Hand plane blade problems.

[Alexandros]

My setup is a T4 with the SG200 and the 2 Japanese Sun Tiger Wheels 800 and 4000 grit.

I am successful in getting most my gouges, chisels and plane blades having sharp. I use the SVS 36 for all since is the only relevant jig I have.

However I came across 2 blades (both of them vintage blades bought in Germany) that I have failed (using the svs36). The burr was extremely hard to get rid of and when I did succeed to bring it to a really good cutting shape (not hair popping sharp as I like), after very few passes on a soft fur I see the edge getting damaged A LOT.
 
Any ideas? I would blame the steel but I am not that experienced and confident to do so.

[John Hancock Sr]

It sounds to me like the old irons have lost their temper. If the steel is too soft then the burr will be difficult to remove.