Defectos de Inclusiones en Fundicion

Continuous Casting Course Inclusions Prof. Brian G. Thomas

Inclusions in Steel Castings


Importance of Inclusions

On Mechanical Properties Fatigue Strength Drawability

On Surface Condition Visible defects Individual particles, line defects, patches


Defects in Final Steel ProductSurface delamination

Slivers

Blisters


Cleanliness and Fatigue Life

Bearing steel


Inclusion size and associated defect

A. Cramb, 1999


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


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)


Argon bubbles catch inclusions


Fluid Flow Validation behind a Rigid Sphere in Water

1.5mm diameter rigid particle in water

Water photo,Clift et al, 1975


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


Effect of Turbulence on Inclusion Trajectories around a 5 mm Bubble

Non-Stochastic Stochastic


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


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


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.


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


Exogenous Inclusions Defects on the Surface of Foundry Product

http://neon.mems.cmu.edu/afs/afs2/window2.html


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


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


Exogenous Inclusions from Refractory

R. Dekkers, et al., ISSTech2003 Conference Proceedings, ISS, Warrandale, PA, 2003, 197-209.


Sand Buildup on Ladle Well Nozzle



SEN Nozzle Clogging


F. Fuhr, et al., "ISSTech2003 Conference Proceedings, ISS, Warrandale, PA, 2003, 165-175.


Entrapped Nozzle Sand

light gray phase: chromite; dark gray phase: silica.


Refractory Type Inclusions

Spinel : Al2O3 75% - MgO 25%

Al2O3 50% - CaO 40% - SiO2 10%


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


Mg-Al Oxide Precipitation

409

ReactionZone

Nitride

Oxide

Ti N

Al Mg O

TiN

MgAl2O4

CaO-SiO2-Al2O3

MnO-SiO2-Al2O3


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


Sources of Inclusions

Deoxidation products Reoxidation (especially from air exposure) Slag carryover Slag entrainment Refractory erosion Nozzle clogs (which break off)


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


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


Importance of Stream Condition

Rough Jet causes:

air entrainmentreoxidation

surface turbulencelevel fluctuationssurface defects

Sommerville and McKeogh, 2nd PTD Conf Proc., ISS, 1981, pp256-268


Slag carryover

Stop steel flow before slag enters next vessel (use slag detection)

Avoid vortexing keep level above critical minimum use vortex inhibitors


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


Surface Entrainment of Slag

Worse with Higher speed surface flow Thicker flux layers Lower flux viscosity Lower interfacial tension


Slag Entrainment mechanism

A. Cramb


Refractory Erosion

Solid particles: loose sand Vessel liners

Thermodynamic attack if slag composition not compatible with

refractory


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


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)


How does calcium treatment work?

Phase equilibria in steelmaking oxides


Control composition to liquify inclusions


Sources of different inclusion sizes

A. Cramb, 1999



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


Inclusion Defects in Foundry Castings


Inclusion defects in foundry castings: bubble plumes


Defectos de Inclusiones en Fundicion

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