msepostdoc-list FW: REMINDER - SEMINAR NOTICE - J. Busch, Mon. 8/27, 2:30 PM, ARMS 3115

[Stacey, Lisa A]

MATERIALS SCIENCE AND ENGINEERING
SEMINAR



Flux Entrapment and Titanium Nitride Defects During Electroslag Remelting

by

Jonathan D. Busch
Masters of Science Final Exam
Advisor:  Prof. M. Krane


ABSTRACT


Electroslag remelted (ESR) ingots of INCOLOY alloys 800 and 825 are particularly prone to macroscale slag inclusions and microscale cleanliness issues.  Formation of these structures near the ingot surface can cause significant production yield losses (~10%) due to the necessity of extensive surface grinding.  Slag inclusions from near the outer radius of the toe end of alloy 800 and 825 ingots were found to be approximately 1 to 3mm in size and have a multiphase microstructure consisting of CaF2, CaTiO3, MgAl2O4, MgO and some combination of Ca12Al14O32F2 and/or Ca12Al14O33.  These inclusions were often surrounded by fields of 1 to 10μm cuboidal TiN particles. A large number of TiN cuboids were observed in the ESR electrode with similar size and morphology to those observed surrounding slag inclusions in the ESR ingots, suggesting that the TiN particles are relics from ESR electrode production process.  Samples taken sequentially throughout the EAF-AOD processes showed that the TiN cuboidals that are found in ESR ingots form between tapping the AOD vessel into the AOD ladle and the casting of ESR electrodes.



Analysis of slag skin at various heights of alloy 825 ingots revealed that the phase fraction of CaF2 decreased, TiCaO3 increased and Ca12Al14O32F2 increased from toe to head.  The increase in TiO2 content suggests that at most a two-fold increase in viscosity would be expected.  Similar analysis of alloy 800 ingots did not reveal significant trends in slag skin composition, possibly due to differences in ingot geometry or the presence of Al toe additions during the remelting of alloy 800.  Directional solidification experiments were conducted to determine the solidification sequences of two common ESR slags: Code 316 (33% CaF2, 33% CaO, and 33% Al2O3) and Code 59 (50% CaF2, 20% CaO, 22% Al2O3, 5% MgO, and 3% TiO2).  In both cases the changes in slag phase fraction as a function of solidification time were not as significant as predicted.  This suggests substantial solute concentrations within each phase, significant gas phase reactions or insufficient imposed temperature gradient for directional planer solidification.OM and SEM analysis revealed a dendriti structure with Ca12Al14O32F2 as the primary phase.  EDS analysis showed that Al segregates to the primary phase while F segregates to the interdendritic region.  Parametric studies using a numerical model of ESR suggests that the ESR process is quite sensitive to changes in slag electrical conductivity and not very sensitive to changes in slag viscosity.


Date:         Monday, August 27, 2012

Time:      2:30 P.M.
Place:        ARMS 3115



Lisa Stacey
Secretary/Development Assistant
Purdue University
School of Materials Engineering
765/494-4100

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