BCMW's ht chopping impact tests

Pile-up is a big factor in hrc non-linear pseudo # for strength. Ferrite/iron (some RA too) allow plastic/displacement caused pileup - a work hardened wall if you want to look it that way. Why is this important? because in order to compute a working-edge diameter(minimum edge MPa/psi meeting maximum tasks MPa). Same calculation for strength of the whole blade, impact load. Fortunately, wimpy human can't even heave past 200 MPa, yup a bar of iron is stronger than you and you happily pay big $ for it - marketed as super tough (aka ductile). Of course, need to operate with very thick edge geometry :rolleyes:

edit: iron and martensite UTS are about 2200 MPa. Yield strength of iron 200-500, martensite 1700-2000 MPa. So martensite slushy by iron = wide apex radius for most EDC tasks. Not about sharpening frequencies, it's about less works (unless you want exercise via cutting/chopping).
 
Ok, so I just watched the video. Believe it or not I don't think you stressed the knife that much. Good beginning test, I think that 67 is way to high based on how quickly your edge damaged on one nail with one hit. But I do think that most steels would take damage quickly at 67 Rc so no surprise there.
 
Thanks for watching and remark. If you happen to know test of untempered high rc blade, please post links. Thanks

I found bouncy baton through nail is very harsh, when force exceed uts and plenty of lateral bad damage is guarantee.
Cobalt said:
Ok, so I just watched the video. Believe it or not I don't think you stressed the knife that much. Good beginning test, I think that 67 is way to high based on how quickly your edge damaged on one nail with one hit. But I do think that most steels would take damage quickly at 67 Rc so no surprise there.
Click to expand...
 
bluntcut said:
Thanks for watching and remark. If you happen to know test of untempered high rc blade, please post links. Thanks

I found bouncy baton through nail is very harsh, when force exceed uts and plenty of lateral bad damage is guarantee.
Click to expand...

No one is abusing high Rc blades for exactly the reason that yours took that damage. Remember, it was one blow that caused that damage. I am sure the point is to see if there is stress crack propagation and there was none which is perfect. So your test was successful, but I am sure you know that there is no way that you can make a 67 Rc blade tough. Even with a more obtuse edge geometry, you will still have damage quickly.
 
Your statement is accurate in the context of abusing a 67rc blade with edc edge geometry.

On other hand - I see. This exactly blade spec would performs very well for folder, small fixed-blade, kitchen knives. IF so then this untampered blade isn't like glass to be broken, right?

Even if a blade made by re-arranged atoms, when force exceed uts - there will be damages. Just hope the damage will be local instead of catastrophic global.

Cobalt said:
No one is abusing high Rc blades for exactly the reason that yours took that damage. Remember, it was one blow that caused that damage. I am sure the point is to see if there is stress crack propagation and there was none which is perfect. So your test was successful, but I am sure you know that there is no way that you can make a 67 Rc blade tough. Even with a more obtuse edge geometry, you will still have damage quickly.
Click to expand...
 
bluntcut said:
Your statement is accurate in the context of abusing a 67rc blade with edc edge geometry.

On other hand - I see. This exactly blade spec would performs very well for folder, small fixed-blade, kitchen knives. IF so then this untampered blade isn't like glass to be broken, right?

Even if a blade made by re-arranged atoms, when force exceed uts - there will be damages. Just hope the damage will be local instead of catastrophic global.
Click to expand...

I would think that a small edc blade likes this with a slightly lower Rc would be great. Keeping it in the 63-65 Rc range could make a great edc/skinner and maintain enough toughness. 67 Rc on anything larger than a 3 to 4 inch blade scares me.
 
I've heard it said that with the fine grain steels like W2, 1095, 52100, etc, that highest "apex stability" is at the as-quenched hardness of 67-68. Now I wouldn't have guessed that myself. I would think highest apex stability would be found at a high RC number, maybe 65-66, but with a low temperature temper to help relieve quench stresses. Interesting test, Luong. I check this thread every day!
 
Thanks, Stuart!

I figure that 'apex stability' in this context, you meant - thinnest sustain/working apex radius/width per intended tasks. If we delve/think hard about 'stresses', which implies defects prevent thinnest possible apex radius. I view 'relieving' (especially low temperature) as reducing plate martensite sheer factor and possibly minor transitional carbide precipitation from twin plates. Opposite of plate martensite is under-hardened, which obviously mean % of ferrite all around and that would also require a thicker working apex.

Precipitation w/o coarsening isn't bad but once temperature high enough - beside coarsening, other transformations maybe also undesirable. Looking a small edge wedge, strongest compressive & lateral would be 100% high/weaved lath martensite. Ideally damages should be isolated to martensite cell at the most/furthest from origin of damaging force.

Funny how we are so condition to accept - tempering as necessary in ht. An ET may view tempering as medicine to for 'stresses' sickness. And secondary hardening tempering is like chemo. I like to shoot for healthy matrix but yeah will compromise/take-med when have to but won't denied metallurgical reality (best of my knowledge at this point in time).

samuraistuart said:
I've heard it said that with the fine grain steels like W2, 1095, 52100, etc, that highest "apex stability" is at the as-quenched hardness of 67-68. Now I wouldn't have guessed that myself. I would think highest apex stability would be found at a high RC number, maybe 65-66, but with a low temperature temper to help relieve quench stresses. Interesting test, Luong. I check this thread every day!
Click to expand...
 
It was painful to break the 52100 64rc jb in half. Hardness readings (grind the blade flat) were 64-67rc. Higher hardness areas have higher % of plate martensite. Lower 1/2" of the blade looks great. Painful but glad, since now I know high variation in thermal mass = high deviation in lattice structure. I will keep the W2 65rc JB around. IDK whether this JB has same problem of 52100 or not. Edge of W2 JB is fine against cinder block & rocks however I will torch the W2 jb tang & spine, just ensure lower half of the blade remain to be ~65rc.

I've some ht tuning to do before I can produce/knit more consistence microstructure for a blade with 1/32" edge and 1/4" thick spine. Torch the spine will be use to allow better bending due to thick geometry, however isn't acceptable work-around for inconsistencies.

Next batch of blades will be semi-production. Will harvest blades with consistent microstructure and learn from blades with inconsistent microstructure. 41+ small & large blades (supports chopping) using steels: W2; 52100; O1; Hitachi Blue#2; CruforgeV. If blue#2 worked out, I will get some 1.2519 (I think, it's better & cheaper than blue#2). *note: all are low Cr%. Aim to produce blades with working hardness 64-66RC.
 
What is an ultimate steel ht goal/grail in term of engineer for max strength and max toughness?

For me, I would like a highest packing fraction/efficency (not the same as packing ratio) possible at room temperature. Tight packing mean lower atomic distance to adjacent atom, in turn stronger electromagnetic grid/lattice (strength) and allow more stretching (toughness) before lattice slip or tear. Austenite is a closed-pack (100%) but unstable very close to deactivation (collapse) to lower potential energy well/crater. Well hexagonal structure (eta) also a closed-pack but this has a narrow stability temperature window and very low % of global microstructure. Cryo could produces some small % eta but it's mostly at grain & cell boundaries (more/less a calving process of high dislocation sites).

Next best is martensite at 79% packing fraction, which can convert/taken up to 0.8%C from aust matrix (i.e. excess C will precipitate or stuck in RA). Plate twin martensite uneven C & Fe distribution and large gaps, so Electromagnetic Grid (EG) is weaker than lath. Grain & carbide boundaries are porous (in comparison to contiguous lattice), so bond and partial EG are even weaker than plate-mart.

Aust -> mart phase change is akin to structural domino. mart is up to 4% volumetric larger than aust. pearlitic vol is almost similar to mart. Obviously, there are dimensional constraints in this phase change, which cause variety dislocation issues. Elemental (Cr, Mo, Mn, Ni, Si, etc..) add further constraint, think it as adding height to crater ridge - where the inside the crater is martensite. This where temper & 2nd temp range temper come in to ease dimensional constraint and give sufficient energy to cross over the ridge. Looking back, this shuffling process avg to increase distance between atoms. When the goal is to build a paramid, impossible build a good one if internal & foundation blocks required to reduce dimension(tempering) and insert hard blocks (precip carbide) in the cracks.
 
I put a Cumaru wood (aka Brazilian Teak) handle on the 0.325" thick 65rc W2 JB.

My next batch of blades (a 17" OAL JB in 1/4" thick O1 steel) with target working hardness 64-67rc range for large to small knives.

Rough blanks:

OxJIHKB.jpg
 
Finding out the breaking limits of heat treated W2 steel. And just for a perspective - It would be difficult to find a knife out there of any steel and hardness with same edge geometry, which would withstand tests prior to destructed tests (baton AB and cinderblock).

2 Knives
W2 0.125" thick, 65rc & 67rc
0.01" behind edge thick
Sharpened 30 degrees inclusive bevel

Notes:
1) Baton through Burly African Blackwood: 67rc chipped to 0.04" thick cross section. 65rc chipped to 0.02" thick cross section.

2) fixed 65rc blade 0.02" BET and 16dps. Battoned 10+ times to that piece of African Blackwood - no edge damage.

Thanks for watching (25 minutes) & comments.
[video]https://youtu.be/_fCqTEp-h6A[/video]
 
My interpretation of this data - as lath martensite is approaching 98+% and hardness goes toward 68rc, plate martensite could grows from zero toward 2%. So 65rc-67rc is the diminishing-return intersection. My 65-65.5rc zone is a hybrid where plate is almost zero % and other phases intersperse w/i lath lattice. That said, for kitchen usage (non bone chopping) 68rc w/ up to 2% of plate martensite is w/i operational range. 65-66rc would be more suitable for kitchen edge geometry sub 0.006" BET and 8-10dps.

As you probably notice from the video, a phonebook slicing 15dps edge experienced extremely high psi when chop Gaboon Ebony or Cumaru. The edge would deform if hrc is below 62rc and chip/fracture if higher hardness (when using std ht). There was certainly some lateral force involved with deflected chops, therefore strength & toughness are needed to support/withstand this type of chopping. I believe edges from video experience similar psi to a heavy chopper edge because chopper momentum would penetrate the wood deeper, thus similar impulse. I speculate, apex of 3V/PD1 62rc phone slicing 0.01" BET; 15dps edge would deform or chip under this type of impact. 60rc Infi at similar edge geometry would dent badly. I would be great & appreciative, if someone with 3V/PD1/Infi perform similar tests.
 
I've tested impact limits for quite a few higher alloyed steels (zwear; 10v; aebl; elmax; d2; ...). When facing high impact into hard material (i.e. high psi), edge geometry below 18dps and with matrix hardness less than 63rc, apex would suffers fracture and or deformation.

I just shot this video of 63-64rc CPM-4V blade going through similar tests as 65 & 67rc W2 blades.

Finding the limits of a 63-64rc CPM-4V blade
0.150" spine, 0.015" & 0.013" behind edge thick
15dps with 20dps micro bevel

Note on 20dps micro bevel: if cutting bevel is at 15dps (which is 2.57 times weaker than 20dps). Failure starts too early and became stress risers, in turn break the blade too early. I've quite a few high carbide volume blades broken at sub 17dps cutting bevel.

Notes baton through African Blackwood cross grain:
1. chipped to about 0.02" thick cross section.
2. blade broken into half at the 2nd chipped (stress riser)

Thanks for watching (2 segments. 12 minutes total) & comments.
[video]https://youtu.be/vkWtqkW3UHY[/video]
 
Last edited:
Interesting results. How many more steels are on your test list? Your last post and previous tests include quite a few of the popular "high-end" steels.
 
Tested 20cv/m390; cts-xhp; spectrumwear; 3v; cpm-154; s35vn; s110v; k390; m4; m2 and few more can't recall right now. Will do more tests for sure... maybe should take more videos too.

btw: 4V 2nd test BET is 0.013" not 0.010" (daylight + precise caliper). 1/4" from apex is ~0.060" thick cross section (vs. W2 ~0.041).

dogrunner said:
Interesting results. How many more steels are on your test list? Your last post and previous tests include quite a few of the popular "high-end" steels.
Click to expand...
 
Just watched the 2 videos. Impressive!:thumbup:
I think people might start to get impatient, when is production date is. :confused:

PS : I like the narrative for the 25 mins :D
 
Thanks, Chris!

You are right, many might grew tired of waiting/watching BCMW... I often feel impatient as well however discipline waltz with production. I like to think, I am in the 'Do It Right The First Time' realm rather than 'Analysis Paralysis'.

Chris "Anagarika";15933247 said:
Just watched the 2 videos. Impressive!:thumbup:
I think people might start to get impatient, when is production date is. :confused:

PS : I like the narrative for the 25 mins :D
Click to expand...

Updates:

***
More tests were done on W2 & 52100 & Cfv ht. So my ht hrc target as follow:
***

67rc - for thinnest possible working apex:
a) low/no impacts: kitchen (0.004-0.010" BET, 7-13dps), twisty/whittle (0.10-0.015", 13-20dps depend on material hardness & steering)
b) moderate impacts: kitchen (chopping & bone contacts) & outdoor (0.010-0.020", 15-20dps or 15dps/20dps micro)

65rc - tougher with slightly thicker apex radius than 67rc
a) similar to 67rc but thinnest working BET probably be around 0.005"
b) similar to 67rc
c) high impacts (chopper class): 0.020-0.030" BET, 18-20dps

63rc - tougher than 65rc and slight increase in apex radius
a) thinnest working BET 0.008"
b)+c)
e) hard uses: breaking up brick/concrete/cinderblock/.. baton through hard & twisty stuff. 0.04" BET, 30dps.
+ I might make&test a (or 2) blade similar to Bussie BM but in 1/4" thick.

61rc - decent tough & too much ductility = relatively easy (ok 61rc isn't that soft) mushy/dent edge. Best uses for very large blades.
* outside of testing, I am not sure about usefulness this hrc.

Paused 58 blades batch...

***
Start:
Applied ht and cross-steel-class tests
***
I have an applied ht formula(use knowledge from ht low Cr steels) for 4+%Cr steels. Will see how well, new ht can knit/weave a great matrix for steels with high dislocation/stress aust&mart matrices along with influence of alloying elements chemistry physics.
4x D2 (65, 63, 61rc)
4x 3V (63, 61 and whatever achievable highest hrc)
4x Aebl (65, 63)

If time permits, LN2 dewar gets a refill.
 
You must log in or register to reply here.
Back
Top