meuharris wrote:
I got a garden knife some years (10?) ago and it was the sharpest I
had ever used -like cut glass. .
It was serrated and it would cut through small branches like butter
(we used them for pruning young trees)
The downside was it was really brittle and if you were tempted to
push it instead of drawing it towards you it would snap.
Would that have been a carbon steel blade?
Where could I order them from (I don't seem to have much joy in
googling *carbon steel blade* so maybe it is some other manufacturing
method.....

What you had was probably a pruning saw. Sharpened to cut on the pull stroke
rather than the push stroke like a conventional saw has two advantages. You
can use it more easily in confined spaces and when it's working the blade is
in tension rather than compression so it can be harder and more brittle
because it'll be less likely to bend and break. That means it can take a
longer lasting edge. The disadvantage is you can't put as much down force
into the cut as you can when pushing a saw.

Brittleness in steel is mainly a function of the hardness rather than the
carbon content. A blade heat treated to very high hardness levels will hold
an edge for longer but snap easily. A softer blade will blunt quickly but be
easier to resharpen. The trick is getting the balance right. If it was plain
carbon steel it would have rusted quickly after outdoor use and if it was
stainless steel it wouldn't. That might tell you more about what it was made
from. Spring steel, about the most elastic steel you can make is actually
just a plain carbon steel heat treated and then tempered back to reduce the
hardness.
--
Dave Baker