| Summary: | 碩士 === 大同工學院 === 材料工程學系 === 84 === Mn element can increase and refine pearlite thus enhances
strength in cast iron. However, matrix of cast iron
would become embrittled when intercellular carbides formed due
to excess amount of Mn (>0.7%)[40]. In this study, the
effects of different Mn amount (0.31%, 0.35%, 0.56%,
0.97%) on mechanical properties of ductile iron of various
thickness in as-cast state and after full annealing / sub-
critical annealing were investigated. The results indicated
that the strength and hardness increased with amount of Mn,
but the ductility and impact values decreased. Strength
and hardness decreased with increasing section thickness, but
the effects on ductility and impact values were
indefinite. After heat treatment , strength and ductility
of the sub-criticaly annealed was superior to those after full
annealing ,but hardness was worse off. For both full
annealing and sub-critical annealing , the strength increased
and ductility decreased with section size ,but the effects on
impact values and hardness have no definite correlation.
Attempts were made to explain the mechanical behavior based on
microstructural features.
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