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.

MM
I bought my CPM REX M4 from Jantz. Didn't see it anywhere else.
Running at .225" thick and will require a bit of flat grinding.
For smaller quantities, the supply houses often have std sizes cheaper than going direct and paying setup and process fees.
We will have to compare results when get some knives done.
Tim

I get mine from alpha knife supply, they have a bunch.

MM

Not familiar with them.
Wow, they do have a selection of sizes.
Do you also use Peters H.T.???
Tim

I use peter’s it’s literally 40 minutes from my house. I get all my steel from alpha , tons of selection on a bunch of different steel . Good prices and they always ship quick.

MM

AKS is good people!

Since folks hafta hunt, I am providing a shortcut (since I just went to find them on the interweb . . .
https://www.alphaknifesupply.com/shop/

I looked at their web site yesterday.
I called them to get some info and clarify some questions.

I decided I wanted to make my first purchase from them and wanted to
talk to someone with steel product knowledge
--such as what is the reason/difference in some offer and .146" and at .152"

I was told that no sales were taken over the phone and all my questions
should be directed to the web site.
The only specific info I did get was that they "get M4 from a variety of manufacturers".
Not the kind of response I get form the suppliers I currently use.

Doesn't mean I won't use them sometime in the future, but....
Tim

That's a first for me to hear. I do all phone orders because I had a glitch in their website which would not let me put Oklahoma in the order form. I just write down item numbers and give that yo them.

Same here , usually order over the phone.

Well the lady I talked with said absolutely no phone orders.?????

I may try again at a later date. I am all set for now from Sheffield and Jantz.
Tim

I have not ordered anything in about 3 months so maybe something has changed. Next order will be the M4 though.

So the blanks are surface ground down to .160" thick.
They drill quite easy for fastener hole locations.
Shaping the profile seems to grind really easy.

I have not started on the bevel grinds yet.
I am doing 8 blades flat ground and my nephew is doing 2 blades hollow ground.

Bos H.T. is going to get me 62.5 Rc when I am done with the bevel grinding.

If I do more, I will try to buy from Alpha at a thickness close to what I want to end up using.
I will need to be able to talk with someone knowledgeable there which I could not do previously.
They have a lot of sizes and thicknesses, but told me they buy M4 from several mfrs. and did
not know what the process or how accurate the surface grinding was to make their flat stock or if
they could verify the Mfr of the specific bar.
I will only buy Crucible made M4 steel.

I the weather warms up above freezing I will start on the bevel grinding.

Sam. I have one blank that will be just the nuts for your "semi skinner". I am stretching one out longer for myself.
I have one set of greenish camel scales that are a near match (I believe) for the knives you have.
Tim

and the handle should be 4 3/4 inches.

4 3/4"??????? Is that a change I did not get????

Your pm said different, " For this type knife, the handle does not need to be as long as I usually go for. 3 3/4 inch would be fine"
------so it will be less than 4".
Too late to add steel.


Tim

laughing. brain fart Tim. carry on.

Tim,
It seems most makers using M4 are going 64+ Rc? Why did you choose to go lower with yours?

Crucible rates it for 63-65 Rc.
The furnace a Bos HT (according to Paul) max temp will come a few degrees short of able to hit more than 63.5 (possibly 64).
I shaped and ground two blade blanks that were 63.5 when I rockwelled them and that seemed just fine. They ,led me to this project.
If I end up feeling that I need another 1 to 1.5 points when these are done, I will look to go higher but doubt I will need it.
We will see.
Tim

My nephew, son, Sam and myself will be working with a couple of the finished knives.
I do not plan on doing a destruct test, but do plan on extensive use to see how the edge retention is.
When I get the knives done, I may have one more for someone to put through its paces.
They will be hunter and skinner patterns with some sort of drop point front end.
Sam gives them a pretty good work out, so we will see.

Those blades that are being heat treated to 65 Rc are of what general shape and purpose of use??????

I miss spoke above when I posted 62.5 Rc as the target. S/B 63.5, maybe to 64.
Not sure what a point or so difference makes at the end of the spectrum.
Tim

Tim,
That would have been my next question, in your experience how much difference would one or two Rc points really make? Once a blade is to that level I'm guessing the difference between 63.5 and 65 Rc would be pretty negligible.

With a Rc value in the mid 50s, a couple points is noticeable if you are paying attention.
Not sure how noticeable a point or two will be in the low/mid 60s with this or any steel that
can be treated up to the mid 60s.

With 154 steel, I noticed a little difference when going from 59 to 61----I think.
Sometimes your mind takes over and your perception is jaded.
In field use, IF I did not know which blade was at which Rc, I might not be able to get it right more than 50% of the time.

In my opinion/experience the "differences" touted in the many variations of steel chemistry/performance are only readily
noticeable with lab equipment and not so obvious in field use.
But hey...........There are a lot of companies that make "Kleenex" and without the label who would know which?????
Tim

That's what I think... say it's D2, telling the difference between 60 Rc and 62 Rc in the field would be pretty hard I think. Probably could between the 57-58 Rc some production companies run D2 and the 60+ most custom makers treat to. Gotta get to that certain level and after that it's more a matter of grind, ect. that determines the performance of a blade rather than one or two points on the heat treat scale.

Got the blades heat treated.
Targeted 63-64 Rc.
Put an aged industrial micarta handle on one today. Gotta sharpen it and see how it preforms.

One will be going to Mannlicher. I will get it together next week and then a sheath.
I am sure Sam will put it thru its paces as he always does, and then let us know his conclusions.

Got to get loaded and off the the Badger Show now.
Tim

I love it when a plan comes together. I will be in Miami for two weeks. hoping to be back in Gainesville by the 9th of April.

Keep us updated on your cutting results. As I said, my Dowell M4 is definitely one of my favorite small fixed blades.

I put some aged industrial micarta on one of the blades and sharpened it.
Knife is .160" thick, 4" sharpened, 8 3/4" oal drop point. Rc at 63.5.

After some serious batoning and shaving a chunk of very hard aged beech, still shaving sharp.
I will do a couple more similar sessions, but expect more of the same for edge holding.

Sorry that I am pictorally challenged or I would post some pics.
I have 6 more blades of various patterns to handle plus my nephew has two he hollow ground.
I think they are keepers. My "For Tim" pile keeps growing. I may have to let Vince thin the herd for me.

Tim

Well after a bunch more chopping and shaving hard oak, still able to shave arm hair.
Best edge holding of anything I have done.

PS: and it will still push cut a sheet of newspaper.

the skinner should go all season long without sharpening.

Alright guys, i've been following this thread and need to see some pictures.

Since the upset of Photobucket, I have not been able to post pics here. Tried to figure it out but gave up.
I did post a couple in the gallery Rick set up, but can't seem to move them to this thread.

I do have a pic I could send for someone else to post of the 8 blades, two of which are handled.

Sam---pm me your email addy and I will send pic to you if you want to try to post it here.
The problem is, you will see your knife before you open the package and the surprised will be diminished (maybe).
Tim

PM sent

This is Tim's picture of the knives in M4

Thank you Mannlicher.

Imgur.com is the answer to photobucket. Much more user friendly and no extortion.

Thanks Sam
The knife on the far right is the one I have been using to evaluate edge holding.
Still push cuts paper and still on first sharpening with a couple swipes on a strop.

Gotta figure out what I want to keep and how to handle them from this batch.

Allso gotta get better in pics.
Tim

and the one with the bone handle is mine?

Yes, and it sure feels good in my hand. Hope your specs were right for you.
That is the last of the greenish dyed giraffe bone I have. I think you got all I had.
You will have to make a color/material shift if you need another knife.

The bigger blade in the center is your pattern stretched a bit. A "Buffalo Skinner" I am thinking.

Doug has your knife to make a sheath.
Pouch and no loop as requested.

The far left blade and the two in the center I am definitely keeping. The others??????

Thanks
Tim

My edge retention experience from boning out deer, elk, antelope, bison, and bear in the field all settles on how clean the hide was. Any animals that was loaded with dirt dulled any of my edges where as a clean animal left my edge razor sharp. I've removed an elk hide with a 1095 bladed pocket knife but also have knocked the snot out of both my blades (always carry both a folder and a fixed while hunting) while skinning a small black bear.

I'm happy with an edge that will survive the hunting trip. On longer trips I have replacements in camp. On day hunts I never kill more than one animal and at most clean two, mine and my partners.

I know this has been covered several times on this site but... If you're buying a blade with a hardness greater than 60 you had better be have excellent sharpening tools AND skill.

good points Boise. I always have more than one good knife when hunting. Even around here, just miles from the house, I'll have at least two, more likely three, in the day pack. You just never know, plus I like to try different ones when I get a chance to work with a dead animal.

I deep running in to people who can not sharpen "MY xxxx out of yy steel). They have other knives they can sharpen.
Not sure how much is real and how much is perceived.
Most do not start with coarse enough grit, clean enough stones or the ability to hold a consistent angle.
Also, you have to get a burr first, before going with finer grit.

I sharpened blades for 50 years on bench stones and thought I was pretty good until Rick lent me his Edge Pro.
Got one for myself. Consistent angle, clean stones chase the burr. Scary sharp, if you want that.

I am really curious to see how well this M4 at 63.5 Rc holds up in the field.
Two of the 8 blades in pic above will get field tested by 24 hr knife loonies and 1+ by myself of course.

Tim

Tim, I don't consider myself an expert at sharpening but the Edge Pro does allow me to achieve "scary sharp" edges. Except the one ProTech Brend 2 auto, that I like, which causes me fits. I can get it sharp and I did completely skin a black bear with it but I'm unable to achieve that razor sharp edge we all love.

I even had Rick Menefee place a hollow ground edge on it and it arrived sharp but not nearly as sharp as the fillet knife he made me. Plus, the edge didn't hold up, and I don't have the means to replicate the hollow ground edge.

I know you have a history with these blades. Care to share some advice? I suspect wonky heat treat.

Posted this then realized this is a total hijack of your M4 thread - my apology.

Rick
This thread is about done until I get a couple of the M4 blades finished and they get some field testing by some thread members.

In grinding thousands of ProTech blades, I never had a reason to find any heat treat issues.
We ground all heat treated blades.

I do have a couple of the small Brend blades. They were set up pieces and had some minor blems to needing a hand ground repair.
If you want one that is good enough to install, I will send it to you. It may need a couple passes on a surface grinder, depending on knife construction.
I could also give you one that would need a little grinding to be used.

And no, I do not have any interest in tearing yours apart.

As far sharpening that size and style of blade.............
Using the Edge Pro I found that a shim under the blade was needed to keep the stones from riding on the plastic guard that the spine
rests against. I used a popcicle stick. Also a narrow hollow grind can be hard to hold in a consistent position.
A Lansky might not have that issue.

Let me know if you want to try a replacement blade.

We can start a new M4 thread later when something new to report.

Tim

Great thread!

OK guys, there ought to be some initial reports back now.

Mannlicher and I are the only ones that have a knife in hand.

Journeyman's is out for a sheath. He is going to do the more extensive (more lab like) testing plus
field work. His is the second blade from the right.

Sam and I will be more along the lines of field use experience.

I have used the far right knife in the pic of 8 above to do some whittling and batoning.
I am quite impressed with the edge holding, but that is just user impression not
data based. Still a pretty good edge after 15 minutes of whittling and chopping dry and hard
oak and beech wood.

The second and third blade from the left can be available is some one is interested.
Tim

it works fantastic as a kitchen knife. I'm down in Miami again, with no opportunity here to use the knife. Hope to try it out before too long, after I get back to my North Florida home.

No further reports on this steel yet?

Was thinking the same thing. Would like to hear how sharp users are getting their knives. Are they reaching "scary sharp" levels, and how long does it last and how long does it take to sharpen verses 1095.

I have been procrastinating. I bought this one to use with dead animals, and I just have not killed anything this spring. I am not going to chop wood, carve spoons or baton firewood with it.
So far, I know it works well with supermarket meat, and with Antelope, pork and venison from the freezer.

I know--no pics, so it did not happen.

I got to bloody one of the knives I made using CPM-4 on a deer opening morning.
The cutting edge showed no deterioration, but I would expect that with use on just one animal.

The blade I used was .160" thick at the spine and the blade bevel about 85% of the width..
That did prove to be more wedge than ideal for cutting meat.
I would think (as with any steel) that something in the .100" to .125" is a better
thickness for processing meat and skinning.

Hope the three 24hr members who have one of this batch (M4 at 63.5 Rc) get to use them more extensively and
can report on the results.
Tim

Tim, My son shot a fat four point this morning. I used the M4 skinner, along with two of your other knives. The lad and I were very impressed with the performance of the M4 blade. Deer zipper. Shaving sharp after finishing up.

From Frank on M4 blade I made for him
"Tim,

Finally had a chance to use the M4 knife you made me. I used it to skin a frozen whitetail doe and bone it out. The blade held an amazing edge through the skinning to the point where I felt I had to be careful with it. I've cut up quite a lot of deer with quite a few knives and usually don't feel like I have to unduly careful. I was more cautious with your knife. I don't know if you've ever skinned a frozen deer or not, but it's no fun and not far off from skinning an ice cube. The blade had lost some edge by the time I had the deer boned out. I cut against a fair amount of bone while cutting off the fore legs and boning out the loins. Also you end up cutting through the hide and hair pretty often when trying to peel the hide off a frozen carcass. I ended up taking the hide off in 2 pieces just to make it easier, so cut through quite a lot of deer hair. I use a DMT Diafold sharpener in fine grit that's pretty well worn out. 4 strokes per side brought it back to hair shaving sharp.

I have knives in D2 (Ingram and Dozier), S30V folders mostly, Elmax (another maker here), CPM-154 (Page, Hendrix, Davis) and some others. I don't think any of them would have done as well as your M4 blade at Rockwell. I think a thinner blade like 3/32 in a 3.25 inch or so in that steel and temper would be an incredible cutter and take up no room in a pack.

Thanks for making it fore me. I'd be happy to give you more specifics if you'd like, either my message or telephone."
---------------------------------------------------------------------------------------------------------------------------------------------------------------
PS:
I am thinking of doing one more run in a couple months using M4.
If so, I will be going thinner with the material, and smaller with the blades in general.
I went a little on the thick side with the first run thinking the blades were more for heavy duty.
A thinner blade and cutting edge and a 63.5 Rc should be a great cutter and skinner.

Thanks
Tim

MRK, if the second blade from the left in the picture is still available I would like to claim it. Send me a PM please.

Crow

Crow
Yeah, the second from the left and the big one in the center are not handled yet.

I had thought I would make myself a set out of them using a large elk tine to handle them both with.
But, I have "personal" knives up my patootie, so PM coming your way.
Tim

Tim, I think I might be interested in the big semi skinner if that is the last one available. If it is, can you PM me to discuss dimensions and such?

Sure.

Patiently waiting and drooling over pics here.

local
The blades just mentioned recently above are in the pic posted by Mannlicher in the middle of page three of this thread.

The pic of your blade that is in queue for heat treat I sent to you. Blank plus ground along with 10 other blades

I have not mastered the posting of pics here, so once in a while a member helps with that.

Thanks
Tim