From the macro-and micro observations, it is concluded that during the peritectic reaction the dendritic primary crystals are disintegrated into many twists by the liquid which lies in their interstices, and when these twist behave as separate nucleus for each particle, the grain size of the latter becomes very fine.
According as approaching to the peritectic point, the grain refinement becomes more remarkable, because the primary crystals "δ" are disintegrated by the reaction which depend upon the increase of the contact surface between the primary and melt. But if the excess elements are over the point, the dendritic structure appear, because it does not wrap the primary crystals.
These conclusions have been satisfactorily proved in both plain carbon steel and Cr-Mo-Si cast steel. The fineness of the dendritic structures depends upon the degree of dif fusion, fluidity and heat-conductivity. When the diffusion and the heat-conductivity are large, the dendritic crystals have a tendency to become finer, while when the fluidity larger, they more coarse, Further when the freezing interval between liquidus and solidus line is larger, the dendritic structure become more coarse.
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