FR2838134A1 - Anti-micro-recompression inoculant for the treatment of cast iron obtained from an inoculant alloy or mixture of ferrosilicon containing aluminum, lanthanum and possibly calcium - Google Patents

Abstract

An inoculant for the treatment of cast iron in the mould is made up of an inoculant alloy or mixture and possibly a binder. The inoculant alloy or mixture contains (by wt) 2.5 - 5% of aluminum, 0.3 - 8% of lanthanum and possibly up to 2% of calcium with the remainder being ferrosilicon. The inoculant may be obtained by casting the molten alloy (claimed) or by the agglomeration of a mixture or a powdered inoculant alloy (claimed).

Description

to get rid of scratches or dust.

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  Anti-micro-inoculating inoculating pin for treatment of cast iron.

  Field of the Invention The invention relates to an inoculant for the liquid state treatment of cast irons intended for the manufacture of molded parts for which it is desired to obtain a structure free from

  carbides of iron and microretasures.

  STATE OF THE ART Cast iron is a well-known iron-carbon-silicon alloy widely used for the manufacture of mechanical parts. We know that to have good mechanical properties of these parts, we must ultimately obtain an iron + graphite structure, avoiding as much as possible the

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

  Then, the graphite formed can be chosen spherodal, vermicular or lamellar, but the

  essential prerequisite to be met is to avoid the formation of iron carbide.

  To this end, the liquid cast iron undergoes before inoculation treatment which promotes the

  cooling the appearance of graphite rather than that of iron carbide.

  Inoculation treatment is therefore very important. Now it is well known that inoculation, whatever the inoculants used, has an efficiency on liquid cast iron which decreases over time and which, in general, has already decreased by 50% after ten minutes; a person skilled in the art designates this phenomenon under the name of "fading effect". In order to obtain a maximum efficiency, we generally practice progressive inoculation, operating for this several additions of inoculants at different stages of the development of the cast iron. Thus it is common practice to inoculate liquid cast iron as well in a pocket with an inoculating alloy, for example in grains of size between 2 and 10 mm, or between 0.4 and 2 mm, or "jet" > ie when pouring the ladle, with an inoculating alloy in grains of size between 0.2 and 0.7 mm, or else "in the mold", in fact in the feed channels of the molds , by having inserts made of a material on the liquid iron route

  inoculant. These defined shaped inserts are called pawns.

There are two types of plons:

  - the molded pins obtained by molding the molten inoculant.

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  AT Y; J i, r,;, - agglomerated pions obtained from a pressed powder with in general very little

binder, or even without a binder.

  Molded pieces are generally considered the best level of quality;

  however, agglomerated pawns are often claimed for cost reasons.

  The hardness of the casting of a part being very short, the kinetics of dissolution of the pawns must be extremely fast. In addition, we often see in the rooms the presence of

  voids of millimeter or micrometer dimensions referred to as micro-

  blowholes. These defects weaken the parts, moreover, if a subsequent machining of the parts is necessary for example to dress a surface, the fact of falling on such defects leads

  o the inevitable discard of defective parts.

  One known way to avoid the appearance of micro-shrinkage in cast iron parts is the addition of lanthanum in liquid cast iron. This metal from the lanthanide group indeed has the property of reducing the viscosity of the cast iron, not only that of the liquid cast iron just before the start of its solidification, but also that of the cast iron in the course of solidification, that is to say solid + liquid mixture, as if, by adding lanthanum, the moving cast iron became thixotropic. Those skilled in the art can then by correctly drawing their molds,

  gather the shrinkage in the feeder, and thus obtain healthy parts.

  Thus were successively put on the market, first nodulants containing lanthanum, the use of which was reserved for nodular cast iron called GS cast iron, then inoculants of FeSi type with 45% Si and 2% La, also usable good for GS fonts than for

  lamellar graphite fonts called GL fonts.

  All of these products are made of alloys with a low aluminum content, typically less than 1.2% Al and preferably less than 0.8%, because aluminum is also well known to those skilled in the art. in cast iron sometimes leads, at least in the case of molding in 2s sand, to subcutaneous defects, for example micro-porosities, or spherical and millimeter porosities appearing under the surface in contact with the sand, and the formation is due to the generation of hydrogen by reaction between the aluminum contained in the cast iron and the residual traces of moisture which the foundry sand can contain. In the case of shell molding, a protective coating is required and the coating products

  can create similar problems.

  The object of the invention is therefore to obtain effective inoculation while avoiding the formation of

  porosities and micro-shrinkage in cast iron castings.

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  OBJECT OF THE INVENTION The subject of the invention is an inoculating pin intended for the treatment in the mold of molding irons, consisting of an inoculating alloy or mixture and optionally a binder, the inoculating alloy or mixture containing by weight from 2.5 to 5% of aluminum, from 0.5 to 8% of lanthanum, possibly up to 2% of calcium, the rest being ferro-silicon. Preferably, the aluminum content is between 3.5 and 4.5%, and the lanthanum content

between 0.5 and 5%.

Description of the invention

  In the field of inoculants for the treatment of cast iron, alloys based on ferro-silicon containing 75% silicon containing 2% lanthanum are known. These alloys make it possible to obtain cast iron parts with a low level of micro-porosity, but their effectiveness as

  s that inoculants is quite limited. They were never offered in the form of pawns.

  In seeking to develop inoculating pions having both good efficacy against micro-porosities and better inoculating power, the Applicant has tried pions made of an alloy based on ferro-silicon-lanthanum, with the addition of aluminum in quantity

  significantly greater than in the alloys of the prior art.

  The results in terms of reduction of micro-shrinkage have been confirmed, but the addition of aluminum has allowed a significant gain in terms of inoculating power. Very good results have therefore been obtained with molded pins made of an alloy based on ferro-silicon containing: - 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 2.5 to 5%, and preferably from 3.5 to 4.5% of aluminum,

  possibly up to 2% calcium, iron remains.

  The pins can be produced by molding the molten alloy. They can also be so by agglomeration of an alloy powder or of a mixture of alloy powders of o different compositions leading to the same average composition, possibly with a small amount of binder, for example 0.3 3 cm3 of sodium silicate per 100 g of powder. The pawn is preferably prepared from a powder with a particle size of less than 1 mm, in which the particle size fraction between 50 and 250 μm represents more

  by 35%, and the fraction less than 50 m less than 25%.

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Examples

  In the examples which follow, the performance in terms of macro as well as micro shrinkage was assessed by means of the test of casting of "V" test pieces. The test piece consists of a "V" with a height of 10 mm and an angle at the top 40, the width of the branches of the "V" is 20 mm; the thickness of the part is 20 mm. This geometry gives a width of 80 mm at the top of the "V>. On this type of part, the

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

  o To assess the test result, the part is cut to mid-thickness, and the section is examined by optical microscopy to assess the surface of the porosities; the result is expressed in

  relative surface referred to the surface of the cut.

Example 1

  A charge of cast iron was melted in an induction furnace and treated by the Tundish Cover process using an alloy of the FeSiMg type at 5% Mg, 1% Ca without rare earths, at the dose of

kg for 1600 kg of cast iron.

  The analysis of this liquid melt was as follows:

  o C = 3.6% Si = 2.6% Mn = 0.07% P = 0.03% S = 0.003% Mg = 0.039%.

  This cast iron was used to cast V-shaped pieces of geometry identical to that defined in the control test, arranged in a cluster in a 36-piece sand mold, fed by a supply channel where an alloy pin was placed. 75 "FeSi inoculant Foundry

  grade "specially prepared for this test.

  The parts obtained were examined by optical microscopy on a polished section to determine the structure of the metal as a function of the depth and the level of porosity. At

  On the branches, the density of the graphite nodules was counted at 130 / mm2.

  The average porosity of the parts was evaluated at 2.0%.

Example 2

  The test described in Example 1 was repeated identically except for the inoculation treatment for which an alloy pawn of composition was used:

  Si = 72.7% Al = 4.85% Ca = 0.82% La = 0.01% balance Fe.

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  The parts obtained were examined by optical microscopy on a polished section to determine the structure of the metal as a function of the depth and the level of porosity. At the heart of the branches, the density of the graphite nodules was counted at 250 / mm2. Porosity

  average of the pieces was estimated at 2.2%.

Example 3

  The test described in Example N 1 was carried out identically except for the inoculation treatment for which an alloy pawn of composition was used:

  0 Si = 73.1% Al = 4.1% Ca = 0.87% La = 2.1% balance Fe.

  The parts obtained were examined by optical microscopy on a polished section to determine the structure of the metal as a function of the depth and the level of porosity. At

  On the branches, the density of the graphite nodules was counted at 245 / mm2.

  The average porosity of the parts was evaluated at 0.3%.

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Claims (6)

claims   1. Inoculating pin for treatment in the mold of molding irons, consisting of an alloy or an inoculating mixture and possibly a binder, the alloy or inoculating mixture containing by weight from 2.5 to 5% d aluminum, from 0.3 to 8% lanthanum,   possibly up to 2% calcium, the rest being ferro-silicon.   2. Inoculating pion according to claim 1, characterized in that the lanthanum content of   o the alloy is between 0.5 and 5%.   Inoculating pin according to one of claims 1 or 2, characterized in that the content of   aluminum alloy is between 3.5 and 4.5%.   4. Inoculating pin according to one of claims 1 to 3, characterized in that it is obtained by molding of the molten alloy.   5. Inoculating pawn according to one of claims 1 to 3, characterized in that it is obtained by   agglomeration of a powder inoculating mixture or alloy.   6. Inoculating pin according to claim 5, characterized in that it is prepared from a powder with a particle size less than 1 mm, in which the fraction between 50 and   250 m represents more than 35%, and the fraction below 50 m less than 25%.   7. Inoculating pin according to claims 5 or 6, characterized in that the composition of