Just got my CPM M4

N

Nebulae

Joined
Aug 24, 2009
Messages
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I just got 3 feet of CPM M4 from crucible today!!!!:D:D:D:D:D:D Needless to say I am verry excited about the possibilities (no sleep tonight:yawn:) I guess I'm so excited that I'm rambling, but I wanted to share my excitement, and ask for some advice, is M4 tough to grind (its about .3" thick:() and I'm thinking I'm gonna have to send it out for HT so any suggestions (preferably in Texas) would be appreciated, and anything else I might want to know?




Thanks in advance
 
Nebulae said:
I just got 3 feet of CPM M4 from crucible today!!!!:D:D:D:D:D:D Needless to say I am verry excited about the possibilities (no sleep tonight:yawn:) I guess I'm so excited that I'm rambling, but I wanted to share my excitement, and ask for some advice, is M4 tough to grind (its about .3" thick:() and I'm thinking I'm gonna have to send it out for HT so any suggestions (preferably in Texas) would be appreciated, and anything else I might want to know?




Thanks in advance
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M4 is definitely a pain to grind. In my opinion, grinding annealed M4 is like grinding hardened W2 or O1. But the awesome performance makes it worth it. :D

Texas Knifemakers Supply should be able to heat treat it.

BTW, welcome to Bladeforums!
 
Thanks, I was expecting it to be hard to grind, based on its annealed hardness, and everything I'v heard about its wear resistance
 
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Actually not to bad to grind in the annealed condition - once hardened it is a bear. Call me if you want to discuss HT
 
Nebulae,

How wide is the stock? How much are the charging for this super steel? I looked at the Data Sheet and it looks interesting.

Thanks,

Paul
 
its 1.5" wide and only cost $126 (+tax=$137), :D if you order from crucible (call them, they are really nice 800-365-1168 (Scott D. posted this so you might get him), they didn't give me grief about only getting one piece, or not being affiliated w/ a company) I'll get at least 4-5 knives from it so its well worth it, for what I consider to be the best knife steel :D
 
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Walt2 said:
Paul will only take his ovens so high. His HT on M4 turned out at 62.5 for me.
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That's the same hardness on the Spyderco Mule M4's, and they perform very well by all accounts (including mine). I would love 64.5 rc though. Certain custom makers can do it.
 
since I am intending to make rather large knives from the M4 b/c its thick (.3") and because its 1.5" wide I would be wasting allot if I made a knife 1" wide, b/c I cant really make a knives .5" wide and .3" thick, (in retrospect maybe I shoulda got 2 or 3" wide) and b/c the better performance is more noticeable in larger knives, I think I want it around 63-63.5 or maybe 64. 64.5 or even 65 would be OK for a small folder unlikely to get much abuse
 
I think it would be great for a sword, its really tough even at high HRCs really wear resistant and hard . . . but wait you wont need those last qualities will you? Oh, and its really expensive
 
Nebulae said:
I think it would be great for a sword, its really tough even at high HRCs really wear resistant and hard, but wait you wont need those last qualities will you? Oh, and its really expensive
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If you use 1075 or 5160, you'll only be paying $5 worth of steel for a sword length. For M4? That would be hella expensive.

People say grinding annealled M4 would be like grinding hardened 5160 steel. Swords are traditionally forged, stock removal of M4 would be a painful experience. And you'll need to find someone with a high temperature oven that can fit a sword for the heat treat. You also don't need the edge retention of M4 for choppers.

Good thing is that even at 65.5 rc, CPM M4 scores 20 ft-lb on the Charpy impact tests which is about the same as a typical stainless steel at 60 rc. For small knives you should be able to take the hardness way up.
 
besides that I forgot to mention that it's almost impossible to forge! dont forget this is a High Speed Steel! designed to keep its hardness at 700-800 F, and if you did forge you would have to have sustained temps of at least 2000 F, and according to the Data sheet not below 1700 F so even if you got a forge that could heat it and reheat it very fast you would have very little time to forge, besides that would sorta defeat the point of particle metallurgy, if you grow the grains huge. and it would cost a fortune in time, and belts to grind out a sword
BTW I looked at the CPM M54 and it looked good, but they didn't show the impact or bend fracture resistance so its hard to compare (shoulda asked the people at crucible about it :jerkit:)

sorry not picking on you Sam ;)
 
Crucible is still taking their time with mine. Said would take another week to make.

So Ben, what knife are you planning to make? I know a lot of people who could heat treat it if you haven't found one yet, but none of them uses a salt pot for austenizing. They have salt pots for the tempering though.
 
wow hey guys thanks for posting sort of forgott about this one. I am deffinitly going to make a 3.5" necker, and maybe a large 8" fighter, although the problem w/ that is that it would take like 13" and i could get 2 or three small knives out of that so i'm reconsidering. I was just thinking that a smaller knife at 65 Rc out of CPM M4 would probably never need sharpening-well infrequently, here I'll email it to you cotdt, since I havnt had the time or patience to figure out how to get them on the internet
 
Turned out that Crucible's interpretation of 1/8" is 0.156" but it's all good. Covered in smooth black, it is the most beautiful bar of steel that I have ever seen. The other CPM steels I've ordered were never finished this nice.

The CPM M4 turned out to be very easy to grind, about the same as S30V. It must be the powder metallurgy process and the steel being softer in the annealed state. I'd rather grind this than 1084, which grind way too fast, all the sparks blind my vision.

My oven is still unfinished, so I'm going to send it out to be heat treated. Then sharpen it and baton the knife through blocks of concrete.

Tip: When ordering from Crucible, tell them that Cliff Stamp sent you, and they'll make you a really excellent batch of steel like they did for me. You might also get a discount.
 
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Grinding annealed CPM M4 was very easy, slower than grinding 1084 but not bad at all. I used a Dremel and $60 belt grinder, but it can also be done with just hand tools.

Experiment #1: 1.5" blade, CPM-M4
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-2175F austenization, pencil-coated, soaked 5 minutes
-oil quenched to dull red, cooled to r.t. in still air. Got zero warping (yay).
-1020F triple temper straight away, 2 hours each
~65.5 rc

Success. Sharpened blade to 9° per side and did not notice any chipping carving hardwood. I used it to scribe grind lines onto steel blade blanks, cut pretty deep and tip remained sharp. Dropped knife onto concrete floor from 5 ft, only ~1 mm of the tip broke off, fixed it in about 10 minutes. Gets wicked sharp, I can't even whittle hair with it because it cuts the hair in half as soon as it touches. Got some burring when sharpening, a sign of good ductility even at this hardness. It is surprising how tough and chip-resistant this steel is at such high hardness. I should have pushed it to 66 rc (2200F/1000F).

Experiment #2: 4" blade, CPM-M4
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-2100F austenization, in 309 stainless steel foil, soaked 15 minutes
-interrupted oil quench, still air to r.t.
-1000F triple temper straight away, 2 hours each
~63.5 rc

Will do a passaround with this knife, see what others think of this steel at this hardness.

The 2100F/1000F temperature was recommended me by Phil Wilson as a safe bet to start with. But definitely, now I think 63.5 rc is too conservative. Mr. Wilson is doing his own experiments on CPM M4, and I'm eager to see how it compares to CPM 10V, the gold standard for edge retention. It's got 2 points hardness advantage (66 vs 64) but less carbide volume than 10V (12.5% vs 17.5%).

I'll also be heat treating CPM M4 for free, so just ask. I'm greatly interested in the results.
 
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