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Toughness vs. Edge Holding
- Thread starter Don G
- Start date
- Joined
- Apr 19, 1999
- Messages
- 3,560
In knife terms toughness refers to resistance to chipping or breakage.
Edge holding is just that. It is a function of blade metallurgy and hardness.
The trade off between extreme hardness(or best edge holding) and toughness is usually related to tempering or the softening of the blade after heat treating to reduce brittleness although the metal used has some influence here.
It is possible to have a blade that is extremely hard and great edge holding but as brittle as glass which is then tempered to a little softer state where a little of the edge holding is lost but the blade will no longer be brittle. This is sometimes referred to as working temper.
The battle to trade off these two characteristics is why we have so many varieties of knife steels. No one steel is suitable for all purposes so choices have to be made based on intended use, processing parameters, and available facilities.
This battle is often refered to by makers as
"The Flavour of The Month Club". Whenever a new steel is reported on in the mags there is a demand for that steel that quickly subsides when the next report comes out.
------------------
george
www.tichbourneknives.com
sales@tichbourneknives.com
Edge holding is just that. It is a function of blade metallurgy and hardness.
The trade off between extreme hardness(or best edge holding) and toughness is usually related to tempering or the softening of the blade after heat treating to reduce brittleness although the metal used has some influence here.
It is possible to have a blade that is extremely hard and great edge holding but as brittle as glass which is then tempered to a little softer state where a little of the edge holding is lost but the blade will no longer be brittle. This is sometimes referred to as working temper.
The battle to trade off these two characteristics is why we have so many varieties of knife steels. No one steel is suitable for all purposes so choices have to be made based on intended use, processing parameters, and available facilities.
This battle is often refered to by makers as
"The Flavour of The Month Club". Whenever a new steel is reported on in the mags there is a demand for that steel that quickly subsides when the next report comes out.
------------------
george
www.tichbourneknives.com
sales@tichbourneknives.com
I just want to add that the toughness/edge-holding trade-off applies to a given steel at different hardnesses. When you start comparing one steel to another, things get much more complicated.
As a quick (and I hope fairly non-controversial) example, ATS-34 exhibits superlative edge-holding at an Rc of 61 but is also extremely brittle and prone to chipping when that hard. Take it down to 58-59Rc and edge-holding decreases slightly but toughness increases and chipping virtually stops. 440V, in contrast, can reach similar levels of edge-holding (to ATS-34 at 61 Rc) while at an Rc of 57-58, where it is also very tough.
I'm not trying to show by this example that the Rockwell hardness is an ultimate scale, either, just that different steels work differently and direct comparisons are difficult. When just talking one steel, you can generally speak of edge-holding and toughness as a trade-off that is dictated mainly by hardness, but when you talk between steels the water gets muddy very quickly.
-Drew
As a quick (and I hope fairly non-controversial) example, ATS-34 exhibits superlative edge-holding at an Rc of 61 but is also extremely brittle and prone to chipping when that hard. Take it down to 58-59Rc and edge-holding decreases slightly but toughness increases and chipping virtually stops. 440V, in contrast, can reach similar levels of edge-holding (to ATS-34 at 61 Rc) while at an Rc of 57-58, where it is also very tough.
I'm not trying to show by this example that the Rockwell hardness is an ultimate scale, either, just that different steels work differently and direct comparisons are difficult. When just talking one steel, you can generally speak of edge-holding and toughness as a trade-off that is dictated mainly by hardness, but when you talk between steels the water gets muddy very quickly.
-Drew
Edge holding and toughness is thrown around like apple pie. Nobody seems to have a criteria for their claims of edge holding that is very standard. All hemp or manilla
rope is the same. I've got some rope that
I can do over 700 cuts some that the same
blade won't do 75 on and some inbetween.
I'll admit the 75 cut rope is the worst I've
seen but there is a difference. The profile
or geometry of the blade is also a factor.
The amount of pressure put on the blade is also another factor. It always made me wonder about a certain knife that was advertised about edge holding with a wooden malet in the background. It would be interesting to get about a dozen different knive blades and test them on the same piece of rope and measure the same amount of pressure..... it can be done!!!
Goshawk
------------------
http://www.imt.net/~goshawk
Don't walk in tradition just because it feels good!!!!!
Romans 10:9,10
Psalm 91
rope is the same. I've got some rope that
I can do over 700 cuts some that the same
blade won't do 75 on and some inbetween.
I'll admit the 75 cut rope is the worst I've
seen but there is a difference. The profile
or geometry of the blade is also a factor.
The amount of pressure put on the blade is also another factor. It always made me wonder about a certain knife that was advertised about edge holding with a wooden malet in the background. It would be interesting to get about a dozen different knive blades and test them on the same piece of rope and measure the same amount of pressure..... it can be done!!!
Goshawk
------------------
http://www.imt.net/~goshawk
Don't walk in tradition just because it feels good!!!!!
Romans 10:9,10
Psalm 91
All of the above, sorta.
Most steels will change in relationship between their toughness and potential for edge holding depending on the hardness. A general statement would be that the lower the Rockwell hardness, the tougher the blade, or the more shock and impact resistant it is, down to the point that the steel is spring tempered, Rc 48-50. At the same time, the edge holding, or what they call abrasion resistance, increases as the hardness increases, until it reaches the point that it becomes too brittle, and will chip if used hard.
Corduroy made a good point. Each steel is different, and each has a certain point where the tradeoffs become more extreme. Heat treat ATS-34 too hard, and it becomes brittle. Heat treat 440C fairly soft Rc 56-57, and it is not the best at edge holding, but it is very impact resistant, much more than the other 'stainless' steels.
Something like 5160 spring steel is optomized when the hardness of the edge is Rc57-58, since it retains a lot of the toughness it is capable of. Differentially heat treating it so that the back is softer will make it even better.
Some of the new powdered metal technology steels are interesting, since they seem capable of combining the toughness of tool or spring steels, with better edge holding. I've been trying some CPM3V, and it can be used at a fairly high Rc, 59-60, and testing so far seems to indicate that it can hold an edge similar to a harder piece of D-2, but be as tough as a piece of 5160 tempered softer. For a heavy use knife, that is a good combination for all but those who want the steel to be a bit softer and easier to sharpen. According to the manufacturers specs, it too can be pushed even harder, with even better edge holding, but past Rc60, the impact resistance drops off substantially.
A lot depends on what you want to use the steel for, and what you value most, toughness, edge holding, ease of maintenance, or whatever. A lot of folks would be served better by something like a 1095 or 5160 carbon steel blade, or something like 440C stainless. The first are tough and very easy to sharpen, and the other is fairly tough, not bad to sharpen, and corrosion resistant enough to require little maintenance.
The higher end tool steels, like D-2 and M-2 and the new stainless steels, like BG-42, and CPM steels work very well, but the user has to know better how to sharpen them, since they are so good at edge holding. That also means that they also want to stay dull longer too!
madpoet
Most steels will change in relationship between their toughness and potential for edge holding depending on the hardness. A general statement would be that the lower the Rockwell hardness, the tougher the blade, or the more shock and impact resistant it is, down to the point that the steel is spring tempered, Rc 48-50. At the same time, the edge holding, or what they call abrasion resistance, increases as the hardness increases, until it reaches the point that it becomes too brittle, and will chip if used hard.
Corduroy made a good point. Each steel is different, and each has a certain point where the tradeoffs become more extreme. Heat treat ATS-34 too hard, and it becomes brittle. Heat treat 440C fairly soft Rc 56-57, and it is not the best at edge holding, but it is very impact resistant, much more than the other 'stainless' steels.
Something like 5160 spring steel is optomized when the hardness of the edge is Rc57-58, since it retains a lot of the toughness it is capable of. Differentially heat treating it so that the back is softer will make it even better.
Some of the new powdered metal technology steels are interesting, since they seem capable of combining the toughness of tool or spring steels, with better edge holding. I've been trying some CPM3V, and it can be used at a fairly high Rc, 59-60, and testing so far seems to indicate that it can hold an edge similar to a harder piece of D-2, but be as tough as a piece of 5160 tempered softer. For a heavy use knife, that is a good combination for all but those who want the steel to be a bit softer and easier to sharpen. According to the manufacturers specs, it too can be pushed even harder, with even better edge holding, but past Rc60, the impact resistance drops off substantially.
A lot depends on what you want to use the steel for, and what you value most, toughness, edge holding, ease of maintenance, or whatever. A lot of folks would be served better by something like a 1095 or 5160 carbon steel blade, or something like 440C stainless. The first are tough and very easy to sharpen, and the other is fairly tough, not bad to sharpen, and corrosion resistant enough to require little maintenance.
The higher end tool steels, like D-2 and M-2 and the new stainless steels, like BG-42, and CPM steels work very well, but the user has to know better how to sharpen them, since they are so good at edge holding. That also means that they also want to stay dull longer too!
madpoet
Another interesting thread!
Mel: Looking forward to your 3V "little knife"
Can you do differential heat treatment on this CPM steel? I am quite interested in the process and used to ask in rec.knives about which steel can/cannot be heat treated differentially and why, but they kinda got bored and ignored my question.
I can understand edge holding/toughness is like a tradeoff i.e. increasing one might sacrifice the other . I tend to have more difficulty interpreting edge holding v.s. "wear resistance." Is there a relation between these two qualities? Can a knife holds an edge well but has poor wear resistance, or vice versa? Indeed I don't know in what circumstance would the wear resistance be much useful to knives. Imagine if there exists a knife with excellent wear resistance but poor edge holding, we would spend an hour sharpening it and then dull the edge after a few cuts ?
Dew.
Mel: Looking forward to your 3V "little knife"
I can understand edge holding/toughness is like a tradeoff i.e. increasing one might sacrifice the other . I tend to have more difficulty interpreting edge holding v.s. "wear resistance." Is there a relation between these two qualities? Can a knife holds an edge well but has poor wear resistance, or vice versa? Indeed I don't know in what circumstance would the wear resistance be much useful to knives. Imagine if there exists a knife with excellent wear resistance but poor edge holding, we would spend an hour sharpening it and then dull the edge after a few cuts ?
Dew.
Wear resistance has a direct realtionship to
edge holding. I've tried 3v on the same
basis as 52100 as far as differentially hardening and it hasn't worked very well.
If a person were to put a clay on the back
and be able to soak the whole blade at a
higher heat in a furnace ( as I plan to do)
I feel it might work. Talking about trade offs in edge holding and toughness... I haven't found alot of trading off to do with
52100 and I'll tell you right now it ain't no flavor of the month steel it'll be around for
a long time. Toughness is usually tested for
by checking the chipping of the edge and bending. The bending is usually done with
a long thin blade. Try a four inch blade with a distal taper and being between 1/4 and
3/16 at the start of the riccaso. That will
put a test on blade toughness it's very interesting even exciting.
goshawk
------------------
http://www.imt.net/~goshawk
Don't walk in tradition just because it feels good!!!!!
Romans 10:9,10
Psalm 91
edge holding. I've tried 3v on the same
basis as 52100 as far as differentially hardening and it hasn't worked very well.
If a person were to put a clay on the back
and be able to soak the whole blade at a
higher heat in a furnace ( as I plan to do)
I feel it might work. Talking about trade offs in edge holding and toughness... I haven't found alot of trading off to do with
52100 and I'll tell you right now it ain't no flavor of the month steel it'll be around for
a long time. Toughness is usually tested for
by checking the chipping of the edge and bending. The bending is usually done with
a long thin blade. Try a four inch blade with a distal taper and being between 1/4 and
3/16 at the start of the riccaso. That will
put a test on blade toughness it's very interesting even exciting.
goshawk
------------------
http://www.imt.net/~goshawk
Don't walk in tradition just because it feels good!!!!!
Romans 10:9,10
Psalm 91
Cliff Stamp
BANNED
- Joined
- Oct 5, 1998
- Messages
- 17,562
Abrasion resistance is not directly correlated to edge holding. It depends on what you are doing with the blade.
For example comparing an Ontario (1095) and Tramontina machetes. The Ontario machete is much harder, I can literally chop into the Tramontina without indenting the edge on the Ontario. If I use them on soft woods the Ontario goes much longer without getting dull. If I use them on small diameter hardwood the Ontario loses cm size chunks out of the blade and the Tramontina just goes blunt. In this case the Tramontina has better edge holding.
-Cliff
For example comparing an Ontario (1095) and Tramontina machetes. The Ontario machete is much harder, I can literally chop into the Tramontina without indenting the edge on the Ontario. If I use them on soft woods the Ontario goes much longer without getting dull. If I use them on small diameter hardwood the Ontario loses cm size chunks out of the blade and the Tramontina just goes blunt. In this case the Tramontina has better edge holding.
-Cliff
In another thread on 1095 a gentleman from Montana mentioned that 1095 tends to develop microcracks and be prone to premature failure if brine or water quenched as opposed to oil quenched. I seem to remember recently reading similar comments about W2, which was use to be more popular and I think is still used in some files. Although 'brittleness' seems to be due a combination of material, hardness, geometry and application, could the microcracks explain some of the problems that has been seen with Ontario blades breaking during hard use ?
Abrasion resistance is not the same as hardness!!!!!!!!!
Again abrasion resistance is directly related
to edge holding!!!!!!!!
The carbides have a great amout to do with
abrasion resistance and that can have an effect on hardness, but hardness isn't the
main factor in edge holding. I can take a
piece of mild steel and make it harder than
the hubs of hell, and it will cut a piece of
1" rope but it won't hold an edge
worth a tinkers damn. On the other hand take
a blade of 52100 at about 58 rc (approx)an
hold a beautiful edge.
------------------
http://www.imt.net/~goshawk
Don't walk in tradition just because it feels good!!!!!
Romans 10:9,10
Psalm 91
Again abrasion resistance is directly related
to edge holding!!!!!!!!
The carbides have a great amout to do with
abrasion resistance and that can have an effect on hardness, but hardness isn't the
main factor in edge holding. I can take a
piece of mild steel and make it harder than
the hubs of hell, and it will cut a piece of
1" rope but it won't hold an edge
worth a tinkers damn. On the other hand take
a blade of 52100 at about 58 rc (approx)an
hold a beautiful edge.
------------------
http://www.imt.net/~goshawk
Don't walk in tradition just because it feels good!!!!!
Romans 10:9,10
Psalm 91
An interesting project, maybe even a collection or product line, would be some plain, easy to make blades of the same shape and size offered in different materials. Such a line could even serve as a standard of sorts for comparing new materials. The Bladeforum 'Material Test Knife'.
- Joined
- Jul 30, 1999
- Messages
- 724
Edge geometry has a lot to due with toughness. As does hardness. Usually the harder the blade, the better the edge holding, the more brittle,and the harder it is to sharpen. Since I make tactical knives. I am very concerned with all of these aspects. My knives will be used hard. To insure that my knives will last, I flat grind them. This leaves more still behind the edge. This in turn makes them less susceptible to chipping. To insure edge holding, I harden them a lil' more than many makers. Due to the gage of steels I use, in comparison to knife size, they are still very tough. The only draw back is sharpening. They are difficult to sharpen. The plus side to that is that they seem to hold an edge almost indefinetly. As for the sharpening dilemma, I have a solution. It is Lifetime Free Sharpeningstandard on all of my knives.
------------------
Lynn Griffith-Tactical Knifemaker
PKA Member
www.angelfire.com/on2/griffithknives
------------------
Lynn Griffith-Tactical Knifemaker
PKA Member
www.angelfire.com/on2/griffithknives
- Joined
- Mar 31, 1999
- Messages
- 839
Don G
As someone has already mentioned there is no perfect all around steel [or maker].
Since all steels have a trade off [toughness-hardness] ask the maker you are interested in, what his trade off is and why. If he cannot give you the answer go to someone else. Find the maker that answers your questions and the steel that will work best for the type of knife you want.
As someone has already mentioned there is no perfect all around steel [or maker].
Since all steels have a trade off [toughness-hardness] ask the maker you are interested in, what his trade off is and why. If he cannot give you the answer go to someone else. Find the maker that answers your questions and the steel that will work best for the type of knife you want.
From what little I've read on industrial knives and cold work tool steels goshawk seems to have the right perception of what contributes to edge holding. What seems to be missing in some of the easy to access data is the continuous curve of hardness vs toughness and wear resistance, as different sites seem to make their comparisons at slightly different hardness levels and the properties can obviously change a lot. Still, Crucible noted that wear resistance seems to almost be directly related to the amount of vanadium carbides in the cold work steels that they discussed, and the content of carbide, vanadium or otherwise, was used to explain difference in wear resistance between A2 and D2.