The austenitizing treatment (1123-1223K, 1-2 hr) of austempered ductile irons (ADIs) was optimized by the correlation of results from thermal analysis and mechanical properties of ultimate tensile strength (UTS) and impact energy. Experimental results illustrated that a great UTS and optimum toughness were both in relation with great amounts of Q_(sr) and Q_(se), and fast rale in heat evolution (Q_(sr)/t_(sr)) during recalescence of austenite decomposition, where Q_(sr) and Q_(se) are heat evolved for the time period of recalescence and of terminating heat evolution, respectively. The optimized austenitizing treatment for austempered ductile irons developing their superior UTS was at 1173K for 1.5-1.75 hr and that, for performing optimum impact energy, was at 1123K for 1.75-2.0 hours.
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