CN106893945B - Austenitic stainless steel for low temperature, casting thereof and manufacturing method of casting - Google Patents
Austenitic stainless steel for low temperature, casting thereof and manufacturing method of casting Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
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- 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
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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- 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
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- 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
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Abstract
The invention provides an austenitic stainless steel for low temperature use, a casting thereof, and a method for manufacturing the casting, wherein the austenitic stainless steel contains 0.08% or less of C, Mn: 1.0-1.6%, Si: 0.6-1.2%, Cr: 17.0-20.0%, Ni: 10.0-13.0%, Mo: 2.0-3.0%, N: 0.04-0.12%, and the balance of Fe and impurities; the impurities contain less than or equal to 0.04 percent of P, less than or equal to 0.02 percent of S, less than or equal to 0.015 percent of Sn, less than or equal to 0.01 percent of As, less than or equal to 0.01 percent of Pb, and less than or equal to 0.01 percent of Sb, wherein the total content of Sn, As, Pb and Sb is less than or equal to 0.035 percent. The invention controls Ms and Md by adjusting chemical components(30/50)The temperature point, the casting process is reasonably controlled, a high-nickel welding rod is selected, the heat treatment temperature is controlled, and the like, so that the stability of a casting structure is ensured, and the cast steel has good mechanical property and dimensional stability.
Description
Technical Field
The present invention relates to austenitic stainless steel, and more particularly, to austenitic stainless steel for low temperature use applied in an environment of 196 ℃ below zero such as liquid oxygen, liquid nitrogen, and other liquid gases, and a casting and a method for manufacturing the casting.
Background
Generally stainless steels can be divided into several large types depending on the structure: austenitic stainless steel, ferritic stainless steel, duplex stainless steel, martensitic stainless steel, and precipitation-hardened stainless steel; wherein the precipitation hardening stainless steel is not suitable for pressure vessel welding parts; the minimum allowable temperatures for the other class 4 stainless steels are shown in the table below.
At present, the stainless steel used at low temperature (below-100 ℃) in the world is basically austenitic stainless steel (mainly 304 or 316 series); however, since the sealing performance is required to be prevented from being affected by the dimensional stability at low temperature, the sealing performance is mostly prevented from being affected by the dimensional change caused by the volume expansion of martensite transformation when the sealing material is used at low temperature by adopting low-temperature treatment (possibly once or twice) at 196 ℃ below zero in China to enable possible martensite transformation to occur in advance and then carrying out finish machining.
However, the processing mode can only solve the problem of sealing performance, and cannot avoid the influence of low-temperature embrittlement of a martensite structure on the plasticity and toughness of the material; in general, if the ferrite content in the 304 and 316 series materials is too high, the ferrite itself may have a problem of embrittlement at a low temperature.
Therefore, it has become an important issue to avoid or reduce martensite transformation at low temperature and reduce ferrite content, so that the material can ensure sufficient plasticity and toughness without low temperature treatment; the present invention addresses this issue and solves the problem in terms of material properties and manufacturing processes.
Disclosure of Invention
Problems to be solved by the invention
The low-temperature austenitic stainless steel does not generally need to consider corrosion resistance, because the chemical reaction rate is very slow even if corrosive media exist at low temperature, and the low-temperature media are non-aqueous liquefied gases such as liquid oxygen, liquid nitrogen or liquefied gas, and the corrosiveness of the media is very weak. However, the metal material at low temperature must have good plasticity and toughness, high elastic modulus, low thermal conductivity and good weldability, i.e. it must not have the problem of low temperature brittleness.
The metal structure is generally classified into Body Centered Cubic (BCC), body centered cubic (BCT), Face Centered Cubic (FCC), HCP, etc., wherein other structures than the FCC structure have embrittlement problem (i.e., have a embrittlement temperature) at low temperature, so that the steel used at low temperature must be a metal having FCC. The austenitic stainless steel has a FCC structure, has good plasticity and toughness and good welding performance, and is very suitable for being used as a low-temperature material.
However, austenite itself causes martensite to form during cooling or when the material is subjected to stress or strain, and this martensite transformation is an expansion behavior that causes dimensional changes in the component, and in addition to affecting the sealing properties of the material, the material may become brittle due to the formation of brittle martensite. Further, austenitic stainless steel contains varying amounts of ferrite, which has a BCC structure and causes embrittlement problems at low temperatures, and also causes stress (strain) due to a difference in shrinkage size between ferrite and austenite due to a difference in thermal expansion coefficient therebetween, which increases the tendency of martensite formation at low temperatures.
Accordingly, an object of the present invention is to provide a low-temperature austenitic stainless steel, a casting thereof, and a method for manufacturing the casting, in which stability of austenite is improved by adjusting chemical properties, residual stress of the casting is reduced by process control to prevent martensite from being generated at low temperature, and the amount and distribution of ferrite in the structure are controlled to improve low-temperature impact performance.
Means for solving the problems
The technical scheme of the invention is as follows: a low-temperature austenitic stainless steel comprising, in mass%: 0.08% or less, manganese (Mn): 1.0-1.6%, silicon (Si): 0.6-1.2%, chromium (Cr): 17.0-20.0%, nickel (Ni): 10.0-13.0%, molybdenum (Mo): 2.0-3.0%, nitrogen (N): 0.04-0.12%, and the balance of iron (Fe) and inevitable impurities; the impurity contains P not more than 0.04%, S not more than 0.02%, Sn not more than 0.015%, As not more than 0.01%, Pb not more than 0.01%, Sb not more than 0.01%, wherein Sn + As + Pb + Sb not more than 0.035%.
The further preferred scheme is as follows: the chromium-nickel equivalent ratio of the austenitic stainless steel is controlled to be 1.0-1.2, wherein the chromium equivalent = Cr +1.5Si +1.4Mo + Nb-4.99, and the nickel equivalent = Ni +30C +0.5Mn +26(N-0.02%) + 2.77; wherein niobium (Nb) is contained in the impurities.
The further preferred scheme is as follows: the ferrite content in the metallographic structure of the austenitic stainless steel is controlled to be 2-12%.
The further preferred scheme is as follows: the Ms temperature point of the austenitic stainless steel is controlled below 273 ℃ below zero and Md(30/50)The temperature point is controlled below minus 80 ℃; wherein Ms (° C) =1305-41.7Cr-61.1Ni-33.3Mn-27.8Si-36.1Mo-1667(C + N), Md(30/50)（℃）=306-256.7(C+N)-5.1Si-4.5Mn-7.6Cr-16.1(Ni+Cu)-10.3Mo-37.8Nb-17.8; wherein copper (Cu) is contained in the impurities.
The second technical scheme of the invention is as follows: an austenitic stainless steel casting for low temperature use, comprising carbon (C): 0.08% or less, manganese (Mn): 1.0-1.6%, silicon (Si): 0.6-1.2%, chromium (Cr): 17.0-20.0%, nickel (Ni): 10.0-13.0%, molybdenum (Mo): 2.0-3.0%, nitrogen (N): 0.04-0.12%, residual calcium for deoxidation, and the balance of iron (Fe) and inevitable impurities; the impurity contains P not more than 0.04%, S not more than 0.02%, Sn not more than 0.015%, As not more than 0.01%, Pb not more than 0.01%, Sb not more than 0.01%, wherein Sn + As + Pb + Sb not more than 0.035%.
The further preferred scheme is as follows: the chromium-nickel equivalent ratio of the casting is controlled to be 1.0-1.2, wherein the chromium equivalent = Cr +1.5Si +1.4Mo + Nb-4.99, and the nickel equivalent = Ni +30C +0.5Mn +26(N-0.02%) + 2.77; wherein niobium (Nb) is contained in the impurities.
The further preferred scheme is as follows: the ferrite content in the metallurgical structure of the casting is controlled to be 2-12%.
The further preferred scheme is as follows: the Ms temperature point of the casting is controlled below 273 ℃ below zero and Md(30/50)The temperature point is controlled below minus 80 ℃; wherein Ms (° C) =1305-41.7Cr-61.1Ni-33.3Mn-27.8Si-36.1Mo-1667(C + N), Md(30/50)(° C) =306-256.7(C + N) -5.1Si-4.5Mn-7.6Cr-16.1(Ni + Cu) -10.3Mo-37.8 Nb-17.8; wherein copper (Cu) is contained in the impurities.
The further preferred scheme is as follows: the casting is a valve for low temperature.
The third technical scheme of the invention is as follows: a manufacturing method of a low-temperature austenitic stainless steel casting adopts the low-temperature austenitic stainless steel with the proportion, and comprises the following steps:
(1) adding calcium silicon to deoxidize and purify molten steel in the process of melting the stainless steel;
(2) during casting, all casting sand adopts special sand to accelerate the cold shock effect and reduce the carbon content on the surface of the casting;
(3) before the heat treatment of the casting, completing all weld repair of the casting, wherein the weld repair adopts a welding rod with high nickel content;
(4) when the casting is subjected to heat treatment, the heat treatment temperature is controlled to be 1080-1120 ℃.
ADVANTAGEOUS EFFECTS OF INVENTION
The austenitic stainless steel is special low-temperature austenitic stainless steel with high nickel content and a certain amount of nitrogen, has good low-temperature impact toughness, does not influence the sealing performance of castings such as valves and the like due to precipitation of martensite, does not cause the deterioration of low-temperature ductility performance due to embrittlement of ferrite due to precipitation of the martensite, has good welding performance, and does not influence the manufacturing characteristics; therefore, the material can still be used as an extremely excellent low-temperature material without cryogenic treatment, and even has more excellent low-temperature impact performance.
Drawings
FIG. 1 is a schematic view showing the metallographic structure of a sample No. 1 specimen sample 1 at 100X.
FIG. 2 is a schematic view showing the metallographic structure of sample No. 1 specimen No. 2 at 100X.
FIG. 3 is a schematic view of type-IV inclusion class 1 in a sample taken from furnace number 3.
Fig. 4 is a schematic view of the Ш type inclusion class 2 in the sampling of furnace No. 3.
FIG. 5 is a schematic representation of the metallographic phase 50X picric acid corrosion at position A of a No. 6 test bar.
FIG. 6 is a schematic representation of the 100 × picric acid corrosion of the A site of the run No. 6 bar.
FIG. 7 is a graph showing the metallographic phase at position A of the test bar No. 6 of 500 Xbittering acid corrosion.
FIG. 8 is a schematic of metallographic 50X picric acid corrosion at the B site of a No. 6 test bar.
FIG. 9 is a schematic of metallographic 100X picric acid corrosion at the B site of a No. 6 test bar.
FIG. 10 is a graph showing the metallographic phase at position B of the test bar No. 6 of 500 Xpicric acid etching.
Fig. 11 is a line graph showing the amount of dimensional change at low temperature of the F316 casting.
FIG. 12 is a line graph showing the amount of dimensional change at low temperature of CF 8M-DT.
Detailed Description
In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.
The embodiment of the invention adopts, but is not limited to, austenitic stainless steel F316 which is generally used at low temperature, and through increasing the nickel content, ensuring a certain content of nitrogen and reducing the transformation point of martensite, the austenite in the alloy is more stable, and the specific scheme is as follows: a low-temperature austenitic stainless steel comprising, in mass%: 0.08% or less, manganese (Mn): 1.0-1.6%, silicon (Si): 0.6-1.2%, chromium (Cr): 17.0-20.0%, nickel (Ni): 10.0-13.0%, molybdenum (Mo): 2.0-3.0%, nitrogen (N): 0.04-0.12%, and the balance of iron (Fe) and inevitable impurities; the impurity contains P not more than 0.04%, S not more than 0.02%, Sn not more than 0.015%, As not more than 0.01%, Pb not more than 0.01%, Sb not more than 0.01%, wherein Sn + As + Pb + Sb not more than 0.035%.
The embodiment of the invention controls the ferrite content in the structure by controlling the equivalent ratio of chromium to nickel, and the specific scheme is as follows: the chromium-nickel equivalent ratio of the austenitic stainless steel is controlled to be 1.0-1.2, wherein the chromium equivalent = Cr +1.5Si +1.4Mo + Nb-4.99, and the nickel equivalent = Ni +30C +0.5Mn +26(N-0.02%) + 2.77; wherein niobium (Nb) is contained in impurities, namely impurity elements brought in from scrap steel or alloy iron.
The ferrite content in F316 may be as high as 30%, which ferrite may have embrittlement problems at low temperatures, and if the amount is controlled within a certain range and is formed into discrete fine islands, the material is subjected to stress mainly by austenite of the matrix (austenite structure has good low-temperature toughness), so that the low-temperature toughness of the material is not greatly reduced. However, ferrite is advantageous in welding performance, and thus the amount thereof cannot be reduced without limitation. Therefore, the control of the amount of the ferrite in a certain range is crucial to the use of the material performance.
Therefore, in the embodiment of the invention, the ferrite content in the metallographic structure of the austenitic stainless steel is controlled to be 2-12%.
Generally, the residual stress (or strain) of stainless steel can promote the generation of martensite (i.e. increase the initial point of martensite transformation), and when the residual stress is too high, the generation of martensite can be caused, so that the sealing performance of a product is influenced, the material can be embrittled, and the low-temperature toughness performance of the material is reduced, so that how to reduce the residual stress (or strain) of stainless steel is also critical for solving the low-temperature performance.
Therefore, in the present example, the martensite transformation point (Ms) was controlled to be below 273 ℃ and the transformation point (Md) at which 50% of martensite was generated at a strain amount of 30%(30/50)) The temperature is controlled below 80 ℃ below zero, and the specific scheme is as follows: the Ms temperature point of the austenitic stainless steel is controlled below 273 ℃ below zero and Md(30/50)The temperature point is controlled below minus 80 ℃; wherein Ms (° C) =1305-41.7Cr-61.1Ni-33.3Mn-27.8Si-36.1Mo-1667(C + N), Md(30/50)(° C) =306-256.7(C + N) -5.1Si-4.5Mn-7.6Cr-16.1(Ni + Cu) -10.3Mo-37.8 Nb-17.8; wherein copper (Cu) is contained in impurities, namely impurity elements brought in by scrap steel or alloy iron.
The embodiment of the invention also discloses an austenitic stainless steel casting for low temperature free from cryogenic treatment, which contains carbon (C): 0.08% or less, manganese (Mn): 1.0-1.6%, silicon (Si): 0.6-1.2%, chromium (Cr): 17.0-20.0%, nickel (Ni): 10.0-13.0%, molybdenum (Mo): 2.0-3.0%, nitrogen (N): 0.04-0.12%, residual calcium for deoxidation, and the balance of iron (Fe) and inevitable impurities; the impurity contains P not more than 0.04%, S not more than 0.02%, Sn not more than 0.015%, As not more than 0.01%, Pb not more than 0.01%, Sb not more than 0.01%, wherein Sn + As + Pb + Sb not more than 0.035%.
The embodiment of the invention controls the ferrite content in the structure by controlling the equivalent ratio of chromium to nickel, and the specific scheme is as follows: the chromium-nickel equivalent ratio of the casting is controlled to be 1.0-1.2, wherein the chromium equivalent = Cr +1.5Si +1.4Mo + Nb-4.99, and the nickel equivalent = Ni +30C +0.5Mn +26(N-0.02%) + 2.77; wherein niobium (Nb) is contained in impurities, namely impurity elements brought in from scrap steel or alloy iron.
The ferrite content in F316 may be as high as 30%, which ferrite may have embrittlement problems at low temperatures, and if the amount is controlled within a certain range and is formed into discrete fine islands, the material is subjected to stress mainly by austenite of the matrix (austenite structure has good low-temperature toughness), so that the low-temperature toughness of the material is not greatly reduced. However, ferrite is advantageous in welding performance, and thus the amount thereof cannot be reduced without limitation. Therefore, the control of the amount of the ferrite in a certain range is crucial to the use of the material performance.
Therefore, in the embodiment of the invention, the ferrite content in the metallographic structure of the casting is controlled to be 2-12%.
In general, the residual stress (or strain) of the casting promotes the generation of martensite (i.e. the initial point of martensite transformation is improved), and when the residual stress of welding/grinding, the residual stress of casting and the like are too high, the generation of martensite is caused, so that the sealing performance of the casting such as a valve and the like is influenced, the material is possibly embrittled, and the low-temperature toughness performance of the material is reduced, so that how to reduce the residual stress (or strain) of the casting is also critical for solving the low-temperature performance.
Therefore, in the embodiment of the invention, the Ms temperature point of the casting is controlled to be below 273 ℃ below zero and Md(30/50)The temperature point is controlled below minus 80 ℃; wherein Ms (° C) =1305-41.7Cr-61.1Ni-33.3Mn-27.8Si-36.1Mo-1667(C + N), Md(30/50)(° C) =306-256.7(C + N) -5.1Si-4.5Mn-7.6Cr-16.1(Ni + Cu) -10.3Mo-37.8 Nb-17.8; wherein copper (Cu) is contained in impurities, namely impurity elements brought in by scrap steel or alloy iron.
In the embodiment of the invention, the casting is a valve for low temperature, such as an LNG valve, and the like, and may be other low temperature structural members.
In the embodiment of the invention, calcium silicate is added into the casting to deoxidize and purify molten steel in the process of stainless steel melting, special sand is used as casting sand during casting to accelerate the cold shock effect and reduce the carbon content on the surface of the casting, welding rods with high nickel content are used for completing all welding repair of the casting before heat treatment, and the temperature of the casting during heat treatment is controlled to be 1080-1120 ℃.
The embodiment of the invention also discloses a manufacturing method of the low-temperature austenitic stainless steel casting, which adopts the low-temperature austenitic stainless steel with the mixture ratio and comprises the following steps:
(1) adding calcium silicon to deoxidize and purify molten steel in the process of melting the stainless steel;
(2) during casting, all casting sand adopts special sand to accelerate the cold shock effect and reduce the carbon content on the surface of the casting;
(3) before the heat treatment of the casting, completing all weld repair of the casting, wherein the weld repair adopts a welding rod with high nickel content;
(4) when the casting is subjected to heat treatment, the heat treatment temperature is controlled to be 1080-1120 ℃.
In the embodiment of the invention, the special sand in the step (2) is preferably chrome sand.
In the embodiment of the invention, in order to ensure that the welding bead has enough nickel content during welding repair, a special E317 welding rod is preferably adopted in the step (3), so that the unbalance of the iron content of the welding bead is avoided.
In the present example, the ferrite content in the structure was evaluated according to the ASTM a800 specification, and after raising the nickel content in the alloying elements and ensuring a certain amount of nitrogen, in order to ensure that all the cast precipitates are re-soluted into the matrix structure, the heat treatment temperature in step (4) must be raised.
In the embodiment of the invention, Ms and Md are controlled by adjusting chemical components(30/50)Temperature point, reasonable control of the casting process, selection of a high-nickel-content welding rod, control of heat treatment temperature and the like, and guarantee of the stability of a casting structure. The austenitic stainless steel has good mechanical properties, and particularly has excellent impact performance at low temperature; when the valve is used for a long time at low temperature, the dimensional stability is good, and the valve sealing performance cannot be influenced by dimensional change caused by martensite transformation; is very suitable for being used as a raw material for a low-temperature valve structural member.
The reason for specifying the chemical composition of the austenitic stainless steel of the present invention will be described below; the content of each element is mass percent.
C: less than 0.08%
C is generally an austenite forming element and a solid solution strengthening element, and when the alloy is used at high temperature, the carbon content is increased for improving the high-temperature strength; however, since the strength does not need to be increased excessively when the alloy is used at a low temperature, and chromium carbide is easily precipitated and chromium in the matrix is consumed when the amount is increased excessively, the upper limit is generally 0.08%, preferably 0.06% of F316.
Mn：1.0-1.6%
Mn contributes to deoxidation and desulfurization and is an austenite forming element, and has a good effect of lowering the Ms point in connection with the control of the ferrite content, so the lower limit of the content is set at 1.0%, preferably 1.2%. However, when the manganese content is too high, the upper limit is set to 1.6%, preferably 1.4%, because the material becomes brittle and the toughness of the steel is deteriorated.
Si：0.6-1.2%
Si contributes to deoxidation and is a solid-solution strengthening element, and the lower limit thereof is set to 0.6%, preferably 0.8%, since the fluidity of molten steel can be increased in connection with the control of ferrite content; however, since too high a silicon content causes excessive slag inclusion, deteriorates weldability, and raises the embrittlement temperature, the upper limit is limited to 1.2, preferably 1.0%.
P≤0.04%，S≤0.02%
S and P are inevitable impurities, so that the steel is embrittled and is harmful to welding performance, the formed phosphorus sulfide can cause the starting point of cracks at low temperature, particularly the influence of sulfide is larger, so that the phosphorus content is limited to be less than 0.04 percent, and preferably less than 0.03 percent; the sulfur content is limited to 0.02% or less, preferably 0.01% or less.
Cr：17.0-20.0%
Cr is an essential element for stainless steel, is also a ferrite-forming element, is an essential element for controlling the ferrite content, is an element which forms austenite in combination with a nickel element, and has the most effective effect of lowering the Ms point of stainless steel in addition to nickel, so the lower limit thereof is set to 17%, preferably 18.0%; however, the upper limit of the content of chromium is limited to 20%, preferably 19.0%, because the content of ferrite in the microstructure increases and the production cost increases, although the Ms point can be further lowered by too high a content of chromium.
Ni：10.0-13.0%
Ni is an austenite forming element and has stabilityAustenite, good formability and low-temperature toughness, and low Ms point and Md（30/50）The lower limit value is set to 10.0%, preferably 11% or more, because the dot effect is good and the control of ferrite content is concerned; however, since nickel is an expensive alloying element and when the content is too high, not only the production cost is increased, but also the content of ferrite is decreased to deteriorate the weldability, the upper limit value thereof is set to 13%, preferably 12% or less.
Mo：2.0-3.0%
Mo is a ferrite forming element, is related to the control of ferrite content, is also a good solid solution strengthening element and is used for reducing Ms point and Md（30/50）The amount of the surfactant is also effective, so that the lower limit is set to 2.0%, preferably 2.2%; however, when the content is too high, carbide tends to be formed to be detrimental to low-temperature properties and to increase production cost, so that the upper limit is set to 3.0%, preferably 2.8%.
N：0.04-0.12%
N is a strong austenite forming element and is an element for reducing Ms point and Md（30/50）The most effective elements are very effective for improving the strength performance of the stainless steel, so the lower limit value is set to be 0.04 percent, and the optimal value is 0.06 percent; however, if the content is too high, casting porosity is likely to occur, and nitrides with elements such as chromium and molybdenum are likely to be formed, which is disadvantageous in low-temperature performance, so that the upper limit value is set to 0.12%, preferably 0.1%.
Other inevitable impurities
These impurity elements are detrimental to both low-temperature toughness and weldability, and to castability; therefore, the following settings are set: sn is less than or equal to 0.015 percent, As is less than or equal to 0.01 percent, Pb is less than or equal to 0.01 percent, Sb is less than or equal to 0.01 percent, and the sum of the Sn, As and Sb is less than or equal to 0.035 percent, preferably less than or equal to 0.03 percent.
Controlling the content of chromium nickel equivalent and ferrite: the ferrite content in the stainless steel is related to the chromium-nickel equivalent ratio and the heat treatment cooling speed, when the chromium-nickel equivalent is too low, the formed ferrite content is too small, the welding performance is influenced, and therefore the lower limit of the chromium-nickel equivalent ratio is limited to 1.0; however, when the cr-ni equivalent ratio is too high, the content of ferrite formed is too high, and the ferrite is embrittled at a low temperature and causes continuous long ferrite to affect the low-temperature plasticity and toughness, so that the upper limit value is set to 1.2. On the basis of the above, we can ensure that the ferrite content in the structure is 2-12%, preferably 4-10% according to the ASTM A800 specification. The chromium nickel equivalent was calculated according to ASTM a800 as follows: chromium equivalent = Cr +1.5Si +1.4Mo + Nb-4.99; nickel equivalent = Ni +30C +0.5Mn +26(N-0.02%) + 2.77.
Ms temperature point: the Ms temperature point is a transformation point of austenite stainless steel spontaneously forming martensite at low temperature under the condition of no stress or strain, if the temperature is higher than the working condition temperature, the valve material can cause dimension change due to volume expansion caused by martensite transformation to influence the sealing performance, the martensite is hard and brittle, and the ductility performance of the material can be reduced, so that the lower the Ms point is, the better the Ms point is, the design is below 273 ℃ below zero, and the calculation formula of the Ms point is as follows: ms (. degree. C.) =1305-41.7Cr-61.1Ni-33.3Mn-27.8Si-36.1Mo-1667(C + N).
Md(30/50)Temperature point: md(30/50)The temperature point is the temperature point of 50% martensitic transformation caused by 30% strain of austenitic stainless steel, and the austenitic stainless steel casting inevitably has partial residual stress (or strain) due to process factors in the manufacturing process, and the stress (or strain) can raise the temperature of martensitic transformation to be unfavorable for low-temperature performance, so the Md(30/50)The lower the temperature point, the better, but the Md is decreased without limitation by adding carbon, nitrogen or molybdenum, niobium or the like(30/50)Temperature, resulting in the formation of carbonitrides to increase the nickel element to reduce Md(30/50)The temperature will again lead to a reduction of the ferrite content, so Md is controlled without affecting the chromium nickel equivalent to control the ferrite content(30/50)The temperature point is controlled below minus 80 ℃.
Reduction of carbon content on casting surface: the whole casting contact surface is shaped by chrome sand so as to reduce the carbon content on the casting surface.
The molten steel cleanliness improvement-deoxidation mode is as follows: the silicon-calcium alloy is added together with aluminum to form calcium aluminate so as to float the deoxidation product, reduce the melting point of the deoxidation product and increase the flowing property of molten steel.
The heat treatment process comprises the following steps: in order to ensure that the casting segregation structure and the second phase of the casting can be completely dissolved into the matrix structure in a solid solution manner, the heat preservation temperature of 20-40 ℃ is increased on the basis of the heat treatment temperature of common stainless steel; the heat treatment temperature is controlled to be 1080-1120 ℃.
Welding repair: in order to ensure the consistency of the bead structure and the base material structure and avoid weld repair cracks, a welding rod with a high nickel content, preferably an E317 welding rod, is used.
The present invention will be described more specifically with reference to test examples, but the present invention is not limited to these test examples.
Test examples
Materials such as 316 scrap steel, low-carbon ferrochrome and the like are melted by a medium-frequency induction furnace and are prepared into chemical compositions according with the specification in the invention, as shown in the table I. In Table one, six furnace castings were co-smelted, one sample blank according to ASTM A703 specification was poured for each furnace, and the furnace compositions are shown in Table one.
Table one: chemical composition and related parameters
These ingredients and parameters are all in accordance with the requirements of the embodiments of the present invention. And then, the test bar of each heat and the casting are simultaneously put into a furnace for heat treatment, the heat preservation temperature of the heat treatment is set to be 1100 ℃, the heat preservation is carried out for two hours, then the water is quenched, the water temperature does not exceed 40 ℃ during the heat treatment, and the temperature of the casting is 980 ℃ detected by an infrared thermometer before quenching, thus meeting the expectation.
The test bars with the furnace numbers of 2, 4 and 5 are processed into tensile property test bars according to the ASTM A370 specification, a microcomputer-controlled electro-hydraulic servo universal tester WAW-600E is used for carrying out tensile test, the low-temperature Charpy impact test block is used for carrying out impact test at the temperature of 196 ℃ below zero in a double-refrigeration automatic low-temperature impact tester, and the detection values are shown in the table II.
Table two: mechanical Properties
It can be seen that the mechanical properties at room temperature all meet the requirements of the general ASTM A351-CF8M, but it is expected that more importantly, the low temperature impact toughness value is at least 99.39J or more, which is much higher than the impact value required by the advanced foreign countries for use at this temperature (196 ℃ C. below zero), as shown in Table III.
Table three: various specifications for toughness of low-temperature pressure vessel
It is known that the ductility and toughness of the material at low temperature are good, and the material has no embrittlement problem; therefore, the body and other structural parts used as the material for the LNG valve have great advantages.
As shown in FIG. 1-2, a sample was taken from the No. 1 test bar for ferrite content analysis, the detection standard is GB/T13298-: the magnification of the metallographic structure is 100 x, no grain boundary carbide exists in the metallographic structure, the ferrite content of the sample 1 is 9.4%, the ferrite content of the sample 2 is 8.1%, and the average ferrite content is 8.75%; and the ferrite is discontinuous island-shaped or block-shaped structure in the structure; it is confirmed that ferrite in such a proportion greatly contributes to the reduction of weld repair cracks, and that at low temperatures, most of the tensile stress of the material is borne by the austenite structure of the matrix when the material is stressed, without affecting the ductility and toughness properties of the overall material due to the low-temperature brittleness of ferrite.
As shown in FIGS. 3-4, the slag inclusion rate of the sample taken from the furnace No. 3 is analyzed, the determination standard is TB/T2452-93, the detection results are as follows, the type IV inclusion is grade 1, the type Ш inclusion is grade 2, the slag inclusion rate is qualified, it is known that the inclusions in the steel material have large difference between the expansion coefficient and the base metal at low temperature, so the stress problem is caused by different shrinkage when the inclusions are subjected to low temperature, the Ms point is possibly increased to cause martensite transformation, the stress concentration point is more possibly to become the starting point of cracks, and the reduction of the slag inclusion rate is also critical to the service performance of the low-temperature material.
As shown in FIGS. 5-10, the test bar with furnace number 6 was placed in a liquid nitrogen bath for two times of low-temperature treatment at-196 deg.C, and each time of heat preservation was carried outThe time is 2 hours, after the temperature is returned to normal temperature, whether martensite is formed or not is detected, and the detection result is as follows: no martensite is seen in the structure; can determine the temperature at the Ms point and Md at the adjusting chemical element(30/50)The temperature of the point is controlled, and the factor which can generate residual stress in the manufacturing process is reduced, so that the austenitic stainless steel completely without martensite structure can be obtained; thus, there is a necessity to cancel the cryogenic treatment.
As shown in fig. 11-12, the dimensional change of the castings at low temperature, as compared to F316, which is commonly used for the actual cast castings compared to the general low temperature materials, was compared as follows: (1) the percentage change of the F316 size ranges from +0.3 to-1.0, and is mainly concentrated in the range from +0.3 to-0.5 from the data. (2) The percentage of dimensional change of the material (code CF 8M-DT) of the invention is floated from +0.1 to-0.1, and the dimensional change is stable. Therefore, it can be confirmed that the dimensional stability of the material of the present invention is more stable at low temperature than that of the commonly used F316.
Possible development of industry
According to the data, the material of the invention can have high dimensional stability and excellent low-temperature impact performance without cryogenic treatment, can cancel the process that the domestic low-temperature material needs to be subjected to two or even three times of low-temperature treatment at present, can reduce the manufacturing cost and the equipment investment, and also avoids the worries that martensite is possibly generated; the method has great development potential for improving the autonomous ability of domestic industry and replacing imported products.
It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Claims (3)
1. An austenitic stainless steel for low temperature use, characterized in that: contains carbon (C) in mass%: 0.08% or less, manganese (Mn): 1.0-1.6%, silicon (Si): 0.6-1.2%, chromium (Cr): 17.0 to 20.0 percent of the total weight of the mixture,nickel (Ni): 10.0-13.0%, molybdenum (Mo): 2.0-3.0%, nitrogen (N): 0.04-0.12%, and the balance of iron (Fe) and inevitable impurities; phosphorus (P) in the impurities is less than or equal to 0.04 percent, sulfur (S) is less than or equal to 0.02 percent, tin (Sn) is less than or equal to 0.015 percent, arsenic (As) is less than or equal to 0.01 percent, lead (Pb) is less than or equal to 0.01 percent, antimony (Sb) is less than or equal to 0.01 percent, wherein Sn + As + Pb + Sb is less than or equal to 0.035 percent, the chromium-nickel equivalent ratio of the austenitic stainless steel is controlled to be 1.0-1.2, wherein the chromium equivalent = Cr +1.5Si +1.4Mo + Nb-4.99, and the nickel equivalent = Ni +30C +0.5Mn +26(N-0.02%) + 2.77; wherein niobium (Nb) is contained in the impurities, the ferrite content in the metallographic structure of the austenitic stainless steel is controlled to be 2-12%, the Ms temperature point of the austenitic stainless steel is controlled to be below 273 ℃ below zero, and Md(30/50)The temperature point is controlled below minus 80 ℃; wherein Ms (° C) =1305-41.7Cr-61.1Ni-33.3Mn-27.8Si-36.1Mo-1667(C + N), Md(30/50)(° C) =306-256.7(C + N) -5.1Si-4.5Mn-7.6Cr-16.1(Ni + Cu) -10.3Mo-37.8 Nb-17.8; wherein copper (Cu) is contained in the impurities.
2. An austenitic stainless steel casting for low temperature use, characterized in that: contains carbon (C) in mass%: 0.08% or less, manganese (Mn): 1.0-1.6%, silicon (Si): 0.6-1.2%, chromium (Cr): 17.0-20.0%, nickel (Ni): 10.0-13.0%, molybdenum (Mo): 2.0-3.0%, nitrogen (N): 0.04-0.12%, residual calcium for deoxidation, and the balance of iron (Fe) and inevitable impurities; phosphorus (P) in the impurities is less than or equal to 0.04 percent, sulfur (S) is less than or equal to 0.02 percent, tin (Sn) is less than or equal to 0.015 percent, arsenic (As) is less than or equal to 0.01 percent, lead (Pb) is less than or equal to 0.01 percent, antimony (Sb) is less than or equal to 0.01 percent, wherein Sn + As + Pb + Sb is less than or equal to 0.035 percent, the chrome-nickel equivalent ratio of the casting is controlled to be 1.0-1.2, wherein the chrome equivalent = Cr +1.5Si +1.4Mo + Nb-4.99, and the nickel equivalent = Ni +30C +0.5Mn +26(N-0.02 percent) + 2.77; wherein niobium (Nb) is contained in impurities, the ferrite content in the metallographic structure of the casting is controlled to be 2-12%, the Ms temperature point of the casting is controlled to be below-273 ℃, Md(30/50)The temperature point is controlled below minus 80 ℃; wherein Ms (° C) =1305-41.7Cr-61.1Ni-33.3Mn-27.8Si-36.1Mo-1667(C + N), Md(30/50)(° C) =306-256.7(C + N) -5.1Si-4.5Mn-7.6Cr-16.1(Ni + Cu) -10.3Mo-37.8 Nb-17.8; wherein copper (Cu) is contained inAmong the impurities.
3. A method for producing a low-temperature austenitic stainless steel casting, characterized by using the low-temperature austenitic stainless steel of claim 1, and comprising the steps of:
(1) adding calcium silicon to deoxidize and purify molten steel in the process of melting the stainless steel;
(2) during casting, all casting sand adopts special sand to accelerate the cold shock effect and reduce the carbon content on the surface of the casting;
(3) before the heat treatment of the casting, completing all weld repair of the casting, wherein the weld repair adopts a welding rod with high nickel content;
(4) when the casting is subjected to heat treatment, the heat treatment temperature is controlled to be 1080-1120 ℃.
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| CN109136771A (en) * | 2018-10-19 | 2019-01-04 | 太原钢铁(集团)有限公司 | austenitic stainless steel and preparation method thereof |
| CN109877274B (en) * | 2019-03-23 | 2020-12-01 | 江苏亿阀股份有限公司 | Casting process of ultralow-temperature valve casting |
| CN111441001A (en) * | 2020-05-08 | 2020-07-24 | 徐州优尚精密机械制造有限公司 | Low-temperature-resistant functional stainless steel casting and manufacturing method thereof |
| CN111850430B (en) * | 2020-07-23 | 2021-08-06 | 杭州科技职业技术学院 | Composite material for LNG (liquefied natural gas) ultralow-temperature valve and preparation method of composite material |
| CN116694987A (en) * | 2023-04-28 | 2023-09-05 | 湖州永兴特种不锈钢有限公司 | Austenitic stainless steel used in ultralow temperature environment |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007002319A (en) * | 2005-06-27 | 2007-01-11 | Nippon Steel & Sumikin Stainless Steel Corp | Inexpensive austenitic stainless steel wire having superior ductility, high strength and high corrosion resistance |
| CN101994068A (en) * | 2009-08-25 | 2011-03-30 | 宝山钢铁股份有限公司 | Austenitic stainless steel plate and manufacture method thereof |
| KR20110071508A (en) * | 2009-12-21 | 2011-06-29 | 주식회사 포스코 | Austenitic stainless steel for gas nitriding and gas nitriding method of the same |
| KR20130053621A (en) * | 2011-11-15 | 2013-05-24 | 주식회사 포스코 | Thick austenitic stainless steel and manufacturing method using the same |
| CN103521946A (en) * | 2013-11-02 | 2014-01-22 | 丹阳市华龙特钢有限公司 | High-strength austenitic stainless steel submerged-arc welding wire |
| CN104611643A (en) * | 2015-01-21 | 2015-05-13 | 内蒙古科技大学 | 316 austenitic stainless steel with nitrogen increased and nickel decreased and preparation method thereof |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54121224A (en) * | 1978-03-14 | 1979-09-20 | Kubota Ltd | Cast stainless steel for extremely low temperature use |
-
2017
- 2017-02-08 CN CN201710068442.3A patent/CN106893945B/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007002319A (en) * | 2005-06-27 | 2007-01-11 | Nippon Steel & Sumikin Stainless Steel Corp | Inexpensive austenitic stainless steel wire having superior ductility, high strength and high corrosion resistance |
| CN101994068A (en) * | 2009-08-25 | 2011-03-30 | 宝山钢铁股份有限公司 | Austenitic stainless steel plate and manufacture method thereof |
| KR20110071508A (en) * | 2009-12-21 | 2011-06-29 | 주식회사 포스코 | Austenitic stainless steel for gas nitriding and gas nitriding method of the same |
| KR20130053621A (en) * | 2011-11-15 | 2013-05-24 | 주식회사 포스코 | Thick austenitic stainless steel and manufacturing method using the same |
| CN103521946A (en) * | 2013-11-02 | 2014-01-22 | 丹阳市华龙特钢有限公司 | High-strength austenitic stainless steel submerged-arc welding wire |
| CN104611643A (en) * | 2015-01-21 | 2015-05-13 | 内蒙古科技大学 | 316 austenitic stainless steel with nitrogen increased and nickel decreased and preparation method thereof |
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