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粉末高速鋼(P/M HSS)鑽頭鑽孔 遇硬點卡住, 钻头邊刃斷於孔壁上, 鑽頭繼續旋轉, 磨擦生熱, 使一部份材料昇溫而生相變化. 組織受熱而生相變化之區域 冶金術語稱為 熱影響區(Heat Affected Zone, HAZ). 下圖左邊為S45C. 素材金相組織 :45%肥粒鐵(白色)+55%波來鐵(咖啡色), 磨擦熱由最右邊往左傳入, 使一層素材經歷了淬火回火的過程. A左邊工件(淺褐色部份)溫度超過A3溫度, 故肥粒鐵幾乎全不見了. A右邊為高速鋼鑽頭切刃屑片, 溫度更高, 使此屑片也重新淬火, 但因合金高, 餘熱尚未能將其回火, 故葯水浸蝕後, 顏色稍白皙......
A P/M HSS drill got stuck while drilling a hole. Drill lips were torn off and stuck to workpiece of 1045. A short inteval of friction generated high heat that soften and distorted the drill lips. An area of HAZ (marked A below) also formed and is ajacent to the drill lips.
上:500x; 斷在孔壁上的鑽頭邊刃, 基地為新生(fresh)麻田散鐵. 下:1000x (at 12 x 9 cm) HSS 鑽身之金相, 合金碳化物微粒(耐磨相) 均勻分怖在回火麻田散鐵基地(結合相)上 .
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