THE STRENGTH OF FERRITE IN ANNEALED ARMCO IRON AND HYPOEUTECTOID STEELS

The strength of ferrite in an armco iron with varying grain sizes and in five hypoeutectoid steels with varying volume fraction of the const ituent phases have been studied using microhardness measurements. In a rmco iron, the strength of ferrite derived from its proportionality wi th microhardness, is found to decrease with increasing grain size acco rding to the existing Hall-Fetch relations. But the strength of ferrit e in hypoeutectoid steel is found to vary considerably, even when the grain sizes in ferrite are almost constant. On the other hand, strengt h of ferrite in lypoeutectoid steel bears a strong functional relation ship with volume fraction of the constituent phases. The variation of strength of ferrite in hypoeutectoid steel is explained on the basis o f thermal residual stress exerted by the presence of pearlite.