Abstract
The dual-phase (DP) banded microstructure in HSLA steels, particularly API X52, often results in anisotropic mechanical performance due to non-uniform phase distribution. This study investigates the effect of austenitizing and intercritical annealing treatments on the morphology and mechanical properties of DP microstructures. API X52 steel samples were austenitized at 950, 1050, and 1150 °C, followed by intercritical annealing (Step Quenching, SQ) at 740, 780, and 800 °C to form ferrite-martensite dual-phase structures. Microstructural analysis revealed that increasing the austenitizing temperature significantly reduced banding. At 1150 °C, the banded structure was fully dissolved, producing a more homogeneous martensite dispersion. Hardness increased with intercritical temperature due to higher martensite content, while excessive austenitizing led to grain coarsening and reduced hardness. Charpy impact tests revealed a general decrease in absorbed energy with increasing austenitizing temperature, except at 1150 °C, where microstructural isotropy resulted in a slight recovery of toughness. SEM fracture surfaces confirmed ductile behavior, with a dimple morphology indicative of a uniform microstructure. These results demonstrate that austenitizing at 1150 °C followed by intercritical annealing is an effective route to suppress banding and improve mechanical isotropy in dual-phase API X52 steel.

Key words
austenitization, ferrite, banded structure, Charpy impact, hardness, dual phase

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