本研究採用S50C分別進行沃斯回火熱處理與Q&P熱處理，並研究鋼材經這兩種不同熱處理後之顯微組織與機械強度。
實驗結果顯示，S50C分別經MS點上(350°C)與下(320、290、260°C)不同溫度之沃斯回火熱處理60分鐘後，MS點上之沃斯回火熱處理只會生成下變韌鐵與少量的殘留沃斯田鐵，而持溫溫度低於MS點之沃斯回火處理則由回火麻田散鐵、下變韌鐵與殘留沃斯田鐵所組成。
為應用上考量，拉伸試驗以雙環型試片作為拉伸試片。隨沃斯回火溫度的提高，影響回火麻田散鐵、下變韌鐵與殘留沃斯田鐵的相比例，因此使硬度與雙環型試片之抗拉強度皆隨沃斯回火溫度的提高而降低；另外進行260°C不同時間之沃斯回火，除了以雙環型試片進行拉伸試驗外，並製作標準拉伸試片以比較無notch effect影響下之拉伸性質。結果顯示隨著時間的增加，雙環型試片之抗拉強度約都只剩標準拉伸試片的70 %，受到notch effect的影響並無太大差異；而位移量下降幅度則低於標準拉伸試片，可知260°C持溫時間愈短的試片，其延性受notch effect的影響幅度較明顯。
當S50C經由不同條件之Q&P熱處理後，微觀組織皆為回火麻田散鐵、下變韌鐵與殘留沃斯田鐵所組成。隨著partitioning溫度的提升，麻田散鐵內的碳往鄰近沃斯田鐵相擴散而達到不同程度之回火，使S50C的抗拉強度與硬度皆因此而明顯地下降；而partitioning時間的增加也會使S50C的抗拉強度與硬度有下降的趨勢，下降趨勢可分為0 ~ 15分鐘變化較明顯之區間與15 ~ 60分鐘變化和緩之區間。
透過本實驗兩種熱處理方式所得之最佳條件為經260°C沃斯回火熱處理15分鐘組(A26015)，其雙環型試片抗拉強度約為1350 MPa，而標準拉伸試片則可達約1930 MPa，皆較於約300°C淬火回火者佳。

In this study, the microstructure and mechanical properties of S50C were investigated after austempering and Q&P heat treatment, respectively.
The results showed that lower bainite and a small amount of retained austenite were formed after austempering heat treatment with holding temperature 350°C which is above Ms for 60 minutes while tempered martensite, lower bainite and retained austenite were observed after austempering heat treatment with holding temperature 320, 290 and 260°C which are below Ms for 60 minutes. For application, the eyeglass specimen was used as tensile test specimen. With the holding temperature increased, the phase fraction of tempered martensite, lower bainite and retained austenite were varied, which lead to the decrease of the hardness and tensile strength of eyeglass specimen. In addition, the specimen was under austempering heat treatment for different holding time at 260°C and the tensile strength of standard tensile test specimen was examined as comparison to tensile strength without notch effect. The result indicated that the tensile strength of eyeglass specimens were about 70 % of that measured from the standard specimen, and the amount of displacement of eyeglass specimens decreased less than that measured from the standard specimen with the increase of holding time. That is, the notch effect on the tensile strength of eyeglass specimen with different holding time at 260°C was not obvious. But notch effect on the ductility with short holding time at 260°C was obvious.
Tempered martensite and lower bainite and retained austenite were formed after different conditions of Q&P heat treatment. As partitioning temperature increased, the tensile strength and hardness of S50C were decreased because the carbon in martensite diffused to adjacent austenite which caused different degree of tempering. Tensile strength and hardness of S50C decreased as partitioning time increased. Moreover, the decrease of tensile strength and hardness with holding time for 5 to 15 minutes was more obvious than 15 to 60 minutes.
In this work, the optimum condition among austempering and Q&P heat treatment was that obtained by austempering heat treatment at 260°C for 15 minutes (A26015). Tensile strength of eyeglass specimen is about 1350 MPa and the standard tensile test specimen is up to about 1930 MPa, both of them are better than those after tempering at 300°C.

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