A Question About Rockwell Hardness

R

rummels

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How does a person know what they are getting with respect to Rockwell hardness when they buy a knife? Most manufacturers give a range for hardness when they describe their knives, yet many of the discussions I have read indicate that there can be a noticeable difference between a steel that is 58 HRC and the same steel at 60 HRC.

For example, Ankerson's excellent info on edge retention he shows S30V at 60 HRC being in Category 5 and S30V that is at 58.5 HRC being in Category 7. So when I look at a manufactures description of a knife that says their steel is 58-60 HRC, how do I know whether I am getting a knife with 58 HRC or a knife with 60 HRC, and does it make that big of a difference?

Thanks
Rummels
 
It's fairly easy to see the difference a single point of hardness can make. Now, hardness is more of a general description and not so much a precise value. It's a average taken from three testing points on the blade and you can have variation of .1-1 point of hardness on any given sample.

A large knife maker heat treats a large volume of blades at the same time, they don't get individual heat treatments like you find with a custom knife maker thus the reason for a 1-2 point spread in factory hardness.
 
I know this isnt really the kind of answer you're looking for, but.....
I agree with what others have said about the variation. A company pumping out thousands of knives has a hard time keeping track of things that "small".
After a bit of use, like cutting wood or cardboard, check the edge and it can tell you alot about how hard it is.
From what Ive noticed, a certain company tends to treat all of their knives relatively the same.
Cold Steel tends to be softer, Kershaw tends to be a bit harder, and BUCK falls somewhere in the middle.
IMO, YMMV.
 
Testing is conducted on samples. The machine gives ASTM numbers in a 'range' +- 1. It's not an exact number. Do think of it in these terms. However, it is defined. DM
 
Jason B. said:
It's fairly easy to see the difference a single point of hardness can make. Now, hardness is more of a general description and not so much a precise value. It's a average taken from three testing points on the blade and you can have variation of .1-1 point of hardness on any given sample.

A large knife maker heat treats a large volume of blades at the same time, they don't get individual heat treatments like you find with a custom knife maker thus the reason for a 1-2 point spread in factory hardness.
Click to expand...

But which is it, number 1 or 2?

Does a Rockwell format of "58-60" indicate that all points on the blade fall within that range....or....a 'margin of error' of two points in the whole blade hardness among all pieces treated in a batch? It's still two different things.

Isn't it?
 
Interesting thread. I think a lot of people get duped into buying supersteels that perform at a certain level at optimal RC, only to get a mass produced blade that's been heat treated to a much lesser hardness and thus really not the at the same level of performance they might have expected. I have an SnG in S110V and I had it tested by Big Chris and it came back at 60rc. I think ideal for that steel is 62-64rc. Maybe Jim Ankerson will stop by to comment for exact details, but I remember reading a test of his that indicated that 110v had lesser edge retention than s30v when both are hardened to 60rc. I might be fuzzy on the details, though.
 
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It's a great question, but one for which there is no easy answer. You can have the blade tested for hardness, but that's expensive and a hassle. Basically, it comes down to luck. I had a blade tested that was supposed to be 60-62 Rc. It turned out to be 59 Rc (could have been 59.x). So the spread can be larger than the target hardness advertised.

You can look at the type of damage your edge shows when you push it hard within your normal use of knives. If the edge rolls, your blade probably lacks hardness (strength) for the types of use you give it. If it chips, it probably lacks toughness, which could mean it is run too hard for your uses.
 
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