Abstract No. 46
Study of element segregation in steel
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Ann De Vyt, Chris Xhoffer and Jan Scheers
ArcelorMittal Global R&D Gent (Belgium)
Modern types of high strength steel typically contain a lot of Mn and C. These
elements, among others, are known to segregate strongly during solidification.
This enriched area cannot be removed once it is present. After rolling, bands
of segregation occur. These bands are not just bands with different
compositions but also with different microstructures. As such, the mechanical
properties vary within the steel. Therefore it is necessary to study the extent of
this segregation analytically.
Studying segregation zones requires a combination of sensitivity and lateral
resolution. Depending on the techniques used, either one or the other, or both
can be achieved.
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When segregation occurs near the surface and parallel to it, GDOES is a fast
and sensitive technique that allows local analysis due to its excellent depth
resolution.
With Laser Ablation ICP-MS a line scan studying various elements can be
acquired across a section of the sample. ICP-MS also gives excellent
sensitivity but its lateral resolution may be insufficient.
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EPMA and TOF-SIMS combine sensitivity and lateral resolution and provide
similar results with an advantage for SIMS regarding the elements in low
concentration.
Figure 1: After Nital etching of HSLA steels, segregation bands are often
observed. Their presence indicates a heterogeneous distribution of
specific elements at micro scale. TOF-SIMS elemental maps and line
scans across segregation bands (dim.: 300x300μm).
Abstract No. 46
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Various examples will be given showing the advantages of the used
techniques, compared to each other.
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Study of element segregation in steel
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CETAS 2015
Session 12
Micro and nano scale characterization
• Segregation in materials refers to the enrichment of a material
constituent at a free surface or an internal interface of a
material
• In steel it can be an enrichment or a depletion of certain
elements in the central line, at grain boundaries or at the
surface
• It influences the mechanical properties of the steel
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Definition
¾ How can we study it?
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Element segregation
• EPMA linescan
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Element segregation
• Centre line segregation
• Some elements are known to segregate strongly during
solidification
• This enriched area cannot be removed once present.
• After rolling, bands of segregation occur.
• These bands are not just bands with different compositions but
also with different microstructures.
¾The mechanical properties vary within the
steel.
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Decarburization
• Carbon present at the surface of steel reacts with oxygen
containing species forming CO at high temperatures
• Surface concentration of carbon decreases
• Can be beneficial or detrimental depending on the application of
the steel
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1 mm
• EPMA and TOF-SIMS
C
Si
Mn
1 mm
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Element segregation
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300µm
¾Need to know
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Surface hardening
• Various techniques to analyze N
• EPMA versus hardness
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Decarburization
• Metallography combined with
• GDOES depth profiling before and after annealing
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Surface hardening
• LIBS
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Intensités N normalisées
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• SIMS
1,00E+04
9,00E+03
8,00E+03
Top
7,00E+03
Bottom
6,00E+03
5,00E+03
4,00E+03
3/4
3,00E+03
1/4
2,00E+03
1,00E+03
0,00E+00
1/2
0
200
Distance
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Surface hardening
400
600
800
9
1000
8
1200
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Local enrichments
• EPMA gives combination of sensitivity and lateral resolution
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• GDOES
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Surface hardening
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Fe4N needles
Grain Boundaries rich in N
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Inclusion analysis
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Inclusion analysis
• Local enrichments can lead to particles
• Fracture risks
• Centre fracture visible
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• SEM-EDX particle analysis
• Performed at ¼ thickness and ½ thickness
¾Potential cause of fracture
¾Search for inter laboratory cross check
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Conclusions
ƒ To study variations in the local element concentration several
requirements are needed for the technique used:
• Good sensitivity
• Good lateral resolution
• Good depth resolution
ƒ Examples were shown, proving that many techniques can be
used
• For sensitive surface analysis GDOES seems a good
solution
• SIMS gives a reasonable combination of sensitivity and
lateral resolution
• For optimal resolution EM and EPMA are preferred
ƒ Inter laboratory tests are very welcome.
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30/03/2012
Chris Xhoffer
Cynthia Roegiers
Dimitri Monteyne
Henrique Duarte Alvarenga
LIST
TASCON
Applied Spectra
¾For the scientific stuff
All of you
¾For you attention
Confidential - ArcelorMittal Global Research and Development Gent
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