CN113862421B - Manufacturing method of cake-shaped large-thickness forging - Google Patents
Manufacturing method of cake-shaped large-thickness forging Download PDFInfo
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- CN113862421B CN113862421B CN202111116461.1A CN202111116461A CN113862421B CN 113862421 B CN113862421 B CN 113862421B CN 202111116461 A CN202111116461 A CN 202111116461A CN 113862421 B CN113862421 B CN 113862421B
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- 238000005242 forging Methods 0.000 title claims abstract description 76
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 25
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 106
- 239000010959 steel Substances 0.000 claims abstract description 106
- 238000010438 heat treatment Methods 0.000 claims abstract description 58
- 238000000034 method Methods 0.000 claims abstract description 56
- 238000011282 treatment Methods 0.000 claims abstract description 34
- 239000002893 slag Substances 0.000 claims abstract description 22
- 238000003723 Smelting Methods 0.000 claims abstract description 17
- 238000001816 cooling Methods 0.000 claims abstract description 12
- 230000001681 protective effect Effects 0.000 claims abstract description 12
- 238000007670 refining Methods 0.000 claims abstract description 12
- 239000002994 raw material Substances 0.000 claims abstract description 11
- 238000009849 vacuum degassing Methods 0.000 claims abstract description 8
- 238000006243 chemical reaction Methods 0.000 claims abstract description 6
- 238000003825 pressing Methods 0.000 claims description 19
- 239000007789 gas Substances 0.000 claims description 17
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 16
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 14
- 239000001301 oxygen Substances 0.000 claims description 14
- 229910052760 oxygen Inorganic materials 0.000 claims description 14
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 11
- OSMSIOKMMFKNIL-UHFFFAOYSA-N calcium;silicon Chemical compound [Ca]=[Si] OSMSIOKMMFKNIL-UHFFFAOYSA-N 0.000 claims description 10
- 239000000843 powder Substances 0.000 claims description 10
- 235000010627 Phaseolus vulgaris Nutrition 0.000 claims description 9
- 244000046052 Phaseolus vulgaris Species 0.000 claims description 9
- 229910052782 aluminium Inorganic materials 0.000 claims description 9
- 229910000963 austenitic stainless steel Inorganic materials 0.000 claims description 7
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 claims description 5
- 229910001634 calcium fluoride Inorganic materials 0.000 claims description 5
- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 claims description 5
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 claims description 5
- 239000000292 calcium oxide Substances 0.000 claims description 5
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 3
- 238000004321 preservation Methods 0.000 claims description 2
- 229910001873 dinitrogen Inorganic materials 0.000 claims 2
- 229910000859 α-Fe Inorganic materials 0.000 abstract description 18
- 239000012535 impurity Substances 0.000 abstract description 10
- 239000003795 chemical substances by application Substances 0.000 abstract description 3
- 230000008569 process Effects 0.000 description 40
- 239000012467 final product Substances 0.000 description 10
- 229910052751 metal Inorganic materials 0.000 description 9
- 239000002184 metal Substances 0.000 description 9
- 229910052757 nitrogen Inorganic materials 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- 239000000463 material Substances 0.000 description 6
- 238000002844 melting Methods 0.000 description 6
- 230000008018 melting Effects 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 238000005204 segregation Methods 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 238000005520 cutting process Methods 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 239000004411 aluminium Substances 0.000 description 3
- 238000002425 crystallisation Methods 0.000 description 3
- 230000008025 crystallization Effects 0.000 description 3
- 238000005261 decarburization Methods 0.000 description 3
- 238000000265 homogenisation Methods 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000013461 design Methods 0.000 description 2
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- 230000001965 increasing effect Effects 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 238000003754 machining Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 239000011574 phosphorus Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
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- 239000000126 substance Substances 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- 239000011593 sulfur Substances 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 1
- 229910000805 Pig iron Inorganic materials 0.000 description 1
- 235000011941 Tilia x europaea Nutrition 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000008186 active pharmaceutical agent Substances 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 229910000765 intermetallic Inorganic materials 0.000 description 1
- 239000004571 lime Substances 0.000 description 1
- 239000002932 luster Substances 0.000 description 1
- 238000010309 melting process Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
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- 230000000630 rising effect Effects 0.000 description 1
- 150000004760 silicates Chemical class 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- 239000002918 waste heat Substances 0.000 description 1
Classifications
-
- 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
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
- C22B9/16—Remelting metals
- C22B9/18—Electroslag remelting
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Forging (AREA)
Abstract
The embodiment of the invention provides a manufacturing method of a cake-shaped large-thickness forging piece, which comprises the following steps: smelting in an electric furnace: the method comprises the steps of (1) putting raw materials into an electric furnace for smelting, and charging protective gas to obtain first molten steel; refining outside a furnace: refining the first molten steel by using a ladle, and performing vacuum degassing treatment to obtain a first steel ingot; electroslag remelting: adding slag and deoxidizing agent, and performing electroslag remelting treatment on the first steel ingot to obtain a second steel ingot; homogenizing: heating the second steel ingot to a first set temperature in a stepwise heating mode; forging: performing upsetting and multiple drawing on the second steel ingot to obtain a third steel ingot; solution heat treatment: and heating the third steel ingot to the second set temperature, preserving heat for a set time, and cooling the third steel ingot in the conversion time. The manufacturing method provided by the embodiment of the invention can reduce the impurity elements, inclusion content and ferrite content of the forging, improve the grain size grade, and the obtained forging has higher structure uniformity and stability.
Description
Technical Field
The embodiment of the invention relates to the field of steel manufacturing, in particular to a manufacturing method of a cake-shaped forging with large thickness.
Background
The large heat exchanger is arranged in the reactor, heat is transferred to cold fluid through the heat exchanger, and finally high-temperature steam is generated through the steam generator, so that the generator set is pushed to realize power supply.
Tube plates and flanges of heat exchangers such as an intermediate heat exchanger of a secondary loop main cooling system and an independent heat exchanger of an accident waste heat discharging system in a fast neutron reactor run for a long period at high temperature, so that the material needs to be ensured to have higher fatigue strength and creep-fatigue resistance, better intergranular corrosion resistance, good durability and excellent tissue stability, and material irradiation embrittlement does not occur in a service life.
Therefore, the tube plate and the flange of the heat exchanger in the fast neutron reactor are often manufactured by adopting large-size thick-wall austenitic stainless steel forgings, and the manufacturing difficulty is high because the sizes and the thicknesses of the forgings are large.
Disclosure of Invention
In view of this, it is desirable to provide a method of manufacturing a cake-shaped forging of large thickness.
In order to achieve the above purpose, the technical solution of the embodiments of the present application is implemented as follows:
the embodiment of the invention provides a manufacturing method of a cake-shaped large-thickness forging piece, which is characterized by comprising the following steps of:
smelting in an electric furnace: the method comprises the steps of (1) putting raw materials into an electric furnace for smelting, and charging protective gas to obtain first molten steel;
refining outside a furnace: refining the first molten steel by using a ladle, and obtaining a first steel ingot through vacuum degassing treatment;
electroslag remelting: adding slag and deoxidizing agent, and performing electroslag remelting treatment on the first steel ingot to obtain a second steel ingot;
homogenizing: heating the second steel ingot to a first set temperature in a stepwise heating mode;
forging: performing multiple upsetting treatment and multiple drawing treatment on the second steel ingot to obtain a third steel ingot;
solution heat treatment: and heating the third steel ingot to a second set temperature, preserving heat for a set time, and cooling the third steel ingot within the conversion time.
In some embodiments, the shielding gas in the electric furnace smelting step is nitrogen, and the purity of the nitrogen is greater than 99.99%.
In some embodiments, the slag in the electroslag remelting step includes calcium fluoride, aluminum oxide, and calcium oxide.
In some embodiments, the deoxidizer in the electroslag remelting step comprises silicon-calcium powder and aluminum beans, wherein the silicon-calcium powder has an oxygen content of less than 200ppm.
In some embodiments, the homogenizing step comprises: heating the second steel ingot to 400-500 ℃ and keeping for 2-3 h, then continuously heating the second steel ingot to 830-870 ℃ according to a first heating rate and keeping for 2-4 h, and continuously heating the second steel ingot to 1190-1250 ℃ according to a second heating rate and keeping for more than 30h; wherein the first heating rate is less than or equal to 100 ℃/h, and the second heating rate is less than or equal to 80 ℃/h.
In some embodiments, the forging step has a forging ratio of greater than 3 per pass and a total forging ratio of greater than 10.
In some embodiments, the upsetting and the drawing process in the forging step are performed alternately, and the last process is the upsetting process.
In some embodiments, the last upsetting process comprises: and when the second steel ingot is upset to the height-diameter ratio range of 0.9-1.1, the second steel ingot is processed by adopting a mode of combining wide anvil pressing and narrow anvil rotating pressing.
In some embodiments, said heating said third ingot to a second set temperature comprises: and heating the third steel ingot to 1050-1060 ℃ according to a third heating rate, wherein the third heating rate is less than or equal to 130 ℃/h.
In some embodiments, the cooling treatment in the solution heat treatment step is water cooling; and/or, the switching time is less than 1min; and/or, the set time is greater than or equal to 5 hours.
The manufacturing method in the embodiment of the invention can obviously reduce the contents of impurity elements, inclusions and ferrite in the finally obtained forging; the probability of mixed crystal structure generation is reduced, the grain size in the forging is obviously reduced, the grain size grade is improved, the core grain size of the forging can be ensured to be more than 3 grades, the grain size of the surface and the core position of the forging is controlled within the range of 3-4.5 grades, and the grain size grade difference is not more than 1.5; the ferrite content of any position in the finally obtained forge piece can be effectively reduced, the ferrite content can be less than 1%, the probability of transformation from ferrite in the forge piece to sigma brittle phase after long-term use is reduced, and the possibility that impact toughness, durability and fatigue performance do not meet design requirements due to the fact that the ferrite content is too high is effectively reduced. The forging piece obtained by the manufacturing method in the embodiment of the invention has the advantages that the high-temperature yield strength, the tensile strength, the permanent strength, the creep resistance and the low cycle fatigue limit are obviously improved, wherein the allowance of the high-temperature yield strength is more than 10% compared with the ASME standard, the allowance of the high-temperature permanent strength and the creep resistance is more than 30% compared with the ASME standard, and the obtained forging piece has higher tissue uniformity and stability.
Drawings
FIG. 1 is a flow chart of a manufacturing method according to an embodiment of the invention;
FIG. 2 is a schematic view of typical grain sizes of the core of a forging obtained by the manufacturing method according to an embodiment of the present invention;
FIG. 3 is a schematic view of typical grain sizes of the surface of a forging obtained by the manufacturing method according to an embodiment of the present invention;
FIG. 4 is a schematic view of typical grain size of a core of a forging obtained by a conventional process;
FIG. 5 is a schematic view of typical grain size of the surface of a forging obtained by a conventional process;
FIGS. 6 and 7 are schematic diagrams of ferrite distribution of forgings obtained by the manufacturing method according to an embodiment of the present invention at 200 times magnification using the worst field method;
fig. 8 and 9 are schematic diagrams of ferrite distribution of forgings obtained by the manufacturing method in the conventional process under a magnification of 200 times by adopting a worst view field method.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and technical features in the embodiments may be combined with each other, and the detailed description in the specific embodiments should be interpreted as an explanation of the gist of the present application and should not be construed as undue limitation to the present application.
Taking a sodium-cooled fast neutron reactor as an example, various large-size forgings need to be installed in the sodium-cooled fast neutron reactor to meet the severe use requirements in the reactor. Wherein, the tube plate and the flange are typical cake-shaped large-thickness forgings, the outer diameter size of the tube plate forgings of the intermediate heat exchanger can reach 2300mm (millimeter ), the axial height of the blank before processing can exceed 450mm, and the heat treatment thickness exceeds 850mm; the outer diameter of the flange forging of the intermediate heat exchanger is about 3000mm, the axial height of the flange before rough machining is more than 400mm, and the heat treatment thickness is more than 400mm. In order to obtain the forge piece meeting the requirements of performance and quality, the embodiment of the invention optimizes the manufacturing method of the forge piece from three aspects of smelting, forging and heat treatment.
The cake-shaped forging means that the ratio of the height dimension to the outer diameter dimension of the forging is 1 or less, and the large thickness means that the heat treatment thickness is 300mm or more.
The embodiment of the invention provides a manufacturing method of a cake-shaped large-thickness forging piece, referring to fig. 1, the manufacturing method comprises the following steps:
s1, electric furnace smelting: and (3) putting the raw materials into an electric furnace for smelting and charging protective gas to obtain the first molten steel. The probability of oxidation of the raw materials can be reduced by introducing protective gas in the process of melting the raw materials.
S2, refining outside the furnace: and refining the first molten steel by using a ladle, and obtaining a first steel ingot through vacuum degassing treatment. The ladle refining can further adjust the components in the first molten steel, thereby reducing impurities in the first molten steel. The first molten steel is subjected to vacuum degassing to remove hydrogen and nitrogen therein under vacuum. The purity of the material before the subsequent electroslag remelting treatment can be ensured by combining ladle refining and vacuum degassing treatment, and redundant gas elements and nonmetallic impurity elements can be removed as much as possible.
The vacuum degassing treatment may be performed by a VOD method (Vacuum Oxygen Decarburization, vacuum oxygen decarburization method), that is, oxygen decarburization and argon stirring of the first molten steel under vacuum.
It is understood that lime may be added to adjust the alkalinity during ladle refining.
S3, electroslag remelting: and adding slag and deoxidizing agent, and performing electroslag remelting treatment on the first steel ingot to obtain a second steel ingot. Illustratively, the first steel ingot is used as a consumable electrode, the end of the consumable electrode is inserted into slag of an electroslag furnace, after the arc is started by electrifying, remelting voltage and remelting current are adjusted to enable the end of the consumable electrode to be slowly melted, molten metal is gathered into metal droplets and falls off from the end of the consumable electrode under the action of gravity, and the metal droplets pass through a slag pool to enter a metal molten pool and are cooled and condensed to form a second steel ingot. Impurities of the first steel ingot can be further removed through electroslag remelting treatment, so that a second steel ingot with good surface quality, uniform structure and refined grains is obtained.
S4, homogenizing: and heating the second steel ingot to the first set temperature in a stepwise heating mode. So that carbide distribution in the second steel ingot is homogenized, high-temperature ferrite is sufficiently eliminated, component segregation is reduced, and mechanical properties of the second steel ingot are further improved.
S5, forging: and performing multiple upsetting treatment and multiple drawing treatment on the second steel ingot to obtain a third steel ingot. The second steel ingot is subjected to plastic deformation continuously through multiple upsetting and drawing, so that the defects of cast loosening, air holes, segregation and the like generated in the smelting processes of the second steel ingot are reduced, the microstructure is optimized, the microstructure is more compact, and meanwhile, the complete metal streamline is saved.
S6, solution heat treatment: and heating the third steel ingot to the second set temperature, preserving heat for a set time, and cooling the third steel ingot within the conversion time. So that the metallographic structure in the third steel ingot is converted into a single austenite structure, thereby ensuring that the third steel ingot has good mechanical property and corrosion resistance, and eliminating internal stress and cold work hardening phenomenon.
Compared with the traditional forging manufacturing process, the manufacturing method provided by the embodiment of the invention can obviously reduce the contents of impurity elements, inclusions and ferrite in the finally obtained forging; the probability of mixed crystal structure generation is reduced, the grain size in the forging is obviously reduced, the grain size grade is improved, the core grain size of the forging can be ensured to be more than 3 grades, the grain size of the surface and the core position of the forging is controlled within the range of 3-4.5 grades, and the grain size grade difference is not more than 1.5; the ferrite content of any position in the finally obtained forge piece can be effectively reduced, the ferrite content can be less than 1%, the probability of transformation from ferrite in the forge piece to sigma brittle phase after long-term use is reduced, and the possibility that durability and fatigue performance do not meet design requirements due to overhigh ferrite content is effectively reduced. The forging obtained by the manufacturing method in the embodiment of the invention has obviously improved high-temperature yield strength, tensile strength, endurance strength, creep resistance and low cycle fatigue limit, wherein the allowance of the high-temperature yield strength is more than 10% compared with ASME (American Society of Mechanical Engineers ) standard, the allowance of the high-temperature endurance strength and creep resistance is more than 30% compared with ASME standard, and the obtained forging has higher tissue uniformity and stability.
It is understood that the raw materials charged in the electric furnace smelting step may be iron ore, pig iron, or the like.
It will be appreciated that the raw materials, after being completely melted in an electric furnace, need to be sampled and analyzed to monitor the content of carbon, phosphorus, sulfur and other elements affecting the quality of the final product.
It can be understood that before pouring the raw materials into the electric furnace, the protective gas should be introduced into the furnace body of the electric furnace in advance, so that the furnace body is filled with the protective gas, and the protective gas is continuously introduced in the process of melting the raw materials, so that the raw materials are always in the protective atmosphere in the melting process, and the probability of entering the electric furnace by external oxygen is reduced.
It will be appreciated that the shielding gas introduced during the electric smelting step should not react with the material in the first molten steel.
Specifically, in some embodiments, the shielding gas in the electric furnace smelting step is nitrogen, and the purity of the nitrogen is greater than 99.99%. The nitrogen is used as an inert gas, has stable chemical property, is not easy to react with other substances, is easy to prepare and has low use cost. By improving the purity of the shielding gas, the occurrence probability of the situation that the material in the first molten steel excessively absorbs oxygen to cause the increase of inclusions in the subsequent electroslag remelting step is reduced.
It will be appreciated that the shielding gas should be pre-heated prior to being fed into the electric furnace to increase the melting rate of the feedstock.
In the electroslag remelting process, the selection of slag components directly influences the technological index and quality of the final smelting finished product, so that the components and the quality ratio of slag need to be reasonably screened.
Specifically, in some embodiments, the slag in the electroslag remelting step includes calcium fluoride, aluminum oxide, and calcium oxide. Wherein, the calcium oxide can increase the alkalinity of slag and improve the desulfurization efficiency of slag system.
When the mass ratio of the slag is selected, the prepared slag has the advantages of low melting point and good fluidity, so that the melting speed of a consumable electrode in the electroslag remelting process is reduced, and the effect of removing inclusions is improved. Specifically, in some embodiments, the calcium fluoride is present in a mass ratio ranging from 55% to 65%, the aluminum oxide is present in a mass ratio ranging from 15% to 25%, and the calcium oxide is present in a mass ratio ranging from 15% to 25%.
It can be understood that in the process of electroslag remelting treatment, the voltage and current are required to be controlled, a mode of low voltage and large current is adopted, voltage and current fluctuation is reduced, stable power supply parameters are ensured, the electrode melting speed and the molten pool crystallization speed are relatively stable, the influence of molten pool disturbance on crystallization quality is avoided, and therefore crystallization ripple segregation in the second steel ingot is reduced.
It will be appreciated that prior to the electroslag remelting process, a consumable electrode is inserted and placed into the slag prior to charging the bath of the electroslag remelting with a protective gas, and that the protective gas is continuously charged throughout the electroslag remelting process to ensure that the electroslag remelting process is conducted in a protective atmosphere. Specifically, in some embodiments, the shielding gas is argon. Thereby enhancing the control of the content of hydrogen element in the electroslag remelting process.
It is understood that a cooling device may be provided in the electroslag remelting device to forcibly cool the generated molten metal pool to improve the efficiency of the electroslag remelting process.
It will be appreciated that in the electroslag remelting step, the oxygen content is reduced by the deoxidizer, and the composition of the deoxidizer needs to be optimized in order to improve the deoxidizing effect of the deoxidizer.
Specifically, in some embodiments, the deoxidizer in the electroslag remelting step comprises a silicon-calcium powder. The silicon-calcium powder should be screened multiple times so that the silicon-calcium powder has an oxygen content of less than 200ppm (parts per million) by mass. The content of oxygen elements entering slag from the silicon-calcium powder is reduced, and the deoxidizing effect of the silicon-calcium powder is improved.
In some embodiments, the deoxidizer in the electroslag remelting step comprises aluminum beans. Compared with aluminum powder, the aluminum beans have small contact area with slag, so that the reaction rate of the aluminum beans is slower, the oxygen content is prevented from rising due to excessive oxidation of the deoxidizer, the deoxidization can be continuously carried out in the whole electroslag remelting process, the reduction of the slag system is maintained, and the deoxidization effect is improved.
It will be appreciated that the surface of the selected aluminium beans should have a metallic luster, i.e. the oxidation level of the surface of the selected aluminium beans is low, in order to reduce the oxygen elements carried into the slag by the oxide layer of the surface of the aluminium beans.
It is understood that the temperature gradient, the holding time and the heating rate should be reasonably arranged during the homogenization treatment to improve the homogenization effect of the carbide distribution.
Specifically, in some embodiments, the homogenizing step comprises: heating the second steel ingot to 400 ℃ (degree centigrade, the temperature is kept at 500 ℃ for 2-3 hours, then continuously heating the second steel ingot to 830-870 ℃ according to the first heating rate and keeping the temperature for 2-4 hours, and then continuously heating the second steel ingot to 1190-1250 ℃ according to the second heating rate and keeping the temperature for more than 30 hours; wherein the first heating rate is less than or equal to 100 ℃/h (degree centigrade per hour, celsius per hour) and the second heating rate is less than or equal to 80 ℃/h. Thereby further improving the uniformity of the structure in the second ingot.
It will be appreciated that the deposition of impurities is liable to occur at the head of the second ingot. At the tail part of the second steel ingot, the residual quantity of the consumable electrode is less at the end stage of the electroslag remelting process, and the current and the voltage are unstable, so that segregation is easy to generate. Therefore, before the second ingot is forged, the portion of the second ingot having poor quality needs to be treated to improve the quality of the final product.
Specifically, in some embodiments, the head and tail of the second ingot are cut off. After cutting, more impurities in the head and the tail can be removed, the influence of harmful shrinkage cavities and excessive segregation on the product is reduced, and a part with more uniform components is obtained.
In some embodiments, the second ingot has a tail cut rate of greater than or equal to 5% and a head cut rate of greater than or equal to 3%. Thereby obtaining a part of the second steel ingot with better tissue homogenization degree and improving the quality of a final finished product.
It will be appreciated that due to the relatively large size and mass of forging required, a suitable forging press may be selected for the forging process. Specifically, in some embodiments, a forging press having a forging capacity greater than or equal to 6500t (ton ) is employed.
It will be appreciated that in some embodiments, the forging is performed using a three pier three-pull process or a three pier two-pull process, so as to make the transverse and longitudinal forging of the third ingot uniform and have better mechanical properties.
It will be appreciated that the forging of each upsetting and drawing process is relatively large, as the dimension of the forging in the vertical direction is much smaller than the dimension in the horizontal direction, for example, for tube sheets, flanges, etc., where the forging ratio is the ratio of the cross-sectional areas of the forging before and after deformation.
Specifically, the forging ratio per pass in the forging step is greater than 3 and the total forging ratio is greater than 10. Therefore, a third steel ingot which is convenient to process into a disc forge piece or an annular forge piece is finally obtained, and the subsequent machining workload is reduced while the mechanical property requirement is met.
It will be appreciated that in some embodiments, the upsetting and withdrawal processes in the forging step are alternated to break up the grains in the third ingot and improve its mechanical properties.
The last treatment was a upsetting treatment, so that a second ingot having a dimension in the vertical direction much smaller than that in the horizontal direction was finally obtained.
It will be appreciated that the last upsetting treatment may be optimised to further improve the mechanical properties of the material.
Specifically, in some embodiments, the last upsetting process includes: and when the second steel ingot is upset to the height-diameter ratio range of 0.8-1.2, the second steel ingot is processed by adopting a mode of combining wide anvil pressing and narrow anvil rotating pressing.
Firstly, the second steel ingot is extruded by adopting a wide anvil pressing, namely, adopting a large anvil width ratio and a large pressing rate, so that the center part of the second steel ingot is greatly deformed, thereby reducing internal pores and eliminating looseness.
The large anvil width ratio is larger than or equal to 0.68, and the large pressing rate is that the pressing height is larger than or equal to 20% of the second steel ingot.
The anvil width ratio is the ratio of the width of the anvil to the height of the test piece.
And (5) carrying out narrow anvil rotary pressing after the wide anvil pressing is finished. Transferring the second steel ingot to a rotating platform, enabling the second steel ingot to rotate along with the rotating platform, and simultaneously pressing down by using a narrow anvil. The extruded metal mainly flows along the circumferential direction, namely, the extruded metal is pulled out along the circumferential direction, the height of the second steel ingot is reduced, the inner diameter and the outer diameter are synchronously increased, the final appearance size of the second steel ingot is favorable for meeting the process requirements, and the mechanical property of the core part of the second steel ingot is improved.
After the narrow anvil is rotated and pressed, if the final appearance size of the second steel ingot fails to meet the process requirement, the wide anvil pressing treatment can be reused until the size meets the requirement to obtain a third steel ingot.
It can be appreciated that the final temperature and the temperature rise speed of the third steel ingot need to be optimized to further improve the mechanical properties of the third steel ingot when the third steel ingot is heated to the second set temperature.
Specifically, in some embodiments, heating the third ingot to the second set temperature comprises: and heating the third steel ingot to 1050-1060 ℃ according to a third heating rate, wherein the third heating rate is less than or equal to 130 ℃/h.
It will be appreciated that the set time in the solution heat treatment is greater than or equal to 5 hours, thereby allowing sufficient time for the intermetallic compound to dissolve into solid solution.
It will be appreciated that in solution heat treatment, increasing the cooling rate facilitates obtaining carbon supersaturated austenite. For example, in some embodiments, the cooling process is water-cooled, and the characteristic of large specific heat capacity of water is used to rapidly cool the third steel ingot. As another example, in some embodiments, the conversion time in the solution heat treatment is less than 1 minute, enabling the third ingot to be rapidly cooled.
The list of impurities contained between the final product obtained in one embodiment of the present invention and the austenitic stainless steel obtained in the conventional process is compared as follows.
The specific manufacturing flow adopted in this example is as follows:
putting iron ore into an electric furnace for smelting and charging nitrogen with the purity of 99.995 percent to obtain first molten steel; refining the first molten steel by using a ladle, and performing vacuum degassing treatment by using a VOD method to obtain a first steel ingot; adding slag consisting of 60% by mass of calcium fluoride, 20% by mass of aluminum oxide and 20% by mass of slag, and 150ppm by mass of aluminum beans and silicon-calcium powder with oxygen content, and performing electroslag remelting treatment on the first steel ingot to obtain a second steel ingot; heating the second steel ingot to 450 ℃ and keeping the temperature for 2.5 hours, then continuously heating the second steel ingot to 850 ℃ at the speed of 100 ℃/h and keeping the temperature for 3 hours, and then continuously heating the second steel ingot to 1200 ℃ at the speed of 80 ℃/h and keeping the temperature for 32 hours; cutting off the head part and the tail part of the second steel ingot in a mode that the tail cutting rate of the second steel ingot is 5% and the head cutting rate of the second steel ingot is 3%; forging the second steel ingot by adopting a forging press with the forging capacity of 6500t through a three-pier three-drawing process, wherein the forging ratio of each pass is 4 and the total forging ratio is 12, and processing the second steel ingot in the last upsetting treatment through a mode of combining the pressing of a wide anvil and the rotating pressing of a narrow anvil to obtain a third steel ingot; the third ingot was heated to 1055 c at a rate of 130 c/h, and after 5h of heat preservation, the third ingot was water-cooled for 1min, thereby obtaining the final product, which is the example.
Table 1 comparison of impurity element contents between the final product obtained in this example and austenitic stainless steel obtained by conventional processes.
| Manufacturing process | S content | P content | O content | H content | Al content |
| Embodiments of the invention | ≤30ppm | ≤150ppm | ≤35ppm | ≤5ppm | ≤0.03％ |
| Traditional process | ≤250ppm | ≤300ppm | ≤100ppm | ≥15ppm | ≥0.06％ |
Table 2 comparison of inclusion content between the final product obtained in this example and austenitic stainless steel obtained by conventional process.
Note that: (1) In table 1, S represents sulfur element, P represents phosphorus element, O represents oxygen element, H represents hydrogen element, and Al represents aluminum element.
(2) In table 2, the type a inclusions are sulfides, the type B inclusions are alumina, the type C inclusions are silicates, the type D inclusions are spherical oxides, and the type DS inclusions are single-particle spherical inclusions.
(3) The comparative mode in Table 2 uses the method of rating nonmetallic inclusion in GB/T10561-2005.
According to fig. 2 to 5, the final product obtained in this example was compared with the microscopic grain size of the thick-walled austenitic stainless steel forging obtained by the conventional process in combination with the method for determining the average grain size of metals in GB/T6394-2002. The final product of this example had a core grain size of 3.0 grade and a surface grain size of 4.0 to 4.5 grade. The grain size of the center part of the traditional process is 2.0 grade, and the surface grain size is 3.0 grade. Compared with the embodiment, the traditional process can not meet the requirement that the grain size of the core part of the forging piece and the grain size of the surface are all above 3 grades.
According to fig. 6 to 9, the worst view field observation is carried out on the full-size full section of the forging by combining the metallographic determination method of the alpha-phase area content in GB/T13305-2008, and the ferrite content of the final product obtained in the embodiment is obtained and compared with the ferrite content of the austenitic stainless steel thick-wall forging obtained by the traditional process. The final product obtained in the examples had a ferrite content of less than 1%, whereas in the conventional process the ferrite content was more than 1%.
The various embodiments/implementations provided herein may be combined with one another without conflict.
The foregoing description is only of the preferred embodiments of the present application and is not intended to limit the same, but rather, various modifications and variations can be made by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.
Claims (5)
1. A method of manufacturing a pie-shaped, large thickness forging for making a large size, thick wall austenitic stainless steel forging, the method comprising the steps of:
smelting in an electric furnace: the method comprises the steps of (1) putting raw materials into an electric furnace for smelting, and charging protective gas to obtain first molten steel;
refining outside a furnace: refining the first molten steel by using a ladle, and obtaining a first steel ingot through vacuum degassing treatment;
electroslag remelting: adding slag and deoxidizer, and performing electroslag remelting treatment on the first steel ingot to obtain a second steel ingot, wherein the slag comprises calcium fluoride, aluminum oxide and calcium oxide, and the deoxidizer comprises silicon-calcium powder and aluminum beans;
homogenizing: heating the second steel ingot to 400-500 ℃ and keeping for 2-3 h, then continuously heating the second steel ingot to 830-870 ℃ according to a first heating rate and keeping for 2-4 h, and continuously heating the second steel ingot to 1190-1250 ℃ according to a second heating rate and keeping for more than 30h; wherein the first heating rate is less than or equal to 100 ℃/h, and the second heating rate is less than or equal to 80 ℃/h;
forging: and performing multiple upsetting treatments and multiple drawing treatments on the second steel ingot to obtain a third steel ingot, wherein the upsetting treatments and the drawing treatments are alternately performed, the last treatment is the upsetting treatment, and the final upsetting treatment comprises: when the second steel ingot is upset to the height-diameter ratio range of 0.9-1.1, the second steel ingot is processed by adopting a mode of combining wide anvil pressing and narrow anvil rotating pressing, wherein the wide anvil pressing is adopted firstly, the anvil width ratio is larger than or equal to 0.68, and the large pressing rate is that the pressing height is larger than or equal to 20% of the second steel ingot; a forging press with forging capacity larger than or equal to 6500t is adopted;
solution heat treatment: and heating the third steel ingot to 1050-1060 ℃ according to a third heating rate, wherein the third heating rate is less than or equal to 130 ℃/h, and cooling the third steel ingot within the conversion time after the heat preservation is carried out for a set time.
2. The method according to claim 1, wherein the shielding gas in the electric furnace smelting step is nitrogen gas, and the purity of the nitrogen gas is more than 99.99%.
3. The method of claim 1, wherein the silicon-calcium powder has an oxygen content of less than 200ppm.
4. The method of claim 1, wherein the forging step has a forging ratio of greater than 3 per pass and a total forging ratio of greater than 10.
5. The method according to claim 1, wherein the cooling treatment in the solution heat treatment step is water cooling; and/or, the switching time is less than 1min; and/or, the set time is greater than or equal to 5 hours.
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