# Rockwell Hardness Testing



## Cody Killgore

Hey guys.

As I've gotten more and more into metallurgy, I've found that I really wanted to verify that my heat treatment is what I think it is. A month or so ago, I purchased a table top rockwell hardness tester. I bought a nice calibration test block that was certified, and my machine seems to be reading very accurately.

That said, if anyone on the forum wants to have a knife tested, I would be more than happy to do it. I would just ask that you pay shipping both ways.

Keep in mind on the rockwell tests, that a test on the bevel of a knife is not necessarily accurate as some of the force could be deflected. It really needs to be at a point on the knife where both sides are flat and parallel. I have been testing my knives on the tang, very close to the ricasso (underneath where the knife scales will be going).

Also the tester works by pushing a diamond point into the knife with a known force (150kgf) and measuring how far it penetrates. 1 point of Rockwell equates to about 2 microns penetration. Therefore, these indentations are very small but you probably would not want one in a place that would show on your knife (unless you intend to do more grinding there). Lastly, the place you want tested needs to be as smooth as you would get it to get the most accurate results. I've found a 220 finish seems to be adequate most of the time, but more would probably be a bit better.

*Please note: While I am extraordinarily careful when handling knives, I won't be held responsible for any damage dealt to the knife during the testing.*

Below is a picture of the type of indentation I'm talking about on a test block. This block is about 2" round.







Just wanted to offer in case anyone was curious as to whether they were achieving the hardness that they were shooting for.



Cody

Reactions: Informative 1


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## Kevin

That's very generous of you Cody. I would like to make this a sticky (I don't believe I have ever done that for a member's thread) if it's all right with you. You might want to add a clause that you are not responsible for any damage to the knife whether it is your fault or not. And also request that they be sent via priority in order to be able to be accounted for. Not a rule just making suggestions. 

I'm sure you know how to test a knife without damaging and if you did I know you could fix a blemish etc. if you dropped it but better safe than sorry.


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## Cody Killgore

Ok, I added a real quick disclaimer. I'll have to revise it later. That would be fine with me.


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## Foot Patrol

Cody how do you do your heat treatment?

I have been using 1084 and I do it by heating the cutting edge of the blade past magnetic and then quenching (x3). The tang does not get directly heated in the gas forge and therefore I would expect a much lower Rockwell than the blade. I usually get 58 / 59 RW.

Btw thanks for the offer to test. Great idea.


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## Cody Killgore

Foot Patrol said:


> Cody how do you do your heat treatment?
> 
> I have been using 1084 and I do it by heating the cutting edge of the blade past magnetic and then quenching (x3). The tang does not get directly heated in the gas forge and therefore I would expect a much lower Rockwell than the blade. I usually get 58 / 59 RW.
> 
> Btw thanks for the offer to test. Great idea.



Hey man,

First, I just want to say that I do not claim myself an expert on heat treatment. There is a ton left for me to learn and many people know much more than I do. I have picked up most of my knowledge on the subject from reading metallurgy books.

For most simple carbon steels such as 1084, heating to non-magnetic is fairly accurate. When a steel loses magnetism, it is actually measuring the curie point which doesn't have anything to do with the phase change to austenite. The curie point is around 1414F and the critical range for those steels are around 1450-1500. In a forge, most people overheat just a bit so it ends up being about right. I only mention this because it pains me to see people heat to non-magnetic with a high-alloy steel and quench when they are most likely 500F off or so. Also for eutectoid steels such as 1084, no real soak time is required as all the carbon can go into solution quite easily. 1084 is an awesome steel for the way you heat treat. When you get into hypereutectoid steels (steels have > 0.8% carbon), they will require some additional soak time to let the excess carbon go into solution. Same goes for hypoeutectoid (< 0.8% carbon) where it takes more time to evenly distribute the carbon that's already stretched thin.

I can get a little OCD about heat treating so I do use a digitally controlled heat treat oven to make sure my temperatures are as close to perfect as they can be. My next big purchase is a molten salt bath. 

I also make sure to use commercial quench oils. The heat treating industry spent millions developing these products and they are made to quench thousands of times with no problems. In addition, their quench speeds are known. If you look at the IT diagram for 1095, you can see that in order for it to get full martensite forming (full hardness), it actually has to be cooled from 1450ish to 900ish in less than 1 second. You need a really fast quenchant for that.

One option for testing blades done where the tang doesn't necessarily harden, is to test a flat near the spine before too much more grinding is done. The indention is very small so it can usually be ground out depending on how much you intend to grind post heat-treat. That being said, if you are differentially hardening/tempering you may just be out of luck as far as testing goes (at least with my equipment). 

I usually don't triple quench, but I have read in one of the metallurgy books that multiple quenches further shrinks/refines the grain structure which would be a good thing.

That was probably more information than you wanted, I just have way too much of this jumbling around in my head


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## Foot Patrol

Thanks for your insight. I know who to go to if I have any questions now. I am only a beginner so I still have a lot to learn.


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## robert flynt

Cody, Along with testing the hardness how do you performance test your blades, chop deer antler, cut rope, brass rod test, etc?


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## NYWoodturner

Cody - very generous offer. As a new knife make that does my own heat treating as well, I would love to know my accuracy level beyond a set of files.
I would also be reluctant to take advantage of your generosity without recognizing the value of your time and offering something in return. Just putting it out there for for others to consider. 
Scott


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## Cody Killgore

robert flynt said:


> Cody, Along with testing the hardness how do you performance test your blades, chop deer antler, cut rope, brass rod test, etc?



Robert, usually, I at least carry it around for a couple days and put it to good use and see how it holds up. For quantitative stuff, I've started to cut rope on a scale with a cutting board on it and measure the amount of force required to slice. I also cut cardboard and see how many cuts it takes before it will no longer slice newspaper easily. I've never really been a big believer of the brass rod test. To me, it just seems like there are too many variables at play there, though I don't have anything against those that swear by it. I might need to give it a shot. I also might have to try the chopping deer antler thing


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## robert flynt

Cody Killgore said:


> robert flynt said:
> 
> 
> 
> Cody, Along with testing the hardness how do you performance test your blades, chop deer antler, cut rope, brass rod test, etc?
> 
> 
> 
> 
> Robert, usually, I at least carry it around for a couple days and put it to good use and see how it holds up. For quantitative stuff, I've started to cut rope on a scale with a cutting board on it and measure the amount of force required to slice. I also cut cardboard and see how many cuts it takes before it will no longer slice newspaper easily. I've never really been a big believer of the brass rod test. To me, it just seems like there are too many variables at play there, though I don't have anything against those that swear by it. I might need to give it a shot. I also might have to try the chopping deer antler thing
Click to expand...

Even though I Rc. test the blade I like to use the rod test to see if the blade is chippy or if the edge will curl, if it's chippy you can hear the edge chipping. Choping deer antler will also let you know if the heat treat is right though it is a little more distructive and you could break a blade or cury the edge pretty good. I've been able to push some steels past the recommended hardness through diffrent heat treats and those test have let me know whether they were to brittle or not. Had a customer who wanted a knife made with Cowry steel because of it's hardness capability. Went exactly by heat treating instructions but the rod test proved it to be chippy at Rc. 66 and had to draw it back to Rc 64 before it wasn't. Had I not done this there might have been a problem and an unhappy customer.


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## Strider

Mr. Cody I support your will to know whether the HT went well. As I've done tons of HTs, can't count them frankly, I have an advice or two. 
You are right about the flatness of the piece being measured. Moreover, it has to be sanded and clean, not necessarily mirror polished, but it must not have any cracks, bumps, irregularities, scratch marks etc- they all affect test results. Do not worry if you get different results in a small surface area, lets say 5 mm square, as crystal structure of steel isn't uniform and various carbides occur randomly, I'd say. And I might say if you tested a piece incorrectly you can't get a higher result, only lower. So, faulty measures are shown as very lower result. The highest result is the most accurate (as my professor claims).
The hardness of the edge itself cannot be measured, as previously stated (it's not flat, and its on an angle)...so, I dare to say it is 1/2- 2 HRCs higher than the thicker parts, that is, if the HT has been done properly. And yes, leaving test marks on visible places isn't very eye appealing, but it might be a testimony of quality (Puma knives). 
Have in mind, the hardness is only one of the properties parameter, and it can go hand-to-hand with strength...but it doesn't have to. The most accurate method of testing hardness is by HV (Vickers) method, but, unfortunately, it is still uncommon among us knife-enthusiasts. But...it is not necessary for us knifemakers, rather an overkill. 

Hope I helped!

Reactions: Informative 2


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## steve Pannell

I have begun experimenting with double quenching on some steels. I got the technique from a guy that has been working in heat treatment for Haliburton down hole tools for almost 30 years. 
The purpose of this method is to further refine both austenite and martensite grain size. It does take some finesse in a gas forge to keep from decarbing the metal. So far the blades have responded extremely well to sharpening and edge holding especially the crucible carbon steels. They have also tested fairly high for hardness after tempering. I may try going to 3 tempering cycles and soften them a point more. RC 63 and higher are pretty slow to grind an edge bevel on. The last 3 blades my neighbor tested for me were W2 @ 62.8, [email protected] and 80CRV2 @ 68.6 all tested after tempering. I have mine tested at the ricasso near the fade. The 80CRV2 is some awesome hard stuff after a double quench.

Reactions: Way Cool 1


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## NeilYeag

*it pains me to see people heat to non-magnetic with a high-alloy steel and quench when they are most likely 500F*


John at Black Bear forge did a good video on this subject. And his test certainly indicated that most steels do go non magnetic in some cases substantially below critical temp. I do my heat treat in the forge and normally take the approach of going to non magnetic and then back in the fire for 2 minutes longer. I have a set of hardness test files and with the O1 that I use, I can get the item to 65 with one quench. After normalizing the best that I can determine I am around 57 to 59. Interesting I have tried running tempering cycles and then no tempering cycle. I really did not see any difference at least in the O1. Wish I had a "real" test machine, but out of my budget at the moment.


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## steve Pannell

I don't put much importance on the non magnetic stage either. I'm kinda old school I guess although I do have a magnet handy just to see when the crossover happens on certain steels. Mostly I go by eyeball method and work in a shaded darkened area where I can see the color of the metal and be able to watch as it goes into solution which most times is well beyond non magnetic time wise. When I see the dark shadow inside the blade fade away and know that the metal has thoroughly equalized and is a uniform color all across, I know it's ready for a fast dip in the brine or oil. I only work with high carbon steels so there is really no big secrets to my methods. I think one key to a successful heat treat is having a good forge that uses up all the oxygen in the burn---or having one of them high dollar electric thingamawatchits with all the bells and whistles and blinking lights and buzzers.

Reactions: Informative 1


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## NeilYeag

steve Pannell said:


> ---or having one of them high dollar electric thingamawatchits with all the bells and whistles and blinking lights and buzzers.



Yep out of my budget too! For me I do try to be as consistent and repeatable as possible.


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## Bill Clancy

Cody Killgore said:


> Robert, usually, I at least carry it around for a couple days and put it to good use and see how it holds up. For quantitative stuff, I've started to cut rope on a scale with a cutting board on it and measure the amount of force required to slice. I also cut cardboard and see how many cuts it takes before it will no longer slice newspaper easily. I've never really been a big believer of the brass rod test. To me, it just seems like there are too many variables at play there, though I don't have anything against those that swear by it. I might need to give it a shot. I also might have to try the chopping deer antler thing


I pretty recently got a PT50b edge tester from these guys. Its a standardized test using a filament on a scale...very similar to your idea with a scale & a rope, just way miniaturized. It changed my sharpening game. https://edgeonup.com/


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