Terminology Questions: Wear Resistence, Strength, and Toughness

[Peter_E_Ryt]

I just read the little primer on the different steels at the top of the page and have a few questions regarding a few of the words.

Wear resistence is "the ability to withstand abrasion." How does this differ from stength? What about toughness? Cardboard is specifically mentioned in the tidbit involving toughness, and I'd think that it'd be a more abrasion related issue.

I do have it correct when I think of abrasion resistence as the edge being able to hold up to what it's cutting while being dulled down as little as possible, right?

Thanks!

 

[65535]

I would assume abrasion resistance would also effect it's sharpening ease.

 

[HoB]

I do have it correct when I think of abrasion resistence as the edge being able to hold up to what it's cutting while being dulled down as little as possible, right?

Actually, no. Abrasion resistance is quite literally the resistance against abrasion. But dulling is not only a mechanism of abrasion. The edge can go dull because of chipping, or rolling as well as by abrasion. Abrasion resistance is usually achieved by increased carbide volume. Hardness also plays a roll but is less important than you might think. Imagine a car tire: A car tire is not nearly as hard as steel but the rubber has enormous abrasion resistance which is the reason why you loose no more than 1/4" over 50,000 mi. Wear resistance is the most important aspect when thinking of sharpening. Modern abrasives can sharpen any steel, but a highly wear resistant steel need a lot more elbow grease to remove the same amount of material as a low wear resistant steel. Cardboard I would consider very abrasive, so abrasion resistance is important, but usually you find hard impurities in cardboard, which you hit while cutting, which can lead to chipping of the edge, so toughness is also to be considered (see below).

Strength is the resistance against deformation. This applies not only to the blade itself but most importantly to the edge which (because of its thinness) is easily deformed. On many non abrasive materials, the edge tends to dull by rolling such as cutting veggies on a cutting board. You can sharpen the edge by "bending it back" with a steel (burnishing). The stronger the edge, the less likely it is to roll. Strength and hardness are usually very closely related, but carbide volume is also a factor. Usually the strength of the edge (very important qualifier!) decreases with very large carbide volumes (the carbides are insufficiently supported).

There are several toughness measures. To keep it simple lets reduce it to two: Impact toughness and tensional toughness. Both are a measure how much energy you can put into the steel before it breaks, but one is a shock load and one is under a slowly (semi-statical) applied load. The failure mechanism is quite different. Often though a steel with high impact toughness has also high tensional toughness and vice versa, but that is not guaranteed. High toughness will prevent an edge from chipping or a blade from breaking, though tensional toughness considers the TOTAL deformation energy. A steel that has high toughness is not guaranteed to return to true after it is being deformed. The maxium energy that you can put into a material before it takes a set is referred to "resiliance".

 

[Peter_E_Ryt]

Thanks for the replies, yall!

According to Dictionary.com, abrasion is:

The process of wearing down or rubbing away by means of friction.

This would mean that ease of sharpening (or lack thereof), edge retention, and how easily the steal scratches are all functions of wear resistence. Did I miss any?

Strength is a hardness thing- but it can be Rc hardness or the hardness of the carbides that effect it.

Toughness works in an almost inverse manner- the less brittle, the more it can put up with, correct?

Thanks again!

 

[Jared Stenoien]

scratching the blade would actually be a function of hardness things like talonite are very soft, but very wear resistant

 

[L. Uebelein]

The way I understand strength and toughness, I could be wrong,

Strength: the ability to resist bending

Toughness: the ability to resist breaking

 

[HoB]

Well, as I said, wear resistance affects edge retention but only on abrasive media. Edge retention is dependent on all three: hardness (prevents the edge from bending), toughness (prevents the edge from chipping), wear resistance (prevents the edge from being abraded).

How easily it scratches is both hardness and wear resistance.

A picky material scientist would say that brittleness and toughness are not opposites, but for a general understanding I would say, it is perfectly fine to view brittleness and toughness as direct opposite.

 

[mete]

Toughness is a measure of impact strength ! It involves things such as fracture mechanics and is especially needed in such blades as kukris and machetes....Wear resistance - while the carbides are what provides wear resistance some carbides are better than others especially V, Mo, W so we see these in the most wear resistant tool steels. As far as toughness nickel has always been known to impart toughness as in L-6 !!

 

[Peter_E_Ryt]

Woooooooo- more replies!

I think that I've got it down- stength and toughness aren't overly compliced, however, I'd like to ask more question to make sure that I've got wear resistence down.

What exactly does wear resistence do for a blade? (This is THE question- if I can figure out its specific importance, I can figure out why/how it works). Abrasion resistence seems a little broad, and I can't seem that I've got the wrong idea of what abrasion resistence is in the first place ... so is there someone who could put it in different terms?

scratching the blade would actually be a function of hardness things like talonite are very soft, but very wear resistant

Does that mean soft as in a low Rc value, or soft as in soft carbides, because from what I've tried to piece together, wear resitence comes from carbide hardness.

Edit- I believe that I understand wear resistence now, but don't understand talonite. It holds a mean edge for a long time because of the amazing wear resistence, but is still very flexible because of the way that the carbides form their matrices (I think that's the right word). It's also supposed to be easyish to grind because of it's softness (Rc value coming from the way the carbides link). Why wouldn't the wear resistence (hard carbides?) cause problems with grinding it down like it does with D2 (I think)? Isn't the belt removing metal via abrasion (like scraping your knee on a sidewalk)?