本文研究800H循環風扇側板的破損原因。試驗方法為外觀觀察、成分分析、敏化試驗、材質金相與破斷面分析。綜合試驗結果研判，800H側板破損機制為材質不均。側板的材質成分符合800H規範；草酸試驗顯示側板有敏化問題，材料強度降低；800H應為沃斯田鐵組織的金相，但在側板裂紋破斷面兩側的上、下表面皆有柱狀晶，中間則是沃斯田鐵組織；中間的Ni含量與上、下表面的Ni相差10%以上，此區域已非原800H材料。研判側板局部受熱達800H的熔點溫度的高溫，液態合金靠傳熱冷卻，表面生長的柱狀晶；厚度中心位置溫度下降緩慢形成等軸晶的沃斯田鐵；導致Ni往受熱區遷移。破斷面很明顯分成兩側的崎嶇區與中間的平坦區，恰好對應到截面金相觀察所看到的三明治金相結構。破斷面起始於側板外緣的小缺口多；這些小缺口剛好碰到上、下表面都有柱狀晶的區域，在粗大柱狀晶區域裂紋裂的快，快速撕裂穿側板。

This study the cause of damage to the 800H circulation fan side plate. The test methods of appearance observation, composition analysis, sensitization test, material metallography and fracture surface analysis were included. The results were shown the 800H side-plate failure by uneven matter. The material composition of the side plate met the 800H specification; oxalic acid test shown that the side plate had sensitization problems and the material strength was reduced; 800H should be the metallographic structure of the Austenite, but the upper and lower surfaces of the cracks on both sides of the side plate shown columns Crystals, the middle was Austenite; the difference of Ni content between the middle and the upper and lower surfaces were more than 10%, this area was not the original 800H. That concluded which side plate was locally heated to a high temperature of 800H melting point temperature, the liquid alloy cooled by heat transfer and the columnar crystal grew on the surface; the temperature at the center of the thickness dropped slowly to form equiaxed Austenite, meanwhile the Ni migrates to the heated area. The surface of fractured was clearly divided into the rugged area on both sides and the middle flat area, which corresponded exactly to the metallographic structure of the sandwich phenomenon shown in the cross-section metallography. The fracture started from the small gap at the outer edge of the side plate, which hit the columnar crystals on both the upper and lower surfaces, cracks quickly in the coarse columnar regions and torn through the side plates.