deliver more liquid to compensate for contraction. Higher silicon leads directly to higher nodule count, more
ferrite and early carbon precipitation. To minimize shrink- age, the CE should be on target with the maximum carbon content and the minimum silicon content. Enough silicon should be used to avoid carbides and strengthen the ferrite to meet properties but not excessively more. Too much silicon can lead to excessive initial expansion effect with too little occurring in the last iron to freeze. Normally excessive nodule count that leads to shrinkage has a structure where the nodule size appears identical throughout, as all the nodules started forming early during freezing (Fig. 3).
合适，而且碳含量尽可能高些，硅含量尽可能低些。 应有足够的硅含量，以避免碳化物，强化铁素体，从 而满足性能要求，但不能过量。太多的硅可导致过度 的初期膨胀作用而在铸铁凝固后期石墨膨胀太少。在 组织中大多数尺寸相同的条件下，石墨球数过多，就 会导致收缩，因为所有的石墨球形成都在凝固初期形 成（图3）。
加入量太多孕育剂或采用铋增加石墨球数都能导致 尺寸均匀的大量石墨球。石墨球数多对减少收缩是有
Fig. 2. These charts show the maximum CE to avoid nodule flotation for square bars, modulii and flat plate sections for three silicon levels poured at 2,550F. The curves are extended to show the section thicknesses where the CE must be eutectic or slightly below.
表2、这些图表显示 为了避免石墨球漂 浮的最大碳当量， 方棒、模数和平板 在2550F情况下包 含纯硅的三条显示 线。延长的弧线显 示的是最厚部分的 CE含量必须等于或 略低于上述线条。
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION May 2013
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