EP1312691A1 - Austenitic heat resistant alloy with improved castability and transformation, method of making steel slabs and wires - Google Patents

Abstract

An austenitic alloy with improved hot casting and transformation behavior has a defined composition, which also satisfies two relationships between its component elements. <??>An austenitic alloy with improved hot casting and transformation behavior has a defined composition, which also satisfies the two following relationships between its component elements: <??>(a) in relation with the mode of solidification: <??>(b) balance a = eq Nia - 0.5 x eq Cra is less than 3.6 where: <??>(c) eq Cra = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al = 4 x V and where:; <??>(d) eq Nia = Ni + 22 x C + 0.5 x Cu; <??>(e) in relation to the residual ferrite content; <??>(f) balance b = eq Nib - 2 x eq Crb is greater than - 41 where; <??>(g) eq Crb = Cr + 0.7 x Si + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where:; <??>(h) eq Nib = Ni + 22 x C + 0.5 x Cu + 0.5 x Mn. <??>Independent claims are also included for the following: <??>(a) the fabrication of a billet from this austenitic alloy; <??>(b) the fabrication of a wire from this austenitic alloy; <??>(c) the fabrication of bar from this austenitic alloy; <??>(d) an austenitic alloy piece able to be machined or hot or cold shaped or knitted from such a billet, wire or bar. <??>The composition of the austenitic alloy is, by wt: <??>(a) carbon : 0.010 - 0.04%; <??>(b) nitrogen : 0 - 0.01%; <??>(c) silicon less than 2%; <??>(d) nickel : 16 - 19.9%; <??>(e) manganese less than 8%; <??>(f) chromium : 18.1 - 21%; <??>(g) titanium : 1.8 - 3%; <??>(h) molybdenum less than 3%; <??>(i) copper less than 3%; <??>(j) aluminum less than 1.5%; <??>(k) boron less than 0.01%; <??>(l) vanadium less than 2%; <??>(m) sulfur less than 0.2%; <??>(n) phosphorus less than 0.4%; <??>(o) up to 0.5% at least of an element chosen from yttrium, cerium, lanthanum and other rare earth metals; <??>(p) the remainder being iron and production and deoxidization impurities.

Description

The present invention relates to an austenitic alloy for heat resistance to improved flowability and transformation.

Steels for mechanical strength when hot include martensitic steels usable up to about 550 ° C, austenitic stainless steels with a hardening of intermetallic phase, which can be used up to 650 ° C about. Nickel or cobalt alloys are also used, generally hardened by precipitation of intermetallics.

Austenitic stainless steels for mechanical resistance to heat, such as steel referenced n ° 1.4980, according to European standard EN10269, also referenced AISI 660 according to ASTM A453, are frequently used in bolts and struck parts, in particular in fasteners for automobile exhaust elements, such as as turbochargers or upstream exhaust downpipes. We meet them also, in the form of drawn wires, in knits for the mechanical setting of the catalysts exhaust. We also know applications of these steels in the field of hot springs or exhaust hoses made up of rolled tubes - welded then corrugated, and on the other hand sheaths of woven metal wires.

The composition of AISI 660 steel has a moderate chromium content of about 15%, about 1% molybdenum, 0.3% vanadium. The character austenitic, necessary for keeping hot, is ensured by a massive addition of nickel, that is to say of the order of 24%.

The hardening and the creep resistance are ensured by an addition of approximately 2% of titanium, which combines between 600 ° C and 750 ° C with part of the nickel to form intermetallics of the Ni ₃ Ti type. The composition of the steel may also contain elements such as Mo, V, Al which also contribute to hardening and to keeping hot by replacing the titanium atoms in the Ni ₃ Ti compound.

• un coût élevé, notamment en raison de la teneur importante en nickel,
• une difficulté d'élaboration car lors de la coulée il y a formation de ségrégations, qui, faute de précautions particulières, provoquent des déchirures en coulée continue ou lors du laminage à chaud ; par conséquent, il est nécessaire de pratiquer une élaboration coûteuse par re fusion avec meulage des demi-produits et contrôle renforcé sur produits finis.

The disadvantages of this steel include:

• a high cost, in particular due to the high nickel content,
• a difficulty of development because during casting there is formation of segregations, which, for lack of special precautions, cause tears in continuous casting or during hot rolling; therefore, it is necessary to practice a costly production by re-fusion with grinding of semi-finished products and reinforced control on finished products.

• une difficulté de laminage car les ségrégations abaissent fortement le point de brûlure. De ce fait, le laminage ne peut être effectué au-delà de 1150°C environ, pour éviter la formation de graves défauts comme par exemple des criques. Compte tenu de la contrainte d'écoulement élevée de l'alliage en dessous de cette température, le laminage ne peut être effectué que sur certaines installations particulièrement robustes. De plus, la vitesse de laminage doit être réduite pour éviter tout réchauffage au-delà du point de brûlure.
• une limitation des tenues à l'oxydation et à la corrosion à chaud du fait de ses faibles teneurs en chrome et en silicium, dans des conditions d'exposition particulièrement intense, comme par exemple les lignes d'échappement.
• une difficulté d'usinage de pièces en raison notamment de la faible teneur en soufre.
• une difficulté de soudage, dans le cas notamment de tôles en AISI 660 soudées entre elles, avec ou sans apport de fil du même alliage, car une forte tendance à la fissuration à chaud est observée.

To reduce segregation, silicon should be limited to less than 0.3%, carbon to less than 0.050%, copper to less than 0.5%, sulfur to less than 0.002 %, phosphorus at a content less than 0.025%, lead at a content less than 0.0005% etc ... These limitations represent additional costs for the elaboration in steelworks.

• a difficulty of rolling because the segregations strongly lower the burn point. As a result, the rolling cannot be carried out beyond approximately 1150 ° C., to avoid the formation of serious defects such as for example cracks. Given the high flow stress of the alloy below this temperature, rolling can only be carried out on certain particularly robust installations. In addition, the rolling speed should be reduced to avoid reheating beyond the burn point.
• a limitation of resistance to oxidation and to hot corrosion due to its low chromium and silicon contents, under particularly intense exposure conditions, such as for example exhaust lines.
• difficulty in machining parts due in particular to the low sulfur content.
• a difficulty in welding, in particular in the case of AISI 660 sheets welded together, with or without the addition of wire of the same alloy, since a strong tendency to hot cracking is observed.

• l'acier AISI 660 cité ci-dessus,
• un brevet IMPHY N° FR 94 14 942 décrivant la composition suivante :
• Ni : 16% à 25% ; Cr : 16% à 18,5% ; Ti : >1 %, Mn : 0% à 2%.
• un brevet NIPPON KOKAN JP 62267453 décrivant la composition suivante : C < 0,01% ; Ni : 10% à 18% ; Cr : 13% à 20% ; Ti > 1,5% ; Mn : 0% à 2%.

In the family of austenitic steels for mechanical resistance to heat, hardened by precipitation of intermetallic Nickel - Titanium, we know:

• the AISI 660 steel mentioned above,
• an IMPHY patent N ° FR 94 14 942 describing the following composition:
• Ni: 16% to 25%; Cr: 16% to 18.5%; Ti:> 1%, Mn: 0% to 2%.
• a NIPPON KOKAN JP 62267453 patent describing the following composition: C <0.01%; Ni: 10% to 18%; Cr: 13% to 20%; Ti>1.5%; Mn: 0% to 2%.

Theoretical knowledge of the phases present, during solidification or in solid phase, in the quaternary alloys Fe - Cr - Ni - Ti, turns out to be incomplete. She has was published by V. RAGHAVAN in 1996 in "Phase diagrams of quaternary iron alloys ", ed. The Indian Institute of Metals, pp 374 to 380. The area analyzed does not extend not to compositions containing more than 1.7% of Ti.

We have noticed that the main difficulties encountered with AISI steel 660 come from its solidification mode, which turns out to be a direct solidification in the form of austenite, unlike the majority of stainless steels austenitics, which solidify into ferrite, which then turns to lower austenite temperature.

The alloy according to the IMPHY patent, with a limited chromium content, is solidifying austenitic, as we will demonstrate later. It is therefore prone to problems casting and rolling linked to segregation.

The composition of the alloy according to the NIPPON KOKAN patent has a low nickel content associated with a chromium content of between 13% and 20%. The nickel content may not be sufficient to cure and hold effective creep at 650 ° C and above. In addition, the very low carbon content, less than 0.010% makes it unsuitable for production in air. It does not solidify probably not in all ferrite cases.

The object of the invention is to propose an alloy of the austenitic stainless type for mechanical resistance to heat, which can be produced economically and particularly suitable for continuous casting and hot processing.

0,010% < carbone < 0,04%

0% < azote < 0,01%

silicium < 2%

16% < nickel < 19,9%

manganèse < 8%

18,1% < chrome < 21%

1,8% < titane < 3%

molybdène < 3%

cuivre < 3%

aluminium < 1,5%

bore < 0,01%

vanadium < 2%

soufre < 0,2%

phosphore < 0,04%

et éventuellement jusqu'à 0,5% d'au moins un élément choisi parmi l'yttrium, le cérium, le lanthane et les autres terres rares,
le reste étant du fer et des impuretés résultants de l'élaboration ou de la désoxydation,
ladite composition satisfaisant en outre les deux relations suivantes :

• en relation avec le mode de solidification :
• reliquat a = éq Ni_a- 0,5x éq Cr_a < 3,60 où,
• éq Cr_a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, et où,
• éq Ni_a = Ni + 22 x C + 0.5 x Cu,
• en relation avec le taux de ferrite résiduel :
• reliquat b = éq Ni_b- 2 x éq Cr_b > - 41 où,
• éq Cr_b = Cr + 0.7 x Si + 1,37 x Mo + 3 x Ti + 6 x Al + 4 x V, et où,
• éq Ni_b = Ni + 22 x C + 0.5 x Cu + 0,5 x Mn.

The subject of the invention is an austenitic alloy for heat resistance with improved flowability and transformation, the composition of which comprises, in% by weight:

0.010% <carbon <0.04%

0% <nitrogen <0.01%

silicon <2%

16% <nickel <19.9%

manganese <8%

18.1% <chromium <21%

1.8% <titanium <3%

molybdenum <3%

copper <3%

aluminum <1.5%

boron <0.01%

vanadium <2%

sulfur <0.2%

phosphorus <0.04%

and possibly up to 0.5% of at least one element chosen from yttrium, cerium, lanthanum and the other rare earths,
the remainder being iron and impurities resulting from production or deoxidation,
said composition further satisfying the following two relationships:

• in relation to the solidification mode:
• balance a = eq Ni _a - 0.5x eq Cr _a <3.60 where,
• éq Cr _a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where,
• éq Ni _a = Ni + 22 x C + 0.5 x Cu,
• in relation to the residual ferrite content:
• balance b = éq Ni _b - 2 x éq Cr _b > - 41 where,
• éq Cr _b = Cr + 0.7 x Si + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where,
• éq Ni _b = Ni + 22 x C + 0.5 x Cu + 0.5 x Mn.

• la teneur en chrome est supérieure à 18,5%,
• la teneur en manganèse est supérieure à 2%,
• la teneur en silicium est supérieure à 1%,
• la teneur en nickel est supérieure à 18%,
• la teneur en aluminium est supérieure à 0,3%,
• la teneur en soufre est supérieure à 0,030%,
• la composition satisfait la relation suivante, toutes teneurs en % massiques :
  • en relation avec l'absence de formation de phase sigma fragilisante : valeur c = Cr + 1,5x Si + 1,5 x V + 1,2 Mo < 22.

In preferred embodiments, the invention may include the following characteristics, taken alone or in combination:

• the chromium content is greater than 18.5%,
• the manganese content is more than 2%,
• the silicon content is greater than 1%,
• the nickel content is greater than 18%,
• the aluminum content is greater than 0.3%,
• the sulfur content is greater than 0.030%,
• the composition satisfies the following relationship, all contents in% by mass:
  • in relation to the absence of weakening sigma phase formation: c value = Cr + 1.5x Si + 1.5 x V + 1.2 MB <22.

a) élaborer la composition sous air au four électrique,

b) l'affiner au convertisseur A.O.D.,

c) la couler en continu sous forme de blooms,

d) laminer à chaud lesdits blooms après réchauffage entre 1100 et 1200°C en billettes.

A second object of the invention is constituted by a process for manufacturing a billet made of an alloy of composition in accordance with the invention and which comprises the steps consisting in:

a) developing the composition in air in an electric oven,

b) refine it with the AOD converter,

c) pour it continuously in the form of blooms,

d) hot rolling said blooms after reheating between 1100 and 1200 ° C in billets.

e) laminer à chaud après réchauffage entre 1100 et 1200°C des billettes obtenues par le procédé de fabrication de billettes conforme à l'invention, pour obtenir du fil-machine,

f) recuire ledit fil-machine,

g) le décaper,

h) le tréfiler ou l'étirer.

A third object of the invention consists of a process for manufacturing alloy wires of composition in accordance with the invention and which comprises the steps consisting in:

e) hot rolling after heating between 1100 and 1200 ° C of the billets obtained by the billet manufacturing process according to the invention, in order to obtain wire rod,

f) annealing said wire rod,

g) pickling it,

h) draw it or stretch it.

e) laminer à chaud après réchauffage entre 1100 et 1200°C des billettes obtenues par le procédé de fabrication de billettes conforme à l'invention, pour obtenir des barres,

f) et recuire lesdites barres.

A fourth object of the invention consists of a method for manufacturing alloy bars of composition according to the invention and which comprises the steps consisting in:

e) hot rolling after reheating between 1100 and 1200 ° C of the billets obtained by the billet manufacturing process according to the invention, to obtain bars,

f) and annealing said bars.

A fifth object of the invention consists of the alloy parts which can be obtained by machining or hot or cold forming, or knitting, from a billet, wire or bar obtained by one of the processes according to the invention.

The description which follows and the appended figures presented in a non- exhaustive will make the invention well understood.

Figures 1a and 1b are micrographs on the solid state of solidification showing the phases formed at the start of solidification, with on the one hand, in FIG. 1a, in a example of invention 13605, the presence of ferrite in the dendrite axis, in plain text on the figure, and on the other hand, in figure 1b, corresponding to a counter example on steel IMPHY of the prior art, the presence of dendrites with an austenitic axis.

Figures 2, 3 and 4 show hot ductility curves of the compositions of Table 1; the burn points, estimated by the temperature at which the ductility is maximum, are shown in Table 2. The invention presented relates to an alloy austenitic for heat resistance with flowability and improved transformation.

Following studies carried out on castings, with determination of the mode of solidification, from the burn point, of the phases present at equilibrium between 1060 ° C and 1240 ° C as well as at 720 ° C and 600 ° C, the ductility in hot tension known as "forgeability", resilience at 20 ° C and creep resistance at 650 ° C, the inventors have found a general composition with which the problems of steels and alloys presented in the prior art are resolved in particular in the field of hardening, of resistance to creep, and especially in the solidification field, ensuring a ferritic solidification with subsequent transformation into solid phase of the whole from ferrite to austenite.

Composition 1 :

0,010% < carbone < 0,04%

0% < azote < 0,01%

silicium < 2%

16% < nickel < 19,9%

manganèse < 8%

18,1% < chrome < 21%

1,8% < titane < 3%

molybdène < 3%

cuivre < 3%

aluminium < 1,5%

bore < 0,01%

vanadium < 2%

soufre < 0,2%

phosphore < 0,04%

et éventuellement jusqu'à 0,5% d'au moins un élément choisi parmi l'yttrium, le cérium, le lanthane et les autres terres rares,
le reste étant du fer et des impuretés résultants de l'élaboration ou de la désoxydation,
ladite composition satisfaisant en outre les deux relations suivantes :

• en relation avec le mode de solidification :
• reliquat a = éq Ni_a- 0,5x éq Cr_a < 3,60 où,
• éq Cr_a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, et où,
• éq Ni_a = Ni + 22 x C + 0.5 x Cu,
• en relation avec le taux de ferrite résiduel :
• reliquat b = éq Ni_b- 2 x éq Cr_b > - 41 où,
• éq Cr_b = Cr + 0.7 x Si + 1,37 x Mo + 3 x Ti + 6 x Al + 4 x V, et où,
• éq Ni_b = Ni + 22 x C + 0.5 x Cu + 0,5 x Mn,

La composition 1 peut en outre satisfaire la relation suivante :

• en relation avec l'absence de formation de phase sigma fragilisante : valeur c = Cr + 1,5x Si + 1,5 x V + 1,2 Mo < 22.
• le durcissement et la tenue au fluage sont assurés par des précipités intermétalliques à base de Ni₃ Ti, obtenus lors de traitements de vieillissement vers 700-750°C,
• les quantités de Ti et Ni sont suffisantes pour assurer cette précipitation durcissante,
• la teneur en nickel est nettement inférieure à 24 %,
• le mode de solidification est, de façon surprenante, pour ce type d'alliage, ferritique, avec transformation ultérieure en phase solide de la quasi-totalité de la ferrite en austénite,
• le point de brûlure, température au-delà de laquelle il y a perte de ductilité en traction par début de fusion locale, est, de façon favorable, supérieure à 1100°C et de préférence supérieure à 1150°C,
• la teneur pondérée, valeur c, en éléments sigmagènes Cr, V, Mo, Si, est suffisamment faible pour éviter la précipitation de phase sigma et la fragilisation lors d'une utilisation entre 600 et 750°C.
• les combinaisons des éléments formateurs d'austénite ou de ferrite sont définies par les équivalents éqNi_a et éqCr_a pour ce qui concerne le mode de solidification, et éqNi_b et éqCr_b pour ce qui concerne la ferrite résiduelle après corroyage et recuits. De plus, la composition satisfait aux relations suivantes tous les éléments étant en % massique :
• pour assurer le caractère ferritique de la solidification et le point de brûlure élevé, en relation avec le mode de solidification :
• reliquat a = éq Ni_a - 0,5x éq Cr_a < 3,60 où,
• éq Cr_a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, et où,
• éq Ni_a = Ni + 22 x C + 0.5 x Cu,
• pour limiter, à des traces, la teneur en ferrite après transformation à chaud et recuit :
• reliquat b = éq Ni_b - 2 x éq Cr_b > - 41 où,
• éq Cr_b = Cr + 0.7 x Si + 1,37x Mo + 3 x Ti + 6 x Al + 4x V, et où,
• éq Ni_b = Ni + 22 x C + 0.5 x Cu + 0,5 x Mn,
et, éventuellement :

• pour assurer l'absence de fragilisation lors de l'utilisation entre 600°C et 750 °C : Cr + 1.5 x Si + 1.5 x V + 1.2 x Mo < 22

According to the invention, a composition 1 corresponds to the following weight composition:

Composition 1:

0.010% <carbon <0.04%

0% <nitrogen <0.01%

silicon <2%

16% <nickel <19.9%

manganese <8%

18.1% <chromium <21%

1.8% <titanium <3%

molybdenum <3%

copper <3%

aluminum <1.5%

boron <0.01%

vanadium <2%

sulfur <0.2%

phosphorus <0.04%

and possibly up to 0.5% of at least one element chosen from yttrium, cerium, lanthanum and the other rare earths,
the remainder being iron and impurities resulting from production or deoxidation,
said composition further satisfying the following two relationships:

• in relation to the solidification mode:
• balance a = eq Ni _a - 0.5x eq Cr _a <3.60 where,
• éq Cr _a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where,
• éq Ni _a = Ni + 22 x C + 0.5 x Cu,
• in relation to the residual ferrite content:
• balance b = éq Ni _b - 2 x éq Cr _b > - 41 where,
• éq Cr _b = Cr + 0.7 x Si + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where,
• éq Ni _b = Ni + 22 x C + 0.5 x Cu + 0.5 x Mn,

Composition 1 can also satisfy the following relationship:

• in relation to the absence of weakening sigma phase formation: c value = Cr + 1.5x Si + 1.5 x V + 1.2 MB <22.
• hardening and creep resistance are ensured by intermetallic precipitates based on Ni ₃ Ti, obtained during aging treatments at around 700-750 ° C.,
• the quantities of Ti and Ni are sufficient to ensure this hardening precipitation,
• the nickel content is much less than 24%,
• the solidification mode is, surprisingly, for this type of alloy, ferritic, with subsequent transformation into solid phase of almost all of the ferrite into austenite,
• the burn point, temperature above which there is loss of ductility in traction by the onset of local melting, is favorably greater than 1100 ° C. and preferably greater than 1150 ° C.,
• the weighted content, value c, of sigmagenic elements Cr, V, Mo, Si, is sufficiently low to avoid precipitation of the sigma phase and embrittlement when used between 600 and 750 ° C.
• the combinations of the austenite or ferrite forming elements are defined by the equivalents éqNi _a and éqCr _a as regards the solidification mode, and éqNi _b and éqCr _b as regards the residual ferrite after working and annealing. In addition, the composition satisfies the following relationships, all the elements being in% by mass:
• to ensure the ferritic nature of solidification and the high burn point, in relation to the mode of solidification:
• balance a = eq Ni _a - 0.5x eq Cr _a <3.60 where,
• éq Cr _a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where,
• éq Ni _a = Ni + 22 x C + 0.5 x Cu,
• to limit the ferrite content to traces after hot transformation and annealing:
• balance b = éq Ni _b - 2 x éq Cr _b > - 41 where,
• éq Cr _b = Cr + 0.7 x Si + 1.37x Mo + 3 x Ti + 6 x Al + 4x V, and where,
• éq Ni _b = Ni + 22 x C + 0.5 x Cu + 0.5 x Mn,
and eventually :

• to ensure the absence of embrittlement during use between 600 ° C and 750 ° C: Cr + 1.5 x Si + 1.5 x V + 1.2 x Mo <22

• pour améliorer la tenue au fluage : Ni > 18 %
• pour améliorer la tenue à l'oxydation et à l'environnement : Si > 1 %
• pour améliorer la tenue à l'oxydation et au fluage : Al > 0,3 %
• pour améliorer l'usinabilité : S > 0,030 %

Preferably,

• to improve creep resistance: Ni> 18%
• to improve resistance to oxidation and the environment: If> 1%
• to improve resistance to oxidation and creep: Al> 0.3%
• to improve machinability: S> 0.030%

• une amélioration de la tenue à l'oxydation et à la corrosion à chaud,
• une amélioration de l'usinabilité.
• une capacité de soudage de l'alliage selon l'invention sur lui-même dans le domaine de la soudure TIG ou laser ou en tant que matériau d'apport dans le domaine de la soudure MIG ou TIG avec apport, avec suppression de la tendance à la fissuration à chaud.

It is noted in comparison with the steels of the prior art cited:

• an improvement in resistance to oxidation and to hot corrosion,
• improved machinability.
• a welding capacity of the alloy according to the invention on itself in the field of TIG or laser welding or as a filler material in the field of MIG or TIG welding with filler, with suppression of the trend to hot cracking.

0,010% < carbone <0,04%,

azote < 0,01%,

0,01% < silicium < 2%,

16% < nickel < 19,9%,

2 % < manganèse < 8%,

18,1% < chrome < 21%,

1,8% < titane < 3%,

0,01% < molybdène < 3%,

0,01% < cuivre < 3%,

0,0005% < aluminium < 1,5%,

0,0001% < bore < 0,01%,

0,01% < vanadium < 2%,

0% < soufre < 0,2%,

phosphore < 0,04%, le reste étant du fer et autres éléments en traces, résiduels ou micro - addition.

In another preferred composition 2 produced according to the invention.
Composition 2:

0.010% <carbon <0.04%,

nitrogen <0.01%,

0.01% <silicon <2%,

16% <nickel <19.9%,

2% <manganese <8%,

18.1% <chromium <21%,

1.8% <titanium <3%,

0.01% <molybdenum <3%,

0.01% <copper <3%,

0.0005% <aluminum <1.5%,

0.0001% <boron <0.01%,

0.01% <vanadium <2%,

0% <sulfur <0.2%,

phosphorus <0.04%, the remainder being iron and other trace, residual or micro - addition elements.

• pour assurer le caractère ferritique de la solidification et le point de brûlure élevé :
• reliquat a = éq Ni_a- 0,5x éq Cr_a < 3,60 où,
• éq Cr_a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, et où,
• éq Ni_a = Ni + 22 x C + 0.5 x Cu,
• pour limiter à des traces la teneur en ferrite après transformation à chaud et recuit :
• reliquat b = éq Ni_b- 2 x éq Cr_b > - 41 où,
• éq Cr_b = Cr + 0.7 x Si + 1,37 x Mo + 3 x Ti + 6 x Al + 4 x V, et où,
• éq Ni_b = Ni + 22 x C + 0.5 x Cu + 0,5 x Mn,
et éventuellement :

• pour assurer l'absence de fragilisation lors de l'utilisation entre 600 et 750 °C : Cr + 1.5 x Si + 1.5 x V + 1.2 x Mo < 22

In addition, the composition satisfies the following relationships, all the elements being in% by mass:

• to ensure the ferritic nature of solidification and the high burn point:
• balance a = eq Ni _a - 0.5x eq Cr _a <3.60 where,
• éq Cr _a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where,
• éq Ni _a = Ni + 22 x C + 0.5 x Cu,
• to limit the ferrite content to traces after hot transformation and annealing:
• balance b = éq Ni _b - 2 x éq Cr _b > - 41 where,
• éq Cr _b = Cr + 0.7 x Si + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where,
• éq Ni _b = Ni + 22 x C + 0.5 x Cu + 0.5 x Mn,
and eventually :

• to ensure the absence of embrittlement during use between 600 and 750 ° C: Cr + 1.5 x Si + 1.5 x V + 1.2 x Mo <22

• pour améliorer la tenue au fluage : Ni > 18%
• pour améliorer la tenue à l'oxydation et à l'environnement : Si > 1%
• pour améliorer la tenue à l'oxydation et au fluage : Al > 0.3 %
• pour améliorer l'usinabilité : S > 0,030 %

Preferably,

• to improve creep resistance: Ni> 18%
• to improve resistance to oxidation and the environment: If> 1%
• to improve resistance to oxidation and creep: Al> 0.3%
• to improve machinability: S> 0.030%

In composition 2 of the invention, the manganese content is greater than 2%.

According to the invention, the relationships allow the compositions to be selected. ferritic solidification, without residual ferrite and not forming a sigma phase.

Table 1 shows examples of casting carried out under vacuum for the production of the alloy according to the invention, as well as counter-examples of castings not responding to the invention, and compositions according to the cited prior art.

a) sur lingot :

• le mode de solidification, par micrographie
• la quantité de ferrite mesurée par méthode magnétique sur lingot brut et sur lingot réchauffé 15 min à 1240°C.

b) sur produit corroyé par forgeage :

• les quantités de ferrite résiduelle, par mesures magnétiques, après recuit de 1 heure à 980°C ou 1060°C.
• la ductilité en traction à chaud rapide avec une montée à la température d'essai à une vitesse de 10°C/s, un maintien pendant 80 s, une traction rapide à 14 s-1, une mesure de la striction diamétrale. Par une série d'essais à température croissante, on évalue la température à partir de laquelle la ductilité chute rapidement, en raison d'un début de fusion locale. Cette température appelée point de brûlure ne doit pas être dépassée au réchauffage avant laminage et pendant le laminage, sous peine de créer des défauts.

c) sur produit corroyé par forgeage puis recuit pendant une heure à une température de 980°C ou 1060°C puis vieilli pendant 16 heures à une température de 720°C :

• la présence de phase sigma, par micrographie, et, lorsqu'il y en a, la quantité de phase sigma par une méthode de diffraction des rayons X,
• les propriétés mécaniques en traction, la dureté et la résilience à température ambiante,
• la résilience après vieillissement supplémentaire de 200 h à 600 °C,
• la résistance au fluage à rupture à 650°C sous 385 Mpa par mesure du temps à la rupture et l'allongement à la rupture.

It has been studied in particular:

a) on ingot:

• solidification mode, by micrograph
• the quantity of ferrite measured by magnetic method on raw ingot and on ingot reheated for 15 min at 1240 ° C.

b) on product wrought by forging:

• the quantities of residual ferrite, by magnetic measurements, after annealing for 1 hour at 980 ° C or 1060 ° C.
• the ductility in rapid hot traction with a rise in the test temperature at a speed of 10 ° C / s, a hold for 80 s, a rapid traction at 14 s-1, a measurement of the diametral constriction. By a series of tests at increasing temperature, the temperature from which the ductility drops rapidly, due to the onset of local melting, is evaluated. This temperature, known as the burn point, must not be exceeded during reheating before rolling and during rolling, as this may create defects.

c) on a product wrought by forging and then annealed for one hour at a temperature of 980 ° C or 1060 ° C and then aged for 16 hours at a temperature of 720 ° C:

• the presence of sigma phase, by micrograph, and, where there is one, the quantity of sigma phase by an X-ray diffraction method,
• mechanical properties in tension, hardness and resilience at room temperature,
• the resilience after additional aging of 200 h at 600 ° C.,
• resistance to creep at break at 650 ° C under 385 Mpa by measurement of time at break and elongation at break.

In the area of solidification of the alloy, for the composition according to the invention, the solidification takes place first in the form of dendritic ferritic axes, which contain residual ferrite after cooling, as shown in the figure 1a, unlike the known and observed cases of AISI 660 reference steel and the alloy according to the IMPHY patent, the solidification of which begins by forming austenite, as shown in Figure 1b.

reliquat a = éq Ni_a- 0,5x éq Cr_a < 3,60 où,

éq Cr_a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, et où,

éq Ni_a = Ni + 22 x C + 0.5 x Cu,

permet de sélectionner les compositions à solidification ferritique.It has been established that, in the fields of composition of the invention, the criterion:

balance a = eq Ni _a - 0.5x eq Cr _a <3.60 where,

éq Cr _a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where,

éq Ni _a = Ni + 22 x C + 0.5 x Cu,

allows the selection of ferritic solidification compositions.

The presence of more than 1% of ferrite after reheating to 1240 ° C translates also the possibility of existence of this equilibrium phase at high temperature, at near the solidification point.

Figures 2, 3 and 4 show hot ductility curves of the compositions studied; ductility is measured by delta Φ, which is the diametral necking at break; that is to say the relative variation in diameter at the level of the rupture; the points of burn estimated by the temperature at which the ductility is maximum, are reported on table 2.

It appears that solidification in ferritic mode or beginner in ferrite, allows to obtain burn points higher than 1100 ° C, unlike solidification in austenitic mode.

Solidification in ferritic mode, obtained when the above criterion is respected, allows to reheat and laminate ingots or semi-finished products at normal speed between 1100 and 1200 ° C, preferably between 1120 and 1180 ° C, in a range of usual temperatures for stainless steels and compatible with furnaces reheating and mechanical dimensions of rolling mills.

The residual ferrite measured on product wrought by forging from 1100 ° C in 18 mm octagonal bar, and annealed for 1 hour at 980 ° C or 1060 ° C, is transferred to the table 2.

reliquat b = éq Ni_b- 2 x éq Cr_b > - 41 où,

éq Cr_b = Cr + 0.7 x Si + 1,37 x Mo + 3 x Ti + 6 x Al + 4x V, et où,

éq Ni_b = Ni + 22 x C + 0.5 x Cu + 0,5 x Mn,

permet de sélectionner les compositions à solidification ferritique présentant moins de 3% de ferrite résiduelle après traitement dans le domaine 980°C - 1060°C, de façon à limiter la perte de tenue au fluage.Certain ferritic solidification compositions contain more than 1% ferrite. This residual ferrite should have a lower creep resistance than that of the austenitic phase. The criterion :

balance b = éq Ni _b - 2 x éq Cr _b > - 41 where,

éq Cr _b = Cr + 0.7 x Si + 1.37 x Mo + 3 x Ti + 6 x Al + 4x V, and where,

éq Ni _b = Ni + 22 x C + 0.5 x Cu + 0.5 x Mn,

allows the selection of ferritic solidification compositions having less than 3% residual ferrite after treatment in the range 980 ° C - 1060 ° C, so as to limit the loss of creep resistance.

After wrought by forging, annealing at 980 ° C or 1060 ° C and treatment of aging for 16 hours at 720 ° C., all the compositions were observed by optical metallography after electro-nitric attack. In addition to residual ferrite, we observes, on certain compositions, the presence of an intermetallic phase, which has been identified, by X-ray diffraction, as the sigma phase. The dosages quantitative data are shown in Table 2.

The presence of the sigma phase is known to decrease the resilience and toughness of austenitic steels. A criterion was determined to ensure the absence of the sigma phase in the aged state: Cr + 1.5 x Si + 1.5 x V + 1.2 x Mo <22.

The above criterion therefore makes it possible to ensure a level of resilience sufficient to the treated state as well as after hot use.

The characteristics of traction and hardness are reported in table 2 measured at room temperature after forging, annealing for 1 hour at 980 ° C or 1060 ° C and aging for 16 hours at 720 ° C.

High hardnesses are obtained on flows 13606 and 13604, due to sigma phase formation.

The characteristics obtained on flows 13747, 13748 and 13605 are close to those of the AISI 660 grade.

Cast 13470, with higher Ni and Ti contents, has characteristics higher.

Creep rupture tests at 650 ° C under 385 MPa were carried out on the flows 13468 Imphy and 13605. The requirements usually required for hot fixings, especially more than 100 breaking hours, and more than 5% elongation at break are respected.

According to the invention, a minimum carbon content of 0.010% is necessary for allow the preparation "under air" in installations such as electric oven more refining at AOD and in the bag, without using vacuum or vacuum.

A maximum carbon content of 0.040% is necessary to avoid lowering strongly the liquidus of the alloy and increase the solidification interval of the alloy, making continuous casting impossible.

In addition, the carbon combines with a part of the titanium in the form of carbides of the TiC type, which is no longer available to harden the alloy in the aged state in the form of Ni ₃ Ti. This phenomenon should be minimized by limiting the carbon content.

A maximum nitrogen content of 0.010% is the result of the reaction, in the liquid metal, titanium added in large quantities with the nitrogen already present: there are formation and decantation of TiN nitrides in ladles and tundish, and the nitrogen content of the cast product cannot exceed the previous value.

Silicon is generally present in the composition, at least in trace amounts whose order of magnitude is 0.001% in steel products.

Silicon contributes to the formation of ferrite and sigma phase. A content maximum of 2.0% is necessary to avoid accelerated formation of the latter weakening phase.

Silicon contributes to improving resistance to oxidation and the hot environment, by the formation of more or less continuous layers of silica or silicates under the other oxides. A significant addition, for example more than 1% is therefore useful when solidification takes place in ferritic mode. Addition notable, for example between 0.2 and 2% is possible without formation of segregations important, as may be the case in certain solidification processes when solidification takes place in austenitic mode.

A minimum content of 0.001% manganese is generally present as a residue originating in particular from ferroalloys.

During production, manganese oxidizes easily during blowing oxygen intended to bring the carbon to the required level and; a maximum content of 8% is necessary to allow ripening under yield conditions correct addition of manganese.

We have found that manganese has the specific interest of promoting the ferritic solidification mode, while on the contrary favoring the elimination of the residual ferrite during annealing between 900 ° C and 1200 ° C, especially on product hot processed. It does not cause sigma phase formation.

As it is necessary to obtain the ferritic solidification mode while avoiding an excess of the other ferrite-forming elements, such as Cr, Mo, Si, W, excess which would cause embrittlement by sigma phase formation during manganese is particularly useful when you want to harden strongly the alloy by a significant nickel content.

The addition of manganese causes an increase in the thickness of the calamines on hot rolled or annealed products or during use. An addition of silicon, for example of more than 1%, then makes it possible to reduce the oxidation to a level usual.

A minimum content of 16% nickel, in combination with a titanium greater than 1.8%, is necessary to obtain significant hardening during aging between 650 ° C and 750 ° C. This hardening by precipitation of intermetallics, of the Ni ₃ Ti type, is necessary for the mechanical resistance at room temperature of the fasteners, as well as for their resistance to heat in tension and in creep.

A maximum content of 19.9% nickel is imposed for reasons especially economic.

To improve creep resistance, nickel can be brought above 18%. In these conditions, the hardening that occurs during aging at 720 ° C reaches practically already its maximum.

Given the level of nickel necessary to harden the alloy, a content minimum 18.1% chromium is required to counteract the formation effect of nickel austenite and obtain a ferritic solidification, in particular when the other ferrite-forming elements, such as Si, Mo, Mn, Ti, Al, V, are at a low level or close to their minimum content.

A content limited to a maximum of 21% of chromium is necessary to avoid the formation of weakening sigma phase during treatments at 720 ° C or during use in the range between 600 ° C and 700 ° C.

A minimum content of 1.8% of titanium is necessary to obtain sufficient hardening during aging treatments or when used in the range between 600 ° C and 750 ° C. A fine precipitation based on Ni ₃ Ti then occurs, which contributes to the mechanical resistance to heat, in particular under creep conditions.

Titanium is also present in the alloy in the form of titanium nitride, titanium carbide and titanium phosphide.

A content limited to 3.0% is necessary to avoid the lowering of the liquidus and the formation, during solidification, of coarse intermetals which can harm the tréfilabilité.

A minimum content of 0.010% molybdenum is generally present in the state traces during industrial processing.

Molybdenum contributes to the formation of ferrite during solidification and to the formation of hardening intermetallics, replacing titanium atoms. The addition of molybdenum improves the heat resistance of the alloy, in thereby increasing the precipitate content and the shear strength.

A maximum content of 3% is necessary to avoid phase formation sigma in association with chromium as well as the presence of residual ferrite.

A minimum content of 0.010% copper is generally present as processing residue.

Copper contributes to the formation of austenite and helps reduce the rate of residual ferrite, just like nickel.

A maximum content of 3% is imposed to avoid strong segregation during of the casting and the formation of a copper-rich phase greatly lowering the point of burn.

A minimum content of 0.0005% aluminum is generally present as that processing residue.

The addition of aluminum increases the content of hardening precipitates and the heat resistance, replacing the titanium atoms.

Furthermore, aluminum can be used to increase the ferritic character of the alloy during solidification, without the disadvantage of generating the sigma phase weakening when maintained at temperatures in the range between 550 ° C. and 700 ° C.

A maximum content of 1.5% aluminum is necessary to avoid depletion of nickel during the formation of intermallics and the presence of ferrite residual.

A minimum content of 0.0001% of boron is generally present in the state of traces.

The presence of boron, at a rate of 10 to 30 ppm, for example, allows a slight improvement of hot ductility in the temperature range between 800 ° C and 1100 ° C.

A maximum content of 0.01% is necessary to avoid excessive lowering of the solidus and the burn point it causes.

A minimum content of 0.01% vanadium is generally present as that processing residue.

Vanadium, ferritizing element and sigma phase former, can be added to contribute to the hardening by substitution of the titanium atoms in the intermetallic compounds.

A maximum content of 2% vanadium is necessary to avoid the formation sigma phase, in combination with the chromium present.

A minimum content of 0.0001% sulfur is generally present as refining residue.

Sulfur can be maintained voluntarily, or preferably added more 0.030%, to improve the machinability of the alloy, thanks to the presence of sulfides and titanium carbosulfides formed during solidification, which improve fragmentation shavings. This addition is made possible by the ferritic solidification mode, because the addition of sulfur does not significantly degrade the hot ductility during rolling, unlike the prior art, with austenitic solidification and marked segregations.

A maximum content of 0.2% is necessary to avoid the risks of opening length of the semi-finished products, along the elongated sulphides, during rolling at hot.

A minimum content of 0.001% phosphorus is generally present as that processing residue.

A maximum content of 0.040% phosphorus is necessary to avoid the presence of large particles of titanium phosphides formed during solidification and which may adversely affect wire drawing.

Other elements such as cobalt, tungsten, niobium, zirconium, tantalum, hafnium, oxygen, magnesium, calcium, may be present as residues from processing or deoxidation; other elements can be added voluntarily in quantities not exceeding 0.5% to improve properties specific, such as resistance to oxidation by micro - addition of yttrium, cerium, lanthanum and other rare earths.

Example of industrial processing of a steel according to the invention and of the properties of industrial end product according to the invention:

a)élaboration sous air au four électrique

b)affinage au convertisseur A.O.D.

c)coulée en continue sous forme de blooms de 1 tonne de section carrée 205 x 205 mm

d)laminage à chaud depuis 1100°C en billettes de 500 kg de section carrées de 120x 120 mm

e) laminage à chaud des billettes de 120x 120 mm, depuis 1100°C, en couronnes de 500 kg de fil-machine de 5.5 mm

f) recuit en couronne

g) décapage

h) tréfilage

A 35-ton casting No. 141067 was produced on industrial production tools; of composition according to the invention, indicated in Table 1. The operations carried out, successfully and with a low rate of defects, on this casting were as follows:

a) preparation in air in an electric oven

b) refining with the AOD converter

c) continuous casting in the form of blooms of 1 ton of square section 205 x 205 mm

d) hot rolling from 1100 ° C into billets of 500 kg square section of 120x 120 mm

e) hot rolling of 120 × 120 mm billets, from 1100 ° C., into 500 kg rings of 5.5 mm wire rod

f) annealed in a crown

g) pickling

h) wire drawing

By comparison, the same operations were carried out on several castings of the AISI 660 grade, which gave rise to many faults (cracks on blooms, cracks on billets, straws and scales on wire rod). Usually the AISI grade 660 is cast in the form of ingots without using the continuous casting process.

Therefore, this industrial test demonstrated the superiority of the composition according to the invention for obtaining stainless steel wire rod capable of withstanding hot by an economical process including an elaboration in air, an AOD refining and a continuous casting operation in blooms.

a) une facilité de coulée, le mode de solidification ferritique permettant de couler des blooms ou brames en continu sans formation de défauts de coulée, ségrégations centrales, filets ségrégés, déchirures à chaud ; on évite ainsi le recours à la coulée en lingot suivie d'une opération supplémentaire de blooming ou de slabbing, qui est nécessaire sur les alliages de l'art antérieur.

b) une économie de matières premières, notamment de nickel, par rapport aux aciers AISI 660 couramment utilisés.

c) une facilité d'élaboration ; en effet, contrairement aux alliages de l'art antérieur, il n'est pas nécessaire de rechercher des teneurs particulièrement faibles en silicium, cuivre, soufre, phosphore, plomb, antimoine, bismuth pour éviter les problèmes de ségrégation et de déchirures à chaud et ségrégations ; par conséquent, la charge de matière première est simplifiée et plus économique, et l'élaboration «à l'air» en four électrique et AOD, sans passage par le vide ou en dépression, devient possible.

d) une facilité de laminage, le réchauffage et le laminage des lingots, blooms de coulée continue et demi-produits est possible entre 1100°C et 1200°C ; pour les alliages de l'art antérieur, il ne peut dépasser, sans risque de criques et déchirures à chaud, 1100°C sur les produits bruts de coulée et 1150°C après un premier laminage.

Compared with the austenitic stainless steels for high temperature fasteners of the prior art, the alloy according to the invention has several advantages:

a) ease of casting, the ferritic solidification mode allowing continuous blooms or slabs to be cast without the formation of casting defects, central segregations, segregated threads, hot tears; this avoids the use of ingot casting followed by an additional blooming or slabbing operation, which is necessary on the alloys of the prior art.

b) savings in raw materials, in particular nickel, compared to commonly used AISI 660 steels.

c) ease of preparation; in fact, unlike the alloys of the prior art, it is not necessary to seek particularly low contents of silicon, copper, sulfur, phosphorus, lead, antimony, bismuth to avoid the problems of segregation and hot tears and segregation; Consequently, the loading of raw material is simplified and more economical, and the preparation "in the air" in an electric furnace and AOD, without passing through vacuum or vacuum, becomes possible.

d) ease of rolling, reheating and rolling of ingots, continuous casting blooms and semi-finished products is possible between 1100 ° C and 1200 ° C; for alloys of the prior art, it cannot exceed, without risk of hot cracks and tears, 1100 ° C on the raw casting products and 1150 ° C after a first rolling.

e) une tenue à l'oxydation et à l'environnement. L'alliage proposé comporte effectivement une forte teneur en chrome, qui assure une bonne tenue à l'oxydation et à la corrosion à chaud lors de l'utilisation, par exemple entre 500°C et 750°C. Il peut en outre contenir du silicium, qui joue le même rôle.

f) une usinabilité améliorée en cas d'addition de soufre, par exemple supérieure à 0,030%, qui permet de restaurer une usinabilité correcte, à l'inverse de l'acier AISI 660 et des autres alliages de l'art antérieur, qui ne contiennent pas de soufre, car leur transformation à chaud devient impossible si le soufre est présent en quantité significative.

g) une bonne soudabilité, l'alliage proposé étant soudable avec une tendance très réduite à la fissuration à chaud, par rapport aux alliages de l'art antérieur, grâce à son mode de solidification ferritique et à l'absence de fortes ségrégations de solidification. Il peut notamment être soudé sur lui-même en TIG ou par laser ou par résistance électrique, ou être utilisé en fil de métal d'apport en MIG ou TIG ou en électrodes, pour le soudage.

Consequently, the installations dimensioned for common stainless steels can be used to roll this steel, and it is not necessary to slow down the rolling speed considerably to avoid internal tears by overheating, at the end of rolling.

e) resistance to oxidation and the environment. The proposed alloy does indeed have a high chromium content, which ensures good resistance to oxidation and to hot corrosion during use, for example between 500 ° C. and 750 ° C. It can also contain silicon, which plays the same role.

f) improved machinability in the event of addition of sulfur, for example greater than 0.030%, which makes it possible to restore correct machinability, unlike AISI 660 steel and other alloys of the prior art, which do not contain no sulfur, because their hot transformation becomes impossible if the sulfur is present in significant quantity.

g) good weldability, the proposed alloy being weldable with a very reduced tendency to hot cracking, compared with the alloys of the prior art, thanks to its ferritic solidification mode and to the absence of strong solidification segregations . It can in particular be welded to itself in TIG or by laser or by electrical resistance, or be used in filler metal wire in MIG or TIG or in electrodes, for welding.

• ancrages intérieurs de fours,
• pièces de fours de cimenterie,
• soupapes d'admission ou d'échappement de moteurs automobiles,
• fixations et boulonnerie d'échappement automobile,
• ressorts utilisés à chaud,
• tresses de fils et parois tubulaires de flexibles ondulés pour, par exemple, l'échappement automobile,
• tricots de fils pour par exemples, les tapis transporteurs de fours, les calages de catalyseurs d'échappements,
• fibres et tricots de fibres pour presses de formage à chaud du verre,
• tôles soudées, par exemple pour chambres de combustion de turbines,
• fil d'apport de soudage, barres usinées,
• anneau synchro de turbine à ailettes fixes à orientation variable de turbocompresseurs automobile : pièces en tôle,
• segment d'étanchéité annulaire pour turbocompresseurs automobile.

The alloy according to the invention can be used in particular in the following fields:

• oven interior anchors,
• cement kiln parts,
• automobile engine intake or exhaust valves,
• automotive exhaust fixings and bolts,
• hot springs,
• braids of wires and tubular walls of corrugated hoses for, for example, automobile exhaust,
• yarn knits for example, oven conveyor belts, shims of exhaust catalysts,
• fibers and knitted fibers for hot glass forming presses,
• welded sheets, for example for turbine combustion chambers,
• welding filler wire, machined bars,
• turbine synchro ring with fixed fins with variable orientation of automotive turbochargers: sheet metal parts,
• annular sealing segment for automotive turbochargers.

Claims (12)

Austenitic alloy for heat resistance with improved flowability and transformation, the composition of which comprises, in% by weight: 0.010% <carbon <0.04% 0% <nitrogen <0.01% silicon <2% 16% <nickel <19.9% manganese <8% 18.1% <chromium <21% 1.8% <titanium <3% molybdenum <3% copper <3% aluminum <1.5% boron <0.01% vanadium <2% sulfur <0.2% phosphorus <0.04% and possibly up to 0.5% of at least one element chosen from yttrium, cerium, lanthanum and the other rare earths,
the remainder being iron and impurities resulting from production or deoxidation,
said composition further satisfying the following two relationships: in relation to the solidification mode: balance a = eq Ni _a - 0.5x eq Cr _a <3.60 where, éq Cr _a = Cr + 0.7 x Si + 0.2 x Mn + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where, éq Ni _a = Ni + 22 x C + 0.5 x Cu, in relation to the residual ferrite content: balance b = éq Ni _b - 2 x éq Cr _b > - 41 where, éq Cr _b = Cr + 0.7 x Si + 1.37 x Mo + 3 x Ti + 6 x Al + 4 x V, and where, éq Ni _b = Ni + 22 x C + 0.5 x Cu + 0.5 x Mn. The alloy of claim 1, further characterized in that the chromium content is greater than 18.5%. An alloy according to any of claims 1 or 2, further characterized in that the manganese content is greater than 2%. An alloy according to any of claims 1 to 3, further characterized in that the silicon content is greater than 1%. An alloy according to any of claims 1 to 4, further characterized in that the nickel content is greater than 18%. The alloy of any of claims 1 to 5, further characterized in that the aluminum content is greater than 0.3%. An alloy according to any of claims 1 to 6, further characterized in that the sulfur content is greater than 0.030%. An alloy according to any of claims 1 to 7, further characterized in that the composition satisfies the following relationship: in relation to the absence of weakening sigma phase formation: c value = Cr + 1.5x Si + 1.5 x V + 1.2 MB <22. Method for manufacturing an alloy billet, the composition of which is according to any one of Claims 1 to 8, characterized in that it comprises the steps consisting in: a) developing the composition in air in an electric oven, b) refine it with the AOD converter, c) pour it continuously in the form of blooms, d) hot rolling said blooms after reheating between 1100 and 1200 ° C in billets. Method for manufacturing alloy wires, the composition of which is according to any one of Claims 1 to 8, characterized in that it comprises the steps consisting in: e) hot rolling after reheating between 1100 and 1200 ° C of the billets obtained by the process according to claim 9, to obtain wire rod, f) annealing said wire rod, g) pickling it, h) draw it or stretch it. Method for manufacturing alloy bars, the composition of which is according to any one of Claims 1 to 8, characterized in that it comprises the steps consisting in: e) hot rolling after reheating between 1100 and 1200 ° C of the billets obtained by the process according to claim 9, to obtain bars, f) and annealing said bars. Alloy part obtainable by machining or hot or cold forming, or knitting, from a billet, a thread or a bar obtained by the process according to any one of claims 9 to 11.

Images