球铁前轮毂和差速器原采用手工造型，用外冷铁解决缩孔缺陷。

Manual molding had been used for the nodular iron front wheel boss and differential mechanism case, and chills were used to prevent shrinkage defects.

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结果表明，冷却不足使组织中出现网状及小块状铁素体，导致硬度偏低，加之磨削加工痕迹较粗是引起前轮毂早期断裂的原因。

Results showed that ferrite net and lower hardness due to low cooling rate, coarser finish machining resulted in the fracture during earlier stage of rotary bending fatigue test.

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