Aging-Induced Transformations of Maraging-400 Alloys
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INTRODUCTION
AMONG the maraging steels, the maraging-400 has the highest cobalt content and presents the greatest yield strength.[1] However, to the best of our knowledge, maraging-400 steel has not been previously characterized, either crystallographically (i.e., by Rietveld refinement) or magnetically. Only studies focusing on the mechanical properties have been reported in literature.[2] Thus, describing other physical properties of this material and comparing them with those of the rest of the maraging steel family is still an open issue. In this sense, we have conducted an investigation aiming to characterize the crystalline structure and magnetic properties of a maraging-400 alloy (i.e., 13.0Ni15.0Co10.0Mo0.2Ti), solubilized and aged in typical conditions. Recently, we reported preliminary results on the crystallographic and magnetic properties of the as-solubilized and aged maraging-400 alloy, prepared with high-purity metals.[3] It was shown that the solubilized steel is martensitic, with a tetragonal crystalline structure, and ferromagnetic, similar to maraging-350 steel. However, some aged maraging-400 alloys revealed different dynamics of phase
T.J.B. ALVES, G.C.S. NUNES, L.F.S. TUPAN, F.F. IVASHITA and A. PAESANO Jr. are with the Universidade Estadual de Maringa´, Av. Colombo, 5790, Maringa´, PR, 87020-900, Brazil. Contact e-mail: [email protected] P.W.C. SARVEZUK is with the Universidade Tecnolo´gica Federal do Parana´, Campo Moura˜o, Brazil. C.A.S. DE OLIVEIRA is with the Universidade Federal de Santa Catarina, Floriano´polis, Brazil. Manuscript submitted November 21, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
transformation and precipitation during aging, in comparison with aged maraging-350 steels. Therefore, it is very interesting to go on with this investigation in order to better understand the structural and magnetic properties of maraging-400 steel. In this paper, we present the results of a more complete research on this type of alloys, heat-treated for longer periods and at higher temperatures than before. The study was conducted by applying X-ray diffraction, Mo¨ssbauer spectroscopy, and hardness measurements. Comparisons between the results obtained for these alloys and those obtained for aged maraging-350 steels are presented. It will be shown that the higher cobalt and molybdenum content present in maraging-400 steels is responsible for significant differences regarding the final aged state.
II.
MATERIALS AND METHODS
The maraging-400 alloys were made by arc-melting iron with the alloy elements (i.e., Ni, Co, Ti, and Mo; purity > 99.9 pct). Each resultant button (~ 1 g) was re-melted at least three times in order to maximize the sample’s homogeneity. Then, slices (/ [ 1 mm) were taken from the re-melted button using a precise metallographic cutter with a diamond saw. These plates, with rounded contours, were heat-treated under argon atmosphere at 1050 C for 1 hour for solubilization. Further, they were manually sanded on both sides, with 100-, 600-, and 1200-grit sandpaper. The sa
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