FR2839082A1 - INOCULATING ALLOY ANTI MICRORETASSURE FOR PROCESSING MOLDING WAFERS - Google Patents

Abstract

The invention relates to inoculant alloys for the treatment of cast iron containing (by weight) from 0.005 to 3% of an element of the bismuth, lead and antimony group, from 0.3 to 10% of metals. rare earth and possibly aluminum up to 5% and calcium up to 1, 5%, the rest being ferro-silicon, lanthanum constituting more than 90% rare earth metals entering its composition. The alloys according to the invention allow effective inoculation of the cast iron and avoid the appearance of micro-shrinkage in the molded parts.

Description

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  Inoculant alloy anti microretassure for processing cast irons.

  FIELD OF THE DISCLOSURE The invention relates to the treatment in the liquid state of cast iron for the manufacture of parts for which it is desired to obtain a structure free from iron carbides and a

0 absence of micro-shrinkage.

  State of the art Cast iron is a well-known iron-carbon-silicon alloy widely used for the manufacture of mechanical parts. It is known that to obtain good mechanical properties of these parts, it is necessary to obtain in fine a structure iron + graphite avoiding as much as possible the

  formation of Fe3C type iron carbides which harden and weaken the alloy.

  Then it can be said that the graphite forms either spheroidal, vermicular or lamellar, but the essential prerequisite to fulfill is to avoid the formation of fen carbide For this purpose, the liquid iron undergoes before casting a treatment of inoculation which favors The appearance of graphite rather than that of fen carbide is very important. The inoculation treatment is therefore very important. Now it is well known that inoculation, whatever the inoculants used, has on the liquid iron an effectiveness which decreases over time and which, in general, has already dropped by 50% after about ten minutes. the man of 2s art designates this phenomenon under the name of "fading effect". In order to obtain maximum efficiency, inoculation is generally carried out in a gradual manner, consisting of several injections of inoculants at different stages of the smelting process. Thus it is common practice to inoculate the molten iron, on the one hand in a pocket with an inoculant alloy, for example grains of size between 2 and 10 mm or between 0.4 and 2 mm, on the other hand < "au jet", that is to say the casting of the pocket with an inoculant grain size of between 0.2 and 0.7 mm, and finally << in the mold >>, in fact in the feeding channels of the molds, arranging inserts made of an inoculating material on the path of the liquid cast iron. These inserts of definite shape are called pawns. There are two types of pions:

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there

  mold pions obtained by molding the molten inoculant.

  agglomerated pions obtained from a pressed powder with generally very few

binding, or even without binder.

  The molded pieces are considered by the person skilled in the art as the best level of quality; However, agglomerated pawns are often preferred for reasons of cost. The duration of the casting of a piece being very running, the kinetics of dissolution of the pions must be

extremely fast.

  Moreover, those skilled in the art often find in the rooms the presence of vices of

  millimetric or micrometric dimensions designated as micro-shrinkage.

  0 These defects weaken the parts; in addition, if further machining of the pieces is necessary, for example to establish a surface, the fact of sinking on such defects leads to scrapping

inevitable defective parts.

  One known means of avoiding the appearance of micro-shrink in cast iron parts is the addition of lanthanum to the molten iron. This metal of the group of lanthanides has the property of reducing the viscosity of the melt, not only that of the liquid melt just before the beginning of its solidification, but also that of the melt during solidification, that is to say solid + liquid mixture. Everything happens as if, by aj out of lanthanum, the melting in movement became thixotropic. The person skilled in the art can then, by correctly drawing his molds, gather the sinkholes in the feeder and thus obtain parts

seines.

  Thus, lanthanum-containing nodulisers were used successively, the use of which was reserved for the nodular felts mentioned in the GS font, and then of FeSi inoculants containing 45% Si and 2% La, which could also be used. good for GS fonts that for

  lamellar graphite cast iron font font GL.

  The object of the invention is to provide inoculant alloys for the treatment of liquid cast iron for efficient inoculation, especially during "in-mold" treatment,

  while avoiding the formation of micro-porosites in the parts obtained by molding.

  OBJECT OF THE INVENTION The object of the invention is to provide inoculating alloys for the treatment of cast iron containing (by weight) from 0.005 to 3% of a bismuth, lead and antimony group element of 0, 3 to 10% rare earth metals and possibly aluminum up to 5%

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  and calcium up to 1.5%, the rest being ferro-silicon, lanthanum is more than

  % of the rare earth metals used in its composition.

  The alloy preferably contains bismuth at a content of between 0.2 and 1.5%, and preferably between 0.7 and 1.3%. The lanthanum content is advantageously between 0.3 and 8%, and preferably between 0.5 and 3%. The presence of at least 0.8% aluminum is

  advantageous, and its content is preferably between 1 and 3.5%.

  The alloy according to the invention may be packaged in the form of a powder or a mixture of alloy powders of different compositions, or in the form of molded pions from the molten alloy, or agglomerated from a powder. or a mixture of powders. This powder preferably has a particle size of less than 1 mm, with a particle size fraction between 50 and 250 m, representing more than 35% by weight of the total, and

  fraction less than 50 m representing less than 25% of the total.

Description of the invention

  Since an inoculant is intended by nature to lead to the production of pig iron in which the carbon is present in the form of graphite, it has appeared desirable to the plaintiff to

  develop an inoculant with anti-microburst properties.

  Thus, 75% FeSi-based inoculant alloys were firstly added with an anti-microbissure element that could be either lanthanum or germanium. As regards germanium, the required contents range from 0.3 to 6%. As for lanthanum,

  they range from 0.3 to 8%, and preferentially from 0.5 to 5%.

  But more interesting solutions emerged by imagining inoculant alloys in which the same element can fulfill several functions: thus it appeared as particularly interesting, starting from an alloy such as that described in US Patent 4432793 (Nobel-Bozel), based on ferrosilicon and containing up to 3% bismuth, lead or antimony, and up to 3% rare earth, add an anti-micro porosite element such as lanthanum, and contract the formula obtained by optimizing the total of

  lanthanum and other rare earths in a Fe-Si-Bi-La alloy.

  The applicant first verified that these new alloys anti microporosites, conditioned in the usual granulometries, namely between 2 and 7 mm, or between 0.4 and 2 mm for treatment in pockets, and between 0.4 and 0.7 mm for jet treatment, had good properties as inoculants. Next, the preparation of pions

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  with these same alloys. The result in terms of reduction of the micro -poro site has

  This is confirmed despite the contribution of bismuth in final melting.

  Thus, very good results have been obtained with molded pieces made of FeSi-type alloy containing: s from 60 to 80%, and preferably from 72 to 78% of silicon, from 0.3 to 8%, and preferably from 0.5 to 5% of lanthanum, from 0.2 to 1.5%, and preferentially from 0.7 to 1.3% of bismuth,

  from 0.8 to 5%, and preferably from 1% to 3.5% of aluminum.

o Examples

  To perform the examples described below, a cast iron filler was melted in an induction furnace and processed by the Tundish Cover process using a customary inoculant alloy. of FeSiMg 5% Mg and 1% Ca containing no rare earths, at the dose of 20 kg for 1600 kg of cast iron. The analysis of this liquid iron was as follows:

  C = 3.7%, Si = 2.6%, Mn = 0.07%, P = 0.03%, S = 0.003%, Mg = 0.038%.

  Macro-like performance of micro-porosite has been assessed by means of

  the "V" test piece casting test.

  In this test, the test specimen consists of a "V" with a height of 110 mm and an apex angle

  40, the width of the branches of the "V" being 20 mm and the thickness of the piece of 20 mm.

  This geometry gives a width of 80 mm at the top of the "V", a unit volume of 69 cm3, and a unit mass of 480 g to 500 g according to the quality of the cast iron. On this type of piece,

  the porosites appear selectively in the reentrant part of the "V".

  To evaluate the result of the test, the part is cut to half-thickness, and the section is examined by optical microscopy to evaluate the surface of the porosites; the result is expressed in

  relative area related to the surface of the cut.

Example 1

  A pouch of processed cast iron from the preliminary operation was inoculated into the pocket by means of an inoculant powder mixture of particle size of between 2 and 10 mm, of composition: "Foundry Grade", predominantly Fe, used a the dose of 200 ga the

ton of cast iron.

  s 2839082 This cast iron was used to cast V geometric pieces identical to those defined in the control test, arranged in a cluster in a 36-piece sand mold fed by

  a supply channel where a filter constituted of a refractory foam was provided.

  The resulting pieces were examined by optical microscopic poke cutting to determine the structure of the metal according to the depth and the level of porosity.

  At the heart of the branches, the density of graphite nodules was measured at 120 / mm2.

  The average porosity of the pieces was evaluated at 2.4%.

Example 2

  A second treated cast iron bag from the preliminary operation was inoculated into the bag by means of an inoculant alloy with a particle size of between 2 and 10 mm composition: Si = 75.4%, Al = 0.94%, Ca = 0, 86%, La = 2.2%, Bi = 0.92%, balance mainly Fe,

  It is used at the rate of 200 g per ton of pig iron.

  This cast iron was used to cast V geometric pieces identical to those defined in the control test, arranged in a cluster in a 36-piece sand mold fed by

  a supply channel where a filter constituted of a refractory foam was provided.

  The resulting pieces were examined by optical microscopic poke cutting to determine the structure of the metal according to the depth and the level of porosity. the

  of the branches, the density of graphite nodules was counted at 360 / mm2.

  The average porosity of the pieces was estimated at 0.3%.

Example 3

  A third pocket of processed cast iron from the preliminary operation was used to cast geometric V-pieces identical to those defined in the control test, arranged in a cluster in a 36-piece sand mold fed by a control channel. a 25 g counter made of inoculant alloy for treatment in the motile, of composition:

  If = 73.6%, Al = 3.92%, Ca = 0.78%, La = 2.1%, Bi = 0.97%, mainly balance Fe.

  The resulting pieces were examined by optical microscopic poke cutting to determine the structure of the metal according to the depth and the level of porosity. the

  of the branches, the density of the graphite nodules was counted at 320 / mm2.

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  The average porosity of the pieces was evaluated at 0.2%.

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  Rev en d icatio nss 1. Inoculant alloy for cast iron, containing (by weight) 0.005 to 3% of a bismuth, lead and antimony group, 0.3 to 10% rare earth metals and possibly aluminum up to 5% and calcium up to 1.5%, the rest being ferro-silicon, characterized in that lanthanum constitutes more than 90% of the

  rare earth metals used in its composition.

  2. Alloy according to claim 1, characterized in that it contains from 0.3 to 8% of lanthanum

and 0.2 to 1.5% bismuth.

  3. Alloy according to one of claims 1 or 2, characterized in that its bismuth content

is between 0.7 and 1.3%.

  4. Alloy according to one of claims 1 to 3, characterized in that its lanthanum content

is between 0.5 and 5%.

  5. Alloy according to one of claims 1 to 4, characterized in that its aluminum content

is between 0.8 and 5%.

  6. Alloy according to claim 5, characterized in that its aluminum content is

between 1 and 3.5%.

2s

  7. Alloy according to one of claims 1 to 6, characterized in that it is conditioned in

powder.

  8. Alloy according to one of claims 1 to 6, characterized in that it is conditioned under

  form of pions for "in the mold" treatment.

  9. Alloy according to claim 8, characterized in that the pin is obtained by molding of

the molten alloy.

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  10. Alloy according to claim 8, characterized in that the pion is obtained by

agglomeration of a powder.

  11. Alloy according to claim 10, characterized in that the particle size of the powder is s <1 mm, the particle size fraction between 50 and 250, um representing more than

  % by weight of the total, and the fraction less than 50 m less than 25%.

  12. Alloy according to one of claims 10 or 11, characterized in that the composition

  average of the alloy is obtained by mixing powders of alloys with compositions