Modelling and simulation of the microstructure of ESR ingots for power generation forgings

Dally, Robert (2017). Modelling and simulation of the microstructure of ESR ingots for power generation forgings. University of Birmingham. Ph.D.

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Abstract

Microstructural analysis was carried out on commercial FB2 steel ingots (via lab and ESR) and directionally solidified (DS) trial ingots to investigate phase formations and microsegregation across the diameter. All samples had a martensitic microstructure, and a solute-rich eutectic region containing Mo-rich borides. This was consistent with Thermo-Calc (thermodynamic) modelling. An improved constant was calculated based on DS experiments to provide a more accurate prediction of cooling rates.

Microsegregational analysis was carried out using scanning electron energy dispersive x-ray spectroscopy (SEM-EDS). Compositional sorting methods were compared against semi-analytical models. The weighted interval rank sort (WIRS) sort was most appropriate. Partition coefficients calculated from WIRS results were found to reasonably fit the Scheil model for ferrite stabilising elements. No reasonable fit was found for austenite stabilisers.

DICTRA simulations predict partitioning behaviour of solute after the peritectic transformation which creates a segregated dendritic structure; opposite of what is found experimentally.

Heat treatments showed formation of detrimental boron nitride clusters in the eutectic regions. These form due to boron released from the Mo-rich borides combining with nitrogen (segregated to this region).

DSC experiments carried out show a large difference in phase formation temperatures during solidification when compared to Thermo-Calc and DS experiments.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):