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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/10—Sintering only
  • B22F3/1003—Use of special medium during sintering, e.g. sintering aid
  • B22F3/1007—Atmosphere
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
  • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
  • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
  • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
  • C22C33/0285—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5% with Cr, Co, or Ni having a minimum content higher than 5%
• • 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
  • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
  • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
  • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
  • B22F2009/0824—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid with a specific atomising fluid
  • B22F2009/0828—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid with a specific atomising fluid with water
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

• the invention concerns atomised iron based powders having good high temperature oxidation resistance, more particular powders which are pre-alloyed with chromium and aluminium.
• FeCrAl-alloys Conventional iron based alloys containing typically Fe and 10-30% Cr and 1-10% Al, so-called FeCrAl-alloys, have been found highly useful in various high temperature applications, due to their good oxidation resistance and can be used at temperatures as high as 1200-1400 DEG C. Thus, such materials have been used in the production of electrical resistance elements and as carrier materials in motor vehicle catalysts. As a result of its aluminium content, the alloy is able to form at high temperatures and in the majority of atmospheres an impervious and adhesive surface oxide consisting substantially of A12O3. This oxide protects the metal against further oxidation and also against many other forms of corrosion, such as carburization, sulphuration etc.
• US5970306 describes a method for manufacturing high temperature resistant shaped parts from a FeCrAl-powder by hot isostatically pressing (HIP).
• HIP hot isostatically pressing
• DE4235141 descibes a method of producing a part made from hot pressed powder based on a FeCrAl-alloy in which the powder is initially exposed to an oxygen-contg. atmos. to produce an chromium oxide protective layer around the particles.
• US6761751 describes a method of producing an FeCrAl material by gas atomization, wherein in addition to containing iron (Fe), chromium (Cr) and aluminium (Al) the material also contains minor fractions of one or more of the materials molybdenum (Mo), hafnium (Hf), zirconium (Zr), yttrium (Y), nitrogen (N), carbon (C) and oxygen (O).
• This object is solved by an atomised iron based powder pre-alloyed with 10,5-30 wt% Cr, 3-15 wt% Al and 5-20 wt% Cu.
• pre-alloying the powder with Cu it is possible to sinter a component in conventional sintering processes and maintaining satisfactory material properties of the sintered component which component also have excellent high temperature oxidation resistance.
• an iron based powder pre-alloyed with 10,5-30 wt% Cr, 3-15 wt% All, 5-20 wt% Cu and 8-20 wt% Ni is proposed.
• the powders of the invention are preferably produced by providing a melt of iron and the alloying elements, water atomizing the melt whereby the powder forms from atomized droplets upon solidification.
• a sintered component can be produced from the powders of the invention by a) providing a sintering material comprising the powder of the invention; b) forming a green body from the sintering material; and c) sintering the green body in a reducing or neutral atmosphere, at an atmospheric pressure or below, and at a temperature above 1100 0 C.
• the sintering material could e.g. be loose sintered, cold compacted or warm compacted. Concerning cold compaction or warm compaction the sintering material is a mixture between a binder and/or a lubricant with the powder of the invention.
• Cold compaction is performed at temperatures below 100 0 C, preferably at a compaction pressure within the range of 100 -1000 MPa.
• Warm compaction is performed at temperatures within the range of 100-200 0 C, preferably at a compaction pressure within the range of 300 -1000 MPa.
• the sintering material could be a mixture between a binder and/or a lubricant with the powder of the invention, but also the powder it self i.e. without mixing the powder with a binder and/or a lubricant.
• the sintering material could be poured into a form where after the form containing the sintering material is inserted into the sintering furnace. For instance filters having excellent high temperature oxidation resistance can be produced by loose sintering the powder of the invention.
• a sintered component which exhibits excellent high temperature oxidation resistance may be produced from the powder of the invention which sintered component has a sintered density above 6,5 g/cm 3 , a tensile strength above 500 MPa and a yield strength above 400 MPa.
• FIG.1 shows a Fe-Cu phase diagram
• FIG 2A shows metallographic picture of a test bar comprising Cr, Al, Cu and Fe
• FIG 2B shows metallographic picture of a test bar comprising Cr, Al and Fe
• FIG 3 A shows metallographic picture of a test bar comprising Cr, Al, Cu, Ni and Fe
• FIG 3B shows metallographic picture of a test bar comprising Cr, Al, Ni and Fe.
• the invention concerns pre-alloyed iron based powders comprising more than 10,5 wt% chromium, as well as certain amounts of aluminium and copper.
• FeCrAl-alloys have been shown to exhibit excellent oxidation resistance at high temperatures, but are unfortunately difficult to sinter under atmospheric pressure or below (vacuum). That is the reason why compounds based on FeCrAl powders are produced by the HIP- process (as described in e.g. US5970306).
• pre-alloying with copper was reduced with an improved sintered structure as the outcome - compared to a reference material without copper.
• the copper content is shown to facilitate the formation of sintering necks as can be seen from the accompanying metallographic pictures. We believe that this effect occurs due to a break-up of the aluminium oxide layer by liquidised copper. Admixing copper and a FeCrAl-powder were also tested but sintering did not significantly improve in that case.
• the powders of the invention are made by making a melt of iron and the desired alloying elements.
• the melt is thereafter atomised whereby the powder is formed from the atomized droplets upon solidification.
• the atomization is performed according to conventional technology, e.g. gas or water atomization.
• the melt blend is water atomized, since a water atomised powder is easier to compact than a gas atomized powder.
• the powder forms due to the water atomization the powder is oxidized and thin chromium and aluminium oxide layers forms on the surface of the powder particles.
• the aluminium content should be above 3%, preferably the aluminium content should be above 5%, in order to obtain the desired oxidation resistance.
• the upper limit for the aluminium content is set to 15 wt%, and in fact it is preferred to have the aluminium content below 12 wt%.
• the boundaries for the copper content were derived from the tests described below. Accordingly it the copper content should be above 5 wt% to facilitate the formation of sintering necks and providing a sintered component having good high temperature oxidation resistance. Further the Cu-content should be below 20 wt%, powders having higher Cu-content may very well be useful for certain applications, but they are not within the scope of the present invention.
• Figure 1 shows the Fe-Cu phase diagram, but it is believed that that Cu will influence a system in a similar way.
• a certain amount of liquid phase must be formed, i.e. the area of ( ⁇ Fe +L) is of interest. Since the diagram is for the pure Fe-Cu system the information retrieved from it can only be used as a guideline.
• the amount of liquid phase formed during the sintering is required to break up the aluminium oxides but excess amounts of liquid phase collapses the structure during sintering.
• the amount of liquid phase formed is related to the chemical composition and the sintering temperature. The element having the strongest influence of the formation of liquid is copper. That is why different sintering temperatures depending of copper content of the samples were applied before the oxidation test.
• the powder can also be pre-alloyed with austenite-forming elements in particular nickel, but also the nickel equivalent manganese.
• austenite-forming elements nickel is also known to have a beneficial effect on the oxidation resistance which of course is desirable in the applications intended for the powders of the invention.
• nickel is to be included in the powder it is preferred that the nickel content is in the interval of 8-20 wt%.
• Manganese can also be an additional austenite forming alloying element, preferably the manganese content is below 3 wt%.
• Cobalt is normally not used since it is comparably expensive.
• the carbon content is low, since carbon has a tendency to cause intergranular corrosion why preferably the carbon content should be less than 0,1 wt% carbon.
• the carbon content was about 0,02 wt% or lower.
• the nitrogen content is below 0,2 wt%.
• test samples and the reference sample were produced by filling a form (10mm diameter and 2mm thickness) with the powder of interest, followed by smoothing out the surface without compacting the powder. This procedure provides samples with high specific area (ca 45% porosity).
• test samples were sintered in a 100 % hydrogene atmosphere for 30 minutes at a temperature depending of the Cu content according to the following table:
• the reference sample was sintered in a 100% hydrogen atmosphere for 30 minutes at 1320 0 C.
• the oxidation tests were carried out in a laboratory furnace, a Lenton 12/50/300, at a temperature of 800 0 C in air.
• Six samples could be tested at the same time by placing them on a sample holder and at each test run two of the samples were reference samples.
• Powder chemical comp. Weight Weight gain Increase in weight [wt%], bal. Fe gain [g] ref. [g] relative to reference [%]
• Table 2 shows that difference in oxidation resistance between samples containing Cu and Al and reference samples is further pronounced at temperatures above 800 degree Celcius. Furthermore, the composition having a Al content of 5,5 % and a Cu content of 15 % seems to have better oxidation resistance compared to the composition having 10 Al and 10 % Cu.
• EXAMPLE 3 In order to evaluate the effect of added Cu-content with regard to sintered density, tensile strength and yield strength, four different powders having were compared. The powders were as in example 1 and 2 water atomized powders. The powders were mixed with 1% of Acrawax® . The mixes were compacted at a compacting pressure of 600 MPa into tensile test bars. The test bars were sintered for 30 minutes at 1320 degrees Celsius in an atmosphere of 100 % hydrogen. Sintered density, tensile strength and yield strength were measured. The results are shown in table 3.
• FIG. 2A shows metallographic picture of a test bar comprising 22Cr + 5,5Al +10Cu+ bal.
• FIG 2B shows metallographic picture of a corresponding reference test bar comprising 22Cr + 5, 5 Al+ bal.
• FIG 3 A shows metallographic picture of a test bar comprising 22Cr + 5,5Al + 18Ni + 8Cu+ bal.
• Fe and FIG 2B shows metallographic picture of a corresponding reference test bar comprising 22Cr + 5, 5 Al+ 18Ni + bal.

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• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Powder Metallurgy (AREA)
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• Preventing Corrosion Or Incrustation Of Metals (AREA)
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• 2007
  • 2007-06-20 ES ES07748599T patent/ES2375159T3/es active Active
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