Dual Ferrite-Martensite Treatments of an ASTM A588 HSLA Steel
During the past several years duplex ferrite-martensite (DFM) steels have received increasing attention for improved strength and weight applications, since they contain characteristic microstructural features that combine high strength with good formability. ASTM A588 is one of the most widely used classes of high strength low alloy (HSLA) steels. It possesses the atmospheric corrosion resistance property as well as relatively high yield strength (∼35 kg/mm2) in the normalized condition. DFM treatments has been applied to the A588 steel.The treatments consisted of initial austenitization and quenching to form 100% martensite, followed by annealing in the (α+γ) region at different temperatures and subsequent quenching. The DFM structure samples were also tempered at 200°-600°C for one hour. Phase diagram of a model steel and the schematic of treatments are shown in Figs. 1(a) and 1(b), respectively. Hardness, ultimate tensile strength, yield strength, elongation and Charpy impact values were measured for thermally treated samples.