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
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/002—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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium

Definitions

• the invention relates to a deformable, ferritic steel alloy.
• Alloys of this type are used, inter alia, for the production of electrical heating elements and catalyst supports. These materials form a dense, firmly adhering aluminum oxide layer, which protects them from destruction. This protection is improved by the addition of so-called reactive elements such as Ca, Ce, La, Y, Zr, Hf, Ti, Nb, which improve the adhesiveness and / or reduce the layer growth, as described in the “Handbook of High-Temperature Materials Technology, Ralf Bürgel, Vieweg Verlag, Braunschweig 1998 ", from page 274.
• the aluminum oxide layer protects the metallic material from rapid oxidation. It grows itself, albeit very slowly. This growth takes place with the consumption of the aluminum content of the material. If there is no more aluminum, other oxides (chromium and iron oxides) grow. The metal content of the material is consumed very quickly and the material fails. The time to failure is called lifespan. Increasing the aluminum content therefore extends the service life.
• EP-B 0387670 an alloy with (in mass%) 20 to 25% Cr, 5 to 8% Al and additions of 0.03 to 0.08% yttrium 0.004 to 0.008% nitrogen, 0.020 up to 0.040% carbon, and approximately equal parts 0.035 to 0.07% Ti and 0.035 to 0.07% zirconium, and max. 0.01% phosphorus, max. 0.01% magnesium, max. 0.5% manganese, max. 0.005% sulfur, remainder iron addressed, whereby the sum of the contents of Ti and Zr in% is 1.75 to 3.5 times as large as the sum of the contents of C and N in mass% as well as impurities due to melting. All or part of Ti and Zr can be replaced by hafnium and / or tantalum or vanadium.
• EP-B 0290719 an alloy with (in mass%) 12 to 30% Cr, 3.5 to 8% Al, 0.008 to 0.10% carbon, max. 0.8% silicon, 0.10 to 0.1% manganese, max. 0.035% phosphorus, max. 0.020% sulfur, 0.1 to 1.0% molybdenum, max.
• nickel 1% nickel, and the additives 0.010 to 1.0% zirconium, 0.003 to 0.3% titanium and 0.003 to 0.3% nitrogen, calcium plus magnesium 0.005 to 0.05%, and rare earth metals from 0.003 to 0.80 %, Niobium of 0.5%, rest of iron described with usual accompanying elements, which is used for example as wire for heating elements for electrically heated furnaces and as a construction material for thermally stressed parts and as a film for the production of catalyst supports.
• the iron-chromium-aluminum alloy Cr AI 14 4 can be manufactured more easily by the aluminum content lowered to approx. 4 to 4.5 mass% than the alloys described above with more than 5 mass% aluminum. But it shows still embrittlement phenomena, which lead to increased production costs for hot forming.
• GB-A 476,115 shows an iron alloy, particularly suitable as electrical resistance, which contains the following elements: 6.1 - 30% Cr, 3 - 12% Al, 0.07 - 0.2% C, 4% Ti , Rest of Fe as well as contamination due to melting.
• the Ti content is bound to the C content in such a way that it should not be less than 3 times the C content.
• Preferred ranges for Cr are> 8%, for AI> 5%, for C> 0.085%.
• the metal composite foil contains a carrier layer made of ferritic steel strip, which is provided on both sides with an outer layer made of aluminum or an aluminum alloy.
• the carrier layer is formed from an alloy, with (in mass%) 16-25% Cr, rare earths, Y or Zr in contents between 0.01-0.1%, Fe rest. Furthermore, AI in contents between 2 and 6% can be added. Preferred Cr contents are above 20%.
• EP-A 0402 640 discloses a stainless steel foil as a carrier element for catalysts and their production.
• the foil is formed from an alloy of the following composition (in mass%): 1.0-20% Al, 5-30% Cr, up to 2% Mn, up to 3% Si, up to 1% C, balance Fe and manufacturing-related impurities.
• Preferred ranges for AI are between 5.5 and 20%.
• Y, Sc or rare earths can be added in limits up to 0.3% are, wherein at least one of the elements Ti, Nb, Zr, Hf, V, Ta, Mo, W can be provided in contents up to 2%.
• Levels ⁇ 4% AI require Cr contents> 25%.
• the invention has for its object to provide an inexpensive iron-chromium-aluminum alloy that has a similar or better life than Cr AI 14 4, but has an even lower brittleness and thus improved formability, but at the same time the same technical functionality as Cr AI 14 4 has.
• an iron-chromium-aluminum alloy with a long service life with (in mass%)> 2 to 3.6 mass% aluminum and> 10 to 20% chromium and additions of 0.1 to 1% Si, Max. 0.5% Mn, 0.01 to 0.2% yttrium and / or 0.01 to 0.2% Hf and / or 0.01 to 0.3% Zr, max. 0.01% Mg, max. 0.01% Ca, max. 0.08% carbon, max. 0.04% nitrogen, max. 0.04% phosphorus, max. 0.01% sulfur, max. 0.05% copper, and max. 0.1% molybdenum and / or tungsten and manufacturing-related impurities, the rest iron
• the Al content can preferably be set within limits of 2.5-3.55% and the Cr content within limits of 13-17%.
• the most effective way to reduce brittleness is to reduce the aluminum content.
• this has the disadvantage that the specific electrical resistance also decreases and the service life decreases.
• the brittleness is also increased by chromium, silicon, carbon and nitrogen, which is why these elements should also be kept as low as possible.
• the same technical functionality for a heating conductor which is used for the electrical generation of heat, can be achieved if the surface power, the power on the heating element, the total resistance of the heating element and the service life of the heating element remain constant with any change in the material.
• Weight M B / M A * jp B lp A • ⁇ B l ⁇ A
• Example: Material A: PA 1, 25 ⁇ mm 2 / m
• the oxidation constant k is a measure of the quality of the oxide layer k smaller than with a poorer oxide layer, the smaller k is, the longer the life.
• the subject of the invention is in addition to heating conductors for heating elements, for. B. a household appliance, or as a construction material in furnace construction can also be used as a film, for example as a carrier film for catalysts.
• Table 1 shows various iron-chromium-aluminum alloys, the table containing batches that have been melted on an industrial scale as well as in a laboratory.
• the test is carried out on wires with a diameter of 0.40 mm, from which wire coils with 12 turns, a coil diameter of 4 mm and a coil length of 50 mm are produced.
• the wire coils are clamped between two power supplies and heated up to 1200 ° C by applying a voltage. The heating takes place for 2 minutes each, then the power supply is interrupted for 15 seconds. At the end of the service life, the wire fails because the remaining cross-section melts. The total time that the wire was heated, without the interruption times, is given as the service life in the following.
• the large-scale batch T1 and the laboratory batches T2 and T3 represent the state of the art for Cr AI 14 4, with (in mass%) approx. 14.5% chromium, 4.5% aluminum, approx. 0.3% manganese , approx. 0.2% silicon and as a reactive element 0.17 to 0.18% zircon. They have lifetimes of 49 hours for the T3 laboratory batch, 63 hours for the T2 laboratory batch and 77 hours for the T1 industrial batch.
• Batches H1 to H6 are batches with an aluminum content of more than 5% by mass and various additions of silicon, manganese, zirconium, titanium, hafnium and yttrium and other additives such as calcium, magnesium, carbon and nitrogen.
• the aluminum content has been reduced from 4.5 to 3.55 mass% compared to the laboratory batch according to the prior art T2.
• the service life was reduced from 63 hours to 34 hours.
• Batch L3 with an aluminum content of 3.55% and a zirconium content of 0.053% and a hafnium content of 0.042% and an yttrium content of 0.02% has a service life of 90 hours.
• Batch M1 has a lifetime of 92 hours with an aluminum content of 2.78% and a zircon content of 0.05% and a hafnium content of 0.03% and an yttrium content of 0.02%.
• Charge M2 has a life of 126 hours with an aluminum content of 2.71% and a zirconium content of 0.05% and a hafnium content of 0.03% and an yttrium content of 0.04%.
• Batch M4 has a lifetime of 85 hours with an aluminum content of 2.8% and a zircon content of 0.03% and a hafnium content of 0.03% and an yttrium content of 0.03%.
• the alloy according to the invention must contain additions of 0.01 to 0.2% yttrium, and / or 0.01 to 0.2% Hf and / or 0.01 to 0.3% Zr.
• Batch L1 shows that even with the addition of zirconium, hafnium and yttrium with an aluminum content of 1.55%, only a service life of 9.3 hours is achieved. Even with the addition of zirconium, hafnium and yttrium and an aluminum content of only 2.24%, Charge M3 only has a lifespan of 72 hours, which is in the range of the batches according to the prior art.
• the Alloy according to the invention should therefore have an aluminum content of more than 2%.
• Chromium contents between 14 and 17% have no decisive influence on the service life like the comparison of the batches M1 containing zirconium, hafnium and yttrium with 14.85% chromium and 2.78% aluminum and batch L2 with 16.86% chromium and 2.55 % Aluminum shows.
• a certain chromium content is necessary, since chromium promotes the formation of the particularly stable and protective ⁇ - A 0 3 layer. According to HM Herbelin, M Mantel, Colloque C7, Suppleement au Journal de Physique III, Vol. 5, Novembre 1995, pages C7-365 to 374, this still happens with a chromium content of 13%, but a chromium content of 6% is no longer sufficient ,
• Table 1 lists the impact energy at room temperature, 50 ° C, 100 ° C and 150 ° C on standard DMV samples (see W. Domke, Materials Science and Testing, Verlag W. Gerardet, Essen, 1981, from page 336).
• the impact energy is low for a ferritic steel in the case of the brittle fracture occurring at low temperatures (low position), in the case of ductile, easily deformable behavior high (high position) with a steep increase within a few degrees from the low position to the high position. In this area, the impact energy can be widely scattered.
• the temperature at which the transition from the high position to the low position takes place is called the notch impact transition temperature.
• a material is the more brittle the larger the grain size or, in the case of iron-chromium-aluminum materials, the higher the content of alloying elements such as aluminum, chromium, silicon, nitrogen, carbon, phosphorus and sulfur. Due to your manufacturing route as a laboratory batch, all impact tests in Table 1 have one very large grain size of approximately 200 to 400 ⁇ m, which is very unfavorable. Therefore, all samples are in the low position at room temperature, with the samples with the lowest aluminum content, the lowest chromium content and the lowest carbon content having the highest impact energy, as shown by batches M1, M2, M3, M4 and L1.
• Charge M4 has a slightly lower notch impact energy than Charge M2 with a similar aluminum and chromium content, since it has a higher carbon content.
• Charge L2 has a slightly lower impact energy than Charge M2 because it has a higher chromium content. Nitrogen, phosphorus and sulfur act similarly to carbon, the contents of which should therefore advantageously be kept low. It turns out that the aluminum content must not exceed 3.6% in order to keep the embrittling effect of the aluminum as low as possible.
• the brittle behavior of the iron-chromium-aluminum alloys is significantly reduced by lowering the aluminum content to below 3.6%.
• This is further supported by low levels of silicon, carbon, nitrogen, phosphorus and sulfur.
• the carbon content is therefore limited to max. 0.08%, the nitrogen content to max. 0.04%, the phosphorus content to max. 0.04% and the sulfur content to max. 0.01 Mass% limited.
• Phosphorus and sulfur also have an unfavorable effect on the service life, so that the lowest possible levels of these elements are also advantageous from this point of view.
• the chromium content should also be as low as possible. Due to the requirements regarding the service life, the silicon and chromium content cannot be reduced to almost zero, but must be at least 0.1% silicon and 10% chromium. However, no more than 20% chromium and 1% silicon should be added in order to achieve the lowest possible brittleness.
• the alloy according to the invention must have an at least 10% longer lifespan in order to compensate for the disadvantage of the smaller wire diameter.
• the batches according to the invention all have an at least 50% longer lifespan, the use of the alloy according to the invention additionally has the advantage of an increased lifespan.
• Manganese is limited to 0.5% by mass because this element reduces the resistance to oxidation. The same applies to copper.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Resistance Heating (AREA)
• Powder Metallurgy (AREA)
• Cookers (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Carbon Steel Or Casting Steel Manufacturing (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Conductive Materials (AREA)
• Catalysts (AREA)

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• 2002
  • 2002-04-25 CN CN02808847.6A patent/CN1226439C/zh not_active Expired - Lifetime
  • 2002-04-25 EP EP02730208A patent/EP1381701B1/de not_active Expired - Lifetime
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