrying out three-stage heating and forging on the continuous casting billet obtained in the step (1) to obtain a forged billet;
(3) sequentially perforating and hot rolling the forging blank in the step (2) to obtain a pierced billet;
(4) carrying out hot expanding on the pierced billet in the step (3) to obtain a tubular billet;
(5) and (4) sequentially carrying out cold drawing and solution treatment on the capillary pipe in the step (4) to obtain the large-caliber duplex stainless steel seamless steel pipe.
According to the invention, the chemical components are accurately controlled through electric furnace primary smelting, LF refining and VOD decarburization refining, the contents of non-metallic inclusions, impurity elements, residual elements and harmful elements are reduced, and the purity of stainless steel and the proportion of two phases of austenite and ferrite in a duplex stainless steel seamless steel pipe are ensured; the method can obtain larger diameter-changing rate by adopting once intermediate frequency thermal expansion treatment, improves the working efficiency, has flexible production mode, and is suitable for producing large-caliber duplex stainless steel seamless steel pipes with various varieties and specifications.
It is noted that the raw materials of the molten steel include dephosphorized molten iron, ferrochrome and scrap steel.
As a preferred embodiment of the present invention, the end point of LF refining in step (1) is S.ltoreq.0.005%, for example, 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, etc., and O.ltoreq.25 ppm, for example, 5ppm, 8ppm, 10ppm, 12ppm, 17ppm, 20ppm, 22ppm, 25ppm, etc., in the discharge.
It is worth to say that the purity of the molten steel can be improved through LF refining and VOD decarburization refining, and the proportion of ferrite and austenite is ensured through accurately controlling chemical components.
Preferably, the casting in step (1) is performed in an argon protective atmosphere. And purging a casting blank cavity with argon before pouring, starting pouring when the measured oxygen concentration is lower than 4%, and continuously blowing argon for protection in the pouring process to prevent molten steel from being secondarily oxidized.
As a preferable technical solution of the present invention, the three-stage heating in step (2) includes a first-stage heating, a second-stage heating, and a third-stage heating, which are sequentially performed.
Preferably, the first stage heating comprises: raising the temperature to 750-850 ℃ at the heating rate of 60-90 ℃/h, and keeping the temperature for 1-1.5h, so as to ensure that the internal temperature of the continuous casting billet is uniform and prepare for the rapid heating in the second stage.
It is worth to be noted that the heating rate of the first stage is 60-90 ℃/h, for example, 60 ℃/h, 65 ℃/h, 70 ℃/h, 75 ℃/h, 80 ℃/h, 85 ℃/h, 90 ℃/h, etc.; raising the temperature to 750-850 ℃, for example 750 ℃, 760 ℃, 770 ℃, 780 ℃, 790 ℃, 800 ℃, 810 ℃, 820 ℃, 830 ℃, 840 ℃, 850 ℃ and the like; the heat preservation time is 1-1.5h, for example, 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h and the like.
Preferably, the second stage heating comprises: heating to 960-980 ℃ at the heating rate of 150 ℃/h of 120-; the heating rate of the second stage heating is faster, because 800-.
It is worth to be noted that the heating rate in the second stage is 120-; the temperature may be raised to 960 ℃ and 980 ℃ and may be, for example, 960 ℃, 962 ℃, 965 ℃, 968 ℃, 970 ℃, 973 ℃, 975 ℃, 977 ℃, 980 ℃.
Preferably, the third stage heating comprises: raising the temperature to 1080-1150 ℃ at the heating rate of 90-100 ℃/h, and preserving the temperature for 3-5h, so as to fully diffuse the elements, eliminate the element segregation of the branch crystals and the intercritical crystals of the cast tissue and make the tissue uniform.
It is worth to be noted that the heating rate in the third stage is 90-100 ℃/h, for example, 90 ℃/h, 92 ℃/h, 94 ℃/h, 96 ℃/h, 98 ℃/h, 100 ℃/h, etc.; raising the temperature to 1080-1150 ℃, for example 1080 ℃, 1090 ℃, 1100 ℃, 1110 ℃, 1120 ℃, 1130 ℃, 1140 ℃, 1150 ℃ and the like; the heat preservation time is 3-5h, for example, 3h, 3.2h, 3.5h, 3.7h, 4h, 4.3h, 4.5h, 4.8h, 5h and the like. As a preferable technical scheme of the invention, the forging in the step (2) comprises longitudinal forging and transverse forging.
Preferably, the longitudinal forging adopts a radial forging machine.
Preferably, the longitudinal forging has a draw deformation ratio of 1.8 to 2.5, which may be, for example, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, etc.
Preferably, the equipment adopted by the transverse forging is a quick forging machine, the quick forging machine is provided with an online surface defect cleaning device, surface defects which can be generated during each hot forging can be timely cleaned at a high temperature, and cracking with large depth caused by defect accumulation is prevented.
Preferably, the transverse forging has a compression set ratio of 1.5 to 2.2, which may be, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, etc.
Preferably, the forging temperature in step (2) is 1050-.
Preferably, the finish forging temperature of the forging in the step (2) is 960-.
It should be noted that when the temperature of the billet drops to approximately 960 c during forging, the billet should be re-heated to the initial forging temperature. By controlling the initial forging temperature, the final forging temperature, the drawing deformation ratio of longitudinal forging and the compression deformation ratio of transverse forging, the cast tree-shaped structure of the continuous casting billet and the anisotropy of the material can be effectively eliminated, the shape of inclusions is improved, the inclusions and coarse grains are crushed, the two-phase structure is refined and uniform, and the plasticity and the toughness of the material are improved.
Preferably, the forging in the step (2) is performed not less than 3 times, and may be performed 3 times, 4 times, 5 times, 6 times, 8 times, 10 times and the like.
Preferably, the total forging ratio of the forging of step (2) is > 5, and may be, for example, 5.1, 5.5, 6, 7, 8, 9, 10, 12, 15, 18, 20, etc.
It is worth explaining that the invention can fully crush coarse grains, eliminate looseness, shrinkage cavity and anisotropy by selecting proper opening forging temperature and finish forging temperature and comprehensively using a radial forging machine and a quick forging machine to carry out upsetting and drawing out on a continuous casting billet, so that two phases of austenite and ferrite are uniformly distributed, and the surface forging defect is reduced.
As a preferable technical scheme of the invention, before the perforation in the step (3), the forging blank in the step (2) is subjected to first annealing at 1050-; the temperature of the first annealing is 1050-; the time of the first annealing is 1-2h, for example, 1h, 1.2h, 1.4h, 1.5h, 1.6h, 1.8h, 2h and the like; the cooling rate of the first cooling is 100-; the first cooling may be, for example, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃ or the like.
It is worth to say that the temperature of the first annealing is 1050-1150 ℃, which can not only prevent the harmful phases of sigma phase and the like from being fully dissolved due to too low temperature, but also prevent the crystal grains from growing due to too high temperature; the cooling rate of the first cooling is 100-2N phase, gamma2And separating out the phases.
Preferably, the perforating step of step (3) comprises: after a positioning hole is punched in the center of the round surface of the forging blank, the temperature is raised to 1150-fold-0 ℃ at the temperature rise rate of 2.5-3 ℃/min, the temperature is preserved for 150-fold-150 min, and then the punching is carried out on a conical roller puncher; the heating rate is 2.5-3 deg.C/min, such as 2.5 deg.C/min, 2.6 deg.C/min, 2.7 deg.C/min, 2.8 deg.C/min, 2.9 deg.C/min, 3 deg.C/min, etc.; the temperature is raised to 1150-; the temperature is maintained for 120-150min, such as 120min, 125min, 130min, 135min, 140min, 145min, 150min, etc.
It is worth to be noted that before the positioning holes are punched, the forging blank is peeled by a peeling machine; the temperature rise rate is 2.5-3 ℃/min, and the temperature can rapidly pass through the sensitive temperature range of 800-.
Preferably, the rolling ratio of the hot rolling in the step (3) is more than 3, and can be 3.1, 3.5, 3.8, 4, 4.5, 5, 6, 7, 8, 9, 10, 15, 18, 20, etc., for example.
As a preferable technical scheme of the invention, before the thermal expansion in the step (4), the temperature of the pierced billet obtained in the step (3) is raised to 1050-; the temperature rise rate of the second annealing is 2.5 to 3 ℃/min, for example, 2.5 ℃/min, 2.6 ℃/min, 2.7 ℃/min, 2.8 ℃/min, 2.9 ℃/min, 3 ℃/min or the like; the temperature of the second annealing is 1050-; the second annealing time is 90-120min, such as 90min, 95min, 100min, 105min, 110min, 115min, 120min, etc.; the cooling rate of the second cooling is 120-; the second cooling is carried out at 20-50 deg.C, and may be, for example, 20 deg.C, 25 deg.C, 30 deg.C, 35 deg.C, 40 deg.C, 45 deg.C, 50 deg.C, etc.
It is worth mentioning that the second anneal acts as a destressing; the cooling rate of the second cooling is 120-2N phase, gamma2Separating out a phase; the strength and hardness of the pierced billet are reduced through the second annealing and the second cooling, the plasticity is improved, and the subsequent cold and hot processing is facilitated.
Preferably, the lubricant comprises powdered graphite powder, flake graphite powder and water.
Preferably, the mass ratio of the powdered graphite powder to the flaky graphite powder to the water is 1 (1.2-1.8): (2.5-3.5), and may be, for example, 1:1.2:2.5, 1:1.2:2.8, 1:1.2:3, 1:1.2:3.3, 1:1.2:3.5, 1:1.5:2.5, 1:1.5:2.8, 1:1.5:3, 1:1.5:3.2, 1:1.5:3.5, 1:1.8:2.5, 1:1.8:2.8, 1:1.8:3, 1:1.8:3.2, 1:1.8:3.5, 1:1.3:2.5, 1:1.4:2.5, 1:1.6:2.5, 1:1.3: 1.7: 1.5, 1:1.5: 1.6:2.5, 1:1.5, 1:1.8:3.5, 1:1.5, 1.7:3.5, 1.5, 1:1.5, 1.8:3.5, 1: 3.5, etc.
Preferably, the particle size of the powdered graphite powder is 55-65 μm, and may be 55 μm, 56 μm, 57 μm, 5859 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm, or the like, for example.
Preferably, the particle size of the crystalline flake graphite powder is 80-90 μm, and may be, for example, 80 μm, 82 μm, 84 μm, 85 μm, 86 μm, 88 μm, 90 μm, or the like.
Preferably, the temperature of the thermal expansion in step (4) is 960-.
Preferably, the thermal expansion ratio in step (4) is 1.2-1.5, and may be, for example, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, etc.
Preferably, the expanding advancing speed of the thermal expansion in the step (4) is 30-60mm/min, such as 30mm/min, 33mm/min, 35mm/min, 37mm/min, 40mm/min, 42mm/min, 45mm/min, 48mm/min, 50mm/min, 52mm/min, 55mm/min, 57mm/min, 60mm/min, etc.
Preferably, the heating outer diameter of the induction heating coil in the step (4) is 90-110mm more than the outer diameter of the hollow billet after hot expansion, for example, the heating outer diameter can be 90mm, 92mm, 95mm, 98mm, 100mm, 103mm, 105mm, 107mm, 110mm, etc., so as to ensure the heat penetration depth of induction heating and avoid overburning of the surface of the hollow billet.
Preferably, the length of the induction heating coil in the hot expanding in the step (4) covers the deformation zone of the pierced billet and extends forwards and backwards for 300mm and 500mm respectively, for example, 300mm, 320mm, 50mm, 380mm, 400mm, 430mm, 450mm, 470mm, 500mm and the like, so as to ensure that the pierced billet is fully preheated and reaches the specified hot expanding temperature when entering the deformation zone.
Preferably, after the heat expansion deformation in the step (4), the cooling mode of the pierced billet entering the sizing area is forced air cooling.
It is worth explaining that in the hot expanding process, the pierced billet enters the sizing area after passing through the deformation area, and the pierced billet in the sizing area rapidly passes through the sensitive temperature interval where the harmful phase and the brittle phase are separated out by utilizing forced air cooling.
As a preferable technical scheme of the invention, before the cold drawing in the step (5), the temperature of the capillary in the step (4) is raised to 1050-; the temperature rise rate of the third annealing is 2.5-3 ℃/min, for example, 2.5 ℃/min, 2.6 ℃/min, 2.7 ℃/min, 2.8 ℃/min, 2.9 ℃/min, 3 ℃/min, etc.; the temperature of the third annealing is 1050-; the third annealing time is 90-120min, such as 90min, 95min, 100min, 105min, 110min, 115min, 120min, etc.; the cooling rate of the third annealing is 120-260 deg.C/s, which can be, for example, 120 deg.C/s, 140 deg.C/s, 160 deg.C/s, 180 deg.C/s, 200 deg.C/s, 220 deg.C/s, 240 deg.C/s, 260 deg.C/s, etc.; the third annealing may be carried out at 20 to 50 ℃ and may be, for example, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃ or the like.
It is worth to say that the cooling rate of the third cooling is 120-260 ℃/s, which can not only avoid the precipitation of harmful phases such as sigma phase caused by lower cooling rate, but also prevent the generation of quenching cracks or Cr caused by over-high cooling rate2N phase, gamma2Separating out a phase; the strength and the hardness of the hollow billet are reduced through the third annealing and the third cooling, the plasticity is improved, and the subsequent cold drawing processing is facilitated.
Preferably, the number of cold drawing passes in step (5) is 1-3, and may be, for example, 1, 2, or 3.
It is worth to be noted that when the number of cold drawing passes is 2 or 3, the intermediate product is subjected to heat treatment between every two cold drawing passes; during heat treatment, the temperature is raised to 1050-1120 ℃ at the heating rate of 2.5-3.0 ℃/min, the temperature is preserved for 90-120min, and then the mixture is taken out of the furnace and is rapidly cooled by water.
Preferably, the speed of the cold drawing in step (5) is 0.2-0.6m/min, and may be, for example, 0.2m/min, 0.25m/min, 0.3m/min, 0.35m/min, 0.4m/min, 0.45m/min, 0.5m/min, 0.55m/min, 0.6m/min, etc.
Preferably, the wall thickness reduction amount of the cold drawing in the step (5) is 1.5-3.5 mm/pass, and may be, for example, 1.5 mm/pass, 1.8 mm/pass, 2.0 mm/pass, 2.2 mm/pass, 2.5 mm/pass, 2.7 mm/pass, 3 mm/pass, 3.2 mm/pass, 3.5 mm/pass, or the like.
It is worth to say that the invention effectively avoids the cracks and surface cracks which often occur in the processes of perforation, hot rolling, hot expanding and heat treatment by selecting proper heating schedule and cooling rate, and prevents the precipitation of brittle phase and intermetallic compounds. Particularly, the medium-frequency thermal expansion process is successfully applied to the manufacture of the large-caliber duplex stainless steel seamless steel tube by selecting a proper thermal expansion temperature and adopting a forced air cooling mode after thermal expansion deformation, and large diameter expansion and wall reduction can be simultaneously completed.
Preferably, the temperature of the solution treatment in the step (5) is 1040-.
Preferably, the time of the solution treatment in the step (5) is 1-2h, and may be 1h, 1.2h, 1.4h, 1.5h, 1.6h, 1.8h, 2h and the like.
It is worth to say that the solution treatment is carried out by heating to 1040-1080 ℃ at the heating rate of 2.5-3.0 ℃/min, keeping the temperature for 1-2h, and transferring the product to water with the initial temperature not more than 35 ℃ within 60s for rapid cooling after being taken out of the furnace, so as to obtain the optimal ratio of austenite to ferrite, good pitting corrosion resistance and comprehensive mechanical property.
As a preferred technical scheme of the invention, the preparation method comprises the following steps:
(1) carrying out electric furnace primary smelting, LF refining and VOD decarburization refining on the molten steel in sequence, and pouring in an argon protective atmosphere to obtain a continuous casting billet;
(2) sequentially carrying out three-stage heating on the continuous casting slab in the step (1), wherein the three-stage heating comprises a first-stage heating, a second-stage heating and a third-stage heating which are sequentially carried out, the temperature of the first-stage heating is increased to 750-fold sand 850 ℃ at the temperature increasing rate of 60-90 ℃/h, and the temperature is kept for 1-1.5 h; the second stage heating is carried out to raise the temperature to 960-980 ℃ at the temperature raising rate of 120-150 ℃/h; heating to 1080-; then, forging at least 3 times to obtain a forged blank;
wherein, forging comprises longitudinal forging and transverse forging: longitudinally forging the radial forging machine in a radial forging machine until the drawing deformation ratio is 1.8-2.5, and transversely forging the radial forging machine in a rapid forging machine until the compression deformation ratio is 1.5-2.2; controlling the initial forging temperature of 1050-;
(3) performing first annealing on the forging blank in the step (2) at 1050-; after a positioning hole is punched in the center of the round surface of the forging blank, the temperature is raised to 1150-1190 ℃ at the temperature rise rate of 2.5-3 ℃/min, and the temperature is preserved for 150 min; then, perforating on a conical roller perforating machine; then hot rolling is carried out, the rolling ratio of the hot rolling is controlled to be more than 3, and a pierced billet is obtained;
(4) heating the pierced billet in the step (3) to 1050-1120 ℃ at the heating rate of 2.5-3.0 ℃/min, carrying out second annealing for 90-120min, carrying out second cooling to 20-50 ℃ at the cooling rate of 120-260 ℃/s, and coating a lubricant on the inner wall of the pierced billet; then carrying out thermal expansion at the temperature of 960-1000 ℃, controlling the expansion ratio of the thermal expansion to be 1.2-1.5 and the advancing speed of the expanded pipe to be 30-60mm/min, and obtaining a capillary;
wherein, the lubricant comprises 55-65 μm powdered graphite powder, 80-90 μm crystalline flake graphite powder and water according to the mass ratio of 1 (1.2-1.8) to 2.5-3.5; in the thermal expansion, the heating outer diameter of the induction heating coil is 90-110mm more than the outer diameter of the capillary after the thermal expansion, and the length of the induction heating coil covers the deformation area of the pierced billet and extends for 500mm forward and backward respectively; after the thermal expansion deformation, the cooling mode of the pierced billets entering the sizing area is forced air cooling;
(5) heating the capillary tube in the step (4) to 1050-; performing cold drawing for 1-3 times at a speed of 0.2-0.6m/min, and controlling the wall thickness reduction amount of the cold drawing to be 1.5-3.5 mm/time; and carrying out solution treatment at 1040-1080 ℃ for 1-2h to obtain the large-caliber duplex stainless steel seamless steel tube.
The third purpose of the invention is to provide the application of the large-caliber duplex stainless steel seamless steel pipe, which is used for a seawater pipeline system.
The recitation of numerical ranges herein includes not only the above-recited numerical values, but also any numerical values between non-recited numerical ranges, and is not intended to be exhaustive or to limit the invention to the precise numerical values encompassed within the range for brevity and clarity.
Compared with the prior art, the invention has the following beneficial effects:
(1) the large-caliber duplex stainless steel seamless steel pipe has the advantages of wide size range, high size precision and good inner and outer surface quality; the purity is high, and the inclusion content is low; the metallographic structure is a two-phase structure with balanced ratio of austenite and ferrite, no brittle phase and intermetallic compound are precipitated, and no mixed crystal field of view exists;
(2) the large-caliber duplex stainless steel seamless steel pipe has excellent corrosion resistance and mechanical property, and meets the technical protocol requirements of the duplex stainless steel seamless steel pipe for a seawater pipeline system and a seabed water pipeline of a nuclear power plant;
(3) according to the preparation method of the large-caliber duplex stainless steel seamless steel tube, the chemical components are accurately controlled through primary smelting, LF refining and VOD decarburization refining, the contents of non-metallic inclusions, impurity elements, residual elements and harmful elements are reduced, the purity of the stainless steel is ensured, and the optimal proportion of two phases of austenite and ferrite in the duplex stainless steel seamless steel tube is ensured by matching with a proper heating and cooling system on the basis of accurately controlling the chemical components, so that the harmful phases and intermetallic compounds are prevented from being separated out after hot processing;
(4) the preparation method of the large-caliber duplex stainless steel seamless steel tube can obtain larger diameter-changing rate by adopting one-time intermediate frequency hot-expanding treatment, improves the working efficiency, has flexible production mode, and is suitable for producing large-caliber duplex stainless steel seamless steel tubes with various varieties and specifications.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a large-caliber duplex stainless steel seamless steel pipe and a preparation method thereof, wherein the preparation method comprises the following steps:
(1) carrying out electric furnace primary smelting, LF refining and VOD decarburization refining on the molten steel in sequence, and pouring in an argon protective atmosphere to obtain a continuous casting billet;
(2) sequentially carrying out three-stage heating on the continuous casting slab in the step (1), wherein the three-stage heating comprises a first-stage heating, a second-stage heating and a third-stage heating which are sequentially carried out, the temperature of the first-stage heating is increased to 850 ℃ at a temperature increasing rate of 80 ℃/h, and the temperature is kept for 1 h; heating to 960 ℃ at a heating rate of 150 ℃/h in the second stage; heating to 1100 ℃ at a heating rate of 90 ℃/h in the third stage, and keeping the temperature for 4 h; then, forging for 3 times to obtain a forged blank;
wherein, forging comprises longitudinal forging and transverse forging: longitudinally forging the radial forging machine in a radial forging machine until the elongation deformation ratio is 2.5, and transversely forging the radial forging machine in a rapid forging machine until the compression deformation ratio is 2; controlling the initial forging temperature of forging to be 1100 ℃, the final forging temperature to be 960 ℃, and the total forging ratio of forging to be 6;
(3) performing first annealing on the forging blank in the step (2) at 1150 ℃ for 1h, and then performing first cooling to 50 ℃ at a cooling rate of 150 ℃/s; after punching a positioning hole in the center of the round surface of the forging blank, heating to 1150 ℃ at the heating rate of 3 ℃/min, and preserving heat for 150 min; then, perforating on a conical roller perforating machine; then hot rolling is carried out, the rolling ratio of hot rolling is controlled to be 5, and a pierced billet is obtained;
(4) heating the pierced billet in the step (3) to 1120 ℃ at a heating rate of 3.0 ℃/min, carrying out second annealing for 90min, carrying out second cooling to 50 ℃ at a cooling rate of 200 ℃/s, and coating a lubricant on the inner wall of the pierced billet; then carrying out hot expanding at the temperature of 1000 ℃, controlling the expansion ratio of the hot expanding to be 1.5 and the advancing speed of expanding to be 45mm/min, and obtaining a capillary;
wherein the lubricant comprises 55-micron powdered graphite powder, 80-micron flaky graphite powder and water in a mass ratio of 1:1.5: 3; in the hot expanding, the heating outer diameter of the induction heating coil is 110mm more than the outer diameter of the tubular billet after the hot expanding, and the length of the induction heating coil covers the deformation zone of the pierced billet and extends 500mm respectively forwards and backwards; after the thermal expansion deformation, the cooling mode of the pierced billets entering the sizing area is forced air cooling;
(5) heating the tubular billet in the step (4) to 1120 ℃ at a heating rate of 3.0 ℃/min, carrying out third annealing for 90min, carrying out third cooling to 50 ℃ at a cooling rate of 200 ℃/s, and smearing a mineral oil lubricant on the inner wall of the tubular billet; performing cold drawing for 2 times at the speed of 0.5m/min, and controlling the wall thickness reduction amount of the cold drawing to be 3.5 mm/time; and carrying out solution treatment for 1h at 1080 ℃ to obtain the large-caliber duplex stainless steel seamless steel tube.
The large-caliber duplex stainless steel seamless steel pipe obtained in the embodiment has the outer diameter of 711mm, the radial-wall ratio of 65, the straightness of 1.3mm/m and the surface roughness of 9.2 mu m.
Example 2
The embodiment provides a large-caliber duplex stainless steel seamless steel pipe and a preparation method thereof, wherein the preparation method comprises the following steps:
(1) carrying out electric furnace primary smelting, LF refining and VOD decarburization refining on the molten steel in sequence, and pouring in an argon protective atmosphere to obtain a continuous casting billet;
(2) sequentially carrying out three-stage heating on the continuous casting blank in the step (1), wherein the three-stage heating comprises a first-stage heating, a second-stage heating and a third-stage heating which are sequentially carried out, the temperature of the first-stage heating is increased to 750 ℃ at a temperature increasing rate of 60 ℃/h, and the temperature is kept for 1.5 h; heating to 970 ℃ at the heating rate of 120 ℃/h in the second stage; in the third stage, heating to 1150 ℃ at the heating rate of 100 ℃/h, and keeping the temperature for 3 h; then, forging for 4 times to obtain a forged blank;
wherein, forging comprises longitudinal forging and transverse forging: longitudinally forging the radial forging machine in a radial forging machine until the elongation deformation ratio is 1.8, and transversely forging the radial forging machine in a rapid forging machine until the compression deformation ratio is 1.5; controlling the initial forging temperature of forging to be 1100 ℃, the final forging temperature to be 1000 ℃ and the total forging ratio of forging to be 5;
(3) performing first annealing on the forging blank in the step (2) at 1100 ℃ for 1.5h, and then performing first cooling to 40 ℃ at a cooling rate of 100 ℃/s; after punching a positioning hole in the center of the round surface of the forging blank, heating to 1150 ℃ at the heating rate of 2.5 ℃/min, and preserving heat for 130 min; then, perforating on a conical roller perforating machine; then hot rolling is carried out, and the rolling ratio of hot rolling is controlled to be 3, so as to obtain a pierced billet;
(4) heating the pierced billet in the step (3) to 1100 ℃ at a heating rate of 2.5 ℃/min, carrying out second annealing for 100min, carrying out second cooling to 40 ℃ at a cooling rate of 120 ℃/s, and coating a lubricant on the inner wall of the pierced billet; then carrying out thermal expansion at the temperature of 960 ℃, controlling the expansion ratio of the thermal expansion to be 1.2 and the advancing speed of pipe expansion to be 60mm/min, and obtaining a capillary;
wherein the lubricant comprises 65-micron powdered graphite powder, 85-micron flaky graphite powder and water in a mass ratio of 1:1.2: 3.5; in the hot expanding, the heating outer diameter of the induction heating coil is 90mm more than the outer diameter of the hollow billet after the hot expanding, and the length of the induction heating coil covers the deformation zone of the hollow billet and extends to the front and the back by 400mm respectively; after the thermal expansion deformation, the cooling mode of the pierced billets entering the sizing area is forced air cooling;
(5) heating the tubular billet in the step (4) to 1100 ℃ at a heating rate of 2.5 ℃/min, carrying out third annealing for 100min, carrying out third cooling to 20-50 ℃ at a cooling rate of 120 ℃/s, and coating a mineral oil lubricant on the inner wall of the tubular billet; performing cold drawing for 3 times at the speed of 0.6m/min, and controlling the wall thickness reduction amount of the cold drawing to be 1.5 mm/time; and carrying out solution treatment for 2h at 1040 ℃ to obtain the large-caliber duplex stainless steel seamless steel pipe.
The large-caliber duplex stainless steel seamless steel pipe obtained in the embodiment has the outer diameter of 610mm, the radial-wall ratio of 76, the straightness of 1.4mm/m and the surface roughness of 11 μm.
Example 3
The embodiment provides a large-caliber duplex stainless steel seamless steel pipe and a preparation method thereof, wherein the preparation method comprises the following steps:
(1) carrying out electric furnace primary smelting, LF refining and VOD decarburization refining on the molten steel in sequence, and pouring in an argon protective atmosphere to obtain a continuous casting billet;
(2) sequentially carrying out three-stage heating on the continuous casting billet in the step (1), wherein the three-stage heating comprises a first-stage heating, a second-stage heating and a third-stage heating which are sequentially carried out, the temperature of the first-stage heating is increased to 800 ℃ at a heating rate of 90 ℃/h, and the temperature is kept for 1.2 h; heating to 980 ℃ at the heating rate of 130 ℃/h in the second stage; in the third stage, heating to 1080 ℃ at the heating rate of 95 ℃/h, and keeping the temperature for 5 h; then, forging for 3 times to obtain a forged blank;
wherein, forging comprises longitudinal forging and transverse forging: longitudinally forging the radial forging machine in a radial forging machine until the drawing deformation ratio is 2, and transversely forging the radial forging machine in a rapid forging machine until the compression deformation ratio is 2.2; controlling the initial forging temperature of forging to be 1050 ℃, the final forging temperature to be 960 ℃, and the total forging ratio of forging to be 5;
(3) performing first annealing on the forging blank obtained in the step (2) at 1050 ℃ for 2h, and then performing first cooling to 20 ℃ at a cooling rate of 200 ℃/s; after punching a positioning hole in the center of the round surface of the forged blank, heating to 1180 ℃ at the heating rate of 2.8 ℃/min, and preserving heat for 120 min; then, perforating on a conical roller perforating machine; then hot rolling is carried out, the rolling ratio of hot rolling is controlled to be 4, and a pierced billet is obtained;
(4) heating the pierced billet in the step (3) to 1050 ℃ at a heating rate of 2.8 ℃/min, carrying out second annealing for 120min, carrying out second cooling to 20 ℃ at a cooling rate of 260 ℃/s, and coating a lubricant on the inner wall of the pierced billet; then carrying out hot expanding at the temperature of 980 ℃, controlling the expansion ratio of the hot expanding to be 1.4 and the advancing speed of expanding to be 30mm/min, and obtaining a capillary;
wherein the lubricant comprises 60-micron powdered graphite powder, 90-micron flaky graphite powder and water in a mass ratio of 1:1.8: 2.5; in the hot expanding, the heating outer diameter of the induction heating coil is 100mm more than the outer diameter of the hollow billet after the hot expanding, and the length of the induction heating coil covers the deformation zone of the hollow billet and extends forwards and backwards by 300mm respectively; after the thermal expansion deformation, the cooling mode of the pierced billets entering the sizing area is forced air cooling;
(5) heating the capillary tube in the step (4) to 1050 ℃ at a heating rate of 2.8 ℃/min, carrying out third annealing for 120min, carrying out third cooling to 20 ℃ at a cooling rate of 260 ℃/s, and smearing a mineral oil lubricant on the inner wall of the capillary tube; performing cold drawing for 1 pass at the speed of 0.2m/min, and controlling the wall thickness reduction amount of the cold drawing to be 2 mm/pass; and carrying out solution treatment at 1040-1080 ℃ for 1-2h to obtain the large-caliber duplex stainless steel seamless steel tube.
The large-caliber duplex stainless steel seamless steel pipe obtained in the example has an outer diameter of 914mm, a radial-to-wall ratio of 61, a straightness of 1.3mm/m and a surface roughness of 10 μm.
Example 4
This example provides a large-caliber duplex stainless steel seamless steel tube and a method for manufacturing the same, referring to the method of example 1, with the difference that: the heating rate of the second stage heating in the step (2) is 90 ℃/h, and in the step (4), the cooling mode of the pierced billets entering the sizing area is natural cooling; namely, the preparation method comprises the steps of:
(1) carrying out electric furnace primary smelting, LF refining and VOD decarburization refining on the molten steel in sequence, and pouring in an argon protective atmosphere to obtain a continuous casting billet;
(2) sequentially carrying out three-stage heating on the continuous casting slab in the step (1), wherein the three-stage heating comprises a first-stage heating, a second-stage heating and a third-stage heating which are sequentially carried out, the temperature of the first-stage heating is increased to 850 ℃ at a temperature increasing rate of 80 ℃/h, and the temperature is kept for 1 h; heating to 960 ℃ at a heating rate of 90 ℃/h in the second stage; heating to 1100 ℃ at a heating rate of 90 ℃/h in the third stage, and keeping the temperature for 4 h; then, forging for 3 times to obtain a forged blank;
wherein, forging comprises longitudinal forging and transverse forging: longitudinally forging the radial forging machine in a radial forging machine until the elongation deformation ratio is 2.5, and transversely forging the radial forging machine in a rapid forging machine until the compression deformation ratio is 2; controlling the initial forging temperature of forging to be 1100 ℃, the final forging temperature to be 960 ℃, and the total forging ratio of forging to be 6;
(3) performing first annealing on the forging blank in the step (2) at 1150 ℃ for 1h, and then performing first cooling to 50 ℃ at a cooling rate of 150 ℃/s; after punching a positioning hole in the center of the round surface of the forged blank, heating to 1150 ℃ at the heating rate of 2.5 ℃/min, and preserving heat for 150 min; then, perforating on a conical roller perforating machine; then hot rolling is carried out, the rolling ratio of hot rolling is controlled to be 5, and a pierced billet is obtained;
(4) heating the pierced billet in the step (3) to 1120 ℃ at a heating rate of 3.0 ℃/min, carrying out second annealing for 90min, carrying out second cooling to 50 ℃ at a cooling rate of 200 ℃/s, and coating a lubricant on the inner wall of the pierced billet; then carrying out hot expanding at the temperature of 1000 ℃, controlling the expansion ratio of the hot expanding to be 1.5 and the advancing speed of expanding to be 45mm/min, and obtaining a capillary;
wherein the lubricant comprises 55-micron powdered graphite powder, 80-micron flaky graphite powder and water in a mass ratio of 1:1.5: 3; in the hot expanding, the heating outer diameter of the induction heating coil is 110mm more than the outer diameter of the tubular billet after the hot expanding, and the length of the induction heating coil covers the deformation zone of the pierced billet and extends 500mm respectively forwards and backwards; after the thermal expansion deformation, the pierced billet entering the sizing area is cooled naturally;
(5) heating the tubular billet in the step (4) to 1120 ℃ at a heating rate of 3.0 ℃/min, carrying out third annealing for 90min, carrying out third cooling to 50 ℃ at a cooling rate of 200 ℃/s, and smearing a mineral oil lubricant on the inner wall of the tubular billet; performing cold drawing for 2 times at the speed of 0.5m/min, and controlling the wall thickness reduction amount of the cold drawing to be 3.5 mm/time; and carrying out solution treatment for 1h at 1080 ℃ to obtain the large-caliber duplex stainless steel seamless steel tube.
The large-caliber duplex stainless steel seamless steel pipe obtained in the embodiment has the outer diameter of 711mm, the radial-wall ratio of 65, the straightness of 1.3mm/m and the surface roughness of 9.2 mu m.
The large-caliber duplex stainless steel seamless steel pipe obtained in the embodiment is graded in grain size according to GB/T6394-2017, and the results are listed in Table 1.
(II) sampling from the large-caliber duplex stainless steel seamless steel pipe obtained in the above example, and carrying out non-metallic inclusion inspection and rating according to method A of GB/T10561-2005, and classifying A fine, B fine, C fine, D fine and D fineSThe test values of the grades are listed in table 1.
Thirdly, respectively cutting out a full-thickness sample (respectively marked as sample 1 and sample 2) from the head end and the tail end of the large-caliber duplex stainless steel seamless steel pipe obtained in the embodiment to detect the ferrite content, evaluating according to GB/T13298-2015 metallographic method for alpha-phase area content in stainless steel, and measuring the ferrite content and the austenite content under a microscope with the magnification of 400 times; observing whether the metallographic specimen has a sigma phase, an X phase and a pi phase precipitated phase under a 500-time optical microscope and a 1000-time scanning electron microscope; the results are shown in Table 2.
And (IV) testing the mechanical properties of the large-caliber duplex stainless steel seamless steel pipe obtained in the embodiment by the following method:
hardness: testing the surface hardness by adopting a Brinell hardness tester;
and (3) normal temperature tensile test: tensile strength, yield strength and elongation were tested as described in GB/T228.1-2010;
and (3) impact test: testing the impact energy at-40 ℃ for 3 times according to the method described in GB/T229-;
flattening test: testing according to the method described in GB/T246-2017;
instantaneous high-temperature tensile test: the plastic elongation strength was tested as described in GB/T228.2-2015, the temperatures being set at 50 deg.C, 100 deg.C, 150 deg.C, 200 deg.C, 250 deg.C, respectively;
the results of the mechanical property test, impact toughness test and crush test of examples 1-3 above are shown in Table 3.
(V) the corrosion resistance of the large-caliber duplex stainless steel seamless steel pipe obtained in the embodiment is tested by the following method:
pitting corrosion test: carrying out a pitting corrosion test on the sample according to the method A of GB/T17897-2016, wherein the test temperature is 22 +/-1 ℃, and the corrosion rate is detected after the sample is corroded in 6% ferric trichloride solution for 72 hours;
intergranular corrosion test: carrying out intercrystalline corrosion test on the sample according to an E method specified in GB/T4334-; if no intergranular corrosion crack exists, the test is qualified;
chloride stress corrosion test: performing a chloride stress corrosion test on the sample according to YB/T5362-2006, soaking the sample in boiling magnesium chloride solution with the boiling point of 155 +/-1 ℃, simultaneously applying tensile stress of 360MPa (80% yield strength) to the sample, performing visual inspection by using a 10-time magnifier after 96-hour test, and observing whether the surface of the sample has cracks or not; if no crack exists, the test is qualified;
the results of the corrosion resistance test of the above examples are shown in Table 4.
TABLE 1
TABLE 2
TABLE 3
TABLE 4
(1) From examples 1 to 3 in Table 1, it can be seen that: the large-caliber duplex stainless steel seamless steel pipe has high purity, low inclusion content, A fine grade, B fine grade, C fine grade, D fine grade and D fine gradeSThe grade test grades are not more than 1.0; the grain size is more than 7 grades, and the range of the grain size is less than or equal to 2 grades;
(2) from examples 1 to 3 in Table 2, it can be seen that: in the metallographic structure of the large-caliber duplex stainless steel seamless steel pipe, the ratio of austenite to ferrite is relatively balanced; no harmful phase sigma phase, X phase and pi phase are separated out;
(3) from examples 1 to 3 in Table 3, it can be seen that: the large-caliber duplex stainless steel seamless steel pipe has excellent mechanical property, and meets the requirements of GB/T21833.2-2020 that the tensile strength is more than or equal to 620MPa, the yield strength is more than or equal to 450MPa, the elongation is more than or equal to 25 percent, and the hardness is less than or equal to 290 HBW; in an instantaneous high-temperature tensile test, the plastic elongation strength of the large-caliber duplex stainless steel seamless steel pipe meets the requirement value of GB/T21833.2 (the requirement value is that the plastic elongation strength is more than or equal to 415MPa at 50 ℃, more than or equal to 360MPa at 100 ℃, more than or equal to 335MPa at 150 ℃, more than or equal to 310MPa at 200 ℃ and more than or equal to 295MPa at 250 ℃);
(4) from examples 1 to 3 in Table 4, it can be seen that: the large-caliber duplex stainless steel seamless steel pipe has excellent corrosion resistance, and the corrosion rate measured by a pitting corrosion test is far less than 10 mg/(dm) of GB/T21833.2-2020 and the technical protocol requirement2D); the intergranular corrosion test and the chloride stress corrosion test are both qualified.
(4) From the comparison between example 1 and example 4 in tables 1-4, it can be seen that the heating rate of the second stage heating in step (2) in example 4 is 90 ℃/h, which is lower than the temperature of the present invention, preferably 150 ℃/h, and the pierced billet entering the sizing zone is cooled naturally in the step (4) of hot expanding; in the second stage heating and hot expansion area, the sensitive temperature range of 800-960 ℃ is not rapidly passed, so that harmful phases are precipitated, although the precipitated harmful phases are not completely dissolved after the subsequent annealing treatment and the solution treatment, and the residual harmful phases can influence the plasticity, impact toughness and corrosion resistance of the large-caliber duplex stainless steel seamless steel pipe.
In conclusion, the chemical components, the metallographic structure, the mechanical property, the corrosion resistance and the size of the large-caliber duplex stainless steel seamless steel pipe meet the requirements of ASTM A789 and GB/T21833.3-2020 and technical protocols of duplex stainless steel seamless steel pipes for seawater pipeline systems of nuclear power plants.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.
Claims (10)
1. A large-caliber duplex stainless steel seamless steel pipe is characterized in that the outer diameter of the large-caliber duplex stainless steel seamless steel pipe is 610-914mm, the radial-wall ratio is more than 60, the grain size is more than 7 grade, and the range of the grain size is less than or equal to 2 grade; the ferrite content of the large-caliber duplex stainless steel seamless steel pipe is 48-53%, and the balance is austenite.
2. The large-caliber duplex stainless steel seamless steel tube according to claim 1, wherein the large-caliber duplex stainless steel seamless steel tube has a straightness of < 1.5 mm/m;
preferably, the surface roughness of the large-caliber duplex stainless steel seamless steel pipe is less than 12.5 mu m.
3. A method for manufacturing a large-caliber duplex stainless steel seamless steel tube according to claim 1 or 2, wherein the method comprises the following steps:
(1) carrying out electric furnace primary smelting, LF refining and VOD decarburization refining on the molten steel in sequence, and pouring to obtain a continuous casting billet;
(2) sequentially carrying out three-stage heating and forging on the continuous casting billet obtained in the step (1) to obtain a forged billet;
(3) sequentially perforating and hot rolling the forging blank in the step (2) to obtain a pierced billet;
(4) carrying out hot expanding on the pierced billet in the step (3) to obtain a tubular billet;
(5) and (4) sequentially carrying out cold drawing and solution treatment on the capillary pipe in the step (4) to obtain the large-caliber duplex stainless steel seamless steel pipe.
4. The method for preparing the large-caliber duplex stainless steel seamless steel tube according to the claim 3, wherein the LF refining in the step (1) has the end points that S is less than or equal to 0.005 percent and O is less than or equal to 25ppm in discharging;
preferably, the casting in step (1) is performed in an argon protective atmosphere.
5. The method for producing a large-caliber duplex stainless steel seamless steel pipe according to claim 3 or 4, wherein the three-stage heating of the step (2) comprises a first-stage heating, a second-stage heating and a third-stage heating which are sequentially performed;
preferably, the first stage heating comprises: heating to 750-850 ℃ at the heating rate of 60-90 ℃/h, and preserving heat for 1-1.5 h;
preferably, the second stage heating comprises: heating to 960-980 ℃ at the heating rate of 150 ℃/h of 120-;
preferably, the third stage heating comprises: raising the temperature to 1080-1150 ℃ at the temperature raising rate of 90-100 ℃/h, and preserving the temperature for 3-5 h;
preferably, the forging of step (2) includes longitudinal forging and transverse forging;
preferably, the longitudinal forging adopts a radial forging machine;
preferably, the longitudinal forging has a draw deformation ratio of 1.8 to 2.5;
preferably, the equipment adopted by the transverse forging is a quick forging machine, and the quick forging machine is provided with an online surface defect cleaning device;
preferably, the transverse forging has a compression set ratio of 1.5 to 2.2;
preferably, the forging temperature of the step (2) is 1050-;
preferably, the finish forging temperature of the forging in the step (2) is 960-1000 ℃;
preferably, the forging in the step (2) is not less than 3 times;
preferably, the total forging ratio of the forging of step (2) is > 5.
6. The method for preparing a large-caliber duplex stainless steel seamless steel tube as claimed in any one of claims 3 to 5, wherein before the piercing in the step (3), the forging blank in the step (2) is subjected to a first annealing at 1050-;
preferably, the perforating step of step (3) comprises: after a positioning hole is punched in the center of the round surface of the forging blank, the temperature is raised to 1150-fold-0 ℃ at the temperature rise rate of 2.5-3 ℃/min, the temperature is preserved for 150-fold-150 min, and then the punching is carried out on a conical roller puncher;
preferably, the rolling ratio of the hot rolling of the step (3) is more than 3.
7. The method for preparing a large-caliber duplex stainless steel seamless steel tube as claimed in any one of claims 3 to 6, wherein before the hot expanding in the step (4), the temperature of the pierced billet obtained in the step (3) is raised to 1050-;
preferably, the lubricant comprises powdered graphite powder, flake graphite powder and water;
preferably, the mass ratio of the powdered graphite powder to the flake graphite powder to the water is 1 (1.2-1.8) to 2.5-3.5;
preferably, the particle size of the powdered graphite powder is 55-65 μm;
preferably, the particle size of the crystalline flake graphite powder is 80-90 μm;
preferably, the temperature of the thermal expansion in the step (4) is 960-1000 ℃;
preferably, the thermal expansion ratio of the step (4) is 1.2-1.5;
preferably, the pipe expanding advancing speed of the hot expanding in the step (4) is 30-60 mm/min;
preferably, the heating outer diameter of the induction heating coil in the step (4) is 90-110mm more than the outer diameter of the capillary after thermal expansion;
preferably, the length of the induction heating coil in the step (4) covers the deformation zone of the pierced billet and extends for 300mm and 500mm respectively forwards and backwards;
preferably, after the heat expansion deformation in the step (4), the cooling mode of the pierced billet entering the sizing area is forced air cooling.
8. The method for preparing a large-caliber duplex stainless steel seamless steel tube according to any one of claims 3-7, wherein before the cold drawing in the step (5), the temperature of the capillary in the step (4) is raised to 1050-;
preferably, the cold drawing in the step (5) is performed for 1-3 times;
preferably, the speed of the cold drawing in the step (5) is 0.2-0.6 m/min;
preferably, the wall thickness reduction amount of the cold drawing in the step (5) is 1.5-3.5 mm/pass;
preferably, the temperature of the solution treatment in the step (5) is 1040-;
preferably, the time of the solution treatment in the step (5) is 1-2 h.
9. The method for producing a large-caliber duplex stainless steel seamless steel pipe according to any one of claims 3 to 8, wherein the method comprises the steps of:
(1) carrying out electric furnace primary smelting, LF refining and VOD decarburization refining on the molten steel in sequence, and pouring in an argon protective atmosphere to obtain a continuous casting billet;
(2) sequentially carrying out three-stage heating on the continuous casting slab in the step (1), wherein the three-stage heating comprises a first-stage heating, a second-stage heating and a third-stage heating which are sequentially carried out, the temperature of the first-stage heating is increased to 750-fold sand 850 ℃ at the temperature increasing rate of 60-90 ℃/h, and the temperature is kept for 1-1.5 h; heating to 960-; heating to 1080-; then, forging at least 3 times to obtain a forged blank;
wherein, forging comprises longitudinal forging and transverse forging: longitudinally forging the radial forging machine in a radial forging machine until the elongation deformation ratio is 1.8-2.5, and transversely forging the radial forging machine in a rapid forging machine until the compression deformation ratio is 1.5-2.2; controlling the initial forging temperature of 1050-;
(3) performing first annealing on the forging blank in the step (2) at 1050-; after a positioning hole is punched in the center of the round surface of the forging blank, the temperature is raised to 1150-1190 ℃ at the temperature rise rate of 2.5-3 ℃/min, and the temperature is preserved for 150 min; then, perforating on a conical roller perforating machine; then hot rolling is carried out, the rolling ratio of hot rolling is controlled to be more than 3, and a pierced billet is obtained;
(4) heating the pierced billet in the step (3) to 1050-; then carrying out thermal expansion at the temperature of 960-;
wherein, the lubricant comprises 55-65 μm powdered graphite powder, 80-90 μm crystalline flake graphite powder and water according to the mass ratio of 1 (1.2-1.8) to 2.5-3.5; in the thermal expansion, the heating outer diameter of the induction heating coil is 90-110mm more than the outer diameter of the capillary after the thermal expansion, and the length of the induction heating coil covers the deformation area of the pierced billet and extends for 500mm forward and backward respectively; after the thermal expansion deformation, the cooling mode of the pierced billets entering the sizing area is forced air cooling;
(5) heating the capillary tube in the step (4) to 1050-; performing cold drawing for 1-3 times at a speed of 0.2-0.6m/min, and controlling the wall thickness reduction amount of the cold drawing to be 1.5-3.5 mm/time; and carrying out solution treatment at 1040-1080 ℃ for 1-2h to obtain the large-caliber duplex stainless steel seamless steel tube.
10. Use of a large caliber duplex stainless steel seamless steel pipe according to claim 1 or 2, characterized in that the large caliber duplex stainless steel seamless steel pipe is used for seawater piping systems.
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