Can't find better words then the Ted Tenold's ones to describe the following pictures that shows the grouped martensite called "Nie" in japanese swords :
quote...
Nie is basically "spheroidal martensite" which are clumps of martensitic growth propogated by long high heat and maintained in a rapid agressive quench.
...unquote.
pictures by Keith Larman (
http://moderntosho.com ) :
close-close-close up :
