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In the present study, in order to investigate the effect of impact angle and sand jet pressure on the erosion rate and residual stress in sand molding operation, the experiments are performed using gray cast iron, pearlitic ductile iron (PDI) and austempered ductile iron (ADI) as workpiece materials. To fulfill this objective, experimental tests are conducted in full factorial design with workpiece material, impact angle and jet pressure as input and erosive wear rate and residual stress as output parameters. According to the results, variation of impact angle of erosive particles intensively affects the erosion rate of materials in a way that, among the experiments which are carried out in lower impact angles (15 to 30°), ADI cast iron shows the maximum erosive strength however as the impact angle shifts to higher values (75 to 90°), PDI cast iron becomes more resistance against erosion. It can also be noted from the SEM images that in sand shooting process, the presence of flake graphite in gray cast iron causes more formed and grown cracks which significantly intensifies its erosion rate relative to ADI and PDI cast irons. Additionally, comparative analysis of results revealed that formation of surface micro cracks in gray cast iron material causes less induced compression residual stresses relative to ADI cast iron whose great stiffness leads to higher magnitudes of compression residual stress in sand molding operation.

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The main goal of present work is to identify the appropriate austenitising category to achieve the austempered ductile irons with dual matrix structure having the best possible machinability. In this regard, specimens of low-alloyed ferritic spheroidal graphite cast iron were prepared by casting process. In order to obtain a mixed ferrite-austenite structures having different volume fraction of austenite phase, samples were subjected to one of two processes: a) partial austenitising at 870 ^oC for various times (5 to 60 min) or b) intercritical austenitising at various temperatures (750, 765, 780 and 800 ^oC) for 60 minutes. After that they were austempered in molten salt at a temperature of 350 ^oC for one hour. During turning with a lathe equipped with a force dynamometer, the cutting forces of the workpieces were measured as a general adopted criterion for machinability investigation. According to the obtained results, with the increase of partial austenitising time or intercritical austenitising temperature, the volume fraction of the ausferrite phase increased, but the cutting force decreased initialy and then increased. For a certain percentage of the ausferrite phase, the turning of samples prepared with partial austenitising process was associated with lower cutting force, compared to the samples obtained by the intercritical austenitising process. In general, it can be concluded that the maximum machinability of dual matrix ductile iron austempered at 350 ^oC is achieved when the selected austenitising temperature and time results to creation dual matrix structure containing 39 ±  3 Vol% ausferrite phase