EP4234770A1 - Ferritbasierter edelstahl und komponente für abgas - Google Patents

Ferritbasierter edelstahl und komponente für abgas Download PDF

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Publication number
EP4234770A1
EP4234770A1 EP21882927.3A EP21882927A EP4234770A1 EP 4234770 A1 EP4234770 A1 EP 4234770A1 EP 21882927 A EP21882927 A EP 21882927A EP 4234770 A1 EP4234770 A1 EP 4234770A1
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EP
European Patent Office
Prior art keywords
mass
less
content
stainless steel
ferritic stainless
Prior art date
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Pending
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EP21882927.3A
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English (en)
French (fr)
Inventor
Yoshitomo Fujimura
Takahito HAMADA
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Nippon Steel Stainless Steel Corp
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Nippon Steel Stainless Steel Corp
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Publication of EP4234770A1 publication Critical patent/EP4234770A1/de
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    • 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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    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/10—Oxidising
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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
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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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
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    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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    • C21D8/0236—Cold rolling
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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    • 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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    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
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    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
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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
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/06—Solid state diffusion of only metal elements or silicon into metallic material surfaces using gases
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    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
    • C23C30/005—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process on hard metal substrates
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    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
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    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/10—Oxidising
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    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
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    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
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    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
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    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
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    • C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
    • C25F1/02—Pickling; Descaling
    • C25F1/04—Pickling; Descaling in solution
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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 ferritic stainless steel and a component for exhaust gas. More specifically, the present invention relates to ferritic stainless steel having excellent red scale resistance in a high-temperature water vapor atmosphere and a component for exhaust gas obtained using the ferritic stainless steel as a material.
  • stainless steel is heated up to a high temperature of 300°C to 900°C in the case of being used in applications such as exhaust gas path materials, stove combustion equipment, fuel cell members or plant-related materials.
  • the stainless steel is used in environments where water vapor is contained, and thus there are cases where red scale (Fe-based oxide) is generated. This generated red scale does not only have a probability of scattering to adhere to and adversely affect other components depending on the case but also provokes a cause of thickness reduction by oxidation and a decrease in high-temperature strength.
  • Patent Document 1 and Patent Document 2 describe that, when Si is added, diffusion of Cr is promoted, the amount of a Cr-based oxide formed is improved and an oxide coating is strengthened. Therefore, inventions described in Patent Document 1 and Patent Document 2 improve water vapor oxidation resistance and red scale resistance.
  • An objective of the present invention is to provide ferritic stainless steel having excellent red scale resistance and a component for exhaust gas having excellent red scale resistance for which the ferritic stainless steel is used as a material.
  • the gist of the present invention for solving the above-described problem is as described below.
  • ferritic stainless steel having excellent red scale resistance and a component for exhaust gas having excellent red scale resistance.
  • ferritic stainless steel according to one embodiment of the present invention (ferritic stainless steel according to the present embodiment), a manufacturing method of ferritic stainless steel according to the present embodiment and a component for exhaust gas that is obtained using the ferritic stainless steel according to the present embodiment as a material (component for exhaust gas according to the present embodiment) will be described.
  • the following description is intended to make the gist of the invention better understandable and does not limit the present invention unless particularly otherwise described.
  • “A to B" indicates A or more and B or less.
  • the term "stainless steel” means a stainless-steel material for which a specific shape is not limited. Examples of this stainless-steel material include a steel sheet, a steel pipe, a steel bar and the like.
  • the composition of components (chemical composition) that ferritic stainless steel contains in one embodiment of the present invention is as described below.
  • the ferritic stainless steel is formed of, in addition to each component to be described below, iron (Fe) and/or a small amount of an impurity (impurity) that can be incorporated from a raw material or in a manufacturing step.
  • Cr is an essential element for forming a passive film and ensuring corrosion resistance.
  • Cr is also effective for ensuring red scale resistance.
  • the Cr content is 10.50 mass% or more.
  • the Cr content is preferably 12.50 mass% or more.
  • the Cr content is 25.00 mass% or less.
  • the Cr content is preferably 23.00 mass% or less.
  • Si is an effective element for improving red scale resistance.
  • the Si content is 0.05 mass% or more.
  • the Si content is preferably 0.10 mass% or more.
  • the Si content is 2.50 mass% or less.
  • the Si content is preferably 2.00 mass% or less.
  • Cu is an element that is contained to ensure high-temperature strength. In order to obtain this effect, the Cu content is 0.01 mass% or more. The Cu content is preferably 0.02 mass% or more.
  • the Cu content is 1.80 mass% or less.
  • the Cu content is preferably 1.60 mass% or less.
  • Nb is an element that is contained to ensure high-temperature strength.
  • the Nb content is 0.001 mass% or more.
  • the Nb content is preferably 0.05 mass% or more and more preferably 0.10 mass% or more.
  • the Nb content is 1.00 mass% or less.
  • the Nb content is preferably 0.70 mass% or less and more preferably 0.45 mass% or less.
  • Mn is an element that improves the adhesion of scale in ferritic stainless steel.
  • the Mn content is 0.05 mass% or more.
  • the Mn content is preferably 0.10 mass% or more.
  • the Mn content is set to 1.50 mass% or less.
  • the Mn content is preferably 1.20 mass% or less.
  • Ni is an element that improves the corrosion resistance of ferritic stainless steel. In order to obtain this effect, the Ni content is 0.01 mass% or more. The Ni content is preferably 0.05 mass% or more.
  • the Ni content is 0.50 mass% or less.
  • the Ni content is preferably 0.30 mass% or less.
  • the C content is 0.025 mass% or less.
  • the C content is preferably 0.020 mass% or less.
  • the C content is preferably as small as possible and may be 0%; however, when the C content is decreased more than necessary, the cost increases, and thus the C content may be set to 0.002 mass% or more.
  • the P content is 0.040 mass% or less.
  • the P content is preferably 0.030 mass% or less.
  • the P content is preferably as small as possible and may be 0%; however, when the P content is decreased more than necessary, the cost increases, and thus the P content may be set to 0.001 mass% or more.
  • the S content is 0.003 mass% or less.
  • the S content is preferably 0.002 mass% or less.
  • the S content is preferably as small as possible and may be 0%; however, when the S content is decreased more than necessary, the cost increases, and thus the S content may be set to 0.0001 mass% or more.
  • the N content is 0.025 mass% or less.
  • the N content is preferably 0.020 mass% or less.
  • the N content is preferably as small as possible and may be 0%; however, when the N content is decreased more than necessary, the cost increases, and thus the N content may be set to 0.003 mass% or more.
  • Al is an effective element for improving the corrosion resistance of ferritic stainless steel and improving scale resistance.
  • Al is an effective element as a deoxidizing agent at the time of steel making.
  • the Al content is 0.002 mass% or more.
  • the Al content is preferably 0.008 mass% or more.
  • the Al content is 0.200 mass% or less.
  • the ferritic stainless steel according to one embodiment of the present invention may further contain one or more of 0.01 mass% or more and 2.5 mass% or less of W, 0.01 mass% or more and 3.00 mass% or less of Mo, 0.001 mass% or more and 0.500 mass% or less of Ti, 0.0002 mass% or more and 0.0100 mass% or less of B, 0.0002 mass% or more and 0.0030 mass% or less of Ca, 0.001 mass% or more and 0.50 mass% or less of Hf, 0.01 mass% or more and 0.40 mass% or less of Zr, 0.005 mass% or more and 0.50 mass% or less of Sb, 0.01 mass% or more and 0.30 mass% or less of Co, 0.001 mass% or more and 1.0 mass% or less of Ta, 0.002 mass% or more and 1.00 mass% or less of Sn, 0.0002 mass% or more and 0.30 mass% or less of Ga, 0.01 mass% or more and 0.50 mass% or less of V, 0.001 mass% or more and 0.20 mass%
  • the amounts thereof may be 0% and may be amounts below the ranges to be described below.
  • W is an element that may be contained to ensure high-temperature strength.
  • the W content is preferably 0.01 mass% or more.
  • the W content is more preferably 0.1 mass% or more.
  • the W content is 2.5 mass% or less.
  • the W content is preferably 1.5 mass% or less and more preferably 1.3 mass% or less.
  • Mo is an element that may be contained to ensure high-temperature strength and red scale resistance.
  • the Mo content is preferably 0.01 mass% or more.
  • the Mo content is 3.00 mass% or less.
  • the Mo content is preferably 2.50 mass% or less.
  • Ti is an element that is capable of making ferritic stainless steel into a ferritic single phase at 900°C to 1000°C by reacting with C and/or N and improves red scale resistance and workability. Therefore, Ti may be contained. In the case of obtaining this effect, the Ti content is preferably 0.001 mass% or more. The Ti content is preferably 0.010 mass% or more and more preferably 0.050 mass% or more.
  • the Ti content is 0.500 mass% or less.
  • the Ti content is preferably 0.300 mass% or less and more preferably 0.250 mass% or less.
  • the B is an element that improves the secondary workability of formed articles manufactured using ferritic stainless steel.
  • the B content is preferably 0.0002 mass% or more.
  • the B content is 0.0100 mass% or less.
  • the B content is preferably 0.0080 mass% or less or 0.0030 mass% or less.
  • Ca is an element that promotes high-temperature oxidation resistance. Therefore, Ca may be contained as necessary. In the case of obtaining this effect, the Ca content is preferably 0.0002 mass% or more.
  • the Ca content is 0.0030 mass% or less.
  • Hf is an element that improves corrosion resistance, high-temperature strength and oxidation resistance. Hf may be contained as necessary. In the case of obtaining this effect, the Hf content is preferably 0.001 mass% or more. The Hf content is more preferably 0.01 mass% or more.
  • the Hf content is 0.50 mass% or less.
  • Zr is an element that improves high-temperature strength, corrosion resistance and high-temperature oxidation resistance. Therefore, Zr may be contained as necessary. In the case of obtaining this effect, the Zr content is preferably 0.01 mass% or more.
  • the Zr content is 0.40 mass% or less.
  • Sb is an element that improves high-temperature strength. Therefore, Sb may be contained as necessary. In the case of obtaining this effect, the Sb content is preferably 0.005 mass% or more. The Sb content is more preferably 0.01 mass% or more.
  • the Sb content is 0.50 mass% or less.
  • Co is an element that improves high-temperature strength. Therefore, Co may be contained as necessary. In the case of obtaining this effect, the Co content is preferably 0.01 mass% or more.
  • the Co content is 0.30 mass% or less.
  • Ta is an element that improves high-temperature strength. Therefore, Ta may be contained as necessary. In the case of obtaining this effect, the Ta content is preferably 0.001 mass% or more. The Ta content is more preferably 0.01 mass% or more and still more preferably 0.1 mass% or more.
  • the Ta content is 1.0 mass% or less.
  • Sn is an element that improves corrosion resistance and high-temperature strength. Therefore, Sn may be contained as necessary. In the case of obtaining this effect, the Sn content is preferably 0.002 mass% or more. The Sn content is more preferably 0.01 mass% or more.
  • the Sn content is 1.00 mass% or less.
  • Ga is an element that improves corrosion resistance and hydrogen embrittlement resistance. Therefore, Ga may be contained as necessary. In the case of obtaining this effect, the Ga content is preferably 0.0002 mass% or more. The Ga content is more preferably 0.01 mass% or more.
  • Ga being excessively contained degrades weldability and toughness. Therefore, the Ga content is 0.30 mass% or less.
  • V is an element that fixes solid solutions of C and N in steel as compounds and improves the ductility or workability of steel. Therefore, V may be contained as necessary. In the case of obtaining this effect, the V content is preferably 0.01 mass% or more.
  • V being excessively contained degrades the workability of steel. Therefore, the V content is 0.50 mass% or less.
  • Mg is a deoxidizing element and also an element that refines the structures of slabs to improve formability. Therefore, Mg may be contained as necessary. In the case of obtaining this effect, the Mg content is preferably 0.0003 mass% or more.
  • Mg being excessively contained causes deterioration of corrosion resistance, weldability and surface quality, and thus the Mg content is 0.003 mass% or less.
  • REM refers to a generic term for scandium (Sc) and 15 elements of lanthanum (La) through lutetium (Lu) (lanthanide elements).
  • Sc scandium
  • La lanthanum
  • Lu lutetium
  • any one of the lanthanide elements may be contained singly or two or more lanthanide elements may be contained.
  • any one lanthanide element is contained as REM, for example, as described below, any one of La and Ce may be contained or a lanthanide element other than La and Ce may be contained singly.
  • the combination of the elements is not particularly limited, and, as one example, La and Ce may be contained or a plurality of lanthanide elements that is contained in misch metal may be contained as REM by the addition of misch metal.
  • REM is an element that improves the cleanliness of stainless steel and improves high-temperature oxidation resistance. Therefore, REM may be contained as necessary. In the case of obtaining these effects, the REM content is preferably 0.001 mass% or more. The REM content is more preferably 0.01 mass% or more.
  • the REM content is 0.20 mass% or less.
  • La may be contained as REM.
  • La is an element that improves the cleanliness of stainless steel and improves high-temperature oxidation resistance and, furthermore, an element that improves red scale resistance and scale exfoliation resistance.
  • the La content is preferably set to 0.001 mass% or more.
  • the La content is more preferably 0.01 mass% or more.
  • the La content is 0.20 mass% or less.
  • the La content is preferably 0.10 mass% or less, and, when the cost is taken into account, the La content is more preferably 0.05 mass% or less and still more preferably 0.03 mass% or less.
  • Ce may be contained as REM.
  • Ce is an element that improves the cleanliness of stainless steel and improves high-temperature oxidation resistance and, furthermore, an element that improves red scale resistance and scale exfoliation resistance.
  • the Ce content is preferably 0.001 mass% or more.
  • the Ce content is more preferably 0.01 mass% or more.
  • the Ce content is 0.20 mass% or less.
  • the Ce content is preferably 0.05 mass% or less.
  • the chemical composition of the ferritic stainless steel according to the present embodiment can be obtained from a depth position of 1/4 of the sheet thickness from the surface (a position within a range of 1/8 to 3/8 of the thickness from the surface in the thickness direction is permitted) by performing an element analysis by an ordinary method such as ICP-AES.
  • C and S may be measured using a combustion-infrared method
  • N may be measured using an inert gas melting-thermal conductivity method
  • O may be measured using an inert gas melting-infrared absorption method.
  • At least one type of oxides of oxides containing 5 mass% or more ofAl and oxides containing 5 mass% or more of Si are present on the surface, and, among the oxides present on the surface, the number of oxides having a diameter D of 0.1 ⁇ m or more and 2.0 ⁇ m or less (hereinafter, referred to as "Al/Si-based oxide”) is 10 or more per 93 ⁇ m 2 , the diameter D being represented by the following formula (1).
  • D Dmax + Dmin / 2 (In the formula (1), Dmax is the maximum diameter of each oxide on the surface, and Dmin is the minimum diameter of each oxide on the surface.)
  • the dimensions of the oxides on the surface of the ferritic stainless steel can be measured with, for example, a scanning electron microscope (SEM).
  • a SEM photograph of the surface of a steel material is captured using a scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • the area of one visual field is set to 93 ⁇ m 2 .
  • the maximum diameter and minimum diameter of each oxide are calculated from this SEM photograph with image analysis software, for example, "Photoshop (registered trademark)” (manufactured by Adobe Inc.).
  • the amounts of Al and Si in each oxide on the surface of the ferritic stainless steel can be measured by, for example, energy dispersive X-ray spectroscopy (EDS). That is, EDS makes it possible to determine whether or not an oxide is the oxide to be counted for the number of the oxides (the oxides containing 5 mass% or more ofAl or the oxides containing 5 mass% or more of Si).
  • EDS energy dispersive X-ray spectroscopy
  • the "maximum diameter" of an oxide means the maximum width between two parallel lines that sandwich the oxide when seen in a plan view.
  • the "minimum diameter” of an oxide means the minimum width between two parallel lines that sandwich the oxide when seen in a plan view.
  • the Al/Si-based oxides act as a protective coating.
  • the Al/Si-based oxides grow by heating and the oxygen partial pressures around the Al/Si-based oxides decrease. Since Al, Si, Cr and Fe are more likely to be oxidized in this order, Al, Si and Cr are more preferentially oxidized than Fe. Therefore, the growth of the Al/Si-based oxides makes it possible to reduce the generation of red scale, which is a Fe-based oxide.
  • the number of the Al/Si-based oxides on the surface of the ferritic stainless steel is preferably 25 or less and more preferably 22 or less per 93 ⁇ m 2 . In this case, the luminosity on the surface of the ferritic stainless steel improves, and the designability can be kept favorable.
  • luminosity means CIE1976 luminosity L* that is measured using a D65 light source in a diffuse lighting mode by receiving light in a direction at 8° with respect to the normal line to the surface of the ferritic stainless steel at a visual field angle of 10° visual field for a measurement time of one second.
  • the effect of improving red scale resistance by the oxide is weak. Therefore, in the present embodiment, only oxides having a diameter D of 0.1 ⁇ m or more are taken into account.
  • the Al/Si-based oxides may decrease the luminosity of the surface of the ferritic stainless steel and degrade the designability of the ferritic stainless steel. Therefore, it is preferable to control the number of oxides that contain 5 mass% or more of Al or Si and have a diameter D of 0.1 ⁇ m or more and 2.0 ⁇ m or less on the surface of the ferritic stainless steel to a predetermined range.
  • the number of oxides that contain 5 mass% or more of Al or Si and have a diameter D of more than 2.0 ⁇ m is preferably small (for example, five or less per 93 ⁇ m 2 ) and most preferably zero.
  • the luminosity of the surface of the ferritic stainless steel is improved, and the designability of the ferritic stainless steel can be improved.
  • the present inventors paid attention to the Al/Si-based oxides on the surface of the ferritic stainless steel and came to obtain a knowledge that ferritic stainless steel having excellent red scale resistance can be realized by controlling the number of the Al/Si-based oxide to a predetermined range.
  • a passive film is present on the surface of the ferritic stainless steel according to the present embodiment, in addition to the Al/Si-based oxides, a passive film is present in a thickness of 2.0 to 8.0 nm.
  • the passive film refers to a highly dense and highly adhesive coating composed of chromium oxyhydroxide hydrate mainly containing Cr and chromium oxide.
  • the thickness of the passive film can be obtained using a radio-frequency glow discharge spectroscopy (GDS). Specifically, the oxygen concentrations are analyzed at 2.5 nm pitches in the thickness direction from the surface using a GDS analyzer (for example, GD-Profiler 2 manufactured by Horiba, Ltd. or an equivalent device), a range from the surface to a position where the oxygen concentration shows a value that is half the peak value is defined as the passive film, and the thickness thereof is measured and obtained.
  • GDS analyzer for example, GD-Profiler 2 manufactured by Horiba, Ltd. or an equivalent device
  • GDS measurement conditions are as described below.
  • the ferritic stainless steel according to the present embodiment is used at a high temperature where water vapor is contained, the Al/Si-based oxides grow, and the oxygen partial pressures around the Al/Si-based oxides are decreased.
  • the ferritic stainless steel has a surface form where the formation of an Fe-based oxide, which becomes an origin of red scale, has reduced and the formation of Cr, Al and Si-based oxides has increased and thereby has excellent red scale resistance.
  • [Cr] + [Si] + [Al] is preferably 20.0 (mass%) or more.
  • each of the Cr content [Cr], the Si content [Si] and the Al content [Al] is no need to limit each of the Cr content [Cr], the Si content [Si] and the Al content [Al] in the range from the surface to 1.0 ⁇ m, but the Si content and/or the Al content are each preferably 3.0 mass% or more from the viewpoint of an effect of suppressing red scale.
  • the Al/Si-based oxides grow slowly for a certain period of time; however, when 100 hours or longer has elapsed, the oxides do not change significantly, and thus it is considered that the presence states of Cr, Si and Al also do not change significantly.
  • the ferritic stainless steel according to the present embodiment has been used as a component of an exhaust gas path material, stove combustion equipment, a fuel cell member, a plant-related material or the like, it is considered that the amounts of Cr, Al and Si in the surface layer area satisfy the formula (2).
  • a component for exhaust gas according to the present embodiment is obtained by working the ferritic stainless steel according to the present embodiment as a material. Therefore, in a stage of being obtained by working or the like (before being used as a component), the component for exhaust gas according to the present embodiment contains, as the chemical composition, 0.05 mass% or more and 2.50 mass% or less of Si, 0.05 mass% or more and 1.50 mass% or less of Mn, 0.025 mass% or less of C, 0.040 mass% or less of P, 0.003 mass% or less of S, 0.025 mass% or less of N, 0.01 mass% or more and 0.50 mass% or less of Ni, 10.50 mass% or more and 25.00 mass% or less of Cr, 0.01 mass% or more and 1.80 mass% or less of Cu, 0.002 mass% or more and 0.200 mass% or less of Al, 0.001 mass% or more and 1.00 mass% or less of Nb, 0 mass% or more and 2.5 mass% or less of W, 0 mass% or more and 3.00 mass% or less
  • Dmax is the maximum diameter of the oxide on the surface
  • Dmin is the minimum diameter of the oxide on the surface
  • CIE1976 luminosity L* that is measured using a D65 light source in a diffuse lighting mode by receiving light in a direction at 8° with respect to the normal line to the surface at a visual field angle of 10° visual field for a measurement time of one second is 60 or more.
  • this component for exhaust gas according to the present embodiment is held in an atmosphere of 300°C to 900°C for 100 hours or longer, in a range from the surface to 1.0 ⁇ m, when the Cr content is represented by [Cr], the Si content is represented by [Si] and the Al content is represented by [Al] by unit mass%, the following formula (2) is satisfied. Cr + Si + Al ⁇ 18.0
  • the component for exhaust gas according to the present embodiment is, for example, a component of exhaust gas path materials, stove combustion equipment, fuel cell members, plant-related materials or the like, and, in a case where the component for exhaust gas has been used for a certain period of time under normal conditions in such applications (after use), in a range from the surface to 1.0 ⁇ m, when the Cr content is represented by [Cr], the Si content is represented by [Si] and the Al content is represented by [Al] by unit mass%, the following formula (2) is satisfied. Cr + Si + Al ⁇ 18.0
  • the Cr content [Cr], the Si content [Si] and the Al content [Al] in the range from the surface to 1.0 ⁇ m can be measured using GDS.
  • the analysis region is set to ⁇ 4 mm, and all elements other than C and N that are contained in each steel are selected and measured at 2.5 nm pitches up to a depth of 1.0 ⁇ m. From the measurement results, the amount of each of Cr, Al and Si at a position where each of Cr, Al and Si shows a peak in a depth range of up to 1.0 ⁇ m is calculated.
  • ferritic stainless steel having excellent red scale resistance in which the number of the Al/Si-based oxides on the surface is 10 or more per 93 ⁇ m 2 can be obtained by, for example, the following manufacturing method.
  • FIG. 1 is a flowchart showing an example of the manufacturing method of ferritic stainless steel according to the present embodiment.
  • a manufacturing method of a ferritic stainless-steel strip in the present embodiment includes a pretreatment step S1, a hot rolling step S2, an annealing step S3, a first pickling step S4, a cold rolling step S5, a final annealing step S6, a nitric acid electrolysis step S7 and a final pickling step S8.
  • the pretreatment step S1 first, steel having a chemical composition adjusted so as to be in the above-described range of the present invention is melted using a melting furnace with a vacuum or argon atmosphere, and this steel is cast to manufacture a slab. After that, a slab piece for hot rolling is cut out from the slab. Then, the slab piece is heated to a temperature range of 1100°C to 1300°C in the atmosphere. The time during which the slab piece is heated and held is not limited. In the case of performing the pretreatment step industrially, the casting may be continuous casting.
  • the hot rolling step S2 is a step of manufacturing a hot-rolled steel strip having a predetermined thickness by the hot rolling of the slab (steel ingot) that is obtained in the pretreatment step S1.
  • the conditions for the hot rolling are not limited and may be adjusted depending on required mechanical characteristics or the like.
  • the annealing step S3 is a step of softening the steel strip by heating the hot-rolled steel strip obtained in the hot rolling step S2.
  • This annealing step S3 is a step that is performed as necessary and may not be performed.
  • the first pickling step S4 is a step of washing off scale adhering to the surface of the steel strip using a pickling liquid such as a liquid mixture of hydrochloric acid or nitric acid and hydrofluoric acid.
  • the cold rolling step S5 is a step of rolling the steel strip from which scale has been removed in the first pickling step S4 to be thinner.
  • the final annealing step S6 is a step of heating the steel strip rolled to be thin in the cold rolling step S5 to remove strain and softening the steel strip.
  • the final annealing step is a step of forming internal oxides, which are oxides of Al, Si or the like, together with outer layer oxides such as (Fe, Cr) 3 O 4 or Cr 2 O 3 .
  • annealing in the final annealing step S6 is performed at a temperature of approximately 900°C to 1100°C for a time within a range of 30 to 90 seconds in, as an atmosphere, the atmosphere or a combustion gas atmosphere of liquefied combustion gas (LNG) or the like depending on alloy components.
  • LNG liquefied combustion gas
  • the nitric acid electrolysis step S7 is a step of performing an electrolytic treatment on the steel strip obtained in the final annealing step S6 in a nitric acid aqueous solution. In the nitric acid electrolysis step S7, oxides adhering to the surface of the steel strip are partially removed.
  • the outer layer oxides such as (Fe, Cr) 3 O 4 or Cr 2 O 3 have been formed.
  • the internal oxides which are mainly oxides of Al, Si or the like, have been formed between these outer layer oxides and the base material.
  • nitric acid electrolysis step S7 nitric acid electrolysis is performed under conditions where a majority of the internal oxides remain while a majority of the outer layer oxides are removed. While the majority of the internal oxides remain, it is preferable that some of the internal oxides slightly exfoliate and are put into a state of being easily removable by the final pickling step S8.
  • the nitric acid concentration in the nitric acid electrolysis step S7 is preferably 150 g/L or lower. In this case, it is easy to leave 10 or more Al/Si-based oxides per 93 ⁇ m 2 on the surface of the steel strip after the final pickling step S8.
  • the nitric acid concentration in the nitric acid electrolysis step S7 is preferably 100 g/L or higher in order to obtain an amount of the Al/Si-based oxides on the surface after the final pickling step in a preferable range.
  • the nitric acid concentration in the nitric acid electrolysis step S7 is preferably 130 g/L or higher in order to efficiently remove the outer layer oxides within a short period of time.
  • the liquid temperature in the nitric acid electrolysis step S7 is preferably 70°C or lower and more preferably 60°C or lower. In this case, it is easy to leave 10 or more Al/Si-based oxides per 93 ⁇ m 2 on the surface of the steel strip after the final pickling step S8.
  • the liquid temperature in the nitric acid electrolysis step S7 is preferably 50°C or higher and more preferably 60°C or higher. In this case, it is possible to efficiently remove the outer layer oxides within a short period of time.
  • the current density in the nitric acid electrolysis step S7 is preferably 150 mA/cm 2 or lower. In this case, it is easy to leave 10 or more Al/Si-based oxides per 93 ⁇ m 2 on the surface of the steel strip after the final pickling step S8.
  • the current density in the nitric acid electrolysis step S7 is preferably 100 mA/cm 2 or higher, more preferably 120 mA/cm 2 or higher and still more preferably 130 mA/cm 2 or higher In this case, it is possible to efficiently remove the outer layer oxides within a short period of time.
  • the electrolysis time in the nitric acid electrolysis step S7 is more preferably 120 seconds or shorter. In this case, it is possible to leave 10 or more Al/Si-based oxides per 93 ⁇ m 2 on the surface of the steel strip after the final pickling step S8.
  • the electrolysis time in the nitric acid electrolysis step S7 is preferably 60 seconds or longer. In this case, it is possible to reliably remove a majority of the outer layer oxides, put some of the internal oxides into a state of being easily exfoliated and obtain an amount of the Al/Si-based oxides remaining after the final pickling step in a preferable range.
  • the final pickling step S8 is a step of immersing the steel strip after the nitric acid electrolysis step S7 into a pickling liquid such as a liquid mixture of nitric acid and hydrofluoric acid.
  • a pickling liquid such as a liquid mixture of nitric acid and hydrofluoric acid.
  • the internal oxides that have slightly exfoliated in the nitric acid electrolysis step S7 are removed. This makes it possible to remove Al/Si-based oxides that are present more than necessary while ensuring 10 or more Al/Si-based oxides per 93 ⁇ m 2 on the surface of the steel strip and to improve the luminosity.
  • a step such as polishing finish or the formation of a plating layer is further performed as a finishing step for improving red scale resistance.
  • a finishing step has a problem in that there is a need to introduce a new device for the finishing step and the manufacturing cost becomes high. From such a viewpoint, there is a demand for a manufacturing method for manufacturing ferritic stainless steel having excellent red scale resistance without increasing the manufacturing cost.
  • the component for exhaust gas according to the present embodiment can be obtained by working the above-described ferritic stainless steel according to the present embodiment into a predetermined component shape by a well-known working method.
  • each stainless steel shown in Table 1 is indicated by "mass%".
  • a remainder other than each component shown in Table 1 is Fe and an impurity.
  • underlines in Table 1 indicate that the range of each component that is contained in stainless steel according to each comparative example of the present invention is outside the range of the present invention.
  • ferritic stainless steels produced so as to have a chemical composition within the range of the present invention were defined as kinds of steel A1 to A10.
  • ferritic stainless steels produced so as to have a chemical composition outside the range of the present invention were defined as kinds of steel B 1 to B3.
  • Table 2 is a table showing conditions that were used to manufacture steel materials of steel materials Nos. 1 to 46 using the kinds of steel A1 to A10 and the kinds of steel B 1 to B3 and the evaluation results of each steel material. Conditions used upon the manufacturing of each steel material shown in Table 2 are as described below.
  • the number of Al/Si-based oxides on the surface of the steel material was measured as described below.
  • a SEM photograph of the surface of the steel material was captured using a scanning electron microscope (SEM) SU5000 (manufactured by Hitachi High-Tech Corporation) at a magnification of 10000 fold.
  • the dimensions of one visual field was 8.34 ⁇ m in length and 11.2 ⁇ m in width, and the area of one visual field was 93 ⁇ m 2 .
  • an element analysis was performed using energy dispersive X-ray spectroscopy (EDS) (manufactured by Horiba, Ltd.) at an accelerating voltage of 15 kV for an analysis time of 60 seconds.
  • EDS energy dispersive X-ray spectroscopy
  • the thicknesses of passive films were measured by the above-described method. While not shown in the tables, the thicknesses of passive films were 2.0 to 8.0 nm.
  • FIG. 2A and FIG. 2B show examples of the SEM photographs captured by the above-described method.
  • the number of Al/Si-based oxides present on the surface of the steel material No. 6, which is an invention example was 10 or more in one visual field.
  • the number of Al/Si-based oxides present on the surface of the steel material No. 8, which is a comparative example was less than 10 in one visual field.
  • the number of oxides that contained 5 mass% or more of Al or Si and had a diameter D of 0.1 ⁇ m or more and 2.0 ⁇ m or less that is, the number of the Al/Si-based oxides, was 19 in one visual field.
  • the numbers of Al/Si-based oxides were less than 10 per 93 ⁇ m 2 .
  • a 20 mm ⁇ 25 mm test piece was cut out from each steel material. This test piece the test piece was continuously heated at 600°C for 100 hours in an atmospheric environment where the water vapor concentration was 10 vol% with an assumption of a status where a petroleum-based fuel had been combusted. The weight gain was calculated from a change in mass before and after the test.
  • red scale resistance evaluation As a criterion for red scale resistance evaluation, when the weight gain was 0.20 mg/cm 2 or less, the red scale resistance was determined to be excellent.
  • the Cr, Si and Al contents at an arbitrary place in the test piece were measured using glow discharge spectroscopy (GDS) (GD-Profiler 2 manufactured by Horiba, Ltd.).
  • GDS glow discharge spectroscopy
  • An analysis region was set to ⁇ 4 mm, and the Cr, Si and Al contents were measured at 2.5 nm pitches up to a depth of 1.0 ⁇ m from the surface.
  • the luminosity on the surfaces of the steel materials Nos. 1 to 46 was measured in the following way.
  • the luminosity L* was less than 60.

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EP21882927.3A 2020-10-23 2021-10-22 Ferritbasierter edelstahl und komponente für abgas Pending EP4234770A1 (de)

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JP2016128591A (ja) * 2013-03-26 2016-07-14 新日鐵住金ステンレス株式会社 溶接部靭性と耐水漏れ性に優れる貯湯・貯水容器用フェライト系ステンレス鋼およびその製造方法
JP6390594B2 (ja) * 2015-11-13 2018-09-19 Ｊｆｅスチール株式会社 フェライト系ステンレス鋼
KR102030158B1 (ko) * 2017-12-26 2019-10-08 주식회사 포스코 표면 품질이 우수한 린 듀플렉스 스테인리스강의 제조방법
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