Investigation of heat affected zone softening in armour steels Part 2 – Mechanical and microstructure heterogeneity

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Flash processed (FP) steels have shown potential for armour applications based on the response to ballistic loading. In this research, weldability of these steels was studied and compared to commercial high hard (HH) armour steel. Simulated heat affected zone (HAZ) microstructures in these steels were investigated by comprehensive microscopy and hardness mapping. HAZ softening in HH steel was observed on heating to a peak temperature below Ac1 due to overtempering of original microstructure. In FP steel, the softening was associated with allotriomorphic ferrite formation when heated to a peak temperature between Ac1 and Ac3. The transformation kinetics, softening, and hardening characteristics are rationalised based on changes in prior austenite grain size, cooling rate and underlying chemical heterogeneity.