Abstract
Two austempered ductile iron (ADI) heats transformed at a temperature of 380 °C in periods ranging from 2 minutes to 9 hours have been studied in detail, with emphasis on the relation between the microstructure matrix composition and mechanical properties. The matrix microstructure and mechanical properties of ADI are influenced especially by the dwell time (sometimes also referred to as holding time) at isothermal transformation temperature. ADI matrix called ausferrite consists primarily of acicular ferrite and stabilized austenite. However, for short dwells some amount of martensite can occur in the matrix, which degrades the mechanical properties of ADI. The ADI with optimal combination of mechanical properties was obtained for a transformation dwell of 60 minutes, when the maximum amount of stabilized austenite in the matrix microstructure was obtained.

Key words
Iron; phase transformation, tensile test, fatigue test, transmission electron microscop

Full text (185 KB)