CPM-M4 Katana

i think you misunderstood me lol. i didn't mean that forging product better steel than controlled hot roll sheet. what i mean is that the deformation caused by forging does refines the carbide and grain. controlled hot roll does the same thing.

another fact is that stock remove limited the heat treat method you can do to the steel. stock removing, stress relieving, quenching, cyro and tempering. in the other hand, forging can personally control deformation with thermal cycling to further refine the carbide. however, the bladesmith also taking the risk at extra abusing and hammer flaw.
 
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hammerfall said:
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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Why does fine pearlite with fine carbide result in increased performance? I'm pretty much only interested in tempered martensite having tried 20 blades in lower bainite, tough yes but not worth the hassle when air hardening shock steel is available.

I believe the cpm steels all have the correct hot working processes applied.

Curious about your thoughts on the toughness of various alloys, though this post has greatly deviated from the OP's question... L6 at rc58 has about half the toughness of s5 at rc58 on the charts I can find, with "straight" carbon eutectoids about half the toughness of L6. I would think that's a deal breaker for any blade going to be subjected to impact. There is more to the data though, as I have also seen charts with 1095 rating fair for shock loads due to the core of the blade not ever being fully hardened.

Agreed we need to exercise more but I swing a hammer a lot and it is dirty asymmetrical work, with many health hazards.
 
fine pearlite and fine carbide improves in the later heat treat. it gives a ideal structure for futhur hardening. finer and rounder the pearlite the easier you can maintain the finer grain size when austenitlizing. finer and more dispred carbide you have, the higher rate of nulcleation you will have. this result the nulcleation of more and finer grain instead of making the grain growth in size. thus you will have tougher and stronger martensite.

i have tried plenty of cpm steel as well. i have no doubt they have the good quality and correct hot work process. but such process might not fit my specific design.

about toughness, personally i think the C-charpy impact toughness is something to catch customer's eyes. elestic deformation absorves too much impact energy in the test, especially when higher hardness is occured. s5 shock resistance steel are way overated by their C-charpy impact toughness. i had trid it with U-charpy 10 times at the same heat treatment condition with cpm data sheet, i got something like between 20~27j. in this case l6 would proform better than s5.

toughness on the sheet has too much trick to play with. there is a way can better reflect the toughness. i think its the rate of plastic deformation divide the total impact energy if i remember right.
 
I don't really see why having the energy absorbed in elastic deformation in the C-notch test would be a bad thing. Especially at the higher hardnesses, where there is no ductility to absorb the energy, it can't go anywhere else without fracture.

In the end, you have to use the test that best represents your observations in service. If the U-notch gives better representation of observed behavior, then that's the one to use. The use and review of data from these tests gives you a starting place with a hand full of steels. Further refinement and testing will give a test that predicts behavior for your (anyones) specific use. The best of the narrow choice of alloys in the most representative test is the one to use. Of course it get pretty complicated, since there is almost always more than one criteria, and they typically oppose each other, i.e. grindability in manufacture vs. wear resistance of final part.

Keep in mind that the Charpy family of tests gets a lot of scatter at the hardness levels we like for knives. Maybe not so much with swords, since they typically run at lower hardnesses. The torsional toughness test was developed to represent behavior that was observed at higher hardnesses. The behavior was not predicted reliably by the Charpy family of tests. This follows the same pattern that lead to the Charpy and Izod tests. They were developed to predict behavior that ductility in a tensile test did not predict.
 
BladeChemist said:
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.
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I tried to forge the first 2 swords that I made form M4 because I could only get bars 36” long and I want a sword with a 40” length. I tried to stretch the tang with a press but ended up crumbling about 8” of steal. M4 can be forged but has a very small window and is not forgiving.

I don’t make sword out of M4 any more but I still use it for my Bladesports competition cutters. To increase the toughnes of M4 we use it at RHC 61. This is the sweet spot for this steal.

Dan
 
me2 said:
I don't really see why having the energy absorbed in elastic deformation in the C-notch test would be a bad thing. Especially at the higher hardnesses, where there is no ductility to absorb the energy, it can't go anywhere else without fracture.

In the end, you have to use the test that best represents your observations in service. If the U-notch gives better representation of observed behavior, then that's the one to use. The use and review of data from these tests gives you a starting place with a hand full of steels. Further refinement and testing will give a test that predicts behavior for your (anyones) specific use. The best of the narrow choice of alloys in the most representative test is the one to use. Of course it get pretty complicated, since there is almost always more than one criteria, and they typically oppose each other, i.e. grindability in manufacture vs. wear resistance of final part.

Keep in mind that the Charpy family of tests gets a lot of scatter at the hardness levels we like for knives. Maybe not so much with swords, since they typically run at lower hardnesses. The torsional toughness test was developed to represent behavior that was observed at higher hardnesses. The behavior was not predicted reliably by the Charpy family of tests. This follows the same pattern that lead to the Charpy and Izod tests. They were developed to predict behavior that ductility in a tensile test did not predict.
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hi me2.

i am not saying higher C-charpy impact toughness is a bad thing. however this test does not shows the best repersents for swords nor knife.

my point is, upon heavy impact expecially for swords(used for hacking and slashing) you can't avoid the pastic deformation at the impact location of the edge. the pastic deformation happening together with the elastic deformation. in this case notch sensitivity and crack sensitivity have to be taken account. a c notch charpy test shows very little on both.
 
i do use both V and U for impact resistance steel. acctrully, most of time i use V, U and unnotched all together to futhur observe how one specific alloy reacting to the impact.
 
ah, fascinating... reminds me of an article showing S7 at high hardness as tougher than H13 9points softer, which was not predicted... we almost need edge-specific tests for blades... is compressive strength a big factor?
 
wnease said:
ah, fascinating... reminds me of an article showing S7 at high hardness as tougher than H13 9points softer, which was not predicted... we almost need edge-specific tests for blades... is compressive strength a big factor?
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compressive strength is also important. but as a sword blade i believe its a lesser factor compare to bending stress, deflection and toughness; since you need it for hacking, thursting and sometimes deflecting the incoming mace lol.
 
compressive strength is better used for reflexing static loading stress(press cut, shearing).

as a sword, it needs to take more dynamic loading(impact, hacking and cleaving).

for example, blade made of m2 might press cut a blade made of s7. but when you swing them at each other with enough dynamic load. m2 might crack upon the impact.
 
hammerfall said:
compressive strength is better used for reflexing static loading stress(press cut, shearing).

as a sword, it needs to take more dynamic loading(impact, hacking and cleaving).

for example, blade made of m2 might press cut a blade made of s7. but when you swing them at each other with enough dynamic load. m2 might crack upon the impact.
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but since that not how a katana is used, it's a bit of a moot point. Changing the sword to something like a gladius would be more in line with the use your talking about.
 
its the weapon that serves the man, not man who serves weapon. katana doesn't make you give up your advantage on anything. when technology is able to make katana a better weapon, why keep it crippled for only traditional fighting style?

also even a sword like katana it still need tougness to withstand impact from incoming blow. or this kind of crap will happen.

brokenkatana.png


during WW2, a cheap massive producted chinese sword met the katana. japanese officer attacked first. however chinese officer did not parry. instead he meet the katana with a head on cleave. and the result is the picture above. fotunately he survived, and in his interview he had complianed about the chinese office' s lacking of swordmanship, using sword like a mace and broke his loving sword. its from this japanese soldier's own tell.
 
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