The softening region in the heat-affected zone of ultra-fine grained steels consists of coarse and fine ferrite grains.
The strength and toughness of the dual-sized ferrite region were evaluated in terms of Vickers hardness and ductile-brittle transition temperature (DBTT), respectively.
In this study, the average grain size of the dual-sized ferrite region was expressed in terms of arithmetical average (dar) and weighted average (dwt), respectively.
It was found that the strength proportionally varied with (dar)-1/2 while the ductile-brittle transition temperature showed a monotonic relation with (dwt)-1/2 for the dual-sized ferrite region.
