Journal
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
Volume 49A, Issue 7, Pages 2951-2962Publisher
SPRINGER
DOI: 10.1007/s11661-018-4654-8
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Funding
- DOCTORADO NACIONAL [21130630]
- FONDECYT from the Chilean Government [11110098, 11121384, 1150457]
- Proyecto de insercion de capital humano avanzado from the Chilean Government [79112035]
- Create-Net Project [H2020-MSCA-RISE/644013]
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A 12 pct Cr martensitic/ferritic steel was designed and produced to study Laves and Z-phase as precipitation hardening particles under creep conditions (650 A degrees C). According to thermodynamic calculations, W and Cu additions were selected to ensure the precipitation of Laves after tempering. It is known that Z-phase formation does not follow the classical nucleation theory. Indeed, MX particles are transformed into Z-phase by Cr diffusion from the matrix to the precipitate. Therefore, to promote fast Z-phase formation, Ta, Co, and N additions were used to produce Ta-MX, which will be transformed into Z-phase. The main result achieved was the precipitation of Laves after tempering, with a particle size of 196 nm. As regards to Z-phase, the transformation of Ta-MX into Z-phase after tempering was confirmed by the formation of hybrid nanoparticles of 30 nm. Although W and Ta have a low diffusion in the martensitic/ferritic matrix, characterization of the precipitates after isothermal aging revealed that Laves and Z-phase have fast growth kinetics, reaching 400 and 143 nm, respectively, at 8760 hours. Consequently, creep test at 650 A degrees C showed premature failures after few thousand hours. Therefore, it is expected that future research in the field of martensitic/ferritic steels will focus on the growth and coarsening behavior of Laves and Z-phase.
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