leometwu的部落格

黑皮角鐵切片

模具鋼是"過共析"鋼, 熱處理不當時晶界會產生"晶界碳化物"而使"韌性極度劣化".

極低碳鋼(<0.10C%)的退火組織是 肥粒鐵F+波來鐵P(數量極少). 此時, 有些小面積的層片狀波來鐵P內的兩相(Ferrite+Karbide)會分離成只剩下圖中箭頭所指的"碳化物"K. 這個現象稱為"分離共析" 如果是共晶混合物的分離, 則稱為"分離共晶" (divorced eutectic), 也可譯成"離異共晶. 

這是中部一家規模很大的汽車零件外銷工廠 所做的檢驗報告. 請了一個半調子的金相檢驗工程師(德國人, 台灣女婿?)所做的錯誤報告. 去年發生過一次, 今年又發生了. 誰說遠來的和尚會唸經? 用英文寫的部份是要給他看的.去年與他會面時 他說他有在看我的 部落格.

浸蝕不均, 導致誤判. 建議使用浸浴式腐蝕(immersion eching). 腐蝕不要用滴的或刷的. 滴上幾滴浸蝕液再用棉花棒刷開, 常會有此不均勻的現象. 訓練/經驗不足時 就會誤判. 以下就是檢驗者的判讀原文:

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 X

Subgrains in larger grains cannot be counted as grains.

With high hardness number obtained from cooling directly from hot rolling, this condition is often faked as Q/T condition. Many dishonest companies do this fraud.

 下: 右側為衝床切邊 故有塑性流動痕跡. 鍍了銅

Real thing:4140 quench quenched to fully martensitic (HRC should be >58) and high-temp. tempered  to HRC 30 +/- 5 to obtain highest toughness. Since bringing down hardness from 58~60 to 25~35 HRC requires a lot of heat energy (cost). Fake stuff appeared: Cool the as-rolled 4140 steel bar with forced air or water-mist to obtain the hardness of 25+ HRC. Their microstrctures are shown below. They may have the correct hardness, but since the microstructure are not correct. So their toughness will not meet the requirement. Buyers of auto parts be aware of this fact and do not get cheated by those Mr. Smart who sell you parts with fake Q/T process.