Rockwell Testing Question

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Wowndeye

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Apr 15, 2014
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I just found a machine shop in town that has a Rockwell scale who will test my blades so I can evaluate my home heat treats that I'm doing with a two brick forge and quenching in canola oil I'm super excited!

Being that I know nothing about the process, is there anything I should be aware of before going in? Can a blade edge be tested? Will it leave a mark on the blade? Any indications they possibly may not be testing right?

The owner asked what range I was looking to test in and because I'm only working with 1/8" 1080 and 1/4" 5160 right now I told him in the upper 50's, lower 60's possibly.

I'm just making hunter style knives right now. I don't have the numbers in my head at the moment, but in anyone's experience, is there a desirable number I should shoot for for each? And what would be considered an unacceptable low number?

Thanks!
 
The test will make a dimple in the steel, and can only be tested on flat parallel surfaces. You have to sand the decarb off or the reading won't be accurate.
 
There are several things to consider and I'll just say up front, I am no expert. First you should make sure they are testing in the Rockwell C scale. You should ask them to verify the tester with a standard before they begin testing your blades. The blades need to be tested on a flat section. Accurate readings cannot be obtained if there is a side load on the diamond caused by not applying even pressure. The test will put a tiny dimple in the steel. It is only a couple thousandths deep but it is difficult to sand out after your blade is hardened. To really understand your process, you should have the blades tested after initial quench and after each temper cycle.

Bob
 
Wowndeye said:
I just found a machine shop in town that has a Rockwell scale who will test my blades so I can evaluate my home heat treats that I'm doing with a two brick forge and quenching in canola oil I'm super excited!

Being that I know nothing about the process, is there anything I should be aware of before going in? Can a blade edge be tested? Will it leave a mark on the blade? Any indications they possibly may not be testing right?

The owner asked what range I was looking to test in and because I'm only working with 1/8" 1080 and 1/4" 5160 right now I told him in the upper 50's, lower 60's possibly.

I'm just making hunter style knives right now. I don't have the numbers in my head at the moment, but in anyone's experience, is there a desirable number I should shoot for for each? And what would be considered an unacceptable low number?

Thanks!
Click to expand...

All the posters I'm sure will give you a better answer. I'm using 5160 as well and the paperwork I got with it said 56-58 was ideal RC.
 
Rangerbob has it right. The ideal is to test out of quench (I do this on a coupon to prevent risk of cracking the blade) to assure you got full hardness. This isn't practical in your situation though. Then temper a bit lower than you are aiming for, and increase tempering temp at approximately 25f for each Rc1.0 you want to adjust. It isn't exact, but its a pretty close relationship of 25f to Rc1.0.

Follow the information on Kevin Cashen's site, and if you get unusual readings, try a few coupons and have them tested at full hardness without temper. If you aren't getting full hardness, figure out why, and fix the problem. Alternatively, if you are getting full hardness, but the temper comes out wrong, then you know where to look.
 
Perfect guys, thank you!

So if I temper them and they come out harder than ideal, I can I do an additional temper at a slightly higher temp to drop the number? It's. No big deal to do a tempering cycle that long after the initial temper?

Willie, are you saying for every 25 degrees I raise tempering temp, it drops Rc by 1, give or take?

I was thinking of doing a few coupons with a little variety, just to see how the the metal responds to the tempering.

Do most knife makers actually test each individual blade? And to they test at the ricasso or in the handle area?

Thank you again everyone!
 
Correct, if they come out too hard, then you can temper 25f higher which on average will drop the Rc value by 1.0. There is variation of course, but it's a good general rule. The first temper should be relatively soon to relieve stress and help finish the transformation. After, you can wAit a long time and re-temper as needed. You can only go softer, not harder though.

I don't know about other makers, but I test each blade and walk my tempers to get the Rc value I want for the steel and the application. This prevents problems such a a misidentified bar of steel, which doesn't harden properly. It happens once in a while.
 
I would suggest, if the shop is not immediatly next your door, to do a quick temper. If your heat treatment went well the blade should be in danger of cracking even without external causes (like falling on the floor). Testing as quenched is a good thing, but with a snap temper is safer to move the blade to the shop and back home, and still gives a good insight on your process.
That said, Willie's tip of heat treating a little sample (with flat and parallel surfaces, the same thickness of the knife) together with your blade is the very best option you have for an as quenched reading. You can bring the as quenched sample and the snap tempered blade
 
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