Abstract
Tungsten and tungsten with chrome and copper were added to a molten iron in reducing condition and the iron was cast iron a green sand mould and then the cast structures and mechanical properties were examined. The specimens prepared by this procedure were annealed at 300°, 400° and 500°C for 3 hours and cooled in a furnace. The results obtained were summarized as follows:
1) After adding 0.6∼3.0% of tungsten, 0.2% of chrome with tungsten and 1.0% of copper with tungsten to molten irons, they were poured into sand moulds of different diameters (10, 20, 30, 40 and 50 mm in diameter).
By microscopic observation and hardness measurements, a structural diagram of acicular cast iron was determined.
2) The obstruction of graphitization by tungsten is weak and even in the specimen of 10 mm diameter containig 2.6%C, 1.8%Si and 3.0%W, white iron or mottled iron structure is not appeared.
3) The high quality acicular cast iron has better mechanical properties than plain high grade cast iron. That is, the former has 24∼33 in Rockwell C hardness, 56∼64 kg/mm2 in tensile strength, 910∼1160 kg in bending strength 6.5∼7.5 mm in toughness.
4) The mechanical properties of the acicular cast iron were improved considerably when it was annealed at low temperature such as 300°C for 3 hrs. It showed, 59.5∼74.2 kg/mm2 in tensile strength, 1020∼1450 kg in bending strength 7.0∼9.2 mm in toughness, 26.3∼36.0 in Rockwell C hardness.
5) The tensile and bending strength became lower with the increase of carbon saturation degrees.
