How to distinguish between a blade of HRC 59 and a blade of HRC 64

[BrownBear]

I've been told that a hard Japanese knife with a high HRC has the advantage over a Western knife with a low HRC that it doesn't roll. So one can also put a more acute angle on it. But it will chip easier. All things dependent on the steel and the heat treatment, of course, but as a general line.

However, a blade with an HRC of 59 or so doesn't roll anymore, or it is very hard to make it do so. How then do you distinguish in practice between a blade with and HRC of 59 and a blade with an HRC of 64, other than that the latter will chip easier?

 

[user 16756]

you can only generalize across steels, and the same steel at 59 and 64 will act very differently. the rockwell scale, I believe, is not linear, anyway, such that 64 is actually a LOT harder than 59.

in GENERAL, higher hardness increases wear resistance while reducing toughness.

heat treats are usually a compromise, and some comprises are better for certain tasks than others. I think 59 is ok for pocket knives, especially great thick ones like most "tactical" folders. but for a kitchen knife that ground extremely thin behind the edge, and then with a very acute edge angle, you need something a bit more aggressive.

 

[123cut]

As a consumer/user you can't tell. You need a Rockwell meter for that. Makers tend to point out HRC to inform users of a knive's wear resistance potential.

As others have stated, there is an inverse relationship to toughness and wear resistance in relation to hardness. 57-59 tends to be the Rockwell area to shoot for if a maker wants increased toughness, 61-64 for increased wear resistance.

I'm not an expert about kitchen knives (that's why I'm here), but I do know on field knives there needs to be a balance between toughness and wear resistance. In the kitchen users aren't wood working or awling or cutting across wood grain, so toughness isn't as much of a concern. I suppose kitchen knife makers will aim for better wear resistance with enough toughness to avoid edge rolling and/or chipping. The only exception I can think of would be a cleaver. That kind of knife would probably need to be heat treated to a lower harness to increase toughness. Chopping through bones has a tendency to deform edges, they'd need to be tough.

It needs to be noted steal choice is also important because different steels react to heat treatment differently. Some steels can't surpass 62HRC, they'll become too brittle. But, that's a different thread.

 

[malexthekid]

I would also add that higher HRC doesn't mean an edge will chip easier just that it is more prone to chipping than rolling at the point of failure

 

[bkdc]

My HRC59 knives roll. My personal preferred sweet spot is 60-62. You can't distinguish them without a meter, but after a period of use and of sharpening experience, you can develop a gestalt estimate of your blade's hardness.

 

[panda]

64 is really high, they feel more dense while cutting.

 

[vai777]

put them on the stones to sharpen, they will be completely different in feel

 

[gic]

I have a set of files I bought on Amazon Japan (also available in the US but much more expensive) that let you do some rough HRC testing.

I have found that HRC 58-59 is fine on certain knives when I simply put a 15 degree angle on them (possibly with a microbevel). I wouldn't take them down to 10 degrees like I do with many of my harder knives though, 10 degrees with or without a microbevel seems to work fine on 61HRC

 

[Sabaki]

Massproducers often choose "stainless" steel with a Carbon content around 0.45-0.55% (Cr 13-14% and some other alloys to) to keep the grainsize small without any heat treating before hardening, it's a lot cheaper this way and there hardness will reach around 54-58 (59) on the rockwell scale without being brittle.
Their downside is that you cant grind these knives to thin behind the edge because it will roll or fold over to easy.

Other makers can choose a "better stainless" steel with Carbon content around 0.6-0.8% (Cr 13-14%...) with mostly small and very few big grain size and do a good heat treating to releaf any stress in the steel and harden this up to 60-63 without being brittle.
If all done well the steel can be made with a very thin edge and still hold it to make a very good performer!

You can do a test on your edge and see how much flex it can take using a Bic lighter, press the edge against the lighter at 45 degree angle to see how much it flexes. Be careful!
The massproduced knife can flex a little before it remains bent, the good maker's knife can take quite a flex and come back to true.
A very hard steel +63Hrc with very high Carbon content can also take quite a flex but if pushed beyond it's limit it will chip due to bigger grainsize!

 

[Adrian]

I suspect that the noticeable difference in feel you get between say a single bevel, hard steel carbon J knife, and a softer steel German knife is largely down to the different blade profiles. You develop a preference for one or the other for particular tasks.

The only time I have ever had significant micro chipping of high quality hard carbon J knives, was when the knives were new and were just going through the first couple of sharpenings. This is normal and soon passes. The thing that will prevent chipping is 1) good board 2) right knife for the job 3) keep it sharp and use good technique. Really, you don't need to worry about it.