Too much R. A. was in the matrix of this D2 (SKD 11) cold work tool steel.
A
B
C
Above: sub-zero treated and tempered, no obvious signs of R. A.;
Below(photo E ~ G): Before sub-zero treatment. Said to have been tempered 3 times at ~500C. Too much R. A. (white) exists in the matrix of the steel. The R. A. caused this tooling to swell and the tooling was scrapped prior to production because of its dimensional change. Primary and secondary carbide particles tinted in various colors. R.A. is white or light-yellow. R. A. dissappeared after sub-zero freezing, as shown in the photos above (A~C).
E
These photos are pieces of art work, I hope they feast your eyes. 
F
G
Below (H): Specimen without color etching, only etched in Nital. Both R.A. and carbide are white in color. Color-etching brings better constrast between the 2 phases, making it easier to tell them apart.
H
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