Difference between hardness/strength and edge retention/wear resistance

B

Bo-dacious

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Aug 13, 2016
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Hey guys, I've been studying knife steels and their characteristics, but I'm a bit confused on something. Maybe I'm just using the wrong sites.
What is the Difference between hardness and strength? The site I'm on didn't differentiate that.

And what is the difference between edge retention and wear resistance? It says wear resistance is the ability to withstand abrasive and adhesive wear. Wouldn't that be edge retention too? Or does ER include impacts and other damage?

Also, could someone explain adhesive wear to me? It says "Adhesive wear occurs when debris is dislodged from one surface and attaches to the other." can someone give examples? And how is debris getting attached to a knife considered damage?

I understand this stuff for the most part, just need a bit of clarification.

Thank you for your time, guys,

Bo
 
How is debris getting attached to your knife considered WEAR? *
That leads me to another question... Is wear and damage the same thing? Or is damage just cracks and chips?

Bo
 
Hardness and strength are related. Hardness is the resistance to indentation like from a hardness test. Strength is generally measured in a specific direction, such as tension, compression or shear. Higher strength generally reults in higher hardness, but not always.

Wear resistance is one component of edge holding. Edges either roll, wear, or break. High hardness prevents rolling, high wear resistance prevents wear, and high ductility and toughness prevent breaking. Its difficult to get very high ratings in all 3, so we have to decide which is more important for the application.

Adhesive wear occurs at the high local pressures involved in cutting, typically when cutting metal, often at high speed, and thus high temperature. The temperature and pressure are sufficient to weld a bit of the workpiece to the tool bit, and then break a piece out of the bit or edge. Adhesive wear is typically not a problem for hand held knives.

Wear is a form of damage, just as cracking and chipping. Increased hardness and strength also increase wear resistance, though steel alloy chemistry is more effective.
 
me2 said:
Hardness and strength are related. Hardness is the resistance to indentation like from a hardness test. Strength is generally measured in a specific direction, such as tension, compression or shear. Higher strength generally reults in higher hardness, but not always.

Wear resistance is one component of edge holding. Edges either roll, wear, or break. High hardness prevents rolling, high wear resistance prevents wear, and high ductility and toughness prevent breaking. Its difficult to get very high ratings in all 3, so we have to decide which is more important for the application.

Adhesive wear occurs at the high local pressures involved in cutting, typically when cutting metal, often at high speed, and thus high temperature. The temperature and pressure are sufficient to weld a bit of the workpiece to the tool bit, and then break a piece out of the bit or edge. Adhesive wear is typically not a problem for hand held knives.

Wear is a form of damage, just as cracking and chipping. Increased hardness and strength also increase wear resistance, though steel alloy chemistry is more effective.
Click to expand...
Excellent post
 
Great post me2. To be honest about all of these properties, they confuse me and your post helped with that. I have a lot of problem deciding what is important. When in doubt go with 1095 is what I always say.
 
Very well said...

I too typically still use 1095 and 440c as the measuring sticks of other steels.
ie. "How much better is it then (1095/440c) at; edge retention, wear resistance, toughness, stainlessness, ease of use, (price)?" etc. To make a somewhat educated decision on knives to purchase...
 
Me2: this is great information thank you! But can you clarify the meanings of tension, compression and shear?

Thanks guys,.
Bo
 
I’ve found that some of the terms for a steel reflects the intended use is confusing when it comes to the same steel used for knives.
I like to refer to the knifesteel faq to help keep me from getting too confused.
 
When you guys say "knifesteel FAQ" do you mean the one on blade forums, the site that's all black with white writing?

Thanks guys,
Bo
 
me2 said:
Hardness and strength are related. Hardness is the resistance to indentation like from a hardness test. Strength is generally measured in a specific direction, such as tension, compression or shear. Higher strength generally reults in higher hardness, but not always.

Wear resistance is one component of edge holding. Edges either roll, wear, or break. High hardness prevents rolling, high wear resistance prevents wear, and high ductility and toughness prevent breaking. Its difficult to get very high ratings in all 3, so we have to decide which is more important for the application.

Adhesive wear occurs at the high local pressures involved in cutting, typically when cutting metal, often at high speed, and thus high temperature. The temperature and pressure are sufficient to weld a bit of the workpiece to the tool bit, and then break a piece out of the bit or edge. Adhesive wear is typically not a problem for hand held knives.

Wear is a form of damage, just as cracking and chipping. Increased hardness and strength also increase wear resistance, though steel alloy chemistry is more effective.
Click to expand...

Great information, me2. Where does "brittleness" fit into these properties? Is that related to ductility?
 
Bo-dacious said:
Me2: this is great information thank you! But can you clarify the meanings of tension, compression and shear?

Thanks guys,.
Bo
Click to expand...

I think I can. Tension is when a piece of steel is being pulled apart. Think of bolts used to hold a hanging flower pot over head or maybe a fishing line pulling in a fish. Another example is rope in a tire swing. Things like rope and fishing line only work I tension.

Compression is when something is being pushed together. A classic example is a column in a building, or the legs of a stool or chair.

Shear is a little trickier to visualize. Take two flat pieces of steel with a couple of holes drilled in them. Now lay one piece on top of the other and bolt them together through the holes. Push the piece on the bottom left and the piece on top right, trying to slide them apart. The bolts are in shear.
 
sparkyvega said: ↑
Great information, me2. Where does "brittleness" fit into these properties? Is that related to ductility?

I look at brittleness in a slightly different way. Take a knife and lock the handle into a vise with the blade sticking up... Then use a vise-grip (or whatever) and try to bend (flex) the knife-blade sideways to a different angle. A brittle blade (too hard) will snap before the blade gets bent over too far, whereas a steel with a softer heat-treat will sometimes allow the blade to be bent over to a full 90 degrees and then it returns again to a straight position when the vise-grip is removed. Some knives may also bend without breaking, but might not return to a perfectly straight position again. Many factors here...steel and chemical composition, parameters of heat-treat, Rockwell hardness, etc. CPM-3V is a steel which is tough enough to withstand this type of stress from some manufacturers. Again, heat-treat will affect brittleness or toughness....
 
Please understand that when I use terms like tension, compression etc. I am primarily using the materials/engineering definitions. Others use these terms more casually and in the knife industry they can have slightly different meanings. SonnyDaze example is an example.

From my perspective, what you (Sonnydaze) are describing is a fairly complicated case of all three types of stress, as well as ductility. Ductility is the ability to permanently stretch without cracking or breaking. Plastic soda can rings have high ductility. Glass soda bottles have none.

The outside of the bend is in tension. The inside is in compression. Down the center, there is a fair bit of shear stress, as the outer and inner sides are trying to slide past each other. This shear is usually not enough to cause any trouble though.

If I may, I would like to differentiate between bending and flexing. Bending implies a permanent set is left even when the blade is released. Flexing indicates the blade returned to straight when released.

With that out of the way, the outside of the bend needs sufficient ductility to stretch without cracking. However, if only flexing is happening, no ductility is required. I have flexed blades as hard as 66 HRc to 90 degrees a dozen times with no effect on the blade. I have also bent them and after straightening, there was no noticeable difference. Heat treatment plays a role in toughness, ductility, and bending. As long as a blade is only being flexed, the only thing heat treatment determines is when bending starts. Cross sectional geometry and blade length affect flexing.
 
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