So how much harder is 60 HRC than 59 HRC?

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KennyB

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Jan 19, 2010
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I see rockwell hardness numbers thrown around a lot, but I've never really seen anything that clearly defines how much harder 60 HRC is than 59 HRC. I looked around at the way the HR numbers are actually calculated, and found that in terms of measuring the depressions and everything that are actually used to get the hardness value, there's only a .000079" inch difference in depth in steel per HRC point. So I could then pretty easily visualize/imagine how deep each particular hardness value is penetrated--for example steel at 67 HRC will be penetrated .0025" into the steel, where as the diamond cone intender would penetrate .0035" at 55 HRC.

So at least that gives me a bit more sense to the level of difference between each value, but just knowing these numbers don't really translate into how much more wear resistance or how much more tensile strength a particular steel has at a particular hardness level. So I guess when someone compares 58 HRC to 60 HRC, how do you really quantify that difference?

I get the feeling that it's simply a matter of researching/studying how certain types of steels perform at varying hardness levels and then using that experience to decide on the appropriate value?
 
The scale is logarithmic, because the indenter is not the same area throughout its height. As you move up from the tip, the indenter gets larger, being conical in shape. So there is both a depth and circumference increase in the metal displaced.

Hardness testing is not for wear resistance; and while there is a general relationship to tensile strength, there is not an accurate conversion.
 
KennyB said:
So at least that gives me a bit more sense to the level of difference between each value, but just knowing these numbers don't really translate into how much more wear resistance or how much more tensile strength a particular steel has at a particular hardness level. So I guess when someone compares 58 HRC to 60 HRC, how do you really quantify that difference?
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There are a lot of variables there, two blades at the same HRC hardness can perform very differently depending on the tempering process.

It's not really something that can be answered in an absolute set in stone, this is the way it is manner.
 
From the "grinding" mods I've done on my BM grip (154cm 58-60RC) and my ZT(154cm 60-61RC), I can def say (at least in my case) the ZT's steel is harder
 
People who live in the rural southeastern US can understand it better. First you go out and catch yourself a big frog, then you pull out one of the hairs from the frog's back. The width of the hair is about equal to the difference between 59 and 60.
 
In truth Rockwell hardness is a value given because we cannot explain hardness properly.

The hardness of a object is not a equal value but a average because it changes throughout the material.

The indenter of a Rockwell machine pre-loads the surface then let's the steel relax before taking a measurement, this pre-load removes surface variation and allows a sequential value to be given.

I still have a hard time understanding that concept given the method of testing, but them the facts :)
 
Damn tough subject and a very good question.

How much different 8Cr13MoV @ 58-59 (Enlan) vs 60 (Resilience)? Perhaps someone that tested them can share the observation?
 
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