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Creep Modeling of 9-12%Cr Ferritic Steels Accounting for Subgrain Size Evolution

[+] Author Affiliations
Luca Esposito, Alcide Bertocco

University of Napoli “Federico II”, Naples, Italy

Gabriel Testa, Nicola Bonora

University of Cassino and Southern Lazio, Cassino, Italy

Paper No. PVP2018-84671, pp. V06AT06A056; 5 pages
doi:10.1115/PVP2018-84671
From:
  • ASME 2018 Pressure Vessels and Piping Conference
  • Volume 6A: Materials and Fabrication
  • Prague, Czech Republic, July 15–20, 2018
  • Conference Sponsors: Pressure Vessels and Piping Division
  • ISBN: 978-0-7918-5167-8
  • Copyright © 2018 by ASME

abstract

The enhanced performance of new creep-resistant steels is the result of optimized microstructures. Clearly, the microstructure stability at high temperature is essential for the long-term use of this steels generation. In the recent scientific literature, several research addresses the correlation between the microstructure degradation and the creep performance loss. General aim is to introduce state variables able to describe the metallurgy history of the material affecting its current and future response. The possibility to integrate this metallurgical information in predictive modeling is very attractive. In this work, a new creep model for 9-12%Cr ferritic steels, in the framework of the Continuum Damage Mechanics (CDM), is proposed. The damage variable, usually not related to the underlying physics, may have a metallurgical meaning introducing the kinetic law for subgrain evolution. The microstructure of 9-12%Cr steels is designed to produce the 100% martensite during quenching treatment. Since martensite is not a thermodynamic equilibrium phase, the microstructure evolves exhibiting lath widening and subgrains coarsening. The subgrains growth can be ascribed to the creep strain accumulation and consequently the proposed formulation uses the subgrain size evolution to predict the creep rate beyond the minimum creep rate mainly affected by the recovery processes.

Copyright © 2018 by ASME
Topics: Creep , Steel , Modeling , Accounting

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