How Chipping of Edges Happens at a Microscopic Level

[Larrin]

Larrin, I'd be interested in your thoughts about stress risers, especially at plunge lines where they can become a stress riser, and whether sharpening choils centered in the plunge line can block stress lines, but also with thumb holes, thumb studs, jimping and even saw teeth on the spine.

I wonder if there’s a good modeling software we could use to predict the degree of stress localization.

I am also interested in stress risers forming along coarse edges. On my choppers, I usually go with a coarse edge, mostly because it's going to get dull fast anyway so time spent on a refined edge is wasted. But from your essay, it would seem that choppers would have stronger edges if sharpened all the way through the finer grits.

Thanks for your post.

Certainly from the articles referenced in the post we know that coarse edges are bad, but it would be fun to do a study to determine how fine the edges need to be.

 

[chiral.grolim]

I wonder if there’s a good modeling software we could use to predict the degree of stress localization.

Certainly from the articles referenced in the post we know that coarse edges are bad, but it would be fun to do a study to determine how fine the edges need to be.

I have another question along these lines:

Grind-scratches typically run perpendicular to the edge but cracks typically propagate parallel to the edge. You typed:

First of all I think it’s clear that there are scratches in the edge from sharpening which as described earlier can act as preferential sites for crack initiation. In the second image as marked with arrows you can see the cracks that formed parallel to the edge as shown in this article. And the chips themselves are longer than they are tall perhaps indicating that the cracks formed by cracks linking up along the rolling direction...

However, the "perhaps" here seems quite the stretch when there seems to be a much more obvious explanation (unless I misunderstanding what we are seeing), namely that for the crack to propagate perpendicular to the edge it would need to propagate through thicker material "climbing the bevel". If a crack initiates at a grind-scratch in the apex, there are suddenly two "tag ends" of low thickness that can be bent out of alignment with relative ease to a certain height/thickness beyond which the path of least resistance lies to the side, i.e. parallel to the edge or back up toward the apex. Micro-chipping paths are, afterall, 3 dimensional. In order for the crack to play "connect-the-dots" as you describe in the article, it will limit those dimensions according to the path of least resistance. As such, one would expect the path (or rather the plain) of fracture to carve out a section near the edge rather than flake out sections running way up the bevel even if they follow the scratches, because up the bevel there is less bending-stress giving the fracture room to grow (so to speak).

The question I would ask is (and perhaps you already know and can definitely clarify), Would a micro-chip in a steel knife ever really run taller than it is long/wide regardless of 'rolling direction'? I would be very interested to see a comparison of microchipping in a blade deliberately bevelled parallel to the rolling direction rather than bevelled perpendicular thereunto, to see whether or not the cracks at this scale really line up with the rolling direction (and carbide stringers) or not. Or would such a blade quickly fracture up the scratches in the bevel without experiencing the micro-chips seen in Sandvik's images? Consider blades like the Razel, ground with perpendicular edges. I have never heard that one of those edges is more prone to microchipping (due to rolling-direction alignment) than the other edge, but perhaps it has not been thoroughly investigated...

 

[Larrin]

However, the "perhaps" here seems quite the stretch when there seems to be a much more obvious explanation (unless I misunderstanding what we are seeing), namely that for the crack to propagate perpendicular to the edge it would need to propagate through thicker material "climbing the bevel". If a crack initiates at a grind-scratch in the apex, there are suddenly two "tag ends" of low thickness that can be bent out of alignment with relative ease to a certain height/thickness beyond which the path of least resistance lies to the side, i.e. parallel to the edge or back up toward the apex. Micro-chipping paths are, afterall, 3 dimensional. In order for the crack to play "connect-the-dots" as you describe in the article, it will limit those dimensions according to the path of least resistance. As such, one would expect the path (or rather the plain) of fracture to carve out a section near the edge rather than flake out sections running way up the bevel even if they follow the scratches, because up the bevel there is less bending-stress giving the fracture room to grow (so to speak).

The question I would ask is (and perhaps you already know and can definitely clarify), Would a micro-chip in a steel knife ever really run taller than it is long/wide regardless of 'rolling direction'? I would be very interested to see a comparison of microchipping in a blade deliberately bevelled parallel to the rolling direction rather than bevelled perpendicular thereunto, to see whether or not the cracks at this scale really line up with the rolling direction (and carbide stringers) or not. Or would such a blade quickly fracture up the scratches in the bevel without experiencing the micro-chips seen in Sandvik's images? Consider blades like the Razel, ground with perpendicular edges. I have never heard that one of those edges is more prone to microchipping (due to rolling-direction alignment) than the other edge, but perhaps it has not been thoroughly investigated...

I know what the literature shows in terms of chip formation, and they all found cracks linking up along carbides and/or impurities, which are typically "the path of least resistance." Whether the thickening edge in a knife blade can also affect the formation of the cracks I can't say. Hand sharpened knife edges often have scratches that are parallel to the edge, depending on the technique and the sharpening method chosen. Maybe someone will do a study.

 

[maximus83]

Certainly from the articles referenced in the post we know that coarse edges are bad, but it would be fun to do a study to determine how fine the edges need to be.

Thanks for the research and article! You make a nice use of technical illustrations for concepts, something we use a lot of in my work.

Question on your comment: Do you mean coarse edges in general are bad? And if so, could you give the specific links to the research that demonstrates that (would help narrow it down as I probably won't have time to work through all the referenced articles)? Interested to read that, also I'm sure folks who usually hang out in maintenance like FortyTwoBlades , @David Martin, @HeavyHanded, @Jason B. and others, would be interested as well.

 

[FortyTwoBlades]

Thanks for the research and article! You make a nice use of technical illustrations for concepts, something we use a lot of in my work.

Question on your comment: Do you mean coarse edges in general are bad? And if so, could you give the specific links to the research that demonstrates that (would help narrow it down as I probably won't have time to work through all the referenced articles)? Interested to read that, also I'm sure folks who usually hang out in maintenance like FortyTwoBlades , @David Martin, @HeavyHanded, @Jason B. and others, would be interested as well.

Coarse edges have increased edge retention in slicing cuts but reduced edge retention in pushing cuts. Chopping is push-cutting and coarse edges are inherently more prone to rolling/buckling under impact.

 

[Larrin]

This article was strictly covering chipping of edges. I know in rope slicing Phil Wilson says he gets best results with 325 grit finish. It would be fun to do a CATRA study with a range of different finish levels in sharpening.

 

[chiral.grolim]

I know what the literature shows in terms of chip formation, and they all found cracks linking up along carbides and/or impurities, which are typically "the path of least resistance." Whether the thickening edge in a knife blade can also affect the formation of the cracks I can't say. Hand sharpened knife edges often have scratches that are parallel to the edge, depending on the technique and the sharpening method chosen. Maybe someone will do a study.

Did Sandvik happen to indicate the steel types for their promotional images showing edge damage?

Another question:

At high stress levels the researchers found that cracks initiated at the surface with large carbides at the origin of the fracture. The stress level required for surface initiation in D2 was 1100 MPa, but for the modified steel was 1800 MPa. This is why when loaded to a similar stress level the modified steel with less carbide and smaller carbides lasts for 1-2 orders of magnitude more cycles than D2. The difference is greatest for a small number of cycles and high stresses which is the region of interest for knives when it comes to chipping resistance.

The number of cycles to fracture becomes infinite for the tested steels below a stress amplitude of ~600 (units), indicating the endurance limit of the steels. Why do you assert that we should be looking at amplitudes much greater than this for knife edges? Link to an article suggesting it? My reading has indicated that using a steel knife to cut a V-groove through 65ST6 aluminum imparts a stress of only 300 MPa, well below the stress indicated here for infinite durability from cyclic loading. Using a knife to cut vegetables and meats, carve wood, slice through rope, etc. usually imparts far less stress on the edge than metal cutting. As such, the above data would be irrelevant for all but the machining of steel parts and of effectively no interest for knives, not so?

This article was strictly covering chipping of edges. I know in rope slicing Phil Wilson says he gets best results with 325 grit finish. It would be fun to do a CATRA study with a range of different finish levels in sharpening.

https://www.bladeforums.com/threads/some-catra-test-results.930333/
"...I ordered some steel, had it laser cut to shape, heat treated by a commercial provider, hollow ground on automated liquid cooled grinders, finish ground by a professional knifemaker, sharpened by a professional sharpener, and eventually tested on a CATRA knife edge tester with their ISO standard. 16 blades were cut. The steel was from the same manufacturer, shipped from the same distributor, blanked on the same machine, heat treated at the same location, ground on the same equipment, sharpened by the same person with the same equipment, tested on the same machine, and tested within one 48 period. The rockwell hardness was tested and the edge angles measured with a laser goniometer...
...
Edge polish - Sharpening was done with a jig to maintain consistent angles, on monocrystalline diamond, and checked with a laser goniometer. Not very large differences, quite in line with the other factors except for edge angle. For the slicing cut against silica bearing paper, 25 micron edges did best 71% of the runs, 3 micron took second place in 57% of the runs, and 45 micron was last in 71% of the runs. I did not compare each combination of grits, but did find that for the average difference between first place finishers (most often 25 micron, but not always) and second place (again, 3 micron just more than half) was 4.5%. From first to third (most often 45 micron) was 12% on average..."

In hardheart's testing, 325-grit (45 micron) was worse than 800-grit (25 micron), but I have not found a scholarly publication on the matter... Silica-impregnated cards are only one medium *shrug*

 

[Larrin]

The number of cycles to fracture becomes infinite for the tested steels below a stress amplitude of ~600 (units), indicating the endurance limit of the steels. Why do you assert that we should be looking at amplitudes much greater than this for knife edges? Link to an article suggesting it? My reading has indicated that using a steel knife to cut a V-groove through 65ST6 aluminum imparts a stress of only 300 MPa, well below the stress indicated here for infinite durability from cyclic loading. Using a knife to cut vegetables and meats, carve wood, slice through rope, etc. usually imparts far less stress on the edge than metal cutting. As such, the above data would be irrelevant for all but the machining of steel parts and of effectively no interest for knives, not so?

The stress on the edge is dependent on the edge geometry, since as you know stress is load divided by cross sectional area. Therefore the stresses seen by different types of knives can be much higher than 300 MPa. Otherwise there would never be any chipping. I’m surprised you’ve never seen a chipped edge in a knife but I assure you they exist.

I stated that the stress levels of interest for chipping would have to be high for two reasons:
1) If the stresses are so low as to be below the fatigue limit then it wouldn’t be chipping. Since I am writing about the conditions that lead to chipping it would be nonsensical to say that the region of interest is below the fatigue limit.
2) If a given stress level requires much over 1000 cycles for failure then it would be unlikely to occur with typical use. Therefore the region of interest where chipping would occur is at higher stress levels, ie with a lower number of cycles.

 

[Larrin]

https://www.bladeforums.com/threads/some-catra-test-results.930333/
"...I ordered some steel, had it laser cut to shape, heat treated by a commercial provider, hollow ground on automated liquid cooled grinders, finish ground by a professional knifemaker, sharpened by a professional sharpener, and eventually tested on a CATRA knife edge tester with their ISO standard. 16 blades were cut. The steel was from the same manufacturer, shipped from the same distributor, blanked on the same machine, heat treated at the same location, ground on the same equipment, sharpened by the same person with the same equipment, tested on the same machine, and tested within one 48 period. The rockwell hardness was tested and the edge angles measured with a laser goniometer...
...
Edge polish - Sharpening was done with a jig to maintain consistent angles, on monocrystalline diamond, and checked with a laser goniometer. Not very large differences, quite in line with the other factors except for edge angle. For the slicing cut against silica bearing paper, 25 micron edges did best 71% of the runs, 3 micron took second place in 57% of the runs, and 45 micron was last in 71% of the runs. I did not compare each combination of grits, but did find that for the average difference between first place finishers (most often 25 micron, but not always) and second place (again, 3 micron just more than half) was 4.5%. From first to third (most often 45 micron) was 12% on average..."

In hardheart's testing, 325-grit (45 micron) was worse than 800-grit (25 micron), but I have not found a scholarly publication on the matter... Silica-impregnated cards are only one medium *shrug*

Thanks for the link!

 

[chiral.grolim]

The stress on the edge is dependent on the edge geometry, since as you know stress is load divided by cross sectional area. Therefore the stresses seen by different types of knives can be much higher than 300 MPa. Otherwise there would never be any chipping. I’m surprised you’ve never seen a chipped edge in a knife but I assure you they exist.

I stated that the stress levels of interest for chipping would have to be high for two reasons:
1) If the stresses are so low as to be below the fatigue limit then it wouldn’t be chipping. Since I am writing about the conditions that lead to chipping it would be nonsensical to say that the region of interest is below the fatigue limit.
2) If a given stress level requires much over 1000 cycles for failure then it would be unlikely to occur with typical use. Therefore the region of interest where chipping would occur is at higher stress levels, ie with a lower number of cycles.

1) If the stress levels are below the fatigue limit, presumably it would be below the yield strength as well. Is there some reason to think that the stresses involved in knife use are below the yield strength but above the fatigue limit such that cyclic loading should come into play? You even state:

Typically low-cycle fatigue is at sufficiently high stress levels where small amounts of yielding (permanent deformation) occurs. Micro-chipping and chipping of edges occurs in the low-cycle fatigue region [7]. Low-cycle fatigue is more greatly controlled by toughness and less by the slow crack growth dominated by high-cycle fatigue...

2) 1000 cycles? I think even 10 is unlikely in typical knife use. When stress is applied to the edge in such a direction and at such an amplitude that it induces strain beyond the yield point, then it requires no cycling at all to initiate a crack on less ductile material. The data on cycling is irrelevant if there is not evidence indicating that is how knife-edge chipping occurs.

Yes, I have seen knife edge degradation from chipping, it most often appears to occur at a site of deformation in the edge - the edge is "turned aside" by a continuous force until it reaches yield point whereupon it takes a bend and is more easily caught in the midst of a cut and fractured out from the edge. As you indicated, the thinner the cross-section, the easier it is to bend the steel out of alignment with the cut and crack it away. Chips rarely proceed high into the bevel because the blade is thicker there and so stiffer and less prone to being strained beyond the yield point. If there are carbides in the edge preventing strain, fracture toughness is reduced, as you have detailed, meaning that the edge allows less strain before cracking.

So what is the typical level of stress encountered by a knife edge during the cutting of various media? Such data would be excellent to have, particularly in regard to determining whether yield-strength and toughness measurements collected from larger/thicker specimens are accurate to predicting behavior at such smaller scales. The trouble I have encountered is that most of the information I have found details the force required for a blade edge to make a cut through a material, it does not detail how much lateral stress is being placed on the knife edge during the cut. I suppose that could be calculated from the geometry of the blade-edge and the angle of cut, but I am concerned that the final values will indicate that our measurements of steel strength and toughness from 5mm specimens and the like are not applicable at 5um, particularly when carbides in the edge can be that large all by themselves in many knife steels...

 

[Mikel_24]

Thanks a lot for sharing! And yes, I think we are all expecting someone here....

 

[Gaston444]

He is a Cliffstamp fan who claims that all CPM steels are inferior to 420j2 for knives.

I just mention what is routinely observable:

One thing I took away from this article, is that in using these steels for chopping tasks, the edge geometry must be made appropriate to the task.
Thanks again Larrin!

That's curious, because chopping, edge angles and bevel thickness are never mentioned once in the entire article. In fact the term "edge geometry" does not appear once. Amazing what can be read into things...

I'll tell you what I took away from it:

Quote: "It is very common for custom knifemakers to use cryogenic processing of their steels which eliminates most of the retained austenite in the steel. I wrote a forum post about what retained austenite is and what cryo treatments do. Toughness testing usually shows an increase in toughness with greater retained austenite, as can be seen in this figure for 440C [5]:

However the concern sometimes is that through stressing of the steel with retained austenite present that the austenite will transform to (untempered) martensite and therefore the brittle phase will act to reduce toughness. However, fatigue testing of material paints a different picture, where the retained austenite containing steel, which converts to martensite during cyclic loading, has higher resistance to fracture."



Translation: In attempting to make things better (and more expensive), custom makers often make things worse...

Quote: "Another conventionally cast steel with a lower carbide volume, however, showed superior resistance to fracture due to its higher fracture toughness from a small carbide volume combined with a relatively large average distance between carbides."

Which is interesting.

My favourite though is this:

Quote: Therefore side loading requires less stress to fracture the edges and chipping can occur along the carbide bands [15]:

If the knives are oriented along the transverse direction instead, then the tips of the blades would fail more easily in a similar fashion"



This all by itself could explain the discrepancy in my first photo: It probably should be a major item of knife choice to decide how the blade is oriented to the rolling grain.

Since most customs are preoccupied with overall strength, they are likely cut along the grain. Since cheapo factory knives don't care, or go for the easiest layout, they might be cutting them perpendicular to the grain, resulting in superior edges.

Yes there is a cost in point strength, but it can be alleviated by point design. The primary purpose is to cut after all... I have to say that generally, if you exclude a Randall Model 12 and its unique forged stainless (which was not much better than equal), I have never seen custom knives that out-performed good factory knives with equivalent geometry. The prevalence of CPMs in customs, relative to cheaper "conventional" factory steels, has made this discrepancy even greater...

Gaston

 

[danbot]

That's curious, because chopping, edge angles and bevel thickness are never mentioned once in the entire article. In fact the term "edge geometry" does not appear once. Amazing what can be read into things... Gaston

From Larrin's article:

Chipping

Chipping, as differentiated from micro-chipping, is on a more macroscopic scale and requires high stresses that exceed the fracture toughness, KC, of the steel to allow rapid propagation of large cracks. Therefore those types of chips occur either in a single high application of stress or a very small number of cyclic stresses. Avoiding these types of chips requires either a change in use, higher toughness by changing material or heat treatment, or change in edge geometry [17]:

Did you really read it?

 

[WilliamEdward]

I just mention what is routinely observable:

That's curious, because chopping, edge angles and bevel thickness are never mentioned once in the entire article. In fact the term "edge geometry" does not appear once. Amazing what can be read into things...

I'll tell you what I took away from it:

Quote: "It is very common for custom knifemakers to use cryogenic processing of their steels which eliminates most of the retained austenite in the steel. I wrote a forum post about what retained austenite is and what cryo treatments do. Toughness testing usually shows an increase in toughness with greater retained austenite, as can be seen in this figure for 440C [5]:

However the concern sometimes is that through stressing of the steel with retained austenite present that the austenite will transform to (untempered) martensite and therefore the brittle phase will act to reduce toughness. However, fatigue testing of material paints a different picture, where the retained austenite containing steel, which converts to martensite during cyclic loading, has higher resistance to fracture."



Translation: In attempting to make things better (and more expensive), custom makers often make things worse...

Quote: "Another conventionally cast steel with a lower carbide volume, however, showed superior resistance to fracture due to its higher fracture toughness from a small carbide volume combined with a relatively large average distance between carbides."

Which is interesting.

My favourite though is this:

Quote: Therefore side loading requires less stress to fracture the edges and chipping can occur along the carbide bands [15]:

If the knives are oriented along the transverse direction instead, then the tips of the blades would fail more easily in a similar fashion"



This all by itself could explain the discrepancy in my first photo: It probably should be a major item of knife choice to decide how the blade is oriented to the rolling grain.

Since most customs are preoccupied with overall strength, they are likely cut along the grain. Since cheapo factory knives don't care, or go for the easiest layout, they might be cutting them perpendicular to the grain, resulting in superior edges.

Yes there is a cost in point strength, but it can be alleviated by point design. The primary purpose is to cut after all... I have to say that generally, if you exclude a Randall Model 12 and its unique forged stainless (which was not much better than equal), I have never seen custom knives that out-performed good factory knives with equivalent geometry. The prevalence of CPMs in customs, relative to cheaper "conventional" factory steels, has made this discrepancy even greater...

Gaston

Larrin could you chime in here? Genuinely curious to hear from a real authority in metallurgical science in the face of other members strongly held assertions.
Want help to parse our what’s real, and what’s not.

 

[Larrin]

Larrin could you chime in here? Genuinely curious to hear from a real authority in metallurgical science in the face of other members strongly held assertions.
Want help to parse our what’s real, and what’s not.

He is making several assertions and I'm not sure which ones to respond to. In terms of side loading and using cheap steels, the PM steels have less banding and therefore are less susceptible to the potential side loading phenomena. That was shown in the article:

 

[bhyde]

I just mention what is routinely observable:

That's curious, because chopping, edge angles and bevel thickness are never mentioned once in the entire article. In fact the term "edge geometry" does not appear once. Amazing what can be read into things...

I'll tell you what I took away from it:

Quote: "It is very common for custom knifemakers to use cryogenic processing of their steels which eliminates most of the retained austenite in the steel. I wrote a forum post about what retained austenite is and what cryo treatments do. Toughness testing usually shows an increase in toughness with greater retained austenite, as can be seen in this figure for 440C [5]:

However the concern sometimes is that through stressing of the steel with retained austenite present that the austenite will transform to (untempered) martensite and therefore the brittle phase will act to reduce toughness. However, fatigue testing of material paints a different picture, where the retained austenite containing steel, which converts to martensite during cyclic loading, has higher resistance to fracture."



Translation: In attempting to make things better (and more expensive), custom makers often make things worse...

Quote: "Another conventionally cast steel with a lower carbide volume, however, showed superior resistance to fracture due to its higher fracture toughness from a small carbide volume combined with a relatively large average distance between carbides."

Which is interesting.

My favourite though is this:

Quote: Therefore side loading requires less stress to fracture the edges and chipping can occur along the carbide bands [15]:

If the knives are oriented along the transverse direction instead, then the tips of the blades would fail more easily in a similar fashion"



This all by itself could explain the discrepancy in my first photo: It probably should be a major item of knife choice to decide how the blade is oriented to the rolling grain.

Since most customs are preoccupied with overall strength, they are likely cut along the grain. Since cheapo factory knives don't care, or go for the easiest layout, they might be cutting them perpendicular to the grain, resulting in superior edges.

Yes there is a cost in point strength, but it can be alleviated by point design. The primary purpose is to cut after all... I have to say that generally, if you exclude a Randall Model 12 and its unique forged stainless (which was not much better than equal), I have never seen custom knives that out-performed good factory knives with equivalent geometry. The prevalence of CPMs in customs, relative to cheaper "conventional" factory steels, has made this discrepancy even greater...

Gaston

It wasn't so long ago that I asked you to provide the proof in these magazine articles pertaining to CPM steels. Nothing, despite being asked by so many to cite your sources..Credible sources.
Whenever you are asked a legitimate question in regards to your wild assertions, you ignore it only to pop up in a thread days later with more of the same.
You aren't contributing anything of use to the community but you are hurting those that come here to learn. It's really hard for anyone to separate the wheat from the chaff.

Your time sprinkling the forum with turdlets has come to an end.

 

[Larrin]

In terms of edge geometry I should mention also that the major terms defined in the article all specify cross-section. Stress on the edge is load divided by cross section and the "K" factor in relation to a growing crack is dependent on stress. Maybe I could have called out how this relates to edge geometry more, but essentially edge geometry is everything. Thinner edges see higher stresses. That's one part of what makes edge geometry so important. Of course we also know that thinner edges cut better and last longer so there are difficult balances in knife design.

 

[stabman]

It wasn't so long ago that I asked you to provide the proof in these magazine articles pertaining to CPM steels. Nothing, despite being asked by so many to cite your sources..Credible sources.
Whenever you are asked a legitimate question in regards to your wild assertions, you ignore it only to pop up in a thread days later with more of the same.
You aren't contributing anything of use to the community but you are hurting those that come here to learn. It's really hard for anyone to separate the wheat from the chaff.

Your time sprinkling the forum with turdlets has come to an end.

Thank you!!!

 

[danbot]

Larrin So would the retained austenite that transforms to untempered martensite that can close the crack eventually, under continued high stress low cycle or low stress high cycle, eventually be detrimental because it's untempered martensite? Or is it "shielded" somehow within the "matrix"?

 

[DeadboxHero]

I just mention what is routinely observable:

That's curious, because chopping, edge angles and bevel thickness are never mentioned once in the entire article. In fact the term "edge geometry" does not appear once. Amazing what can be read into things...

I'll tell you what I took away from it:

Quote: "It is very common for custom knifemakers to use cryogenic processing of their steels which eliminates most of the retained austenite in the steel. I wrote a forum post about what retained austenite is and what cryo treatments do. Toughness testing usually shows an increase in toughness with greater retained austenite, as can be seen in this figure for 440C [5]:

However the concern sometimes is that through stressing of the steel with retained austenite present that the austenite will transform to (untempered) martensite and therefore the brittle phase will act to reduce toughness. However, fatigue testing of material paints a different picture, where the retained austenite containing steel, which converts to martensite during cyclic loading, has higher resistance to fracture."



Translation: In attempting to make things better (and more expensive), custom makers often make things worse...

Quote: "Another conventionally cast steel with a lower carbide volume, however, showed superior resistance to fracture due to its higher fracture toughness from a small carbide volume combined with a relatively large average distance between carbides."

Which is interesting.

My favourite though is this:

Quote: Therefore side loading requires less stress to fracture the edges and chipping can occur along the carbide bands [15]:

If the knives are oriented along the transverse direction instead, then the tips of the blades would fail more easily in a similar fashion"



This all by itself could explain the discrepancy in my first photo: It probably should be a major item of knife choice to decide how the blade is oriented to the rolling grain.

Since most customs are preoccupied with overall strength, they are likely cut along the grain. Since cheapo factory knives don't care, or go for the easiest layout, they might be cutting them perpendicular to the grain, resulting in superior edges.

Yes there is a cost in point strength, but it can be alleviated by point design. The primary purpose is to cut after all... I have to say that generally, if you exclude a Randall Model 12 and its unique forged stainless (which was not much better than equal), I have never seen custom knives that out-performed good factory knives with equivalent geometry. The prevalence of CPMs in customs, relative to cheaper "conventional" factory steels, has made this discrepancy even greater...

Gaston

I just mention what is routinely observable:

That's curious, because chopping, edge angles and bevel thickness are never mentioned once in the entire article. In fact the term "edge geometry" does not appear once. Amazing what can be read into things...

I'll tell you what I took away from it:

Quote: "It is very common for custom knifemakers to use cryogenic processing of their steels which eliminates most of the retained austenite in the steel. I wrote a forum post about what retained austenite is and what cryo treatments do. Toughness testing usually shows an increase in toughness with greater retained austenite, as can be seen in this figure for 440C [5]:

However the concern sometimes is that through stressing of the steel with retained austenite present that the austenite will transform to (untempered) martensite and therefore the brittle phase will act to reduce toughness. However, fatigue testing of material paints a different picture, where the retained austenite containing steel, which converts to martensite during cyclic loading, has higher resistance to fracture."



Translation: In attempting to make things better (and more expensive), custom makers often make things worse...

Quote: "Another conventionally cast steel with a lower carbide volume, however, showed superior resistance to fracture due to its higher fracture toughness from a small carbide volume combined with a relatively large average distance between carbides."

Which is interesting.

My favourite though is this:

Quote: Therefore side loading requires less stress to fracture the edges and chipping can occur along the carbide bands [15]:

If the knives are oriented along the transverse direction instead, then the tips of the blades would fail more easily in a similar fashion"



This all by itself could explain the discrepancy in my first photo: It probably should be a major item of knife choice to decide how the blade is oriented to the rolling grain.

Since most customs are preoccupied with overall strength, they are likely cut along the grain. Since cheapo factory knives don't care, or go for the easiest layout, they might be cutting them perpendicular to the grain, resulting in superior edges.

Yes there is a cost in point strength, but it can be alleviated by point design. The primary purpose is to cut after all... I have to say that generally, if you exclude a Randall Model 12 and its unique forged stainless (which was not much better than equal), I have never seen custom knives that out-performed good factory knives with equivalent geometry. The prevalence of CPMs in customs, relative to cheaper "conventional" factory steels, has made this discrepancy even greater...

Gaston

Cryoed, no chippy.

Show me which way the grain is going on this sheet of steel? Is it rolling or transverse?