First off check the edge under magnification and determine the cause of blunting. It will be by either; fracture, deformation, or wear. It can also be by corrosion or hot hardness issues but these are not likely in this situation.
If the problem is deformation (not enough hardness) then you should see stress lines in the edge parallel to the edge as well as a lot of straight on rippling. Check the edge straight on as well as to the side. Edges which are too soft will actually be rippled and you can see them take an "s" shape if you look straight down. The edge will look like :
\/\/\/\/\/
instead of :
------------
If the edge has fractured (not enough impact toughness and ductility) the ripples will be much smaller and usually nonexistant, what you will see is very sharp notches in the edge when viewed side on. If you don't see either of these effects then the primary cause of blunting is just wear.
Before you switch to a new steel you can try raising the hardness on M2 (depending on how it is blunting, if you are seeing fracture this obviously isn't a good idea), including a cryo soak after the quench and before the tempering (mainly for wear resitance), as well as modifications to the geometry.
If the edge damage doesn't extend past the secondary bevel then the primary bevel can be lowered further, this will actu to increase the cutting ability and thus lower the various stresses on the edge.
If the edge is getting damaged then you can try adding a very slight microbevel which is more obtuse, it only needs to be of a depth to negate the damage, which can be as small as microns which means just 1-3 passes on the sharpening abrasive.
As for other steels, it is likely at that speed and cutting that media that the blade is getting very hot so you are constrained to the high speed steels. To advance in wear resistance you have a lot of options up to CPM REX 121 which offers significant more wear resistance (about twice) and can be hardened to 70+HRC, and has a much higher red hardness, however the toughness is significantly less than M2.
As a sort of trivial upgrade, CPM M4 REX offers better wear, toughness and red hardness so it would be worth looking into directly. CPM REX M35 does similar but offers better hot hardness improvement.
So in short :
1) inspect the edge under magnification side on and straight down and determine the nature of the blunting
2) consider altering the heat treatment and/or geometry
3) switch to a steel which has improvement in the critical area (hardness, toughness, wear resistance or hot hardness).
Of course as well I would really critically look at the finished edge under magnifiction to inspect the quality of sharpening you may see benefits from altering the sharpening method or abrasive.
-Cliff
