Fracture toughness J Q and fatigue crack growth da/dN x deltaK have been studied in two dual-phase steels used in the automotive industry, with 8.8% to 12.5% of martensite volumetric fraction. The main difference between the steels is the chemical composition: one of the steels had chromium additions while the other had silicon as an alloy element. Silicon steel presents higher fracture toughness than chromium steel. It was not noticed significant effect of anisotropy in both steels, while an increase of side grooves decreased the value of J Q of the materials. The two steels present a similar behavior in fatigue crack growth resistance with no significant effect of anisotropy. An increase of R ratio increased the crack growth rates and decreased the value of deltaKth of the materials.
fracture toughness; fatigue resistance; dual phase steels; automotive application
