EP2316979A1 - Ferritischer edelstahl zur verwendung bei der herstellung eines harnstoffwassertanks - Google Patents

Ferritischer edelstahl zur verwendung bei der herstellung eines harnstoffwassertanks Download PDF

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EP2316979A1
EP2316979A1 EP09800430A EP09800430A EP2316979A1 EP 2316979 A1 EP2316979 A1 EP 2316979A1 EP 09800430 A EP09800430 A EP 09800430A EP 09800430 A EP09800430 A EP 09800430A EP 2316979 A1 EP2316979 A1 EP 2316979A1
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less
urea water
stainless steel
mass
effective amount
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English (en)
French (fr)
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EP2316979A4 (de
Inventor
Nobuhiko Hiraide
Haruhiko Kajimura
Akihiko Takahashi
Shigeru Maeda
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Nippon Steel Stainless Steel Corp
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Nippon Steel and Sumikin Stainless Steel Corp
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a ferrite stainless steel being used for a device that reduces NO x from exhaust gas by using a urea aqueous solution (urea water) in an internal combustion engine, mainly in a diesel engine, and, in particular, for equipments in a urea-Selective Catalytic Reduction (SCR) system for vehicles and the like, specifically, for a urea water tank that is utilized when storing, producing, and transporting urea water.
  • urea aqueous solution urea water
  • SCR urea-Selective Catalytic Reduction
  • the urea SCR system is one of the NO x reducing systems and in which urea water is used as a NO x reducing agent.
  • urea water has an advantage of being safe and relatively easy to treat; and as a result, it is being examined for application to stationary NO x reducing systems for distributed power-supply facilities installed in urban areas and the like, as well as automobiles.
  • the urea water sprayed into the exhaust gas is decomposed by heat and moisture so as to produce ammonia.
  • the urea water used in the above-described case is a urea aqueous solution (urea water) having a high concentration of 25 to 45%.
  • a urea aqueous solution having a concentration of about 32.5% and the lowest freezing point is used, which is prescribed in "NO x reduction additive in diesel engines -AUS 32- Part 1: Properties" by JIS K2247-1 (The Automotive Standards JASO E502 is also a similar standard).
  • the standards also strictly prescribe the concentration of impurity elements, and elements in relation to stainless steel are prescribed to fulfill Fe: less than 0.5, Cr: less than 0.2, Ni: less than 0.2, Cu: less than 0.2 (all in the units of mg/kg).
  • Any material being used for a urea water tank needs to have extremely high corrosion resistance. Because it is not permitted that the concentration of impurities in the urea water exceeds the range prescribed in the above-mentioned regulations due to elution from materials used in equipments for storing, producing, and transporting the urea water. In addition, since the tank is normally used outside, as in automobiles, and for a long time period of ten years or more, there is a concern that the tank is penetrated by rainwater, sea-salt particles and the like, which may lead to leakage of the urea water in the tank. Since leakage of the urea water may cause a deterioration in function of the NO x reducing system, this needs to be avoided. Therefore, any material being used for the urea water tank needs to have an excellent corrosion resistance against salt damage on the outside surface.
  • Patent Document 1 discloses a supply device of high grade urea water and a method for supplying high grade urea water using the same.
  • Patent Document 1 discloses a supply device which includes: an electromotive pump having a high grade urea water supply port equipped with an air-removing mechanism and an exhaust hose equipped with a gun nozzle; and a high-density polyethylene intermediate bulk container (IBC) tank having a net volume of 1200 to 1500L.
  • the electromotive pump is preferably made of reinforced plastic and the pump shaft is preferably made of one of stainless alloy (SUS304), Hastelloy, and Inconel alloy.
  • SUSS304 refers to austenite stainless steel, and in Patent Document 1, there is not any direct description regarding ferrite stainless steel.
  • Patent Document 2 discloses two-phase stainless steel for a urea-producing plant, welding materials, a urea-producing plant and equipment thereof.
  • Patent Document 2 discloses two-phase stainless steel containing Cr: 26% or more and less than 28%, Ni: 6 to 10%, Mo: 0.2 to 1.7%, and W: more than 2% and 3% or less.
  • Urea is synthesized from ammonia and carbon dioxide gas under high temperatures and high pressures. Urea has highly corrosive nature due to the existence of intermediate products of the synthesis reaction such as ammonium carbamate and the like. Therefore, it is necessary to use materials that can endure corrosion wastage so as to prevent internal substances from being leaked.
  • Patent Document 3 discloses ferrite stainless steel having excellent brazeability. It is disclosed that the ferrite stainless steel is suitable for members having complicated shapes and produced by brazed welding, such as a urea water tank or the like being used for a urea SCR system for vehicles.
  • the present invention aims to provide a ferrite stainless steel suitable for a device that reduces NO x from exhaust gas by using urea water in an internal combustion engine, mainly in a diesel engine, and, in particular, for equipments in a urea SCR system for vehicles and the like, specifically, a urea water tank that is utilized when storing, producing, and transporting urea water.
  • An elution amount of consitituent elements eluted from the ferrite stainless steel into a high-concentration urea aqueous a solution (urea water) is small, and the ferrite stainless steel has an excellent corrosion resistance against salt damage.
  • the inventors of the present invention have found that it is important to form a passive film containing Cr in the surface of a steel in order to reduce an elution amount of the constituent elements of the steel into a urea aqueous solution having a high concentration of 25 to 45% on the inside surface and to attain an excellent corrosion resistance against salt damage on the outside surface, and consequently, it is necessary to contain an appropriate amount of Cr. It is well known that the corrosion resistance of the steel is improved by forming a passive film containing Cr on the steel surface.
  • the passive film formed on the steel used for the urea water tank may elute or the steel located below the passive film may elute, at the instant when the tank in a normal pre-use state of being exposed to air is exposed to a high-concentration urea aqueous solution.
  • a ferrite stainless steel containing 10% or more of Cr can form a uniform passive film that can suppress an elution of the passive film formed on the surface of the steel and an elution of the steel located below the passive film via the passive film in the urea water having a high concentration of 25 to 45% used in the urea water tank (Japanese Patent Application No. 2008-62598 ).
  • the forming of the uniform passive film capable of suppressing the elution is also important to enhance the resistance against chloride ions contained in sea-salt particles and the like; and thereby, the occurrence of the corrosion is suppressed.
  • the urea water tank which is the subject of the present invention is normally joined and assembled by welding or brazing.
  • an oxide film is formed on the surface of a steel in the welded (or brazed) portions. Even in the case where the oxide film is formed, it is still necessary to suppress an elution of the constituent elements from the steel into a high-concentration urea water on the inside surface and to suppress a corrosion due to the salt damage on the outside surface. Since the diffusion rate of Cr in a ferrite stainless steel is greater than that in an austenite stainless steel, a lack of Cr just below the oxide film can be suppressed.
  • the amount of Cr necessary to suppress the elution from the welded (or brazed) portions in the ferrite stainless steel can be made smaller than that in the austenite stainless steel.
  • the inventors of the present invention have found that the effective amount of Cr as expressed by any one of the following Equations (I), (II), and (II) needs to be 10% or more so as to secure the amount of Cr just below the oxide film and to fulfill the regulation in relation to the elution of the constituent elements into a high-concentration urea water (Fe: ⁇ 0.5, Cr: ⁇ 0.2, Ni: ⁇ 0.2, Cu: ⁇ 0.2 (all in the units of mg/kg)) in the case where the oxide film is formed (herein, the atomic symbols in Equations (I) to (III) represent the contents of the elements (expressed by mass %), and the numerical values shown in front of the atomic symbols represent constant numbers). In addition, it has been found that the effective amount of Cr needs to be 15% or more so as to suppress a corrosion due to the salt damage that is severer than the high-concentration urea water.
  • Equations (I) to (III) are alloy element indices where an influence of Si, Mn, Ti, and Nb contained in the steel on an effect of improving corrosion resistance due to Cr is taken into consideration, and are utilized for calculating a numerical value as an index of an effective amount of Cr that contributes to the improvement of the corrosion resistance of the steel.
  • Si is a useful element that forms an oxide just below chromium oxide so as to suppress the oxidation of Cr.
  • Mn accelerates the generation of a spinel type oxide containing Cr and Mn so as to reduce the effective amount of Cr.
  • Ti remarkably accelerates the growth of Cr oxide so as to considerably reduce the effective amount of Cr.
  • Nb has an effect to reduce the effect of Ti of accelerating the growth of chromium oxide so as to suppress the decrease in the effective amount of Cr due to Ti.
  • molten brazing metal needs to adhere and spread out on the surface of a stainless steel.
  • the wettability of brazing metal is affected by a surface film formed on the stainless steel in a brazing atmosphere.
  • Ti and Al which are oxidized more easily than Fe and Cr, form oxides so as to hinder the adhering and spreading out of the brazing metal; and thereby, the brazeability is degraded.
  • Ti and Al solid solutions contribute to a formation of such an oxide film.
  • the Ti and Al solid solutions exist as relatively stable nitrides even at the brazing temperature, the Ti and Al solid solutions do not contribute to the film formation; and therefore, the Ti and Al solid solutions do not hinder the adhering and spreading out of the brazing metal. From these viewpoints, the relationship between the contents of Ti and Al and the adhering-and-spreading-out property (wettability) of the brazing metal has been studied.
  • the urea water tank which is the subject of the present invention needs to have a strength, it is desirable to suppress the decrease in the strength after brazing.
  • brazing is conducted at high temperatures within a range of 1000 to 1100°C such as Ni brazing and Cu brazing, it has been considered that it is important to suppress the decrease in the strength induced by grain coarsening.
  • the present invention aims to provide a ferrite stainless steel for use in producing a urea water tank which has an improved corrosion resistance against salt damage together with the properties described in the previous two Japanese Patent Applications. That is, the present invention aims to provide the ferrite stainless steel showing a small degree of elution of constituent elements into a high-concentration urea water and an excellent corrosion resistance against salt damage.
  • a ferrite stainless steel showing a small degree of elution of constituent elements into a high-concentration urea water and an excellent corrosion resistance against salt damage. Therefore, it is possible to provide a preferred material used for a device that reduces NO x from exhaust gas by using urea water in an internal combustion engine, mainly in a diesel engine, and, in particular, a device related to a urea SCR system for vehicles, and preferred for a tank being used when storing, producing, and transporting urea water.
  • C Since C degrades intergranular corrosion resistance and formability, it is necessary to adjust the content of C to be at a low level. Therefore, the content of C is set to be in a range of 0.05% or less. However, since an excessively low content leads to the increase in refining cost, it is desirable to set the content of C to be in a range of 0.002% or more.
  • N is a useful element for pitting corrosion resistance; however, N degrades the intergranular corrosion resistance and the formability. Therefore, it is necessary to adjust the content ofN to be at a low level. Accordingly, the content ofN is set to be in a range of 0.05% or less. However, since an excessively low content leads to an increase in refining cost, it is desirable to set the content of N to be in a range of 0.002% or more.
  • Si is useful as a deoxidization element, and is also an effective element for corrosion resistance; however, Si degrades the formability. Therefore, the content of Si is set to be in a range of 0.02 to 1.5%.
  • Mn is useful as a deoxidization element; however, Mn degrades corrosion resistance when an excessive content of Mn is included. Therefore, the content of Mn is set to be in a range of 0.02 to 2%.
  • Cr is the most important element in the present invention, and the content of Cr needs to be at least 15% or more so as to reduce an elution amount of constituent elements into high-concentration urea water and to attain an excellent corrosion resistance against salt damage.
  • the upper limit of the content of Cr is set to 23% or less.
  • the content of Cr is preferably in a range of 16% or more, and more preferably in a range of 18% or more.
  • Nb and Ti A urea water tank which is the subject of the present invention is often jointed and assembled by welding or brazing.
  • Nb and Ti are useful elements having the effects of fixing C and N and improving the intergranular corrosion resistance in welded (or brazed) portions.
  • Nb and Ti cause a negative effect on the formability and the manufacturability. Therefore, the content of either one or both ofNb and Ti is set to be in a range of 8(C+N) to 1%, and preferably in a range of 8(C+N) to 0.6% (herein, C and N represent the contents of C and N (expressed by mass %); respectively, and the numerical values shown in front of the atomic symbols represent constant numbers).
  • the content of Ti needs to be controlled to fulfill Ti-3N ⁇ 0.03 so as to secure a satisfactory brazeability (herein, the atomic symbols in the equation represent the contents of the elements (expressed by mass %), and the numerical values shown in front of the atomic symbols represent constant numbers).
  • the value of Ti-3N is preferably in a range of 0.02% or less.
  • the effective amount of Cr expressed by any one of Equations (I), (II), and (III) is set to be in a range of 15% or more (herein, the atomic symbols in Equations (I) to (III) represent the contents of the elements (expressed by mass %); and the numerical values shown in front of the atomic symbols represent constant numbers).
  • the effective amount of Cr Cr+4Si-2Mn (I)
  • the effective amount of Cr Cr+4Si-2Mm-10Ti (II)
  • the effective amount of Cr Cr+4Si-2Mm-(10Ti-3Nb) (III)
  • the effective amount of Cr calculated by the Equations (I) to (III) is necessary to set to be in a range of 10% or more so as to obtain a ferrite stainless steel showing a remarkably small degree of elution of constituent elements into high-concentration urea water and an excellent corrosion resistance that fulfills JIS K2247-1 by securing the amount of Cr just below an oxide film under conditions where the oxide film is formed in the steel surface, such as the case where the steel is subjected to welding or brazed jointing.
  • the present invention demands the corrosion resistance against salt damage on the outside surface, and it is necessary to set the effective amount of Cr to be in a range of 15% or more, preferably in a range of 16% or more, and more preferably in a range of 18% or more so as to be compatible with the corrosion resistance in high-concentration urea water.
  • Mo If necessary, it is possible to contain 3% or less of Mo so as to improve the corrosion resistance.
  • the content of Mo needs to be 0.3% or more so as to obtain a stable effect. If an excessive content of Mo is included, Mo degrades the formability, and Mo leads to an increase in cost since Mo is expensive. Therefore, it is preferable to contain Mo at a content within a range of 0.3 to 3%.
  • Ni If necessary, it is possible to contain 3% or less of Ni so as to improve the corrosion resistance.
  • the content ofNi needs to be 0.2% or more so as to obtain a stable effect. If an excessive content ofNi is included, Ni degrades the formability, and Ni leads to an increase in cost since Ni is expensive. Therefore, it is preferable to contain Ni at a content within a range of 0.2 to 3%.
  • Cu If necessary, it is possible to contain 3% or less of Cu so as to improve the corrosion resistance.
  • the content of Cu needs to be 0.2% or more so as to obtain a stable effect. If an excessive content of Cu is included, Cu degrades the formability, and Cu leads to an increase in cost since Cu is expensive. Therefore, it is preferable to contain Cu at a content within a range of 0.2 to 3%.
  • V If necessary, it is possible to contain 3% or less of V so as to improve the corrosion resistance.
  • the content of V needs to be 0.2% or more so as to obtain a stable effect. If an excessive content of V is included, V degrades the formability, and V leads to an increase in cost since V is expensive. Therefore, it is preferable to contain V at a content within a range of 0.2 to 3%.
  • W If necessary, it is possible to contain 5% or less of W so as to improve the corrosion resistance.
  • the content of W needs to be 0.5% or more so as to obtain a stable effect. If an excessive content of W is included, W degrades the formability, and W leads to an increase in cost since W is expensive. Therefore, it is preferable to contain W at a content within a range of 0.5 to 5%.
  • Ca has a deoxidization effect and the like, and is a useful element for refining; and therefore, if necessary, Ca may be included at a content within a range of 0.002% or less. If Ca is contained, it is preferable to contain 0.0002% or more of Ca so as to obtain a stable effect.
  • Mg Mg has a deoxidization effect and the like, and is a useful element for refining, and Mg also refines the microstructure and is useful for improving the formability and toughness. Therefore, if necessary, Mg may be included at a content within a range of 0.002% or less. If Mg is contained, it is preferable to contain 0.0002% or more of Mg so as to obtain a stable effect.
  • B is a useful element for improving the secondary formability. Therefore, if necessary, B may be included at a content within a range of 0.005% or less. If B is contained, it is preferable to contain 0.0002% or more of B so as to obtain a stable effect.
  • C+N In the case where a brazed jointing is conducted to assemble a urea water tank, the content of C+N needs to be in a range of 0.015% or more, and preferably in a range of 0.02% or more so as to suppress a decrease in strength due to grain coarsening which occurs when being brazed. If an excessive content of C and N is included, C and N degrade the intergranular corrosion resistance and the formability. Therefore, it is preferable to set the upper limit of C+N to 0.04% or less.
  • Al has a deoxidization effect and the like, and is a useful element for refining, and Al also has an effect of improving the formability. Therefore, if necessary, Al may be included. In the case where a brazed jointing is conducted to assemble a urea water tank, it is necessary to secure a satisfactory brazeability; and therefore, it is preferable to set the content ofAl to be in a range of 0.5% or less.
  • an unavoidable impurity of P it is preferable to set the content of P to be in a range of 0.04% or less from the perspective of the weldability.
  • S it is preferable to set the content of S to be in a range of 0.01 % or less from the perspective of the corrosion resistance.
  • a molten steel is prepared in a converter or an electric furnace, and the molten steel is refined in an AOD furnace, a VOD furnace, or the like, and the refined molten steel is subjected to a continuous casting or an ingot-making method so as to obtain a slab, and then the slab is subjected to a process of hot rolling-annealing of a hot-rolled steel sheet-pickling-cold rolling-final annealing-pickling so as to manufacture a ferrite stainless steel. If necessity, the annealing of the hot-rolled steel sheet may be omitted, and the process of cold rolling-final annealing-pickling may be repeated.
  • test specimen having a width of 50mm and a length of 70mm was cut off from a cold rolled steel sheet, and one surface of the specimen was subjected to wet-polishing by emery paper down to 400-grit. Then, 0.1g of Ni brazing alloy was placed on the polished surface, and the test specimen was heated at 1100°C in a vacuum atmosphere of 5 x 10 -3 torr (about 0.6666Pa) for ten minutes. After cooling down to room temperature, the area of the brazing metal after heating was measured.
  • the brazeability was evaluated as good if the area of the brazing metal after heating is twice or more of the area of the brazing metal before heating, and the brazeability was evaluated as bad if the area of the brazing metal after heating is less than twice of the area of the brazing metal before heating.
  • Equation (IV) Equation (V) C+N (mass%) 8(C+N) (mass%) Ti+Nb (mass%) 1 -0.050 -0.48 0.03 0.24 0.394 2 -0.043 -0.43 0.028 0.224 0.552 3 -0.026 -0.22 0.016 0.128 0.424 4 -0.021 -0.17 0.03 0.24 0.3 81 5 -0.015 -0.14 0.016 0.128 0.232 6 -0.030 -0.25 0.029 0.232, 0.375 7 0.012 0.17 0.025 0.2 0.442 8 0.021 0.30 0.031 0.248 0.486 9 0.005 0.40 0.027 0.216 0.422 10 0.220 2.24 0.018 0.144 0.252 11 0.084 0.90 0.019 0.152 0.34 12 -0.038 0.20 0.026 0.208 0.354 13 0.026 0.62 0.022 0.176 0.065 14 0.049 0.53 0.019 0.152 0.323
  • the effective amount of Cr column in Table 4 with the symbol of * 1 represents the value of Cr+4Si-2Mn when containing only Nb, the value of Cr+4Si-2Mn-10Ti when containing only Ti, and the value of Cr+4Si-2Mn-(10Ti-3Nb) when containing both of Nb and Ti.
  • the column of Equation IV in Table 4 with the symbol of *2 represents the value of Ti-3N
  • the column of Equation V with the symbol of *3 represents the value of 10(Ti-3N)+Al.
  • the underlined values in Tables 3 and 4 represent values outside the range of the present invention.
  • Example of the Invention 1 17.7 -0.05 -0.54 0.032 0.256
  • Example of the Invention 2 15.6 0.19 1.92 0.01 0.08
  • Example of the Invention 3 17.2 -0.036 -0.36 0.021 0.168
  • Example of the Invention 4 20.2 -0.045 -0.45 0.034 0.272
  • Example of the Invention 5 22.3 0.09 0.87 0.017 0.136
  • Example of the Invention 6 20.1 -0.03 -0.3 0.02 0.16
  • Example of the Invention 7 15.4 -0.10 -0.99 0.059 0.472
  • Example of the Invention 8 20.3 -0.05 -0.45 0.032 0.256
  • Example of the Invention 9 21.3 -0.04 -0.40 0.025 0.2
  • Example of the Invention 10 23.3 -0.03 -0.26 0.017 0.136
  • Example of the Invention 9 21.3 -0.04 -0.40 0.025 0.2
  • Example of the Invention 10 23.3 -0.03
  • test specimen having a width of 20mm and a length of 40mm was cut off from the cold rolled steel sheet, and was subjected to wet-polishing by emery paper down to 600-grit. Then, the test specimen was subjected to a thermal treatment at 700°C in air for one second to simulate welding for obtaining a mock surface status of a welded heat-affected zone. Next, corrosion tests were carried out in which the thermally-treated test specimens of Testing Examples 1 to 14 were immersed in a urea aqueous solution having a concentration of 30% at 60°C for 144 hours.
  • the ratio of the solution volume to the test specimen area was set to 3.6ml ⁇ cm -2 in accordance with the metal corrosion test in "an anti-freezing liquid" of JIS K 2234, and a special grade reagent was used for urea being used for the preparation of the urea aqueous solution. After the completion of the corrosion tests, the corrosion rate was measured by weighing the test specimen, and a solution analysis was carried out by ICPS. The analyzed elements were Fe, Cr, Ni, and Cu.
  • test specimen having a width of 70mm and a length of 150mm was cut off from the cold rolled steel sheet, and were subjected to wet-polished by emery paper down to 320-grit. Then, the test specimen was subjected to a thermal treatment at 700°C in air for one second to simulate welding for obtaining a mock surface status of a welded heat-affected zone. Next, the edge faces and the rear surfaces of the thermally-treated test specimens of Testing Examples 1 to 14 were coated with sealing tapes, and repetitive wet-dry cycle tests were carried out under conditions shown in FIG. 3 . After the completion of 180 cycles, the corrosion product was removed, and the corrosion depths in the corroded areas were measured by the depth of focus of a microscope method.
  • the conditions prescribed in JASO M609-91 were applied.
  • the adhering-and-spreading-out property of brazing metal was measured. Then, the microstructures of the cross sections of the test specimens were observed. The number of crystal grains existing in the sheet depth direction was measured in a 20mm-long range parallel to the rolling direction, and the brazeability was evaluated as good if two or more crystal grains existed in the sheet depth direction, and the brazeability was evaluated as bad if only one crystal grain existed.
  • the steels of Testing Examples 1 to 11 showed the maximum corrosion depths of less than 1 mm in the cyclic corrosion tests; and therefore, the steels of Testing Examples 1 to 11 were evaluated as good in the corrosion resistance against salt damage. Furthermore, the steels of Testing Examples 1 to 11 showed the corrosion rates of less than 0.001g ⁇ m -2 ⁇ h -1 in the immersion tests in the urea aqueous solution, and the amounts of Fe, Cr, Cu, and Ni in the solution after the tests fulfilled the standards of JIS K 2247-1. Therefore, the steels of Testing Examples 1 to 11 were evaluated as good in the corrosion resistance on the inside surface.
  • the steels of Testing Examples 1, 3, 4, 6, 7, 8, 9, 10, and 11 showed the value of C+N of 0.015 or more and fulfilled the Equations (IV) and (V) of the present invention. These steels were evaluated as good in the adhering-and-spreading-out property of brazing metal, and the coarsening of crystal grains was suppressed when being brazed.
  • the steel of Testing Example 5 showed the value of C+N of 0.015 or more; however, this steel did not fulfill the Equations (IV) and (V) of the present invention. In this steel, the coarsening of crystal grains was suppressed; however, this steel was evaluated as bad in the adhering-and-spreading-out property of brazing metal.
  • the steel of Testing Example 2 showed the value of C+N of less than 0.015 and did not fulfill the Equations (IV) and (V) of the present invention.
  • the coarsening of crystal grains occurred remarkably, and this steel was evaluated as bad in the adhering-and-spreading-out property of brazing metal.
  • the steel of Testing Example 12 showed less than 10% in both of the amount of Cr and the effective amount of Cr. This steel showed a low corrosion rate of 0.005g ⁇ m -2 ⁇ h -1 or less in the immersion test in the urea aqueous solution; however, the amounts of Fe and Cr in the solution after the test failed to fulfill the standards of JIS K 2247-1.
  • the steel of Testing Example 13 showed both of the amount of Cr and the effective amount of Cr outside the ranges of the present invention, and the steel of Testing Example 14 showed the effective amount of Cr outside the range of the present invention. These steels fulfilled the standards of JIS K 2247-1, and were evaluated as good in elution characteristics against the urea aqueous solution. However, these steels showed the maximum corrosion depths of 1mm or more in the cyclic corrosion tests; and therefore, these steels had bad corrosion resistances against salt damage.
  • the ferrite stainless steel of the present invention is a prefered material for a device that reduces NO x from exhaust gas by using urea water in an internal combustion engine, mainly in a diesel engine, and in particular, a device related to a urea SCR system for vehicles, and preferred for a tank being used when storing, producing, and transporting urea water.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Exhaust Gas After Treatment (AREA)
EP20090800430 2008-07-23 2009-07-23 Ferritischer edelstahl zur verwendung bei der herstellung eines harnstoffwassertanks Withdrawn EP2316979A4 (de)

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PCT/JP2009/063169 WO2010010916A1 (ja) 2008-07-23 2009-07-23 尿素水タンク用フェライト系ステンレス鋼

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JP5610796B2 (ja) * 2010-03-08 2014-10-22 新日鐵住金ステンレス株式会社 炭化水素燃焼排ガスから発生する凝縮水環境における耐食性に優れるフェライト系ステンレス鋼
JP5684547B2 (ja) * 2010-11-26 2015-03-11 新日鐵住金ステンレス株式会社 尿素ｓｃｒシステム部品用フェライト系ステンレス鋼板およびその製造方法
JP6071608B2 (ja) 2012-03-09 2017-02-01 新日鐵住金ステンレス株式会社 耐酸化性に優れたフェライト系ステンレス鋼板
JP5793459B2 (ja) * 2012-03-30 2015-10-14 新日鐵住金ステンレス株式会社 加工性に優れた耐熱フェライト系ステンレス冷延鋼板、冷延素材用フェライト系ステンレス熱延鋼板及びそれらの製造方法
MY195207A (en) * 2012-09-24 2023-01-11 Jfe Steel Corp Ferritic Stainless Steel
FI124995B (fi) * 2012-11-20 2015-04-15 Outokumpu Oy Ferriittinen ruostumaton teräs
CN105051234B (zh) 2013-03-27 2017-05-10 新日铁住金不锈钢株式会社 铁素体系不锈钢热轧钢板及其制造方法以及钢带
US20180195157A1 (en) * 2014-09-02 2018-07-12 Jfe Steel Corporation Ferritic stainless steel sheet for urea scr casing (as amended)
CN117187700A (zh) * 2019-07-05 2023-12-08 斯塔米卡邦有限公司 尿素装置中的铁素体钢部件
CN111057947A (zh) * 2019-12-09 2020-04-24 宁波宝新不锈钢有限公司 一种具有良好高温强度的铁素体不锈钢及其制备方法
WO2021190994A1 (en) * 2020-03-25 2021-09-30 Casale Sa Use of ferritic steel in the high pressure section of urea plants
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JPWO2010010916A1 (ja) 2012-01-05
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