QT 感應淬火4天後生微裂

leomet

Microcracks appeared 4 days after induction-hardening. Microcracks were caused by the hyper-eutectoid carbide film. The microstructure of the crank shaft is bad, very bad for this application. It should have some ferrite to provide some toughness to the crank shaft. Phote x shows the correct microstructures the crank should have. Arrows in photos K ~ M point out the hyper-eutectoid carbide film that are out-and-out toughness killers.

A:   箭頭: 淬後3, 4天後 才出現的微裂.  金相試片切片取樣位置.  球化率 O.K.!

677, 694, 214, 216 前後各2張: 淬火硬化層的馬氏体(M)組織非常微細.但M基地上隱約可見許多細線狀碳化物.    裂口附近,白色短線為碳化物. . 裂口是因為此極表面的碳化物薄膜而開裂. 照片4,5,6 7:鑄件鑄態組織:  黑球:石墨顆粒; 白色: 塊狀+線狀 碳化物; 其中: 線狀物為初析碳化物.此物會使材料延性/韌性 極度劣化. 金相組織完全無鉄素体,  不符買方要求的QT 500. 但聽說賣方給的出廠檢驗報告一切合格.

To be continued.

[ 本帖最后由 leomet 于 2009-8-18 07:18 编辑 ]