TY - THES

T1 - In-situ study of the dissolution of SiO2 inclusions in secondary steelmaking slags for the production of steel wire

AU - Feichtinger, Stefan

N1 - embargoed until null

PY - 2013

Y1 - 2013

N2 - Non-metallic inclusions are the main reason for steel wire breakage of highly demanding products like tire cord. Therefore efficient removal of non-metallic inclusions by top slags needs to be ensured. The present thesis deals with the dissolution behaviour of SiO2 in different slags. The first part of the present thesis gives an overview of the state of the art of inclusion control during the production of steel wires and of inclusion dissolution studies. The present work is the first to study the dissolution of SiO2 inclusions in steelmaking slags by high temperature-confocal scanning laser microscopy. Scatter of the measurements was reduced by using spherical glassy silica inclusions in the experiments. SEM-EDS analysis and calculation of the relevant phase diagram showed that reaction layers around the particle are not formed during the dissolution which allowed the focus to be kept on the dissolution mechanism. For the first time it was observed that the dissolution mechanism changes as a function of the slag composition. The slag viscosity can be identified as the main influence on reaction mechanism and dissolution time. A new adapted model based on approximations of the diffusion equation which allows the interpretation of changing reaction mechanisms is introduced. Moreover the SiO2 diffusion coefficients are calculated and a regression model for the prediction of the dissolution time of SiO2 in a low alumina slag is presented.

AB - Non-metallic inclusions are the main reason for steel wire breakage of highly demanding products like tire cord. Therefore efficient removal of non-metallic inclusions by top slags needs to be ensured. The present thesis deals with the dissolution behaviour of SiO2 in different slags. The first part of the present thesis gives an overview of the state of the art of inclusion control during the production of steel wires and of inclusion dissolution studies. The present work is the first to study the dissolution of SiO2 inclusions in steelmaking slags by high temperature-confocal scanning laser microscopy. Scatter of the measurements was reduced by using spherical glassy silica inclusions in the experiments. SEM-EDS analysis and calculation of the relevant phase diagram showed that reaction layers around the particle are not formed during the dissolution which allowed the focus to be kept on the dissolution mechanism. For the first time it was observed that the dissolution mechanism changes as a function of the slag composition. The slag viscosity can be identified as the main influence on reaction mechanism and dissolution time. A new adapted model based on approximations of the diffusion equation which allows the interpretation of changing reaction mechanisms is introduced. Moreover the SiO2 diffusion coefficients are calculated and a regression model for the prediction of the dissolution time of SiO2 in a low alumina slag is presented.

KW - non-metallic inclusions

KW - silica

KW - SiO2

KW - wire

KW - tire cord

KW - confocal microscope

KW - dissolution

KW - slags

KW - low alumina

KW - dissolution mechanism

KW - diffusion

KW - nichtmetallische Einschlüsse

KW - SiO2

KW - Draht

KW - Stahlcord

KW - Konfokalmikroskop

KW - Auflösung

KW - Schlacken

KW - Auflösungsmechanismus

M3 - Master's Thesis

ER -