DE2117776A1 - Alloy for treating nodular cast iron melts - Google Patents

Description

Patent Attorneys DIpl.-Ing. R. D ^ ETZ sen.

DIpUn _1;. κ. LAViP.-jECHT 503-I6.892P April 13, 1971

Dr.-ln.-5. Γ ..:.: ... C f Z jr.
Münchon £ 2, SLeinsdorfetr. 10

COMPAGNIE PECHINEY, Paris (France)

Alloy for treating nodular cast iron melts

The present invention relates to a new additive alloy used for treating nodular cast iron melts is determined.

Since MILLIS ¹ discovered the effect that magnesium has on the shape and structure of graphite precipitated in cast iron melts, great advances have been made in the manufacture of KG (ie spheroidal graphite) cast iron melts.

It has become current practice to melt cast iron by means of alloys, often based on Fe-Si, with a content to nodulate magnesium as a nodulating agent. The use of such alloys brings in comparison with the Introducing pure magnesium the advantage of a better distribution of the active element and much less violent reactions, whichever type of introduction is used.

50> (B 15H) -TpE (6)

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When adjusting the amount of magnesium to be introduced to the contents of the cast iron melts in terms of oxygen and of sulfur in a known manner and when working in the absence of anti-modulating elements (e.g. Bi, Pb, Ti), i.e. with new cast iron melt, it is fairly easy to get the graphite to form spheres, as often one can be satisfied with a ferritic-pearlite structure of the matrix of the solidified cast iron melt can.

On the other hand, problems arise if one wishes to produce a K.G. cast iron with a ferritic matrix, which is very desirable because of its good machinability and its great ductility. Indeed, the additional necessary graphitization among other functions of time, since the nodulating effect of the Mg stops after 10 to 15 minutes. Based on a well-known suggestion currently in current practice if you apply two successive treatments to the cast iron melt shortly before casting, namely the Already mentioned nodulation treatment and afterwards an inoculation treatment by means of graphitizing agents, in particular the aim is to remove all or part of the carbides and to reduce the rate of their disappearance of the nodulating agent. The inoculants used are generally silicon alloys, e.g. Rare earths or alkaline earth elements added and which can be made heavier by iron.

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Their introduction takes place in a moment that is as close as possible to finite pouring, e.g. in the mold even including slinging onto the walls of the mold if there is a risk of quenching, in particular Places where the cast piece has thin places that are deposited with a white and therefore brittle structure.

Despite the precautionary measures taken, the known treatment in two procedural steps is often inadequate Results. You must therefore by a heat treatment of the solid metal, i.e. an annealing above of the Ac-z point must be completed. It is for that It will be understood by those skilled in the art that such annealing causes surface degradation and particularly in the case of workpieces with parts of very different thickness can lead to such stresses that permanent deformations result.

The invention is based on the object of specifying an additional alloy with which in a single Process step results in a cast iron with spheroidal graphite and a pronounced ferritic matrix in the raw cast state.

The additional alloy with which this object is achieved is of the iron-silicon-alkaline earth metal-nitrogen type by the following composition:

Si 40 - 55% by weight ,
Mg 3-15 wt. #,
Ba 1.4 - 8.6% by weight ,

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Nitrogen in an amount that the weight ratio Ba / N is between 5 and 50,

Remainder iron and unavoidable impurities that are introduced during production, especially Ca and Al, in a total amount below 2.5 wt. ^, the The alloy is also characterized by a weight ratio Mg / Ba between 1 and 5.

The use of the alloy according to the invention provides considerable advantages. It simplifies the work processes and reduces the heat loss of the molten cast iron. The magnesium losses turn out to be lower, which enables substantial savings on this nodulation element and a more precise control of its final content. It is now known that magnesium stabilizes the carbides by making the transition temperature brittle / ductile of cast iron so increased that it is important to keep its content to a minimum with a good spheroidal graphite formation to adjust the acceptable value. On the other hand, it is no longer necessary to check the content of the cast iron melt to adjust to silicon after the modulation with magnesium and for this expensive silicon alloy additives to use. In fact, thanks to the new additional alloys, the silicon content in the blast furnace or in the Adjust the cupola furnace using less troublesome starting materials.

The various constituents of the alloy according to the invention are balanced in order not to

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to produce only a ferritic matrix, but also an equalization of the shape of the precipitated graphite spheres as well as an insensitivity to interfering elements (in particular carbide formers), which after the production of the cast iron melt has an effect on the tolerance of a degree of recirculation (introduction of waste and return), containing 50 wt.% and more can achieve.

In its preferred composition, the alloy according to the invention is characterized by the following contents:

Si 45 - 50 wt. #,

Mg 7-11 wt. Ji,

Ba 4.5-6 wt. G,

N 0.4-0.6 wt

Balance Fe and the inevitable impurities as a result of manufacture in a total amount below 1.2

As far as the proportions are concerned, the work carried out in the course of the present invention the following preferred weight ratios are determined:

Mg / Ba - 2-0.2,
Ba / N «10-2.

The content of residual magnesium in the cast iron melt

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after treatment with the claimed alloys is a function of the base cast iron melt and the type of obtained cast iron.

# It is usually above 0.01 f> and more generally 0.03 to 0.06 wt.. For this, the amount of alloy to be used is such that the magnesium, in general from 0.08 to 0.03 wt.% Is the molten cast iron to be treated.

The invention therefore also relates to the use of the additive alloy of the invention in an amount in which its magnesium content corresponds to 0.03 to 0.08 wt.% Of the treated molten cast iron, for the treatment of a spheroidal graphite cast iron up to which the residual magnesium content of more than 0, 01, in particular between 0.03 and 0.06

It is known (Swiss Archives, December 1964, Page 367) that the introduction of nitrogen by blowing into the K.G. cast iron melt is a noticeable inoculation can produce, but this technique does not result in a ferritic matrix in the as-cast state.

According to another prior publication (US Pat. No. 3,177,072) it is proposed to nodulate the cast iron melts with the aid of additional alloys of the Pe-Si-Mg-Ca-N type, in which the nitrogen is partly in the form of a suspension of calcium cyanamide.

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The calcium associated with the elements mentioned, however, only results in a much less complete ferritization than those which can be obtained from barium with the aid of alloys, the subject matter of the present invention Invention are. This surprising result is explained in Tables 1 and 2 below, in which one can use A the treatment by an alloy according to the invention, B has a practically identical treatment with the exception, that the alloy contains Ca instead of Ba, and C denotes the usual treatment resulting from a nodulation and subsequent vaccination treatment.

It is in the acidic shaft furnace from a batch with 50 wt.% To a new cast iron and 50 wt.% Gußputzabfall, the cast iron melt forth that are desulfurized using CaC ₂ in a known manner.

The cast iron melt is then transferred to an induction holding furnace. The transfer to this holding furnace allows the adjustment of the silicon content of the cast iron melt before treatment A and B to after Treatment to obtain a cast iron melt with a composition comparable to that of treatment C was subjected.

Treatments A and B exist in the imports as "sandwich" in the molten cast iron to be treated an amount of about 1.8 wt.% Of these melt of an alloy, for the A

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-δSi = 47.8 wt. ^,

Mg = 9.1 ",

Ba = 4.6 ",

Ca = 0.5 ",

Al = 0.18 ",

N = 0.47 ",

Fe remainder up to 100 "

and for B

Si = 47.6% by weight ,

Mg = 9.2 ",

Ca = 5.3 ",

Al = 0.20 ",

N = 0.44 "

contains.

Treatment C (known treatment) is to introduce a "sandwich" in the first molten cast iron to be treated an amount equal to about 1.8 wt.% Of this melt a Nodulisierlegierung "Fe-Si-Mg with 8.10 wt.? Mg" containing:

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Si 47.5 wt Mg = 9.5 " Ba traces Approx 0.2 " Al 0.21 " N traces

Pe remainder to 100 "

and then an amount equal to about 0.8 wt.% of the melt obtained an inoculant, the # Silicon is a ferrosilicon containing 75 wt..

After the treatment, pieces and test pieces are poured.

The three comparative treatments with the alloys A, B, C are carried out with the same cast iron-based alloy that was produced in the induction furnace. Take out 3 times 600 kg in the oven for each of the described items Treatments.

In all cases, the temperature of the cast iron melt in the course of treatments A, B and C is between 1480 ° C and 1520 ° C, the castings and the control specimens are taken at the end of the ladle pour, with the between The time elapsing from the treatment and pouring of the pieces examined is between 10 and 15 minutes.

The following Tables 1 and 2 record the results

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- ίο -

microscopic structural examinations and mechanical tests on raw cast metal »

Table 1 - Microscopic Examination and Analytical Results

Bez. Analysis on cast
pieces (wt. %) Si Mn Mg Appearance
of
Graphite % Ferrite of the pieces as
Puncture the thickness of the
Pieces ^ e in mm) e = 25 e = 5 A. C. 2.72 0.18 0.052 fully
kugelgra
phitic e> 50 90 % 85 % B. 5.6 2.65 0.17 0.040 kugelgra-
phitic,
but with
numerous
chen Ps eu
slats > 95 % 60 % 50 % C. 5.6 2.65 0.21 0.042 fully
kugelgra
phitic 80 % ■
do- 50 % 10 % 70 %

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- li -

Table 2 - Mechanical properties of normalized samples (mean of three samples)

Bez. Elastic limit
for 0.2 %
LE kg / mm ^ Tensile strength
speed
ρ
R, kg / well strain
A %
l _o = 5.65 Sun Brinell
hardness
HB A. 41.6 55.0 22.9 187 B. 35.6 54.5 13.6 201 C. 39.6 57.2 8.6 217

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The tables show that the cast iron melts treated with the alloys according to the invention exhibit markedly different properties from those obtained in the prior art, in particular as regards the degree of ferritization and elongation at break.

In addition, the residual magnesium content results (Table 1) that the use of alloys according to the invention increases the utilization of the nodulating agent considerably.

The following examples are intended to illustrate working examples of the alloys according to the invention certainly:

example 1

With the help of a known immersion device, an amount of 2.250 kg of an alloy according to the invention which, in addition to the iron and the usual impurities, 48.2 wt contains. # silicon, 9.1 wt.% magnesium, 4.75% by weight of barium., 0.4l wt. # nitrogen.

The cast iron obtained has the following composition:

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C = 3.6 wt.

Si = 2.65% by weight ,

Mg = 0.047 wt.

The cast pieces as well as the test specimens show a graphite precipitate of completely spherical shape 12 minutes after the treatment. No carbide is present in the pieces, even in the thin zones. The matrix on the test piece is 90 % ferritic.

Example 2

In a pan 75 kg of cast iron at the temperature of 1510 ⁰ C is carried out by an immersion unit 4 kg of an alloy according to the invention, which in addition to the iron and the usual impurities 47.4 wt.% Silicon, 5.02 wt.% .% nitrogen magnesium, 2.70 wt.% barium, 0.4 wt.% calcium, and 0.30 wt.

After the treatment, the cast iron has the following composition:

C = 3.5% by weight ,
Si = 2.56% by weight ,
Mg = 0.056 wt %.

The cast pieces show a graphite precipitate of completely spherical shape 12 minutes after the treatment

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Shape. There is no carbide in the pieces, even in the thin zones. The matrix on the test piece is 85 to 90 % ferritic.

Example 3

In a pan with a 600 starting from a batch with 40 wt.% Of scrap, 60 wt kg. # Gußputzabfall in the arc furnace cast iron melt produced at the temperature of l48o ° C is carried out in a known "sandwich" called,

additive
Weise, IJ, 2 kg of an alloy according to the invention

the composition:

Si = 49.4% by weight ,

Mg 8.8% by weight ,

Ba = 4.85% by weight ,

Ca = 0.32 wt. Ji,

N = 0.46 wt.

Iron and impurities balance for 100% by weight .

(According to the "sandwich" technique, first bring the Mother alloy to the bottom of a treatment pan, covers it with scrap and feeds it into the pan, where the cast iron melt is to be treated).

After the treatment, the cast iron contains:

C = 3.55% by weight ,
Si = 2.70 wt. Ji,

Mg = 0.058 wt. *.

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Microscopic observation of the cast pieces 14 minutes after the treatment shows a perfect spheroidal graphite structure, a matrix with 75 % ferrite and the total absence of carbides, even on thin zones of the cast pieces.

Example 4

600 kg of cast iron at 1480 ° C. are then treated

additive

"sandwich ¹ method using 25 kg of alloy according to the invention and the composition:

Si 43.2% by weight , Mg 3.6 wt. Ba 1.5% by weight , N 0.19 wt. *,

Iron and impurity = remainder for 100% by weight .

The casting is finished 12 minutes after the treatment. All pieces obtained are made of nodular cast iron. The investigation shows a carbide-free ferritic structure in the as-cast state.

The mean composition is as follows:

C = 3.55% by weight , Si = 2.47% by weight, Mn 0.12% by weight ,

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Mg = 0.051 wt. #, Fe = balance to 100 wt. ^.

Example 5

In a pan with 250 kg cast iron of suitable composition 3.5 kg of an alloy of the composition are introduced to 1460 ° C. by means of a suitable immersion device a:

Ba 6.8 Weight »% T Mg 12.6 Weight · *. N 0.2 Weight .%. Si 48.6 Weight .%,

Iron and impurity = remainder for 100 wt. ^.

The pieces are poured in 8 minutes. The cast iron obtained is spheroidal graphite cast iron. It's in the raw As cast condition free of carbides and this up to a wall thickness of 6 mm.

The composition of the cast iron pieces is:

C = 3.53 wt.

Si = 2.54 wt.

Mn 0.18 wt. #,

Mg = 0.41 wt. #,

% Pe = rest for 100 wt. "

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Claims (1)

Claims 1. Additional alloy for the treatment of spheroidal graphite cast iron smelting, with iron, silicon, an alkaline earth metal and nitrogen, characterized by the following composition: Si 40 - 55 wt. Ji, Mg 5-15 wt. #, Ba 1.4-8.6 wt. Nitrogen in an amount such that the weight ratio Ba / N is between 5 and 50, The remainder is iron and unavoidable impurities that are introduced during manufacture, especially Ca and Al, in a total amount below 2.5 wt. #, Where the alloy is also characterized by a Mg / Ba weight ratio between 1 and 5. 2. Additional alloy according to claim 1, characterized by the following contents: Si 45-50% by weight , Mg 7-11 öew. % y Ba 4.5-6% by weight , N 0.4-0.6% by weight, the remainder iron and the inevitable impurities that 109845/1198 result from the production, in a total amount
below 1.2 wt. J. additional alloy according to claim 1, characterized by the weight ratios Mg / Ba 2 t 0.2,
Ba / N lot 2. 4. Use of an additional alloy according to one of claims 1 to 5 in an amount in which its magnesium content corresponds to 0.03 to 0.08 wt , 01, in particular between 0.03 and 0.06 wt. # _E 109845/1198 Contingent claim 1 1. Additional alloy for the treatment of spheroidal graphite cast iron melts based on iron-silicon-alkaline earth metal-nitrogen, characterized in that it consists of 40-55 wt. % Silicon, 3-15 wt. % Magnesium, 1.4-8.6 wt .% barium, nitrogen in an amount such that the weight ratio of barium / nitrogen between 5 and 50 is, balance iron and introduced the unavoidable production impurities, in particular calcium and aluminum, in a total amount less than 2.5 wt.%, and that the Magnesium / barium weight ratio is between 1 and 3. 109845/1198