1. Korkealämpötilaprosessit
Pyrometallurgiset jalostusprosessit
Lisäaineisto sulkeumien analysoinnista

2. Inclusion analyses
Many inclusions are not found until they cause problems in the final product
Reclamations
Challenges in inclusion analyses
Huge amounts of produced steel vs. small samples
Representativity of samples?
Large (=harmful) inclusions are very rare
Huge amount of inclusions
Does average values tell anything?
Different methods measure/analyze different things
Size, composition, etc.
”Complete” size distribution not obtained using only one method
Some methods are time-consuming
Not fast enough for process control
Some methods do not give 3D-view on inclusions
Online or offline correction

3. Inclusion analyses: Sampling
Samples from different process stages
Lollipop samples from molten steel (BOF, ladle, CC)
Metal cap protection (MCP) or Argon protection (AP) in order to get slag-free samples
Sample pieces from solid steel (slab, plate, sheet)
Samples should be
homogeneous
representative
Sample cooling rate has an effect on inclusions
Secondary inclusions = Inclusions formed after sampling
Fast cooling - small secondary inclusions
Slow cooling - heterogeneous nucleation and inclusion growth

4. Inclusion analyses: Sampling

5. Inclusion analyses: Analysis methods
On-line
OES-PDA (Optical emission spectrometry with pulse discrimination analysis)
LA-ICP-MS (Laser ablation, Inductively coupled plasma source - mass spectrometry)
Off-line
LOM (Light optical microscopy)
SEM (Scanning electron microscopy)
EPMA (Electron probe microanalysis)
EE (Electrolytic extraction)
EE+CCA (Coulter Counter analysis)
EE+SPOS (Single Particle Optical Sensing)
Ultrasonic scanning
LSHR+US
+ Indirect inclusion analysis: Total oxygen content of steel

6. Inclusion analyses: Analysis methods

7. Inclusion analyses: Analysis methods

8. Inclusion analyses: Analysis methods

9. Inclusion analyses: Why 3D methods are needed if they are more expensive and time-consuming?
Small inclusions are not detected from 2D samples due to interference of steel matrix
Shape and real size of inclusions cannot be detected from 2D samples

10. Inclusion analyses: Total oxygen content (Indirect measurement)
Amount of dissolved oxygen is very low in (Al-)killed steel (2...5 ppm)
Variations in total oxygen content are due to variations in amount of inclusions
Measurement of total oxygen content is an indirect method to estimate the amount of inclusions in steel
Correlations between Otot and inclusion-related problems have been reported
Not accurate, but fast and cheap in comparison to actual inclusion analysis methods

11. Inclusion analyses: Microscopy
Magnification of polished sections of samples
Different methods:
Light Optical Microscopy (LOM), Metallographic Microscope Observation (MMO)
Visible light, resolution approximately 200 nm
(Field Emission) Scanning Electron Microscope (FESEM)
Electrons, resolution approximately 1 nm
Back scattered electrons are used to analyze composition
Secondary elecgtrons are used to create an image
Limitations for samples
Electric conductivity
No volatiles
Must endure vacuum
Image from back scattered electrons
Image from secondary electrons

12. Inclusion analyses: Microscopy
Chemical composition analysis with Electron Probe Micro Analyzer (EPMA)
Associated with SEM
Measurement on of either energy or wavelength
Energy-Dispersive X-Ray Spectroscopy (EDS)
Wavelength Dispersive X-Ray Spectroscopy (WDS)
Small volume is being analyzed (< m3)
Depends on the accelerating voltage being used
Approximately same size as inclusions being analyzed
One analysis may contain elements from more than one phase (and from steel matrix)
Automatic Image Analysis (IA) is used to study ”larger” areas to improve representativity
Based on differences in lightness/darkness
Scratches etc. may be considered as inclusions

13. Inclusion analyses: Electrolytic extraction
Principle of the method:
Iron is dissolved selectively into a solvent/electrolyte, whereas inclusions remain undissolved
Some solvents may dissolve some inclusions
Inclusions are filtered and may be studied as a whole
The equipment
Steel sample as anode, Pt-ring as cathode
Ions may transport via salt bridge
Potentiostat is used to control the dissolution
Varying current is used to control the dissolution rate
After dissolution:
Inclusions are filtered from the solvent
Membrane filter (hole size e.g. 0.1 m), vacuum pump
Analysis with SEM (amount, size distribution, composition)
Amount and size distribution may be analyzed with:
Single Particle Optical Sensing Method
Coulter Counter Analysis
Sample
Electrolyte
Potentiostat
Inclusions
Reference
electrode
Salt bridge
Electrolyte
Sample
Pt-ring

14. Inclusion analyses: Electrolytic extraction
Restrictions and limitations:
Solvent/electrolyte must be chosen based on what kind of inclusions are studied
e.g. sulphides are dissolved into acids
Sample volume dissolved is very small
Size distribution lacks information about large inclusions
All the particles in the filter are not inclusions
iron precipitate, Pt-particles, KCl from salt bridge, etc.
Inaccuracy of EDS analysis
Inclusions may be smaller than the volume analyzed
Slow method
Ca-Al-Mg-oxide +
CaS
TiN
CaS

15. Inclusion analyses: OES-PDA
Optical Emission Spectrometry (OES)
Atoms on the surface of steel sample are excited with plasma
When atom returns to the ground state, it emits radiation with a spectrum characteristic to each element
Intensity of different wavelengths is determined
Chemical composition of the sample may be determined
Average value from approximately sparks
Equipment must be calibrated for each sample type (e.g. each steel grade)
Optical Emission Spectrometry with Pulse Discrimination Analysis (OES-PDA)
Analysis of inclusions (composition and size distribution) instead of average compositions of dissolved elements
Principle is similar to OES
Exception: Values of each spark is considered separately
Inclusions create high intensitey peaks that could be detected
Fast method (results ready 2-10 minutes from sampling)
No information about morphology
Suitable for small inclusions (< 12 m) only

16. Inclusion analyses: LA-ICP-MS
Laser Ablation Inductively Coupled Plasma Mass Spectrometry
( Ablation = Evaporation material surface )
Material surface is evaporated with a laser pulse
Particles detached from the sample are ionized with plasma (temperature approximately 8000 C)
Investigation of emission spectrums of detached elements
Any solid material is suitable as a sample
No requirements on the sample size (few g is enough)
No preparation
Possible to detect local variations in the composition
Resolution approximately 1 m
Possibility to detect inclusions from steel matrix

17. Inclusion analyses: LA-ICP-MS

18. More information about inclusion analyses
Karasev A: Proc. of the 9th International Conference on Molten Slags, Fluxes and Salts, 2012.
Janis D, Karasev A & Jönsson P: 8th International Conference on Clean Steel, 2012.
Karasev A, Inoue R & Suito H: ISIJ Int. 41(2001)7,757.
Karasev A & Suito H: ISIJ Int. 44(2004)2,364.
Karasev A, Suito H & Inoue R: ISIJ Int. 51(2011)12,2046.
Karasev A & Inoue R: Material transaction (JIM) 50(2009)2,341.
Ericsson O: Doctoral Thesis, KTH, Stockholm, 2010.
Zhang L & Thomas BG: ISIJ Int. 43(2003)3,271.
Dekkers R: Doctoral thesis. Katholieke Universiteit Leuven, 2002.