Knifemaker opinion - are the optimal hardness ranges for alloys fairly narrow?

[RX-79G]

This is a question for those in the know, not preaching:

In the search for that balance between toughness and edge holding, knifemakers select steels and temper them to get what they feel is an appropriate hardness for the intended use. If you want a chopper, you might select 5160 and temper it down 5 points Hrc, or you could choose W2 and temper it down 10 points. When you arrive at 57 with both, one will be tougher than the other despite the identical hardness. Aside from the fact that it would obviously be 5160, does this suggest that the optimal range of hardnesses is much narrower for all alloys than they are typically produced?

 

[RX-79G]

Continued due to website problems:

I've even read in several places that O1 is pretty much a waste below 60 Hrc. While that could simply be due to TME issues, do you all think that there might be a rule of thumb for the "sweet spot" where each alloy displays its best balance of hardness to toughness. In other words, how big is the range of hardness values where the resulting gain in toughness starts to display diminishing returns?

It certainly is possible I'm imagining this, and while something mathematical could probably be derived by graphing toughness to hardness ratios for a variety of alloys, I'm guessing some of you have already figured that out.


And if I'm completely off base, I'd like to hear that, too. I just can't shake the feeling that taking a steel that quenches to 67 Hrc and tempering down to 55 might be a real waste, providing neither edge holding nor toughness. Or trying to use a steel that goes to 62, at best, and use it at 60 Hrc might also perform relatively poorly.

Thanks for you comments.

 

[Willie71]

There is a sweet spot for the steels I use, where there is a balance between toughness and hardness. O1 is about Rc61. W2 is Rc61-64, depending on use. S35VN is great at Rc60. Aeb-l is Rc62. I use 15n20 at Rc62 for most applications. The mid 50's RC numbers are more about production costs saving on grinding and sharpening, rather than maximizing steel performance. Even with the Rc60+ hardness that I use, I don't see problems with chipping or other edge damage. Choose the right steel, set up the steel for heat treat, and focus on the proper geometry for the application.

 

[RX-79G]

There is a sweet spot for the steels I use, where there is a balance between toughness and hardness. O1 is about Rc61. W2 is Rc61-64, depending on use. S35VN is great at Rc60. Aeb-l is Rc62. I use 15n20 at Rc62 for most applications. The mid 50's RC numbers are more about production costs saving on grinding and sharpening, rather than maximizing steel performance. Even with the Rc60+ hardness that I use, I don't see problems with chipping or other edge damage. Choose the right steel, set up the steel for heat treat, and focus on the proper geometry for the application.

I found something from Roman Landes that suggests a max temper of around 200° C for all knife steels. In other words, if it isn't tough enough at that temp, go pick a different steel.

Thanks!

 

[jdm61]

I recently heard that Adam Desrosiers said that leaving Cru Froge V below say 59-60 results in some undesirable things happening. I have also heard some stories about either steels having some embrittlement problems in the "middle range" hardness.

 

[jdm61]

Warren, do you think that the commercial heat treatments for steel like 1095 that leave them at like 55-57 is perhaps about not wanting to spend the extra money to heat treat a shallow hardening steel properly?

There is a sweet spot for the steels I use, where there is a balance between toughness and hardness. O1 is about Rc61. W2 is Rc61-64, depending on use. S35VN is great at Rc60. Aeb-l is Rc62. I use 15n20 at Rc62 for most applications. The mid 50's RC numbers are more about production costs saving on grinding and sharpening, rather than maximizing steel performance. Even with the Rc60+ hardness that I use, I don't see problems with chipping or other edge damage. Choose the right steel, set up the steel for heat treat, and focus on the proper geometry for the application.

 

[Willie71]

Warren, do you think that the commercial heat treatments for steel like 1095 that leave them at like 55-57 is perhaps about not wanting to spend the extra money to heat treat a shallow hardening steel properly?

I think it's quite probable. All the normalizing, thermal cycling, and tight specs for time/temp/quench conditions would be a huge drain on the bottom line. Without tight controls, there would be issues with chipping or other failures if the hardness was pushed higher. Moving to air hardening steels, and their simpler "recipe" should have fixed this, but in many cases didn't.

 

[RX-79G]

I recently heard that Adam Desrosiers said that leaving Cru Froge V below say 59-60 results in some undesirable things happening. I have also heard some stories about either steels having some embrittlement problems in the "middle range" hardness.

Tempered Martensite Embrittlement, or Blue Embrittlement. It appears to affect all the knife steels I've looked up. It starts at somewhere between 400-450°F and runs up to 550-600°F. So a high carbon steel tempered down to 55 Hrc avoids it.

There may be ways of tempering to 59 without causing it, but I haven't found how. More reason to stay close to a steel's wheelhouse.

 

[jdm61]

The good old 1500/400f will typically give you around 61 with CruForgeV assuming you took care of it before HT. It will also give you bad blisters and very salty new vocabulary trying to hand sand it. 425F supposedly gives you 59+ and the ability to chop though bolts and 10 penny nails. I stick with 61 myself.

Tempered Martensite Embrittlement, or Blue Embrittlement. It appears to affect all the knife steels I've looked up. It starts at somewhere between 400-450°F and runs up to 550-600°F. So a high carbon steel tempered down to 55 Hrc avoids it.

There may be ways of tempering to 59 without causing it, but I haven't found how. More reason to stay close to a steel's wheelhouse.

 

[Willie71]

Tempered Martensite Embrittlement, or Blue Embrittlement. It appears to affect all the knife steels I've looked up. It starts at somewhere between 400-450°F and runs up to 550-600°F. So a high carbon steel tempered down to 55 Hrc avoids it.

There may be ways of tempering to 59 without causing it, but I haven't found how. More reason to stay close to a steel's wheelhouse.

I hadn't thought much about the TME. I rarely temper at 450, let alone higher. From the Verhoeven PDF, it's a bigger problem at 500f to 600f, but as you note, over 425f, you start losing toughness. This sheds new light for me on why the Rc58/59 blades never performed as expected, and why I never had problems with knives above Rc60.

 

[jdm61]

I have heard that the zone can run from 500F or so up to about 800F, which I hank would be more of a problem with air hardening steels at least for knife usage. Does anyone know if it would impact the old school "blue back" temper?

I hadn't thought much about the TME. I rarely temper at 450, let alone higher. From the Verhoeven PDF, it's a bigger problem at 500f to 600f, but as you note, over 425f, you start losing toughness. This sheds new light for me on why the Rc58/59 blades never performed as expected, and why I never had problems with knives above Rc60.

 

[Don Hanson III]

I have no use for a W2 blades below 60 Rc. Typically hit 62-63 and never have any issues, even in large blades.

 

[jdm61]

But we cheat a bit with W2 in that the spine won't get that hard on a big blade so you get the benefits of "selective" hardening/tempering with some of the problems. I remember Bill Moran saying that in his experience, W2 was almost as tough as 5160, but it took and held a better edge.

I have no use for a W2 blades below 60 Rc. Typically hit 62-63 and never have any issues, even in large blades.

 

[Don Hanson III]

But we cheat a bit with W2 in that the spine won't get that hard on a big blade so you get the benefits of "selective" hardening/tempering with some of the problems. I remember Bill Moran saying that in his experience, W2 was almost as tough as 5160, but it took and held a better edge.

Well, I cheat whenever I can.

 

[Willie71]

W2 is almost the perfect steel, if there could be such a thing.

 

[me2]

IMHO, the range for specific steels for knife use is pretty narrow if you want optimal performance. It gets wider the lower your standards.

 

[RX-79G]

I have long thought W2 doesn't get used enough. Interesting comments.

 

[jdm61]

It was not readily available for a good while unless you knew a certain guy in Missouri and even today, the commercially available flat stuff costs about 25-30% more than 1084 or 1095. We had similar availability issues with 52100 in the past and it also costs a bit more.

I have long thought W2 doesn't get used enough. Interesting comments.

 

[Willie71]

It was not readily available for a good while unless you knew a certain guy in Missouri and even today, the commercially available stuff costs about 25-30% more than 1084 or 1095.

The vanadium in the W2 available to us now makes a noticeable improvement in its performance compared to 1095. The 1095 kitchen knives I made gust don't hold as fine of an edge as long, and chip easier. They are certainly not bad, but I've not had a single complaint on a W2 knife yet. Most rave about them. Not to mention, with clay less hamons like this, they are simply gorgeous.

[/url]IMG_5926 by Wjkrywko, on Flickr[/]

 

[Don Hanson III]

W2 is almost the perfect steel, if there could be such a thing.

Yes it is & just about the only mono steel I use any more.