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
  • C22C38/36—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.7% by weight of carbon
• • 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
  • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
• • 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
  • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12639—Adjacent, identical composition, components
  • Y10T428/12646—Group VIII or IB metal-base
  • Y10T428/12653—Fe, containing 0.01-1.7% carbon [i.e., steel]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12771—Transition metal-base component
  • Y10T428/12861—Group VIII or IB metal-base component
  • Y10T428/12951—Fe-base component
  • Y10T428/12958—Next to Fe-base component
  • Y10T428/12965—Both containing 0.01-1.7% carbon [i.e., steel]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12771—Transition metal-base component
  • Y10T428/12861—Group VIII or IB metal-base component
  • Y10T428/12951—Fe-base component
  • Y10T428/12972—Containing 0.01-1.7% carbon [i.e., steel]
  • Y10T428/12979—Containing more than 10% nonferrous elements [e.g., high alloy, stainless]

Definitions

• the present invention relates to an austenitic cobalt stainless steel ultra resistant to erosive cavitation.
• Patent application EP-A-85 420 115.9 filed on June 24, 1985 by the Applicant describes and claims an austenitic stainless steel with cobalt having a very high resistance to high intensity erosive cavitation, which steel is, by its resistance, particularly useful for the manufacture or repair of parts of hydraulic machines.
• the austenitic stainless steel described and claimed in this EP-A-85 420115.9 is characterized in that, on the one hand, it comprises: from 8 to 30% by weight of Co, from 13 to 30% by weight of Cr, from 0.03 to 0.3% by weight of C, up to 0.3% by weight of N, up to 3.0% by weight of Si, up to 1.0% by weight of Ni, up to 2% by weight of Mo, and up to 9% by weight of Mn, the remaining percentage being essentially made up of Fe, and in that, on the other hand and above all, its content of elements known as ferritizing (Cr, Mo, Si), in elements known as austenitizing (C, N, Co, Ni, Mn) and, among these ferritizing elements and austenitisants, in elements known to increase or decrease the energy of stacking fault, is suitably chosen and adjusted so that at least 60% and preferably at least 85% by weight of the steel is, at the ambient temperature, in a cubic phase with a metastable centered face ⁇ having a sufficiently low stacking
• the composition as well as the very particular structure of this stainless steel were "selected" by the inventor after numerous searches carried out following the discovery of the fact that the Low hardness cobalt stainless steels containing as little as 8% by weight of cobalt have an erosive cavitation resistance as good as that of alloys containing up to 65% cobalt, provided that at least 60% by weight of said stainless steels with a low cobalt content or, at room temperature, in a cubic phase with a metastable centered face ⁇ having a stack fault energy sufficiently low that it can be transformed under the effect of cavitation in a compact hexagonal phase ⁇ and / or in martensite ⁇ showing fine warping of deformation.
• the "soft" Fe-Cr-Co-C alloys which have a fine cavitation-induced weaving, which weaving is specific to low energy fault crystal. stacking (EFE), also have an effective resistance to cavitation by means of the following various mechanisms: - work hardening and accommodation of high stresses, delaying the initiation of fatigue cracks; - extension of the planar covering over the entire surface of the alloy retaining the latter smooth during an entire incubation period, and - continuous absorption of the incident cavitation energy by the production of a high density of dislocation and fine eroded particles thus leading to low rates of erosion.
• the present invention is based on the discovery that results and advantages similar to those previously obtained tiated, namely a very high resistance to erosive cavitation, a relatively low cost price and a multitude of possible uses in particular for the manufacture of parts of hydraulic machines, can be obtained with "harder" cobalt stainless steels, may contain up to 2% by weight of carbon, up to 5% by weight of silicon and up to 16% by weight of manganese.
• At least 60% by weight of the cobalt stainless steel according to the invention must be, at room temperature, in a cubic phase with face centered with the lowest possible stack fault energy.
• This last condition namely a very low stack fault energy of the cubic austenitic phase with centered face ⁇ , is an essential element of the invention, since it is absolutely necessary that the steel is capable, under the effect of cavitation, to deform to show a fine deformation chewing making it ultra resistant.
• This deformation can be carried out in certain cases without phase change.
• This deformation can also be obtained by transformation of the cubic phase with centered face ⁇ , into compact hexagonal phase ⁇ and / or into martensite ⁇ .
• the Cobalt is undoubtedly one of the most interesting insofar as it has the advantage, in addition to lowering the EFE, of preserving the stability of the austenitic phase of steel over a large concentration range.
• the stainless steel according to the invention which contains less than 30% by weight of cobalt and up to 70% by weight of iron, can thus have a stack fault energy as low as that of alloys with a high cobalt content, and a substantially identical fine deformation coupling (see also the article by DA Woodford and Al, "A Deformation Induced Phase Transformation Involving a Four-Layer Stacking Sequence in Co-Fe Alloy ", Met. Trans., Vol.2, page 3223, 1971) where it is indicated that in Fe-Co alloys, only 15% by weight of iron is sufficient to completely remove the transformation induced by cavitation from the ⁇ phase to the ⁇ phase).
• chromium has a very strong interaction with cobalt and iron to promote the formation of low energy crystals due to stacking failure.
• the surface layer of the Fe-Cr-Co-C alloys according to the invention shows, after exposure to cavitation, a very fine mesh network in a cubic phase with centered face ( ⁇ phase), in a compact hexagonal phase (phase ⁇ ) or in a martensitic phase ⁇ .
• ⁇ phase cubic phase with centered face
• phase ⁇ compact hexagonal phase
• ⁇ martensitic phase
• the localized hardening associated with this fine chewing ensures an extension of the chewing to the whole exposed surface at the beginning of the exposure to cavitation (incubation period). This explains why the exposed surface remains so flat and smooth during the incubation period, if we compare it to the surface of strong relief which we obtain with more deformable materials. Smoother surfaces are, in fact, less prone to attack by localized tangential microjets than occur during each implosion due to cavitation.
• the only surface relief undergone by the cobalt stainless steels according to the invention is the above-mentioned fine deformation chewing.
• This fine chewing leads to very low rates of erosion taking into account the fact that the particles eroded at the junction of the meshes are very fine.
• the large quantity of newly created surfaces for a given quantity of metal lost by erosion is another effective means of absorbing the energy of incident cavitation.
• the austenitic cobalt stainless steel according to the invention advantageously comprises: from 10 to 12% by weight of Co, from 16 to 18% by weight of Cr, from 0.4 to 0.5% by weight of C, from 2.5 to 3.5% by weight of Si, and from 4.5 to 5.5% by weight of Mn, the remaining percentage essentially consisting of Fe and residual impurities.
• the Co stainless steels according to the invention are soft. These steels are less expensive than conventional alloys with a high Co content such as STELLITE 6 TM or STELLITE 21 TM, while having substantially the same resistance to cavitation.
• the stainless steel according to the invention offers an economical alternative to alloys of the STELLITE 21 TM type currently used to protect hydraulic machines against the effects of erosive cavitation.
• Welding wires or electrodes made from the steel according to the invention can be used to repair damage due to cavitation. Hydraulic machine parts or entire groups can also be cast or completely covered with this steel which is cheaper than STELLITE and is capable of being hot rolled and cold for the development and manufacture of hydraulic machine elements with high resistance to cavitation.
• the invention has for another object any stainless steel part for the manufacture or repair of hydraulic machines, when said part is made or covered with a Co stainless steel with high resistance to cavitation according to the invention.
• the stainless steel parts according to the invention have a cavitation resistance at least equal to the parts made of harder alloys of the STELLITE-1 or -6 type. Since the stainless steels according to the invention are soft, they are much easier to grind. In fact, the parts according to the invention have all the advantages of parts made from soft alloys with a high Co content, of the STELLITE-21 type, but at a lower cost.
• the resistance to erosive cavitation of the steels and alloys tested was measured by ultrasonic cavitation test according to standard ASTM-G32.
• the weight losses of 16 mm cylindrical samples vibrating at 20 kHz at a double amplitude of 50 ⁇ m in distilled water at 22 ° C were measured every five hours for twenty five hours using a precise electrical balance to the tenth of a milligram.
• the materials tested are listed in the following TABLE I, where their nominal composition, their hardness and their cavitation erosion rate are also found.
• Co steels according to the invention listed in TABLE I were prepared by melting on a copper plate cooled with water in a small laboratory arc furnace or in an induction furnace, an appropriate mixture of several of the constituents carbon steel, 304 stainless steel, STELLITE 21, ferrochrome, electrolytic cobalt, ferromanganese and ferrosilicon. It should be noted that the compositions of all these experimental steels with the exception of the two STELLITES which were tested for reference, all fall within the composition range of the cobalt stainless steel according to the invention.
• the content of the cobalt stainless steel according to the invention in elements known as ferritisants (Cr, Mo, Si) and austenitisants (C, N, Co, Ni, Mn) must be appropriately chosen and adjusted so as to stabilize the austenite, particularly in the case of rapid cooling, so as to promote deformation of the ⁇ phase or an induced transformation of this ⁇ phase into the ⁇ phase or in martensite, the high resistance to cavitation of the steels according to the invention resulting mainly from their composition where the elements known to increase the energy of stacking fault, namely, for example, nickel, are replaced as much as possible by elements known to lower this stacking fault energy such as Co, Si, Mn and N and thus lead to finer deformation coupling.
• ferritisants Cr, Mo, Si
• austenitisants C, N, Co, Ni, Mn
• the cobalt stainless steels according to the invention can advantageously be used for the manufacture and repair of parts or groups of hydraulic machines, such as turbines, pumps, taps, etc. They can be used either as coverings welded on carbon steel, either as base material, cast or in the form of sheet metal, for the manufacture of machines made of stainless steel. These steels can also be hot or cold rolled and developed into welding wires or electrodes to replace the much more expensive STELLITE-21 used to repair cavitation damage in hydraulic turbines.

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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 Steel (AREA)
• Heat Treatment Of Articles (AREA)
• Hydraulic Turbines (AREA)
• Treatment Of Steel In Its Molten State (AREA)

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• 1986
  • 1986-06-30 CA CA000512811A patent/CA1269548A/fr not_active Expired - Lifetime
  • 1986-10-23 US US06/922,404 patent/US4751046A/en not_active Expired - Lifetime
  • 1986-12-18 DE DE8686420305T patent/DE3675547D1/de not_active Expired - Lifetime
  • 1986-12-18 EP EP86420305A patent/EP0250690B1/de not_active Expired - Lifetime
  • 1986-12-24 JP JP61306683A patent/JPS6311653A/ja active Pending
• 1987
  • 1987-06-29 CH CH2454/87A patent/CH674522A5/fr not_active IP Right Cessation
  • 1987-06-30 AU AU74945/87A patent/AU589281B2/en not_active Ceased

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