Influence of grain size distribution on the Hall–Petch relationship of welded structural steel

Abstract

The strength of polycrystalline metals increases with a decrease in grain size according to the Hall-Petch relationship. However, heterogeneous microstructures deviate from this relationship dependingon the distribution of grain sizes. This paper introduces a rule of mixtures based approach fordetermining the characteristic length of the microstructure for heterogeneous weld metal. Theproposed grain size parameter, the volume-weighted average grain size, is measured experimentallyfor nine structural steel weld metals and two base materials. The weld metals are found to have alarge variety of grain size distributions that are noticeably broader than those of the base material dueto differences in phase contents. The results show that the volume-weighted average grain size is ableto capture the influence of grain size distribution on the strength of welded structural steel. Based onthe experimental results, a modified Hall-Petch relationship is formulated for the strength predictionof heterogeneous microstructures. The modified relationship is also found to be applicable to datafrom the literature.