某國營事業單位10-4 送驗; 自稱金屬科老醫師(40年次) 所照的彩蝕金相照片, 不敢藏私, 與大家分享.
疲勞裂面=緩裂區 (abc線右側); 過載裂面=驟裂區; 此破裂屬: 單向拉應力, 單側, 多源點起裂.
Photos of color etching that feast your eyes; Network of carbide is very harmful to tensile strength and toughness of any steel. It is the culprit to this fatigue fracture.
Above: color etching 彩色腐蝕: T.M. matrix tinted and network of carbide stands out; Below: normal nital etching: network of grain boundary carbide shown in color etching above, is nowhere to be seen here.
Dark field technique is used to high-light (凸顯)dispersed carbide particles and network of carbide.
Below: SEM photos; GB Carbide (pointed by arrows) is well-known as "toughness killer"
Intergranular fracture, caused by G.B. carbides; Fracture surface shows rock-candy(冰糖)feature.
此疲勞破裂的 root cause: 乃人員操作不當所引起. 板手長度是經過設計的, 不能隨興加長.
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