The student Elena Mora Serrano obtained an OUTSTANDING qualification

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The student Elena Mora Serrano obtained an OUTSTANDING qualification

THESIS

The student Elena Mora Serrano obtained an OUTSTANDING qualification

2022·04·12

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Thesis title: Applicability of a Dynamic Recrystallization Model for an Open Die Forging Process for the As-Cast Superaustenitic Stainless Steel Alloy 28.

Court:

  • Chairmanship: Andrea Ghiotti (University of Padua)
  • Vocal:Andreas Sterzing (Fraunhofer IWU)
  • Vocal:Iban Vicario Gómez (Fundación Tecnalia Research & Innovation)
  • Vocal: Pilar Esteban Pascual (TUBACEX)
  • Secretary:Zigor Azpilgain Balerdi (Mondragon Unibertsitatea)

Abstract:

In the petrochemical industry, extreme conditions require materials that can withstand high fatigue pressures and highly corrosive environments. In the last decade, the use of super austenitic steels (SASS) has increased due to their excellent properties in these environments. Alloy 28 high nickel super austenitic steel has a resistance to corrosion and high fatigue cycles, becoming one of the main options for manufacturing pipes for the petrochemical industry.

SASS has a purely austenitic structure due to its high nickel content, an alloy that gives the material high toughness and good forging behaviour. However, it also makes it susceptible to variations in the process factors, and controlling these conditions is essential. One of the most critical parameters determining a material's mechanical behaviour is the microstructure, so it is crucial to predict it.

Simulation software is used to reproduce the manufacturing process and obtain the mechanical properties to predict the state of the material. Therefore, it is necessary to determine a mathematical model that predicts the material's behaviour and calculates the material parameters for a specific model.

In this project, the microstructural evolution of Alloy 28 has been studied for an open die forging process. Furthermore, the file will be used to reproduce, through the FORGE® forming process analysis software, the industrial process of obtaining forged round bars from TUBACEX, manufacturer of pipes for Oil & Oil&Gas applications.

An exhaustive bibliographic search was carried out to understand and identify all the phenomena that occur during the transformation of the material subjected to hot deformation and how they can be studied at a laboratory scale. Furthermore, the conditions that perform hot compression tests were determined, and the results of the stress-strain curves and microstructures obtained after deformation were analysed. Finally, the model's parameters to be implemented in the simulation are determined with the results obtained.

Finally, the model obtained during this study is validated by comparing it with the one used by the manufacturer. Although this reference model is industrially validated, it does not precisely consider the physical phenomena involved in a hot process, allowing a more accurate material model.