Method for production of ductile iron

Abstract

The present invention relates to a method for nodularizing treatment of ductile iron using a ladle treatment method for nodularizing of a magnesium ferrosilicon alloy, where a magnesium ferrosilicon nodularizing alloy consisting essentially of 40 to 80% by weight of silicon, 2 to 15% by weight of magnesium, 0.3 to 5% by weight of lanthanum, 0 to 6% by weight of calcium, 0 to 5% by weight of aluminum, the balance being iron, is added to the ladle whereafter the molten iron is supplied to the ladle.

Description

[0001] The present invention relates to a method for the manufacture of ductile cast iron with spheroidal or compacted graphite and a ferrosilicon based nodularizer alloy.[0002] Cast iron is typically produced in cupola or induction furnaces, and generally contains between 2 to 4 percent carbon. The carbon is intimately mixed with the iron and the form, which the carbon takes in the solidified cast iron, is very important to the characteristics and properties of the iron castings. If the carbon upon solidification takes the form of iron carbide, then the cast iron is referred to as white or carbidic cast iron and has the physical characteristics of being hard and brittle which in certain applications are undesirable. If the carbon takes the form of flake-like graphite, the cast iron is soft and machinable and is referred to as grey cast iron. If magnesium and rare earth's are used to treat the liquid grey iron, the carbon will take the form of spheroidal or nodular graphite and is r...

AI Technical Summary

Benefits of technology

[0013] It has now been found that the use of pure lanthanum as the only rare earth source in the MgFeSi nodularizer alloy surprisingly further improves the performance of the ductile iron ladle treatment method compared to such nodularizers containing cerium or misch metal. Thus the number of nuclei is substantially increased and the risk for chill and shrinkage formation in the ductile or compacted graphite iron is minimized.

[0017] It has surprisingly been found that when a magnesium ferrosilicon alloy is used in the ladle treatment method according to the present invention, the number of nuclei formed when the magnesium ferrosilicon alloy is added to cast iron, is increased thus obtaining higher nodule counts and an improved suppression of iron carbide formation using the same amount of alloy as with conventional ladle treatment methods and alloys.

[0018] Further, by the present invention it has been found that the shrinkage tendency of the ductile cast iron is greatly reduced or even eliminated when using the method according to the present invention. It has also even been found that the present invention may provide sufficient nucleation power to the ductile cast iron to avoid chill and shrinkage formations only with a very small, or even without, inoculant addition following the nodularizing treatment process.SHORT DESCRIPTION OF THE FIGURES

Problems solved by technology

If the carbon upon solidification takes the form of iron carbide, then the cast iron is referred to as white or carbidic cast iron and has the physical characteristics of being hard and brittle which in certain applications are undesirable.

In casting iron products from liquid cast iron, there will always be a risk for the formation of iron carbides in thin sections of castings.

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