WO2024257639A1 - Matériau d'acier inoxydable biphasé à base de ferrite et austénite ainsi que procédé de fabrication de celui-ci, et structure pour acide phosphorique cru - Google Patents

Matériau d'acier inoxydable biphasé à base de ferrite et austénite ainsi que procédé de fabrication de celui-ci, et structure pour acide phosphorique cru Download PDF

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WO2024257639A1
WO2024257639A1 PCT/JP2024/020240 JP2024020240W WO2024257639A1 WO 2024257639 A1 WO2024257639 A1 WO 2024257639A1 JP 2024020240 W JP2024020240 W JP 2024020240W WO 2024257639 A1 WO2024257639 A1 WO 2024257639A1
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stainless steel
phosphoric acid
duplex stainless
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慧 中辻
明訓 河野
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Nippon Steel Stainless Steel Corp
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Nippon Steel Stainless Steel Corp
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Priority to EP24823259.7A priority Critical patent/EP4667612A1/fr
Priority to CN202480032433.7A priority patent/CN121127617A/zh
Priority to JP2025527842A priority patent/JPWO2024257639A1/ja
Publication of WO2024257639A1 publication Critical patent/WO2024257639A1/fr
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    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
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    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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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
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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
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
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    • 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
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C—CHEMISTRY; METALLURGY
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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
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
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    • 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

Definitions

  • the present invention relates to a ferritic-austenitic duplex stainless steel material, a manufacturing method thereof, and a structure for crude phosphoric acid.
  • Patent Document 1 proposes using a ferritic-austenitic duplex stainless steel material with a specified composition instead of the austenitic stainless steel material that has traditionally been used as a storage tank steel material.
  • Patent Document 2 also proposes using a ferritic-austenitic duplex stainless steel material with a specified composition for sulfuric acid plants that handle crude sulfuric acid and sulfuric acid storage tanks.
  • Patent Document 3 proposes a ferritic-austenitic duplex stainless steel material with excellent corrosion resistance in a trace hydrogen sulfide environment as a stainless steel material to be used for line pipes used in transporting oil and natural gas.
  • crude phosphoric acid is one of the chemicals transported by chemical tankers.
  • Crude phosphoric acid is a basic raw material for fertilizers, detergents, feed, medicines, etc., but Japan has few phosphorus resources and relies on imports by sea transport for most of it.
  • crude phosphoric acid contains corrosive substances such as F - and Cl - derived from phosphate rock, and therefore corrosion (including discoloration such as blackening) occurs on the inner surface of the tank when crude phosphoric acid is transported. Therefore, after the transportation of crude phosphoric acid, maintenance such as repair and cleaning is performed on the inner surface of the tank in order to prevent contamination, and new chemicals are loaded. Such maintenance is very laborious and frequent, and is therefore a problem in terms of cost and time in chemical transportation.
  • austenitic stainless steel materials with good corrosion resistance such as SUS316L and 329J3L
  • SUS316L and 329J3L have been used for the inner surface of the tank of a chemical tanker that transports crude phosphoric acid.
  • SUS316L corrodes when crude phosphoric acid is stored, and the demand for alternative materials is growing day by day. Therefore, it is considered that the ferritic-austenitic duplex stainless steel materials described in Patent Documents 1 to 3 may be applied to the inner surfaces of storage tanks of chemical tankers that transport crude phosphoric acid.
  • ferritic-austenitic duplex stainless steel materials described in Patent Documents 1 to 3 are more cost effective than Ni-rich austenitic stainless steels, their corrosion resistance to sulfides, crude phosphoric acid, etc. is inferior to that of SUS316L.
  • Patent Document 4 proposes an austenitic stainless steel material with adjusted contents of Cr, Ni, Mo, and Cu, which affect corrosion resistance to crude phosphoric acid.
  • the austenitic stainless steel material described in Patent Document 4 is effective to a certain extent against corrosion caused by crude phosphoric acid, but it has been confirmed that corrosion (particularly blackening) occurs on the inner surface of the tank of a chemical tanker that actually transports crude phosphoric acid. Therefore, there is a demand for further improvement in corrosion resistance to crude phosphoric acid, as well as improvement from an economical perspective by reducing the content of expensive elements such as Ni.
  • the present invention is directed to a ferritic-austenitic duplex stainless steel material, which is superior from an economical point of view to an austenitic stainless steel material, and aims to provide a ferritic-austenitic duplex stainless steel material having excellent corrosion resistance to crude phosphoric acid and a method for producing the same.
  • Another object of the present invention is to provide a structure for crude phosphoric acid which has excellent corrosion resistance against crude phosphoric acid and can reduce maintenance costs and time.
  • Crude phosphoric acid is produced by dissolving phosphate rock with sulfuric acid, and is transported as a liquid on a chemical tanker. Crude phosphoric acid contains low concentrations of F - (fluorine ion) and Cl - (chlorine ion), which are corrosive substances that preferentially dissolve the austenite phase, causing a decrease in the corrosion resistance of crude phosphoric acid.
  • the present invention has a composition, on a mass basis, of C: 0.100% or less, Si: 0.05 to 1.50%, Mn: 0.05 to 2.00%, Ni: 4.00 to 9.00%, P: 0.050% or less, S: 0.0040% or less, Cr: 23.0 to 30.0%, N: 0.100 to 0.250%, Cu: 0.01 to 2.00%, Mo: 0.50 to 2.50%, Al: 0.100% or less, Nb: 0.200% or less, with the balance being Fe and impurities;
  • DF 7.2(Cr+0.8Mo+0.78Si)-8.9(Ni+0.03Mn+0.72Cu+22C+21N)-44.9...
  • each element symbol represents the content (mass%) of each element
  • the austenite phase has the following formula (2): (0.8Cr) 2 +2Ni+7Mo+30Cu+30N ⁇ 340... (2) (wherein the element symbols represent the contents (mass%) of each element)
  • the present invention also relates to a soaking process in which a rolled material containing, by mass, C: 0.100% or less, Si: 0.05 to 1.50%, Mn: 0.05 to 2.00%, Ni: 4.00 to 9.00%, P: 0.050% or less, S: 0.0040% or less, Cr: 23.0 to 30.0%, N: 0.100 to 0.250%, Cu: 0.01 to 2.00%, Mo: 0.50 to 2.50%, Al: 0.100% or less, Nb: 0.200% or less, and the balance being Fe and impurities, is soaked at a soaking temperature of 950 to 1150 ° C.
  • the present invention relates to a method for producing a ferritic-austenitic duplex stainless steel material, wherein the quenching start temperature is a temperature of 950 to 990°C and is a temperature lower than the soaking temperature.
  • the present invention relates to a structure for crude phosphoric acid comprising the above-mentioned ferritic-austenitic duplex stainless steel material.
  • the present invention it is possible to provide a ferritic-austenitic duplex stainless steel material having excellent corrosion resistance to crude phosphoric acid and a method for producing the same. Furthermore, according to the present invention, it is possible to provide a structure for crude phosphoric acid which has excellent corrosion resistance against crude phosphoric acid and can reduce maintenance costs and time.
  • the ferritic-austenitic duplex stainless steel material according to an embodiment of the present invention (hereinafter simply referred to as "duplex stainless steel material”) has a composition containing C: 0.100% or less, Si: 0.05-1.50%, Mn: 0.05-2.00%, Ni: 4.00-9.00%, P: 0.050% or less, S: 0.0040% or less, Cr: 23.0-30.0%, N: 0.100-0.250%, Cu: 0.01-2.00%, Mo: 0.50-2.50%, Al: 0.100% or less, Nb: 0.200% or less, with the balance being Fe and impurities.
  • the term “stainless steel material” refers to a material formed from stainless steel, and the shape of the material is not particularly limited. Examples of the material shape include a plate shape (including a strip shape), a rod shape, a tube shape, and the like. In addition, the material may be various shaped steels having a cross-sectional shape such as a T-shape or an I-shape.
  • the term “ferritic-austenitic” refers to a metal structure that is mainly composed of two phases, ferritic and austenitic, at room temperature.
  • the term “ferritic-austenitic” also includes metal structures that contain small amounts of phases other than ferritic and austenitic phases (e.g., martensite phase, etc.).
  • impurities refers to components that are mixed in due to various factors in raw materials such as ores and scraps and in the manufacturing process during industrial production of stainless steel materials, and are acceptable within a range that does not adversely affect the present invention.
  • impurities also include unavoidable impurities.
  • “xx% or less” means that the content is xx% or less, but includes an amount exceeding 0% (particularly, above the impurity level).
  • the duplex stainless steel material according to the embodiment of the present invention may further contain one or more selected from Ti: 0.050% or less, B: 0.0050% or less, Ca: 0.0010 to 0.0100%, Mg: 0.0001 to 0.0020%, Zr: 0.090% or less, Co: 3.00% or less, V: 1.000% or less, Ta: 0.200% or less, Sn: 0.100% or less, O: 0.0050% or less, W: 1.000% or less, and REM: 0.100% or less, as necessary.
  • Ti 0.050% or less
  • B 0.0050% or less
  • Ca 0.0010 to 0.0100%
  • Mg 0.0001 to 0.0020%
  • Zr 0.090% or less
  • Co 3.00% or less
  • V 1.000% or less
  • Ta 0.200% or less
  • Sn 0.100% or less
  • W: 1.000% or less REM: 0.100% or less
  • Silicon is an element that is used as a deoxidizing element and is added to improve oxidation resistance. From the viewpoint of obtaining these effects, the silicon content is set to 0.05% or more. From the viewpoint of stably securing these effects, the amount of Si is preferably 0.10% or more, 0.20% or more, or 0.30% or more. On the other hand, if the Si content is too high, the two-phase The stainless steel material becomes hard, and the toughness and workability are reduced. Therefore, from the viewpoint of suppressing the reduction in toughness and workability, the Si content is set to 1.50% or less. From the viewpoint of stably securing it, it is preferably 1.45% or less, 1.40% or less, 1.35% or less, or 1.30% or less.
  • Mn has the effect of increasing the austenite phase and increasing the solid solubility of nitrogen to suppress bubble defects during manufacturing. From the viewpoint of obtaining this effect, the Mn content is set to 0.05% or more. In order to stably ensure this effect, the Mn content is preferably 0.10% or more or 0.20% or more. On the other hand, if the Mn content is too high, the corrosion resistance and hot workability are deteriorated. Therefore, from the viewpoint of suppressing the deterioration of corrosion resistance and hot workability, the Mn content is set to 2.00% or less. % or less, preferably 1.80% or less, 1.70% or less, or 1.60% or less.
  • Ni is an austenite stabilizing element and has the effect of improving corrosion resistance by suppressing the progress of corrosion.
  • the Ni content is set to 4.00% or more.
  • the Ni content is 4.10% or more, 4.20% or more, 4.30% or more, 4.40% or more, or 4.50% or more.
  • the Ni content is set to 9.00% or less. From the viewpoint of cost reduction, the Ni content is set to It is preferably 8.50% or less, 8.00% or less, or 7.80% or less.
  • P is an element that is inevitably mixed into duplex stainless steel materials, and is also contained in raw materials such as Cr. If the P content is too high, formability decreases, so the lower the P content, the better.
  • the P content is set to 0.050% or less. From the viewpoint of stably suppressing the deterioration of formability, the P content is preferably set to 0.045% or less or 0.040% or less.
  • the lower limit of P is not particularly limited, but removing P requires a very high refining cost, so the P content may be set to 0.001% or more in consideration of economic efficiency.
  • S is an element that is inevitably mixed into duplex stainless steel materials, and it can combine with Mn to form inclusions that can become the starting point for rusting.
  • the lower limit of the S content is not particularly limited, but removing S requires a very high refining cost. Therefore, from the viewpoint of economy, the S content is set to 0.0001% or more. Good too.
  • Cr strengthens the passive film, thereby improving the corrosion resistance against crude phosphoric acid.
  • Cr also has the effect of repairing the passive film after Fe is dissolved.
  • the Cr content is set to 23.0% or more.
  • the Cr content is set to 23.5% or more, 24.0% or more, or 24.5% or more.
  • the Cr content is set to 30.0% or less.
  • the Cr content is set to 29.8% or less, % or less, 29.4% or less, 29.2% or less, or 29.0% or less is preferable.
  • N 0.100-0.250%>
  • NH4 + ammonium ion
  • the N content is set to 0.100% or more.
  • the N content is set to 0.120% or more.
  • N is an element that greatly affects the precipitation of chromium nitrides, and if it is contained in a large amount, the amount of chromium nitrides precipitated increases, In order to suppress these, the N content is set to 0.250% or less. In order to stably suppress these, the N content is set to 0.230% or less or 0. It is preferable that the ratio is 220% or less.
  • Cu is an element that improves acid resistance, particularly corrosion resistance against crude phosphoric acid containing sulfuric acid, and has the effect of suppressing the dissolution of Fe from the surface of the duplex stainless steel material when acidic condensed water adheres to the material.
  • the Cu content is set to 0.01% or more.
  • the Cu content is set to 0.05% or more, 0.10% or more, 0.20% or more, % or more, or 0.25% or more.
  • the Cu content is set to 1.80% or less, 1.50% or less, 1.00% or less, or 0.80% or less. preferable.
  • Mo has the effect of improving corrosion resistance and also has the effect of repairing the passive film after Fe dissolution. In particular, it prevents Fe from dissolving on the surface of duplex stainless steel material and causing corrosion (especially blackening).
  • the Mo content is set to 0.50% or more.
  • the Mo content is set to 0.80% or more, 0.90% or more. % or more, or 1.00% or more.
  • the Mo content is set to 2.50% or less. From the viewpoint of reducing costs, the Mo content is preferably 2.30% or less or 2.20% or less.
  • Al is an element contained for desulfurization and deoxidization. However, if a large amount of Al is contained, it will lead to an increase in raw material costs and manufacturing costs, so the Al content is set to 0.100% or less.
  • the Al content is preferably 0.090% or less or 0.080% or less from the viewpoint of stably reducing increases in raw material costs and manufacturing costs.
  • the lower limit of the Al content is not particularly limited. From the viewpoint of obtaining the above-mentioned effects, the Al content is preferably 0.001% or more.
  • Nb has the effect of suppressing the precipitation of chromium nitrides by forming a compound with N.
  • the Nb content is set to 0.200% or less.
  • the Nb content is preferably 0.190% or less or 0.180% or less.
  • the lower limit of the Nb content is not particularly limited, but from the viewpoint of obtaining the above-mentioned effects, the Nb content is preferably 0.001% or more.
  • Ti has the effect of preventing coarsening of the heat-affected zone during welding of duplex stainless steel material and of forming fine equiaxed crystals in the solidified structure, and therefore can be contained as necessary.
  • the Ti content is set to 0.050% or less.
  • the Ti content is From the viewpoint of stably securing this effect, it is preferable that the Ti content is 0.045% or less or 0.040% or less.
  • the lower limit of the Ti content is not particularly limited, but from the viewpoint of securing the above effect, The Ti content is preferably 0.001% or more.
  • B has the effect of improving hot workability, and therefore can be contained as necessary. However, if the B content is too high, the corrosion resistance is significantly reduced. From the viewpoint of suppressing the reduction in corrosion resistance, the B content is set to 0.0050% or less. From the viewpoint of stably ensuring this effect, the B content is preferably set to 0.0040% or less or 0.0030% or less. The lower limit of the content is not particularly limited, but from the viewpoint of obtaining the above-mentioned effects, the B content is preferably 0.0003% or more.
  • Ca is an element that enhances corrosion resistance. It is believed that Ca reduces inclusions that are the starting point of corrosion in an environment where crude phosphoric acid is present, and inhibits the elution of Fe. Therefore, it is included as necessary. From the viewpoint of ensuring this effect, the Ca content is set to 0.0010% or more. From the viewpoint of stably ensuring this effect, the Ca content is set to 0.0015% or more or 0. It is preferable that the Ca content is 0.0020% or more. On the other hand, if the Ca content is too high, hot work cracks are likely to occur and the corrosion resistance is also reduced. From the viewpoint of suppressing these, the Ca content is set to 0.0100% or less. From the viewpoint of stably suppressing these, the Ca content is preferably 0.0090% or less, 0.0080% or less, or 0.0070% or less.
  • Mg can be added as necessary since it has the effect of not only deoxidizing but also refining the solidified structure.
  • a high Mg content increases the cost in the steelmaking process.
  • the Mg content is set to 0.0020% or less. From the viewpoint of reducing costs, the Mg content is preferably set to 0.0019% or less or 0.0018% or less. Therefore, the Mg content is set to 0.0001% or more.
  • Zr can be added as necessary because it has the effect of forming carbides and nitrides in duplex stainless steel materials and refining crystal grains.
  • the Zr content is set to 0.090% or less.
  • the Zr content is set to 0.090% or less in order to stably secure this effect. From this viewpoint, it is preferable that the Zr content is 0.085% or less.
  • the lower limit of the Zr content is not particularly limited, but from the viewpoint of obtaining the above-mentioned effects, the Zr content is preferably 0.001% or more or 0.005% or more. It is preferable that:
  • Co is an austenite stabilizing element and can be contained as necessary.
  • the Co content is set to 3.00% or less. From the viewpoint of reducing costs, the Co content is preferably 2.80% or less or 2.60% or less.
  • the lower limit of the Co content is not particularly limited, but from the viewpoint of obtaining the above-mentioned effects, The Co content is preferably 0.01% or more.
  • V is an element that improves corrosion resistance and can be added as necessary. However, if the V content is too high, the load during rolling increases and manufacturing defects are more likely to occur.
  • the V content is preferably 0.950% or less from the viewpoint of stably suppressing the formation of manufacturing defects. From the viewpoint of obtaining the above-mentioned effects, the V content is preferably, but not limited to, 0.010% or more, or 0.050% or more.
  • Ta forms carbides and nitrides in duplex stainless steel materials and has the effect of additionally increasing corrosion resistance, so it can be added as necessary.
  • the Ta content is set to 0.200% or less because the toughness is reduced by the carbides and nitrides formed. From the viewpoint of stably securing this effect, the Ta content is set to 0.170% or less or 0.150% or less.
  • the lower limit of the Ta content is not particularly limited, but from the viewpoint of obtaining the above-mentioned effects, the Ta content is preferably 0.001% or more or 0.005% or more.
  • Sn is an element that improves corrosion resistance, and therefore may be contained as necessary. However, if the Sn content is high, hot workability is reduced, so the Sn content is set to 0.100% or less. From the viewpoint of stably ensuring this effect, the Sn content is preferably 0.050% or less, 0.030% or less, or 0.010% or less. The Sn content is not particularly limited, but from the viewpoint of obtaining the above-mentioned effects, the Sn content is preferably 0.0001% or more, or 0.0003% or more.
  • O is an element that affects hot workability, so it is desirable to have as little O as possible. Therefore, the O content is set to 0.0050% or less. From the viewpoint of stably securing the O content, the O content is preferably 0.0048% or less. On the other hand, the lower limit of the O content is not particularly limited, but reducing the O content leads to an increase in manufacturing costs. The content is preferably 0.0001% or more.
  • W is an element that improves corrosion resistance, and can be added as necessary. However, if the W content is too high, the load during rolling is increased, and manufacturing defects are more likely to occur.
  • the W content is set to 1.000% or less. From the viewpoint of stably ensuring this effect, the W content is preferably set to 0.900% or less or 0.800% or less.
  • the lower limit is not particularly limited, but from the viewpoint of obtaining the above-mentioned effects, the W content is preferably 0.005% or more, or 0.010% or more.
  • REM rare earth elements
  • the REM content is set to 0.100% or less. From the viewpoint of stably ensuring this effect, the REM content is preferably set to 0.095% or less or 0.090% or less.
  • the lower limit of the content is not particularly limited, but from the viewpoint of obtaining the above-mentioned effects, the REM content is preferably 0.001% or more, 0.005% or more, or 0.010% or more.
  • REM is a general term for 17 elements, including Sc, Y, and 15 elements from La to Lu (lanthanoids), and the REM content means the total content of these elements.
  • lanthanides are industrially added in the form of misch metals.
  • the value of DF represented by the following formula (1) is 45.0 to 70.0, preferably 48.0 to 69.5, and more preferably 50.0 to 69.0.
  • DF 7.2(Cr+0.8Mo+0.78Si)-8.9(Ni+0.03Mn+0.72Cu+22C+21N)-44.9...
  • the element symbols represent the contents (mass%) of each element.
  • DF is an index representing the amount of ferrite phase. Therefore, 100-DF means the amount of austenite phase. However, since DF is an index determined based on the content of elements, it should be noted that it may not match the amount of austenite phase actually measured.
  • the austenite phase preferably satisfies the following relational expression (2).
  • the element symbols represent the contents (mass%) of each element.
  • formula (2) is a formula expressing the relationship between the contents of five elements (Cr, Ni, Mo, Cu, and N) that affect the preferential dissolution of the austenite phase in the crude phosphoric acid.
  • the value of the left side of formula (2) is preferably 345 or more, more preferably 350 or more, and even more preferably 355 or more.
  • the upper limit of the value of the left side of formula (2) is not particularly limited, but is, for example, 800 or 700.
  • the content of each element in the austenite phase used to calculate the relational expression (2) can be measured by EPMA (electron probe microanalyzer). Specifically, a mirror-polished sample of a thickness-wise cross section of a duplex stainless steel material parallel to the rolling direction is used for qualitative analysis by EPMA. A portion that can be clearly determined to be an austenite phase based on the Ni content is identified by qualitative mapping of Ni for the entire cross section. Then, Cr, Ni, Mo, Cu and N are quantitatively analyzed at approximately the center of the identified austenite phase. Quantitative analysis is performed at 10 or more points, and the average value is taken as the content result for each element.
  • EPMA electron probe microanalyzer
  • the austenite phase preferably contains 21.0-30.0% Cr, 7.5-12.0% Ni, 0.30-2.00% Mo, 0.3-2.1% Cu, and 0.10-0.35% N.
  • the Cr content is preferably 22.0-25.5%
  • the Ni content is 8.0-12.0%
  • the Mo content is 1.20-1.80%
  • the Cu content is 0.4-0.9%
  • the N content is 0.25-0.33%.
  • the duplex stainless steel material according to the embodiment of the present invention preferably satisfies the relational expression of the following formula (3).
  • Expected CPT - Actual CPT ⁇ 10°C ...
  • the expected CPT is the pitting corrosion initiation temperature (°C) calculated by 2.5Cr + 7.6Mo + 3.19N - 26 (where Cr, Mo and N represent the Cr, Mo and N contents (mass%) in the duplex stainless steel material, respectively), and the measured CPT is the pitting corrosion initiation temperature (°C) measured by a pitting corrosion resistance test in accordance with ASTM G48E.
  • the measured CPT tends to decrease when chromium nitrides precipitate
  • the CPT difference expected CPT - measured CPT
  • the amount of chromium nitrides precipitated is small.
  • the relational expression (3) when the relational expression (3) is satisfied, the precipitation of chromium nitrides is suppressed, and corrosion resistance can be sufficiently ensured.
  • the relational expression (3) when the relational expression (3) is not satisfied, there is a risk that the corrosion resistance will decrease due to the precipitation of chromium nitrides.
  • the duplex stainless steel material according to the embodiment of the present invention may be either hot-rolled or cold-rolled, but when used for storage tanks of chemical tankers, etc., it is preferable to use hot-rolled material.
  • the thickness of the duplex stainless steel material according to the embodiment of the present invention is not particularly limited and may be adjusted appropriately depending on the application, but is generally 20.0 mm or less, preferably 15.0 mm or less, and more preferably 10.0 mm or less.
  • the thickness refers to the circle-equivalent diameter of the cross section.
  • the thickness refers to the thickness at any point on the cross section.
  • the duplex stainless steel material according to the embodiment of the present invention has excellent corrosion resistance against crude phosphoric acid, and therefore can be used for various members that may come into contact with crude phosphoric acid.
  • the duplex stainless steel material according to the embodiment of the present invention is suitable for use in a structure for crude phosphoric acid.
  • the term "crude phosphoric acid structure" refers to various facilities that handle crude phosphoric acid. Examples of the crude phosphoric acid structure include a phosphoric acid manufacturing plant, a phosphoric acid storage tank (including a storage tank of a ship), a phosphoric acid transport pipe, etc.
  • the method for producing a duplex stainless steel material according to the embodiment of the present invention is not particularly limited as long as it is a method capable of producing a duplex stainless steel material having the above-mentioned characteristics.
  • a method for producing a duplex stainless steel material according to an embodiment of the present invention includes a soaking step, a first cooling step, and a second cooling step.
  • the soaking step is a step of soaking the rolled material having the above composition at a soaking temperature of 950 to 1150° C. for more than one minute. If the soaking temperature is less than 950°C, the chromium nitride cannot be sufficiently dissolved. If the soaking temperature exceeds 1150°C, the amount of ferrite phase increases and it becomes difficult to control the composition of the austenite phase within a predetermined range. From the viewpoint of stably suppressing these problems, the soaking temperature is preferably 1000 to 1100°C. The soaking time may be more than 1 minute, but is preferably less than 10 minutes in consideration of production efficiency and production costs.
  • the rolled material can be produced by a conventional method, for example, by vacuum melting a stainless steel having the above composition to form a steel slab, which is then hot rolled.
  • the first cooling step is a step of slowly cooling the rolled material obtained in the soaking step to a quenching start temperature at a cooling rate of 5° C./sec or more and less than 10° C./sec. If the cooling rate in the first cooling step is 10° C./sec or more, it becomes difficult to control the composition of the austenite phase within a predetermined range. From the viewpoint of stably suppressing this problem, the cooling rate in the first cooling step is preferably 9° C./sec or less, more preferably 8° C./sec or less, and even more preferably 7° C./sec or less.
  • the cooling method in the first cooling step is not particularly limited, but may be, for example, air cooling.
  • the second cooling step is a step of rapidly cooling (at a cooling rate of 10° C./sec or more) the rolled material obtained in the first cooling step from the rapid cooling start temperature.
  • the quenching start temperature is a temperature of 950 to 990°C, and is a temperature lower than the above-mentioned soaking temperature. If the quenching start temperature is less than 950°C, the amount of ferrite phase generated increases, resulting in a decrease in corrosion resistance. If the quenching start temperature exceeds 990°C, it becomes difficult to control the composition of the austenite phase within a predetermined range. From the viewpoint of stably suppressing these problems, the quenching start temperature is preferably 960 to 980°C.
  • the quenching end temperature is not particularly limited, and may be, for example, room temperature.
  • the cooling method in the second cooling step is not particularly limited, but may be, for example, water cooling.
  • the structure for producing crude phosphoric acid according to the embodiment of the present invention includes the above-mentioned duplex stainless steel material.
  • This structure for producing crude phosphoric acid may further include a member other than the above-mentioned duplex stainless steel material.
  • the structure for producing crude phosphoric acid according to the embodiment of the present invention can be manufactured by processing the above-mentioned duplex stainless steel material into a predetermined shape and then assembling it by welding or the like.
  • the structure for crude phosphoric acid is not particularly limited, but is preferably a phosphoric acid production plant, a phosphoric acid storage tank, or a phosphoric acid transport pipe.
  • Stainless steels having the compositions shown in Tables 1-1 and 1-2 were melted in MgO crucibles in a 50 kg vacuum induction furnace in a laboratory and cast into flat steel ingots with a thickness of about 100 mm.
  • the main body of the flat steel ingot was processed into a material for hot rolling, heated to 1180°C, and then held at that temperature for 1 hour, and then hot rolled into a hot-rolled sheet with a thickness of 12 mm.
  • the values of DF and expected CPT were calculated based on the content of each element.
  • a duplex stainless steel sheet was obtained by performing a soaking step, a first cooling step, and a second cooling step under the conditions shown in Table 2.
  • the first cooling step was performed by air cooling, and the cooling rate was controlled by controlling the flow rate of the cooling gas.
  • the second cooling step was performed by water cooling to room temperature.
  • ⁇ Content of each element in the austenite phase The content of each element in the austenite phase was measured by EPMA (electron probe microanalyzer). Specifically, a sample was mirror-polished in the thickness direction of a duplex stainless steel material parallel to the rolling direction, and a qualitative analysis was performed by EPMA. The EPMA was performed at an acceleration voltage of 15 kV, and a lattice-like measurement was performed in an area of 300 ⁇ m x 300 ⁇ m at intervals of 0.76 ⁇ m, resulting in a total of 140,625 pieces of data. In the qualitative analysis, a portion that can be clearly determined to be an austenite phase from the Ni content was identified by qualitative mapping of Ni for the entire cross section.
  • EPMA electron probe microanalyzer
  • ⁇ Corrosion test> A test piece of 10 mm x 80 mm x 2 mm was taken from the duplex stainless steel plate and wet-polished over the entire surface using a No. 600 grindstone. Next, an aqueous solution simulating crude phosphoric acid containing 70% by mass phosphoric acid, 0.4% by mass F -ions , and 0.04% by mass Cl -ions was prepared. Next, the container containing this aqueous solution was kept at 50°C, and half of the test piece was immersed in it for 6 hours. Then, the corrosion rate (mm/y) was calculated from the mass change (corrosion weight loss) before and after immersion. If the corrosion rate is 0.15 mm/y or less, it can be determined that the corrosion resistance is excellent. Since the corroded area is both the gas phase and the liquid phase, the corrosion rate was calculated using the entire area of the test piece. Furthermore, the test pieces after the above tests were visually evaluated for discoloration (blackening).
  • the measured CPT was determined in accordance with ASTM G48E by taking a test piece of 50 mm x 25 mm x 2 mm thickness (thickness from a position 1 mm deep from the outermost surface) from a duplex stainless steel plate, carrying out a pitting test on the test piece at an aqueous solution temperature of 30° C., and measuring the CPT (Critical Pitting Temperature). Note that when measuring the CPT, pitting that occurred on the end face (cross section in the thickness direction) of the test piece was not counted, and only pitting that occurred on the 50 mm x 25 mm surface was counted.
  • the CPT difference (expected CPT - actual CPT) was calculated using the actual CPT thus obtained and the expected CPT calculated above.
  • the CPT difference was represented as ⁇ when it was 10°C or less, and ⁇ when it was more than 10°C.
  • the duplex stainless steel plate had a predetermined composition and DF, and the austenite phase satisfied the relational expression of formula (2), so it was confirmed that the corrosion rate was slow and the corrosion resistance to crude phosphoric acid was excellent.
  • the soaking temperature was too high, so that the element concentrations in the austenite phase could not be controlled, and the relational expression (2) was not satisfied.
  • the corrosion resistance against crude phosphoric acid was insufficient.
  • the cooling rate in the first cooling step was too fast, so that the element concentrations in the austenite phase could not be controlled and the relational expression (2) was not satisfied.
  • the present invention can provide a ferritic-austenitic duplex stainless steel material with excellent corrosion resistance to crude phosphoric acid, and a manufacturing method thereof. Furthermore, the present invention can provide a structure for crude phosphoric acid that has excellent corrosion resistance to crude phosphoric acid and can reduce maintenance costs and time.
  • the present invention can be configured as follows.
  • (Aspect 1) On a mass basis, it has a composition including C: 0.100% or less, Si: 0.05 to 1.50%, Mn: 0.05 to 2.00%, Ni: 4.00 to 9.00%, P: 0.050% or less, S: 0.0040% or less, Cr: 23.0 to 30.0%, N: 0.100 to 0.250%, Cu: 0.01 to 2.00%, Mo: 0.50 to 2.50%, Al: 0.100% or less, Nb: 0.200% or less, and the balance being Fe and impurities;
  • the following formula (1): DF 7.2(Cr+0.8Mo+0.78Si)-8.9(Ni+0.03Mn+0.72Cu+22C+21N)-44.9...
  • each element symbol represents the content (mass%) of each element
  • the austenite phase has the following formula (2): (0.8Cr) 2 +2Ni+7Mo+30Cu+30N ⁇ 340... (2) (wherein the chemical symbols represent the content (mass%) of each element)
  • (Aspect 2) The ferritic-austenitic duplex stainless steel material according to aspect 1, further comprising one or more selected from, by mass, Ti: 0.050% or less, B: 0.0050% or less, Ca: 0.0010-0.0100%, Mg: 0.0001-0.0020%, Zr: 0.090% or less, Co: 3.00% or less, V: 1.000% or less, Ta: 0.200% or less, Sn: 0.100% or less, O: 0.0050% or less, W: 1.000% or less, and REM: 0.100% or less.

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Abstract

L'invention concerne un matériau d'acier inoxydable biphasé à base de ferrite et austénite qui présente une composition contenant, en termes de masse, ０,１００％ ou moins de C, ０,０５ à １,５０％ de Si, ０,０５ à ２,００％ de Mn, ４,００ à ９,００％ de Ni, ０,０５０％ ou moins de P, ０,００４０％ ou moins de S, ２３,０ à ３０,０％ de Cr, ０,１００ à ０,２５０％ de N, ０,０１ à ２,００％ de Cu, ０,５０ à ２,５０％ de Mo, ０,１００％ ou moins de Al et ０,２００％ ou moins de Nb, le reste étant constitué de Fe et d'impuretés. Une valeur DF représentée la formule (1) ＤＦ＝７,２（Ｃｒ＋０,８Ｍｏ＋０,７８Ｓｉ）－８,９（Ｎｉ＋０,０３Ｍｎ＋０,７２Ｃｕ＋２２Ｃ＋２１Ｎ）－４４,９　・・・　（１） (dans la formule, les symboles des éléments représentent la teneur (en % en masse) de chaque élément), est comprise entre ４５,０ et ７０,０. Une phase austénitique satisfait la relation de la formule (2) （０,８Ｃｒ）2＋２Ｎｉ＋７Ｍｏ＋３０Ｃｕ＋３０Ｎ≧３４０　・・・　（２） (dans la formule, les symboles des éléments représentent la teneur (en % en masse) de chaque élément).
PCT/JP2024/020240 2023-06-15 2024-06-03 Matériau d'acier inoxydable biphasé à base de ferrite et austénite ainsi que procédé de fabrication de celui-ci, et structure pour acide phosphorique cru Ceased WO2024257639A1 (fr)

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CN202480032433.7A CN121127617A (zh) 2023-06-15 2024-06-03 铁素体-奥氏体系双相不锈钢钢材及其制造方法、以及粗磷酸用结构物
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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11269612A (ja) 1998-03-19 1999-10-05 Nippon Steel Corp 粗製硫酸用ステンレス鋼およびその製造方法
JP2002121655A (ja) 2000-10-18 2002-04-26 Nippon Steel Corp 耐食性に優れた粗製リン酸用ステンレス鋼
WO2009119895A1 (fr) 2008-03-26 2009-10-01 新日鐵住金ステンレス株式会社 Acier inoxydable duplex faiblement allié dans lequel les zones affectées par la chaleur de soudage présentent une bonne résistance à la corrosion et une bonne ténacité
JP2016053213A (ja) * 2014-09-02 2016-04-14 日本冶金工業株式会社 二相ステンレス鋼板とその製造方法
JP2018059157A (ja) 2016-10-06 2018-04-12 新日鐵住金株式会社 二相ステンレス鋼
WO2018181990A1 (fr) * 2017-03-30 2018-10-04 新日鐵住金ステンレス株式会社 Acier inoxydable à deux phases et son procédé de fabrication

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11269612A (ja) 1998-03-19 1999-10-05 Nippon Steel Corp 粗製硫酸用ステンレス鋼およびその製造方法
JP2002121655A (ja) 2000-10-18 2002-04-26 Nippon Steel Corp 耐食性に優れた粗製リン酸用ステンレス鋼
WO2009119895A1 (fr) 2008-03-26 2009-10-01 新日鐵住金ステンレス株式会社 Acier inoxydable duplex faiblement allié dans lequel les zones affectées par la chaleur de soudage présentent une bonne résistance à la corrosion et une bonne ténacité
JP2016053213A (ja) * 2014-09-02 2016-04-14 日本冶金工業株式会社 二相ステンレス鋼板とその製造方法
JP2018059157A (ja) 2016-10-06 2018-04-12 新日鐵住金株式会社 二相ステンレス鋼
WO2018181990A1 (fr) * 2017-03-30 2018-10-04 新日鐵住金ステンレス株式会社 Acier inoxydable à deux phases et son procédé de fabrication

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP4667612A1

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