The role of toughness in slicing edge retention

Fancier

Fancier

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A popular rope testing thread inspired a couple of questions about the role of toughness in improving slicing wear resistance.
I'm still wondering about that relationship, and rather than side track a thread that a lot of people have bookmarked I decided to start a new one.
The back story is that it seems to me that toughness isn't very relevant in slicing wear resistance as long as you have enough toughness to prevent the blade from gross failure.
I base this on the observation that the most wear resistant steels tend to have lower impact resistance (are less tough) especially when treated to be very hard, and when very hard the steel has improved wear resistance.
I'm not saying that toughness isn't a good property in a knife steel, but I do think that for the purposes of increasing the slicing wear resistance trading a lower toughness for increased hardness is a good practice.
This might bring up the old argument about whether is it better to use a low carbide steel with a thinner profile or to use a high carbide steel with a thicker profile. It is possible that the original discussion would have gone in that direction, which is one of the reasons that I stopped posting on that thread.
So, for knives of the same blade geometry, hardness, and sharpness, what would you gain in slicing wear resistance by using a tougher steel?
 
Wear resistance is a completely different property than toughness.
 
I tried to tell you that very same thing in the other thread. Believe me now? When making a steel choice, you need to determine what the main use of the knife will be and choose accordingly. If you're making a slicer, wear resistance is of greater importance than toughness. When making a chopper, toughness is more important than wear resistance.
Any knifemaker worth his salt should be able to ask you a few questions about how a knife will be used and come up with the proper combination of steel choice, hardness, & edge geometry.
Extreme toughness is a property that is wasted if it isn't needed. That's why you don't see people making Chef's knives out of S7, it would be overkill in toughness and give up an extreme amount of edge holding to other steels better suited for knives of that type. Toughness is WAY over-rated in most knives. As long as the blade doesn't chip out when the knife is being used for its intended tasks then all is well.
 
Also, a lot of people confuse toughness & strength. Toughness is about impact resistance at the edge. Strength has more to do with lateral stresses such as prying, torqueing, etc..
 
Given the same blade geometry (and as long as that geometry is sufficient to prevent edge failure given the intended work) wear resistance will trump toughness when it comes to edge retention. In other words, high wear resistance steels will highly resist wear. :p

The only part of this discussion that is actually interesting IMO is whether or not a tougher/stronger steel can accomplish the same work in a thinner geometry than what is required for a high wear resistance steel. If the answer is yes, then it becomes interesting to question what difference that could have on cutting ability and edge retention.
 
I believe that Stellite 6K is around 47 HRC, and even at that very low hardness, is still not tough by any means. Although I believe that with the carbides it contains, the edge retention is quite high when the blade is used in the appropriate application.
 
kniferbro said:
I think OP means "the effect of toughness on EDGE RETENTION"
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Increased toughness is an improvement if it does not also decrease strength. Edges may be dulled by abrasive wear, chipping (fracturing), or rolling (plastic deformation.) Increased toughness improves resistance to chipping damage, increased strength increases resistance to rolling damage, and increased wear resistance increases...resistance to wear. :D

Depending on the application range of a given tool it may sometimes be worth increasing resistance to one of these edge retention mechanisms at the expense of another.
 
Darrin Sanders said:
I tried to tell you that very same thing in the other thread. Believe me now? When making a steel choice, you need to determine what the main use of the knife will be and choose accordingly. If you're making a slicer, wear resistance is of greater importance than toughness. When making a chopper, toughness is more important than wear resistance.
Any knifemaker worth his salt should be able to ask you a few questions about how a knife will be used and come up with the proper combination of steel choice, hardness, & edge geometry.
Extreme toughness is a property that is wasted if it isn't needed. That's why you don't see people making Chef's knives out of S7, it would be overkill in toughness and give up an extreme amount of edge holding to other steels better suited for knives of that type. Toughness is WAY over-rated in most knives. As long as the blade doesn't chip out when the knife is being used for its intended tasks then all is well.
Click to expand...

This should be a sticky somewhere....
 
Surfingringo said:
Given the same blade geometry (and as long as that geometry is sufficient to prevent edge failure given the intended work) wear resistance will trump toughness when it comes to edge retention. In other words, high wear resistance steels will highly resist wear. :p

The only part of this discussion that is actually interesting IMO is whether or not a tougher/stronger steel can accomplish the same work in a thinner geometry than what is required for a high wear resistance steel. If the answer is yes, then it becomes interesting to question what difference that could have on cutting ability and edge retention.
Click to expand...

Something I'd like to know too.
 
Surfingringo said:
Given the same blade geometry (and as long as that geometry is sufficient to prevent edge failure given the intended work) wear resistance will trump toughness when it comes to edge retention. In other words, high wear resistance steels will highly resist wear. :p

The only part of this discussion that is actually interesting IMO is whether or not a tougher/stronger steel can accomplish the same work in a thinner geometry than what is required for a high wear resistance steel. If the answer is yes, then it becomes interesting to question what difference that could have on cutting ability and edge retention.
Click to expand...

Lance, by nature, tougher steels allow thinner geometry for the same main use a knife will see. When making any type of knife your goal should be to make it as thin and as hard as possible without any edge damage during the use it was designed for.
Think of steel choice as selecting a channel on a TV or radio. Think of hardness & edge geometry as fine tuning. Toughness all boils down to how much you actually need to perform a given task. If you use a steel that is tougher than you need for a given application then you're giving up something and there is a pretty good chance that its wear resistance.
Most people don't need as much toughness as they think they do. 10V is not considered to be a tough steel but I have personally drove a 10V blade through cross grain hard Maple with no damage. Next I drove it through cross grain Osage Orange with no damage. Finally I drove it through an Axis antler tine that was about 3/4" in diameter and the only damage was a slight shiny spot in the area that was in contact with the antler. If you wanna call that damage. The blade was .080" at the Ricasso, was approx. .010" behind the edge, & the hardness was RC-63.
Geometry makes a big difference in the exact same knife. I've made knives that were ground extremely thin that chipped out slightly but once the chip was removed it performed the same task with no damage due to the slight change in geometry.
Everything is a trade-off. To gain something in one area, you have to give up something in another area. Hey, that sounds a lot like women don't it? LOL
 
Darrin Sanders said:
I tried to tell you that very same thing in the other thread. Believe me now? When making a steel choice, you need to determine what the main use of the knife will be and choose accordingly. If you're making a slicer, wear resistance is of greater importance than toughness. When making a chopper, toughness is more important than wear resistance.
Any knifemaker worth his salt should be able to ask you a few questions about how a knife will be used and come up with the proper combination of steel choice, hardness, & edge geometry.
Extreme toughness is a property that is wasted if it isn't needed. That's why you don't see people making Chef's knives out of S7, it would be overkill in toughness and give up an extreme amount of edge holding to other steels better suited for knives of that type. Toughness is WAY over-rated in most knives. As long as the blade doesn't chip out when the knife is being used for its intended tasks then all is well.
Click to expand...
Hello Darrin, I believed you then, and I believe you now.
I did want to see a little more discussion on the topic in a more general environment without taking up space in Ankerson's thread.
Thanks for your input and your patience. :)
 
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