Scanning squid microscope differentiation of ferromagnetic steel phases

The remanent magnetization of ferromagnetic steel with five different microstructures has been studied using a microscope based on a high-transition-temperature d.c. Superconducting QUantum Interference Device (SQUID). The samples were prepared using different heat treatments, beginning with the same material composition. Each sample was magnetized in turn in a magnetic field of 50 mT, and the remanent magnetization was studied by scanning the sample over the SQUID using a two-dimensional translation stage with a range of 50 x 50 mm(2). With a sample-to-SQUID separation of 400-500 mu m, this procedure yielded a two-dimensional magnetic field image produced by the local remanent magnetization of the sample. In addition, microstructural information has been obtained using optical imaging, allowing the magnetic images to be correlated with the underlying microstructure. (C) 2000 Acta Metallurgica Inc. Published bq Elsevier Science Ltd. All rights reserved.