Relationship between magnetic properties and hardness on recovery and recrystallization process in cold rolled steel

Nondestructive evaluation (NDE) of degradation remains a critical issue in maintenance technology for infrastructure constructions, e.g., of bridges or highways, and in the metal industry. NDE techniques using magnetic measurements are effective for investigating degradation of steels before crack initiation: good correlations exist between magnetic and mechanical properties of the material, because both depend on the underlying microstructure. Dislocations and grain boundaries represent the most relevant microstructural features in the present case: an important issue to evaluate is then how they contribute qualitatively and quantitatively to the magnetic and mechanical properties of the material. For this purpose, we prepared cold-rolled low-carbon steel to induce dislocations and to change shape in grains, and annealed the steels at 773 and 873 K to further alter the distribution of dislocations and grain morphologies. The magnetic and the mechanical properties under cold-rolling and heat treatment were then investigated.