CPM-M4 Katana

BladeChemist

BladeChemist

Joined
Aug 19, 2010
Messages
261
You'll have to excuse my drooling, but is there anything stopping CPM-M4 from being differentially tempered?

I'm wondering how, in comparison to other steels, would differentially tempered CPM-M4 in a Katana-type profile perform. It's well known for impact resistance (cutting competitions) and from my own experience it takes a very sharp and resilient mirror polished edge.

If one were so ordered from a willing custom maker, would the necessary bar stock be available, or would some sort of forging be necessary? Alternatively, has anyone heard of this steel being used to make +24" blades?
 
M4 is not a good material for a Katana you need a more flexable outcore with a high carbon inner core...now if you used the M4 for just the inner core that is fine but a Katana needs to give more for combat and be resilient.
 
So even M4 left fairly soft is going to need a heck of a lot more flexibility/toughness? I was hoping the differentially tempered part would have taken care of that.

^5160- Nope, still stuck on the concept of a one-steel blade based on CPM-M4. Makes me wonder why they use it in cutting competitions in their longer knives/choppers. Obviously not a 3-foot long blade with a Katana profile, but what's the length limit then? And does it work best in a high-width chopper style blade?
 
check with gayle bradley in weatherford tex. he was one of the very 1st to use m4 in choppers. real nice guy.
dennis
 
M4 will air harden. I'm not sure a differential hardening would work too well.
 
me2 said:
M4 will air harden. I'm not sure a differential hardening would work too well.
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I made a D2 skinner and drew the temper with a torch and aluminum heat sinks on the edge (hardness differential verified during sandblasting), I realize this isn't a differential hardening (I think you are right, just about impossible to dif-harden alloys that need long soak times) but the spine can be softened.

CPM M4 isn't tough compared to shock steels, or for example L6 and CPM 3V. Making it soft at the back will make it bend in hard use (abuse?) but I bet in skilled hands a CPM M4 sword would be fantastic on tatami
 
but I bet in skilled hands a CPM M4 sword would be fantastic on tatami
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A skilled maker? A skilled practitioner?

Give me a break, there is a video of a blunt medieval type (6150 steel iirc and fwiw) cutting tatami. Could you rephrase that to make a little more sense of what exactly the steel type has to do with cutting a mat?

I am sorry that this poor reader now has a headache and was prompted to respond in what may read as negative but to write the above with no qualifying information is causing an infarction of my screen. :)

Cheers

GC
 
Differential hardening would be very difficult, and differential tempering, apparently, is unnecessary, as seen by the cutting competition performance of CPM M4. Even at 3/8" thick and 2" wide, I doubt the knives see the kind of impact a sword would.

I've seen the video of the "dull" sword cutting the tatami and wondered about it. In theory, the CPM M4 blade could be made with lower bevel angles and better geometry to cut with less effort. You run into a compromise though, as you can only thin the blade so far. Some mass is needed to help get the blade through the rolled mat. I think you'd end up with a full flat grind profile with no secondary bevel. Just a triangle from spine to edge with about a 15 degree inclusive edge, assuming 1/4" stock. This all assumes that such a profile won't just come apart on the first cut.

As far as what steel has to do with cutting a mat, there is a quote that floats around here. Geometry cuts, steel determines the limit of functional geometry.
 
horseclover said:
A skilled maker? A skilled practitioner?

Give me a break, there is a video of a blunt medieval type (6150 steel iirc and fwiw) cutting tatami. Could you rephrase that to make a little more sense of what exactly the steel type has to do with cutting a mat?

I am sorry that this poor reader now has a headache and was prompted to respond in what may read as negative but to write the above with no qualifying information is causing an infarction of my screen. :)

Cheers

GC
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sorry bud I meant it would cut lots and lots of tatami without the need for resharpening for a long time!
 
dhaines said:
M4 is not a good material for a Katana you need a more flexable outcore with a high carbon inner core...now if you used the M4 for just the inner core that is fine but a Katana needs to give more for combat and be resilient.
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But that is not how katanas are made, at least traditional ones. They have a hard OUTER layer wrapped around a softer core that is only exposed on the spine of the blade.
 
M4 works very well for cutting competition knives but has its limitations when it comes to swords. I have made six swords out of M4 with RHC of 61 to 58 and found that it is not as good as 3V. M4 holds a very good edge and the swords had no problem with wood and bamboo targets but chipped on cow femurs.

Dan
 
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Dan Keffeler said:
M4 works very well for cutting competition knives but has its limitations when it comes to swords. I have made six swords out of M4 with RHC of 61 to 58 and found that it is not as good as 3V. M4 holds a very good edge and the swords had no problem with wood and bamboo targets but chipped on cow femurs.

Dan
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That is really insightful- thanks for adding that to the discussion. I wonder- did you attempt to forge M4, or is that not really feasible? Just wondering if the toughness could be improved upon at the extremes.
 
i don't think M4 is a good steel for swords. and for myself i would never rely on the toughness table given by the steel company, that thing has too much trick to play with. most high speed tool steel shows the unotched charpy impact toughness, and many test has been done with larger sized sample. in this case the elestic deformation abserbs most of shock resistance, which can't show the true charactoristic of toughness. the high number will caught your eye of course, thats the reason they put it there.

as for making sword, i would suggest s7, l6 or 5160. marquench or salt bath to get low bainite. it will have great toughness while still be able to hold good edge.
 
SShepherd said:
why do you think forging would make a difference ?
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the correct controlled forging process will refines the grain and carbide.

for example heavy duty spring steel 60si2mn, rapid quenching after high temperature deformation, then follow by high temperature tempering (usually arround ac1 something). this can very well replace the annealing process. results the fine pearlite with very fine carbide of nano leavl. cause greatly increase in proformance.

and most important, forging makes you swing the hammer, which is extra exercise for your everyday life. good health and long life.
 
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