EP2920335B1 - Inoculant alloy for thick cast-iron parts - Google Patents

Description

The present invention relates to an inoculating alloy for the treatment of cast iron.

Cast iron is a well-known iron-carbon alloy widely used for the manufacture of mechanical parts. Cast iron is obtained by mixing the constituents of the alloy in the liquid state at a temperature between 1320 and 1450 ° C before casting in a mold and cooling the alloy obtained.

During its cooling, the carbon can adopt several physicochemical structures depending on several parameters.

When carbon combines with iron and forms iron carbide Fe ₃ C (also called cementite), the resulting cast iron is called white cast iron. White cast iron has the characteristic of being hard and brittle, which is undesirable for certain applications.

If carbon appears as graphite, the resulting cast iron is called gray cast iron. Gray cast iron is softer and can be worked.

To obtain cast iron parts having good mechanical properties, it is therefore necessary to obtain a structure of the cast iron comprising the maximum of carbon in graphite form and to limit as much as possible the formation of these iron carbides which harden and weaken the alloy.

In the absence of any particular inoculation treatment, however, carbon tends to associate with iron to form iron carbide. It is therefore necessary to treat the cast iron in the liquid state so as to modify the carbon association parameters and obtain the desired structure.

To this end, the liquid cast iron undergoes an inoculation treatment aimed at introducing into the cast iron graphitizing components or graphitization supports commonly called germs which will promote, during the cooling of the cast iron in the mold, the appearance of graphite. rather than iron carbide.

In general, the components of an inoculant are therefore elements favoring the formation of graphite and the decomposition of iron carbide during the solidification of the cast iron. By way of example, mention may be made of carbon, silicon, calcium, aluminum, etc.

Obviously, an inoculant can be designed to perform other functions and to this end include other components having an effect particular. Cast iron can also undergo additional prior or subsequent treatments.

In particular, it may therefore be desired, depending on the properties sought, for the graphite formed to be spheroidal, vermicular or lamellar.

Either graphitic form can be obtained preferentially by a particular treatment of the cast iron using specific components.

Thus, for example the formation of spheroidal graphite can be favored by a so-called nodulating treatment aiming mainly at bringing to the melting of magnesium in an amount sufficient for the graphite to be able to grow so as to form round particles (spheroids or nodules).

These nodulizing components are generally added in the form of a specific alloy (nodulizing alloy) prior to the inoculating treatment of the cast iron during a particular treatment.

Thus, the nodulating alloy essentially makes it possible to influence the shape of the graphite nodules, while the inoculating product aims to increase the number of these nodules and to homogenize the graphitic structures.

Mention may also be made of the addition of desulphurizing products, or of products making it possible to specifically treat certain defects in the melting process as a function of the initial composition of the liquid melting bath, such as micro-shrinkage and pitting, which may appear during cooling.

These treatments can be carried out in one or more stages and at different times during the production of the cast iron.

Most inoculants are conventionally manufactured from a ferro-silicon alloy of the FeSi ₄₅ , FeSi ₆₅ or FeSi _{75 type} with adjustment of the chemistry according to the targeted composition of the inoculant. It can also be mixtures of several alloys.

It should be noted that the inoculation efficiency of the cast iron part also depends on its thickness (or else on the speed of solidification).

In areas of small thickness, cooling faster, there is a higher risk of carbide formation.

Conversely in areas of greater thickness, cooling will be slower (2 to 4 hours) and will favor the formation of graphite.

It follows that the parts with zones of different thicknesses may have different physicochemical structures from one zone to another, which is not desirable.

In addition, the control of germination in very thick areas remains difficult and can lead to obtaining a non-uniform structure.

For very thick pieces, when the inoculation process is not mastered, the formation of degenerate graphite and / or "chunky" graphite can reduce the mechanical properties of cast iron. To resolve these defects, the founder generally proceeds to the addition of pure Antimony in the liquid metal.

The addition of pure antimony into the liquid metal poses problems of precision because the rate of introduction is very low (of the order of 10 to 30 g per ton of liquid pig iron). The addition yield of pure antimony is between 50 and 80% and the useful amount introduced is therefore difficult to control.

If the quantity is not sufficient, degraded graphite can form in the structure.

Conversely, if the quantity introduced exceeds the objective, antimony will tend to greatly increase the proportion of perlite, an undesired phase in ferritic structures.

In the case of addition of pure antimony, the founder must also combine Rare Earths (abbreviated as TR or RE for “Rare Earths”) in order to obtain a maximum improvement in the shape of the graphite. Likewise, if the quantity of Rare Earths is insufficient, the part will present a graphite defect of type "spiky". Conversely, if the quantity of Rare Earth is too strongly dosed, the graphite defect will be rather of the “chunky” type, which occurs mainly when the raw materials used are relatively pure

These graphite defects, of the “spiky” or “chunky” type, degrade the mechanical properties of the cast iron, and in particular the tensile strength and the impact resistance of the formed part.

The introduction of pure antimony into the liquid cast iron furthermore causes it to vaporize and thus gives rise to a large gassing. It was measured that with the addition of pure antimony, the threshold for release of antimony in the working environment was greater than 0.5 mg / m ³ , exposure limit value (ELV set by regulation ). Operators must therefore work with a respirator against particles of type N95 or more.

The treatment of thin parts has already been the subject of specific inoculant development. The documents FR2511044A1 , FR2855186A1 and EP0816522A1 describe such an inoculant for thin parts.

Such an inoculant according to these documents for thin parts comprises in particular an inoculating alloy based on ferro-silicon and comprising between 0.005 and 3% by mass of Rare Earths, in particular Lanthanum, as well as between 0.005 and 3% by mass of bismuth, lead or antimony in a ratio (Bismuth + Lead + Antimony) / Rare Earth between 0.9 and 2.2; bismuth being particularly preferred, the descriptions of these documents relating only to bismuth.

It should be noted that these documents only disclose the use of antimony in a general way but do not contain any specific example or any particular value relating to this element.

Other documents mentioning the use of antimony include the following documents.

The document WO2006 / 068487A1 describes an inoculant comprising a phase modifier component (inoculating function) associated with an agent for modifying the structure of graphite which may be antimony. It should be noted that this structural modification agent is used in mixture with the inoculating compound (ferrosilicon) and not in alloyed form. Antimony is furthermore clearly mentioned as being a promoter of perlite, a phase which, as mentioned previously, is generally not desired. The amount of antimony used is between 3 and 15%, which corresponds to a significant amount probably responsible for the proportion of perlite formed.

The document JP2200718A describes an inoculant consisting of a mixture of ferrosilicon, antimony, calcium silicide and rare earths. Antimony is not used in an alloyed form.

The document JP57067146A describes an alloy based on ferrosilicon comprising between 5 and 50% by mass of antimony and up to 10% of rare earths. In addition to the high proportion of antimony, this alloy is used as a perlite inhibitor, not as an inoculant.

There are also several articles and documents dealing with a nodulizing function (form of graphite) of antimony, which is not the fundamentally desired goal and does not solve the problem of inoculation. (number and quality of nodules). In addition, it is frequently a use of antimony in a mixed and unalloyed form.

There is therefore a need for an inoculating alloy making it possible to improve the treatment of thick parts.

To do this, the present invention provides inoculating alloys according to claim 1 and claim 2.

Thus, it has in fact been unexpectedly found that antimony combined with rare earths in a ferrosilicon-based alloy in the claimed proportions allows effective inoculation, and with stabilization of the spheroids, of thick pieces without the drawbacks of l 'pure antimony mentioned above.

In particular, the introduction of antimony in the form of an alloy makes it possible to achieve a high yield of use of the antimony, of the order of 97 to 99%. The useful quantity introduced is therefore much more precisely known.

The increase in yield thus saves products and simplifies the management of product additions, including for rare earths.

Thanks to this increase in efficiency and the simultaneous reduction of gaseous emissions into the atmosphere, the working conditions are also improved for the operators responsible for the additions.

The use of an alloy according to the invention makes it possible to limit the gaseous evolution of antimony between 0.1 and 0.2 mg / m ³ and the use of a respirator mask is no longer necessary.

It will also be noted that the combination of antimony and rare earths significantly prolongs the time of antimony fading. The effect produced therefore lasts longer in the complete foundry process. It will be noted that the fading time of antimony is even greater than the fading time of bismuth in inoculating alloys for thin parts.

The alloy according to the present application, when added in a pouch or in the oven, can thus make it possible to replace or even eliminate an additional inoculation with a jet or late.

The alloy according to the present application also makes it possible in particular to greatly limit or even avoid the formation of defects in “chunky” or “spiky” type graphite, but also to improve the shape of the graphite by ensuring a nodularity greater than 95% while bringing the spheroids closer to the perfect sphere.

The alloy according to the present application thus ensures a ferrite / perlite matrix which is homogeneous according to the different thicknesses of the part produced, which in particular improves the conditions for subsequent machining of the part.

According to the invention, the antimony to rare earths ratio is between 0.9 and 2.2. Preferably, the Antimony to Rare Earths ratio will be greater than 1.4, preferably 1.6, and less than 2.5; preferably less than 2.

Preferably, the proportion by mass of antimony is greater than 0.3%, preferably greater than 0.5%, more preferably still greater than 0.8%.

Preferably, the proportion by mass of antimony is less than 1.5%, preferably less than 1.3%.

Advantageously, the rare earths comprise lanthanum, preferably only lanthanum.

Preferably, the proportion by mass of rare earths is greater than 0.2%, preferably greater than 0.3%.

Preferably, the proportion by mass of rare earths is less than 1.2%, preferably less than 1%.

The present invention also relates to the use of the inoculant according to the invention.

According to a first variant of use, said inoculant is introduced in the form of powder.

As such, it should be noted that the products described in documents FR2511044A1 and EP0816522A1 had the disadvantage of having a degradation of their particle size over time during storage of the inoculant. The inoculant according to the invention showed great stability in the particle size of the grains under certain conditions.

According to a second alternative embodiment, said inoculant is introduced in the form of a solid insert placed in a casting mold.

The use of the inoculant according to the invention relates to the manufacture of cast iron parts having parts of thickness greater than 6 mm, preferably parts of thickness greater than 20mm, and even more preferably parts of thickness greater than 50mm.

The present invention will be better understood in the light of the description and the examples which follow.

The inoculant according to the invention will be used in the context of an inoculation of a cast iron bath. It can also be used as a precondition for said cast iron as well as as a nodulizer if necessary.

In the context of a typical use of an inoculant, the composition of an inoculating alloy according to the invention comprises: Inoculating alloy - composition 1 Element Quantity (% mass) Yes 45 - 80 It 0.5 - 4 al 0.5 - 3 Sb 0.2 - 2 Rare Earths (especially Lanthanum) 0.2 - 3 Iron Balance

Obviously, the inoculant may also include additional elements providing specific effects depending on the desired properties. This could be more particularly the case in the context of a pre-conditioning treatment of cast iron.

Another inoculating alloy according to the invention has the following composition: Inoculating alloy - composition 2 Element Quantity (% mass) Yes 45 - 80 It 0.5 - 8 al 0.5 - 3 Sb 0.2 - 2 Rare Earths (especially Lanthanum) 0.2 - 3 Ba 2 - 15 mn 2 - 6 Zr 2 - 6 Iron Balance

• en fin de fusion au four à induction
• avant un traitement nodulisant au magnésium, et plus particulièrement entre 1 et 5 minutes avant ce traitement
• en couverture d'un traitement ultérieur de type « Sandwich » ou « Tundish-cover ».
• dans un four de coulée
• lors d'un transvasement entre deux poches (tranfert et coulée, notamment).
• l'inoculant de préconditionnement pourra notamment être ajouté sous la forme d'un fil fourré.

An inoculation treatment will typically consist of adding 0.05 (preferably at least 0.1%) to 0.8% by mass of the inoculant in the iron bath, in particular under the following conditions given as examples:

• at the end of melting in the induction furnace
• before a magnesium nodulating treatment, and more particularly between 1 and 5 minutes before this treatment
• on the cover of a subsequent “Sandwich” or “Tundish-cover” treatment.
• in a casting furnace
• during a transfer between two pockets (transfer and pouring, in particular).
• the preconditioning inoculant could in particular be added in the form of a cored wire.

The particle size of the inoculant according to the invention may be adapted according to its methods of addition.

• Ajout en four à induction : granulométrie jusqu'à environ 40 mm,
• Ajout entre le four à induction et la poche de coulée : granulométrie comprise entre environ 10 et environ 30 mm.
• Ajout en bassin de coulée : granulométrie comprise entre environ 0,4 et environ 2 mm.
• Ajout avant coulée dans le moule : granulométrie comprise entre environ 0,2 et environ 0,5 à 2 mm.
• Ajout sous forme d'insert inoculant placé dans le moule de coulée : inserts de 20g, 40g, 60g, 80g, 300g, 800g, 2kg, 5kg, 10kg, 20kg et 50kg, par exemple.

As examples, we can cite:

• Addition in induction furnace: particle size up to approximately 40 mm,
• Addition between the induction furnace and the ladle: particle size between approximately 10 and approximately 30 mm.
• Addition in pouring basin: particle size between approximately 0.4 and approximately 2 mm.
• Addition before pouring into the mold: particle size between approximately 0.2 and approximately 0.5 to 2 mm.
• Addition in the form of an inoculating insert placed in the casting mold: inserts of 20g, 40g, 60g, 80g, 300g, 800g, 2kg, 5kg, 10kg, 20kg and 50kg, for example.

The inoculating alloy can also be successfully added as an inoculant before filling the casting mold or in bag or late inoculation, after adjusting the chemistry of the alloy (in particular Ba between 1.5 and 5% mass and Ca between 0.5 and 2% mass).

Depending on the metallurgical state of the cast iron after treatment with the inoculating alloy according to the present application, it is possible to omit the post-inoculation step. Indeed, the prolonged maintenance of the inoculation effect over time with the action of antimony makes it possible to significantly reduce the treatments for late inoculations or even allow them to be eliminated. With, for example, the addition of an inoculant containing the Bi / TR pair, the inoculation effect loses 30% over the first 4 minutes. Thus the addition of a late phase inoculant becomes an obligation to recover 100% of the inoculation effect to be achieved. This is not the case with an inoculant according to the present application.

In the context of use as a nodulant with additional inoculating function outside the scope of the invention, the composition of the alloy could be as follows: Nodulating alloy with inoculating effect - composition 3 Element Quantity (% mass) Yes 30 - 60 It 0.2 - 5 al 0.2 - 3 Sb 0.1 - 2 Rare Earths (especially Lanthanum) 0.1 - 3 mg 3 - 12 Iron Balance

The granulometry of the nodulizer (in particular with inoculating function) will be adapted according to the size of the treatment bags. For example, for pockets of 100 to 500 kg of cast iron, we will prefer a particle size between approximately 0.4 and approximately 2 mm, or even up to 7 mm. For pockets of 500 to 1000kg of cast iron, we will prefer a particle size between approximately 2 and approximately 7mm, or between approximately 10 and approximately 30mm. For pockets of more than 1000kg of cast iron, we will prefer a particle size between about 10 and about 30mm.

Examples of use will now be given.

Example 1 (outside the invention): Foundry A - 8 mm thick part. Foundry reference (A1 )

In accordance with the prior art, the liquid pig iron was treated by adding 30 g of antimony to one tonne of liquid pig iron in the induction furnace of pure antimony.

The cast iron was then subjected to a nodulization treatment using a nodulizing alloy of the FeSiMg type comprising a third of an FeSiMg alloy comprising 2% of rare earths and two thirds of a FeSiMg alloy comprising no rare earths.

Finally, the cast iron underwent an inoculation treatment by adding 0.1% by mass of a FeSiMnZr alloy and 0.1% of a FeSiAl alloy to the casting basin, the inoculating alloys being added in the form of insert inoculating in the mold.

Use of an inoculating alloy (A2)

An inoculating alloy containing (in mass proportion): Si = 65% Si, Ca = 1.76% Ca, Al = 1.23%, Sb = 0.15%, TR = 0.16%, Ba = 7.9 %; was used in a proportion of 0.15% by mass of cast iron.

The step of adding pure antimony was eliminated and the nodulating treatment was simplified by using only the nodulating alloy FeSiMg not containing rare earths.

Comparative results

A1 (Reference) A2 Graphite nodularity 95% 98% Melting matrix (% perlite) 8% 3% Elongation 15% 18%

Foundry A treated with an inoculant according to the present application has shown an increase in elongation in tension on test specimens for a grade EN-GJS-400-15.

Example 2 (outside the invention): Foundry B - 200 mm thick part. Foundry reference (B1 )

In accordance with the prior art, the liquid pig iron was treated by adding 20 g of antimony to one tonne of liquid pig iron in the induction furnace of pure antimony.

The cast iron was then subjected to a nodulization treatment using a nodulizing alloy of the FeSiMg type comprising 1% by mass of rare earths and introduced into the cast iron in the form of a cored wire.

Finally, the cast iron underwent an inoculation treatment by adding 0.15% by mass of a FeSiBiTR alloy to the casting basin.

Use of an inoculating alloy (B2)

An inoculating alloy containing as before: Si = 65% Si, Ca = 1.76% Ca, Al = 1.23%, Sb = 0.15%, TR = 0.16%, Ba = 7.9%; was used in a proportion of 0.15% by mass of cast iron.

The step of adding pure antimony was eliminated and the nodulating treatment was simplified by using only a nodulating alloy FeSiMg not containing rare earths (also introduced in the form of cored wire).

Comparative results

B1 (Reference) B2 Graphite nodularity 91% 97% Melting matrix (% perlite) 4% 3% "Chunky" Graphite Defect 15% 0% Resilience at -20 ° C 7 D 12 J

On the impact resistance results, the B2 cast iron obtained results in accordance with the requirements.

Example 3 (outside the invention): foundry C - thin parts (thickness less than 6mm). Foundry reference (C1 )

In accordance with the prior art, the liquid pig iron was treated by adding 25 g of antimony to one tonne of liquid pig iron in the induction furnace of pure antimony.

The cast iron was then subjected to a nodulization treatment using a nodulizing alloy of the FeSiMg type comprising 6.7% by mass of magnesium as well as 1.2% of calcium and 0.98% of rare earths.

Finally, the cast iron underwent a late inoculation treatment by adding 0.12% by mass of an FeSiMnZrBa alloy having a particle size between 0.2 and 5 mm.

Use of an inoculating alloy with nodulizing function (C2)

A nodulating alloy with inoculating function according to composition 3 mentioned above was used.

As in the previous examples, the step of adding pure antimony has been omitted.

The nodulating treatment was carried out using an alloy of the FeSiMg type according to composition 3 of the present application and comprising 6.4% by mass of magnesium as well as 1.3% of calcium, 0.6% of antimony and 1.2% rare earths.

A complementary inoculation was carried out according to a late inoculation method with 0.09% of an FeSiAlCa alloy and 0.009% of an FeSiMnZrBa alloy.

Comparative results

C1 (Reference) C2 Graphite nodularity 93% 98% Melting matrix (% perlite) 15% 4/5% "Chunky" Graphite Defect 4% 0%

By using a C2 nodulant, there is a disappearance of “chunky” graphite defects on all the parts tested.

Thus, the additional inoculation (late inoculation) could be done using a more economical inoculant of the FeSiAlCa type.

Example 4 (outside the invention): foundry D - massive parts. Foundry reference (D1)

In accordance with the prior art, the liquid pig iron was treated by adding 30 g of antimony to one tonne of liquid pig iron in the induction furnace of pure antimony.

The cast iron was then subjected to a nodulization treatment using a nodulizing alloy of the FeSiMg type comprising 9.1% by mass of magnesium as well as 1.4% of calcium and 1.1% of rare earths.

Finally, the cast iron underwent an inoculation treatment by adding an insert of 10 kg per tonne of cast iron of an inoculating alloy FeSiMnZr.

Use of an inoculating alloy (D2)

An inoculating alloy containing: Si = 65% Si, Ca = 1.76% Ca, Al = 1.23%, Sb = 0.15%, TR = 0.16%, Ba = 7.9%; was used as a 10kg insert as for reference.

As in the previous examples, the step of adding pure antimony has been omitted.

The nodulating treatment was carried out using the same alloy as for the reference, namely using a nodulating alloy of the FeSiMg type comprising 9.1% by mass of magnesium as well as 1.4% of calcium and 1.1%. of rare earths.

Comparative results

D1 (Reference) D2 Graphite nodularity 92% 97% Melting matrix (% perlite) 5/10% 0/5% "Chunky" Graphite Defect 2% 0% Tensile strength 370 MPa 420 MPa Elongation 18% 22% Impact resistance at - 20 ° C 10 J 14 J

Cast iron D makes it possible to develop a shade of dark EN-GJS-400-18-LT used in particular in the wind power sector. The use of the inoculant D2 made it possible to significantly increase the impact resistance.

Example 5 (outside the invention): foundry E - thin parts and nodulating treatment. Foundry reference (E1)

The liquid pig iron underwent a nodulization treatment using a nodulizing alloy of the FeSiMg type comprising 9.1% by mass of magnesium as well as 0.8% of bismuth and 0.7% of rare earths.

The cast iron was then subjected to an inoculation treatment according to a late inoculation method by adding 0.18% of an FeSiMnZr alloy having a particle size between 0.2 and 5 mm.

Use of an inoculating alloy with nodulizing function (E2)

A nodulating alloy according to composition 3 mentioned above was used. The alloy used is an FeSiMg type alloy comprising 9.1% magnesium as well as 0.75% antimony and 0.5% rare earths.

The cast iron was then subjected to an additional inoculation treatment according to a late inoculation method by adding 0.17% of an FeSiMnZr alloy having a particle size between 0.2 and 5 mm.

Comparative results

E1 (Reference) E2 Graphite nodularity 91% 95% "Chunky" Graphite Defect 2% 0% Yield Mg 54% 69%

As mentioned above, we find that replacing bismuth with antimony increased the yield of magnesium in cast iron E.

Example 6 (outside the invention): Foundry D on massive parts.

The foundry reference (F1) and the test (F2) using an inoculating alloy were carried out in accordance with Example 4 and the foundry D by inoculating massive parts.

Comparative results

F1 (Reference) F2 Sb yield 67% 98%

It is noted that thanks to the high yield obtained, it is possible to better control the amount of antimony added. The F2 foundry allowed significant savings by reducing the doses of antimony to be added by 31.5%.

Example 7 (outside the invention): Foundry D on massive parts.

The foundry reference (G1) and the test (G2) using an inoculating alloy were carried out in accordance with Example 4 and the foundry D by inoculating massive parts.

Comparative results

G1 (Reference) G2 Sb release in 8 hours 0.7 mg / m ³ 0.1 mg / m ³

It is noted that thanks to the inoculantG2, the release of antimony is greatly limited and much lower than the regulatory threshold of 0.5 mg / m ³ . Working conditions are improved.

Example 8 (according to the invention): foundry H - part 150 mm thick. Foundry reference (H1)

In accordance with the prior art, the liquid pig iron was treated by adding 15 g of antimony to one tonne of liquid pig iron in the induction furnace of pure antimony.

The cast iron was then subjected to a nodulization treatment using a nodulating cored wire (diameter 13 mm, 32% of Mg, 1.2% of TR, 230 g / m of powder)

Finally, the cast iron underwent a late inoculation treatment by adding 0.15% by mass of a FeSiMnZr alloy to the casting jet.

Use of an inoculating alloy according to demand (H2)

An alloy inoculating according to composition 1 [containing Si = 64% Si, Ca = 1.64% Ca, Al = 1.15%, Sb = 0.5%, TR = 0.3%] mentioned above was used in a proportion of 0.2% by mass of cast iron.

The step of adding pure antimony was eliminated and the nodulating treatment was simplified by using only a nodulating alloy FeSiMg not containing rare earths (also introduced in the form of cored wire).

Comparative results

H1 (Reference) H2 (invention) Graphite nodularity 87% 98% Melting matrix (% perlite) 3% 3% "Chunky" Graphite Defect 19% 0% Resilience at -20 ° C 4 D 14 J

On the impact resistance results, the H2 cast iron obtained results in accordance with the requirements.

Claims (11)

1. A ferro-silicon based inoculant alloy for the treatment of a cast iron for the manufacture of parts having portions with thicknesses larger than 6 mm, said inoculant alloy containing

   45-80 weight% of silicon,

   0.5-4 weight% of calcium,

   0.5-3 weight% of aluminum,

   0.2-3 weight% of rare earths,

   0.2-2 weight% of antimony,

   and the balance of iron,

   characterized in that the ratio of antimony to rare earths is comprised between 0.9 and 2.2.
2. The ferro-silicon based inoculant alloy for the treatment of a cast iron for the manufacture of parts having portions with thicknesses larger than 6 mm, said inoculant alloy containing, characterized in that said alloy contains

   45-80 weight% of silicon,

   0.5-8 weight% of calcium,

   0.5-3 weight% of aluminum,

   0.2-3 weight% of rare earths,

   0.2-2 weight% of antimony,

   2-15 weight% of barium,

   2-6% of manganese,

   2-6% of zirconium,

   and the balance of iron,

   characterized in that the ratio of antimony to rare earths is between 0.9 and 2.2.
3. The inoculant alloy according to claim 1 or 2, characterized in that the mass proportion of antimony is greater than 0.3%, preferably greater than 0.5%, still more preferably greater than 0.8%.
4. The inoculant alloy according to claim 1 or 2, characterized in that the mass proportion of antimony is less than 1.5%, preferably less than 1.3%.
5. The inoculant alloy according to any one of claims 1 to 4, characterized in that the rare earths comprise lanthanum, preferably only but lanthanum.
6. The inoculant alloy according to any one of claims 1 to 5, characterized in that the mass proportion of rare earths is greater than 0.3%.
7. The inoculant alloy according to any one of claims 1 to 5, characterized in that the mass proportion of rare earths is less than 1.2%, preferably less than 1%.
8. A use of an inoculant according to any one of claims 1 to 7, for the manufacture of cast iron parts having portions with thicknesses larger than 6 mm, characterized in that said inoculant is introduced in the form of powder.
9. The use of an inoculant according to any one of claims 1 to 7, for the manufacture of cast iron parts having portions with thicknesses larger than 6 mm, characterized in that said inoculant is introduced in the form of a solid insert placed in a casting mold.
10. The use according to claim 8 or 9, for the manufacture of cast iron parts having portions with thicknesses larger than 20 mm.
11. The use of an inoculant according to any one of claims 8 to 10, for the manufacture of cast iron parts having portions with thicknesses larger than 50 mm.