High-strength low-carbon ferritic steel containing Cu-Fe-Ni-Al-Mn precipitates

An investigation of a low-carbon, Fe-Cu-based steel, for Naval ship hull applications, with a yield strength of 965 MPa, Charpy V-notch absorbed impact-energy values as high as 74 J at -40 degrees C, and an elongation-to-failure greater than 15 pct, is presented. The increase in strength is derived from a large number density (approximately 10(23) to 10(24) m(-3)) of copper-iron-nickel-aluminum-manganese precipitates. The effect on the mechanical properties of varying the thermal treatment was studied. The nanostructure of the precipitates found within the steel was characterized by atom-probe tomography. Additionally, initial welding studies show that a brittle heat-affected zone is not formed adjacent to the welds.