Dear all, I used oxford EBSD detector to do a test of ferrite-pearlite. I couldn't help but notice that the band contrast of same phase (BCC iron) from different grains are clearly different. I know that different phases may have different grey levels of BC map, and this character is often used to distinguish ferrite and martensite. But why the adjacent ferrite grains have different grey levels?
It is because there is different orientation and different bands visible in the detector, and/or different orientations react differently to polishing or, in general, to sample prep. During sample prep some orientations could produce different fine-scale topography.,
Grzegorz Cios
Thanks for your reply. If orientation does have an impact on grey level, why it is possible to distinguish ferrite and martensite via BC map? I am a little bit of confused.
This is only true for the specific cases of dual-phase steels. It is well tested for it and so on. Martensite in dual-phase steels will deliver much worse BC than ferrite. In the best case, martensite and ferrite have two separate distributions of BC. Take a look at these papers:
Article Differentiating Ferrite and Martensite in Steel Microstructu...
Article Phase Analysis on Dual-Phase Steel Using Band Slope of Elect...
In your case, you showed us two ferrite grains. There will be ferrite grain BC distribution, lets say, around the value of 150 of BC with some spread related to different orientations and there will be another peak in BC distribution related to martensite at, let's say 90. Martensite in dual-phase steels has lower BC because the martensitic transformation is quite "violent" and there are more defects that are blurring the pattern.
Adding to the answer of Grzegorz Cios , the EBSD software also usually adapts the colorscale limits of the map to the min and max values, or something. This means if you only have ferrrite, the difference between individual ferrite grains will be easier to see. If there is also martensite, the colorscale limtis are probably wider and will make the difference between ferrite grains less clear.
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