Geometry Questions: Scandis really 12 DPS? Is my HT ok?

[direstrats220]

Recently I have been making some 1/8" scandi ground blades in CPM cru-wear, one of my favorite steels. Doing some internet hunting, I've seen that scandi blades bevel angles ranges from 11 to 13 DPS (seems super acute), so I tried out 12.5 degrees as measured by my grinding jig (and confirmed by my guided sharpening system).

I did my normal HT for cru wear, soak at 1575F for 30 min, austenitize at 1950F, plate quench, dry ice + kerosene, temper twice at 400 for 2 hours.
Also did this with no cryo and tempered 3x at 1000F for 2 hours.

On both knives, the edge chips AND/OR rolls when I give it a tiny impact into white oak, not even an aggressive chop, just a light impact. I gave the scandi a microbevel at 17 DPS, and now it's totally fine, no chipping or rolling even with hard chops. Checking hardness (all I have are files), the HRC is maybe 62-63, scratched reasonably easily by the 65, but the 60 it feels like glass.

My questions are: 1) I think my HT is fine, could I improve it? 2) Does this just mean a scandi at this hardness simply isnt tough enough to chop hardwood, even lightly? 3) Are scandis really in the 12 DPS range, and if so do they need to be run softer to increase toughness?

Observations: My moras actually have like a 18 DPS microbevel. My enzo trapper is more like 15 DPS. At 12.5 DPS true zero grind scandi, the knife obliterates softwoods.

I was hoping the impressive toughness of cru wear would allow a finer edge angle than I would normally try. Anyone have experience with this type of edge refinement they could share?

 

[Lorien]

any chance you're grinding too hot?

 

[Hella Bread]

Recently I have been making some 1/8" scandi ground blades in CPM cru-wear, one of my favorite steels. Doing some internet hunting, I've seen that scandi blades bevel angles ranges from 11 to 13 DPS (seems super acute), so I tried out 12.5 degrees as measured by my grinding jig (and confirmed by my guided sharpening system).

I did my normal HT for cru wear, soak at 1575F for 30 min, austenitize at 1950F, plate quench, dry ice + kerosene, temper twice at 400 for 2 hours.
Also did this with no cryo and tempered 3x at 1000F for 2 hours.

On both knives, the edge chips AND/OR rolls when I give it a tiny impact into white oak, not even an aggressive chop, just a light impact. I gave the scandi a microbevel at 17 DPS, and now it's totally fine, no chipping or rolling even with hard chops. Checking hardness (all I have are files), the HRC is maybe 62-63, scratched reasonably easily by the 65, but the 60 it feels like glass.

My questions are: 1) I think my HT is fine, could I improve it? 2) Does this just mean a scandi at this hardness simply isnt tough enough to chop hardwood, even lightly? 3) Are scandis really in the 12 DPS range, and if so do they need to be run softer to increase toughness?

Observations: My moras actually have like a 18 DPS microbevel. My enzo trapper is more like 15 DPS. At 12.5 DPS true zero grind scandi, the knife obliterates softwoods.

I was hoping the impressive toughness of cru wear would allow a finer edge angle than I would normally try. Anyone have experience with this type of edge refinement they could share?

I think you got a few things mixed up/confused so

for both rolling and chipping geometry reigns supreme as the biggest influence on those qualities but assuming geometry is equal or taken out of the equation this is where toughness/hardness come into play.

toughness is purely a measure of how much it can take without fracturing, in our case that would mean chipping and/or just the blade snapping. Plastic deformation would occur before it fractures which is what happens when the edge rolls. A very high toughness value can possibly roll the edge very easily but will not chip.

For edge rolling higher hardness is what prevents it.

they’re at odds and it’s always a balancing game depending on intended use case.


Scandis (really any type of thin zero grind) are gonna be kinda delicate by nature. In terms of bushcraft stuff they’re good for carving/whittling/feathering/batoning (since the edge would be supported while you’re smacking it) etc not so much straight chopping. But the good thing about it being your gear is you can tweak it to your use case so if you find you need a microbevel there really isn’t anything bad about that nor should you really worry about doing so and rolls/micro chips just kinda come with the territory with the type of use these things get anyway so just don’t overthink it and enjoy the knife, fix it when you can or when it’s necessary

 

[Stacy E. Apelt - Bladesmith]

I would be concerned that chipping and rolling are opposite indicators. Chipping indicates too high hardness or other brittle condition. Rolling indicates too low hardness or other softer condition.

Do you use a water spray on the grinder? On a zero edge knife the edge can easily overheat, especially in the sharpening and polishing stages. I would recommend only doing the basic profile on the grinder and using stones and plenty of lubrication ( oil or soapy water) and doing the final bevels and sharpening on stones.

I'll let Larrin post about the HT temps you gave, but IIRC, the 1000° temper is not what you want for a zero grind knife.

 

[direstrats220]

I would be concerned that chipping and rolling are opposite indicators. Chipping indicates too high hardness or other brittle condition. Rolling indicates too low hardness or other softer condition.

Do you use a water spray on the grinder? On a zero edge knife the edge can easily overheat, especially in the sharpening and polishing stages. I would recommend only doing the basic profile on the grinder and using stones and plenty of lubrication ( oil or soapy water) and doing the final bevels and sharpening on stones.

I'll let Larrin post about the HT temps you gave, but IIRC, the 1000° temper is not what you want for a zero grind knife.

any chance you're grinding too hot?

I have a paint can full of water next to the grinder and dip the blade after each pass. Tedious and slow but figured it was doing the job since I wasn't burning my fingers. Maybe this demonstrates it wasn't working that well. Instantaneous heating of the thin section near the edge is plausible. I grind bevels with a 36 grit ceramic, clean up the bevels with a 60 grit then a 120 just until the scratches are gone, then switch to flat stones. I'll have to look for some active water cooling options.

Honestly, I don't notice any difference between the dry ice/low temper and none/high temper as far as this behavior, so maybe that is more evidence of edge burning. My HT protocols are right off the data sheet for no cryo, and right off the Z-wear cru-wear article for the cryo.

they’re at odds and it’s always a balancing game depending on intended use case.

I understand this. It seems like these edges are right at the point where both are happening. I've seen this with thin 3V edges, depending on what forces the knives experience, it either chips or rolls. It could also be non-uniform edge hardness from grinder burning.

 

[maxjeg]

Good afternoon.
Sorry, I may have translated your message incorrectly. English is not my native language. Scandinavian knives (Helle, Brusletto, and others) have a general sharpening angle of 28-30 degrees. 14-15 degrees on each side of the blade. Finnish knives (Marttiini, Wood Jewel, Roselli, AK, and others) have a general sharpening angle of 20-22 degrees. 10-11 degrees on one side. Some Finnish knife makers (for example, Puronvarsi) use a convex lens to strengthen the cutting edge.
I hope this is a translation error on my part.

 

[Thescrawnylumberjack]

You don’t need the pre soak at 1575. Ramp to 1950, put the blades in, wait for the oven to rebound, and then start timer.

As said above geometry is the biggest influence.

I’ve also found micro bevels do very little.

13-14 DPS is what I’ve seen mostly from my time. 11-12 DPS is very acute and most if not all steels will have issues holding this edge without taking damage.

The low temper range should be better for your application and corrosion resistance.

 

[Hella Bread]

It could also be non-uniform edge hardness from grinder burning.

I mean the only way that temp would affect it is if you got the steel above the temp you tempered at, Which is damn near impossible on the 1000 temper one it and on the 400 you’d see colors and probably feel it on your fingers long before while grinding if you overheated

Pretty sure it’s just a geometry/use case issue. slap a microbevel on it call it a day. For the next one just go more obtuse to like a 30 deg inclusive

 

[direstrats220]

I mean the only way that temp would affect it is if you got the steel above the temp you tempered at, Which is damn near impossible on the 1000 temper one it and on the 400 you’d see colors and probably feel it on your fingers long before while grinding if you overheated

Pretty sure it’s just a geometry/use case issue. slap a microbevel on it call it a day. For the next one just go more obtuse to like a 30 deg inclusive

Yeah thats a good point. I've definitely burnt tips before, saw a straw color, but that was from carelessness and dull belts.
I just microbeveled to ~17 ish on a stone and they're fine now. A shame because at ~12 DPS the cutting power in soft to medium woods is insane.

 

[direstrats220]

Good afternoon.
Sorry, I may have translated your message incorrectly. English is not my native language. Scandinavian knives (Helle, Brusletto, and others) have a general sharpening angle of 28-30 degrees. 14-15 degrees on each side of the blade. Finnish knives (Marttiini, Wood Jewel, Roselli, AK, and others) have a general sharpening angle of 20-22 degrees. 10-11 degrees on one side. Some Finnish knife makers (for example, Puronvarsi) use a convex lens to strengthen the cutting edge.
I hope this is a translation error on my part.

Thanks for the information and for the picture. Very cool knives! I think you understood my point. 13-14 degrees per side seems closer to what I see on my Helle and Brisa knives, maybe even 15. I wonder how the Finnish knives maintain edge stability in hard woods or with lateral forces.

 

[maxjeg]

Finnish knives don't have the highest hardness. My readings suggest a hardness of +/-58.
Furthermore, when sharpening on a leather strop with paste (I use white Dialux), a microlens is created. This increases the durability of the cutting edge.

Thanks for the information and for the picture. Very cool knives! I think you understood my point. 13-14 degrees per side seems closer to what I see on my Helle and Brisa knives, maybe even 15. I wonder how the Finnish knives maintain edge stability in hard woods or with lateral forces.

 

[Stacy E. Apelt - Bladesmith]

I hope Larrin chimes in about what happens when a high temper at 1000° is done for precipitation hardening followed by accidental edge heating during grinding into the 500° range. My take is that once cooled to room temperature after the initial high temper, you can still damaging the martensitic structure in overheating the edge.

 

[Larrin]

If the temper was done at 1000F then it is safe to heat it to 500F without affecting the temper. You would have to heat the edge to roughly 1000F to start overtempering at that point.

 

[C_Claycomb]

Check out the Kellam Wolverine and SPT blades or Laurie PT blades. Induction hardened to 62HRC at the edge. Low angle, but off hand cannot remember what I measured one at. Articles say 10-11 DPS. Most get a micro bevel. I reckon a zero edge at 12-13DPS is good, but it does depend on what you are cutting.

While there are oak in southern Sweden and Norway, the majority of trees are pine, spruce, birch, willow, and alder. I have seen quite a few people in the US complain about the durability of “Scandi” ground blades when trying to cut white and red oak, hickory, ash, hard maple, etc. Mors Kochanski loved his single bevel Skookum, but all he had around there was aspen, willow, pine and spruce. Low angle and a wide bevel to control shaving depth were more valuable than how the edge behaved impacting hard material.

I once had a prototype “Scandi” in D2 where the bevel wasn’t flat and it took hours and a couple sheets of coarse SC paper to flatten them. I know diamonds are better, I have diamond, but still would think twice about wanting to maintain a wide bevel in an abrasion resistant steel. That means that the lower angle main bevel with micro bevel or convex edge would be more maintainable.

Best of luck, hope you figure out the recipe that works for you!

Chris

 

[Stacy E. Apelt - Bladesmith]

Thanks Larrin, I couldn't remember that scenario.

 

[SwissHeritageCo]

Personal experience is that true zeroed scandis just don't hold up and require a microbevel, regardless of heat treat.

 

[HSC ///]

what is your soak time at the austenitizing temp?
as mentioned already, no need for the presoak