leometwu的部落格

 M5 setscrew fatigue cracking + torsional fracture.  固定車刀塊的 M5 螺絲, 大陸貨. 很短命. 日本品牌, 轉移到大陸生產後品質就出走了樣.

http://www.eng-tips.com/viewthread.cfm?qid=322083

這高週波硬化的齒輪檢驗合格後入庫, 過3~4天後發現整批都裂成這樣. 淬火後麻田散鉄含碳量有高有低*, 導致內部殘留應力 所以發生這種延遲破裂(delayed fracture)---沒使用 光是放著就破裂.    ----* 網目狀肥粒鉄淬火後所得麻田散鉄含碳量很低, 它的麻田散鉄變態膨脹量遠小於於由波來鉄部份變態所得的麻田散鉄, 所以產生內部應力. 起裂點是那些低碳麻田散鉄(強度最弱位置),起裂的力量是: 內部殘留應力.

這底盤零件在澳洲斷裂,寄回. 我檢視後發現, 所有冶金上增加疲勞壽命的原則, 它都違反了. 計有: 1. 牙底尖銳. 2. 螺牙部位高週波硬化. 3. 調質沒成功, 出現晶界(網狀)肥粒鉄. 這樣的零組件, 註定要短命的.

http://www.eng-tips.com/viewthread.cfm?qid=320487

  SNCM439 冷鍛模具束套(stress ring) 尚未使用就發現破裂. 縮配應力大+材料偏析大(大直徑鋼料容易偏析).

平面上的蝕坑 是應力昇高處, 所以微裂萌生於此.

Cast aluminum cylinder with cast-in cast iron liners.  Fatigue cracks were found, at area A and B, but not at C,  and failed the test.  Why and how they cracked? The answer is left to you to ponder.

Engine valve spring that failed prematurely. Arrow shows origin of a fatique fracture. Microcrack initiated from a subsurface inclusion surrounded by matrix in excessive tension state caused by local over-peening.  Overpeening was caused by sharp corners of cut-wire. Interference of coils during compression worsen the situation.

這是另一從頂出銷孔口起裂的例子, 也是碳/氮化物引發的破裂. 輻射紋代表這是一次性的過載引發的破裂. 箭頭所指位置為破裂起源點.

極短命的熱鍛模. A die that failed prematurely.  This tooling broke into 6 pieces. All cracks started from the entrance of ejector pin holes or threaded holes. 破成6塊, 破裂皆起始於底部頂出銷孔口.

SKD 61 (H13) 是高合金鋼,  隨隨便便就焊鉄塊上去, 上機試模, 當然是一鍛就破. (cracked on one stroke).  H13 is a high alloy tool steel. It can not be welded without any preheating. Otherwise, it will crack like this.

A car stayed put in garage for too long a period of  time. Corrosion occurred in the water pipe, and its engine got jammed because of over-heating.

Crankshaft nose.  Fatigue fracture.