Magnetic micro- and nanostructures of unalloyed steels: Domain wall interactions with cementite precipitates observed by MFM

The morphology and content of a cementite phase controls the macroscopic, mechanical and magnetic properties of steels. The influence of the cementite content on the bulk magnetic properties in unalloyed steels was observed in hysteresis loop and Barkhausen noise signals. Globular cementite embedded in a ferrite matrix is characterized by atomic force microscopy and magnetic force microscopy. Size, shape and orientation of the grains influence the domain configuration. When an external magnetic field is applied, the magnetization process occurs mainly in the ferrite matrix. The Bloch walls in the ferrite matrix move, and they are pinned by the cementite precipitates. This microscopic observation correlates with the macroscopic magnetic properties of the investigated material.