碳化物帶為現前高碳鉻軸承鋼中微結構最為常見的問題，其會使鋼材的耐磨耗性與疲勞壽命等各項機械性質的下降，儘管已有許多文獻指出其主要是來自鋼液凝固的微觀偏析組織經熱軋延拉長成的富質合金帶所引發，然而其詳細形成機理與熱處理對其微觀偏析結構的改善成效卻仍然尚未明瞭。
本研究針對SUJ2鋼的熱軋棒材經球化退火後之碳化物帶，藉由SEM、EPMA與EBSD等分析儀器對其球化前後試樣行金相與成分等分析，從中理解其形成機理，同時探討沃斯田鐵化後不同冷卻速率(0.08、2.28與80.7℃/sec)之熱處理對其碳化物帶改善之成效。
實驗結果顯示，鋼中碳化物帶為由鉻微觀偏析帶於鋼材沃斯田鐵化後的冷卻相變與其球化退火過程引發碳成分分布波動所導致，而提高沃斯田鐵化後的冷卻速率可有效改善其後之冷卻相變時的碳成分分布波動，並在約80.7℃/sec的冷卻速率下時，完全抑制碳原子擴散回鉻微觀偏析帶，進而避免碳化物的帶狀聚集。

Carbide banding is one problem of microstructure in high-chromium steel, which has a negative influence on mechanical properties, such as wear resistance and fatigue life etc. Although a lot of works pointed out the formation of the bands due to microsegregation during solidification after hot rolling, however, the formation mechanism and the effect of heat treatment on the structure of microsegregation were still not clear. In this study, the formation mechanism of carbide band in the SUJ2 steel of hot rolling bar after spheroidization annealing was investigated, and the metallography and chemical composition were analyzed using SEM, EPMA, and EBSD before and after spheroidization treatment. At the same time, this study also investigated the effect of the cooling rate (0.08, 2.28 and 80.7℃/sec) on the formation of carbide banding after austenitizing.
The results show the carbide banding resulted from microsegregation band of chromium which is due to the inhomogeneous distribution of carbon content during phase transformation after austenitizing and spheroidization treatment. Furthermore, raise cooling rate after austenitizing can improve the inhomogeneous distribution of carbon content during the cooling process, and restrain the diffusion of carbon back to the microsegregation band completely at the cooling rate about equal to 80.7℃/sec. Increasing the cooling rate is able to avoid the formation of carbide banding.

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