Metallurgy, Production Technology, and Properties of Dual-Phase Sheet Steels
The development of dual-phase (ferrite-martensite) microstructures in hot- and cold-rolled sheet can be accomplished by selecting the hardenability of the steel in relation to the particular thermal cycle used in processing. Intercritical continuous annealing of hot- or cold-rolled sheet when coupled with air- or accelerated-cooling rates can produce dual-phase microstructures in relatively low-alloy steels. In addition to the development of the required ferrite-martensite microstructure that produces a continuous stress-strain curve with low yield strength and high tensile strength, the development of enhanced ductility must be considered. The interrelationship among steel hardenability, processing conditions, microstructure, and mechanical properties is considered for both laboratory- and production-processed intercritically continuous-annealed sheet.