Rockwell Tests-Who does them? How?

A

Akwacko

Joined
Jul 1, 2001
Messages
163
I got to thinking after seeing and taking for granted all kinds of posts that state the Rc. Does the manufacturer of the steel do the test or does the knife maker do it? Some knife makers do their own heat treat or so I've heard. Do they then test their own steel?

Anyone know how the tests are done?

Thanks for any info.

Bruce
 
Copied from my earlier post on the subject.

________________________________________

http://www.mee-inc.com/rockhar.html

http://www.gordonengland.co.uk/hardness/rockwell.htm

The testing of resistance to deformation by the penetration of a diamond cone with a 0.2mm radius spherical tip into the body of a hardened steel sample is only one indicator of physical properties.


B. Levine wrote an excellent summary of hardness testing.

http://pweb.netcom.com/~brlevine/rockw.txt

"quote from Wilson Instruments, maker of Rockwell

hardness testers, "... the Rockwell test is a measure of the

resistance of a material to permanent indentation. Indentation

hardness is not a fundamental property of a material. However,

reliable relationships have been established between the various

tests and important properties of materials -- for example,

tensile strength and machinability. Furthermore, indentation

hardness has become one of the more reliable controls of the heat

treatment and quality of manufactured parts."

The knife community is reading too much into the Rc numbers without considering other physical properties. The Rc is mainly for consistent quality control when heat treating.

Regards,
FK
 
well done, FK, good summary.

but not recommended you try to have it done on your blade. The diamond point will leave a nasty, sharp, little dent.

I also agree with FK, two blade materials can have the same RC hardness and perform differently due to chemistry of the steel. My CPMS30V blade stays sharper longer than my 154CM blade of the same RC hardness number. And even some cheaper plain high carbon steel blades with lower hardness take a better edge. So hard is fine, but don't let that be the main factor.

You can get a pretty good idea if your blade is hardened when you sharpen it. The stones will glide over a real hard blade if you just push lightly. Another test, that you don't want to do, is with a file. Most files are in the RC 60 range. So a file will cut/scratch soft steel real easy but hardened steels will not scratch as easy with a file. You could try it with an old broken blade but it will leave a scratch on your nice new folder if you do it there.

FWIW,
og
 
Rockwell testers can be found used for $2000, from what I have seen. Just a rough number for ya! A lot of knife makers buy their own so they can check their heat treats. The knives I get back from heat treat always have the RC written on them in ink, right near the telltale tiny test divot. The divots aren't that sharp and nasty, so fear not!

I sent Phil Wilson a few knives to test whilst we were talking about RC and steeling. He checked my AFCK and I enjoy the tiny dots! Reminds me of our conversations. And they're so small no one would notice unless they were inspecting the knife real close. Phil Wilson also checked som eknives I had that were used in a hog plant I worked in a few summers. The blades, Victorinox boning knives, were around 52! Soft buggers!

You can learn a lot from RC, but it is only one element for sure!
 
The hardness tests were originally developed to provide an approximate measure of tensile strength. This they do well.However whenpeople try to use it for other things they can have problems. Wear resistance for example, compare Talonite relatively soft with say 1084. Talonite will have much better wear resistance than tha 1084 even though it is much lower hardness. It's best used as an assurance of proper heat treating rather than some absolute number.
 
We have a hardness tester at my work (it's actually right next to my office) and I've tested quite a few of my knives just for curiosity's sake. All of the production knives I've tested fall within spec as specified from their makers. And the dimple isn't deep or sharp at all. I have trouble feelilng them even when I drag my fingernail across the surface.

As others have said, hardness is only part of what you need to consider. I just think it's nice to know that we're really getting what they say we are.
 
I guess that my take on this question is: where do you find an economical source of Rockwell testing services? I have lots of questions about knives in my collection, including some kitchen knives. I would like to know how hard they are. If I could get RC testing done cheaply enough I might have dozens of knives done.

If you have an inside connection to the materials science or mechanical engineering departments of the right colleges it would help, otherwise I don't know where you could go. What might I find in an average American city?
 
Any engineering university will have HRC testers in the materials labs. If the tech guys have some free time they will usually do the test, it only takes a few minutes. Just get the blade hit in a few spots on the flats and look at the consistency.

As for the test, all the mumbo-jumbo aside, a HRC testor basically slams something hard into a knife and sees how big a dent was made, the bigger the dent the softer the material. Just like whacking a piece of wood with a hammer, maple will indent less than pine, thus maple is harder than pine.

As for what it means, hardness is simply resistance to deformation so it correlates very highly to bending of all types. This measures the resistance of the edge to rolling and is thus critical in edge holding in many situations as roll is often dominant.

Of course it isn't the only factor in edge holding, wear resitance, ductility, and toughness are all factors, as well as edge geometry and less direct factors such as handle ergonomics and overall blade shape.

It also has a large effect on edge durability, in extreme impacts, such as chopping into an inclusion (nail, rock), if the steel is too soft it will dent too readily. Of course this is the same property and means by which edges roll, just seen on a different scale.

-Cliff
 
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