EP0004819A1 - Process for the production of ferrous alloys with improved mechanical properties by the use of lanthanum, and ferrous alloys obtained by this process - Google Patents

Process for the production of ferrous alloys with improved mechanical properties by the use of lanthanum, and ferrous alloys obtained by this process Download PDF

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Publication number
EP0004819A1
EP0004819A1 EP79400224A EP79400224A EP0004819A1 EP 0004819 A1 EP0004819 A1 EP 0004819A1 EP 79400224 A EP79400224 A EP 79400224A EP 79400224 A EP79400224 A EP 79400224A EP 0004819 A1 EP0004819 A1 EP 0004819A1
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Prior art keywords
lanthanum
weight
alloy
alloys
ferrous
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German (de)
French (fr)
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EP0004819B1 (en
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Mario Gorgerino
Daniel Videau
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Universelle D'acetylene et D'electro-Metallurgie Cie
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Universelle D'acetylene et D'electro-Metallurgie Cie
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C35/00—Master alloys for iron or steel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/04—Cast-iron alloys containing spheroidal graphite
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60

Definitions

  • the present invention relates generally to the use of lanthanum when developing ferrous alloys such as lamellar cast iron and / or spheroldal graphite, or steels.
  • the present invention relates to a process for the preparation of ferrous alloys making it possible to improve their mechanical properties thanks to the use of lanthanum, in particular in the form of inoculating alloys with a low cerium content or generally with a low content of Rare Earths (including cerium), that is to say with a lanthanum / Rare Earths weight ratio (except lanthanum) at least greater than 2/1 or preferably greater than 10/1 and for certain specific uses greater than 100/1.
  • the invention also relates to alloys inoculating with lanthanum for implementing the method as well as the ferrous alloys obtained by the method of the invention.
  • the method of the invention makes it possible to reduce or eliminate some of the defects of ferrous alloys such as pitting, cavities or shrinkage, carbides in spheroidal graphite cast irons; to eliminate the presence of lamellar gray cast iron carbides; to improve flowability, rolling ability and / or to reduce the anisotropy of steels.
  • Pitting and cavities are two major defects affecting molded parts, in particular spheroidal graphite cast irons. These cavities are also called “shrinkage" and constitute the type B221 defect of the international classification of foundry defects.
  • the bites mentioned above are generally located under the skin of the part and are revealed by shot peening thereof and constitute the defect type B 123 of the international classification of foundry defects.
  • Anisotropy constitutes a defect in steels which often have different mechanical properties in the longitudinal direction compared to the transverse direction, in particular in resilience.
  • Spheroldal graphite cast iron is prepared by adding magnesium to a basic cast iron having the following composition (in percentage by weight):
  • Magnesium is added either in the form of pure metal, or more frequently in the form of Fe - Si - Mg alloys. Some of these latter alloys contain cerium (0.2 to 0.4% of the alloy) which is intended to combat the possible effect of the elements Pb, Bi, As, all anti-nodulizing elements.
  • the cast iron thus treated solidifies according to the two diagrams "Fe - CFe 3 " and "Fe - graphite”.
  • the present invention therefore aims to eliminate the aforementioned drawbacks and to provide a solution which makes it possible to reduce or eliminate certain faults in ferrous alloys such as pitting, cavities in spheroidal graphite cast iron, carbides in lamellar cast iron, anisotropy of steels, which can be used in industrial practice and which allows as much as possible to improve the mechanical properties of said ferrous alloys.
  • the solution consists of a process for the preparation of ferrous alloys, characterized in that it includes the incorporation of at least 0.0001% by weight to approximately 0.5 to 2% by weight of lanthanum in said ferrous alloy during its preparation.
  • this process comprises the incorporation of approximately 0.0001% to approximately 0.01% by weight (ie 100 ppm) of lanthanum into said ferrous alloy during its preparation.
  • the lanthanum can be incorporated in the form of an alloy (s) with any metal capable of forming a homogeneous compound with the lanthanum, that is to say having a solubility diagram with the lanthanum alone or combined with other Rare Earths in a proportion of 0.01 to 90% by weight; or in the form of compounds such as fluoride chloride, oxide obtained from lanthanides, or mixtures thereof, insofar as the lanthanum / Rare Earth weight ratio (except lanthanum is at least greater than 2/1 or preferably greater than 10/1 and for certain specific jobs greater than 100/1.
  • lanthanum inoculating alloys of this particularly preferred invention are alloys based on Si-La-Al, La-Ni, La-Fe-Si, La-Fe-Mn, Si-Ca-Mg-La, La-Cr, Si-La-Mn and where the iron may constitute the balance.
  • these lanthanum inoculating alloys contain other Rare Earths, including cerium, the above-mentioned lanthanum / Rare Earths ratio (except lanthanum) must in all cases be satisfied.
  • certain defects in the cast iron are reduced or eliminated such as defects in the form of pits and cavities or shrinkage and the anisotropy of the steels is reduced, thereby making it possible to obtain ferrous alloys having better properties. mechanical.
  • lanthanum in the form of composite alloys (nodulizers, inoculants, desulphurizers) thus makes it possible to obtain a greater purification of the bath in oxygen and in sulfur which leads to a greater ferritization of the matrix and makes it possible to improve the mechanical characteristics of the ferrous alloys obtained.
  • cerium in relatively large quantities, that is to say already from about 1%, alone or in combination with other Rare Earths, except lanthanum, compared to the proportion lanthanum, as in the case of mischmetal used before, practically does not allow to obtain the improvements obtained with lanthanum according to the present invention having a low content of cerium because the Applicant has discovered that cerium has a harmful effect and antagonistic to lanthanum which manifests itself as soon as the cerium content is already around 1% compared to the proportion of lanthanum.
  • the contents of the components are given as a percentage by weight.
  • a basic cupola is produced using the following composition:
  • This font is produced without inoculation and serves as a reference.
  • the solidification curve obtained on a MECI crucible, with Cr-Ni couple for such a reference cast iron is represented in FIG. 1.
  • This MECI crucible does not modify the solidification of the ingot and in particular ensures solidification quite comparable to that two pieces in a sand mold.
  • the eutectic level is identifiable by an anomaly in the cooling curve which is characterized by a change in inflection of the recorded curve (see Figure 1)
  • the solidification curve obtained, using a MECI crucible, is shown in FIG. 3.
  • the parts obtained have appearance defects such as cavities.
  • the solidification curve shown in FIG. 4 is obtained, which shows an elongation of the solidification interval of the order of 30% and an increase in the temperature of the transformation plateau of the order of 10 ° C.
  • the parts obtained are devoid of cavity.
  • the parts cast with the alloy of the present invention are practically sound, the weights have only a slight dendritic shrinkage while the parts cast according to the prior method have cavities and pits.
  • the alloy 2 according to the present invention makes it possible to obtain weights having only a primary-dendritic recess while the counterweight prepared with the anterior mischmetal has a significant recess or recess.
  • the lanthanum / Rare Earths ratio in the mischmetal is equal to 0.25. This ratio according to the present invention must be, as mentioned above, at least equal to 2, preferably at least equal to 10 and more preferably at least equal to 100.
  • the mischmetal used has the composition mentioned above for alloy 1.
  • Alloy 4 identical to alloy 3 except that we use 0.50% of cerium supplied in the form of Fe-Ce instead of Mischmetal.
  • inoculating alloy usually used in foundries having the following composition (A) is inoculated in a manner known per se.
  • a cast iron is obtained having the composition mentioned in Table III with the physical characteristics also mentioned in Table III.
  • an inoculating alloy according to the present invention having the following composition (B): or 25.10 -4 % by weight of lanthanum or 25 ppm, a cast iron is obtained having the composition and the physical characteristics also mentioned in Table III. It can be seen that the number of graphite spheroids obtained is much more numerous and the effects of quenching (carburetted area) less with the use of the inoculating alloy according to the present invention compared to the known inoculating alloy, and this unexpectedly.
  • lanthanum can solve the problems associated with the deoxidation of steel.
  • a pocket deoxidation is carried out by adding 27 kg of a silico-lanthanum alloy comprising 45% of Si, 0.5% of La, the remainder being iron, or an addition of about 0.20% of the alloy to lanthanum which corresponds to an addition of about 10 -3 % of lanthanum or about 10 ppm.
  • a sample of steel is taken from the pocket after the deoxidation with the lanthanum inoculating alloy of the present invention and a steel is obtained having the following composition:
  • the crystallographic analysis of this steel shows that a steel is obtained comprising micro-inclusions of aluminate and silicate by obtaining refractory globules of small average diameter of the order of 1 to 2 microns and in limited number.
  • the lanthanum according to the present invention in alloy with other metals, including with Rare Earths in so far as the above-mentioned lanthanum / Rare Earths ratio is respected gives the possibility, in the course of the deoxidation kinetics, desulfurization, denitriding and dehydration,. predict and obtain the number of inclusions of the desired size and composition for the steel applications that it is desired to produce, which constitutes a particularly remarkable industrial result.
  • the addition of lanthanum, under the conditions of the present invention makes it possible to reduce the anisotropy of the steels and thereby improve the ratio of the longitudinal and transverse resilience obtained.
  • lanthanum is found in the ferrous alloy in the form of compounds such as oxides, and / or sulfides, and / or nitrides, and / or hydrides, and / or carbides forming non-annoying inclusions in ferrous alloys.
  • lanthanum is incorporated into the ferrous alloy, when it is produced in the form of an alloy inoculant having the following composition (percentage by weight): or
  • the steels prepared by the process of the present invention can be in particular structural steels, special steels, stainless steels, casting or rolling but are not limited to these.

Abstract

L'invention concerne un procédé de préparation d'alliages ferreux; des alliages inoculants comportant du lanthane et des alliages ferreux obtenus par ce procédé. Ce procédé comprend l'incorporation d'au moins 0,0001% à environ 0,5 à 2% en poids de lanthane à l'alliage ferreux lors de son élaboration, notamment sous forme d'alliages inoculants. On obtient ainsi un meilleur dégazage dans le cas d'une fonte ce qui se traduit par une modification de la courbe de solidification qui est représentée à la figure 2. Ce procédé permet de réduire ou supprimer certains défauts des alliages ferreux tels que piqûres et cavités des fontes à graphie sphéroïdal, carbures de la fonte grise lamellaire, d'améliorer la coulabilité, l'aptitude au laminage et l'isotropie des aciers, et d'améliorer les propriétés mécaniques des alliages ferreux.The invention relates to a process for the preparation of ferrous alloys; inoculating alloys comprising lanthanum and ferrous alloys obtained by this process. This process includes the incorporation of at least 0.0001% to about 0.5 to 2% by weight of lanthanum into the ferrous alloy during its preparation, in particular in the form of inoculating alloys. A better degassing is thus obtained in the case of a cast iron, which results in a modification of the solidification curve which is shown in FIG. 2. This process makes it possible to reduce or eliminate certain defects in ferrous alloys such as pits and cavities cast iron with spheroidal writing, carbides of gray cast iron, to improve the flowability, the rolling ability and the isotropy of steels, and to improve the mechanical properties of ferrous alloys.

Description

La présente invention concerne d'une manière générale l'emploi de lanthane lors de l'élaboration d'alliages ferreux tels que fonte lamellaire et/ou à graphite sphéroldal, ou aciers.The present invention relates generally to the use of lanthanum when developing ferrous alloys such as lamellar cast iron and / or spheroldal graphite, or steels.

Plus précisément, la présente invention concerne un procédé de préparation d'alliages ferreux permettant d'améliorer leurs propriétés mécaniques grâce à l'emploi de lanthane, notamment sous forme d'alliages inoculants à faible teneur en cérium ou de manière générale à faible teneur en Terres Rares ( y compris le cérium), c'est-à-dire avec un rapport en poids lanthane/Terres Rares (excepté le lanthane) au moins supérieur à 2/1 ou de préférence supérieur à 10/1 et pour certains emplois particuliers supérieur à 100/1. L'invention concerne également les alliages inoculants au lanthane pour la mise en oeuvre du procédé ainsi que les alliages ferreux obtenus par le procédé de l'invention.More specifically, the present invention relates to a process for the preparation of ferrous alloys making it possible to improve their mechanical properties thanks to the use of lanthanum, in particular in the form of inoculating alloys with a low cerium content or generally with a low content of Rare Earths (including cerium), that is to say with a lanthanum / Rare Earths weight ratio (except lanthanum) at least greater than 2/1 or preferably greater than 10/1 and for certain specific uses greater than 100/1. The invention also relates to alloys inoculating with lanthanum for implementing the method as well as the ferrous alloys obtained by the method of the invention.

Par ailleurs, le procédé de l'invention permet de réduire ou de supprimer certains des défauts des alliages ferreux tels que piqûres, cavités ou retassures, carbures dans les fontes à graphite sphéroldal; de supprimer la présence des carbures en fonte grise lamellaires; d'améliorer la coulabilité, l'aptitude au laminage et/ou de réduire l'anisotropie des aciers.Furthermore, the method of the invention makes it possible to reduce or eliminate some of the defects of ferrous alloys such as pitting, cavities or shrinkage, carbides in spheroidal graphite cast irons; to eliminate the presence of lamellar gray cast iron carbides; to improve flowability, rolling ability and / or to reduce the anisotropy of steels.

Les piqûres et les cavités constituent deux défauts prépondérants affectant les pièces moulées, en particulier les fontes à graphite sphéroidal. Ces cavités sont aussi appelées "retassures" et constituent le défaut genre B221 de la classification internationale des défauts de fonderie. Les piqûres mentionnées précédemment sont généralement situées sous la peau de la pièce et sont révélées par un grenaillage de celle-ci et constituent le défaut genre B 123 de la classification internationale des défauts de fonderie.Pitting and cavities are two major defects affecting molded parts, in particular spheroidal graphite cast irons. These cavities are also called "shrinkage" and constitute the type B221 defect of the international classification of foundry defects. The bites mentioned above are generally located under the skin of the part and are revealed by shot peening thereof and constitute the defect type B 123 of the international classification of foundry defects.

L'anisotropie constitue un défaut des aciers qui possèdent souvent des propriétés mécaniques différents dans le sens longitudinal par rapport au sens transversal, notamment en résilience.Anisotropy constitutes a defect in steels which often have different mechanical properties in the longitudinal direction compared to the transverse direction, in particular in resilience.

La fonte à graphite sphéroldal est préparée par addition de magnésium à une fonte de base ayant la composition suivante(en pourcentage en poids):

Figure imgb0001
Figure imgb0002
Figure imgb0003
Figure imgb0004
Figure imgb0005
 Spheroldal graphite cast iron is prepared by adding magnesium to a basic cast iron having the following composition (in percentage by weight):
Figure imgb0001
Figure imgb0002
Figure imgb0003
Figure imgb0004
Figure imgb0005

Le magnésium est ajouté soit sous forme de métal pur, soit plus fréquemment sous forme d'alliages Fe - Si - Mg. Certains de ces derniers alliages contiennent du cérium (0,2 à 0,4% de l'alliage) qui est destiné à combattre l'effet éventuel des éléments Pb, Bi, As, tous éléments anti-nodulisants. La fonte ainsi traitée se solidifie suivant les deux diagrammes "Fe - CFe3" et"Fe - graphite".Magnesium is added either in the form of pure metal, or more frequently in the form of Fe - Si - Mg alloys. Some of these latter alloys contain cerium (0.2 to 0.4% of the alloy) which is intended to combat the possible effect of the elements Pb, Bi, As, all anti-nodulizing elements. The cast iron thus treated solidifies according to the two diagrams "Fe - CFe 3 " and "Fe - graphite".

On doit noter que l'introduction du magnésium dans la fonte conduit :

  • a) à une tendance à la solidification suivant le diagramme métastable Fe - CFe3 qui donne naissance à des carbures.
  • b) Ce type de solidification implique des surfusions notables. L'importance de ces surfusions est fonction du type de solidification dont une partie s'effectue suivant le diagramme "Fe - CFe3" et dont l'autre partie s'effectue suivant le diagramme "Fe -graphite". Actuellement, le cycle de solidification n'est pas contrôlé par le processus d'élaboration.
  • c) Une inoculation importante permet généralement de revenir au diagramme Fe - graphite, mais les résultats sont irréguliers car fonction des modules de refroidissement des pièces moulées (ou des parties des pièces).
It should be noted that the introduction of magnesium into the cast iron leads to:
  • a) a tendency to solidify along the metastable diagram Fe - CFe 3 which gives rise to carbides.
  • b) This type of solidification involves notable supercooling. The importance of these supercooling depends on the type of solidification, part of which is carried out according to the "Fe - CFe 3 " diagram and the other part of which is carried out according to the "Fe-graphite" diagram. Currently, the solidification cycle is not controlled by the development process.
  • c) A significant inoculation generally makes it possible to return to the Fe - graphite diagram, but the results are irregular because it depends on the cooling modules of the molded parts (or parts of the parts).

Ce procédé permet dans les fontes grises lamellaires de supprimer la présence des carbures. De précédents essais. effectués sur les fontes grises lamellaires, ou l'acier, à l'aide de mischmétal (mélange très variable de 15 éléments de Terres Rares) ou de siliciuresde Terres Rares ont donné des résultats parcellaires, discordants et non utilisables en pratique industrielle.This process makes it possible in gray lamellar cast irons to eliminate the presence of carbides. Previous tests. carried out on gray cast iron, or steel, using mischmetal (very variable mixture of 15 elements of Rare Earth) or silicides of Rare Earth have given patchy results, discordant and not usable in industrial practice.

La présente invention a donc pour but d'éliminer les inconvénients précités et de fournir une solution qui permette de réduire ou supprimer certains défauts des alliages ferreux tels que piqûres, cavités en fonte à graphite sphérotdal, carbures en fonte lamellaire., anisotropie des aciers, qui soit utilisable en pratique industrielles et qui permette autant que possible d'améliorer les propriétés mécaniques desdits alliages ferreux.The present invention therefore aims to eliminate the aforementioned drawbacks and to provide a solution which makes it possible to reduce or eliminate certain faults in ferrous alloys such as pitting, cavities in spheroidal graphite cast iron, carbides in lamellar cast iron, anisotropy of steels, which can be used in industrial practice and which allows as much as possible to improve the mechanical properties of said ferrous alloys.

La solution consiste selon l'invention en un procédé de préparation d'alliages ferreux caractérisé en ce qu'il comprend l'incorporation d'au moins 0,0001 % en poids à environ 0,5 à 2% en poids de lanthane audit alliage ferreux lors de son élaboration. De préférence, ce procédé comprend l'incorporation d'environ 0,0001% à environ 0,01 % en- poids (soit 100 ppm) de lanthane audit alliage ferreux lors de son élaboration.According to the invention, the solution consists of a process for the preparation of ferrous alloys, characterized in that it includes the incorporation of at least 0.0001% by weight to approximately 0.5 to 2% by weight of lanthanum in said ferrous alloy during its preparation. Preferably, this process comprises the incorporation of approximately 0.0001% to approximately 0.01% by weight (ie 100 ppm) of lanthanum into said ferrous alloy during its preparation.

Selon une caractéristique davantage préférée, on peut incorporer d'environ 0,001% en poids (soit 10 ppm) à environ 0,01% en poids, de préférence à environ 0,003% (soit 30 ppm) en poids à l'alliage ferreux lors de son élaboration.According to a more preferred characteristic, it is possible to incorporate from approximately 0.001% by weight (or 10 ppm) to approximately 0.01% by weight, preferably to approximately 0.003% (or 30 ppm) by weight into the ferrous alloy during its development.

Selon une autre caractéristique de la présente invention, le lanthane peut être incorporé sous forme d'alliage (s) avec tout métal susceptible de former un composé homogène avec le lanthane, c'est-à-dire présentant un diagramme de solubilité avec le lanthane seul ou associé à d'autres Terres Rares dans une proportion de 0,01 à 90% en poids ; ou sous forme de composés tels que chlorure fluorure, oxyde obtenu à partir de lanthanides, ou leurs mélanges, dans la mesure où le rapport en poids lanthane/Terres Rares (excepté le lanthane est au moins supérieur à 2/1 ou de préférence supérieur à 10/1 et pour certains emplois particuliers supérieur à 100/1.According to another characteristic of the present invention, the lanthanum can be incorporated in the form of an alloy (s) with any metal capable of forming a homogeneous compound with the lanthanum, that is to say having a solubility diagram with the lanthanum alone or combined with other Rare Earths in a proportion of 0.01 to 90% by weight; or in the form of compounds such as fluoride chloride, oxide obtained from lanthanides, or mixtures thereof, insofar as the lanthanum / Rare Earth weight ratio (except lanthanum is at least greater than 2/1 or preferably greater than 10/1 and for certain specific jobs greater than 100/1.

A ce sujet, on peut signaler que l'addition de mischmétal (à forte proportion de cérium) dans l'acier modifie la nature des sulfures en les rendant moins nuisibles mais n'améliore pas la propreté de l'acier qui reste chargé d'une quantité importante d'inclusions. L'invention résout ce problème .In this regard, it can be noted that the addition of mischmetal (with a high proportion of cerium) in the steel modifies the nature of the sulfides by making them less harmful but does not improve the cleanliness of the steel which remains charged with a large amount of inclusions. The invention solves this problem.

On peut signaler qu'éventuellement dans certains cas on peut utiliser le lanthane sous forme de lanthane métal pur ayant de préférence une pureté supérieure à 99%. Les alliages inoculants au lanthane de la présente invention particulièrement préférés sont des alliages à base Si-La-Al, La-Ni , La-Fe-Si, La-Fe-Mn, Si-Ca-Mg-La, La-Cr, Si-La-Mn et où le fer peut constituer le solde. Dans le cas où ces alliages inoculants au lanthane contiennent d'autres Terres Rares, y compris le cérium, le rapport précité lanthane/Terres Rares (excepté le lanthane) doit être dans tous les cas satisfait.It may be noted that possibly in certain cases it is possible to use lanthanum in the form of a lanthanum pure metal preferably having a purity greater than 99%. The lanthanum inoculating alloys of this particularly preferred invention are alloys based on Si-La-Al, La-Ni, La-Fe-Si, La-Fe-Mn, Si-Ca-Mg-La, La-Cr, Si-La-Mn and where the iron may constitute the balance. In the event that these lanthanum inoculating alloys contain other Rare Earths, including cerium, the above-mentioned lanthanum / Rare Earths ratio (except lanthanum) must in all cases be satisfied.

Selon le procédé da la présente invention, on réduit ou supprime certains défauts de la fonte tels que des défauts sous forme de piqûres et cavités ou retassures et on réduit l'anisotropie des aciers en permettant ainsi d'obtenir des alliages ferreux ayant de meilleures propriétés mécaniques.According to the process of the present invention, certain defects in the cast iron are reduced or eliminated such as defects in the form of pits and cavities or shrinkage and the anisotropy of the steels is reduced, thereby making it possible to obtain ferrous alloys having better properties. mechanical.

A ce sujet, la demanderesse a découvert que les défauts précités de la fonte à graphite sphéroldal tels que piqûres et cavités sont dus à la rétention à divers stades d'un gaz émis lors de la solidification. Ce gaz semble être un gaz réducteur car les parois des cavités sont lisses et non oxydées et on peut penser qu'il s'agit soit de C0, soit d'hydrogène, soit d'une combinaison des deux.In this regard, the Applicant has discovered that the aforementioned defects of spheroldal graphite cast iron such as pits and cavities are due to the retention at various stages of a gas emitted during solidification. This gas seems to be a reducing gas because the walls of the cavities are smooth and not oxidized and one can think that it is either C0, or hydrogen, or a combination of the two.

L'apparition de ce gaz réducteur (CO tout au moins) ne serait pas accidentelle, comme prétendu jusqu'à ce jour (matière première oxydée, atmosphère oxydante, etc) mais systématique: à certains stades de la solidification, vraisemblablement au passage du liquidus.The appearance of this reducing gas (CO at least) would not be accidental, as claimed to date (oxidized raw material, oxidizing atmosphere, etc.) but systematic: at certain stages of solidification, probably when the liquidus passes .

En utilisant les propriétés métallurgiques et thermodynamiques de chacun des éléments des Terres Rares, la demanderesse a mis en évidence que celles-ci sont bien spécifiques et parfois antagonistes. En effet, la demanderesse a mis en évidence que :

  • - le cérium et le lanthane présentent une miscibilité totale dans le fer liquide ;
  • -la solubilité du cérium dans le fer à 600°C s'établit entre 0,35 et 0,40%. Cet élément forme alors des composés tels que Ce-Fe5 (dur et cassant), Ce-Fe2 etc.
  • - le lanthane a par contre une faible solubilité dans le fer (pas de composés définis La-Fe).
By using the metallurgical and thermodynamic properties of each of the elements of the Rare Earths, the Applicant has highlighted that these are very specific and sometimes antagonistic. The plaintiff has shown that:
  • - Cerium and lanthanum have total miscibility in liquid iron;
  • -the solubility of cerium in iron at 600 ° C is between 0.35 and 0.40%. This element then forms compounds such as Ce-Fe 5 (hard and brittle), Ce-Fe 2 etc.
  • - on the other hand, lanthanum has a low solubility in iron (no defined compounds La-Fe).

Il résulte de ce qui précède que l'activité de Ce sera faible étant donné qu'il se trouve sous forme de composés inter-métalliques tandis que le lanthane aura une activité forte car il reste disponible pour des réactions avec l'oxygène et le soufre.It follows from the above that the activity of Ce will be low since it is in the form of inter-metallic compounds while lanthanum will have a strong activity because it remains available for reactions with oxygen and sulfur .

L'utilisation du lanthane sous forme d'alliages composites (nodulisants, inoculants, désulfurants) permet d'obtenir ainsi une purification plus importante du bain en oxygène et en soufre ce qui conduit à une plus grande ferritisation de la matrice et permet d'améliorer les caractéristiques mécaniques des alliages ferreux obtenus.The use of lanthanum in the form of composite alloys (nodulizers, inoculants, desulphurizers) thus makes it possible to obtain a greater purification of the bath in oxygen and in sulfur which leads to a greater ferritization of the matrix and makes it possible to improve the mechanical characteristics of the ferrous alloys obtained.

On doit noter que la présence de cérium, en quantités relativement importantes, c'est-à-dire déjà à partir d'environ 1%, seul ou en combinaison avec d'autres Terres Rares, excepté le lanthane, par rapport à la proportion de lanthane, comme dans le cas du mischmétal utilisé auparavant, ne permet pratiquement pas d'obtenir les améliorations obtenues avec le lanthane selon la présente invention ayant une faible teneur en cérium car la demanderesse a découvert que le cérium a un effet néfaste et antagoniste au lanthane qui se manifeste dès que la teneur en cérium est déjà d'environ 1% par rapport à la proportion de lanthane.It should be noted that the presence of cerium, in relatively large quantities, that is to say already from about 1%, alone or in combination with other Rare Earths, except lanthanum, compared to the proportion lanthanum, as in the case of mischmetal used before, practically does not allow to obtain the improvements obtained with lanthanum according to the present invention having a low content of cerium because the Applicant has discovered that cerium has a harmful effect and antagonistic to lanthanum which manifests itself as soon as the cerium content is already around 1% compared to the proportion of lanthanum.

D'autres buts, caractéristiques et avantages de la présente invention apparaîtront plus clairement à la lumière de la description explicative qui va suivre faite en référence aux exemples suivants donnés simplement à titre d'illustration et qui ne sauraient donc en aucune façon limiter la portée de la présente invention. Les exemples 1 à 4 sont illustrés par les figures 1 à 10 des dessins.Other objects, characteristics and advantages of the present invention will appear more clearly in the light of the explanatory description which will follow made with reference to the following examples given simply by way of illustration and which therefore cannot in any way how to limit the scope of the present invention. Examples 1 to 4 are illustrated by Figures 1 to 10 of the drawings.

  • Les figures 1 à 6 représentent des courbes de solidification de fonte à graphite sphéroidal dans lesquelles la température est mentionnée en ordonnées tandis que le temps est mentionné en abscisses.FIGS. 1 to 6 show solidification curves of spheroidal graphite cast iron in which the temperature is mentioned on the ordinate while the time is mentioned on the abscissa.
  • Les figures 7 à 10 montrent les cavités ou retassures obtenues sur des pièces préparées selon l'art antérieur (figures 7, 9 et 10) et selon la présente invention (figure 8).Figures 7 to 10 show the cavities or recesses obtained on parts prepared according to the prior art (Figures 7, 9 and 10) and according to the present invention (Figure 8).

Dans les exemples, les teneurs des composants sont données en pourcentage en poids.In the examples, the contents of the components are given as a percentage by weight.

Exemple 1Example 1

On élabore au cubilot basique une fonte ayant la composition suivante :

Figure imgb0006
Figure imgb0007
Figure imgb0008
Figure imgb0009
 A basic cupola is produced using the following composition:
Figure imgb0006
Figure imgb0007
Figure imgb0008
Figure imgb0009

Cette fonte est élaborée sans inoculation et sert de référence. La courbe de solidification obtenue sur un creuset MECI, à couple Cr-Ni pour une telle fonte de référence est représentée à la figure 1. Ce creuset MECI ne modifie pas la solidification du lingotin et assure en particulier une solidification tout à fait comparable à celle deune pièce dans un moule en sable. Le palier eutectique est repérable par une anomalie dans la courbe de refroidissement qui est caractérisée par un changement d'inflexion de la courbe enregistrée (voir figure 1)This font is produced without inoculation and serves as a reference. The solidification curve obtained on a MECI crucible, with Cr-Ni couple for such a reference cast iron is represented in FIG. 1. This MECI crucible does not modify the solidification of the ingot and in particular ensures solidification quite comparable to that two pieces in a sand mold. The eutectic level is identifiable by an anomaly in the cooling curve which is characterized by a change in inflection of the recorded curve (see Figure 1)

Lorsqu'on incorpore à la fonte précitée, lors de son élaboration, 0,3% en poids d'alliage Si-La-Al (Si=63%; La = 2,1% ; Al = 1,45%, le reste étant du fer), c'est-à-dire 0,0063% en poids de lanthane, soit 63 ppm, on obtient des pièces moulées qui ne présentent pas de cavité. La courbe de solidification obtenue, représentée à la figure 2, montre un allongement de l'intervalle de solidification de l'ordre de 37% par rapport à la courbe de la figure 1 ainsi qu'un décalage en augmentation de 13°C de la température du palier de transformation. Ce déplacement de la position du palier eutectique implique un passage au diagramme Fe-graphite et l'allongement de l'intervalle de solidification permet un dégazage effectif ce qui conduit à la formation de la pièce saine précitée.When incorporating into the above-mentioned cast iron, during its preparation, 0.3% by weight of Si-La-Al alloy (Si = 63%; La = 2.1%; Al = 1.45%, the rest being iron), that is ie 0.0063% by weight of lanthanum, or 63 ppm, molded parts are obtained which do not have a cavity. The solidification curve obtained, represented in FIG. 2, shows an elongation of the solidification interval of the order of 37% relative to the curve in FIG. 1 as well as an increasing shift of 13 ° C in the temperature of the transformation stage. This displacement of the position of the eutectic bearing implies a transition to the Fe-graphite diagram and the lengthening of the solidification interval allows effective degassing which leads to the formation of the aforementioned healthy part.

Exemple 2Example 2

On utilise une fonte de base ayant la composition suivante :

Figure imgb0010
Figure imgb0011
Figure imgb0012
Figure imgb0013
que l'on élabore au four électrique. On inocule lors de son élaboration 0,4% d'alliage inoculant habituellement utilisé par la fonderie ayant la composition suivante :
Figure imgb0014
Figure imgb0015
Figure imgb0016
Figure imgb0017
 We use a basic font with the following composition:
Figure imgb0010
Figure imgb0011
Figure imgb0012
Figure imgb0013
 that we make in the electric oven. 0.4% of the inoculating alloy usually used by the foundry having the following composition is inoculated during its preparation:
Figure imgb0014
Figure imgb0015
Figure imgb0016
Figure imgb0017

La courbe de solidification obtenue, en utilisant un creuset MECI, est représentée à la figure 3. Les pièces obtenues présentent des défauts d'aspect tels que cavités.The solidification curve obtained, using a MECI crucible, is shown in FIG. 3. The parts obtained have appearance defects such as cavities.

Lorsqu'on incorpore, selon la présente invention, lors de l'élaboration de cette fonte , 0,4% d'un alliage ayant la composition suivante :

Figure imgb0018
Figure imgb0019
Figure imgb0020
Figure imgb0021
C'est-à-dire 0,0084% de lanthane, soit 84 ppm.When incorporating, according to the present invention, during the preparation of this cast iron, 0.4% of an alloy having the following composition:
Figure imgb0018
Figure imgb0019
Figure imgb0020
Figure imgb0021
 That is to say 0.0084% lanthanum, or 84 ppm.

On obtient la courbe de solidification représentée à la figure 4 qui montre un allongement de l'intervalle de solidification de l'ordre de 30% et un accroissement de la température du palier de transformation de l'ordre de 10°C. Les pièces obtenues sont dépourvues de cavité.The solidification curve shown in FIG. 4 is obtained, which shows an elongation of the solidification interval of the order of 30% and an increase in the temperature of the transformation plateau of the order of 10 ° C. The parts obtained are devoid of cavity.

Exemple 3Example 3

On utilise une fonte ayant la composition de base suivante :

Figure imgb0022
Figure imgb0023
Figure imgb0024
Figure imgb0025
que l'on élabore au four électrique.We use a font with the following basic composition:
Figure imgb0022
Figure imgb0023
Figure imgb0024
Figure imgb0025
 that we make in the electric oven.

A cette fonte, on incorpore lors de son élaboration 0,4% de l'alliage inoculant habituellement utilisé en fonde- i rie mentionné à l'exemple 2. On obtient la courbe de refroidissement représentée à la figure 5, qui a été enregistrée sur des creusets spéciaux tltellure-S" élec- tronite. Ces creusets sont revêtus d'un enduit carbu- rigène et assurent un refroidissement dans le seul dia- ) gramme métastable "Fe-CFe3". Bien que moins représentatif de la solidification pratique des pièces, ce type de creusets permet d'obtenir un palier eutectique bien marqué ce qui permet de comparer plus aisément les longueurs différentes des paliers eutectiques.During this elaboration, 0.4% of the inoculating alloy usually used in foundry mentioned in Example 2 is incorporated during its melting. The cooling curve shown in FIG. 5 is obtained, which was recorded on special tltellure-S "electretite crucibles. These crucibles are coated with a carburetor coating and provide cooling in the only metastable dia-) gram" Fe-CFe 3 ". Although less representative of the practical solidification of pieces, this type of crucible makes it possible to obtain a well marked eutectic bearing which makes it easier to compare the different lengths of the eutectic bearings.

Selon le procédé de la présente invention, on incorpore, lors de l'élaboration de cette fonte, 0,4% de l'alliage au lanthane, sensiblement exempt de cérium, mentionné à l'exemple 2. On obtient la courbe de refroidissement représentée à la figure 6 qui montre un accroissement de la longueur du palier de transformation de l'ordre de 260% et une augmentation de la température de transformation de 10°C environ par rapport à celle de la figure 5.According to the process of the present invention, 0.4% of the alloy is incorporated during the production of this cast iron. lanthanum, substantially free of cerium, mentioned in Example 2. The cooling curve shown in FIG. 6 is obtained, which shows an increase in the length of the transformation stage of the order of 260% and an increase in the temperature. transformation of about 10 ° C compared to that of Figure 5.

Les pièces coulées avec l'alliage de la présente invention sont pratiquement saines, les masselotes ne présentent qu'une faible retassure dendritique tandis que les pièces coulées selon le procédé antérieur présentent des cavités et des piqûres.The parts cast with the alloy of the present invention are practically sound, the weights have only a slight dendritic shrinkage while the parts cast according to the prior method have cavities and pits.

Afin de comparer l'amélioration des propriétés mécaniques obtenues par le procédé de la présente invention, on a préparé des éprouvettes de traction que l'on a testées, les résultats obtenus sont mentionnés dans le Tableau I suivant :

Figure imgb0026
In order to compare the improvement in the mechanical properties obtained by the process of the present invention, tensile test pieces were prepared which were tested, the results obtained are mentioned in Table I below:
Figure imgb0026

Les gains importants obtenus sur l'allongement et la résilience confirment l'influence de la structure fer- ritique sur les caractéristiques mécaniques.The significant gains obtained in elongation and resilience confirm the influence of the ferritic structure on the mechanical characteristics.

Exemple 4Example 4

A partir d'une fonte de base telle que C = 3,65; Si=2,65; Mn = 0,08 ; S = 0,010 et préparée dans le cadre d'un procédé spécial de nodulisation de la fonte dans le moule (procédé inmold), on a utilisé les deux alliages suivants afin de mettre en évidence l'action du lanthane sur l'aptitute aux cavités ("retassures") de la fonte coulée par ce procédé. Ces deux alliages ont été élaborés à partir d'un alliage mère Fe - Si - Mg :

Figure imgb0027
From a base cast such that C = 3.65; If = 2.6 5 ; Mn = 0.08; S = 0.010 and prepared within the framework of a special process of nodulization of the cast iron in the mold (inmold process), the following two alloys were used in order to highlight the action of lanthanum on the ability to cavities ( "shrinkage") of the cast iron cast by this process. These two alloys were made from a Fe - Si - Mg mother alloy:
Figure imgb0027

Le mischmétal utilisé présente la composition suivante :

Figure imgb0028
Figure imgb0029

  • - Solde = autres Terres Rares.
The mischmetal used has the following composition:
Figure imgb0028
Figure imgb0029
  • - Balance = other Rare Earths.

Les pièces obtenues, en incorporant 1% des alliages 1 et 2, sont représentées en coupe, respectivement aux figures 7 et 8. A partir des figures 7 et 8, on peut constater que l'alliage 2 selon la présente invention permet d'obtenir des masselottes ne présentant qu'une retassure primaire-dendritique tandis que la masselotte préparée avec le mischmétal antérieur présente une cavité ou retassure importante. On doit noter que le rapport lanthane/Terres Rares dans le mischmétal est égal à 0,25. Ce rapport selon la présente invention doit être comme mentionné précédemment, au moins égal à 2, de préférence au moins égal à 10 et encore de préférence au moins égal à 100.The parts obtained, by incorporating 1% of the alloys 1 and 2, are shown in section, in Figures 7 and 8 respectively. From Figures 7 and 8, it can be seen that the alloy 2 according to the present invention makes it possible to obtain weights having only a primary-dendritic recess while the counterweight prepared with the anterior mischmetal has a significant recess or recess. It should be noted that the lanthanum / Rare Earths ratio in the mischmetal is equal to 0.25. This ratio according to the present invention must be, as mentioned above, at least equal to 2, preferably at least equal to 10 and more preferably at least equal to 100.

Des essais mécaniques ont été effectués sur des blocs pour éprouvette obtenus après incorporation de l'alliage 1 ou de l'alliage 2 et sont résumés dans le tableau II suivant :

Figure imgb0030
Mechanical tests were carried out on blocks for test pieces obtained after incorporation of alloy 1 or alloy 2 and are summarized in Table II below:
Figure imgb0030

Les résultats obtenus confirment l'heureuse influence du lanthane sur la structure (ferritisation) et sur la compacité des pièces coulées.The results obtained confirm the happy influence of lanthanum on the structure (ferritization) and on the compactness of the castings.

Afin de confirmer l'action spécifique du lanthane et de mettre en évidence l'action antagoniste du cérium, deux essais complémentaires ont été effectués dans lesquels on incorpore à la fonte, respectivement, 1% des deux alliages suivants :

  • Alliage 3 : Si = 48,2% ; Ca = 0,58% ; Mg = 5,8% ;Ce = 1% (mischmétal 2%) ; Fe = le reste.
In order to confirm the specific action of lanthanum and to highlight the antagonistic action of cerium, two additional tests were carried out in which 1% of the following two alloys are incorporated into the cast iron, respectively:
  • Alloy 3: Si = 48.2%; Ca = 0.58%; Mg = 5.8%; Ce = 1% (mischmetal 2%); Fe = the rest.

Le mischmétal utilisé présente la composition mentionnée précédemment pour l'alliage 1.The mischmetal used has the composition mentioned above for alloy 1.

Alliage 4 identique à l'alliage 3 sauf que l'on emploie 0,50% de cérium apporté sous forme de Fe-Ce au lieu de Mischmétal.Alloy 4 identical to alloy 3 except that we use 0.50% of cerium supplied in the form of Fe-Ce instead of Mischmetal.

Les pièces obtenues avec incorporation des alliages 3 et 4 sont représentées, respectivement, aux figures 9 et 10. On peut constater qu'il n'y a pas de diminution de l'importance des cavités même dans le cas de l'alliage 3 pour lequel on a une teneur finale en La = 0,4% ce qui permet de constater que la présence de cérium en quantité supérieure à 1% en poids par rapport au poids de lanthane inhibe l'effet bénéfique du lanthane.The parts obtained with incorporation of alloys 3 and 4 are shown, respectively, in FIGS. 9 and 10. It can be seen that there is no reduction in the import tance of the cavities even in the case of alloy 3 for which there is a final content of La = 0.4% which shows that the presence of cerium in an amount greater than 1% by weight relative to the weight of lanthanum inhibits the beneficial effect of lanthanum.

Exemple 5Example 5

Lors de l'élaboration d'une fonte hyppereutectique à environ 1310°C, on inocule de manière connue en soi dans celle-ci 0,5% en poids d'alliage inoculant habituellement utilisé en fonderie ayant la composition suivante (A) :

Figure imgb0031
Figure imgb0032
Figure imgb0033
Figure imgb0034
 During the preparation of a hyperpperectic cast iron at approximately 1310 ° C., 0.5% by weight of inoculating alloy usually used in foundries having the following composition (A) is inoculated in a manner known per se.
Figure imgb0031
Figure imgb0032
Figure imgb0033
Figure imgb0034

On obtient une fonte ayant la composition mentionnée au tableau III avec les caractéristiques physiques mentionnées également au tableau III.A cast iron is obtained having the composition mentioned in Table III with the physical characteristics also mentioned in Table III.

En inoculant 0,5% en poids d'un alliage inoculant selon la présente invention, ayant la composition (B) suivante:

Figure imgb0035
Figure imgb0036
Figure imgb0037
Figure imgb0038
soit 25.10-4% en poids de lanthane ou 25 ppm, on obtient une fonte ayant la composition et les caractéristiques physiques mentionnées également au tableau III. On peut constater que le nombre des sphéroïdes de graphite obtenus est bien plus nombreux et les effets de la trempe (zone carburée) moindres avec l'utilisation de l'alliage inoculant selon la présente invention par rapport à l'alliage inoculant connu, et ceci de manière inattendue.
Figure imgb0039
 By inoculating 0.5% by weight of an inoculating alloy according to the present invention, having the following composition (B):
Figure imgb0035
Figure imgb0036
Figure imgb0037
Figure imgb0038
 or 25.10 -4 % by weight of lanthanum or 25 ppm, a cast iron is obtained having the composition and the physical characteristics also mentioned in Table III. It can be seen that the number of graphite spheroids obtained is much more numerous and the effects of quenching (carburetted area) less with the use of the inoculating alloy according to the present invention compared to the known inoculating alloy, and this unexpectedly.
Figure imgb0039

Dans le cas des aciers, le lanthane peut résoudre les problèmes connexes à la désoxydation de l'acier. A ce sujet, pour utiliser au mieux les propriétés désulfurantes du lanthane, il importe de désoxyder préalablement l'acier de manière classique, par exemple par désoxydation préalable au four par addition de 0,8 à 1% en poids d'aluminium que l'on complète par une désoxydation en poche en utilisant des taux de lanthane dans les intervalles précédemment mentionnés, c'est-à-dire en une quantité comprise avantageusement entre 10-4 % et 10-2%, soit de 1 à 100 ppm, et de préférence de 1-10 à 30 ppm.In the case of steels, lanthanum can solve the problems associated with the deoxidation of steel. In this regard, to make the best use of the desulphurizing properties of lanthanum, it is important to deoxidize the steel beforehand in a conventional manner, for example by deoxidation prior to the furnace by adding 0.8 to 1% by weight of aluminum than the it is completed by a pocket deoxidation using lanthanum levels in the above-mentioned intervals, that is to say in an amount advantageously between 10 -4 % and 10-2%, ie from 1 to 100 ppm, and preferably 1-10 to 30 ppm.

Ainsi du fait de la faible quantité de lanthane ajouté, il y a très peu d'inclusions, celles-ci étant bien réparties en éliminant ainsi les viscosités des inclusions ce qui aboutit à un bain d'acier très fluide, à la solidification, et en dernier lieu à un acier très propre.Thus, due to the small amount of lanthanum added, there are very few inclusions, these being well distributed, thus eliminating the viscosities of the inclusions, which results in a very fluid steel bath, solidification, and lastly to a very clean steel.

En outre, la désulfuration quasi complète de l'acier diminue de même la tension superficielle de celui-ci et conduit à une amélioration de sa coulabilité.In addition, the almost complete desulphurization of the steel likewise reduces the surface tension of the latter and leads to an improvement in its flowability.

Ces observations sont confirmées par l'exemple suivant.These observations are confirmed by the following example.

Exemple 6Example 6

On désire préparer un acier ayant la composition chimique suivante :

Figure imgb0040
Figure imgb0041
Figure imgb0042
Figure imgb0043
Figure imgb0044
Figure imgb0045
Figure imgb0046
 We want to prepare a steel with the following chemical composition:
Figure imgb0040
Figure imgb0041
Figure imgb0042
Figure imgb0043
Figure imgb0044
Figure imgb0045
Figure imgb0046

Pour cela, à partir d'un acier de composition classique, on réalise une cculée de 13570 kg dans un four auquel on ajoute 0,07% de carbonne et 0,15% de Mn.To do this, using a steel of conventional composition, a 13570 kg rounding is carried out in an oven to which 0.07% of carbon and 0.15% of Mn are added.

Pour réaliser un affinage de la teneur en oxygène, on effectue une désoxydation préalable au four, selon la méthode traditionnelle, par addition d'environ 0,8% d'aluminium. Après l'addition de l'aluminium, on prélève directement du four un échantillon d'acier dont on obtient la composition suivante :

Figure imgb0047
To achieve refining of the oxygen content, a deoxidation is carried out beforehand in the oven, according to the traditional method, by the addition of approximately 0.8% of aluminum. After the addition of aluminum, a sample of steel is taken directly from the furnace, the following composition being obtained:
Figure imgb0047

L'analyse cristallographique montre que cet acier comporte des macro-inclusions d'aluminate et de silicate et des micro-sulfures.The crystallographic analysis shows that this steel contains macro-inclusions of aluminate and silicate and micro-sulfides.

Selon la présente invention, après ladésoxydation au four précitée à l'aluminium, on réalise une désoxydation en poche en ajoutant 27 kg d'un alliage au silico-lanthane comprenant 45% de Si, 0,5% de La, le reste étant du fer, soit une addition d'environ 0,20% de l'alliage au lanthane ce qui correspond à une addition d'environ 10-3 % de lanthane soit environ 10 ppm.According to the present invention, after deoxidation in the above-mentioned oven with aluminum, a pocket deoxidation is carried out by adding 27 kg of a silico-lanthanum alloy comprising 45% of Si, 0.5% of La, the remainder being iron, or an addition of about 0.20% of the alloy to lanthanum which corresponds to an addition of about 10 -3 % of lanthanum or about 10 ppm.

On prélève un échantillon d'acier dans la poche après la désoxydation à l'alliage inoculant au lanthane de la présente invention et on obtient un acier ayant la composition suivante :

Figure imgb0048
L'analyse cristallographique de cet acier montre que l'on obtient un acier comportant des micro-inclusions d'aluminate et de silicate en obtenant des globules réfractaires de diamètre moyen faible de l'ordre de 1 à 2 microns et en nombre limité.A sample of steel is taken from the pocket after the deoxidation with the lanthanum inoculating alloy of the present invention and a steel is obtained having the following composition:
Figure imgb0048
 The crystallographic analysis of this steel shows that a steel is obtained comprising micro-inclusions of aluminate and silicate by obtaining refractory globules of small average diameter of the order of 1 to 2 microns and in limited number.

Par ailleurs, le lanthane selon la présente invention en alliage avec d'autres métaux, y compris avec des Terres Rares dans la mesure où on respecte le rapport précité lanthane/Terres Rares, donne la possibilité, dans le cours de la cinétique de désoxydation,de désulfuration, de dénitruration et de déshydratation, de. prévoir et d'obtenir le nombre d'inclusions à la taille et à la composition souhaitées pour les applications de l'acier que l'on souhaite produire ce qui constitue un résultat industriel particulièrement remarquable.Furthermore, the lanthanum according to the present invention in alloy with other metals, including with Rare Earths in so far as the above-mentioned lanthanum / Rare Earths ratio is respected, gives the possibility, in the course of the deoxidation kinetics, desulfurization, denitriding and dehydration,. predict and obtain the number of inclusions of the desired size and composition for the steel applications that it is desired to produce, which constitutes a particularly remarkable industrial result.

Ainsi l'addition de lanthane, dans les conditions de la présente invention, permet de réduire l'anisotropie des aciers et d'améliorer de ce fait le rapport des résiliences longitudinale et transversale obtenues.Thus, the addition of lanthanum, under the conditions of the present invention, makes it possible to reduce the anisotropy of the steels and thereby improve the ratio of the longitudinal and transverse resilience obtained.

On doit noter de manière générale que le lanthane se trouve dans l'alliage ferreux sous forme de composés tels qu'oxydes, et/ou sulfures, et/ou nitrures, et/ou hydrures, et/ou carbures formant des inclusions non gênantes dans les alliages ferreux.It should generally be noted that lanthanum is found in the ferrous alloy in the form of compounds such as oxides, and / or sulfides, and / or nitrides, and / or hydrides, and / or carbides forming non-annoying inclusions in ferrous alloys.

En outre, lors de l'élaboration de l'alliage ferreux, si la fonte ou l'acier décante bien, on doit avoir 70% des composés de lanthane formés qui remontent dans le laitier. Ainsi, on trouve en général moins de 30% de composés de lanthane dans l'alliage ferreux obtenu.In addition, during the development of the ferrous alloy, if the cast iron or steel settles well, one must have 70% of the lanthanum compounds formed which go up in the slag. Thus, in general, less than 30% of lanthanum compounds are found in the ferrous alloy obtained.

Avantageusement, le lanthane est incorporé à l'alliage ferreux, lors de son élaboration sous forme d'un alliage inoculant ayant la composition suivante (pourcentage en poids ) :

Figure imgb0049
Figure imgb0050
Figure imgb0051
ou
Figure imgb0052
Figure imgb0053
Figure imgb0054
 Advantageously, lanthanum is incorporated into the ferrous alloy, when it is produced in the form of an alloy inoculant having the following composition (percentage by weight):
Figure imgb0049
Figure imgb0050
Figure imgb0051
 or
Figure imgb0052
Figure imgb0053
Figure imgb0054

Les aciers préparés par le procédé de la présente invention peuvent être notamment des aciers de construction, des aciers spéciaux, des aciers inoxydables, de moulage ou de laminage mais ne sont pas limités à ceux- ci.The steels prepared by the process of the present invention can be in particular structural steels, special steels, stainless steels, casting or rolling but are not limited to these.

Bien entendu, l'invention n'est nullement limitée aux modes de réalisation décrits et représentés qui n'ont été donnés qu'à titre d'exemple. En paxticulier, elle comprend tous les moyens constituant des équivalents techniques des moyens, ainsi que leurs combinaisons si celles-ci sont exécutées suivant son esprit et mises en oeuvre dans le cadre des revendications qui suivent.Of course, the invention is in no way limited to the embodiments described and shown which have been given only by way of example. In particular, it includes all the means constituting technical equivalents of the means, as well as their combinations if these are carried out according to the spirit and implemented in the context of the claims which follow.

Claims (19)

1. Procédé de préparation d'alliages ferreux permettant de réduire ou supprimer certains défauts desdits alliages ferreux tels que piqûres et cavités des fontes à graphite sphéroidal, carbures de la fonte grise lamellaire, d'améliorer la coulabilité, Inaptitude au laminage et l'isotropie des aciers, et d'améliorer les propriétés mécaniques desdits alliages ferreux, caractérisé en ce qu'il comprend l'incorporation d'au moins 0,0001%. à environ 0,5 à 2% en poids de lanthane audit alliage ferreux lors de son élaboration.1. Process for the preparation of ferrous alloys making it possible to reduce or eliminate certain defects in said ferrous alloys such as pits and cavities in spheroidal graphite cast irons, carbides of gray lamellar cast iron, to improve the flowability, unsuitability for rolling and isotropy steels, and to improve the mechanical properties of said ferrous alloys, characterized in that it comprises the incorporation of at least 0.0001%. at about 0.5 to 2% by weight of lanthanum to said ferrous alloy during its preparation. 2. Procédé selon la revendication 1, caractérisé en ce qu'il comprend l'incorporation d'environ 0,0001% à environ 0,01% en poids de lanthane audit alliage ferreux lors de son élaboration.2. Method according to claim 1, characterized in that it comprises the incorporation of about 0.0001% to about 0.01% by weight of lanthanum in said ferrous alloy during its preparation. 3. Procédé selon la revendication 1 ou 2, caractérisé en ce qu'il comprend l'incorporation d'environ 0,001 à environ 0,003 à 0,01% en poids de lanthane audit alliage ferreux, lors de son élaboration.3. Method according to claim 1 or 2, characterized in that it comprises the incorporation of about 0.001 to about 0.003 to 0.01% by weight of lanthanum in said ferrous alloy, during its preparation. 4. Procédé selon l'une des revendications précédentes, caractérisé en ce qu'on prépare une fonte à graphite sphéroidal à partir d'une fonte de base ayant la composition suivante (en pourcentage en poids) ;
Figure imgb0055
Figure imgb0056
Figure imgb0057
Figure imgb0058
Figure imgb0059
Figure imgb0060
à laquelle on incorpore lors de son élaboration du lanthane selon les proportions précitées.4. Method according to one of the preceding claims, characterized in that a spheroidal graphite cast iron is prepared from a base cast iron having the following composition (in percentage by weight);
Figure imgb0055
Figure imgb0056
Figure imgb0057
Figure imgb0058
Figure imgb0059
Figure imgb0060
 which is incorporated during its preparation of lanthanum in the above proportions. 5. Procédé selon l'une des revendications précédentes, caractérisé en ce que le lanthane est incorporé sous forme d'alliages avec tout métal susceptible de former un composé homogène avec le lanthane, c'est-à-dire présentant un diagramme de solubilité avec le lanthane seul ou associé à d'autres Terres Rares (y compris le cérium) dans la proportion de 0,01 à 90% en poids de lanthane, pourvu que l'alliage au lanthane ait une faible teneur en cérium seul ou associé à d'autres Terres Rares.5. Method according to one of the preceding claims, characterized in that the lanthanum is incorporated in the form of alloys with any metal capable of forming a compound homogeneous with the lanthanum, that is to say having a solubility diagram with lanthanum alone or associated with other Rare Earths (including cerium) in the proportion of 0.01 to 90% by weight of lanthanum, provided that the lanthanum alloy has a low content of cerium alone or associated with d 'other Rare Earths. 6. Procédé selon l'une des revendications 1 à.4, caractérisé en ce que-le lanthane est incorporé sous forme de composé tel que chlorure, fluorure, oxyde obtenu à partir de lanthanides, ou de mélanges desdits composés pourvu que ces composés de lanthanide aient une faible.teneur en cérium seul ou associé à d'autres Terres Rares.6. Method according to one of claims 1 to.4, characterized in that the lanthanum is incorporated in the form of a compound such as chloride, fluoride, oxide obtained from lanthanides, or mixtures of said compounds provided that these compounds lanthanide have a low cerium content alone or combined with other Rare Earths. 7. Procédé selon la revendication 5 ou 6, caractérisé en ce que le rapport en poids lanthane/Terres Rares (excepté le lanthane) dans les alliages précités ou composés de lanthanides précités est au moins supérieur à 2/1 ou de préférence supérieur à 10/1 et encore de préférence supérieur à 100/1.7. Method according to claim 5 or 6, characterized in that the lanthanum / Rare Earth weight ratio (except lanthanum) in the aforementioned alloys or compounds of the aforementioned lanthanides is at least greater than 2/1 or preferably greater than 10 / 1 and more preferably greater than 100/1. 8. Procédé selon l'une des revendications 1 à 4, caractérisé en ce que le lanthane est incorporé sous forme de lanthane-métal ayant de préférence une pureté supérieure à 99%.8. Method according to one of claims 1 to 4, characterized in that the lanthanum is incorporated in the form of lanthanum-metal preferably having a purity greater than 99%. 9. Procédé selon la revendication 5, caractérisé en ce que le lanthane est incorporé sous forme d'un alliage à base Si-La-Al, La-Ni, La-Fe-Si, La-Fe-Mn, Si-Ca-Mg-La, La-Cr, Si-La-Mn, et où le fer peut constituer le solde.9. Method according to claim 5, characterized in that the lanthanum is incorporated in the form of an alloy based on Si-La-Al, La-Ni, La-Fe-Si, La-Fe-Mn, Si-Ca- Mg-La, La-Cr, Si-La-Mn, and where iron can make up the balance. 10. Procédé selon la revendication 9, caractérisé en ce gue le lanthane est incorporé sous forme d'un alliage ayant la composition suivante (en % en poids) :10. Method according to claim 9, characterized in that the lanthanum is incorporated in the form of an alloy having the following composition (in% by weight):
Figure imgb0061
Figure imgb0061
Figure imgb0062
Figure imgb0062
Figure imgb0063
Figure imgb0063
Figure imgb0064
Figure imgb0064
Figure imgb0065
Figure imgb0065
 11. Procédé selon la revendication 9, caractérisé en ce que le lanthane est incorporé sous la forme d'un alliage ayant la composition suivante (% en poids)11. Method according to claim 9, characterized in that the lanthanum is incorporated in the form of an alloy having the following composition (% by weight)
Figure imgb0066
Figure imgb0066
Figure imgb0067
Figure imgb0067
Figure imgb0068
Figure imgb0068
Figure imgb0069
Figure imgb0069
Figure imgb0070
Figure imgb0070
 12. Alliages ferreux; caractérisés en ce qu'ils sont préparés par le procédé selon l'une quelconque des revendications précédentes.12. Ferrous alloys; characterized in that they are prepared by the process according to any one of the preceding claims. 13. Alliages ferreux, caractérisés en ce qu'ils possèdent du lanthane libre ou combiné sous forme d'oxydes et/ou de sulfures, et/ou d'hydrures, et/ou de nitrures et/ou de carbures, formant des inclusions non gênantes dans lesdits alliages ferreux.13. Ferrous alloys, characterized in that they have free or combined lanthanum in the form of oxides and / or sulfides, and / or hydrides, and / or nitrides and / or carbides, forming non-inclusions troublesome in said ferrous alloys. 14. Alliages ferreux selon la revendication 12 ou 13, caractérisés en ce qu'il s'agit de fonte, en particulier de la fonte à graphite sphéroidal et/ou à graphite lamellaire.14. Ferrous alloys according to claim 12 or 13, characterized in that it is cast iron, in particular cast iron with spheroidal graphite and / or lamellar graphite. 15. Alliages ferreux selon la revendication 12 ou 13, caractérisés en ce qu'il s'agit d'aciers tels que notamment aciers de construction, aciers spéciaux, aciers inoxydables, de moulage ou de laminage.15. Ferrous alloys according to claim 12 or 13, characterized in that they are steels such as in particular structural steels, special steels, stainless steels, molding or rolling. 16. Alliage contenant du lanthane nécessaire à la mise en oeuvre du procédé selon la revendication 10, caractérisé en ce qu'il a la composition suivante (en % en poids) :
Figure imgb0071
Figure imgb0072
Figure imgb0073
Figure imgb0074
Figure imgb0075
 16. Alloy containing lanthanum necessary for the implementation of the method according to claim 10, characterized in that it has the following composition (in% by weight):
Figure imgb0071
Figure imgb0072
Figure imgb0073
Figure imgb0074
Figure imgb0075
 17. Alliage contenant du lanthane nécessaire à la mise en oeuvre du procédé selon la révendication 11, caractérisé en ce qu'il a la composition suivante (en % en poids) :
Figure imgb0076
Figure imgb0077
Figure imgb0078
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Figure imgb0080
 17. Alloy containing lanthanum necessary for the implementation of the process according to claim 11, characterized in that it has the following composition (in% by weight):
Figure imgb0076
Figure imgb0077
Figure imgb0078
Figure imgb0079
Figure imgb0080
EP79400224A 1978-04-06 1979-04-05 Process for the production of ferrous alloys with improved mechanical properties by the use of lanthanum, and ferrous alloys obtained by this process Expired EP0004819B1 (en)

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JP4974591B2 (en) * 2005-12-07 2012-07-11 旭テック株式会社 Graphite spheroidizing agent and method for producing spheroidal graphite cast iron using the same
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EP0838534A1 (en) * 1996-10-25 1998-04-29 Lucchini Centro Ricerche E Sviluppo S.r.l. Improved resulfurized fine-austenitic-grain steel and process for obtaining it

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