How to distinguish ferrite and bainite with KAM

[Mikewangkang]

hello @AzdiarGazder
I need help with a Matlab® code developed that uses the MTEX toolbox to first define grain boundaries based on selected grain tolerance angles and then calculate the KAM for each pixel. If the misorientation of a pixel exceeds 3°, the program classifies the grains as granular bainite; otherwise, it is classified as polygonal ferrite. The classification algorithm then color-codes the relative sorted grains it determines and calculates the measured granular bainite and polygonal fractions. This is my purpose, I have proceeded to calculate the kam value of each pixel but the follow-up process I don't know how to do.
I would be very grateful if anyone could help!
Wang Kang

[AzdiarGazder]

Hi @Mikewangkang,

There are various methods used to classify and segment ferrite constituents. I am providing 2 examples as follows:

1. One method, which I developed, can be found here.
2. Another method, developed by Sachin Shrestha, can be found here.

You can apply my method by going through the various steps listed in the paper.
Alternatively, I have modified Sachin's method to work within MTEX.
The demonstration script can be found here.

I'd like to highlight a few important points here:
(a) Based on the information you've provided, you seem to suggest that 1 criterion (like KAM) is enough to segment between constituents. However, modern segmentation methods, like the two I've shown above, use multiple criteria to separate between the constituents. Using only 1 criterion is simply not enough to accurately (and consistently) segment between constituents.

(b) A criterion like KAM is a pixel-based criterion. When segmenting constituents, it is advisable to use grain-based criteria like GAM and GOS. This enables cleaner and easier segmentation.

(c) Depending on the thermo-mechanical history of each individual microstructure (and consequently, the map data), the thresholds should be adjusted/changed to accurately (and consistently) segment between constituents. Using 1 threshold value across all microstructures and maps is again simply not correct.

Lastly, if you'd like me to help you with your script, please upload it so that I can have a look.

Hope this helps.

Warm regards,
Azdi

[Mikewangkang]

Dear Professor Azdi,
Thank you very much for your reply, I will study your method well.
Best wishes,
wang kang

[Mikewangkang]

Dear Professor Azdi,
The following is my script. I can calculate the kam diagram, but then I don’t know how to write the script to realize that the kam value greater than 3° is defined as grain shell and others are classified as polygonal ferrite. Can you help me?

%% Import Script for EBSD Data
%
% This script was automatically created by the import wizard. You should
% run the whoole script or parts of it in order to import your data. There
% is no problem in making any changes to this script.

%% Specify Crystal and Specimen Symmetries

% crystal symmetry
CS = {... 
  'notIndexed',...
  crystalSymmetry('m-3m', [2.9 2.9 2.9], 'mineral', 'Iron bcc (old)', 'color', [0.53 0.81 0.98]),...
  crystalSymmetry('m-3m', [3.7 3.7 3.7], 'mineral', 'Iron fcc', 'color', [0.56 0.74 0.56])};

% plotting convention
setMTEXpref('xAxisDirection','east');
setMTEXpref('zAxisDirection','intoPlane');

%% Specify File Names

% path to files
pname = 'D:\桌面\晶体塑性模拟\B钢\B钢EBSD\B750';

% which files to be imported
fname = [pname '\B750-1.crc'];

%% Import the Data

% create an EBSD variable containing the data
ebsd = EBSD.load(fname,CS,'interface','crc',...
  'convertEuler2SpatialReferenceFrame');

% The second parameter that is involved in grain reconstruction is the threshold misorientation angle indicating a grain boundary.
grains = calcGrains(ebsd,'angle',5*degree)

[grains,ebsd.grainId] = calcGrains(ebsd('indexed'));

% remove one-three pixel grains
ebsd(grains(grains.grainSize <= 3)) = [];
[grains,ebsd.grainId] = calcGrains(ebsd('indexed'));

grains = smooth(grains,5);

plot(ebsd('indexed'),ebsd('indexed').orientations)
hold on
plot(grains.boundary,'lineWidth',1.5)
hold off

ebsd = ebsd.gridify;

kam = ebsd.KAM / degree;

% lets plot it
plot(ebsd,kam,'micronbar','off')
caxis([0,15])
mtexColorbar
mtexColorMap LaboTeX
hold on
plot(grains.boundary,'lineWidth',1.5)
hold off

% chose a denoising filter
F = halfQuadraticFilter;
F.alpha = 0.5;

% denoise the orientation map
ebsdS = smooth(ebsd,F,'fill',grains);

% plot the first order KAM
plot(ebsdS,ebsdS.KAM('threshold',2.5*degree) ./ degree,'micronbar','off')
caxis([0,5])
mtexColorbar
mtexColorMap LaboTeX
hold on
plot(grains.boundary,'lineWidth',1.5)
hold off

Best wishes,
wang kang