Thesis defense of Gorka Plata

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Thesis defense of Gorka Plata

THESIS

Thesis defense of Gorka Plata

Title of the thesis: Semi-Solid Forging of Steels: New insights into material behaviour evolution and industrialisation. Obtained the SOBRESALIENTE CUM LAUDE rating and the DOCTOR INTERNACIONAL mention.

2018·12·18

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  • Title of the thesis: Semi-Solid Forging of Steels: New insights into material behaviour evolution and industrialisation
  • PhD programme: DOCTORATE PROGRAMME IN MECHANICAL ENGINEERING AND ELECTRICAL ENERGY
  • Directors of the thesis: Zigor Azpilgain Balerdi y Jokin Lozares Abasolo
  • Court:
    • President: Platon Kapranos (University of Sheffield)
    • Vocal: Carl David Slater (University of Warwick)
    • Vocal: Mohammed Abdul Azeem (University College London)
    • Vocal: Gonzalo Alvarez de Toledo Bandeira (SIDENOR)
    • Secretary: Iñaki Hurtado Hurtado (Mondragon Unibertsitatea)

Abstract

European trends of reduction of emissions and the zero environmental impact together with the globalisation are showing a huge impact on the actual steelmaking and automotive steel components manufacturers. This is therefore driving the European market to higher strength-to-weight materials and more efficient fabrication processes to maintain the competitiveness. For this reason, the Semi-Solid Forging (SSF) of steels could be a real possibility for the industry to stay at the forefront of the market.

This technology has produced automotive steel components reducing the required raw material and energy consumption while attaining as forged mechanical properties. At the present time, the production limit of components via SSF can be as low as 50 components. The understanding of the manner the material evolves during the process (and the reason for the observed soft flow during forging) are still limited.

Considering the high potential of the process, this PhD has focused on trying to give an explanation to the material behaviour. At the same time, a considerable number of components have been manufactured to show the repeatability and durability of the utilised materials and equipment. The results of this investigation aim to bring the SSF closer to the industrial reality.

In terms of the material behaviour analysis, different hypotheses have been proposed and analysed. Both sulphur content and incipient melting has been characterised and no significant impact of these parameters has been seen on the semi-solid forgability of 42CrMo4. However, it has been suggested that other alloys may be more prone to incipient melting compared to the 42CrMo4. Adiabatic heating has shown that a significant temperature can be caused as a result of the high local strains/strain rates. It has not been distinguished whether this can cause liquid formation. However, local softening of the material is, indeed, likely. Further trials for adiabatic heating are needed in order to fully assess its role on the SSF process.

With regard to the component manufacturing, apart from medium carbon steels, Alloy 28 (a high Nickel steel) has also been trialled using this method. In this latter case, which is infamous for its poor forgability, the incipient melting may have enhanced the fluidity of the material enabling an even softer filling. In addition to that, a batch of 250 components has been successfully manufactured attaining the already confirmed cost saving and great mechanical properties apart from the desired repeatability of the process and the minor die degradation.