Classifications

• • 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
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
  • B01J23/74—Iron group metals
  • B01J23/745—Iron
• • 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
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • 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
  • C22C38/04—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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
  • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
  • F01N3/28—Construction of catalytic reactors
  • F01N3/2803—Construction of catalytic reactors characterised by structure, by material or by manufacturing of catalyst support
  • F01N3/2807—Metal other than sintered metal

Definitions

• the present invention relates to a ferritic steel alloy for the use as substrate material in catalytic converters for diesel engines in heavy vehicles at temperatures in the interval of 600-900° C. and a specific relation between the content of chromium and aluminium being satisfied.
• a metal monolith can be manufactured with thinner wall thicknesses, normally between 1 ⁇ 2 and 1 ⁇ 3 in comparison with corresponding ceramic monolith, which gives lower pressure drop, so-called “back pressure”, larger efficient area and larger catalytic capacity.
• the monolith can be made smaller in volume and with a design that is more flexible.
• the thermal conductivity is better in metal, which entails smaller risk of overheating than in ceramic monoliths.
• Diesel engines are frequently used in vehicles having long operating periods and where the cost for shutdown and change of catalytic converter is high. The requirements on service life and reliability of the catalytic converter, and hence the supporting material, are, therefore, also high.
• the most commonly occurring metal foil used for catalytic converters for diesel engines is today the same as is used for petrol engines and consists mainly of a Fe—Cr—Al of 19-21% Cr, 5-7% Al, one or more reactive elements, e.g., Zr, Y, Hf, La and Ce and the balance iron including naturally occurring impurities.
• This material has acceptable, but not optimal, oxidation properties for the temperature intervals used in diesel engines and has poor mechanical properties because of the high content of aluminium, which involves inferior machining properties and a high manufacturing cost.
• a material having good properties in cyclic oxidation at maximum temperatures in the interval of 600-900° C. and good production economy is mainly of a Fe—Cr—Al of 19-21% Cr, 5-7% Al, one or more reactive elements, e.g., Zr, Y, Hf, La and Ce and the balance iron including naturally occurring impurities.
• This material has acceptable, but not optimal, oxidation properties for the temperature intervals used in diesel engines and has poor
• Today's exhaust emission-control materials are optimized for the purification of exhaust fumes from petrol engines, which operates at temperatures above 900° C. and particularly between 1000-1200° C. It is generally known that Fe—Cr—Al-alloys form an ⁇ -aluminium oxide at temperatures above 900-950° C., which gives lower oxide growth and better oxidation properties than ⁇ -aluminium oxide. Experience has shown that Fe—Cr—Al-alloys require an aluminium content of over 4.5% in order to form single-phase ⁇ -aluminium oxide applied in catalytic converters. Catalytic converters for diesel engines are assumed to have an operating temperature below 600° C.
• a Fe—Cr—Al-alloy forms a mixed oxide substantially consisting of chromic oxide and ⁇ -aluminium oxide where the chromic oxide is less stable and risks being evaporated or peeled off from the surface, while the aluminium oxide is considerably more stable.
• An oxide to the greatest part composed of aluminium oxide is, from experience, also advantageous for the adhesion of the coating, a so-called wash-coat that is applied to the metal surface of the completed monolith.
• JP2002004011 aims at the use in exhaust systems at temperatures between 650-800° C., but as in the previous example, the material is not alloyed with aluminium and hence has a similar oxidation resistance and is accordingly not suitable for the use as foil material in a catalytic converter in diesel vehicles.
• a ferritic steel alloyed with a balanced quantity of chromium, aluminium and reactive elements that has the following composition (in % by weight): Ni up to 1 Cr 15-25 Al 0.75-3.7 Si max 0.6 Mo and/or W 0-3 Ti and/or Nb 0-1 C up to 0.2 N up to 0.2 one or more of the reactive elements Zr, Hf and REM
• the content of Zr and/or Hf is >0-0.5% by weight, preferably >0-0.2% by weight.
• the reactive element is REM, such as Ce, Sc, La and Y, the content is maximally 0.2% by weight. Irrespective of which reactive element has been chosen, the total content of reactive elements is preferably maximally 0.5% by weight.
• chromic oxide is formed during operation at temperatures up to 900° C., which promotes the formation of a pure aluminium oxide where a relation between high contents of chromium and the aluminium content in the substrate according to the composition above can be observed.
• the chromium content of the alloy should be within the interval of 15.0-25.0% by weight, preferably 17.0-23.0% by weight, most preferably 20-23% by weight.
• Additives of reactive elements such as Zr, Hf and/or rare earth metals (REM) such as, for instance, Sc, Y, La and Ce, improves the oxidation resistance additionally by decreasing the tendency of peeling and flaking, i.e., the tendency of the oxide getting loose from the metal upon cooling or mechanical deformation for both aluminium oxides and chromium oxides.
• REM rare earth metals
• the total content of rare earth metals (REM) should be limited to maximum 0.2% by weight, wherein one or more of the elements Ce, La, Sc and/or Y may be added.
• the preferred content of REM should be within the interval of 0.01-0.2% by weight.
• Addition of one or more of the elements Ti, Nb, Zr and Hf gives, together with carbon and nitrogen, precipitations of carbides and/or nitrides, which provide the material with increased mechanical stability and resistance to grain growth, thereby improving the mechanical properties of the material.
• hafnium is regarded to have similar effect on the properties of the alloy, this element may replace zirconium entirely or partly.
• Zr and/or Hf may be present up to contents of 0.5% by weight in total.
• the preferred content of zirconium and/or hafnium should however be maximum 0.2% by weight, mostly for economical reasons. Preferably, this content should be within the interval of >0-0.2% by weight.
• Ni In aluminium-alloyed ferritic steels, nickel has an embrittling effect, and therefore the content of Ni should be limited to max. 1.0% by weight, preferably max. 0.7% by weight.
• Molybdenum may be added in the alloy in order to achieve improved strength at temperatures above 600° C.
• molybdenum may entirely or partly be replaced by tungsten in order to obtain a similar effect.
• the content of Mo and/or W should be 0 up to 3% by weight, preferably >0 up to 2.5% by weight and most preferably >0 up to 1.0% by weight.
• the alloy may also contain impurities, depending on the raw material and the manufacturing process.
• impurities such as Mg, which may for this type of alloys cause pores during casting, and should therefore not be present in contents above 0.05% by weight.
• V which may have a positive effect on the grain size in the steel but implies a higher cost and should therefore not be present in contents above 0.1% by weight.
• a third example of such an impurity is Co, which increases the cost for the material, whereby the Co content should be limited to maximally 0.05% by weight. Co may also imply contamination of other steel grades.
• a further example of an impurity is Cu. Cu deteriorates among other things the hot ductility for this type of alloys and may therefore render the material difficult to hot work, whereby the Cu content should be limited to maximally 0.05% by weight.
• the material according to the invention has obtained a considerable decrease of the oxidation rate in the temperature range of 600-900° C., which is the critical temperature range for the use as supporting material in catalytic converters for diesel engines.
• the alloy satisfies the formula Cr+3Al ⁇ 26, preferably Cr+3Al ⁇ 29, within the stated limits of chromium and aluminium, which gives a favourable oxide formation and oxide composition.
• additives of reactive elements such as rare earth metals, for example Sc, Y, La and/or Ce, contribute to a good adhesion of the oxide and thus decreases the risk of peeling and flaking at these temperatures.
• the alloy has also good mechanical properties in both warm as well as cool state, which entails low manufacturing costs and a good economy in the completed product.
• the final product of the material may be manufactured in the form of strip or foil having a thickness of less than 200 ⁇ m or in the form of wire having a diameter of less than 200 ⁇ m, and is intended for use as supporting material in catalytic converters for diesel engines at temperatures that maximally amounts to 600-900° C.
• Table 1 shows some examples of compositions of an alloy according to the present invention, as well as a comparative example.
• Example 2 Example 3
• Example 4 (% by (% by (% by (% by (% by Element weight) weight) weight) Ni 0.18 0.24 0.28 0.08 Cr 20.95 20.94 22.42 22.11 Al 3.2 3.09 2.94 0.83 Mo ⁇ 0.01 0.01 2 2.02 W ⁇ 0.01 0.01 ⁇ 0.01 ⁇ 0.01 Ti 0.01 0.004 0.1 0.12 Nb ⁇ 0.01 0.01 0.81 0.77 Zr (/Hf) ⁇ 0.01 0.01 ⁇ 0.01 0.002 C 0.1 0.01 0.105 0.097 Si 0.39 0.28 0.45 0.11 P 0.011 0.013 0.016 ⁇ 0.003 S 0.01 0.0001 0.01 0.001 N 0.013 0.018 0.022 0.032 Mn 0.1 0.11 0.18 0.11 Ce 0.036 0.044 0.016 0.009 La 0.018 0.022 0.008 0.0045 Co 0.02
• the alloy according to the present invention may be manufactured by conventional pyrometallurgy and casting with ingot casting or continuous casting followed by hot working and then cold working into final dimension.
• the product may be further machined to foil, thin strip or wire.
• the alloy may also be directly cast into strip, sheet-metal plate or foil having width/thickness relation of >50 with thickness after casting of below 5 mm, followed by cold working or a combination of hot and cold working.
• Feasible alternative ways of manufacture are that a substrate material having lower aluminium content is coated with pure aluminium or an aluminium alloy so that the proper composition is attained.
• Coating of the substrate alloy with aluminium alloy may be effected by previously known processes, such as, for instance, dipping in melt, electrolytic coating, roll bonding of strips of the substrate alloy and the aluminium alloy, deposition of solid alloy of Al from a gas phase by so-called CVD- or PVD-techniques.
• the coating with alloy of Al may be effected after the substrate alloy has been rolled down to the desired final thickness of the product, or in larger thickness.
• a diffusion annealing may be carried out in order to provide a homogenization of the material after which rolling in one or more steps is carried out in order to provide the completed product. Rolling may also take place directly on a coated product having larger thickness than the desired completed thickness. In this case, the rolling may be followed by annealing.
• An example of manufacture of foil of a Fe—Cr—Al-alloy by PVD-deposition is disclosed in patent U.S. Pat. No. 6,197,132 B1.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Catalysts (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Exhaust Gas After Treatment (AREA)
• Exhaust Gas Treatment By Means Of Catalyst (AREA)

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• 2004
  • 2004-04-16 SE SE0401046A patent/SE528027C2/sv not_active IP Right Cessation
• 2005
  • 2005-04-13 US US11/578,252 patent/US20070292300A1/en not_active Abandoned
  • 2005-04-13 KR KR1020067021290A patent/KR20070004836A/ko not_active Withdrawn
  • 2005-04-13 EP EP05732168A patent/EP1740732A1/en not_active Withdrawn
  • 2005-04-13 CN CNA2005800114069A patent/CN1942599A/zh active Pending
  • 2005-04-13 WO PCT/SE2005/000523 patent/WO2005100628A1/en active Application Filing

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