I want to share my experience with Rex 45 so far
I feel the best way is to compare it to CPM M4 which is a steel we are all familiar with and gets compared often to Hap40/Rex 45
First testing is sharpening to a high sharpeness freehand on benchstones and comparing small differences in the edge quality and other characteristics.
Using a 1000 grit CBN waterstone the factory bevel scratches where removed and the knives where fully Apexed and deburred off the stone.
Some quick notes on testing.
-Bigger burrs were made then I usually do in order to clean out the deep factory grind lines.
-1000 grit was chosen since it highlights the best comprise between toothy bite and polished precision.
-both blades were new and unsharpened by me before I tested.
Before sharpening I noticed the factory edge on Rex 45 had less aggression at the edge then the M4. It was Sharp but had less bite when gently sliding my finger pads down the edge.
Rex45 grinds very easy on the stones and wants to polish well. The M4 was also good in this regard and noticed the M4 was softer because the stone had more "grip" on the bevel then the rex45. I could feel more cutting on the M4.
Both had a stubborn burr that had to be feathered off on a worn scotchbrite pad after being weakened and reduced on the CBN stone. For M4 this is common if you create a larger burr (of course the burr isn't truely stubborn like 8cr13mov but it's noticable when compared to the top steels) as for Rex 45 I'll need more Sharpening on REX 45 to confirm if this is the norm since it was the first sharpening from the factory which always has a little overheated metal to remove by hand Sharpening and because I made a larger burr then normal. Neither of these steels deburr as good as Cruwear.
The edges were both sharp and crisp off the stone, the REX 45 was noticably less aggressive. It took a very keen edge but had less bite compared to the M4. This tells me that more of the carbides in the REX 45 are finer then M4 and used to promote the higher hardness by strengthening the grains of the matrix.
However in M4, I feel its more aggressive due to larger carbides with more volume just hanging out and promoting more wear resistance and edge aggression over stability and keeness but we'll have to test more to see.
Both edges were treetoping sharp and would catch free hanging hairs immediately after 1um diamond stroping.
The M4 had more "grab" yet the REX 45 seemed keener.
At 0.5 um diamond that magic happened for Rex45, feathered the hair like a boss and took a nice polish at the bevel from the strop.
The M4 could not feather after 0.5um the M4 was just too aggressive and kepted popping the hairs rather then curling it into a ribbon desipte going back several times.
M4 needed those carbides smoothed out more so I jumped to 0.25um diamond to feather.
Rex 45 at 0.25um very very keen, I was able to whittle a hair into a little Christmas tree.
So far, I'd say people will enjoy the properties of Rex 45, while M4 prefers a more toothy finish Rex 45 will prefer the opposite which is unique amongst Crucible steels let alone US steels. It's interesting to a US steel closer to the properties of a japanese steel which have more of a bias toward Polished edges.
I'm going to do a rope cut test next when I get time, before I got to try the knives I was guessing Rex45 would out cut M4 on rope due to the chemistry and hardness. However based on what I'm seeing off the stones I don't think Rex 45 has the aggression to smoke M4 with a toothier edge on manilla rope. We'll see what happens.
After that it will be interesting to test the edge stability and toughness with more controlled destructive edge testing.