ES2777934T3 - Inoculant alloy for thick castings - Google Patents

Abstract

Inoculant alloy based on ferrosilicon for the treatment of a foundry for the manufacture of pieces that have parts with thicknesses greater than 6 mm, said inoculant alloy containing 45-80% by mass of silicon, 0.5-4% by mass of calcium, 0.5-3% by mass of aluminum, 0.2-3% by mass of Rare Earths, 0.2-2% by mass of antimony, and the rest of iron, characterized by the fact that the relationship between antimony and Rare Earths is between 0.9 and 2.2.

Description

description

Inoculant alloy for thick castings

The present invention relates to an inoculant alloy for treating cast iron.

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

In ^its cooling, carbon can adopt various physicochemical structures depending on various parameters.

When carbon associates with iron to form iron carbide Fe3C (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 in the form of graphite, the resulting cast iron is called gray cast iron. Gray cast iron is softer and can be worked.

In order to obtain castings that have good mechanical properties, it is therefore necessary to obtain a cast structure comprising the maximum amount of carbon in the form of graphite and to limit as much as possible the formation of these iron carbides that harden and embrittle the cast. alloy.

In the absence of any particular inoculation treatment, carbon however tends to associate with iron to form iron carbide. Therefore, it is necessary to treat the melt in the liquid state in such a way that the carbon association parameters are modified and the desired structure is obtained.

To this end, the liquid cast iron undergoes an inoculation treatment that foresees the introduction into the casting of graphitizing components ^or supports for graphitization, commonly called germs, which will favor, when the casting is cooled in the mold, the appearance of graphite rather than of iron carbide.

In general, the components of an inoculant are therefore elements that favor 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 fulfill other functions and to this end comprise other components that have a particular effect. The cast iron can also undergo additional prior ^or subsequent treatments.

Thus, depending on the properties sought, it is particularly desirable that the graphite formed be spheroidal, vermicular ^or laminar.

One ^or the other graphical form can preferably be obtained by a particular treatment of the cast iron with the help of specific components.

^Thus , for example, the formation of spheroidal graphite can be favored by a so-called nodular treatment, which mainly envisages supplying magnesium to the cast iron in sufficient quantity so that the graphite can grow in such a way as to form round particles (spheroids ^or nodules).

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

The nodular alloy thus makes it possible to essentially influence the shape of the graphite nodules, whereas the inoculant product provides for increasing the number of these nodules and homogenizing the graphite structures.

It is also possible to mention the addition of desulphurizing products, ^or of products that make it possible to specifically treat certain failures of the foundry depending on the initial composition of the liquid foundry bath, such as micro-plugs and punctures, which can appear when cooling takes place. .

These treatments can be carried out one ^or more times and at different times during the manufacture of the cast iron.

Most of the inoculants are usually manufactured from a ferro-silicon alloy of the type FeSÍ45, FeSÍ65 ^or FeSÍ75 with adjustment of the chemistry according to the expected composition of the inoculant. It can also be mixtures of various alloys.

It should be noted that the inoculation efficiency of the casting also depends on ^its thickness ( ^or also on the solidification rate).

In thin areas, when cooling more quickly, a higher risk of carbide formation will be observed.

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

As a result, the parts with zones of different thickness may have different physicochemical structures from one zone to another, which is undesirable.

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

For thick parts, when the inoculation procedure is not mastered, the formation of degenerate graphite and / or "chunky" graphite can reduce the mechanical properties of the cast iron. To solve these failures, the smelter generally proceeds to the addition of pure antimony to the liquid metal.

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

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

Conversely, if the amount introduced exceeds the target, antimony will have a tendency to greatly increase the proportion of pearlite, an unwanted phase in ferritic structures.

In the case of addition of pure antimony, the smelter must also associate Rare Earths (abbreviated as TR ^or RE for "Rare Earths") in order to obtain a maximum improvement of the graphite shape. Likewise, if the amount of Rare Earths is insufficient, the part will present a "spiky" type graphite defect. On the other hand, if the amount of Rare Earths is dosed to a large extent, the graphite defect will be rather of the "chunky" type, which essentially occurs 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 impact resistance of the formed part.

The introduction of pure antimony into the liquid iron also causes ^its vaporization and thus produces a strong release of gases. It has been measured that with the addition of pure antimony, the antimony release threshold in the work environment was greater than 0.5 mg / m3, the exposure limit value (ELV set by the regulations). Therefore, operators must work with a particulate respirator of type N95 ^or higher. The treatment of thin pieces has already been the subject of specific inoculant developments. L ^{i I} FR 251 044A1, FR ^2855186-1 and EP0816522A1 describe an inoculant for such thin parts.

Said inoculant according to these documents for thin pieces comprises in particular an inoculant 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 Earths between 0.9 and 2.2; bismuth being particularly preferred, the descriptions in these documents refer only to bismuth.

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

Among the other documents that mention the use of antimony, the following documents can be cited. Document WO2006 / 068487A1 describes an inoculant comprising a phase modifying component (inoculant function) associated with an agent for modifying the structure of graphite which can be antimony. It should be noted that this structure modifying agent is used in a mixture with the inoculant compound (ferrosilicon) and not in an alloyed form. Furthermore, antimony is clearly mentioned as a promoter for pearlite, which phase, as mentioned above, is generally not desired. The amount of antimony used is between 3 and 15%, which corresponds to a significant amount, probably the origin of the proportion of pearlite formed.

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

JP57067146A describes a ferrosilicon-based alloy 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 pearlite inhibitor, and not as an inoculant.

There are also several articles and documents that deal with a nodular function (graphite form) of antimony, which is not the main objective sought and does not solve the problem of inoculation (number and quality of nodules). Furthermore, it is frequently a question of a use of antimony in mixed and unalloyed form.

Therefore, there is a need for an inoculant alloy that allows to improve the treatment of thick pieces. To this end, the present invention proposes a inoculant alloys according to claim 1 and claim 2. A ^{s t,} in effect, it has been found unexpectedly that antimony alloyed with a rare earth in a ferrosilicon based alloy in proportions claimed allowed efficient inoculation, and with stabilization of the spheroids, of thick pieces without the disadvantages of pure antimony indicated above.

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

The increased yield thus enables product savings and simplifies the management of product additions, including for rare earths.

Thanks to this increase in performance and the simultaneous reduction of gaseous emissions into the atmosphere, 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 release of antimony gases to between 0.1 and 0.2 mg / m3 and the use of a respirator is no longer necessary.

It will also be seen that the antimony / rare earth association lengthens the attenuation time of antimony significantly. The effect produced therefore lasts longer in the entire casting process. It will be seen that the attenuation time of antimony is even longer than the attenuation time of bismuth in inoculating alloys for thin pieces.

The alloy according to the present application, when added by ladle ^or in the furnace, can thus make it possible to replace ^or even eliminate an additional jet ^or late inoculation.

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

The alloy according to the present application thus makes it possible to ensure a homogeneous ferrite / pearlite matrix according to the different thicknesses of the manufactured part, which in particular improves the subsequent machining conditions of the part. According to the invention, the ratio between antimony and rare earths is between 0.9 and 2.2. Preferably, the ratio between antimony and rare earths will be greater than 1.4, preferably 1.6 and less than 2.5; preferably less than 2.

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

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

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

Preferably, the rare earth mass proportion is greater than 0.2%, preferably greater than 0.3%. Preferably, the rare earth mass proportion 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 a powder.

It should be noted in this regard that the products described in documents FR2511044A1 and EP0816522A1 suffered from the drawback of exhibiting a degradation of ^their particle size over time on storage of the inoculant. The inoculant according to the invention has shown great stability in the granulometry of the grains under certain conditions.

According to a second embodiment variant, 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 provides for the manufacture of castings having parts with thicknesses greater than 6 mm, preferably parts with thicknesses greater than 20 mm, and even more preferably parts with thicknesses greater than 50 mm.

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

The inoculant according to the invention is used in the context of inoculation of a molten bath. It can also be used in the preconditioning of said casting, as well as a pelletizer if necessary.

Within the framework of a typical use of an inoculant, the composition of an inoculant alloy according to the invention comprises:

Inoculant Alloy - Composition 1

Obviously, the inoculant may also include additional elements that provide particular effects depending on the properties sought. This may more particularly be the case in the context of a preconditioning treatment of the cast iron.

Another inoculant alloy according to the invention has the following composition:

Inoculant Alloy - Composition 2

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

- at the end of the melting in the induction furnace

- before a nodular treatment with magnesium, and more particularly between 1 and 5 minutes before this treatment

- as a "Sandwich" ^or "Tundish-cover" post-treatment cover.

- in a casting oven

- in a transfer between two spoons (transfer and casting, in particular).

- the preconditioning inoculant in the form of a sheathed wire may in particular be added.

The granulometry of the inoculant according to the invention can be adapted according to ^its methods of addition.

As examples, one can cite:

- addition in induction furnace: granulometry up to approximately 40 mm,

- addition between the induction furnace and the ladle: particle size between approximately 10 and approximately 30 mm.

- addition in the pouring tank: granulometry between approximately 0.4 and approximately 2 mm.

- addition before casting in the mold: granulometry between approximately 0.2 and approximately 0.5 to 2 mm.

- addition in the form of an inoculant insert placed in the casting mold: inserts of 20 g, 40 g, 60 g, 80 g, 300 g, 800 g, 2 kg, 5 kg, 10 kg, 20 kg and 50 kg, per example.

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

Depending on the metallurgical state of the casting after treatment with the inoculating alloy according to the present application, it is possible to suppress the post-inoculation step. The prolonged maintenance of the inoculation effect over time with the action of antimony makes it possible, in fact, to significantly reduce late inoculation treatments ^or even to suppress them. With the addition of, for example, an inoculant containing the Bi / TR pair, the inoculation effect loses 30% during the first 4 minutes. ^Thus , the addition of a late stage inoculant becomes an obligation to recover 100% of the expected inoculation effect. This is not the case with an inoculant according to the present application.

In the framework of use as a pelletizer with additional inoculant function outside the framework of the invention, the composition of the alloy could be as follows:

Nodulating alloy with inoculant effect - composition 3

The granulometry of the pelletizer (in particular with an inoculant function) will be adapted depending on the size of the treatment spoons. For example, for spoons of 100 to 500 kg of cast iron, a particle size of between about 0.4 and about 2 mm, and even up to 7 mm, will be preferred. For buckets of 500 to 1000 kg of cast iron, a particle size of between about 2 and about 7 mm, ^or between about 10 and about 30 mm will be preferred. For spoons of more than 1000 kg of cast iron, a particle size of between about 10 and about 30 mm will be preferred.

Usage examples will now be provided.

Example 1 (outside the invention): casting A - 8 mm thick part.

Casting reference (A1)

According to the prior art, the liquid iron was treated by adding pure antimony in the induction furnace in a proportion of 30 g per one ton of liquid iron.

The foundry has then undergone a pelletization treatment with the help of a FeSiMg type pelletizing alloy comprising one third of a FeSiMg alloy comprising 2% rare earths and two thirds of a FeSiMg alloy that does not comprise rare earths.

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

Use of an inoculant alloy (A2)

An inoculant alloy has been used that contains (in mass proportion): Si = 65% Si, Ca = 1.76% Ca, Al = 1.23%, Sb = 0.15%, TR = 0.16% , Ba = 7.9% in a proportion of 0.15% by melt.

The step of adding pure antimony has been omitted and the pelletizing treatment has been simplified by using only the FeSiMg pelletizing alloy that does not contain rare earths.

Comparative results

Cast iron A treated with an inoculant according to the present application has shown an increase in tensile elongation in control samples for an EN-GJS-400-15 class.

Example 2 (outside the invention): cast iron B - 200 mm thick part.

Casting reference (B1)

According to the prior art, liquid iron has been treated by adding pure antimony in the induction furnace in a proportion of 20 g of antimony per one ton of liquid iron.

The cast iron has then undergone a pelletizing treatment with the aid of a pelletizing alloy of the FeSiMg type comprising 1% by mass of rare earths and introduced into the cast iron in the form of a sheathed wire.

Finally, the foundry has undergone an inoculation treatment by adding 0.15% by mass of a FeSiBiTR alloy to the casting tank.

Use of an inoculant alloy (B2)

An inoculant alloy was used that contains as before: Si = 65% of Si, Ca = 1.76% of Ca, Al = 1.23%, Sb = 0.15%, TR = 0.16%, Ba = 7.9%; in a proportion of 0.15% by melt.

The step of adding pure antimony has been omitted and the pelletizing treatment has been simplified by using only a FeSiMg pelletizing alloy containing no rare earths (also introduced in the form of a sheathed wire).

Comparative results

In the results of resistance to impacts, the casting B2 has obtained results in accordance with the requirements. Example 3 (outside the invention): casting C - thin parts (thickness less than 6 mm), casting reference (C1)

In accordance with the prior art, liquid iron has been treated by adding pure antimony in the induction furnace in a proportion of 25 g of antimony for one ton of liquid iron.

The cast iron has then undergone a pelletizing treatment with the aid of a FeSiMg type pelletizing alloy comprising 6.7% by mass of magnesium as well as 1.2% of calcium and 0.98% of rare earths.

Finally, the foundry has undergone a late inoculation treatment by adding 0.12% by mass of a FeSiMnZrBa alloy with a particle size between 0.2 and 5 mm.

Use of an inoculant alloy with nodular function (C2)

A nodular alloy with inoculant function has been used according to the composition 3 mentioned above. As for the previous examples, the step of adding pure antimony has been omitted.

The nodular treatment was carried out with the aid of 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 procedure with 0.09% of a FeSiAlCa alloy and 0.009% of a FeSiMnZrBa alloy.

Comparative results

Using a C2 pelletizer, a disappearance of "chunky" graphite defects is observed in all controlled parts.

In this way, the additional inoculation (late inoculation) has been possible using a cheaper inoculant of the FeSiAlCa type.

Example 4 (outside the invention): cast iron D - solid parts.

Cast reference (D1)

According to the prior art, the liquid cast iron has been treated by adding pure antimony in the induction furnace in a proportion of 30 g of antimony for one ton of liquid cast iron. The cast iron has then undergone a pelletizing treatment with the aid of a FeSiMg type pelletizing alloy comprising 9.1% by mass of magnesium as well as 1.4% calcium and 1.1% rare earths. Finally, the foundry has undergone an inoculation treatment by adding a 10 kg insert per tonne of cast iron of an inoculating FeSiMnZr alloy.

Use of an inoculant alloy (D2)

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

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

The nodulation treatment was carried out with the help of the same alloy as for the reference, that is, using a nodulation alloy of the FeSiMg type comprising 9.1% by mass of magnesium as well as 1.4% of calcium and 1.1% rare earth.

Comparative results

The D foundry makes it possible to produce a class of EN-GJS-400-18-LT foundry used in particular in the wind turbine sector. The use of the inoculant D2 has made it possible to increase the resistance to impacts significantly.

Example 5 (outside the invention): casting E - thin pieces and pelletizing treatment.

Cast reference (E l)

The liquid cast iron has undergone a pelletization treatment with the help of a FeSiMg type pelletizing alloy comprising 9.1% by mass of magnesium as well as 0.8% bismuth and 0.7% rare earths.

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

Use of an inoculant alloy with nodular function (E2)

A pelletizing alloy has been used according to the composition 3 mentioned above. The alloy used is a FeSiMg-type alloy comprising 9.1% magnesium as well as 0.75% antimony and 0.5% rare earths.

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

Comparative results

As mentioned above, replacing bismuth with antimony has been found to increase magnesium yield in smelter E.

Example 6 (outside the invention): casting D in solid pieces.

The casting reference (F1) and the test (F2) using an inoculating alloy have been carried out according to example 4 and casting D by inoculating solid pieces.

Comparative results

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

Example 7 (outside the invention): casting D in solid pieces.

The casting reference (G1) and the test (G2) using an inoculant alloy have been carried out according to example 4 and casting D by inoculating solid pieces.

Comparative results

It is found that thanks to the inoculant G2, the release of antimony is very limited and well below the regulatory threshold of 0.5 mg / m3. Working conditions have been improved.

Example 8 (according to the invention): cast iron H - 150 mm thick part.

Cast reference (H1)

According to the prior art, liquid cast iron has been treated by adding pure antimony in the induction furnace in a proportion of 15 g of antimony per one ton of liquid cast iron. The cast iron has subsequently undergone a pelletizing treatment with the help of a pellet-lined wire (diameter 13 mm, 32% Mg, 1.2% TR, 230 g / m of powder)

Finally, the foundry has undergone a late inoculation treatment by adding 0.15% by mass of a FeSiMnZr alloy to the casting jet.

Use of an inoculant alloy according to the application (H2)

An inoculant alloy was used according to composition 1 [containing Si = 64% Si, Ca = 1.64% Ca, Al = 1.15%, Sb = 0.5%, TR = 0.3%] mentioned above in a proportion of 0.2% by melt. The step of adding pure antimony has been omitted and the pelletizing treatment has been simplified by using only a FeSiMg pelletizing alloy that does not contain rare earths (also introduced in the form of a coated wire).

Comparative results

Regarding the results of resistance to impacts, the H2 cast iron has obtained results in accordance with the requirements.

Claims (11)

claims 1. Inoculant alloy based on ferrosilicon for the treatment of a foundry for the manufacture of pieces that have parts with thicknesses greater than 6 mm, containing said inoculant alloy 45-80% by mass of silicon, 0.5-4% by mass of calcium, 0.5-3% by mass of aluminum, 0.2-3% by mass of Rare Earths, 0.2-2% by mass of antimony, and the rest of iron, characterized in that the relationship between antimony and Rare Earths is between 0.9 and 2.2. 2. Inoculant alloy based on ferrosilicon for the treatment of a foundry for the manufacture of parts that have parts with thicknesses greater than 6 mm, containing said inoculant alloy, characterized in that said alloy contains 45-80% by mass of silicon, 0.5-8% by mass of calcium, 0.5-3% by mass of aluminum, 0.2-3% by mass of Rare Earths, 0.2-2% by mass of antimony, 2-15% by mass barium, 2-6% manganese, 2-6% zirconium, and the rest of iron, characterized in that the relationship between antimony and Rare Earths is between 0.9 and 2.2. Inoculant alloy according to claim 1 ^or 2, characterized in that the proportion by mass of antimony is greater than 0.3%, preferably greater than 0.5%, more preferably greater than 0.8%. 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. Inoculant alloy according to any of claims 1 to 4, characterized in that the rare earths comprise lanthanum, preferably only lanthanum. 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. Inoculating 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. Use of an inoculant according to any of claims 1 to 7, for the manufacture of castings that have parts with thicknesses greater than 6 mm, characterized in that said inoculant is introduced in powder form. 9. Use of an inoculant according to any of claims 1 to 7, for the manufacture of castings that have pieces with thicknesses greater than 6 mm, characterized in that said inoculant is introduced in the form of a solid insert placed in a mold casting. Use according to claim 8 ^or 9, for the manufacture of castings having parts with thicknesses greater than 20 mm. 11. Use of an inoculant according to any of claims 8 to 10, for the manufacture of castings having parts with thicknesses greater than 50 mm.