On the Flow Instability associated with Dynamic Strain Ageing of Ferritic Spheroidal Graphite Cast Iron

AbstractFerritic spheroidal-graphite cast irons of four different silicon contents from 2.0 wt% to 3.4 wt% were deformed in tension at various strain rates and test temperatures. The results indicate certain types of flow instability at certain temperature ranges of dynamic strain ageing. By judging from the characteristics of the flow patterns and apparent activation energies, it is suggested that interstitial carbon plays the major role in low temperature flow instability, whereas the high temperature flow instability is mainly affected by substitutional silicon. The above suggestion on the role of substitutional silicon is also supported by static strain ageing tests.As indicated by the data obtained at the onset temperature of flow instability, the activation energy for carbon diffusion increases with increasing silicon content. Rationalisation based on a nearest-neighbour pair bonding model shows that the addition of substitutional silicon raises the activation energy for carbon diffusion by raising ...