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+--- Thread: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES (/showthread.php?tid=318)
RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - grepper - 05-08-2018
You have a good point. I agree that the test media can roll an edge. Just cutting through some thin paper once will cause a razor blade to dull. It’s just those dents that you show seemed excessive. But then, I’ve never tried sharpening to 8° so the thinness of that edge may account for it.
Maybe it could be called a SERT (Structural Edge Rolling Tester).
RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - EOU - 05-09-2018
Very interesting stuff KG and very well done. Do you think that carbon content may be an indicator of the edges propensity to roll or are you prepared to venture a guess just yet? Can't get Jan's recitation of the carbon content of cast out of our minds. Doesn't seem like cast would have much of tendency to roll.
RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - KnifeGrinders - 05-09-2018
(05-09-2018, 03:42 PM)EOU Wrote: Very interesting stuff KG and very well done. Do you think that carbon content may be an indicator of the edges propensity to roll or are you prepared to venture a guess just yet? Can't get Jan's recitation of the carbon content of cast out of our minds. Doesn't seem like cast would have much of tendency to roll.
Lower Carbon SWIBO (0.5%) is more resilient to rolling than the higher carbon Global (7%), both of HRC 56-58.
On the other hand, a milder SCANPAN steel of even less Carbon 0.45% and little less hardness HRC 56-57 is less resistant to rolling.
Razors that is so springy that can hold the thinnest edge usually have 0.6% Carbon and HRC 56.
By that, neither Carbon contents, nor hardness can clearly indicate good rolling resistance, at least there is no linear relation.
Resilience to rolling seems to be related to the steel elasticity, compressive strength to be exact; of laboratory indicators it is Yield Strength, but the yield strength is never mentioned among commonly listed knife properties.
To me, the resilience to rolling is a steel meta-property, somehow related to its matrix.
The highest yield strength have spring steels, they should be the most rolling-resistant.
Spring steels may have as low Carbon as 0.1% and as high as 1%, it is the special heat treatment and tempering that makes them springy, not the composition.
Well, they all are to have at least 0.5% of Mn, but all the knives I've SET-tested have the same 1% Mn.
RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - Mark Reich - 05-10-2018
HERE is a link to chemical composition (C- .55-.65% ; Cr-14.5- 18?% ; Mn- 1%) with comments and comparisons of CHROMOVA 18 to AUS6, possibly with addition of Cr.
The thing that is most surprising and beyond anything I've ever seen is the thinness of the bevels you're working with, Mr. KG. I don't think I've ever heard of medium carbon stainless steel taken to such low angles. Did you really see something recommending 15° included for Global knives?
I would expect no thinner than 15°/side. In fact, 15dps is normally reserved for higher carbon/hardness blades of RHC 60+. It's amazing that your data seems to fly in the face of commonly held beliefs.
Also, very interesting that 10dps resists rolling with SET, but 8dps is deformed by BESS media. It's hard to understand that maximum edge retention and edge failure are within 2dps.
Your discoveries are totally remarkable and unique. Thank you very much for your outstanding dedication!
RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - KnifeGrinders - 05-10-2018
(05-10-2018, 12:05 PM)Mark Reich Wrote: HERE is a link to chemical composition (C- .55-.65% ; Cr-14.5- 18?% ; Mn- 1%) with comments and comparisons of CHROMOVA 18 to AUS6, possibly with addition of Cr.
The thing that is most surprising and beyond anything I've ever seen is the thinness of the bevels you're working with, Mr. KG. I don't think I've ever heard of medium carbon stainless steel taken to such low angles. Did you really see something recommending 15° included for Global knives?
I would expect no thinner than 15°/side. In fact, 15dps is normally reserved for higher carbon/hardness blades of RHC 60+. It's amazing that your data seems to fly in the face of commonly held beliefs.
Also, very interesting that 10dps resists rolling with SET, but 8dps is deformed by BESS media. It's hard to understand that maximum edge retention and edge failure are within 2dps.
Your discoveries are totally remarkable and unique. Thank you very much for your outstanding dedication!
You must be right, Mark - the Global Knives website states an "angle between 10 and 15 degrees" - but this should be read as dps.
They also make single-bevel knives with 16 degrees angle, but of a better steel than their Classic line that was used in the test.
RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - KnifeGrinders - 05-10-2018
Isn't the manufacturer's inertia surprising (and appalling)?
Our research is in line with Cliff Stamp's and his has been known to knife people for a decade, yet knives are produced sharpened at the least effective edge angle, as are sharpening devices, even the Spyderco's sharpmaker.
But what really amazes me in the SET data is how much we underestimate the role of rolling in the knife blunting.
Looking at the steel maker's datasheets, not every mentions the compressive strength, but every does the wear resistance.
I see rolling as the main blunting factor in the common use, while the wear is the main factor in industrial blades.
At meat processing plants, where a knife is sharpened after 5 hours of use, it is almost exclusively rolling against the tendons - the edge doesn't wear much cutting flesh, definitely not within the 5 hours before it is sent to re-sharpening. The meat plant operators of a higher grade master steeling so well that keep their knives shaving sharp within that time - and all the steeling does is straightening the rolled edge.
SET method therefore, with its focus primarily on edge rolling, is more pertinent to the butcher's and kitchen knife use, than wear testing methods like CATRA's
RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - Jan - 05-11-2018
Generally we can say, that hardness of heat treated steels correlates with yield stress and the ultimate tensile strength. (YS is stress when steel starts to deform plastically. UTS is the maximum stress steel can take, but also a measure of fracture energy necessary to break steel in a tensile test.)
[attachment=648]
The already quoted prof. Foell says: ”What is commonly known as "hardness" is nothing more than the yield stress, just measured in different units”.
Jan
RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - Jan - 05-11-2018
(05-10-2018, 03:36 PM)KnifeGrinders Wrote:(05-10-2018, 12:05 PM)Mark Reich Wrote: HERE is a link to chemical composition (C- .55-.65% ; Cr-14.5- 18?% ; Mn- 1%) with comments and comparisons of CHROMOVA 18 to AUS6, possibly with addition of Cr.
The thing that is most surprising and beyond anything I've ever seen is the thinness of the bevels you're working with, Mr. KG. I don't think I've ever heard of medium carbon stainless steel taken to such low angles. Did you really see something recommending 15° included for Global knives?
I would expect no thinner than 15°/side. In fact, 15dps is normally reserved for higher carbon/hardness blades of RHC 60+. It's amazing that your data seems to fly in the face of commonly held beliefs.
Also, very interesting that 10dps resists rolling with SET, but 8dps is deformed by BESS media. It's hard to understand that maximum edge retention and edge failure are within 2dps.
Your discoveries are totally remarkable and unique. Thank you very much for your outstanding dedication!
You must be right, Mark - the [url=Global Knives website][/url]Global Knives website states an "angle between 10 and 15 degrees" - but this should be read as dps.
They also make single-bevel knives with 16 degrees angle, but of a better steel than their Classic line that was used in the test.
In my understanding the edge rolling occurs when the edge is more ductile than brittle.
When the bevel angle is very small (e.g. 8 dps or less) than the edge is not sufficiently supported by the steel behind the edge and crinkles.
For a larger bevel angle (e.g. 10 dps and more) there is more steel behind the edge and this support may prevent the edge from crinkling. In this situation the edge selects suitable direction and rolls over/folds to one side.
Jan
RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - EOU - 05-11-2018
Great post Jan and put very succinctly. Makes perfect and very logical sense to us. Your use of the term "crinkle" was, as our good friend Rupert would say, "spot on".
RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - Mark Reich - 05-11-2018
Hi Mr. Jan, thank you for your interesting contributions. You always make me think, which is a good thing. I wouldn't always respond if I didn't care to learn something. Normally I learn that there is usually more than one way to see or say anything.
I don't understand why prof. Foell would consider "yield strength" to be just another term for hardness. Either he's over simplifying or this system is oddly redundant. It seems like different steels should have different plasticity, while being the same hardness.
For instance, one steel may have a maximum hardness of Rc55, and be brittle at that hardness, while another steel with a maximum hardness of Rc62, tempered to Rc55 would be completely different.
What do you think they were doing to the steel to arrive with such a perfectly plotted graph?
It seems odd that there is a steel that can go from Rc 30 to Rc 55 in the same phase, let alone be so linear.
I'm sure you have recognized that I have a hard time applying scholastic theories and statements to my understanding. Please don't ever think I don't value your input highly.