Quick and dirty hardness testing for old dirty carbon??

I've been trying to buy various old dirty carbon on the bay and at thrift shops, they are great fun to practice thinning and sharpening on and after I am done they make awesome presents - wish the prices haven't gone up so much of course But even at current prices, a 30$ forgecraft thinned and hand sharpened has be the equivalent of a low end carbon steel J-knife, no??

Forgies are pretty hard though, the wonderful folks at Bloodwrrot tested a bunch of mine for me and none were less then 58 or 59 and the chefs knifes were 61 or so.

Still I am often curious how hard the steel is on some of the other knives I pick up. The stones I use cut so quickly that time on the stone isn't a great measure. So then I got to thinking, isn't ordinary window glass mid 50's in HRC? If so can I use the idea of scratches glass pretty easily = probably at least 57-58. Doesn't do anything = really soft < 55?

Files are not a bad test. A normal steel file will begin to shift steel at around 63hrc, you can buy a set of small round files graded to different hardnesses, if you can remove a little material with the file, move down to the next hardness and test etc.
But if your sharpening and using the knives that will give you a good idea as well. How do they wear, deformation or small chips. After thinning, when you flex the edge with your fingernail does it deform, or pushed hard will it make a tiny chip? This will tell you more about the HT as a whole with the chosen steel, different steels behave differently at different hardnesses and can behave differently with different heat treatments at the same hardnesses too, so I wouldn't get hung up on figures.

Gic Fixing up old carbons is fun. Here in Hawaii you can find old Japanese blades from the plantation days. I hate to think how many of those rusty blades have been tossed out.

Swap meet & garage sales you can find cheap blades worth bringing back. Like to hunt down old carving sets on E-Bay & polish them up, then put a sharp edge on them. Got a nice late 1890's Art Nouveau style with sterling silver collars and endcaps flowing lines beautiful set.

gic said:

I've been trying to buy various old dirty carbon on the bay and at thrift shops, they are great fun to practice thinning and sharpening on and after I am done they make awesome presents - wish the prices haven't gone up so much of course But even at current prices, a 30$ forgecraft thinned and hand sharpened has be the equivalent of a low end carbon steel J-knife, no??

Forgies are pretty hard though, the wonderful folks at Bloodwrrot tested a bunch of mine for me and none were less then 58 or 59 and the chefs knifes were 61 or so.

Still I am often curious how hard the steel is on some of the other knives I pick up. The stones I use cut so quickly that time on the stone isn't a great measure. So then I got to thinking, isn't ordinary window glass mid 50's in HRC? If so can I use the idea of scratches glass pretty easily = probably at least 57-58. Doesn't do anything = really soft < 55?

Click to expand...

Similar to WillC's test, Murray Carter uses a bic lighter to conduct a flex test.
[video=youtube;dU3ALY8OmZk]https://www.youtube.com/watch?v=dU3ALY8OmZk[/video]

Interesting video from Carter. I went immediately to my practice Tojiro Shirogami and tried to chip it like in the video. It didn't work, it just flexed but did not want to chip ?!

Must be really soft or what? It is presumably in the 60-61 range...

Not necessarily, Carter knows the steel he is using intimately. In fine carbide steels and when you get a fine and even distribution of carbides in the process of heat treatment, the steel is tough. To either chip or distort the steel, its pushed to its limit where it must either distort or chip. Note that carter wants to see a small amount of distortion around the tiny chip, this shows it is on the tough side of stable hardness still, at least thats how it behaves on a thin edge. Tough fine grained steels can show distortion on a thin edge even around 62/63hrc Its a trait of the fine carbides and toughness and how it behaves on a thin edge, it will flex and should return, push it to destruction point and it will either distort or chip. I like the finger nail test better, because it shows the knife is thin enough at the edge. Take Kato as a different example, it will flex and pushed hard make a tiny chip with no distortion, it shows the maker is using the steel right to the boundaries of edge stability where it will hold its edge longest and small chips with no distortion are easier to hone out. But there is nothing wrong with steel being on the tough side and showing a little distortion, and like I say this can happen up to 63 hrc in fine carbide steels. Only if the edge flexes and takes very little effort to distort, and you notice constant distortion in use, then you might consider it on the soft side, especially if that then forces you to keep the knife thicker at the edge.

My surprise came from the fact that since I started with Japanese knives I am constantly reading how brittle they are. I am really careful and I handle my good knives properly. I never had any big chip, except some minor micro chipping.

When I saw that Carter video I said to my self to put the bad/practice knife to the test. To finally once make a proper chip to see how much effort it takes. To my surprise it didn't want to chip at all!

Of course I will not be trying this on the other knives