Post on 23-Nov-2015
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Inclusions in Steel Castings
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Importance of Inclusions
On Mechanical Properties Fatigue Strength Drawability
On Surface Condition Visible defects Individual particles, line defects, patches
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Defects in Final Steel ProductSurface delamination
Slivers
Blisters
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Cleanliness and Fatigue Life
Bearing steel
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Inclusion size and associated defect
A. Cramb, 1999
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Inclusion Morphologies
Globularliquid in solid steel
(Slag)
Dendriticoxygen rich environment(eg. short time after Al
addition or reox.)
Clusterlong time
(less oxygen, many collisions)
(a)
1000
(b)
1000
400m
2D
3D
10m
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Al2O3 Inclusion Morphology - SEM
Dendriticshort time after Al addition (oxygen rich environment)
Coral Shapelong time
1. (less oxygen, many collisions)2. (Ostwald ripening of dendritic)
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Argon bubbles catch inclusions
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Fluid Flow Validation behind a Rigid Sphere in Water
1.5mm diameter rigid particle in water
Water photo,Clift et al, 1975
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Attachment Probability: Steps in Inclusion attachment to Bubble
Attachment probability, PC
columninparticlesattachedparticlesPC #
#=
Particle trajectory through molten steel
2. Sliding (time for film drainage)1. Collision / oscillation
3. Stable attachment
RisingBubble
Inclusions
Burty et al, 1993
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Effect of Turbulence on Inclusion Trajectories around a 5 mm Bubble
Non-Stochastic Stochastic
Continuous Casting Course Inclusions Prof. Brian G. Thomas
0.20.40.60.81.01.21.41.61.82.0
0.0 0.5 1.0 1.5 2.0Attachment probability (%)
Dis
tanc
e fro
m th
e ai
xs /
d B
Effect of Turbulence on the Attachment of Inclusion to Bubble
Stochastic model: collision diameter 4mm, 16.5% attachment in totalNon-Stochastic model: collision diameter 0.34mm,11.6% attachment in total
50m inclusions to 1 mm bubble, k
Continuous Casting Course Inclusions Prof. Brian G. Thomas
0 20 40 60 80 100 120 14010-6
10-4
10-2
100
102
104 Bubble size 1mm 2mm 5mm 10mm
Num
ber o
f inc
lusi
ons
atta
ched
on
a bu
bble
Inclusion diameter (m)
How Many Inclusions Attached to a Bubble?
Measurements, Kiriha et al, ISIJ, 2004
Increases with larger bubbles and smaller particles
Photos, Zhang et al, 2004
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Defects in Steel
Inclusion Sliver
Pencil blister SliverR. Gass, et al., ISSTech2003 Conference Proceedings, ISS, Warrandale, PA, 2003, 3-18.
H. Yin and H.T. Tsai, ISSTech2003 Conference Proceedings, ISS, Warrandale, PA, 2003, 217-226.
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Defects in Steel
P. Rocabois, et al, ISSTech2003 Conference Proceedings, ISS, Warrandale, PA, 2003, 995-1006.
Pencil pipe inclusions from refractory
Sliver from mold slag inclusions
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Exogenous Inclusions Defects on the Surface of Foundry Product
http://neon.mems.cmu.edu/afs/afs2/window2.html
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Indigenous Inclusions
- Deoxidation products, normally < 50m, but possibly > 50m if clustered;
- Precipitated inclusions during cooling/solidification process of steel, normally with small sizes.
10m
Dendritic aluminaRefs: L. Zhang, B. Thomas. ISIJ, No.3, 2003
Ref.: Ravi Rastogi and Alan Cramb, Personal communication, 2002,
Alumina cluster
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Exogenous Inclusions- Reoxidation products, by
- FeO, MnO, SiO2 and other oxides in the slag and refractory linings
- Exposure to the atmosphere;
- Slag entrapment (of interest)- Other sources (of interest):
- well block sand- loose dirt- broken refractory brickwork - ceramic lining particles.
- Chemical reactions (Ca treatment)
Emulsification of slag
Erosion/Reoxidation
http://neon.mems.cmu.edu/afs/afs2/window2.html
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Exogenous Inclusions from Refractory
R. Dekkers, et al., ISSTech2003 Conference Proceedings, ISS, Warrandale, PA, 2003, 197-209.
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Sand Buildup on Ladle Well Nozzle
H. Yin and H.T. Tsai, ISSTech2003 Conference Proceedings, ISS, Warrandale, PA, 2003, 217-226.
Continuous Casting Course Inclusions Prof. Brian G. Thomas
SEN Nozzle Clogging
H. Yin and H.T. Tsai, ISSTech2003 Conference Proceedings, ISS, Warrandale, PA, 2003, 217-226.
F. Fuhr, et al., "ISSTech2003 Conference Proceedings, ISS, Warrandale, PA, 2003, 165-175.
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Entrapped Nozzle Sand
light gray phase: chromite; dark gray phase: silica.
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Refractory Type Inclusions
Spinel : Al2O3 75% - MgO 25%
Al2O3 50% - CaO 40% - SiO2 10%
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Inclusions A. Cramb studies
Inclusions in Aluminum Killed Steel
3 Microns 10 Microns
Sample Crossection - aluminum killed 1006
MnS nucleated from alumina
Alumina before etching
Alumina from Deoxidation after etching sample
Alumina by Deoxidation after etching sample
Alumina Deoxidation Inclusions
alumina
Levitated / Deoxidized Steel Droplet
100 microns
Levitated / Deoxidized Steel - Extracted Inclusions
100 microns
Levitated / Deoxidized Steel - Extracted Inclusions
10 microns
TiN precipitated from alumina in a clog
TiN in Tisulc grade
Continuous Casting Course Inclusions Prof. Brian G. ThomasTwin Growth
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Mg-Al Oxide Precipitation
409
ReactionZone
Nitride
Oxide
Ti N
Al Mg O
TiN
MgAl2O4
CaO-SiO2-Al2O3
MnO-SiO2-Al2O3
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Inclusion Chemistry
Manganese Silicate Mn-Si killed steel - deox or re-ox
Manganese Alumino Silicate Mn-Si killed steel containing less than 0.005 Al Deox or reox
Alumina Deox or reox of steel containg more than 0.005
Al
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Sources of Inclusions
Deoxidation products Reoxidation (especially from air exposure) Slag carryover Slag entrainment Refractory erosion Nozzle clogs (which break off)
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Deoxidation products
Form as solubility limits are exceeded Alumina Manganese silicate Iron oxide Manganese oxide Iron sulphide Manganese sulphide
Small initial size (0.5 - 20 microns) Multi-layer composition as conditions evolve
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Reoxidation
Every exposure of steel to air generates large dendritic inclusions
Avoid air exposure by: Free-open ladles Avoid excessive stirring in ladle Maintain optimized slag coverage Shroud Stream control (open pour) No leaks (good seals; preheat refractories to avoid
cracking
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Importance of Stream Condition
Rough Jet causes:
air entrainmentreoxidation
surface turbulencelevel fluctuationssurface defects
Sommerville and McKeogh, 2nd PTD Conf Proc., ISS, 1981, pp256-268
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Slag carryover
Stop steel flow before slag enters next vessel (use slag detection)
Avoid vortexing keep level above critical minimum use vortex inhibitors
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Slag Entrainment
Large globules: 20-1000 microns (1 mm) Identified by composition:
(furnace,ladle, tundish, or mold slag) Causes
Shear from fast surface flows Vortexing (near end of vessel drainage) Stream impact (open pouring) Surface turbulence poor level control)
During drainage,
At corners in a complex flow pattern
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Surface Entrainment of Slag
Worse with Higher speed surface flow Thicker flux layers Lower flux viscosity Lower interfacial tension
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Slag Entrainment mechanism
A. Cramb
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Refractory Erosion
Solid particles: loose sand Vessel liners
Thermodynamic attack if slag composition not compatible with
refractory
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Inclusion detection
Total oxygen content (alumina) Microscope examination Slime extraction Ultrasonic evaluation of solid cone-shaped
speciman (Timken) Online inclusion sensors in liquid steel Surface defects in final product
Large inclusions worst - total O2 is misleading
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Clean Steel Practices
Control slag chemistry Prevent reoxidation (avoid air exposure: slag
cover / submerged nozzles / argon) Stable refractories Inclusion modification (eg. Ca treatment) Optimize flow
argon stirring in ladle, tundish impact pads, dams, and weirs Mold tundish streams (billet) and SEN (slabs)
Continuous Casting Course Inclusions Prof. Brian G. Thomas
How does calcium treatment work?
Phase equilibria in steelmaking oxides
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Control composition to liquify inclusions
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Sources of different inclusion sizes
A. Cramb, 1999
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Inclusion Defects in Continuous Casting of Steel
Inclusion defects from:- nozzle clogging- air entrainment- entering nozzle from upstream- mold slag entrainment
- Level fluctuations
- Surface hook formation
Water
Spray
Molten Steel Pool
Solidifying Steel Shell
Flux Rim
Submerged Entry Nozzle
Support Roll
Roll Contact
Ferrostatic Pressure
Bulging
Roll
Nozzle
Nozzle
copper mold
Liquid Flux
Air Gap
Flux Powder
jet
nozzle portargon
bubbles
Inclusion particles and bubbles
Resolidified Flux
Contact Resistances
Oscillation Mark
entrainment
CL
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Inclusion Defects in Foundry Castings
Continuous Casting Course Inclusions Prof. Brian G. Thomas
Inclusion defects in foundry castings: bubble plumes
Continuous Casting Course Inclusions Prof. Brian G. Thomas