leometwu的部落格

檢查結果: 過度酸洗, 蝕刻晶界成凹槽. 隨後的染黑(或磷酸膜處理)再填滿這些凹口.但凹口應力集中效應已經使此軸強度劣化.  此例類似於AISI 420 晶界腐蝕. 都是表面晶界先受損. 形成應力集中位置.

黃色箭頭為裂口蔓延方向.

好幾年前的 handout.  po 出來給"初級班"同學看.

 左: 樹木年輪 age ring

下:如樹木年輪的部份 為裂紋緩慢進行之痕跡, 材料破壞學稱為Beach mark 海灘紋. 其中心為裂紋起始點 (鍛塊中心缺陷密度高), 逐漸往外擴大, 最後剩下的面積承受不了負荷, 驟然破裂, 產生輻射紋.

Hot forging die died of  1. coarse grains, 2. brittle gas nitrided layer(?)

1985年 所做檢驗. Inspected in 1985 . A bent-and-welded loop, pickled and hot-dip zinc coated. All loops cracked open after hot-dip zinc coating . Tensile stress induced after bending the loop. H atoms were picked-up during pickling. Upon hot-dipping of zinc, H atoms diffused to grain boundaries and form H2 and expanded and, cracked open the loop.

A JIS SKD 11 (DIN 1.2379) tooling was submitted to check the cause of the crack, initiating from the sharp key groove. I was told that this tooling cracked under a single blow of a hand hammer.  Coarse,  grainboundary carbide (GBK) network is clearly seen at 100X. It was left from a faulty material. These GBK formed after  forging of an ingot. Note the parallel twin boundary  carbide. SEM photo shows the flat surfaces of twin boundaries.  Inspected in 1984 in MIDC. 1984 我於台中金屬中心擔任 破損分析/金相檢驗 工作所攝.

簡述: 送驗者說他使用前 習慣性用手鎚敲一下, 就從鍵槽底裂開了. 故送驗以了解: 是材料或熱處理出問題, 為何如此不堪一敲?

200 x, 200x, 1000x  at 12x8 cm;  經鏡面拋光的不銹鋼塑膠射出成形模具(大立光電的), 粒界腐蝕源自冷卻水孔, 致使昂貴的模具夭壽.  Micrograph of a prematurely failed plastic injection tooling made of stainless steel. Grainboundary corrosion cracks initiated from inner wall of cooling conduits. Multiple, branched cracks is usually SCC----Stress Corrosion Cracking.