How tough is rex 45?

D

drebs

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Dec 6, 2014
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Hey guys trying to figure out the toughness on rex-45 I don’t think it’s been tested on larrins page knifesteelnerds. So I’m looking at the data sheet what is this saying ? My rex 45 para 3 is at 67 and I have a m4 para 3 at 63.

https://imgur.com/gallery/FbSpxih

there are 2 different metrics here.. Charpy c notch and bend fracture. So anyone know what larrins charts are based off of on toughness? For M4 They obviously don’t equal 28 at 63 as the data sheet says on his chart they are 15 at 61. However on the data charts they are pretty close at bend fracture strength.

I’m just trying to figure out is rex as tough as m4, maybe 1/2? Any ball park ideas what steels it may be close to?
 
Rex 45 is tougher than M4. Nothing scientific for me, this is just from real world use. I've hit those big staples cutting boxes before and chipped out my M4 blades. I've hit the same staples with my Rex 45 blade and there's not even a dull spot on the edge.
 
I haven't chipped either ... in similar uses cutting everything from cardboard, twine and ropes to shaving and cutting notches in all types of wood ... soft to hardwoods. I will say that I have had a couple very minor rolls in M4 but not in Rex 45 I would guess the higher hardness on Rex 45 may be why. Not sure that equals tougher than M4 or if it's just a product of slightly softer M4. Both serve me pretty well I don't get into all the scientific data so much as how they perform for my uses.
 
If I'm not mistaken, Rex 45 is the American equivalent to Japanese HAP 40.
I have a Delica in HAP 40 and it is a very thin blade hardened to at least, I'd say, somewhere in the low-mid 60's HRC.
I've used the Delica quite a bit at work doing HVAC and have regularly overshot a cut into
the sides of panels and air handlers (sheet metal), hit staples in boxes, hit staples in duct work etc.
No serious chipping to report.
My Delica in HAP 40 seems tough for what it is.

For what my anecdotal evidence is worth, I'd say most of the blades I've seen in rex 45 would be considered fairly chip resistant/ tough after you take into account their edge thickness and heat treating. What impresses me the most is it's toughness level in conjunction with the
edge retention. You wouldn't normally expect such a hard and thin knife to be that chip resistant.
 
Larrin’s charpy data is not directly comparable to Crucible’s data due to the different specimen geometries.

The only toughness data I have been able to find for REX 45 is in Crucible’s data sheet. Crucible’s bend fracture strength data is probably the most useful info you will find on this subject.
 
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The source you linked to probably gives you the answer you are looking for:

The C-notch Charpy test broke the Rex 45 (67 Rc) sample at 20 joules.
It broke the M4 (63 Rc) sample at 28 joules.

At those hardnesses, M4 is clearly tougher -- more resistant to breaking and chipping.

I don't know what method Larrin used to determine toughness, perhaps a different Charpy, such as the V-notch Charpy. But different toughness measures come up with different results.

From Crucible's site:
"Toughness, as considered for high hardness knife steels, is the relative resistance of a material to breakage, chipping, or cracking under impact or stress. Toughness may be thought of as the opposite of brittleness. Toughness testing is not as standardized as hardness testing. It may be difficult to correlate the results of different test methods. Common toughness tests include various impact tests and bend fracture tests."
SelectorKnifePocketRotatedCrucibleLLC.pdf

Carpenter's site also shows M4 at 65 Rc is quite a bit tougher than Rex 45 at 67 Rc.
cpm_rex_45.pdf
 
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