AISI 440C 屬高含碳量之麻田散鐵系不銹鋼，其擁有極佳的硬度、耐腐蝕性及機械強度，因此常應用於工業軸承及醫療等耐磨耗及耐腐蝕部分。本研究利用PM製程將440C-NbC預合金粉末與黏黏劑PVA造粒後，經加壓成形後，以1250°C至1290°C燒結溫度進行真空燒結，求得最佳燒結溫度及其燒結密度，再經淬火均質化及不同回火溫度熱處理，觀察金屬間化合物的析出行為及機械性質。
實驗結果顯示，在1280°C時可達到液相燒結，其密度為7.63 g/cm3，而當熱處理後硬度表現亦為最佳，具有56 HRC。對照微觀結構可以發現隨回火溫度升高，其晶界之M23C6析出碳化物減少，多固溶回基底中，而NbC則是細小且均勻散佈在基地中形成析出強化相。熱處理前後腐蝕之形貌可觀察出燒結後因沿晶析出之碳化物造成粒間腐蝕，熱處理後因M23C6固溶回基地再以小顆粒析出，雖然進一步提升基地之強度，但其就為基地之晶粒腐蝕，晶界上則存在少量析出之耐腐蝕性佳的碳化鉻。整體來說，淬火與回火熱處理能夠有效改善碳化
物大小，並具有強化基地之效果。

AISI 440C is a high carbon martensitic stainless steel with excellent hardness, moderate corrosion resistance and good strength. Therefore, it's commonly used in industrial bearings and medical appliances which need both good wear resistance and corrosion resistance. In this study, a spray dried pre-alloyed 400C powder, alloyed with 1.5 wt% Nb, was uniaxially die-pressed, and sintered at temperature ranging from 1250°C to 1290°C in a vacuum furnace. Furthermore, a series heat treatment processes, including austenitizing temperature at 1040°C, N2 gas quenching to room temperature, and tempering at 160°C, 200°C, and 230°C, was performed to examine the variation of mechanical properties associated with evolution of microstructure.
The experimental results showed that a high sintered density of 7.63 g/cm3 was achieved at sintering temperature of 1280°C, whose hardness can be as high as 56 HRC after heat treatment. A large portion of the carbide in the grain boundaries dissolved back to the grains after heat treatment, while the precipitates of NbC hardening phase are small and spread evenly inside the grains. Nevertheless, pull-out of large carbide grains for the heat- treated specimens sintered at 1280°C and 1290°C and indicate that the tempering time is too short for the re-dissolution of the carbides from the grain boundaries. The as-sintered specimen shows intergranular corrosion, due to the precipitation of carbides along the grain boundaries. On the other hand, grain boundaries become more corrosion resistant than the grains for the heat-treated specimens.

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