The shear and volume change accompanying the austenite to martensite transformation upon cooling from above the critical temperatures produce numerous free mobile dislocations in the surrounding ferrite matrix. Upon application of the load, free dislocations move with stresses much less than that required to move restrained dislocations as commonly found in ferrite-pearlite steels, so dual phase steels yield plastic flow at lower stresses of equivalent tensile strength. Magnitude of work hardening in dual phase steels at low strains too large to be explained by dislocation.

Martensite is the principal load bearing constituent. Volume percent of martensite and steel strength are linearly related. Carbon content is also important though, and separate linear relationships exist. Martensite strength can be increased by decreasing its particle size.

Continuous annealed. Upon heating the steel above the critical temperature, islands of carbon-rich, nonequilibrium austenite form at the carbide locations. Heating temp determines volume fraction of austenite and carbon content that can exist. Carbon Migration.

Batch annealed. Similar to those observed during continuous annealing. However, grain size and substructure are characteristic of slower cooling rates