Dual ferrite-martensite treatments of a high-strength low-alloy ASTM A588 steel

Abstract

Dual ferrite-martensite (DFM) treatments of an ASTM A588 steel have been investigated. The treatments consisted of initial austenitization and quenching to form 100% martensite, followed by annealing in the (α + γ) region and subsequent quenching. It was found that DFM microstructures of the steel contained continuous globular martensite along the prior austenite grain boundaries and acicular martensite within the prior austenite grains. The DFM of the steel exhibited the superb combinations of strength and elongation over a range of elongation 15% to 20% in a 3 cm gauge length. For a sample with 18% elongation, the yield strength was 49 kg mm⁻² (70 × 10³ p.s.i.) and the ultimate tensile strength 68 kg mm⁻² (97 × 10³ p.s.i.). The type of initial microstructure prior to the dual phase treatment is of prime importance in the determination of the morphology of DFM structure. The results show that the initial martensite structure is more advantageous than the initial pearlite plus proeutectoid ferrite and austenite structures.