Effects of Solid Solution Treatments on the Microstructure and Mechanical Properties of a Nanoscale Precipitate-Strength
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NANOSCALE precipitation-strengthened ferritic steels have generated considerable interest in recent years as promising structural materials for their exceptional properties and affordability.[1–3] The strength of nanophase-strengthened steel results from the replacement of carbon by Cu-rich nano-precipitates,[4–10] and the presence of ferrite instead of martensite in the main phase. The strength of such nanophase-strengthened steel is mainly due to the nano-precipitates, whereas the ductility and toughness are strongly dependent on the matrix structure.[11–13] Recently, the formation of nanoscale precipitates in a ferritic matrix was reported in Cu-containing steels that had undergone an aging treatment. The ductility and toughness of nanoscale precipitation-strengthened steels
Y. ZHAO, H. GUO, S.S. XU, M.J. MAO, and Z.W. ZHANG are with the Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, P.R. China. Contact e-mail: [email protected] L. CHEN is with the Key Laboratory of Neutron Physics and Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics (CAEP), Mianyang 621999, China. O. GOKHMAN is with the Department of Physics, South Ukrainian National Pedagogical University, Odessa 65020, Ukraine. Manuscript submitted August 23, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
were attributed to the interaction of nanophases with screw dislocations.[14,15] It is believed that fine Cu-rich precipitates are easily cut by dislocations and that double kinks form owing to the strain field around semi-coherent precipitates, which are flexible in the bcc matrix.[5,16,17] Many studies have sought to elucidate the strengthening mechanisms of precipitates in terms of their crystal structures, element composition, formation mechanisms, and distribution.[8,18–20] However, studies on the effect of reasonable solid solution treatments (SST) on enhanced ductility and toughness remain limited. The mechanical properties of nanoscale precipitation-strengthened steels are notoriously dependent not only on the size, density, and distribution of nanoscale precipitates but also on the matrix microstructures.[21,22] These microstructures are mainly controlled by SST, whereas aging processes cannot alter the microstructure but only slightly affect the grain size.[23] SST is an important heating process for controlling the matrix microstructure and dislocation density.[24] In general, the purpose of using SST for precipitation-strengthened alloys is to dissolve the alloying element at a high temperature, thereby obtaining a supersaturated solid solution by fast cooling.[25] SST plays two roles in the fabrication of nanoscale precipitation-strengthened ferritic steel. One is to dissolve the alloying elements uniformly within the matrix; the other resembles austenitization. Austenitization, followed by cooling, is well known to significantly influence the size,
morphology, and s
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