Fracture toughness is a parameter for evaluating the quality of components including pipelines and pressure vessels. Because fracture toughness standards require destructive laboratory testing, they cannot be conducted in the field. Nonlinear ultrasonic evaluation presents a novel solution to non-invasively characterize fracture toughness. Ultrasonic testing is used to estimate the nonlinearity of steel samples. These samples were additionally tested destructively for toughness characteristics, with the aim to establish correlations between these destructive and nondestructive techniques.