Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1982-11-29
1985-10-01
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
75 53, 75 58, 75130R, C22C 3308
Patent
active
045444072
DESCRIPTION:
BRIEF SUMMARY
The invention refers to a process for producing cast iron castings with a vermicular graphite structure.
Cast iron with a vermicular graphite structure (GGV) is a comparatively new material to be listed between grey cast iron (GGL) and spheroidal graphite cast iron (GGG). Due to its mechanical properties such as its tensile strength, toughness and modulus of elasticity as well as because of its heat conductivity, the GGV material is particularly well suited for diesel engine cylinder heads, moulds for steel making plants and turbo-supercharger housings, which means that GGV is normally suited for parts not subjected to shocklike temperature changes. In such applications GGV is superior to GGL. As compared to GGG, GGV has a higher heat conductivity and better pouring technique properties. In particular the decay effect of the magnesium in the treated cast iron melt is less distinct, so that a pouring time even above 20 minutes is possible. In addition thereto, the reduced inclination to shrinkage cavities and better machinability are a further advantage of GGV.
The metal GGV can be produced by a magnesium (Mg) or calcium carbide (CaC.sub.2) treatment of the initial melt, after which treatment titanium (Ti) or a cerium metal mixture is being added. A CaC.sub.2 desulphurization is e.g. described in the German Patent Specification (DE-PS) 1 911 024 and a titanium addition in the published German Patent Application (DE-OS) 1 533 279.
In DE-OS 2 458 033 an appropriate process has been described, in which an initial melt is being pretreated with magnesium until the sulphur content falls to 0.1 percent, while the lapse of time between the magnesium treatment and the addition of lanthanide series metals is so stipulated, that no nodular graphite is being produced. It is, however, not explained how this lapse of time can be determined. This DE-OS, furthermore, teaches, that a desired creation of vermicular graphite is not possible by means of pure magnesium only.
It is the object of the present invention to remove the disadvantages cited above and to propose a process and an apparatus on the basis of the prior art, for fast, economical and exact production of cast iron with vermicular graphite.
This object is being achieved by means of the features listed in the characterizing portion of claim 1.
Advantageous further developments of the invention have been described in the dependent claims.
Contrary to the opinion in the cited DE-OS 2 458 033 it was found, that the production of GGV is possible by desulphurization by means of pure magnesium.
As compared with calcium carbide desulphurization, desulphurization by pure magnesium has the advantage, that the duration of the desulphurization can be reduced by about 80 percent.
Furthermore, those foundries, which have installed a pure magnesium converter for the production of spheroidal graphite cast iron, possess a great advantage. It is then possible, on a short notice, and if necessary for a short period of time, to change to the production of GGV, which requires only a corresponding weight reduction of the pure magnesium added to the melt. This is in particular interesting for the reason that the demand for GGV is still relatively low, as compared with GGG.
A separate container with a supply device for, e.g. calcium carbide, is not required. Furthermore, addition of titanium is, e.g. because of the created titanium carbide, not recommended, since it is difficult to solve this material. The process according to the invention does not require the harmful addition of titanium.
Initial melts which can be treated by the process according to the invention have the following typical composition.
The treatment with pure magnesium is preferably carried out in a converter for pure magnesium according to DE-PS 18 15 214, 22 16 796 and 22 15 416 at a temperature from 1450.degree. to 1520.degree. C. and gives the following typical analysis:
A very exact work performance is important. It is necessary that the weight of the melt to be treated, its sulphur content and the weight of th
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Becker Emil
Hoffmann Horst
Linkert Reinhold
George Fischer Aktiengesellschaft
Rosenberg Peter D.
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