全氫封盒退火爐循環風扇破裂原因探討

Investigation on Cracking of Circulating Impeller in Full Hydrogen Batch Annealing Furnace

本文針對一全氫封盒退火爐之循環風扇破損、斷裂之原因進行探討。分別進行外觀觀察、硬度測量、微觀觀察、成分分析及破斷面分析。由分析結果推論：全氫封盒退火爐中鋼片表面的油脂會被還原成C與H，C與H會進一步反應成甲烷（CH4），如C + 2 H2＝CH4平衡式。如果CH4含量高則反應傾向左邊，C有機會沿晶界進入葉片材料中，使得碳化物在表面晶界首先析出，接著擴展到晶粒中。循環風扇葉片材料因封盒退火爐的甲烷爐氛，導致材料碳化，使得材料變硬且脆，其中最表層硬度最高，韌性也最差。葉片表面發生脆化與承受較大循環風扇旋轉應力作用，進而出現沿晶微裂紋，裂紋進一步以穿晶或沿晶方式向材料內部傳播，導致葉片破裂。

This study is to analyze the fracture of the impellers, which had been used in the steel annealing furnace with full hydrogen operation state. The experimental methods included visual observation, Vickers’ hardness test, micro-scoping, composition analysis, scanning electro-microscopy analysis and fractured surface observation. The results revealed that, while the steel was exposed to hydrogen at high temperatures, the greases on the steel surface and H, the following reaction could occur to form methane (CH4), as C + 2 H2 ＝ CH4 equilibrium. If the content of methane was high, the reaction shifted to the left, the more C present to penetrated to the impeller by way of grain boundaries from the surface to the material insides. As exposed to the methane atmospheres in the batch annealing furnace operation, the impeller was carburization, the materials become lack of ductility, harden and lower the shock resistance especially in the top layer. Due to the interaction of brittle and circulating stress, the impeller become cracking along the grain boundaries, first, then intergranular or transgranular cracks was proceeded from the surfaces to insides of the materials, finally, the impeller was fractured and ruptured.