日立 SLD 鋼材. 鋼廠自己調查報告: 說了一大堆理由, 都是別人的問題, 就是看不到自己材料有大問題. O.D.> 500 mm 鋁鍛模, 上線壓不到 1000個就發現裂紋. (使用廠商說: 正常情況 可壓10萬次以上). 模具素材有殘存晶界碳化物(GBK)*, 韌性低劣. 破裂是必然的事. 此物一般都發生於大塊料鍛造後生成. 料越大越有此問題. 加工前花點小錢, 先檢驗一下材料金相, 不合格就不要做. 即可避免此大損失. 那些大顆粒的共晶碳化物與此破裂無關 不要推說直徑大, 碳化物顆粒分佈難免.基地殘留沃斯田鉄數量眾多 是熱處理回火不足所致, 這是模具早夭的次要原因. * GBK are easy crack initiation sites because they are blazor-sharp. They cup open steel matrix easily. Their tip radii are so small that the stress induced at the tip front can easily "rip open" grainboundaries. These GBK appeared after billet forging and the steel mill is responsible for it. But, it's only natural that they turned a blind eye to (視而不見) this material defect of their own. The very large eutectic carbides have nothing to do with this failure. It is the grainboundary carbide network (GBK) that caused the failure of this aluminum wheel forging die with O.D. of > 500 mm. 引發模具早期破裂的是這些晶界碳化物(GBK),
Once again, grainboundary carbide caused a forging tooling to fail prematurely. 
碳化物在此, 可視之為"無物"--- 也就是空孔/空隙. 大又圓渾的孔, 曲率半徑大, 應力集中問題不大. 細薄片形的空隙, 就是裂縫. 材料未上線就有這些微裂縫, 一使用受力, 就會迅速蔓延, 終至破裂. 注意這是淬火加熱固溶後所剩餘的. 素材內更多此物.
These GBK line up along the prior dendrite arm boundaries of the ingot. 此例GBK 出現的位置就是我常說的 鑄錠的 dendrite arm boundaries. 此物使韌性極度劣化, 故模具早夭.
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