WO2014076404A1

WO2014076404A1 - Inoculant alloy for thick cast-iron parts

Info

Publication number: WO2014076404A1
Application number: PCT/FR2013/052710
Authority: WO
Inventors: Aurélie FAY; Mourad TOUMI; Thomas Margaria; Daniel BERRUEX
Original assignee: Ferropem
Priority date: 2012-11-14
Filing date: 2013-11-12
Publication date: 2014-05-22
Also published as: MX2015006053A; CA2889124A1; PL2920335T3; PT2920335T; UA116218C2; CN104812922A; JP2016503460A; FR2997962B1; BR112015010975A2; CA2889124C; ES2777934T3; FR2997962A1; KR20150083998A; SI2920335T1; DK2920335T3; ZA201503205B; US20150284830A1; EP2920335B1; EP2920335A1

Abstract

The invention relates to an inoculant alloy for the treatment of thick cast-iron parts, based on ferrosilicon and containing between 0.005 and 3 wt. % of rare earths, and characterised in that it also contains between 0.2 and 2 wt. % of antimony.

Description

Inoculant alloy for thick cast iron parts

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

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

During its cooling, the carbon can adopt several physico-chemical structures depending on several parameters.

When carbon associates with iron and forms iron carbide FesC (also called cementite), the resulting iron is called white cast iron. White cast iron has the characteristic of being hard and brittle, which is undesirable for some applications.

If the carbon appears as graphite, the resulting melt 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 melt in the liquid state so as to modify the carbon association parameters and obtain the desired structure.

To this end, the liquid iron undergoes an inoculation treatment to introduce in the cast graphitizing components or supports to graphitization commonly called germs that will promote, when cooling the cast iron in the mold, the appearance of graphite rather than iron carbide.

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

Of course, an inoculant may be designed to perform other functions and include for this purpose other components having a special effect. Cast iron may also undergo additional pretreatment or subsequent treatment.

In this way, the desired properties may be obtained, whether the graphite formed is spheroidal, vermicular or lamellar.

One or the other 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 may be favored by a so-called nodulising treatment aimed mainly at providing the magnesium melt in sufficient quantity so that the graphite can grow so as to form round particles (spheroids or nodules).

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

Thus, the nodulising alloy essentially affects the shape of the nodules of graphite, while the inoculating product aims to increase the number of nodules and homogenize the graphitic structures.

It is also possible to mention the addition of desulfurizing products, or products which make it possible to specifically treat certain defects of the cast iron as a function of the initial composition of the molten bath, such as micro-shrinkage and pitting, which may appear during cooling.

These treatments can be performed in one or more times and at different times during the manufacture of the cast iron.

Most inoculants are conventionally made from a ferro-silicon alloy type FeSi _45, FeSi or FeSi65 _{May 7} with adjustment of chemistry the following composition referred 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 the rate of solidification).

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

Conversely, in areas of greater thickness, cooling will be slower (2-4 hours) and will favor the formation of graphite. It follows that the parts with areas of different thicknesses may have physico-chemical structures different from one area to another, which is not desirable.

In addition, control of germination in areas of great thickness remains difficult and may lead to obtaining a non-uniform structure.

For parts of heavy duty, when the inoculation process is not controlled, the formation of degenerate graphite and / or "chunky" graphite can reduce the mechanical properties of the cast iron. To solve these defects, the smelter usually proceeds to the addition of pure antimony in the liquid metal.

The addition of pure antimony in 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 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 may form in the structure.

Conversely, if the quantity introduced exceeds the target, the antimony will tend to strongly increase the proportion of perlite, unwanted phase in the ferritic structures.

In the case of adding pure antimony, the smelter must also associate rare earth (abbreviated TR or RE for "Rare Earths") in order to obtain a maximum improvement of the shape of the graphite. Similarly, if the amount of rare earth is insufficient, the piece will have a graphite defect type "spiky". Conversely, if the amount of rare earth is too high, the graphite defect will be more of a "chunky" type, which essentially happens when the raw materials used are relatively pure.

These defects of graphite, type "spiky" or "chunky" degrade the mechanical properties of the cast iron, including 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 causes a strong release of gas. It was measured that with the addition of pure antimony, the threshold of release of antimony in the working environment was greater than 0.5 mg / m ³ , limit value of exposure (TLV fixed by the regulations). Operators should therefore work with a respirator against N95 or larger particles.

The treatment of low-thickness parts has already been developed with specific inoculants. Documents FR251 1044A1, FR2855186A1 and EP0816522A1 describe such an inoculant for thin parts.

Such a disadvantage according to these documents for thin parts includes, in particular, the fact that it is based on ferro-silicon and comprises between 0.005 and 3% by mass of rare earths, in particular lanthanum, as well as between 0.005 and 3% by weight of bismuth, lead or antimony in a ratio of rare earths / (Bismuth + Lead + Antimony) of 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 disclose the use of antimony only in general but do not contain any specific examples or particular values for this element.

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

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

J P220071 8A discloses an inoculant consisting of a mixture of ferrosil hereum, antimony, calcium silicide and rare earths. Antimony is not used in allied form.

JP57067146A describes a ferrosilicon-based alloy comprising between 5 and 50% by weight 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, and not as an inoculant.

There are also several articles and documents dealing with a nodulising function (graphite form) of antimony, which is not the aim fundamentally sought after and does not solve the problem of inoculation (number and q uality of nodes). In addition, it is frequently a use of antimony in a mixed and unalloyed form.

There is therefore a need for an inoculant alloy to improve the treatment of thick parts.

For this purpose, the present invention aims an inoculant alloy for the treatment of ferrous silicon-based cast iron thick pieces, containing between 0.005 and 3% by mass of rare earths, characterized in that it also contains between 0.2 and 2% by weight of antimony.

In fact, it has been unexpectedly found that antimony alloyed with rare earths in a ferrosilicon alloy according to the claimed proportions allowed for efficient inoculation, and with stabilization of the spheroids, of thick workpieces without the disadvantages of pure antimony mentioned 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 introduced is therefore much more precisely known.

The increase of the yield thus allows a saving of the products and simplifies the management of the additions of products, this including for the rare earths.

Thanks to this increase in yield 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 release of antimony between 0, 1 and 0.2 mg / m ³ and the use of a respirator mask is no longer necessary.

It should also be noted that the antimony / rare earth combination lengthens the fade time of antimony significantly. This produces a longer effect in the complete foundry process. It should be noted that the fade time of antimony is even greater than the fade time of bismuth in inoculant alloys for thin parts.

The alloy according to the present application, when added in the bag or in the oven, may thus make it possible to replace or even eliminate an additional inoculation to the jet or late. The alloy according to the present application also makes it possible especially to limit greatly or even to avoid the formation of "chunky" or "spiky" type graphite defects, 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 homogeneous ferrite / perlite matrix according to the different thicknesses of the manufactured part, which notably improves the subsequent machining conditions of the part.

Preferably, the antimony ratio on rare earths will be greater than 1, 4, preferably 1, 6, and less than 2.5; preferably less than 2.

According to a first variant embodiment, the inoculant alloy also comprises magnesium. It will then be a nodulizer with additional inoculant effect.

In particular, it has unexpectedly been found that unlike the bismuth already used, antimony made it possible to obtain a better yield of the magnesium introduced into the melt.

Regarding bismuth, it is known that the latter accelerates the decantation of magnesium in the cast iron and that it thus loses more active magnesium for the transformation of lamellar graphite into spheroidal graphite. The best assimilation of antimony in the form of a nodulizer according to the invention makes it possible to ensure a good stability of the residual magnesium between 1350 ° C. and 1580 ° C.

According to a second variant embodiment, the inoculant alloy does not contain magnesium.

Preferably, the ratio of rare earths to antimony is between 0.9 and 2.2.

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 mass ratio of rare earths is greater than 0.2%, preferably greater than 0.3%.

Preferably, the mass ratio 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 powder form.

It should be noted in this respect that the products described in documents FR251 1044A1 and EP081 6522A1 had the disadvantage of having a deterioration in the frequency of time during the 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 variant embodiment, said inoculant is introduced in the form of a solid insert placed in a casting mold.

Preferably, the use of the inoculant according to the invention is aimed at producing cast iron parts having parts of thickness greater than 6 mm, preferably parts with thicknesses greater than 20 mm, and even more preferentially parts of thickness greater than 50mm.

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

The inoculant according to the invention will typically be used in the context of an inoculation of a melt bath. It can also be used in pre-conditioning of said cast iron and as a noduliser if necessary.

In the context of a typical use of a nonchalant agent, the composition of an inoculating alloy according to the invention may comprise, for example:

Item Quantity (% mass)

If 45 - 80

Ca 0.5 - 4

Al 0.5 - 3

Sb 0.2 - 2

Rare earth 0.2 - 3 (especially

Lanthanum)

Iron Balance

Inoculant alloy - composition 1

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

By way of example, the inoculant alloy may thus have 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 weight of the inoculant in the melt bath, especially in the following conditions. for example:

- at the end of fusion in the induction furnace

- before a n uctive treatment w ith the mag usin u m, and especially between 1 and 5 minutes before this treatment - as a cover for a subsequent "Sandwich" treatment or

"Tundish-cover". - in a casting furnace

- During a transfer between two pockets (tranfer and casting, in particular).

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

The frequency range of the harmful agent according to the invention can be adapted according to its addition modalities.

By way of examples, mention may be made of:

- Addition in induction furnace: particle size up to about 40 mm, - Addition between the firing at i n d u ction and the po po d e co u lée: particle size between about 10 and about 30 mm.

- Addition in bass-n neck: particle size between about 0.4 and about 2 mm.

Addition before casting in the slack: particle size of between about 0.2 and about 0.5 to 2 mm.

- Addition as inoculant insert placed in the casting mold: inserts of 20g, 40g, 60g, 80g, 300g, 800g, 2kg, 5kg, 10kg, 20kg and 50kg, for example.

The inoculant mixture can also be added successfully as an inoculant before filling the casting mold or in inoculation in the bag or later, after adjusting the chemistry of the alloy (especially 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 inoculant alloy according to the present application, it is possible to eliminate the post-inoculation step. Indeed, the prolonged maintenance of the effect of inoculation over time with the action of antimony makes it possible to significantly reduce the treatments of late inoculations or even to remove them. With, for example, the addition of an inoculant containing the Bi /

TR, 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 nodulizer with additional inoculant function, the composition of the alloy will also include magnesium. By way of example, the composition of such a nodulising alloy with inoculant function may be as follows:

Nodulising alloy with inoculant effect - composition 3

The generalization of the nodulizer (especially with inoculant function) according to the invention will be adapted according to the size of the treatment pockets. For example, for bags of 100 to 500 kg of cast iron, preference will be given to a particle size of between about 0.4 and about 2 mm, or even up to 7 mm. For pockets of 500 to 1000 kg of cast iron, preference will be given to a particle size of between about 2 and about 7 mm, or between about 10 and about 30 mm. For pockets of more than 1000 kg of cast iron, preference will be given to a particle size of between about 10 and about 30 mm.

Examples of use will now be given. Example 1: foundry A - piece of thickness 8 mm.

Foundry Reference (A1)

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

The cast iron was then subjected to nodulisation treatment using a FeSiMg type nodulising alloy comprising one third of a FeSiMg alloy comprising 2% of light earth and one third of a FeSi alloy. Mg does not include rare earths.

The cast iron finally underwent an inoculation treatment by adding 0.1% by weight of a FeSiMnZr alloy and 0.1% of an alloy to the tundish. FeSiAI, the inoculant alloys being added as inoculant insert in the mold.

Use of an Inoculant Alloy According to the Invention (A2)

An alloy inoculating according to the composition 2 mentioned above and 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 weight of cast iron.

The step of adding pure antimony was suppressed and the nodulizing treatment was simplified using only the non-rare earth FeSiMg nodulising alloy.

Comparative results

The foundry A treated with an inoculant according to the present application showed an increase in tensile elongation on control specimens for a grade EN-GJS-400-15.

Example 2: foundry B - piece 200 mm thick. Foundry Reference (B1)

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

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

The cast iron finally underwent an inoculation treatment by adding 0.15% by weight of a FeSiBiTR alloy to the casting basin.

Use of an inoculant alloy according to demand (B2) An inoculant alloy according to composition 2 mentioned above and containing as above: 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 weight of cast iron.

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

Comparative results

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

Example 3: foundry C - thin pieces (thickness less than

6mm).

Foundry Reference (C1)

According to the prior art, the liquid iron was treated by adding in the induction furnace pure antimony in a proportion of 25 g of antimony per one ton of liquid iron.

The pig iron then underwent a nodulisation treatment using a nodulising alloy of FeSiMg type comprising 6.7% by weight of magnesium as well as 1.2% of calcium and 0.98% of rare earths.

The cast has finally undergone a late inoculation treatment by adding

0, 1 2% by weight of a FeSiMnZrBa alloy having a particle size of between 0.2 and 5mm. Use of an inoculant alloy according to demand with nodulising function (C2)

A nodulising alloy with inoculant function according to the composition 3 mentioned above was used.

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

The nodulising treatment was carried out using a FeSiMg-type alloy according to composition 3 of the present application and comprising 6.4% by weight of magnesium and 1.3% of calcium, 0.6% by weight. antimony and 1.2% rare earths.

Complementary inoculation was performed according to a late inoculation method with 0.09% FeSiAICa alloy and 0.009% FeSiMnZrBa alloy. Comparative results

Using a nodulizer according to the present application there is a disappearance of "chunky" graphite defects on all the parts controlled.

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

Example 4: foundry D - massive pieces

Foundry Reference (D1)

According to the prior art, the liquid iron was treated by adding in the induction furnace pure antimony in a proportion of 30 g of antimony per one ton of liquid iron. The pig iron then underwent a nodulisation treatment using a nodulising alloy of FeSiMg type comprising 9.1% by weight of magnesium as well as 1.4% of calcium and 1.1% of rare earths.

The cast iron finally underwent an inoculation treatment by adding an insert of 10 kg per ton of cast iron of a FeSiMnZr inoculating alloy.

Use of an inoculant alloy according to demand (D2)

An inoculant alloy according to composition 2 mentioned above and containing: Si = 65% Si, Ca = 1, 76% Ca, Al = 1, 23%, Sb = 0.1 5%, TR = 0.16%, Ba = 7.9%; was used as a 10kg insert as for the reference.

The nodulising treatment was carried out using the same alloy as for the reference, namely by using a nodulising alloy of FeSiMg type comprising 9.1% by weight of magnesium and 1.4% of calcium and 1, 1% rare earths.

Comparative results

The D-cast iron makes it possible to elaborate a shade of EN-GJS-400-18-LT darkening used in particular in the wind energy sector. The use of the inoculant according to the demand has made it possible to increase the impact resistance significantly. Example 5: Foundry E - thin parts and nodulising treatment.

Foundry Reference (E1)

The molten iron was subjected to a nodulisation treatment using a FeSiMg type nodulising alloy comprising 9.1% by weight of magnesium and 0.8% of bismuth and 0.7% of rare earths.

The melt then underwent inoculation treatment according to a late inoculation method by adding 0.18% of a FeSiMnZr alloy having a particle size of between 0.2 and 5 mm.

Use of a demand-inoculating alloy with nodulising function (E2)

A nodulising alloy according to the composition 3 mentioned above was used. The alloy used is a FeSiMg type alloy comprising 9.1% magnesium and 0.75% antimony and 0.5% rare earths.

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

Comparative results

As mentioned above, it is found that replacing the bismuth with antimony increased the yield of magnesium in the E cast iron. Example 6: Foundry D on massive pieces.

The foundry reference (F1) and the test (F2) using an inoculant alloy according to the application were made according to Example 4 and the foundry D by inoculating massive pieces.

Comparative results

It can be seen that, thanks to the high yield obtained, it is possible to better control the quantity of antimony added. The F2 foundry has saved a lot by reducing the dose of antimony by 31.5%.

Example 7: Foundry D on massive pieces.

The foundry reference (G1) and the test (G2) using an inoculant alloy according to the application were carried out according to Example 4 and the foundry D by inoculating massive pieces.

Comparative results

It can be seen that, thanks to the inoculant according to the present application, the release of antimony is strongly limited and well below the regulatory threshold of 0.5 mg / m ³ . The working conditions are improved.

Example 8: foundry H - piece 150 mm thick.

Foundry Reference (H1) According to the prior art, the liquid iron was treated by adding in the induction furnace pure antimony in a proportion of 15 g of antimony per one ton of liquid iron.

The cast iron then underwent a nodulisation treatment with a nodulated thicker wire (diameter 13 mm, 32% Mg, 1.2% TR, 230 g / m powder)

The cast iron finally underwent a late inoculation treatment by adding to the casting jet 0.15% by weight of a FeSiMnZr alloy. Use of an inoculant alloy according to demand (H2)

An inoculant alloy 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 weight of cast iron.

Comparative results

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

Although the invention has been described with particular examples of embodiment, it is obvious that it is not limited thereto and that it includes all the technical equivalents of the means described and their combinations if they fall into the scope of the invention.

Claims

1. Inoculant alloy for the treatment of ferro-silicon-based cast iron thick parts, containing between 0.005 and 3% by weight of rare earth, characterized in that it also contains between 0.2 and 2% by weight of antimony.

2. Inoculant alloy according to claim 1, characterized in that it also comprises magnesium and is a nodulating alloy.

3. Inoculant alloy according to claim 1, characterized in that it does not contain magnesium.

4. Inoculant alloy according to any one of claims 1 to 3, characterized in that the rare earth ratio on antimony is between

0.9 and 2.2.

Inoculant alloy according to any one of claims 1 to

4, characterized in that the mass proportion of antimony is greater than 0.3%, preferably greater than 0.5%, more preferably greater than

0.8%.

Inoculant alloy according to any one of claims 1 to

5, characterized in that the mass proportion of antimony is less than 1, 5%, preferably less than 1, 3%.

Inoculant alloy according to any one of claims 1 to

6, characterized in that the rare earths comprise Lanthanum, preferably only lanthanum.

Inoculant alloy according to any one of claims 1 to

7, characterized in that the mass ratio of rare earths is greater than 0.2%, preferably greater than 0.3%.

9. Inoculant alloy according to any one of claims 1 to

7, characterized in that the mass ratio of rare earths is less than 1, 2%, preferably less than 1%.

10. Use of an inoculant according to any one of the preceding claims, characterized in that said inoculant is introduced in powder form.

11. Use of an inoculant according to any one of the preceding claims, characterized in that said inoculant is introduced in the form of a solid insert placed in a casting mold.

12. Use of an inoculant according to any one of the preceding claims for the manufacture of cast iron parts having parts of thicknesses greater than 6 mm, preferably parts of thicknesses greater than 20 mm, and even more preferably parts of thickness greater than 50mm.