Title page for ETD etd-11262009-192807


Document Type Master's Dissertation
Author Ndiabintu, Mukadi Jean-Jacques
Email jeanjacquesmukadi@yahoo.fr
URN etd-11262009-192807
Document Title Effect of mould flux on scale adhesion to reheated stainless steel slabs
Degree MSc
Department Materials Science and Metallurgical Engineering
Supervisor
Advisor Name Title
Prof P C Pistorius Supervisor
Keywords
  • scale
  • chromite
  • tendrils of nickel-rich filigree
  • austenite grain boundaries
  • interfacial morphology
  • free oxygen
  • stainless steel
  • mould flux
  • reheating
  • hydraulic descaling
  • internal oxidation
Date 2009-09-02
Availability unrestricted
Abstract
Effects of mould flux contaminant on scale-steel adhesion and hydraulic descaling of scale formed on slabs were investigated. In this investigation, stainless steel type 304 (austenitic with 18% Cr and 8% Ni) and specific mould fluxes were used when growing the scale on contaminated samples under simulated industrial reheating conditions, with subsequent high pressure water hydraulic descaling.

The basic hypothesis was that the steel-scale adhesion depends on the microstructure of different phases present in the scale, the segregation of specific elements at the interface and the interfacial morphology of the scale after reheating.

It was found that mould flux contaminant decreases scale-steel adhesion and therefore improved the descaling effectiveness significantly compared to non contaminated stainless steel.

The descaling effectiveness of contaminated and uncontaminated slab was dependent to the presence of metal free paths (chromite layers along the austenite grains boundaries) and the presence of unoxidized metal in the scale due to nickel enrichment at the interface.

Compared to the uncontaminated samples, the descaling of contaminated samples was efficient which could be due to the fact that some mechanisms which increase scale– steel adhesion (notably nickel enrichment at the interface) were considerably reduced.

For all contaminated samples, the descaling effectiveness after visual observation were close to 100% and it was found that mould flux type 832 ( low basicity) gave a high descaling efficiency with better steel surface quality after descaling compared to mould fluxes type 810 and RF1.

© 2008, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Please cite as follows:

Ndiabintu, Mukadi, J-J 2008, Effect of mould flux on scale adhesion to reheated stainless steel slabs, MSc dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-11262009-192807/ >

E1466/ag

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