Question about black stonewashed hrc

G

gambilonia

Joined
Aug 22, 2020
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13
Hey guys!

I’m planning to buy a new knife, but I have found some information that doesn’t make me very happy.

If you go to Civivi’s website, you will notice black stonewashed blades have 1hrc lower than non black blades.
One of the website users even questioned them, to which they gave a bit of a confusing reply:

“We would like to tell you that usually the hardness of the blade (Nitro-V) is 59-61HRC, but the black coating would be 58-60HRC.
This is because the hardness of the black coating process changes during production.”

Now, this bit of info is keeping me from buying black stonewashed knives, but why is it that the process changes the hrc?
Is it because the top black layer is softer? Or does the whole blade change in hardness?
 
I suspect when they do the HRC indenter test, they do it after the blade has been coated. Yes, the coating is softer than the steel, so the results are skewed slightly lower.

I do not believe the base metal of the blade is softer.

I would not worry about +/- 1 HRC. Knife blade hardness is rarely stated as a definite number, it is always a range to account for steel and process variables.
 
shane45-1911 said:
I suspect when they do the HRC indenter test, they do it after the blade has been coated. Yes, the coating is softer than the steel, so the results are skewed slightly lower.

I do not believe the base metal of the blade is softer.

I would not worry about +/- 1 HRC. Knife blade hardness is rarely stated as a definite number, it is always a range to account for steel and process variables.
Click to expand...
First I’ve ever heard of this theory, but it does make a lot of sense!
I’ve kind of wondered the same thing after hearing about the DLC blades being -1 HRC pretty much across the board on WE/Civivi’s lineup.
 
It may be that the temperature of the process tempers the blade slightly. If this is true it would also increase toughness a bit.

The knife steel nerds would likely know for sure.

Civivi's Nitro-V is very good.
 
nhobo said:
It may be that the temperature of the process tempers the blade slightly. If this is true it would also increase toughness a bit.
Click to expand...

Nope.

The vapor deposition process typically used to apply the coating is not temperature-related, at least not enough to change temper. While the chamber is typically heated, it is not hot enough to change the blade's HRC. It is a process done in a vacuum allowing better molecular adhesion to the substrate (knife blade, in this case).
 
shane45-1911 said:
Nope.

The vapor deposition process typically used to apply the coating is not temperature-related, at least not enough to change temper. While the chamber is typically heated, it is not hot enough to change the blade's HRC. It is a process done in a vacuum allowing better molecular adhesion to the substrate (knife blade, in this case).
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I'm pretty sure the temperature ranges for applying both black oxide and pvd are above typical tempering ranges for blade steels like Nitro-V... Now as for the length of time required at those temperatures before experiencing a drop in hardness, I'm not sure. But several minutes at over 100°F above the tempering range probably does affect it somewhat.

Edited spelling
 
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pholder said:
If they didn’t give Rockwell information on either, you would probably buy the one that you want. I don’t think you will notice one point in actual use.
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It's entirely possible to get a coated AND uncoated blade and have them at the same HRC, given their ranges overlap. I wouldn't worry too much about it, unless you have a specific need for a higher hardness blade.
 
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