Nanometer-sized copper-rich precipitates are an important strengthening element in high-strength low-alloy and low-carbon steels. This 3D atom-probe tomographic reconstruction displays copper-rich precipitates in NUCu-100 steel, designed at Northwestern University to achieve a ultimate tensile strength of 100 ksi (700MPa), for more details see 'Co-precipitation of Copper and Niobium Carbide in a Low Carbon Steel', M.S. Gagliano, PhD Thesis, Northwestern University, 2002. The spatial distributions of individual Cu, Ni, Si, Al, and Mn atoms are shown in a reconstructed volume 2 nm in thickness and with a lateral cross-section of 15 x 14 nm2. It is seen qualitatively that Ni, Al, and Mn are enriched at the locations of the Cu-rich precipitates. For quantitative information on the copper-rich precipitates and the enrichment of Ni, Al, and Mn see 'Interfacial segregation at Cu-rich precipitates in a high-strength low-carbon steel studied on a sub-nanometer scale', D. Isheim, M.S. Gagliano, M.E. Fine, and D.N. Seidman, Acta Materialia Vol. 54(2006) pp. 841-849.