EP0250690A1 - Cobalt-containing austenitic stainless steel, highly resistant against impingement attack - Google Patents

Cobalt-containing austenitic stainless steel, highly resistant against impingement attack Download PDF

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Publication number
EP0250690A1
EP0250690A1 EP86420305A EP86420305A EP0250690A1 EP 0250690 A1 EP0250690 A1 EP 0250690A1 EP 86420305 A EP86420305 A EP 86420305A EP 86420305 A EP86420305 A EP 86420305A EP 0250690 A1 EP0250690 A1 EP 0250690A1
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Prior art keywords
weight
cobalt
cavitation
stainless steel
content
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German (de)
French (fr)
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EP0250690B1 (en
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Raynald Simoneau
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Hydro Quebec
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Hydro Quebec
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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
    • C22C38/36—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)

Abstract

Cet acier est caractérisé en ce que, d'une part, il comprend : de 8 à 30 % en poids de Co, de 13 à 30 % en poids de Cr, de 0,03 à 2,0 % en poids de C, jusqu'à 0,3 % en poids de N, jusqu'à 5,0 % en poids de Si, jusqu'à 1,0 % en poids de Ni, jusqu'à 2 % en poids de Mo, et jusqu'à 16 % en poids de Mn, le pourcentage restant étant essentiellement constitué de Fe, et en ce que, d'autre part, il remplit au moins une des trois conditions suivantes : - sa teneur en C est supérieure à 0,3 %, et/ou - sa teneur en Si est supérieure à 3,0 %, et/ou - sa teneur en Mn est supérieure à 9,0 %. Cet acier inoxydable, qui est utilisable pour la fabrication ou la réparation de pièces de machines hydrauliques, est en outre caractérisé en ce que sa teneur en éléments connus comme ferritisants (Cr, Mo, Si), en éléments connus comme austénitisants (C, N, Co, Ni, Mn) et, parmi ces éléments ferritisants et austénitisants, en éléments connus pour augmenter ou abaisser l'énergie de faute d'empilement, est adéquatement choisie et ajustée de façon à ce qu'au moins 60 % en poids de l'acier soit, à température ambiante, dans une phase cubique à face centrée ayant une énergie de faute d'empilement suffisamment faible pour présenter sous l'effet de la cavitation, un mâclage fin de déformation ou pour, alternativement, pouvoir se transformer sous l'effet de la cavitation, en une phase hexagonale compacte ε et/ou en de la martensite α montrant un mâclage fin de déformation.This steel 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 2.0% by weight of C, up to 0.3% by weight of N, up to 5.0% by weight of Si, up to 1.0% by weight of Ni, up to 2% by weight of Mo, and up to 16% by weight of Mn, the remaining percentage essentially consisting of Fe, and in that, on the other hand, it meets at least one of the following three conditions: - its C content is greater than 0.3%, and / or - its Si content is greater than 3.0%, and / or - its Mn content is greater than 9.0%. This stainless steel, which can be used for the manufacture or repair of parts of hydraulic machines, is further characterized in that its content of elements known as ferritizing agents (Cr, Mo, Si), in elements known as austenitizing agents (C, N , Co, Ni, Mn) and, among these ferritizing and austenitic elements, elements known to increase or decrease the energy of stacking fault, is suitably chosen and adjusted so that at least 60% by weight of the steel either, at ambient temperature, in a cubic phase with a centered face having a sufficiently low stacking energy to present under the effect of cavitation, a fine warping or to alternatively be able to transform under the effect of cavitation, in a compact hexagonal phase ε and / or in martensite α showing a fine warping of deformation.

Description

La présente invention a pour objet un acier inoxydable austénitique au cobalt ultra résistant à la cavitation érosive.The present invention relates to an austenitic cobalt stainless steel ultra resistant to erosive cavitation.

La demande de brevet EP-A-85 420 115.9 déposée le 24 juin 1985 par la Demanderesse décrit et revendique un acier inoxydable austénitique au cobalt possèdant une très forte résistance à la cavitation érosive de forte intensité, lequel acier est, de par sa résistance, tout particulièrement utile pour la fabrication ou la réparation de pièces de machines hydrauliques.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.

L'acier inoxydable austénitique décrit et reven­diqué dans ce EP-A-85 420115.9 est caractérisé en ce que, d'une part, il comporte :
de 8 à 30 % en poids de Co,
de 13 à 30 % en poids de Cr,
de 0,03 à 0,3 % en poids de C,
jusqu'à 0,3 % en poids de N,
jusqu'à 3,0 % en poids de Si,
jusqu'à 1,0 % en poids de Ni,
jusqu'à 2 % en poids de Mo, et
jusqu'à 9 % en poids de Mn,
le pourcentage restant étant essentiellement constitué de Fe,
et en ce que, d'autre part et surtout, sa teneur en éléments connus comme ferritisants (Cr, Mo, Si), en éléments connus comme austénitisants (C, N, Co, Ni, Mn) et, parmi ces éléments ferritisants et austénitisants, en élé­ments connus pour augmenter ou abaisser l'énergie de faute d'empilement, est adéquatement choisie et ajustée de façon à ce qu'au moins 60 % et de préférence au moins 85 % en poids de l'acier soit, à la température ambiante, dans une phase cubique à face centrée métastable γ ayant une énergie de faute d'empilement suffisamment faible pour qu'elle puisse se transformer sous l'effet de la cavitation en une phase hexagonale compacte ou en de la martensite montrant un mâclage fin de déformation.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 γ having a sufficiently low stacking energy so that it can transform under the effect of cavitation into a compact hexagonal or martensite phase showing fine deformation chewing.

Tel qu'indiqué dans le préambule du EP-A-85 420 115.9, la composition ainsi que la structure très particu­lière de cet acier inoxydable ont été "sélectionnées" par l'Inventeur après de nombreuses recherches effectuées suite à la découverte du fait que les aciers inoxydables au cobalt à faible dureté contenant aussi peu que 8 % en poids de cobalt possèdent une résistance à la cavitation érosive aussi bonne que celle, excellente, que possèdent les alliages contenant jusqu'à 65 % de cobalt, à condition qu'au moins 60 % en poids desdits aciers inoxydables à faible teneur en cobalt soit, à température ambiante, dans une phase cubique à face centrée métastable γ ayant une énergie de faute d'empilement suffisamment faible pour qu'elle puisse se transformer sous l'effet de la cavita­tion en une phase hexagonale compacte ε et/ou en de la martensite α montrant un mâclage fin de déformation.As indicated in the preamble to EP-A-85 420 115.9, 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 γ having a stack fault energy sufficiently low that it can be transformed under the effect of cavitation in a compact hexagonal phase ε and / or in martensite α showing fine warping of deformation.

En fait, il avait alors été découvert que,de façon fort surprenante, les alliages "mous" Fe-Cr-Co-C qui possèdent un mâclage fin induit par la cavitation, lequel mâclage est spécifique aux cristaux à faible énergie de faute d'empilement (E.F.E.), possèdent également une résistance efficace à la cavitation au moyen des divers mécanismes suivants :
- écrouissage et accomodation de contraintes élevées, retardant l'initiation de fissures de fatigue ;
- extension du mâclage plan à toute la surface de l'alliage conservant ce dernier lisse durant toute une période d'incubation, et
- absorption continue de l'énergie de cavitation incidente par la production d'une grande densité de dislo­cation et de particules érodées fines conduisant ainsi à de faibles taux d'érosion.In fact, it was then discovered that, very surprisingly, 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.

La présente invention,telle que ci-après décrite et revendiquée, est basée sur la découverte du fait que des résultats et avantages similaires à ceux précédemment men­ tionnés, à savoir une très forte résistance à la cavitation érosive, un relativement bas prix de revient et une multi­tude d'utilisations possibles notamment pour la fabrication de pièces de machines hydrauliques, peuvent être obtenus avec des aciers inoxydables au cobalt plus "durs", pouvant contenir jusqu'à 2 % en poids de carbone, jusqu'à 5 % en poids de silicium et jusqu'à 16 % en poids de manganèse.The present invention, as hereinafter described and claimed, 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.

Sur la base de cette nouvelle découverte, la présente invention a pour objet un nouvel acier inoxydable austénitique au cobalt ultra résistant à la cavitation érosive, caractérisé en ce que :

  • (a) il comprend :
    de 8 à 30 % en poids de Co,
    de 13 à 30 % en poids de Cr,
    de 0,03 à 2,0 % en poids de C,
    jusqu'à 0,3 % en poids de N,
    jusqu'à 5,0 % en poids de Si,
    jusqu'à 1,0 % en poids de Ni,
    jusqu'à 2 % en poids de Mo, et
    jusqu'à 16 % en poids de Mn,
    le pourcentage restant étant essentiellement constitué de Fe, et en ce que :
  • (b) il remplit au moins une des trois conditions suivantes :
    - sa teneur en C est supérieure à 0,3 %, et/ou
    - sa teneur en Si est supérieure à 3,0 %, et/ou
    - sa teneur en Mn est supérieure à 9,0 %, et
  • (c) sa teneur en éléments connus comme ferriti­sants (Cr, Mo, Si), en éléments connus comme austénitisants (C, N, Co, Ni, Mn) et, parmi ces éléments ferritisants et austénitisants, en éléments connus pour augmenter ou abaisser l'énergie de faute d'empilement, est adéquatement choisie et ajustée de façon à ce qu'au moins 60 % en poids de l'acier soit, à température ambiante, dans une phase cubique à face centrée ayant une énergie de faute d'empilement suffisamment faible pour présenter sous l'effet de la cavitation, un mâclage fin de déformation ou pour, alternativement, pouvoir se transformer sous l'effet cavitation, en une phase hexagonale compacte ε et/ou en de la martensite montrant un mâclage fin de déformation.
Based on this new discovery, the present invention relates to a new austenitic stainless steel with cobalt ultra resistant to erosive cavitation, characterized in that:
  • (a) it includes:
    from 8 to 30% by weight of Co,
    from 13 to 30% by weight of Cr,
    from 0.03 to 2.0% by weight of C,
    up to 0.3% by weight of N,
    up to 5.0% by weight of Si,
    up to 1.0% by weight of Ni,
    up to 2% by weight of Mo, and
    up to 16% by weight of Mn,
    the remaining percentage essentially consisting of Fe, and in that:
  • (b) it meets at least one of the following three conditions:
    - its C content is greater than 0.3%, and / or
    - its Si content is greater than 3.0%, and / or
    - its Mn content is greater than 9.0%, and
  • (c) its content of elements known as ferritizing agents (Cr, Mo, Si), in elements known as austenitizing agents (C, N, Co, Ni, Mn) and, among these ferritating and austenitic elements, in elements known to increase or to decrease the stacking fault energy is suitably chosen and adjusted so that at least 60% by weight of the steel is, at ambient temperature, in a face-centered cubic phase having a fault energy sufficiently weak stacking to present under the effect of cavitation, a fine deformation chewing or for, alternatively, being able to transform under the cavitation effect, into a compact hexagonal phase ε and / or into martensite showing a fine warping of deformation.

Comme dans le cas de l'acier décrit et revendiqué dans le EP-A-85 420 115.9, au moins 60 % en poids de l'acier inoxydable au cobalt selon l'invention doit être, à température ambiante, dans une phase cubique à face centrée ayant la plus faible énergie de faute d'empilement possible. Cette dernière condition, à savoir une très fai­ble énergie de faute d'empilement de la phase austénitique cubique à face centrée γ , est un élément essentiel de l'invention, puisqu'il est absolument nécessaire que l'acier soit capable, sous l'effet de la cavitation, de se déformer pour montrer un mâclage fin de déformation le rendant ultra résistant. Cette déformation peut s'effectuer dans certains cas sans changement de phase. Cette déformation peut égale­ment être obtenue par transformation de la phase cubique à face centrée γ , en phase hexagonale compacte ε et/ou en martensite α .As in the case of the steel described and claimed in EP-A-85 420 115.9, 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 γ, 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 γ, into compact hexagonal phase ε and / or into martensite α.

Cette possibilité d'une déformation ou d'une trans­formation de phase sous l'effet de la cavitation, de façon à montrer un mâclage fin, est spécifique aux cristaux à faible énergie de faute d'empilement. Pour obtenir cette faible énergie de faute d'empilement, il est nécessaire de tenir compte de la capacité de chaque élément à abaisser ou augmenter l'énergie de faute d'empilement, et d'ajuster la teneur respective des divers éléments choisis pour cons­tituer l'acier, de façon à ce que l'énergie de faute d'em­pilement de l'ensemble des éléments combinés soit suffi­samment faible pour qu'on obtienne un mâclage fin de dé­formation, lorsque l'acier est sujet à la cavitation. Parmi les éléments connus pour augmenter l'énergie de faute d'empilement (E.F.E.), on peut citer Ni et C. Parmi ceux connus pour abaisser l'E.F.E., on peut citer Co, Si, Mn et N. Bien sûr, ces derniers éléments devront être choisis en priorité pour obtenir le résultat voulu, à savoir une faible E.F.E. Parmi des éléments connus pour abaisser l'E.F.E., le cobalt est sans doute un des plus intéressants dans la mesure où il a l'avantage, en plus d'abaisser l'E.F.E., de conserver la stabilité de la phase austénitique de l'acier sur une grande gamme de concentration.This possibility of a deformation or a phase transformation under the effect of cavitation, so as to show a fine weaving, is specific to crystals with low energy of stacking fault. To obtain this low stack fault energy, it is necessary to take into account the capacity of each element to lower or increase the stack fault energy, and to adjust the respective content of the various elements chosen to constitute the steel, so that the stacking fault energy of all of the combined elements is low enough to obtain a fine warping when the steel is subject to cavitation. Among the elements known to increase the stack fault energy (EFE), we can cite Ni and C. Among those known to lower the EFE, we can cite Co, Si, Mn and N. Of course, these elements must be chosen in priority to obtain the desired result, namely a low EFE Among elements known to lower the EFE, 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.

Il est également nécessaire de tenir compte de la nature même de ces éléments pour que 60 % au moins de l'acier soit effectivement en phase γ . Pour ce faire, il est nécessaire de choisir et adéquatement ajuster la teneur de l'acier en éléments respectivement connus ferritisants (Cr, Mo, Si) et austénitisants (C, N, Co, Ni, Mn).It is also necessary to take into account the very nature of these elements so that at least 60% of the steel is effectively in the γ phase. To do this, it is necessary to choose and adequately adjust the content of the steel in respectively known ferritating (Cr, Mo, Si) and austenitic (C, N, Co, Ni, Mn) elements.

L'exigence pour l'acier selon l'invention de mon­trer un mâclage fin induit par la cavitation est compatible avec le résultat des observations faites dans la littéra­ture, notamment par S. Vaidya et Al. ("The role of Twinning in the Cavitation Erosion of Cobalt Single Crystals", Met. Trans. A., Vol.11A, page 1139, juillet 1980) qui ont attri­bué la forte résistance de la cavitation des alliages à for­te teneur en cobalt à la faible énergie de faute d'empile­ment de ces alliages et à leur mâclage plan de déformation. Il est à noter cependant qu'il est tout à fait surprenant au vu de l'état de la technique, que l'acier inoxydable selon l'invention qui contient moins de 30 % en poids de cobalt et jusqu'à 70 % en poids de fer, puisse ainsi possè­der une énergie de faute d'empilement aussi faible que celle des alliages à forte teneur en cobalt, et un mâclage fin de déformation sensiblement identique (voir également l'article de D.A. Woodford et Al, "A Deformation Induced Phase Transformation Involving a Four-Layer Stacking Sequence in Co-Fe Alloy", Met. Trans., vol.2, page 3223, 1971) où il est indiqué que dans les alliages Fe-Co, seule­ment 15 % en poids de fer est suffisant pour faire complè­tement disparaître la transformation induite par cavita­tion de la phase γ en phase ε ). Une explication possible à ce phénomène particulier est que, dans l'acier inoxyda­ble selon l'invention, le chrome a une très forte interac­tion avec le cobalt et le fer pour promouvoir la formation de cristaux à faible énergie de faute d'empilement.The requirement for the steel according to the invention to show a fine cavitation-induced chewing is compatible with the result of observations made in the literature, in particular by S. Vaidya and Al. ("The role of Twinning in the Cavitation Erosion of Cobalt Single Crystals ", Met. Trans. A., Vol.11A, page 1139, July 1980) who attributed the high cavitation resistance of alloys with high cobalt content to the low energy of stacking fault of these alloys and their warping plane of deformation. It should be noted, however, that it is quite surprising, given the state of the art, that 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 γ phase to the ε phase). One possible explanation for this particular phenomenon is that, in the stainless steel according to the invention, chromium has a very strong interaction with cobalt and iron to promote the formation of low energy crystals due to stacking failure.

La couche de surface des alliages Fe-Cr-Co-C selon l'invention montre, après exposition à la cavitation, un réseau très fin de mâclage dans une phase cubique à face centrée (phase γ ), dans une phase hexagonale compacte (phase ε ) ou encore dans une phase martensitique α . La présence de ce mâclage fin et continu obtenu sous exposi­tion à la cavitation explique la forte résistance à la cavitation de l'alliage, qui, de par son mâclage, possède un moyen efficace d'absorber l'énergie des chocs de cavi­tation par déformation de sa structure cristalline. Ce mâclage fin est également un excellent moyen d'accomoder les contraintes élevées et ainsi retarder la création et la propagation de fissures de fatigue. L'écrouissage loca­lisé associé à ce mâclage fin assure une extension du mâclage à toute la surface exposée au début de l'exposi­tion à la cavitation (période d'incubation). Ceci explique pourquoi la surface exposée demeure aussi plate et lisse durant la période d'incubation, si on la compare à la sur­face de fort relief que l'on obtient avec des matériaux plus déformables. Des surfaces plus lisses sont, en effet, moins sujettes à attaque par les microjets tangentiels localisés que se produisent lors de chaque implosion dûe à la cavitation. Ainsi, pendant la période d'incubation, le seul relief de surface que subissent les aciers inoxy­dables au cobalt selon l'invention est le mâclage fin de déformation ci-dessus mentionné. Ce mâclage fin conduit à de très faibles taux d'érosion compte tenu du fait que les particules érodées à la jonction des mailles sont très fines. La quantité importante de surfaces nouvellement créées pour une quantité donnée de métal perdu par érosion est un autre moyen efficace d'absorber l'énrgie de cavi­tation incidente.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 (γ phase), in a compact hexagonal phase (phase ε) or in a martensitic phase α. The presence of this fine and continuous chewing obtained under exposure to cavitation explains the high resistance to cavitation of the alloy, which, by its chewing, has an effective means of absorbing the energy of cavitation shocks by deformation of its crystal structure. This fine chewing is also an excellent means of accommodating high stresses and thus delaying the creation and propagation of fatigue cracks. 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. Thus, during the incubation period, 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.

Selon un mode tout particulièrement préféré de réalisation, l'acier inoxydable austénitique au cobalt selon l'invention, comprend avantageusement :
de 10 à 12 % en poids de Co,
de 16 à 18 % en poids de Cr,
de 0,4 à 0,5 % en poids de C,
de 2,5 à 3,5 % en poids de Si, et
de 4,5 à 5,5 % en poids de Mn,
le pourcentage restant étant essentiellement consti­tué de Fe et d'impuretés résiduelles.According to a very particularly preferred embodiment, 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.

Bien entendu, la teneur en chacun des éléments ci-dessus mentionnés est adéquatement choisie et ajustée tel qu'expliqué ci-dessus.Of course, the content of each of the above-mentioned elements is suitably chosen and adjusted as explained above.

Des aciers inoxydables tout particulièrement inté­ressants sont identifiés par les numéros S17-3 ; 23 et 59 dans le tableau donné ci-après. Il s'avère, en effet, que ces aciers particuliers sont non seulement très effi­caces (ils ont une résistance à la cavitation sensiblement identique et même, dans le cas de l'acier S17-3, supérieure au STELLITE™ 6), mais également bon marché (à comparer au STELLITE™ qui contient 60 % de Co). On peut, en effet, noter que la composition de ces aciers est très proche de la composition des aciers inoxydables de la série standard 300, la seule différence résidant dans l'absence de nickel (connu pour augmenter l'énergie de faute d'empilement (E.F.E.)), remplacé par une quantité accrue de Co (connu pour abaisser l'E.F.E.).Especially interesting stainless steels are identified by the numbers S17-3; 23 and 59 in the table given below. It turns out, in fact, that these particular steels are not only very effective (they have a substantially identical cavitation resistance and even, in the case of S17-3 steel, superior to STELLITE ™ 6), but also inexpensive (compare to STELLITE ™ which contains 60% Co). We can, in fact, note that the composition of these steels is very close to the composition of stainless steels of the standard 300 series, the only difference residing in the absence of nickel (known to increase the energy of stacking fault. (EFE)), replaced by an increased amount of Co (known to lower EFE).

Tel que précédemment indiqué, les aciers inoxydables au Co selon l'invention sont mous. Ces aciers sont moins chers que les alliages conventionnels à forte teneur en Co tels que le STELLITE 6™ou le STELLITE 21™, tout en ayant sensiblement la même résistance à la cavitation. Il en résulte que l'acier inoxydable selon l'invention offre une alternative économique aux alliages de type STELLITE 21™ utilisés actuellement pour protéger les machines hydrauli­ques contre les effets de cavitation érosive. Des fils ou électrodes de soudure faits à partir de l'acier selon l'invention peuvent être utilisés pour réparer des dommages dus à la cavitation. Des pièces de machines hydrauliques ou des groupes entiers peuvent également être coulés ou complètement recouverts de cet acier qui est moins cher que le STELLITE et est capable d'être laminé à chaud et à froid pour le développement et la fabrication d'éléments de machines hydrauliques à forte résistance à la cavitation.As previously indicated, 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 ™ or STELLITE 21 ™, while having substantially the same resistance to cavitation. As a result, the stainless steel according to the invention offers an economical alternative to alloys of the STELLITE 21 ™ 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.

A la lumière de ce qui précède, l'invention a pour autre objet toute pièce en acier inoxydable pour la fabrication ou la réparation de machines hydrauliques, lorsque ladite pièce est faite ou recouverte d'un acier inoxydable au Co à forte résistance à la cavitation selon l'invention.In the light of the above, 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.

Les pièces en acier inoxydable selon l'invention ont une résistance à la cavitation au moins égale aux pièces faites d'alliages plus durs du type STELLITE-1 ou -6. Les aciers inoxydables selon l'invention étant mous, ils sont beaucoup plus faciles à meuler. En fait, les pièces selon l'invention ont tous les avantages des pièces faites à partir d'alliages mous à forte teneur en Co, du type STELLITE-21, mais à moindre coût.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.

D'autres avantages et caractéristiques de la présente invention ressortiront mieux à la lecture de la description non restrictive qui va suivre d'essais effec­tués par l'Inventeur.Other advantages and characteristics of the present invention will emerge more clearly on reading the non-restrictive description which will follow from tests carried out by the inventor.

PROCEDURE EXPERIMENTALEEXPERIMENTAL PROCEDURE

La résistance à la cavitation érosive des aciers et alliages testés a été mesurée par essai de cavitation ultrasonique selon la norme ASTM-G32. Les pertes en poids d'échantillons cylindriques de 16 mm vibrant à 20 kHz sous une double amplitude de 50 µm dans de l'eau distillée à 22°C furent mesurées toutes les cinq heures pendant vingt cinq heures au moyen d'une balance électrique précise au dixième de milligramme. Les matériaux testés sont listés dans le TABLEAU I suivant, où l'on trouve également leur composition nominale, leur dureté ainsi que leur taux d'érosion à la cavitation.

Figure imgb0001
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 µm 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.
Figure imgb0001

Les aciers au Co selon l'invention énumérés dans le TABLEAU I furent préparés en faisant fondre sur une plaque de cuivre refroidie à l'eau dans un petit four à arc de laboratoire ou dans un four à induction, un mélange approprié de plusieurs des constituants suivants : acier au carbone, acier inoxydable 304, STELLITE 21, ferrochrome, cobalt électrolytique, ferromanganèse et ferrosilicium. Il est à noter que les compositions de tous ces aciers expéri­mentaux à l'exception des deux STELLITES qui furent testés à titre de référence, tombent tous dans la fourchette de composition de l'acier inoxydable au cobalt selon l'invention.The 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.

INTERPRETATION DES RESULTATSRESULTS INTERPRETATION

Les résultats des essais de cavitation érosive re­portés sur le TABLEAU I démontrent clairement que tous les aciers expérimentaux testés ont une résistance à la cavita­tion supérieure ou égale à celle du STELLITE 21, tout en ayant une dureté sensiblement comparable. Un des aciers expérimentaux selon l'invention, le S17-3 a même montré une résistance à la cavitation supérieure à celle du STELLITE 6, tout en ayant une dureté inférieure.The results of the erosive cavitation tests reported in TABLE I clearly demonstrate that all of the experimental steels tested have a resistance to cavitation greater than or equal to that of STELLITE 21, while having a roughly comparable hardness. One of the experimental steels according to the invention, S17-3 has even shown a resistance to cavitation greater than that of STELLITE 6, while having a lower hardness.

Des essais de diffraction aux rayons X et des obser­vations micrographiques effectués concuremment sur certains des aciers testés ont montré également que l'excellente résistance à la cavitation des aciers au cobalt selon l'invention peut être attribuée au réseau fin de mâclage accompagnant la déformation de la phase austénitique γ ou sa transformation en phase hexagonale compacte ε ou en martensite α , ce mâclage induit par cavitation étant spé­cifique aux cristaux à faible énergie de faute d'empilement.X-ray diffraction tests and micrographic observations carried out concurrently on some of the steels tested have also shown that the excellent resistance to cavitation of the cobalt steels according to the invention can be attributed to the fine tapping network accompanying the deformation of the austenitic phase γ or its transformation into a compact hexagonal phase ε or into martensite α, this cavitation-induced masking being specific to crystals with low energy of stacking fault.

Le fait qu'aucun mâclage fin et qu'une faible résis­tance à la cavitation aient pu être observés sur les aciers testés dans le EP-A-85 420 115.9 et qui étaient principa­lement soit ferritiques, soit martensitiques avant d'être sujets à l'exposition à la cavitation, semble indiquer que la déforma­tion ou transformation induite par cavitation en la phase C.F.C γ , en une phase H.C. ε et/ou en de la martensite α . montrant un mâclage fin de déformation, est essentiel pour obtenir une forte résistance à la cavitation. Cette exigence à son tour implique que l'acier inoxydable selon l'invention soit principalement dans une phase austénitique γ à température ambiante.The fact that no fine tapping and a low resistance to cavitation could be observed on the steels tested in EP-A-85 420 115.9 and which were mainly either ferritic or martensitic before being subject to exposure to cavitation, seems to indicate that the deformation or transformation induced by cavitation in the CFC γ phase, in an HC ε phase and / or in martensite α. showing a fine deformation chewing, is essential to obtain a strong resistance to cavitation. This requirement in turn implies that the stainless steel according to the invention is mainly in an austenitic phase γ at room temperature.

Il est donc clair que, tout comme dans le cas de l'acier inoxydable 301, la teneur de l'acier inoxydable au cobalt selon l'invention en éléments connus comme ferritisants (Cr, Mo, Si) et austénitisants (C, N, Co, Ni, Mn) doit être adéquatement choisie et ajustée de façon à stabiliser l'austénite particulièrement dans le cas d'un refroidissement rapide, pour ainsi promouvoir une déforma­tion de la phase γ ou une transformation induite de cette phase γ en phase ε ou en martensite, la forte résistance à la cavitation des aciers selon l'invention résultant principalement de leur composition où les éléments connus pour augmenter l'énergie de faute d'empilement, à savoir, par exemple, le nickel, sont remplacés autant que possible par des éléments connus pour abaisser cette énergie de faute d'empilement tels que Co, Si, Mn et N et ainsi con­duire à un mâclage de déformation plus fin.It is therefore clear that, as in the case of 301 stainless steel, 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 γ phase or an induced transformation of this γ phase into the ε 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.

Les aciers inoxydables au cobalt selon l'invention peuvent avantageusement être utilisés pour la fabrication et la réparation de pièces ou de groupes de machines hy­drauliques, tels que des turbines, des pompes, des robinets, etc... Ils peuvent être utilisés soit comme recouvrements soudés sur de l'acier au carbone, soit comme matériaux de base, coulés ou sous forme de tôle, pour la fabrication de machines toutes faites en acier inoxydable. Ces aciers peuvent, en outre, être laminés à chaud ou à froid et être développés en fils ou électrodes de soudage pour remplacer le STELLITE-21 beaucoup plus cher utilisé pour réparer les dommages de cavitation des turbines hydrauliques.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.

On doit noter qu'aucun traitement thermique ou mécanique spécial n'est requis, dans l'état tel que coulé ou soudé, pour obtenir la meilleure résistance à la cavitation de ces aciers inoxydables austénitiques au cobalt. S'ils doivent être déformés à froid pour des besoins de mise en forme de fil ou de tôle par exemple, on doit alors leur faire subir un traitement thermique de recuit à haute température, comme pour les aciers inoxydables austénitiques standards. Leur meilleure formabilité que les alliages à base de cobalt est un autre avantage économique surtout pour la fabrication en fil de soudage.It should be noted that no special heat or mechanical treatment is required, in the state as cast or welded, to obtain the best resistance to cavitation of these austenitic stainless steels at cobalt. If they have to be cold deformed for the purposes of shaping wire or sheet for example, then they must be subjected to a heat treatment of annealing at high temperature, as for standard austenitic stainless steels. Their better formability than cobalt-based alloys is another economic advantage especially for the manufacture of welding wire.

Claims (11)

1- Acier inoxydable austénitique au cobalt ultra résistant à la cavitation érosive, caractérisé en ce que : (a) il comprend :
de 8 à 30 % en poids de Co,
de 13 à 30 % en poids de Cr,
de 0,03 % à 2,0 % en poids de C,
jusqu'à 0,3 % en poids de N,
jusqu'à 5,0 % en poids de Si,
jusqu'à 1,0 % en poids de Ni,
jusqu'à 2 % en poids de Mo, et
jusqu'à 16,0 % en poids de Mn,
le pourcentage restant étant essentiellement consti­tué de Fe, (b) il remplit au moins une des trois conditions suivantes :
- sa teneur en C est supérieure à 0,3 %,
- sa teneur en Si est supérieure à 3,0 %,
- sa teneur en Mn est supérieure à 9,0 %, et (c) sa teneur en éléments connus comme ferritisants (Cr, Mo, Si), en éléments connus comme austénitisants (C, N, Co, Ni, Mn) et, parmi ces éléments ferritisants et austéniti­sants, en éléments connus pour augmenter ou abaisser l'énergie de faute d'empilement, est adéquatement choisie et ajustée de façon à ce qu'au moins 60 % en poids de l'acier soit, à température ambiante, dans une phase cubi­que à face centrée ayant une énergie de faute d'empilement suffisamment faible pour présenter, sous l'effet de la cavitation, un mâclage fin de déformation ou pour, alter­nativement, pouvoir se transformer, sous l'effet de la cavitation, en une phase hexagonale compacte ε et/ou en de la martensite α montrant un mâclage fin de déformation. 1- Austenitic stainless steel with cobalt ultra resistant to erosive cavitation, characterized in that: (a) it includes:
from 8 to 30% by weight of Co,
from 13 to 30% by weight of Cr,
from 0.03% to 2.0% by weight of C,
up to 0.3% by weight of N,
up to 5.0% by weight of Si,
up to 1.0% by weight of Ni,
up to 2% by weight of Mo, and
up to 16.0% by weight of Mn,
the remaining percentage being essentially made up of Fe, (b) it meets at least one of the following three conditions:
- its C content is greater than 0.3%,
- its Si content is greater than 3.0%,
- its Mn content is greater than 9.0%, and (c) its content of elements known as ferritizing agents (Cr, Mo, Si), in elements known as austenitizing agents (C, N, Co, Ni, Mn) and, among these ferritating and austenitic elements, in elements known to increase or to decrease the stacking fault energy is suitably chosen and adjusted so that at least 60% by weight of the steel is, at ambient temperature, in a face-centered cubic phase having a fault energy sufficiently weak stacking to present, under the effect of cavitation, a fine deformation chewing or to, alternatively, be able to transform, under the effect of cavitation, into a compact hexagonal phase ε and / or into martensite α showing a fine deformation chewing. 2- Acier inoxydable au cobalt selon la revendication 1, caractérisé en ce qu'il comprend :
de 10 à 12 % en poids de Co,
de 16 à 18 % en poids de Cr,
de 0,4 à 0,5 % en poids de C,
de 2,5 à 3,5 % en poids de Si, et
de 4,5 % à 5,5 % en poids de Mn,
le pourcentage restant étant essentiellement consti­tué de Fe avec, le cas échéant, des traces de Mo et N.2- Cobalt stainless steel according to claim 1, characterized in that it 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 with, where appropriate, traces of Mo and N. 3- Acier inoxydable au cobalt selon la revendication 2, caractérisé en ce qu'il comprend :
environ 11,6 % en poids de Co,
environ 16,6 % en poids de Cr,
environ 0,46 % en poids de C,
environ 3,3 % en poids de Si, et
environ 5,3 % en poids de Mn,
le pourcentage restant étant essentiellement consti­tué de Fe avec, le cas échéant, des traces de Mo et N.3- Cobalt stainless steel according to claim 2, characterized in that it comprises:
about 11.6% by weight of Co,
about 16.6% by weight of Cr,
about 0.46% by weight of C,
about 3.3% by weight of Si, and
about 5.3% by weight of Mn,
the remaining percentage essentially consisting of Fe with, where appropriate, traces of Mo and N. 4- Acier inoxydable au cobalt selon la revendication 2, caractérisé en ce qu'il comprend :
environ 8 % en poids de Co,
environ 16,4 % en poids de Cr,
environ 0,41 % en poids de C,
environ 3,5 % en poids de Si, et
environ 5 % en poids de Mn,
le pourcentage restant étant essentiellement consti­tué de Fe, avec, le cas échéant, des traces de Mo et N.4- Cobalt stainless steel according to claim 2, characterized in that it comprises:
about 8% by weight of Co,
about 16.4% by weight of Cr,
about 0.41% by weight of C,
about 3.5% by weight of Si, and
about 5% by weight of Mn,
the remaining percentage consisting essentially of Fe, with, where appropriate, traces of Mo and N. 5- Acier inoxydable au cobalt selon la revendica­tion 2, caractérisé en ce qu'il comprend :
environ 8 % en poids de Co,
environ 16 % en poids de Cr,
environ 0,4 % en poids de C,
environ 3 % en poids de Si, et
environ 5 % en poids de Mn,
le pourcentage restant étant essentiellement cons­titué de Fe avec, le cas échéant, des traces de Mo et N.5- Cobalt stainless steel according to claim 2, characterized in that it comprises:
about 8% by weight of Co,
about 16% by weight of Cr,
about 0.4% by weight of C,
about 3% by weight of Si, and
about 5% by weight of Mn,
the remaining percentage essentially consisting of Fe with, where appropriate, traces of Mo and N. 6- Application des aciers inoxydables austénitiques au cobalt ultra résistant à la cavitation érosive, tels que définis dans la revendication 1 à la réalisation ou au revêtement de pièces d'acier inoxydable au cobalt pour la fabrication ou la réparation de machines hydrauliques.6- Application of austenitic stainless steels with cobalt ultra resistant to erosive cavitation, as defined in claim 1 for the production or coating of stainless steel parts with cobalt for the manufacture or repair of hydraulic machines. 7- Application des aciers inoxydables austénitiques au cobalt ultra résistant à la cavitation érosive, tels que définis dans la revendication 2 à la réalisation ou au revêtement de pièces d'acier inoxydable au cobalt pour la fabrication ou la réparation de machines hydrauliques.7- Application of austenitic stainless steels with cobalt ultra resistant to erosive cavitation, as defined in claim 2 to the production or coating of stainless steel parts with cobalt for the manufacture or repair of hydraulic machines. 8- Application des aciers inoxydables austénitiques au cobalt ultra résistant à la cavitation érosive, tels que définis dans la revendication 4 ou la revendication 5 à la réalisation ou au revêtement de pièces d'acier inoxydable au cobalt pour la fabrication ou la réparation de machines hydrauliques.8- Application of austenitic stainless steels with cobalt ultra resistant to erosive cavitation, as defined in claim 4 or claim 5 in the production or coating of stainless steel parts with cobalt for the manufacture or repair of hydraulic machines . 9- Application des aciers inoxydables austénitiques au cobalt ultra résistant à la cavitation érosive, tels que définis dans la revendication 1, à la réalisation d'élec­trodes ou fils de soudage pour la fabrication ou la répara­tion de machines hydrauliques.9- Application of austenitic stainless steels with cobalt ultra resistant to erosive cavitation, as defined in claim 1, to the production of electrodes or welding wires for the manufacture or repair of hydraulic machines. 10- Application des aciers inoxydables austénitiques au cobalt ultra résistant à la cavitation érosive, tels que définis dans la revendication 2, à la réalisation d'élec­trodes ou fils de soudage pour la fabrication ou la répara­tion de machines hydrauliques.10- Application of austenitic stainless steels with cobalt ultra resistant to erosive cavitation, as defined in claim 2, to the production of electrodes or welding wires for the manufacture or repair of hydraulic machines. 11- Application des aciers inoxydables austénitiques au cobalt ultra résistant à la cavitation érosive, tels que définis dans la revendication 3, à la réalisation d'élec­trodes ou fils de soudage pour la fabrication ou la réparation de machines hydrauliques.11- Application of austenitic stainless steels with cobalt ultra resistant to erosive cavitation, as defined in claim 3, to the production of electrodes or welding wires for the manufacture or repair of hydraulic machines.
EP86420305A 1986-06-30 1986-12-18 Cobalt-containing austenitic stainless steel, highly resistant against impingement attack Expired - Lifetime EP0250690B1 (en)

Applications Claiming Priority (2)

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CA000512811A CA1269548A (en) 1986-06-30 1986-06-30 Austenitic stainless steel allied with cobalt and highly resistant to erosive cavitation
CA512811 1986-06-30

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EP (1) EP0250690B1 (en)
JP (1) JPS6311653A (en)
AU (1) AU589281B2 (en)
CA (1) CA1269548A (en)
CH (1) CH674522A5 (en)
DE (1) DE3675547D1 (en)

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WO2022111908A1 (en) * 2020-11-24 2022-06-02 Otto-Von-Guericke-Universität Magdeburg Martensitic stainless steel alloy having optimized hardness and corrosion resistance

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DE3901028A1 (en) * 1989-01-14 1990-07-19 Bayer Ag NON-RESISTANT MOLDING AND CASTING MATERIALS AND WELDING ADDITIVES FOR BUILDING COMPONENTS ASSOCIATED WITH HOT, CONCENTRATED SWISS ACIDS
DE69410555T2 (en) * 1993-09-03 1999-01-28 Sanyo Special Alloys, Ltd., Tochigi Non-magnetic iron alloy with excellent corrosion resistance and machinability
US5514329A (en) * 1994-06-27 1996-05-07 Ingersoll-Dresser Pump Company Cavitation resistant fluid impellers and method for making same
US5514328A (en) * 1995-05-12 1996-05-07 Stoody Deloro Stellite, Inc. Cavitation erosion resistent steel
FR2761006B1 (en) * 1997-03-21 1999-04-30 Usinor WHEEL FOR MOTOR VEHICLE
US10281903B2 (en) 2015-07-27 2019-05-07 Hitachi, Ltd. Process for design and manufacture of cavitation erosion resistant components
CN113817969B (en) * 2020-06-19 2022-09-27 香港大学 High-strength super-corrosion-resistant non-magnetic stainless steel and preparation method thereof

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CH327362A (en) * 1952-09-10 1958-01-31 Schoeller Bleckmann Stahlwerke Object that is resistant to the oxides present in the combustion residues of liquid fuels at high temperatures
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EP0250690B1 (en) 1990-11-07
AU7494587A (en) 1988-01-07
US4751046A (en) 1988-06-14
JPS6311653A (en) 1988-01-19
CH674522A5 (en) 1990-06-15
DE3675547D1 (en) 1990-12-13
CA1269548A (en) 1990-05-29
AU589281B2 (en) 1989-10-05

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