الفهرس 
Two-step austempring of GGG50 for production of ductile iron, low alloyed Steel subsitistion
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Abstract
Castings made of Austempered ductile iron (ADI) have attracted practicing engineers and researchers, alike, mainly because of its excellent strength and wear properties and also at the same time cheaper to process and produce w.r.t comparative forged steel parts. In this investigation, ductile iron samples from GGG50 were prepared and subjected to a two - step austempering heat treatment cycle following the austenitizing treatment. Six groups of samples were prepared for this heat treatment cycle. All groups of samples were initially austenitized at 900{u00B0}C for one hour, after that they were subjected to two - step austempering process at 400{u00B0}C and 250{u00B0}C respectively, in the 1st step, the samples were rapidly quenched into a salt bath maintained at 400{u00B0}C for one hour (step of constant time and temperature) after that all the samples were taken to the 2nd step by rapid quenching again into a salt bath maintained at 250{u00B0}C (step of variable time throughout six time intervals). The six time intervals were as follow: The first groups of samples were austempered for 0.5h, the second group for 1.5h, the third group for 2hr, the fourth group 2.5h, the fifth group for 3.5 and the group for 4.5h. Effect of this two - step austempering heat treatment on the microstructure and tensile properties of the samples were examined and compared with the properties of a reference low alloy steel type (16 Mn Cr 5). The results have shown that the new two - step austempering process has resulted in moderate improvement in the ultimate tensile strength and the ductility of the resultant ADI compared to one step ADI. The results are analyzed based on the microstructure features which greatly effect the mechanical properties of ADI castings produced