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A high strength low alloy (HSLA)‐100 steel with different initial microstructures (ferrite and martensite) is processed by cold rolling at room temperature to the reduction of thickness about 70%. It is found that the recrystallization kinetics of the sample with a martensitic microstructure is higher than the sample with a ferritic microstructure. Moreover, the results show that the partitioning factor of substitution alloying elements is less effective than the strain in the martensitic phase transformation. Also, hardness results show that the samples with a martensitic microstructure have drastic drop compared with the samples with a ferritic microstructure, which is related to continuous recrystallization. Remarkable ultimate tensile strength and elongation to failure (829 MPa and 27.7%, respectively) are achieved for cold‐rolled martensite after tempering at 625 °C for 360 min. Accordingly, it is also found that the reason for remarkable mechanical properties is the simultaneous presence of recrystallized fine‐grained and deformed martensite, which forms an inhomogeneous microstructure.

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Grain refinement of AZ91 alloy was achieved via the addition of a modified Al-B inoculant to the melt, where a pronounced heterogeneous nucleation effect by AlB2 particles was observed via addition of Al-8 wt-% B master alloy up to 0.3 wt-%. Moreover, hot extrusion remarkably enhanced both strength and ductility via developing an equiaxed microstructure by dynamic recrystallisation (DRX), fragmentation/dissolution of eutectics (containing β-Mg17Al12 compound) during hot deformation, and amending casting defects. Both as-cast and extruded data followed the same Hall–Petch plot, implying that the grain size refinement is the main strengthening mechanism. Accordingly, grain refining via inoculation and thermomechanical processing was found to be a viable approach for the enhancement of strength-ductility trade-off through the improvement of tensile toughness.