Why is everyone obsessed with HCR?

[banjo1071]

Hey
Unpopular opinion here: HRC without knowing the typ of steel and geometry is totally irrelevant. A higher HRC does not make a knife better, nor does it says anythng about sharpness or edge stability.
Example: a razor thin VG10 blade with HRC64 would crumble like swedish knäckebröd.


So why is that so important for you guys?

Cheers
Benjamin

 

[miggus]

Hmm I thought it says something about edge stability after all. I mean, I don't know if VG10 can even go to HRC64. But lets say, a HRC64 blade in Aogami Super vs. an HRC 60 blade in Aogami Super. If I get it right, the HRC64 blade can hold a keener edge than it's softer sibling.

But yeah, there obviously is much more to heat treatment than just this number. If I understand this right, one HRC64 blade can be quite resilient while another HRC64 blade can be very brittle if HT is done badly, or if edge geometry isn't good.

 

[btbyrd]

I don't think it is "so important for us guys." The people on this forum generally know what steels perform well within what hardness ranges. I don't think anyone here cares about HRC independently of steel type or geometry. Or if they do, they're new.

 

[Delat]

Agree with the above. I’ve never seen anyone post “Recommend me an HRC 63 blade I don’t care about the steel.”

Discussions are usually about types of steels and any discussion of HRC is usually tangential. Usually the steel drives the HRC, not vice versa. Most of the steels that seem to be preferred fall into the HRC 60 - 65 range, as when you go higher you need diamond stones or other specialized sharpening gear.

To the extent that I care, I personally care more about toughness or resistance to chipping than HRC. But I actually don’t care too much - I pick a maker I like and try to score whatever he’s got available regardless of steel.

I personally couldn’t tell you what HRC most of my knives are. I know they’re all in the 60-65 range, but would have to look up my notes for any particular knife. As long as it’s not down in the 50’s then I’m happy.

 

[Troopah_Knives]

Hey
Unpopular opinion here: HRC without knowing the typ of steel and geometry is totally irrelevant. A higher HRC does not make a knife better, nor does it says anythng about sharpness or edge stability.
Example: a razor thin VG10 blade with HRC64 would crumble like swedish knäckebröd.


So why is that so important for you guys?

Cheers
Benjamin

I would actually slightly disagree with you. HRC is a measure of strength and everything I have seen suggests that it is essentially the only factor is edge stability. Although that somewhat depends on your definition of edge stability.

But I agree without steel type it doesn't give you much of the picture.

 

[Matt Jacobs]

It is absolutely steel dependent but in my opinion it does matters, a ton. Example at one time I had 3 52100 blades Steelport at 65HRC, ShiHan 61-62(I think) and a 3rd I dont want to bad mouth so I wont name but came in around 58hrc. The Steelport probably had the best retention of any knife I had tried but wasnt easy to sharpen. the ShiHan had really nice retention, great toughness and was a pleasure to sharpen. the 58hrc sucked to sharpen and didnt hold an edge at all. to some degree I think it can give me an some insight into the maker as well. If someone is low hrc or says they are 60-64hrc then I know they dont have there heat treat dialed or dont have a way to test. I am much less likely to give them a shot. Its not the end all be all, if 2 makers are both great and one likes 62hrc and the other likes 64hrc on the same steel then I dont care and will go for geometry, looks etc.

 

[M1k3]

Higher HRC, between 2 steels and same geometry, will also have better edge retention. Within reason.

 

[Jason183]

One thing I’m sure of is I’ll never buy any kitchen knives that’s lower than 60 HRC in the near future, I still prefer lower HRC knives for abusive tasks tho but who knows, in the future there might be more new develop OP steels liked Magnacut that’s indestructible at even higher HRC.

 

[Barmoley]

I don't think anyone cares about hrc in a vacuum. In most cases we talk of it in conjunction with a particular steel. HRC on it's own doesn't mean much. Even knowing the steel doesn't necessarily tell you much since depending on the heat treat you could have same hardness on the same steel and have different toughness. It is something that can be easily measured and reported though. Geometry makes a huge difference, but is not really known on different knives. Toughness is also not reported since it is not easy to measure and requires breaking of the sample tested. Because of this hardness and steel are the only attributes that can be discussed when comparing knives and unlike geometry can't be changed by the end user. In short we assume that the maker did a good heat treat and achieved a certain hardness in the best way possible for a given steel. This of course is a huge assumption, but there is no way to know until the knife has been used extensively and even then unless the heat treat was really bad the end user might not know.

 

[Marcelo Amaral]

I agree. The ultimate test is to use the blade by yourself.

HRC seems to be an easier aspect to measure and understand among several factors that has an impact on blade performance.
It's harder to measure/understand grind, balance, toughness but hardness is easier, so it might have become more popular.
It doesn't mean it is not important: i wish my crappy stainless blades were harder as they simply can't keep a sharp edge for long.

 

[ReiHamono]

I now only cut with diamonds for maximum HRC

 

[Delat]

Funny followup to my earlier post, I just realized I have 2 knives on the way and I don’t even know what steel they are much less the HRC!

Steel used to be much more important to me; these days I just buy the maker and trust them to do their thing.

 

[nickw_]

I only cut with diamonds now for maximum HRC

Agreed. A higher HRC is clearly better. I am so done with Shirogami #1 knives.

Hmm, what else can I upgrade? I know, my copper pots and pans. They are so 18th century. Silver is the best heat conductor of any metal, so I had been thinking about commissioning a set of those, but they seem so nouveau riche. Diamonds are the best heat conductor known to man, so I'll get those instead.

One specification is all anyone needs to know. Clearly it defines everything. It has never been easier to be a connoisseur.

Now, please excuse me while I step to buy a new atomic clock wrist watch.

 

[Chicagohawkie]

Not much of a concern at all. Besides, has anyone ever seen a true certified HRC test on any knife ever? In 10 years, I haven’t.

 

[superworrier]

Not much of a concern at all. Besides, has anyone ever seen a true certified HRC test on any knife ever? In 10 years, I haven’t.

Yeah, and you'll see the same knife at different vendors with different spreads in HRC. I think people who don't know better just try to compare knives by HRC and assume higher = better and that there is a significant difference in 1 or 2 points, which leads to embellishment... also they make the mistake that higher HRC = higher edge retention even when comparing different steels

 

[jedy617]

Because it is the most important factor in terms of edge retention and toughness when comparing a steel from maker to maker (note, it is not the ONLY factor, and I am only talking all things equal.... Like one makers blue 1 vs another. The steels need to be the same, can't compare s90v at 58, and white 1 at 65.)

The difference in 60 hrc magnacut vs 64hrc magnacut for example is about 15% in CATRA tested edge retention. That is quite significant.

 

[jedy617]

Also I wouldn't call that an unpopular opinion at all. Everyone here knows type of steel and geometry matters. Next?

 

[M1k3]

Not much of a concern at all. Besides, has anyone ever seen a true certified HRC test on any knife ever? In 10 years, I haven’t.

Sukenari

 

[jedy617]

Not much of a concern at all. Besides, has anyone ever seen a true certified HRC test on any knife ever? In 10 years, I haven’t.

Tons.

 

[banjo1071]

I would actually slightly disagree with you. HRC is a measure of strength and everything I have seen suggests that it is essentially the only factor is edge stability. Although that somewhat depends on your definition of edge stability.

But I agree without steel type it doesn't give you much of the picture.

Then answer me this: Why are debas (for cutting fish and smashing/cutting through fishbones) traditionally made with a much lower HRC than eg yanagibas or gyutos?

 

[superworrier]

Then answer me this: Why are debas (for cutting fish and smashing/cutting through fishbones) traditionally made with a much lower HRC than eg yanagibas or gyutos?

Probably answered by this: "Although that somewhat depends on your definition of edge stability."

 

[banjo1071]

Most likely, but i cannot see different definitions of edge stability. Either your edge is stable or its not. A edge/blade, that is crumbling away while cutting something hard is not stable or strong. It may be delicate, fine, tough and super sharp and much more. But not strong or stable. Or in other words: a high HRC is not an atribute of strenght.

 

[jedy617]

Edge stability is the ability to hold a lower edge angle without deforming. It's quite scientific actually. People do measure levels to edge stability, for example by sharpening to different angles, and pressing the edges into materials like brass rods. Also You really like the term crumbling huh lol. Hope this helps. All of this information is available from Larrin Thomas, check out his great book if you want to be very well versed in all things steel.

 

[banjo1071]

Yep, I love it (englisch is my third language btw so please excuse my words). I already read Landes and Verhoeven, but not Thomas yet.
Over here the brass rods (or traditionally rings) are used by the knife makers to test if the edge deforms (Nagelgaengig).

Roman Landes defines edge stability a bit different, he includes chipping (crumbling hahaha) on a microscopic level, purity and carbide size..

 

[blokey]

I don't find this an unpopular opinion, at least I would consider other factors like toughness, edge geometry/grind, steel type before crunching HRC numbers. If we only care about HRC ShiHan knives won't be as popular since he usually ht his steel lower than many other smiths, same for some of the forum favorite who also didn't take their ht extreme.

 

[Troopah_Knives]

Over here the brass rods (or traditionally rings) are used by the knife makers to test if the edge deforms (Nagelgaengig).

This is purely a test of hardness harder materials will do better on this test.

"a high HRC is not an attribute of strength." This is simply not true HRC is definitionally a measure of strength and is correlated with yield strength. In order for an edge to "crumble", The yield strength of the material must be exceeded. So increasing that strength will increase the force required to "crumble the edge". In fact, my observation from sharpening many cheaper stainless knives(56 or so RC) is that the dominant form of wear is chipping and not rolling as you might expect.

"Roman Landes defines edge stability a bit differently, he includes chipping (crumbling hahaha) on a microscopic level, purity, and carbide size.."
Yes, I have read through his work but even with his definition hardness seems to have had by far the largest effect on his data set. I certainly think it's possible that those could affect edge stability beyond their contribution to hardness but I wouldn't say that had been conclusively shown.

Basically, any way you cut the cake hardness is either the only factor in edge stability or the most prominent factor in edge stability. Hardness controls whether a given amount of force will damage an edge. Toughness controls what that damage will look like. All of this talk of carbide size etc etc at least in theory is already baked in. Carbides affect both hardness and toughness.\

Again it isn't the only factor but with a proper understanding of the concepts, hardness is a useful way to compare the material properties of two steel despite their other differences.

 

[Troopah_Knives]

Then answer me this: Why are debas (for cutting fish and smashing/cutting through fishbones) traditionally made with a much lower HRC than eg yanagibas or gyutos?

So that the failure mode is more likely to be edge rolling and not chipping. That's not to say that this is necessarily the right engineering choice. Many debas are steel made in Shiro which has very poor ductility at a given hardness. So a change in steel and higher hardness is preferable as it would both increase the amount of force required to deform and edge (Hardness) and the amount of energy that can be absorbed by the edge before breaking (toughness). It's important not to assume tradition always happens upon the best solution from an engineering standpoint. In this case, I would say it is simply making the best of a non-ideal situation.

 

[banjo1071]

This is purely a test of hardness harder materials will do better on this test.

No, they is a tradtitional test in Solingen, if the blade is thin enough behind the edge. This test used be made at the thumbnail (german Daumennagel). Belive me, i have been to Solingen more than once in my life...

https://www.windmuehlenmesser.de/

 

[Troopah_Knives]

This is purely a test of hardness harder materials will do better on this test.

@banjo1071 Sure geometry comes into effect but given fixed geometry this is a test of hardness.

 

[HumbleHomeCook]

No, they is a tradtitional test in Solingen, if the blade is thin enough behind the edge. This test used be made at the thumbnail (german Daumennagel). Belive me, i have been to Solingen more than once in my life...

https://www.windmuehlenmesser.de/

You should start making knives at 51HRC and see how you fare. Please report back.