DE3321312A1 - METHOD FOR PRODUCING A CAST IRON WITH VERMICULAR GRAPHITE - Google Patents

Description

Klöckr: -r-Humbcldt-Deutz AG ■ AflilLI 3 ' ^: ' ^ '1 3 1

5000 Cologne 80, May 20, 1983 D 83/29 AE-ZPB P / B

Process for the production of a cast iron with vermicular graphi t

The invention relates to a method of manufacture a cast iron with a predominantly vermicular graphite form (GGV), in which a base iron melt has a treatment additive is admitted »

In cast iron with vermicular graphite, the graphite precipitates lie predominantly as individual, not directly connected structures that are firmly attached to the base material are anchored. Such a form of graphite precipitate in the material structure, which is also known as worm graphite is according to VDG leaflet P 441, edition 1962 of the association German foundry specialists marked as Type III. The vermicular graphite form can be used as an intermediate link of the Lamellar graphite (gray cast iron), which in cast iron is coherent and not embedded in the base material Formation of finely divided branches is present, and the spheroidal graphite (nodular cast iron) with its not in with each other Related individual graphite spheres can be viewed.

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Vermicular graphite cast iron was initially used as an undesirable precipitate of graphite in the manufacture of cast iron with spheroidal graphite in the case of insufficient treatment with spherical additives or in thick-walled parts viewed from cast iron with spheroidal graphite. In the meantime, however, the special advantages of cast iron with vermicular graphite have become apparent known, which are in particular that cast iron with vermicular graphite is a similarly good casting and Voiding behavior shows like cast iron with lamellar graphite, but with regard to its material properties that of cast iron can be approximated with spheroidal graphite, so that this cast iron is used as an intermediate strength material for example Castings complex in terms of casting technology are ideally suited. In addition, cast iron has vermicular graphite a very good thermal conductivity and due to a low modulus of elasticity can also be used for temperature changes Components, e.g. B. cylinder heads, exhaust manifolds of internal combustion engines, used successfully so that this material will become increasingly important, as far as it succeeds, the difficult To master the production of this material, especially with regard to graded strength ranges.

Various methods of manufacturing compacted graphite cast iron have become known. So is in the GB-PS 1,069,058 describes a manufacturing process in which a nodular cast iron base melt is treated with a treatment additive of magnesium, titanium and rare earth metals is added, with titanium as a disruptive element, the formation of spheroidal graphite should hinder. Such a production method thus provides the necessary for the production of nodular cast iron high demands on the purity of the base iron melt (trace elements, interfering elements) and also leads only if the procedural conditions are exactly observed to 35

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the desired compacted graphite formation, so that this means that considerable manufacturing costs are involved in a large-scale application attack. In addition, the addition of the interfering element titanium can cause carbide formation in cast iron for example, also have a detrimental effect on the material properties and machinability and is in particular disadvantageous with regard to the recyclability of the cast iron piece as a raw material for later cast iron melts.

DE-PS 19 11 024 describes a treatment of a base iron melt with cerium mixed metals or rare earth metals known, but only very pure "low-sulfur Base iron smelting can be used »In addition to the enormous cost factor caused by this, also requires this method a very careful process flow with exact compliance with the process parameters, as a too A high addition of cerium resulted in a high carbide content, so that cast iron has a strong tendency to solidify white.

It is also known (foundry practice No. 22 1982, pages 359-372), cast iron with vermicular graphite by a Targeted under-treatment of base iron melts for cast iron with spheroidal graphite with magnesium alloys or magnesium master alloysir for example FeSiMg alloys. However, this procedure is considered operational Considered very difficult, since on the one hand the sulfur content of the base iron melt is very narrow Boundaries must move and on the other hand the high fading effect of the treated base iron melt requires rapid processing in order to overturn the melt to form, for example, a lamellar graphite formation to exclude.

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The object of the present invention is therefore to provide a process for the production of cast iron with compacted graphite find that can be used on an industrial scale, does not place any special requirements on the base iron smelt and in which on the addition of undesirable accompanying elements in cast iron, e.g. B. titanium, can largely be dispensed with. Furthermore, the method should work with a high degree of efficiency and be inexpensive to carry out.

This object is surprising in the generic method for producing cast iron with compacted graphite Way solved by adding pure magnesium to the base iron melt as a treatment additive.

The pure magnesium treatment according to the invention can Cast iron with vermicular graphite can be reproduced with particular accuracy and, in particular, graded according to strength values produced without the addition of further treatment additives will. In the method according to the invention, in contrast to the known methods, it is even possible sulfur-rich base iron melts, e.g. B. usual gray cast iron melts to the desired cast iron with vermicular graphite to process, which includes a significant cost advantage with regard to large-scale application. The treated base iron melt is advantageously free from any interfering elements such as Titanium, and shows, in contrast to the known base iron melts, a very long decay time, so that the The risk of vermicular graphite formation tipping over into a lamellar structure is greatly reduced, which is apparently due to the non-existent and in known processes inoculating alloy additives is due. Ever

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according to the desired material quality, it is possible according to the invention to subject the base iron melt to a pre-desulphurization before the addition of the pure magnesium, whereby in It has surprisingly been found that predesulfurization by means of pure magnesium is particularly advantageous. It but it is also possible to produce a sulfur-rich base iron melt by other known means, e.g. B. CaC-, Lime, soda or the like before adding the pure magnesium treatment additive to desulfurize.

With the pure magnesium production process according to the invention it is possible with extremely simple and also very inexpensive means to obtain the necessary residual magnesium content in cast iron so that castings are specifically

shear strength graduation from, for example, 200 N / mm to

2
500 N / mm can be reliably and reproducibly produced, with which the intermediate strength ranges of the known gray cast iron grades according to DIN 1691 are continuously covered to the known material groups of cast iron with spheroidal graphite according to DIN 1693. To cover this intermediate strength range, such an addition of pure magnesium has proven to be advantageous that the solidified cast iron contains a proportion of 0.01 to 0.04% by weight of residual magnesium. The base iron melt is preferably 0.05 to 0, 3% by weight of pure magnesium was added as a treatment additive. With regard to the evaporation reaction within the base iron melt, the pure magnesium can particularly advantageously be introduced by means of a dipping pear. Such a dipping bulb is known from DE-PS 22 08 960 and is described in detail there.

May 20, 1983 D 83/29

In the following, the invention will be based on examples using the material identification according to VDG-Merkblatt T 441, Aug. 1962, "Guidelines for the marking of graphite formation" are explained in more detail.

Example 1:

In Example 1, a base iron melted in an electric furnace with 3.70% C, 1.71% Si, 0.25% Mn and 0.025% S was used treated with pure magnesium in various ways. The following table gives an overview of the with this According to the invention, cast iron with vermicular graphite determined different strength values in the finished castings depending on the residual magnesium content.

Per
be analysis C. Si Mn S. Mg CU Strength values Rp N / mm2 313 A ' HB % % % % % % Rm 421 271 % 1 3.68 2.24 0.26 0.002 0.025 0.31 363 255 2 _f 6 197 2 3.68 2.24 0.26 0.02 0.019 0.31 338 223 5 _f 6 170 3 3.68 2.24 0.26 0.002 0.016 0.31 285 224 4.5 156 4th 3.68 2.24 0.26 0.002 0.010 0.31 288 1.3 150 5 3.68 2.24 0.26 0.002 0.01 0.31 IfS 155

with Rm = tensile strength in N / mm ''

2 Rp = yield point in N / mm

A = elongation at break in% HB = Brinell hardness

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From sample no. 1, among other things, a molding box for a large molding plant was cast with a representative wall thickness of 30-40 mm _for the external dimensions 1800 x 1320 x 400 mm and a raw part weight of 1255 kg. The structural evaluation of a Y-sample cast at the same time showed 80% graphite of type III and 20% graphite spheres of type V and VI according to VDG leaflet P 441.

Example 2:

In the example described below, a Flywheel made from a cast iron according to the invention with vermicular graphite manufactured. Here, a customary gray cast iron melt was used as the base iron melt, following the initial analysis used:

Base iron smelter

I% C I% Si I% Mn I% P I% s I I I I I I I I

I 3.59 I 1.99 I 0.62 I 0.11 I 0.053 I.

A total melt of 3.5 t was pre-desulphurized using pure magnesium for the following analysis values: 25th

melt

I% C I% Si I% Mn I% P I% S I

I I I I 1 I.

I 3.56 I 2.03 I 0.61 I 0.11 I 0.006 I.

This pre-desulphurized base iron melt was in one Electric furnace subsequent to a treatment additive addition temperature heated and then with 1.8 kg of pure magnesium, 35

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which was introduced into the base iron melt by means of a dipping pear, treated for the following casting analysis:

Casting analysis
05

C I% Si I% Mn I% P I% S I% Mg

3.55 I 2.36 I 0.58 I 0.11 | 0.009 I 0.017 I.

From this cast iron melt several flywheels, each with a gross weight of 600 kg and a diameter of 1000 mm and a wall thickness of 140 - 150 mm cast. The following strength values were achieved:

1. Υ-2 sample cast with it:

2
Tensile strength Rm = 501 N / mm

Yield limit Rm = 386 n / mm
Elongation at break A = 3.2%
Hardness HB = 222 - 229

2. Two test rods taken vertically from the flywheel:

2 Tensile strength Rm = 344 or 344 N / mm

2 Yield strength Rp = 261 or 261 N / mm

Elongation at break A = 0.8 or 1.0%
Hardness HB = 175 or 179
30th

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3. Two test rods removed from the center of the flywheel

Tensile strength Rm = 357 or 363 N / mm yield point Rp = 334 or 334 N / mm ² elongation at break A = 1.1 or 2.0% hardness HB = 175 or 197

The structural assessment according to the VDG guideline is in each case; 10

1. Υ-2 sample: 85% graphite type in

15% graphite type V + VI

2. Flywheel samples:

80% graphite type III

20% graphite type V + VI

Claims (9)

Klo · ■ f ner-HumhoirJt-Deui- AC 5000 Cologne 80, May 20, 1983 D 83/29 AE-ZPB P / B patent claims 1.1 Process for the production of a cast iron with over-V_j predominantly vermicular graphite form (GGV), in which a base iron melt a treatment additive is added, characterized in that the treatment additive is pure magnesium is. 2. The method according to claim 1, characterized in, that the base iron melt is a customary gray cast iron melt, e.g. a sulfur-rich cupola iron melt, is used. 3. The method according to any one of claims 1 or 2, characterized in that such an amount of pure magnesium as a treatment additive is added that in the solidified cast iron between 0.01 and 0.04 wt .-% residual magnesium is available. 4. The method according to any one of claims 1 to 3, characterized in that the base iron melt an amount of 0.05 to 0.3% by weight of pure magnesium can be added as a treatment additive. 5. 'The method according to any one of the preceding claims, characterized in that the base iron melt before Addition of the pure magnesium treatment additive is subjected to a pre-desulphurization. f! Γ · ιι! · - 2 - May 20, 1983 D 83/29 6. The method according to claim 5, characterized in that that the pre-desulphurisation is carried out using pure magnesium. 7. The method according to any one of claims 5 or 6, characterized in that the iron melt after the pre-desulfurization is heated to a treatment additive addition temperature. 8. The method according to any one of the preceding claims, characterized in that the pure magnesium by means of a Immersion pear is introduced into the base iron melt. 9. The method according to any one of the preceding claims, characterized in that the treated with pure magnesium Base iron melt held ready for the casting process in a holding device protected with inert gas will.