Annealing generally involves three major steps: 1. Heating Stage (Achieve the desired temperature) - In case of steels, this stage usually represents the amount of recrystallization that takes into effect under a defined heating rate. read more
So fine grained structure provides more resisting areas due to presence of more grains and less interstitial positions present inside it. Whereas for a coarse grained structure, there will be less resisting areas due to less grains and more interstitial positions present inside it. read more
Steels castings have invariably coarse austenite grains, which result in coarse ferrite grains, or widmanstatten type of structure with poor impact strength as illustrated in left side of Fig. 5.3 (a) and the fine micro-structure developed by full annealing on right side (schematic). read more