Home Forums Gear Knives and Blades Crucible CPM Rex M4

Anyone have any experience with this????
Calls for a rockwell of 63-65 Rc. Should be able cut nails with that.
I guess the addition of tungsten makes it pretty tough.
I think it was developed as high speed steel to be used on tooling such as wood working planer blades, etc.

I have whittled down a machine wrecked blade out of M2 at 63 Rc into something usable.
WOW does it take and hold an edge.

So, I am thinking of making a couple knives out of the CPM Rex M4. It is kinda pricey but.......

Not sure what pattern(s) or how many. Maybe a big camp and a couple of regular size drop point hunters.
Steel available is 3/32" and 1/4" mill finish.

Anyone have any experience of thoughts??? I would welcome the input.
Thanks
Tim

I have used CPM-M4 for about 6 years I have Peters heat Treating do my M4 blades to 65RC. My evenheat furnace is maxed out trying to heat this stuff. It's amazing steel if you can get past it not being stainless. Never used Rex 4 but it looks as good as M4. Let me know how you make out.

I have a Brett Dowell M4 blade at 65 Rc that is a cutting sumbuck. It's a high hollow grind and ground thin on a B&T pattern. Brett put an acid etch on it and so far no problem with freckling. The acid etch is just turning from black to a nice gun metal grey. Probably my favorite fixed blade.

knifeman Would you have a contact number for Peters Heat Treating????

MOGC You wouldn't possibly have a contact number for Brett would you???

Thanks. I plan on ordering some of this steel.
Tim

Brett's website has both email and phone number...

Well, I got the steel bar. Looks like I may get 6-7 blades out of it, if no problems cutting it.
If the temperature comes up a little, I will go out in the garage and see how hard it is to cut.
I would think the 5.5% Tungsten would make it a little tougher on band saw blades than the
stuff I am used to using.

mrk
If you would, please keep us apprised of the effort to cut that steel.

I talked with Brett yesterday and he said M4 not much different than others for cutting, drilling
and grinding before heat treat. Really tough on belts when hardened.
I will cut some on band saw when the garage thaws out.
Tim

Tim, The one knife style I don't have is the 'semi skinner', you know the curved up blade with a lot of belly? Something like that with some dyed camel bone would be awesome. I can send pictures.

Sam
You are referring to the M4 project I assume.
I had not really figured out anything on the selling end yet till I got a feel for how this stuff works out.
But....
I can look at what you are talking about. Similar to a Buck Bull Nose Skinner?????
Lets see a pic.
I do have one set left (I believe) of that green camel bone.

Tim

Well, I have not done any drilling or grinding yet, but the M4 sure does cut up nice on the band saw.
I did some cutting on 440C, CPM 154 and the CPM REX M4. Not much difference.
Tim

I think you're treading on thin ice when you start getting into anything over 62 rockwell in a knife blade, {CPM} is Crucible Powdered metal, its strong points are with a lack of grain during production you avoid any chance of warpage when you machine through the grains like a hot or cold rolled steel, but when you start getting 63 and or above the same lack of grain structure leads to brittleness and increased chance of breakage. 60/62 is plenty hard, yet far more durable. In my mind any how.

It's not experimental... There is plenty of engineering and practical experience with M4 at 64+ Rc to prove that it works well at those levels.

Crucible specs it's CPM Rex M4 at 63-65 Rc.
I am not making chopping knives, but that steel is popular for high speed wood working
blades for planners, etc so..........

Once you get a blade past the mid 50's Rc, they all can chip or break when used to chop or pry. I know that 440C
at 58Rc will chip if used to chop on a rabbit leg bone.
If you are going to use a knife to chop or pry I suggest a different tool unless in an emergency
situation.

CPM steels give you a fine, uniform grain due to uniform particle size. Kinda like pancake batter --without lumps.

FWIW: I took a blade made out of M4 that is at 63.5 Rc and gave it a very strenuous work out on
seasoned hardwood and had no deformation of the edge from chopping and batoning with it.

We will see. It is not for everyone. To each his own.
PS:
And beside saw cutting well, it seems to drill and grind well also.

Tim

Simply dropping a blade that hard could shatter it, I would just as soon sharpen 60-62 rockwell blade more often than chance the brittleness of a harder blade. To each their own.

I made one out of that couple years ago, Pete’s treated to 62rc, holds an edge along time, fairly rust resistant and tough enough to break a deer down in the field.

MM

I think the 5.5% Tungsten in M4 does a lot for toughness.
You don't see Tungsten in the normal plethora of blade steels being used today.

A lot of the steels being used have trouble getting to 60-62Rc. The variation in
chemistry of steels require specific schedules for proper heat treatment. They all have upper
limits to the hardness they can achieve and not all perform the same at similar Rc either.

I may have to drop one on cement floor just to see what happens.
My knives are mostly made for processing flesh and organic materials, so I
don't currently do any cold chissel or crow bar tests on them.

I was told by some who know that a lot of competition blades are made from M4.

Anyhow, I have been pondering on this project for several years so........
I am sure that a couple of my knife looney friemds will give them a good test.
Tim

If you want an all around, tough as nails, will last thru hell and high water blade try some 8620, you won't be disappointed.

I’ve also read quite a bit about CPM M4 being a common steel for chopping competition blades . Figure if it can handle that i’ll Never give it anything it can’t handle.

U talked me into it, I’m ordering some.

Side note: my current carry blade for hunting is a clip point in S90V heat treated to 62 by Pete’s. I did drop it on concrete and it bounced, and surprisingly nothing to report.

MM

I don't know that much about CPM M4 but steel can be very hard and not be brittle. H Roselli produces a modern Wootz steel with a hardness of 66-68 HRC without being brittle at all. You are correct though that many steels will be very fragile at such hardness. I just wanted you to know that they don't all have to be.