A heavy oil furnace was used to melt and prepare graphite cast iron, and the studies were carried out on the cast iron added with Fe-Si-Mg and it's heat treatment, mechanical properties at room and high temperatures, and the microstructure were examined. To facilitate the comparison, the same examinations were made on common cast iron, cast iron containing phosphorous and ordinary cast steel.
The summary of those examinations are as follows :
1) When the D. C. I. pig is used and it is melted by Tamman furnace and the additional amount of Mg in Fe-Si-Mg is made about 0.6 % of the molten metal in weight, graphite becomes spheroidal and the structure of matrix is almost ferritic.
So that said metal is melted by a heavy oil furnace.
2) The hardness tests at room temperature and 400°C, the oil quenched spheroidal graphite cast iron showed a maximum hardness and the hardnesses are lowered in the order from quenched, tempered as-cast and annealed in furnace sample. But, the differences in hardness at 600°C of these samples were very small.
The hardness of ordinary cast iron was a little inferior than that of spheroidal cast iron of as-cast state, and it almost similar to the hardness of cast iron containing phosphorous.
The hardness of ordinary cast steel is almost same with that of spheroidal cast iron of furnace annealed.
3) Same tendency obtained in hardness test can be seen in the wear resistance test from room temperature up to 500°C.
4) The shock value of spheroidal graphite cast iron annealed in the furnace shows maximum at the room temperature shock test, and it decreases by the order as follows; quenched and tempered specimen, as-forged, and oil quenched.
5) The matrix of oil quenched spheroidal graphite cast iron specimen when it is observed by a microscope, is martensite and that of quenched and tempered specimen is troostic martensite.
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