TY - THES

T1 - Development of a predictive simulation setup for the influence of thermo-mechanical processing on the niobium carbide distribution in PH15-5 steel

AU - Damm, Nina

N1 - no embargo

PY - 2022

Y1 - 2022

N2 - This work aims to develop a predictive simulation setup in MatCalc to reproduce different thermo-mechanical treatments (TMT) of the whole processing route to determine critical processing steps for the formation of coarse niobium carbide (NbC) with a size of 1 µm and more, as these reduce the low-temperature fracture toughness. Therefore, the precipitation of niobium carbide in a PH15-5 steel is investigated experimentally and theoretical, using a scanning electron microscope (SEM) with a resolution limit of 190 nm and the thermokinetic software MatCalc. The TMT were performed in a Gleeble 3800-GTC at 1100 °C and 1180 °C, where coarsening and dissolution were observed, respectively. The relative variation in the experimental data due to segregations was found to be 15 % in the area fraction, 19 % in the number and 1 % in the mean diameter of NbC. The measured area fraction of NbC was one tenth of the equilibrium phase fraction predicted by MatCalc. Consequently, there is either a significant fine phase fraction below the resolution limit and / or a coarse phase fraction with poor statistics. The maximum achievable size of NbC due to secondary precipitation was found to be 550 nm, which is well below the maximum diameter of experimentally NbC, so that they are assumed to be primary niobium carbides. Primary niobium carbides are therefore considered in the MatCalc simulation. The observed trends, dissolution at 1180 °C and coarsening at 1100 °C, were simulated with the developed simulation setup.

AB - This work aims to develop a predictive simulation setup in MatCalc to reproduce different thermo-mechanical treatments (TMT) of the whole processing route to determine critical processing steps for the formation of coarse niobium carbide (NbC) with a size of 1 µm and more, as these reduce the low-temperature fracture toughness. Therefore, the precipitation of niobium carbide in a PH15-5 steel is investigated experimentally and theoretical, using a scanning electron microscope (SEM) with a resolution limit of 190 nm and the thermokinetic software MatCalc. The TMT were performed in a Gleeble 3800-GTC at 1100 °C and 1180 °C, where coarsening and dissolution were observed, respectively. The relative variation in the experimental data due to segregations was found to be 15 % in the area fraction, 19 % in the number and 1 % in the mean diameter of NbC. The measured area fraction of NbC was one tenth of the equilibrium phase fraction predicted by MatCalc. Consequently, there is either a significant fine phase fraction below the resolution limit and / or a coarse phase fraction with poor statistics. The maximum achievable size of NbC due to secondary precipitation was found to be 550 nm, which is well below the maximum diameter of experimentally NbC, so that they are assumed to be primary niobium carbides. Primary niobium carbides are therefore considered in the MatCalc simulation. The observed trends, dissolution at 1180 °C and coarsening at 1100 °C, were simulated with the developed simulation setup.

KW - Niobkarbid (NbC)

KW - PH15-5

KW - Simulationsaufbau

KW - thermomechanische Behandlung

KW - relative Variation

KW - Segregation

KW - primäres Niobkarbid

KW - NbC-Verteilung

KW - Niobium carbide (NbC)

KW - PH15-5

KW - simulation setup

KW - thermo-mechanical treatment

KW - relative variation

KW - segregation

KW - primary niobium carbide

KW - NbC distribution

M3 - Master's Thesis

ER -