The Effect of Cyclic Austempering on Phase Transformation of Ductile Iron

• Main Authors: Bor-Chung Chen, 陳柏均
• Other Authors: Tien-Shou Lei
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/04886556598437926512

碩士 === 國立臺灣科技大學 === 機械工程系 === 97 === 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 ℃.