engleski

The influence of furnace atmosphere during austenitization on microstructure and hardness of austempered ductile iron

The effect of furnace atmosphere during austenitization on properties of austempered ductile iron was investigated. Two sets of ductile iron samples were used. One set of samples was austenitized in normal furnace atmosphere, without protection of decarburization. Second set of ductile iron samples was austenitized in nitrogen protective atmosphere to prevent decarburization. All samples were austenitized at the same temperature of 850°C for 30 minutes. During austenitization in nitrogen atmosphere pressure of 0.3 bars was used. After that samples were austempered on 300°C for different times. Times ranged from 30 minutes to 60 minutes, following experimental plan. At the end, all the samples were air cooled to room temperature. Microstructural analysis was done, and hardness was measured on all samples. Results showed that samples austenitized in nitrogen atmosphere have higher hardness and more carbon rich phases in their microstructure. Mathematical models are derived that describe the hardness of ADI depending on the atmosphere in the furnace and the holding time at austempering temperature.

Austempered ductile iron ; Furnace atmosphere ; Decarburization ; Microstructure ; Hardness ;

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