Scanning squid microscope differentiation of ferromagnetic steel phases

The remanent magnetization of ferromagnetic steel with five different micro structures has been studied using a microscope based on a high-transition-t emperature d.c. Superconducting QUantum Interference Device (SQUID). The sa mples were prepared using different heat treatments, beginning with the sam e material composition. Each sample was magnetized in turn in a magnetic fi eld of 50 mT, and the remanent magnetization was studied by scanning the sa mple 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 p rocedure yielded a two-dimensional magnetic field image produced by the loc al remanent magnetization of the sample. In addition, microstructural infor mation has been obtained using optical imaging, allowing the magnetic image s to be correlated with the underlying microstructure. (C) 2000 Acta Metall urgica Inc. Published bq Elsevier Science Ltd. All rights reserved.