الفهرس 
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Abstract
In this study, microstructure and mechanical properties of thin wall
austempered and intercritically treated ductile iron with a chemical composition
of 3.37 %C, 2.7 %Si, 0.30 % Mn, 0.01 %S, 0.01 %P, and 0.0371 Mg were
investigated. Thin ductile iron samples with different thicknesses of 5, 10, and 15
mm were cast and then heat treated with two different austempering techniques.
The first technique was austenitizing at 810℃ for an hour and then rapidly
quenching in a salt bath at 375℃ for 1 h intercritically austempered ductile iron
(IADI). The second treatment was austenitizing at 900℃, which was above the
upper critical temperature, for an hour and then rapidly quenching in a salt bath
at 375℃ for 1 h austempered ductile iron (ADI). The mechanical properties of
austempered and intercritically austempered thin wall samples were evaluated
and compared to as-cast samples. Samples were fatigue simulated using ANSYS
software and the best condition was experimentally tested using a plane bending
fatigue testing machine. Ultimate strength (1056) MPa and hardness (396 HV)
were obtained for 5 mm ADI sample. Maximum impact toughness (43J) was
achieved for 15 mm IADI sample due to existing of pro-eutectoid ferrite in the
matrix. Maximum simulated fatigue strength (435 MPa) was reported for 5-mm
ADI sample and minimum one (160 MPa) was registered for as-cast DI sample.
For both ADI and IADI irons, fatigue strength decreased with increasing sample
thickness. For 10-mm ADI sample, the simulated fatigue was (407 MPa) which
was relatively very close to the experimental result (417 MPa). For as-cast, ADI
and IADI irons, wear resistance decreased with increasing sample thickness.
Minimum wear rate (2.22×10-6 g/s) was reported for 5-mm ADI sample.
However, due to transforming the retained austenite existing in matrix into
martensite, and maximum wear rate (15.8×10-6 g/s) was registered for 15-mm ascast DI sample at a sliding speed of 2 m/s.