DE1949380B2 - Process for the treatment of cast iron melts for the purpose of spheroidal graphite formation - Google Patents

Description

suffice.

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The invention relates to a method for treating molten cast iron for the purpose of spheroidal graphite formation in two successive stages, the melt initially with a spheroidal graphite former in the form of an alloy containing iron, boron and magnesium, of which in percent by weight expressed magnesium and boron contents of the relationship

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mechanical properties fenitic, pearlitic or to make femtisch-pearlitic.

In the first stage of treatment is the melt

often pure or alloyed magnesium, e.g. B. an Fe-Si-Mg alloy as a curling graphite former sets, while afterwards the inoculation with silicon,

z. B. takes place in the form of an Fe-Si alloy.

Accordingly, a method of the type mentioned is known (GB-PS 1117 467), according to which an alloy consisting essentially of iron, cerium or mischmetal, magnesium and boron is used as the spheroidal graphite former and, in particular, an iron-silicon alloy is used for seeding. Other so-called doping elements for these alloys have also become known or have been the subject of operational tests. For example, in addition to cerium, yttrium, rare earths and calcium are also doping elements for the spheroidal graphite-forming alloys and barium is a doping element for the inoculating alloys. A known method (US-PS 25 27 03 /) provides, after melting the cast iron to be treated, first an additive from the group of lithium, calcium, barium, magnesium, strontium and cadmium alone or in combination with substances such as iron, copper, ^To use zinc and manganese and to add a certain amount of a graphitizing agent for inoculation.

It is also a one-step process for treating molten cast iron for the purpose of spheroidal graphite formation known (OE-PS 1 75 911), according to which the only added alloy is at least three Contains elements of the group boron, potassium, sodium, lithium, calcium, magnesium, barium, cerium, etc.

The known processes lead to castings which, in the unannealed cast state, still contain undesired carbides and whose ferritization in the matrix has not yet reached the optimum level. The required heat treatment time is relatively ^high *

The invention is based on the object of modifying the method mentioned at the beginning so that the treated cast iron is largely free of carbides in the unannealed cast state, an improved one Ferritization effect on the matrix is achieved and the duration of the heat treatment required can be shortened significantly.

According to the invention, this object is achieved in that the nodular graphite-forming Alloy in addition to unavoidable production-related impurities of iron, silicon, magnesium and boron and the ternary seed alloy to be used is silicon and barium in such contains amounts expressed in percent by weight that satisfy the relationship

Ba

lying, treated and then with an iron correspond.

just before potting a spheroidal graphitization treatment and then subjected to an inoculation treatment to form a structure with spheroidal graphite to obtain.

The castings then undergo a heat treatment with the aim of dissolving the carbides and the matrix of cast iron depending on the ones sought

^between

Empties the relationships _1,. Mg

".

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Ba

As in more detail on the basis of the exemplary embodiments rTiutert is obtained by the inventive combined addition of the two alloys in two successive stages in the unannealed As-cast state, castings largely free of carbides, almost complete ferritization of the matrix and a significant reduction in the cost of the heat treatment required for this.

B e i s ρ i e i e

Examples 1, 2 and 3 do not correspond to the invention and on the one hand describe the result according to the prior art (Example 1) and on the other hand the result when using only one of the Elements boron and barium.

Examples 4, 5 and 6 correspond to the invention; the spheroidal graphite alloy contains boron, and the inoculant contains barium.

Example 7 shows the superiority of the method using barium according to the invention versus the known processes by which the inoculant contains calcium.

example 1

In a pan with 75 kg of a cast iron melt of At 1510 ° C., 2,250 kg of a spheroidal graphite-forming alloy are carried out with the aid of an immersion device Fe_ Si-Mg (Mg = 9.1%) a.

After lifting the immersion device again, it is inoculated with 0.375 kg Fe-Si (Si = 75%).

The metal is poured 9 minutes after this treatment.

Example 2

One works as above, but uses 2.250 kg of Fc - Si - Mg - B (Mg - = 9.1%; B = 0.48%) and then 0.375 kg Fe-Si (Si = 75%).

Example 3

One works as above, but uses

ίο 2.250 kg Fe-Si —Mg (Mg = 9.25%) and thereafter

0.420 kg Fe - Si - Ba (Si = 59.5%; Ba = 9.8%).

Example 4

The procedure is as in Example 1, but 2.250 kg are used in accordance with the invention Fe - Si - Mg - B (Mg = 9.1%; B = 0.48%) and then 0.420 kg Fe - Si - Ba (Si = 59.5%; Ba = 9.8%).

Table I below, which shows the composition of iron after casting and its properties thin castings are summarized before each heat treatment, and Figs. 1 to 4 clearly show that only the inventive method castings

results that are free of carbides, have a substantial proportion of ferrite in the matrix and are high have elongation and breaking strength values.

These results could also be obtained by following the procedures of Example 1, 2, or 3, for which it would be

however, a time-consuming heat treatment is required to dissolve the carbides and distribute the carbon to change.

Table I.

Example 1 without B without Ba Example 2
with B
without ba

Example 3
without B
with Ba

Example 4 Invention

Chemical composition after spheroidal graphite formation and inoculation in the process according to the invention (° / ₀ )

C.
Si
Mn
P.

S.
Mg

Properties of the castings before heat treatment

Ferrite in the matrix

Number of balls per mm ²

Carbides

Tensile strength, kg / mm ² *)

Strain, %*)

Yield strength, kg / mm ² *)

*) Standard test samples.

3.60

2.60

0.05

0.023

0.007

0.040

Ferrite pearlite 80 ± present 43.4 6.7 25.5 3.58

2.65

0.06

0.021

0.007

0.046

Ferrite pearlite
± 10
available
44.2
9.4
26.3

3.65

2.54

0.05

0.025

0.009

0.038

90% ferrite

85 ± 15

little

48

13.4

22.5

3.55

2.70

0.08

0.026

0.010

0.048

90% ferrite 105 ± 10 very little 51.8 18.9 28.2

Table I and the figures further show that the method according to the invention leads to a better Magnesium utilization (calculated according to the residual magnesium content of the cast iron) leads to an increase the number of graphite spheres and a greater regularity in their size.

Example 5

kg cast iron to be at 1500 ⁰ C to 5 kg Fe - Si - Mg - B (Mg = 9.1%, and B = 0.48%) and 0.960 kg Fe - Si - Ba (Si = 60%; Ba = 9, 8%) after one currently used in foundries

and the "sandwich" method. A second partial inoculation is then carried out using 0.300 kg of the same Fe-Si-Ba alloy. The cast iron, which was cast after waiting 12 minutes, is nodular, and the metallographic examination shows a 90 ° / ₀ ig ferritic structure. The composition is as follows _{:, fi0 /} _,

0019 ° / P

η na ° / U ₅ UD ^ / _o g

The mechanical properties measured on test objects in the unannealed as-cast state are:

Tensile strength 50 kg / mm

Elongation at break ¹⁷ A.

B e 1 s ρ 1 e 1 6

A ton of cast iron melt at 1480 ° C is used according to the »sandwich process with 14 kg Fe - Si - Mg - B of the composition

_"0/0 ai,
8.1% Mg,
0.45% B and
0 07 V approx

treated. 0.2 kg of mixed silicon metal is then introduced with the immersion device and then inoculated by means of 12 kg Fe - Si - Ba (Si = 60.1%; Ba = 9.4%). The result is a completely nodular, strong British cast iron, the properties of which in the unannealed cast state are as follows:

Yield strength 38 kg / mm ¹

Tensile strength 52.3 kg / mm ²

Elongation at break 13.2%

Example 7

150 kg of the same cast iron melt will have two equal parts A and B of 75 kg divided, which are both held at 1520 ⁰ C. They are both by the "sandwich" method using 2.250 kg of Fe-Si —Mg —B of the composition

47 4 ° / sj

7 ^ 95% Mg 'and

0.51% B

treated. Then carried to the immersion ^device 8 ^{fol end quantities:}

^{In the} subset A according to the invention 0.420 kg Fe-Si-Ba (Si = 61%; Ba = 9.6%). ^A cast iron of just as good quality ^{as that according to Beis} P ' ^{d 4 is obtained}

_{In the amount B} 0.420 kg of a known Fe-Si-Ca alloy (Si = 62.4%; Ca = 10.3%). As with subset A, the appearance of the parts obtained with subset B is good, but they show a _slight , _{real tendency} to form cavities; furthermore, as shown in Table II, cast iron B has more

ao carbides and less ferrite.

Table II

Subset A _{according to}

Invention 2

Part _{amount E}

Composition of the casting 3.67 3 61 iron after the spheroidal graphite 2.67 30 educational and vaccination treatments 0.1 lung 0.02 o ', O2 C. 0.006 0.008 Si 0.048 0.044 Mn 35 ρ S. 90% 75% Mg <1% approximately Properties of cast iron 5% ₄ o before heat treatment Ferrite in the matrix Presence of carbides

1 sheet of drawings

Claims (2)

Patent claims: Ltreatment of cast iron melts for the purpose of spheroidal graphite formation in two successive stages, with the melt initially with a spheroidal graphite former in the form of an alloy containing iron, boron and magnesium, their magnesium and boron contents, expressed in percent by weight, of the relationship in < ^ S ^, 1QQ suffice, treated and then inoculated with an alloy containing iron and silicon is, characterized in that the spheroidal graphite-forming alloy to be added in addition to unavoidable production-related impurities from iron, silicon, Magnesium and boron are made up and the ternary inoculating alloy to be used is silicon and barium in such amounts, expressed in percent by weight, that the relationship 2 _< _§! _ _< Go
Ba correspond. 2. The method according to claim 1, characterized in that that the contents of magnesium and boron or silicon and barium in the to be added both alloys the relationships ..
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