| The purpose of this study is to improve the tensile properties of ductile cast iron with ferritebainite duplex matrix. Ferritic ductile cast iron was heat-treated to produce the following duplex matrixes of various proportions; ferrite-upper bainite, ferrite-lower bainite. To make the second phase, each specimen was austenitized at 880℃, and then heat-treated isothermally at 300℃ or 400℃. Tensile strength, 0.2 proof stress and hardness increased with volume fraction of the second phase without observing the law of mixture. Ductility (elongation, reduction of area) and static absorbed energy data showed a peak at 25-30% regardless of the kinds of the second phases, then reduced. The reason why ductility and static absorbed energy were improved at 25-30% of bainite, in view of measurements of martensite hardness test and strain hardening exponent, is considered to result from the reduction of soluble carbon content in bainite. |
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