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2 Archives of Foundry Engineering

2 2009

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Thin Wall Austempered Ductile Iron (TWADI)

Fraś E., Górny M.

Archives of Foundry Engineering

2009

Vol. 9, iss. 3

45-48

In this paper the analysis of thin walled castings made of ductile iron is considered. It is shown that thin wall austempered ductile iron can be obtained by means of short-term heat treatment of thin wall castings without addition of alloying elements. Metallographic examinations of 2 mm thin walled castings along with casting with thicker wall thickness (20x28 mm) after different austempring conditions are presented. It has been proved that short-term heat treatment amounted 20 minutes of austenitizing at 880 oC followed by holding at 400 oC for 5 minutes causes ausferrite matrix in 2 mm wall thickness castings, while casting with thicker wall thickness remain untransformed and martensite is still present in a matrix. Finally there are shown that thin wall ductile iron is an excellent base material for austempering heat treatments. As a result high mechanical properties received in thin wall plates made of austempered ductile iron.

Mechanism of silicon influence on chills in ductile iron

Górny M.

Archives of Foundry Engineering

2009

Vol. 9, iss. 1

147-150

In the present work an analytical expression that combines the susceptibility of liquid cast iron to solidify according to the Fe-C-X metastable system (also known as the chilling tendency of cast iron, CT) is proposed. A relationship between CT and several factors has been developed. In particular the CT is related to the critical wall thickness (Scr), below which the chill is formed. Theoretical calculations of Scr were made and then compared with experimental outcome for ductile iron melts. The predictions of the theoretical analysis are in rather good agreement with the experimental data.The results can be used as a guide for a better understanding of the effect of technological variables such as the melt chemistry, the holding time and temperature, the spheroidizing and inoculation practice, the resulting nodule count and the type of mold material and pouring temperature, on the resultant chill of the ductile iron.