EP0164678B1 - Steel for the manufacture of large forgings and process for the treatment of this steel - Google Patents

Steel for the manufacture of large forgings and process for the treatment of this steel Download PDF

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EP0164678B1
EP0164678B1 EP85106869A EP85106869A EP0164678B1 EP 0164678 B1 EP0164678 B1 EP 0164678B1 EP 85106869 A EP85106869 A EP 85106869A EP 85106869 A EP85106869 A EP 85106869A EP 0164678 B1 EP0164678 B1 EP 0164678B1
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steel
range
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EP0164678A1 (en
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André Coulon
Chantal Loier
Jean-Pierre Badeau
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Alstom SA
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Alstom SA
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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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/78—Combined heat-treatments not provided for above

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  • the present invention relates to a steel for the manufacture of large forged parts in particular of turbine rotors.
  • the steel according to the invention makes it possible to improve the mechanical properties both in the ambient and in the hot and can be used with steam at 600 ° C.
  • the invention relates to a composition of highly alloyed steel for large forgings for which the addition of Niobium, usual for a steel having hot high resistance to creep is limited correlatively with the addition of nitrogen, the whole elements of addition which must achieve a balance in view avoid the presence of residual ferrite in the structure.
  • an "unbalanced" composition can cause an excess of ferrite in the structure of large parts. We manage to exclude it by carefully dosing the contents of additives.
  • a fairly precise method for carrying out this assay is that of "equivalent chromium and nickel" allowing, by means of coefficients assigned to each element, to assess its aptitude for the formation of ferrite (element alphagenes) and the formation of austenite ( gamma elements).
  • alphagenic elements we find Si, Or, Mo, H, V, Nb, Ti, AI.
  • the gamma elements are C, Mn, Ni, Co and Cu.
  • An alloy composition in accordance with the invention will have, on the basis of the above, a chromium equivalent of between 14.5 and 15.5 and more advantageously between 14.7 and 15.3 a nickel equivalent of between 9 and 10, 2, the optimum ratio between the chromium equivalent and the nickel equivalent should be between 1.49 and 1.65.
  • FIG. 1 represents a diagram where the chrome equivalent is plotted on the abscissa and the nickel equivalent is plotted on the ordinate.
  • the final structures obtained appear in FIG. 1, the straight lines plotted conventionally indicating the passage from one structure to another (A being austenite, M being martensite and 8 F being delta-ferrite).
  • the rectangle a b c d represents the chemical analysis zone limited by the extremes of the conventionally used compositions (7.25 ⁇ Ni eq ⁇ 11.72 and 13.12 ⁇ Cr eq ⁇ 16.65).
  • the optimum is obtained inside the small rectangle efgh (see figure 2) corresponding to 9 ⁇ Ni eq ⁇ 10.2 and 14.5 ⁇ Or eq ⁇ 15.5 in the area ifjkh 1 of this small rectangle between the two lines D and D 'given by the ratio Gold eq / Ni eq equal to 1.49 and 1.65 according to the invention.
  • the part in the alloy according to the invention is subjected after forging to a determined heat treatment.
  • the description which is given below relates to a forged part with a diameter of 1400 mm with a weight of approximately 30 tonnes.
  • this income may include several stages: a first temperature rise up to approximately 560 ° C (540 - 600 ° C) with maintenance for at least 25 h (up to 48 h).
  • a second tempering is carried out to complete the transformation of the possibly remaining austenite into martensite and give the desired characteristics to the part. This treatment is done at a temperature between 650 and 710 ° C (the optimum being around 685 ° C) for a time similar to the first tempering.
  • an expansion treatment will be carried out at a temperature approximately 50 ° C lower than the temperature of the second tempering, with maintenance lasting 25 to 48 hours.
  • the 5d elongations at break are between 13.5 and 21%
  • the necking at break is between 41 and 70%.

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Abstract

The present invention provides a steel containing, by mass: from 0.16% to 0.22% carbon (C) less than 0.3% silicon (Si) less than 0.5% manganese (Mn) from 0.6% to 0.9% nickel (Ni) from 10.7% to 12.3% chromium (Cr) from 0.8% to 1.1% molybdenum (Mo) from 0.2% to 0.35% vanadium (V) from 0.07% to 0.20% niobium (Nb) from 0.05% to 0.11% nitrogen (N2) less than 0.008% boron (B) and not more than the following residual percentages by mass: 0.020% sulfur, 0.020% phosphorous, 0.025% cobalt, 0.010% aluminum, 0.02% titanium, 0.02% tin, 0.10% copper, 0.015% tungsten, 0.020% arsenic, and 0.0025% antimony; the remainder of the alloy being iron; said steel having a nickel equivalent calculated using the formula: Ni eq=30C+0.5Mn+2Ni+25N2+40B, lying in the range 9 to 10.2; and a chromium equivalent calculated using the formula: Cr eq=Cr+2Si+1.5Mo+5V+1.75Nb lying in the range 14.5 to 15.5; the ratio between the chromium equivalent and the nickel equivalent lying in the range 1.49 to 1.65.

Description

La présente invention a trait à un acier pour la fabrication de grosses pieces forgées en particulier de rotors de turbine.The present invention relates to a steel for the manufacture of large forged parts in particular of turbine rotors.

Les rotors de turbine classiques en acier Cr - Mo - V permettent des températures de vapeur de l'ordre de 550° C.Conventional turbine rotors in Cr - Mo - V steel allow steam temperatures of the order of 550 ° C.

Pour permettre une utilisation avec de la vapeur à plus haute température tout en conservant de bonnes propriétés mécaniques on a utilisé des aciers fortement alliés au chrome comme décrit par exemple dans le document FR-A-1 407 452.To allow use with steam at higher temperature while retaining good mechanical properties, steels highly alloyed with chromium were used as described for example in document FR-A-1 407 452.

Dans ce document on décrit un domaie large mnpq (voir figure 2). L'acier selon l'invention permet d'améliorer les propriétés mecaniques tant à l'ambiante qu'à chaud et peut être utilisé avec de la vapeur à 600° C.In this document we describe a large mnpq domain (see figure 2). The steel according to the invention makes it possible to improve the mechanical properties both in the ambient and in the hot and can be used with steam at 600 ° C.

En particulier, la résilience se trouve améliorée ainsi que la résistance au fluage et trois compositions préférentielles sont décrites avec:

  • (Ni eq 7,71; Cr eq 14,27)
  • (Ni eq 8,78; Cr eq 13,5)
  • (Ni eq 7,76; Cr eq 13 94)
  • L'acier selon l'invention permet d'améliorer les propriétés mécaniques tant à l'ambiante qu'à chaud et peut être utilisé avec de la vapeur à 600° C.
  • L'acier selon l'invention contient en masse
  • de 0,16 à 0,22 % de carbone (C)
  • moins de 0,3 % de silicium (Si)
  • moins de 0,5 % de manganèse (Mn)
  • de 0,6 à 0,9 % de nickel (Ni)
  • de 10,7 à 12,3 % de chrome (Cr)
  • de 0,8 à 1,1 % de molybdène (Mo)
  • de 0,22 à 0,35 % de vanadium (V)
  • de 0,07 à 0,20 % de niobium (Ni)
  • de 0,05 à 0,11 % d'azote (N2)
  • moins de 0,008 % de bore (B)
  • et des quantités résiduelles maximales (en % en masse)
  • 0, 020 pour le soufre, 0,020 pour le phosphore, 0, 025 pour le cobalt,
  • 0,010 pour l'aluminium, 0,02 pour le titane, 0,02 pour l'étain, 0, 10 pour le cuivre, 0, 015 pour le tungstène, 0,020 pour l'arsenic et 0, 0025 pour l'antimoine, le complément étant en fer,
  • ledit acier ayant un nickel équivalent calculé selon la formule:
    • Nieq=30 C + 0,5Mn+2 Ni+25 N2+40 B,
    • compris entre 9 et 10,2
    • et un chrome équivalent calculé selon la formule:
    • Creq = Cr + 2 Si + 1,5 Mo + 5 V + 1,75 Nb
    • compris entre 14,5 et 15,5
    • le rapport entre le Cr eq et le Ni eq étant compris entre 1,49 et 1,65.
In particular, the resilience is improved as well as the creep resistance and three preferred compositions are described with:
  • (Ni eq 7.71; Cr eq 14.27)
  • (Ni eq 8.78; Cr eq 13.5)
  • (Ni eq 7.76; Cr eq 13 94)
  • The steel according to the invention makes it possible to improve the mechanical properties both at ambient and hot and can be used with steam at 600 ° C.
  • The steel according to the invention contains in mass
  • 0.16 to 0.22% carbon (C)
  • less than 0.3% silicon (Si)
  • less than 0.5% manganese (Mn)
  • 0.6 to 0.9% nickel (Ni)
  • from 10.7 to 12.3% chromium (Cr)
  • 0.8 to 1.1% molybdenum (Mo)
  • from 0.22 to 0.35% vanadium (V)
  • from 0.07 to 0.20% niobium (Ni)
  • from 0.05 to 0.11% nitrogen (N 2 )
  • less than 0.008% boron (B)
  • and maximum residual quantities (in% by mass)
  • 0.020 for sulfur, 0.020 for phosphorus, 0.025 for cobalt,
  • 0.010 for aluminum, 0.02 for titanium, 0.02 for tin, 0, 10 for copper, 0.015 for tungsten, 0.020 for arsenic and 0.0025 for antimony, complement being of iron,
  • said steel having an equivalent nickel calculated according to the formula:
    • Nieq = 30 C + 0.5Mn + 2 Ni + 25 N 2 +40 B,
    • between 9 and 10.2
    • and an equivalent chromium calculated according to the formula:
    • Creq = Cr + 2 Si + 1.5 Mo + 5 V + 1.75 Nb
    • between 14.5 and 15.5
    • the ratio between Cr eq and Ni eq being between 1.49 and 1.65.

Pour obtenir de bonnes propriétés mécaniques on soumet après forgeage les pièces en acier selon l'invention à un traitement comportant les étapes suivantes:

  • - homogénéisation de la pièce réalisée à une température comprise entre 1130° et 1170°C pendant un temps suffisant pour parachever la mise en solution suivie d'un refroidissement lent au four
  • - austénitisation entre 1050°C et 1130°C suivie d'une trempe ramenant la température à 250° C
  • - revenu lui donnant les caractéristiques finales.
To obtain good mechanical properties, the steel parts according to the invention are subjected after forging to a treatment comprising the following stages:
  • - homogenization of the part produced at a temperature between 1130 ° and 1170 ° C for a time sufficient to complete the dissolution followed by slow cooling in the oven
  • - austenitization between 1050 ° C and 1130 ° C followed by quenching reducing the temperature to 250 ° C
  • - income giving it the final characteristics.

Selon une réalisation préférentielle le revenu comporte les étapes suivantes:

  • - première montée en température jusqu'à une température θ 1 comprise entre 540 et 600°C, de préférence 500°C, avec maintien pendant un temps t au moins égal a 25 h,
  • - refroidissement lent jusqu'à l'ambiante,
  • - seconde montée en température jusqu'à une température 82 comprise entre 850° C et 710°C, de préférence égale à 685° C, avec maintien pendant le temps t moins égal à 25 h,
  • - refroidissement lent jusqu'à l'ambiante,
    et est suivi d'un traitement de stabilisation à une température 83 = 82 -θ0 maintenu pendant un temps au moins égal à 25 h avec θ0 compris entre 30° et 50° C.
According to a preferred embodiment, the income comprises the following stages:
  • first temperature rise to a temperature θ 1 of between 540 and 600 ° C, preferably 500 ° C, with maintenance for a time t at least equal to 25 h,
  • - slow cooling to ambient,
  • - second temperature rise to a temperature 8 2 of between 850 ° C and 710 ° C, preferably equal to 685 ° C, with maintenance for the time t less than 25 h,
  • - slow cooling to ambient,
    and is followed by a stabilization treatment at a temperature 8 3 = 8 2 -θ 0 maintained for a time at least equal to 25 h with θ 0 between 30 ° and 50 ° C.

La présente invention sera mieux comprise à la lumière de la description qui va suivre dans laquelle:

  • - la figure 1 représente dans le système d'axes Cr eq, Ni eq la place du domaine de composition des aciers selon l'invention,
  • - la figure 2 représente dans le même système d'axe le domaine des aciers selon l'invention.
The present invention will be better understood in the light of the description which follows in which:
  • FIG. 1 represents in the axis system Cr eq, Ni eq the place of the field of composition of the steels according to the invention,
  • - Figure 2 shows in the same axis system the field of steels according to the invention.

L'invention concerne une composition d'acier fortement allié pour grosses pièces de forge pour lesquelles l'addition de Niobium, habituelle pour un acier présentant à chaud une résistance élevée au fluage est limitée corrélativement avec l'addition d'azote, l'ensemble des éléments d'addition devant réaliser un équilibre en vue d'éviter la présence de ferrite résiduelle dans la structure.The invention relates to a composition of highly alloyed steel for large forgings for which the addition of Niobium, usual for a steel having hot high resistance to creep is limited correlatively with the addition of nitrogen, the whole elements of addition which must achieve a balance in view avoid the presence of residual ferrite in the structure.

En effet il est notoire que les aciers à 12 % de chrome (10 - 14 %) avec de fortes additions de niobium (0,2 à 0,5 %) en plus du vanadium ont de bonnes propriétés vis-à-vis du fluage. Mais dans le cas de grosses pièces forgées la présence excessive de carbures de niobium à coeur peut entraîner des caractéristiques insuffisantes de la ductilité dans des directions perpendiculaires au sens de corroyage. La nécessaire réduction de la teneur en niobium peut correlativement affecter les proprietés à chaud ce qui n'est pas le but recherché. Il importe donc de limiter au juste nécessaire les teneurs conjointes de niobium et d'azote pour obtenir dans toutes les directions une ductilité acceptable tout en cherchant à mettre totalement en solution les carbonitrures formés lors du traitement thermique. Le choix de la température d'austénitisation ainsi que le temps de maintien, seront ajustés pour un diamètre donné de pièce forgée, à la teneur précise en niobium dans la composition de l'acier de façon à utiliser toute l'efficacité de cette addition.Indeed it is known that steels with 12% chromium (10 - 14%) with strong additions of niobium (0.2 to 0.5%) in addition to vanadium have good properties with regard to creep . However, in the case of large forgings, the excessive presence of niobium carbides in the core can lead to insufficient characteristics of the ductility in directions perpendicular to the direction of working. The necessary reduction of the niobium content can correlatively affect the hot properties which is not the aim. It is therefore important to limit to the necessary minimum the joint contents of niobium and of nitrogen in order to obtain in all directions an acceptable ductility while seeking to completely dissolve the carbonitrides formed during the heat treatment. The choice of the austenitization temperature as well as the holding time, will be adjusted for a given diameter of forged part, to the precise niobium content in the composition of the steel so as to use all the efficiency of this addition.

D'autre part une composition "mal équilibrée" peut entraîner un excès de ferrite dans la structure de grosses pièces. On parvient à l'exclure en dosant soigneusement les teneurs en éléments d'addition. Une méthode assez précise pour réaliser ce dosage est celle des "chrome et nickel équivalents" permettant à l'aide de coefficients affectés à chaque élément d'apprécier son aptitude à la formation de ferrite (élément alphagènes) et à la formation d'austénite (éléments gammagènes). Parmi les éléments alphagènes on trouve Si, Or, Mo, H, V, Nb, Ti, AI. Parmi les éléments gammagènes on trouve C, Mn, Ni, Co et Cu.On the other hand, an "unbalanced" composition can cause an excess of ferrite in the structure of large parts. We manage to exclude it by carefully dosing the contents of additives. A fairly precise method for carrying out this assay is that of "equivalent chromium and nickel" allowing, by means of coefficients assigned to each element, to assess its aptitude for the formation of ferrite (element alphagenes) and the formation of austenite ( gamma elements). Among the alphagenic elements we find Si, Or, Mo, H, V, Nb, Ti, AI. Among the gamma elements are C, Mn, Ni, Co and Cu.

La littérature existante fournit un choix de formules permettant le calcul des équivalents chrome et nickel. On peut citer les travaux de M. SCHNEIDER ou de MM. RICKETT, WHITE, WALTON et BUTLER. Le tableau ci-après donne une indication des coefficients d'aptitude à la formation de ferrite ou d'austénite pour chaque élément d'addition.

Figure imgb0001
The existing literature provides a choice of formulas allowing the calculation of chromium and nickel equivalents. We can cite the works of M. SCHNEIDER or MM. RICKETT, WHITE, WALTON and BUTLER. The table below gives an indication of the coefficients of aptitude for the formation of ferrite or austenite for each addition element.
Figure imgb0001

Les estimations se font en calculant les équations suivantes dans lesquelles les symboles correspondent en masse de l'élément dans l'acier:

  • Nickel équivalent = 30 C + 0,5 Mn + 2 Ni + 25 N2 + 40 B
  • Chrome équivalent = Cr + 2 Si + 1,5 Mo + 5 V + 1,75 Nb
The estimates are made by calculating the following equations in which the symbols correspond in mass to the element in the steel:
  • Nickel equivalent = 30 C + 0.5 Mn + 2 Ni + 25 N 2 + 40 B
  • Chrome equivalent = Cr + 2 Si + 1.5 Mo + 5 V + 1.75 Nb

Une composition d'alliage conforme à l'invention aura, sur la base ce qui précède un équivalent chrome compris entre 14,5 et 15, 5 et plus avantageusement entre 14,7 et 15,3 un équivalent nickel compris entre 9 et 10,2, le rapport optimum entre l'équivalent chrome et l'équivalent nickel devant être compris entre 1,49 et 1,65.An alloy composition in accordance with the invention will have, on the basis of the above, a chromium equivalent of between 14.5 and 15.5 and more advantageously between 14.7 and 15.3 a nickel equivalent of between 9 and 10, 2, the optimum ratio between the chromium equivalent and the nickel equivalent should be between 1.49 and 1.65.

La figure 1 représente un diagramme où l'équivalent chrome est porté en abscisse et l'équivalent nickel est porté en ordonnée. Les structures finales obtenues apparaissent sur la figure 1, les droites tracées indiquant conventionnellement le passage d'une structure à une autre (A étant l'austénite, M la martensite et 8 F la delta- ferrite). Le rectangle a b c d représente la zone d'analyse chimique limitée par les extrêmes des compositions conventionellement utilisées (7,25 < Ni eq < 11,72 et 13,12 < Cr eq < 16,65).FIG. 1 represents a diagram where the chrome equivalent is plotted on the abscissa and the nickel equivalent is plotted on the ordinate. The final structures obtained appear in FIG. 1, the straight lines plotted conventionally indicating the passage from one structure to another (A being austenite, M being martensite and 8 F being delta-ferrite). The rectangle a b c d represents the chemical analysis zone limited by the extremes of the conventionally used compositions (7.25 <Ni eq <11.72 and 13.12 <Cr eq <16.65).

L'optimum est obtenu à l'intérieur du petit rectangle e f g h (voir figure 2) correspondant à 9 < Ni eq < 10,2 et 14,5 < Or eq < 15,5 dans la zone i f j k h 1 de ce petit rectangle comprise entre les deux droites D et D' données par le rapport Or éq/Ni éq égal à 1,49 et 1,65 selon l'invention.The optimum is obtained inside the small rectangle efgh (see figure 2) corresponding to 9 <Ni eq <10.2 and 14.5 <Or eq <15.5 in the area ifjkh 1 of this small rectangle between the two lines D and D 'given by the ratio Gold eq / Ni eq equal to 1.49 and 1.65 according to the invention.

Au-dessus de la droite D on peut trouver de l'austénite résiduelle. En dessous de la droite D' on peut trouver de la ferrite résiduelle. Dans la i f j k h 1 on a de la martensite exempte d'austénite et/ou de ferrite résiduelle.Above the right D we can find residual austenite. Below the right You can find residual ferrite. In i f j k h 1 we have martensite free of austenite and / or residual ferrite.

Sur la figure 2 on a indiqué en pointillé le rectangle mnpq donnant les limites des compositions décrites dans le document FR-A-1 407 452 ainsi que les trois compositions préférentielles décrites dans ce document:

  • 10: (Ni eq 7,71; Cr eq 14,27)
  • 11: (Ni eq 8,78; Cr eq 13,5)
  • 12: (Ni eq 7,76; Cr eq 13,94)
In FIG. 2, the dotted line shows the mnpq rectangle giving the limits of the compositions described in document FR-A-1 407 452 as well as the three preferred compositions described in this document:
  • 10: (Ni eq 7.71; Cr eq 14.27)
  • 11: (Ni eq 8.78; Cr eq 13.5)
  • 12: (Ni eq 7.76; Cr eq 13.94)

Pour obtenir les caractéristiques à l'ambiante et aux températures élevées, on soumet après forgeage la pièce dans l'alliage suivant l'invention à un traitement thermique déterminé. La description qui est faite ci-après concerne une pièce forgée d'un diamètre de 1400 mm d'un poids de 30 tonnes environ.To obtain the characteristics at room temperature and at high temperatures, the part in the alloy according to the invention is subjected after forging to a determined heat treatment. The description which is given below relates to a forged part with a diameter of 1400 mm with a weight of approximately 30 tonnes.

Une homogénéisation de la pièce réalisée à une température comprise entre 1130 et 1170°C pendant un temps suffisant pour parachever la mise en solution est suivie d'un refroidissement au four jusqu'à 700 C environ. Une austénitisation entre 1050 et 1130 °C est suivie d'une trempe (huile, brouillard d'eau ou air pulsé) de façon à ce que la vitesse de refroidissement au coeur de la pièce ne soit pas inférieure à 40-C. h-1: il convient en effet d'éviter une transformation perlitique qui intervient à des vitesses faibles de refroidissement. La température de la pièce est ramenée à une température inférieure à 250° C, la transformation martensitique étant complète à cette température.Homogenization of the part carried out at a temperature between 1130 and 1170 ° C for a time sufficient to complete the dissolution is followed by cooling in the oven to approximately 700 C. Austenitization between 1050 and 1130 ° C is followed by quenching (oil, water mist or forced air) so that the cooling rate at the heart of the room is not less than 40-C. h-1: pearlitic transformation which occurs at low cooling rates should indeed be avoided. The room temperature is brought back to a temperature below 250 ° C, the martensitic transformation being complete at this temperature.

Ensuite la pièce subit un revenu qui lui donnera les caractéristiques finales. En fait ce revenu pourra comporter plusieurs stades: une première montée en température jusqu'à 560°C environ (540 - 600° C) avec maintien pendant 25 h au moins (jusqu'à 48 h). Après refroidissement lent jusqu'à l'ambiante, on procède à un deuxième revenu pour parachever la transformation de l'austénite éventuellement restante, en martensite et donner les caractéristiques désirées à la pièce. Ce traitement se fait à une température comprise entre 650 et 710°C (l'optimum se situant vers 685°C) pendant un temps similaire au premier revenu. Après in refroidissement au four jusqu'à l'ambiante, on procédera à un traitement de détente à une température inférieure de 50° C environ à la température du deuxième revenu avec un maintien de 25 à 48 h.Then the coin undergoes an income which will give it the final characteristics. In fact, this income may include several stages: a first temperature rise up to approximately 560 ° C (540 - 600 ° C) with maintenance for at least 25 h (up to 48 h). After slow cooling to room temperature, a second tempering is carried out to complete the transformation of the possibly remaining austenite into martensite and give the desired characteristics to the part. This treatment is done at a temperature between 650 and 710 ° C (the optimum being around 685 ° C) for a time similar to the first tempering. After cooling in the oven to room temperature, an expansion treatment will be carried out at a temperature approximately 50 ° C lower than the temperature of the second tempering, with maintenance lasting 25 to 48 hours.

On a effectué de nombreux essais avec plusieurs compositions dont les compositions suivantes:

Figure imgb0002
Figure imgb0003
Les traitement thermiques ont été les suivants:
Figure imgb0004
Les résultats de rupture instantanée à 550° C sont pour ces aciers:
Figure imgb0005
 Numerous tests have been carried out with several compositions, including the following compositions:
Figure imgb0002
Figure imgb0003
 The heat treatments were as follows:
Figure imgb0004
 The instant failure results at 550 ° C are for these steels:
Figure imgb0005

Les essais de fluage - extrapolation Larson et Miller à 550°C (paramètre TK (25 + log t) 10-3)

  • 104 h : 282 MPa ± 28
  • 105 h: 185 MPa ± 14
Creep tests - Larson and Miller extrapolation at 550 ° C (parameter TK (25 + log t) 10- 3 )
  • 10 4 h: 282 MPa ± 28
  • 10 5 h: 185 MPa ± 14

Les allongements 5d à rupture sont compris entre 13,5 et 21 %The 5d elongations at break are between 13.5 and 21%

Les strictions à rupture sont comprises entre 41 et 70 %.The necking at break is between 41 and 70%.

Claims (8)

1. A steel containing, by mass:
from 0,16 % to 0,22 % carbon (C)
less than 0,3 % silicon (Si)
less than 0,5 % manganese (Mn)
from 0,6 % to 0,9 % nickel (Ni)
from 10,7 % to 12,3 % chromium (Cr)
from 0,8 % to 1,1 % molybdenum (Mo)
from 0,22 % to 0,35 % vanadium (V)
from 0,07 % to 0,20 % niobium (Mb)
from 0,05 % to 0,11 % nitrogen (N2)
less than 0,008 % boron (B)
and not more than the following residual percentages by mass: 0,020 % sulfur, 0,020 % phosphorus, 0,025 % cobalt, 0,010 % aluminum, 0,02 % titanium, 0,02 % tin, 0,10 % copper, 0,015 % tungsten, 0,020 % arsenic, and 0,0025 % antimony; the remainder of the alloy being iron;
said steel having a nickel equivalent calculated using the formula:
Ni eq = 30C + 0,5 Mn + 2 Ni + 25 N + 40 B,
lying in the range 9 to 10,2;
and a chromium equivalent calculated using the formula: Cr eq = Cr + 2 Si + 1,5 Mo + 5 V + 1,75 Nb
lying in the range 14,5 to 15,5;
the ratio between the chromium equivalent and the the nickel equivalent lying in the range 1,49 to 1,65.
2. A steel according to claim 1, characterized in that the chromium equivalent is in the range 14,7 to 15,3.
3. A steel according to claim 1, characterized in that it contains less than 0,1 % by weight of silicon.
4. A steel according to one of the preceding claims, characterized in that it contains less than 0,3 % of manganese.
5. A steel according to one of the preceding claims, characterized in that it contains 0,005 % boron.
6. A method of heat treating a part made by forging steel according to claim 1, characterized in that the method comprises the following steps:
- the part is homogenized at a temperature lying between 1130° C and 1170° C for sufficient time to complete putting into solution; followed by slow cooling in the oven down to about 700°C,
- the part is austenitized between 1050°C and 1130°C followed by quenching down to a temperature of 250° C; and
- tempering to obtain the final characteristics.
7. A method according to claim 6, characterized in that the tempering operation comprises the following steps:
- a first temperature rise to a temperature θ1lying between 540°C and 600° C, and preferably 560° C, and maintaining said temperature for a period t of not less than 25 h;
- slow cooling to ambient temperature;
- a second temperature rise up to a temperature θ2 lying between 650°C and 710°C, and preferably equal to 685°C, and maintaining said temperature for a period t; and
- slow cooling down to ambient temperature.
8. A method according to claim 7, characterized in that tempering is followed by a stabilization treatment at a temperature 83 = 82 - θ0 maintained for a period of time not less than 25 h with 80 lying in the range between 30° C to 50° C.
EP85106869A 1984-06-05 1985-06-04 Steel for the manufacture of large forgings and process for the treatment of this steel Expired EP0164678B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT85106869T ATE42347T1 (en) 1984-06-05 1985-06-04 STEEL FOR THE PRODUCTION OF LARGE FORGINGS AND METHOD OF TREATMENT OF SUCH STEEL.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8408785A FR2565251B1 (en) 1984-06-05 1984-06-05 STEEL FOR THE MANUFACTURE OF LARGE FORGED PARTS AND PROCESS FOR TREATING THE SAME
FR8408785 1984-06-05

Publications (2)

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EP0164678A1 EP0164678A1 (en) 1985-12-18
EP0164678B1 true EP0164678B1 (en) 1989-04-19

Family

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Application Number Title Priority Date Filing Date
EP85106869A Expired EP0164678B1 (en) 1984-06-05 1985-06-04 Steel for the manufacture of large forgings and process for the treatment of this steel

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EP (1) EP0164678B1 (en)
JP (1) JPS61566A (en)
KR (1) KR930003604B1 (en)
AT (1) ATE42347T1 (en)
CS (1) CS274262B2 (en)
DE (1) DE3569576D1 (en)
FR (1) FR2565251B1 (en)

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JPS62222027A (en) * 1986-03-25 1987-09-30 Nippon Chiyuutankou Kk Manufacture of heat resisting rotor
JPH0621323B2 (en) * 1989-03-06 1994-03-23 住友金属工業株式会社 High strength and high chrome steel with excellent corrosion resistance and oxidation resistance
SE9002276D0 (en) * 1990-06-28 1990-06-28 Abb Powdermet Ab SAFETY MANUFACTURED FULLY THROTTLE CARMETS OF HEATHOLD SOLID MARTENSITIC CR STEEL
FR2746333B1 (en) * 1996-03-22 1998-04-24 Usinor Sacilor METHOD FOR CONTINUOUSLY CASTING A AUSTENITIC STAINLESS STEEL STRIP ON OR BETWEEN TWO MOBILE WALLS WITH SURFACES PROVIDED WITH PITCHES, AND CASTING INSTALLATION FOR IMPLEMENTING SAME
KR20040012227A (en) * 2002-08-01 2004-02-11 서명원 a operation and suction device of sewing machine
US7591909B2 (en) * 2007-08-23 2009-09-22 Transportation Technology Center, Inc. Railroad wheel steels having improved resistance to rolling contact fatigue
KR101444750B1 (en) * 2012-08-31 2014-09-26 한국원자력연구원 the Ni-Cr-Mo low alloy steel improved resistance of temper embrittleness and the manufacturing method thereof
CN103774061B (en) * 2014-01-07 2015-11-18 无锡市派克重型铸锻有限公司 Leaf joint forging and manufacture craft thereof

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Publication number Priority date Publication date Assignee Title
GB833240A (en) * 1956-07-18 1960-04-21 Firth Vickers Stainless Steels Ltd Improvements relating to ferritic alloy steels
FR1407452A (en) * 1964-09-10 1965-07-30 Gen Electric Alloy for the manufacture of large forgings with good properties at room temperature and at high temperature
US3767390A (en) * 1972-02-01 1973-10-23 Allegheny Ludlum Ind Inc Martensitic stainless steel for high temperature applications
JPS5226311A (en) * 1975-08-26 1977-02-26 Mitsubishi Heavy Ind Ltd High-chrome steel for high temperature parts
JPS57123964A (en) * 1981-01-26 1982-08-02 Toshiba Corp Heat resistant 12% cr steel
JPS5837159A (en) * 1981-08-26 1983-03-04 Hitachi Ltd Heat resistant martensite steel
JPS58110661A (en) * 1981-12-25 1983-07-01 Hitachi Ltd Heat resistant steel

Also Published As

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US4689095A (en) 1987-08-25
KR930003604B1 (en) 1993-05-08
DE3569576D1 (en) 1989-05-24
KR860000400A (en) 1986-01-28
FR2565251A1 (en) 1985-12-06
ATE42347T1 (en) 1989-05-15
FR2565251B1 (en) 1987-12-31
CS274262B2 (en) 1991-04-11
JPS61566A (en) 1986-01-06
CS402885A2 (en) 1990-09-12
EP0164678A1 (en) 1985-12-18

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