本論文主旨是探討1種新的沃斯回火策略，沃斯回火溫度是以週期的方式在2溫度之間變化，以探討對球墨鑄鐵相轉換速率的影響。以真空電阻量測系統即時監控與記錄沃斯回火相轉換過程電阻系數的變化。研究分析週期式沃斯回火(Cyclic austempering)與恆溫沃斯回火(Isothermal austempering) 對相轉換動力學的影響，亦觀察顯微組織及測試機械性質，以進一步了解所得到的沃斯回火球墨鑄鐵(ADI)在材質上的差異性。
實驗結果顯示：(1)利用Johnson-Mehl方程式分析第一階段反應的動力學，得到τ值可用以估算出反應完成及進入製程窗間的時間；(2)250~300 ℃週期式溫度速率為0.167 ℃/s及300~350 ℃週期式溫度速率為0.4 ℃/s時可得最小τ值，分別為860 s及664 s；(3)週期式沃斯回火熱處理的基底顯微結構為沃斯肥粒鐵束狀組織型態；(4)在250~300 ℃溫度速率為 0.4 ℃/s的週期式沃斯回火後得到的硬度為HV 585，接近250 ℃恆溫的硬度值，而其反應時間約可減少49 %，由9790 s降為4950 s。

The resistivity of ductile iron was measured to investigate the kinetics of phase transformation during a cyclic austempering. The cyclic austempering was carried out between 2 temperatures with a given rate of change. The resistivity was used to analyze the kinetics of phase transformation during cyclic and isothermal austempering. It is also conduct the microstructure examination and mechanical properties testing. The characteristic of ADI produced from cyclic and isothermal austempering was studied.
The results of this research show that: (1) Johnson-Mehl equation is used to study the kinetics of the stage 1 reaction, time constant(τ) which derived from the equation can be used to estimate the finishing time required for the reaction; (2) Lower values of τ are obtained from two austempering cases, with a rate of 0.167 ℃/s between 250~300 ℃ and a rate of 0.4 ℃/s between 300~350 ℃ respectively; (3) The matrix of ADI from the cyclic austempering is a typical ausferrite structure as that shown in the isothermal one; (4) A hardness of HV 585 is obtained from a austempering process with a rate of 0.4 ℃/s between 250~300 ℃, which reduce the reaction time about 49% when comparing to the isothermal austempering at 250 ℃.

參考文獻
[1] O. Eric, M. Jovanovic, L. Sidanin, D. Rajnovic, and S. Zec, "The austempering study of alloyed ductile iron," Material and design, vol. 27, pp. 617-622, 2006.
[2] Y. Tanaka and H. Kage, "Development and application of austempered spheroidal graphite cast iron," Material Transaction,JIM, vol. 33, pp. 543-557, 1992.
[3] U. Seker and H. Hasirci, "Evaluation of machinability of austempered ductile irons in terms of cutting forces and surface quality," Journal of Materials Processing Technology, vol. 173, pp. 260-268, 2006.
[4] S. K. Putatunda and P. K. Gadicherla, "Influence of austenitizing temperature on fracture toughness of a low manganese austempered ductile iron (ADI) with ferritic as cast structure," Materials science and engineering, vol. 268, pp. 15-31, 1999.
[5] P. P. Rao and S. K. Putatunda, "Investigations on the fracture toughness of austempered ductile irons austenitized at different temperatures," Materials Science and Engineering, vol. 349, pp. 136-149, 2003.
[6] O. Eric, L. Sidjanin, Z. Miskovic, S. Zec, and M. T. Jovanovic, "Microstructure and toughness of CuNiMo austempered ductile iron," Materials letters, vol. 58, pp. 2707-2711, 2004.
[7] R. Elliott, "The role of research in promoting austempered ductile iron," Heat treatment of metals vol. 3, pp. 55-59, 1997.
[8] R. B. Gundlach and E. P. Whelan, "Critical Temperature in ferritic ductile iron," AFS Transactions, vol. 100, pp. 713-718, 1992.
[9] P. P. Rao and S. K. Putatunda, "Influence of microstructure on fracture toughness of austempered ductile iron," Metallurgical and materials transactions vol. 28, pp. 1457-1470, 1997.
[10] V. Bela and Sr.Kovacs, "Austempered ductile iron:fact and fiction," Modern Casting, pp. 38-41, 1900.
[11] N. Darwish and R.Elliott, "Austempering of low manganese ductile irons Part2 influence of austempering temperature " Materials science and technology, vol. 9, pp. 586-602, 1993.
[12] D. Z. Zheng, "The effect of low temperature austempering on austempered ductile iron," M.S. Thesis,National Taiwan University of Science and Technology,Taipei, 2004.
[13] S. R. Kng, "Effect of cooling rate on eutectoid transformation of ductile iron," M.S. Thesis,National Taiwan University of Science and Technology,Taipei, 2003.
[14] R. C. Voigt and C. R. Loper, "Austempered ductile Iron-process controland quality assurance," Journal of heat treating, vol. 3, pp. 291-309, 1985.
[15] B. Kovacs, "Heat Treating of Austempered ductile iron," AFS Transactions, vol. 99, pp. 281-286, 1991.
[16] L. Sidjanin and R. E. Smallman, "Metallography of bainitic transformation in austempering," Material Science and Technology, vol. 8, pp. 1095-1103, 1992.
[17] B. Kovacs, "Heat treating of austempered ductile iron," AFS Transactions, pp. 91-75.
[18] H. K. D. H. Bhadeshia, Bainite in steels, 2 ed. London: IOM Communications, 2001.
[19] M. J. Perez, M. M. Cisneros, and H. F. Lopez, "Wear resistance of Cu-Ni-Mo austempered ductile iron," WEAR, vol. 260, pp. 879-885, 2006.
[20] D. C. Wen, "The study of mechanical properties of austempered ductile iron affected by the existence of martensite," Ph.D. Thesis,National Taiwan University of Science and Technology,Taipei, 1999.
[21] J. Mallia and M. Grech, "Effect of silicon content on impact properties of austempered ductile iron," Material science and technology, vol. 13, pp. 408-414, 1997.
[22] N. Darwish and R.Elliott, "Austempering of low mangnese ductile irons Part 3 variation of mechanical properties with heat treatment conditions," Material science and technology, vol. 9, pp. 882-889, 1993.
[23] B. Y. Lin, E. T. Chen, and T. S. Lei, "The effect of alloy elements on the microstructure and properties of austempered ductile irons," Scripta metallurgica et materialia, vol. 32, pp. 1363-1367, 1995.
[24] D. J. Moore, T. N. Rouns, and K. B. Rundman, "The relationship between microstructure and tensile properties in austempered ductile irons," AFS Transactions, vol. 95, pp. 765-774, 1987.
[25] M. C. Cakir, A. Bayram, Y. Isik, and B. Salar, "The effects of austempering temperature and time onto the machinability of austempered ductile iron.," Material science and engineering, vol. 407, pp. 147-153, 2005.
[26] K. H. W. Seah and S. C. Sharma, "Machinability of alloyed austempered ductile iron," International Journal of Tools Manufact, vol. 35, pp. 1475-1479, 1995.
[27] Y. J. Park, R. B. Gundlach, and J. F. Janowak, "Monitoring the bainite reaction during austempering of ductile iron and high silicon cast steel by resisitivity measurement," AFS Transactions, vol. 95, pp. 87-97, 1987.
[28] B. Y. Lin, "The effect of alloy elements on the austemper-transformation of ductile irons," Ph.D. Thesis,National Taiwan University of Science and Technology,Taipei, 1985.
[29] J. T. Chen, "The sutdy on the transformation kinetics of austempered ductile iron," Ph.D. Thesis,National Taiwan University of Science and Technology,Taipei, 1999.
[30] V. Sista, P. Nash, and S. S. Sahay, "Accelerated bainitic transformation during cyclic austempering," Heat Treating Progress, pp. 45-47, 2008.
[31] C. Y. Lin, "The effect of cooling rate on the eutectoid reaction of high silicon steels," M.S. Thesis,National Taiwan University of Science and Technology,Taipei, 2002.
[32] M. Umemoto, K. Horichi, and I. Tamura, "Transformation kinetics of bainite during isothermal holding and continuous cooling," Transactions ISIJ, vol. 22, pp. 854-861, 1982.