Microstructural Evolution and Mechanical Properties of Fusion Welds in an Iron-Copper-Based Multicomponent Steel
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INTRODUCTION
ADVANCED structural steels require high strength and toughness in combination with good weldability. Recent research conducted at Northwestern University[1–8] has identified a candidate material that meets these requirements. NUCu-140 is a high-strength lowcarbon copper precipitation-strengthened steel that exhibits excellent mechanical properties with a simple chemistry and heat treatment. NUCu-140 is composed of a nominally fine-grained ferritic microstructure with nanoscale Cu-rich precipitates that strengthen the material and NbC precipitates that limit the austenite grain growth. Significant cost savings is achieved in this alloy system through (1) minimization of expensive alloying elements such as Mo, Cr, and V; (2) production through
JEFFREY D. FARREN, Engineer, is with the Welding and Nondestructive Evaluation Carderock Division of the Naval Surface Warfare Center, Bethesda, MD 20817. ALLEN H. HUNTER, Research Assistant, and DAVID N. SEIDMAN, Professor, is with the Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208-3108. JOHN N. DUPONT, Professor, is with the Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015. Contact e-mail: [email protected] CHARLES V. ROBINO, Distinguished Member of the Technical Staff, is with the Joining and Coatings Department, Sandia National Laboratories, Albuquerque, NM 87185. ERNST KOZESCHNIK, Professor, is with the Department of Material Science and Technology, Vienna University of Technology, 1040 Vienna, Austria. Manuscript submitted August 9, 2011. Article published online July 4, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
simple and inexpensive processing techniques; and (3) achievement of structurally sound designs using less material, because of the increased strength and toughness. The use of NUCu-140 as a replacement for conventional structural-plate material permits material and fabrication cost savings approaching 20 pct to 35 pct.[9] An additional benefit of NUCu-140 is that chromium is absent from the alloy, which eliminates the safety hazards associated with the formation of toxic hexavalent chromium in the welding fume.[10] The alloy is also expected to have very good resistance to hydrogen cracking because of the low carbon and alloy content.[11] Extensive research has been performed on the precipitation behavior in the Fe-Cu and Fe-Cu-Ni systems. Investigations have been conducted using a wide range of advanced characterization techniques including transmission electron microscopy (TEM),[12–20] atom-probe tomography,[15,21–23] Mo¨ssbauer spectroscopy,[24] smallangle neutron scattering (SANS),[15,25–30] extended X-ray absorption fine structure (EXAFS),[31–34] positron annihilation,[35] and Doppler spectroscopy.[36] Various simulation and calculation methodologies have also been used to investigate precipitation in the Fe-Cu system including molecular dynamics simulations[37–39] and first-principles calculations.[40] This research has been considered during the development of
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