Traditional Folders & Fixed: Steel 101 - Geometry & Heat Treatment

[jc57]

...I like Case knives. Even though I don't really care for their alloys. They run them too soft. But for most everyday usage, they work just fine. But if I know I'll likely be doing something significant, I'll pull out something modern with better performing, harder alloys.

This pretty much sums it up for me, though I would modify that to "Case and Victorinox knives." For most of what I tend to use a pocket knife for, Case Tru-sharp 420HC or Victorinox 1.4110 seems to do OK. I have modern knives with 154CM and Elmax that I keep handy for anything where I need to do something significant (primarily cutting down cardboard boxes for the trash).

I have rather modest cutting needs outside of the kitchen and so really I don't focus that much on the steel in a slipjoint pocket knife. I do own pocket knives made from the first five steels that Frank listed, and my observation of their relative performance is the same as the ranking Frank gave them. I would also put 440A right around the 420HC neighborhood.

 

[Jack Black]

Oh bother. You pushed my button.

LOL! I wondered how long it'd be before you jumped in Frank! :thumbup:

 

[Blacksprucy]

In regards to carbon steel (1095), has anyone done a test or know how much a heavy patina inhibits or prevents rust compared to a carbon blade without a patina?

 

[knarfeng]

In regards to carbon steel (1095), has anyone done a test or know how much a heavy patina inhibits or prevents rust compared to a carbon blade without a patina?

Well, actually patina is black oxide, a product of a corrosion reaction, aka, a form of "rust". It's less aggressive than the red rust reaction and does not cause pitting.

The amount of "protection" will depend on the exposure conditions.
►If you leave it out in the rain or put in a salt spray cabinet, it isn't going to provide much noticeable help. The black oxide layer is not tightly adhering and red rust will quickly take over when the conditions are right for its formation.
►If you carry it in your pocket where it is mostly dry, the black oxide might help prevent the formation of red rust, because the bare iron is not on the surface. Also, the black oxide will retain oil better than bare polished steel. And oil forms a barrier to moisture and oxygen, the reactants necessary for the chemical reactions that form iron oxides. Of course "in the pocket" usually the conditions are right for the formation of black oxide, so the blade may be still slowly corroding, it just isn't forming red rust.

Corrosion engineers do not consider black oxide in and of itself to offer protection for carbon steel. Even phosphate coatings (aka "parkerizing") are considered to require oil or similar material to actually offer much protection.

Personally, I don't forcibly "patina" carbon steel blades. I keep them lightly oiled and let whatever black spots form as they will. I don't get any red rust when I do this.

 

[Buzzbait]

Oh bother. You pushed my button.

Wow. Awesome post. I agree with every single thing you wrote, although I haven't had the pleasure of using the more fun steels such as M390 and M4.



Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[Wurrwulf]

I have very little experience or knowledge when it comes to any of the topics listed in the title of this thread, so I will be following closely. I will say this: I have a few knives in "tool steel", and I vastly prefer softer, "inferior" steels. I have no interest in taking more than 15 minutes to sharpen a knife, even if it means I have to sharpen more often. Even the diamond stones on my Sharpmarker take forever to make an impact on my D2 knives.

Thinking of heat treats and steel quality raised a question on my mind, though. If you were to heat treat a "super steel" to a couple/few points lower than typical (say 58, instead of 61), would the edge retention deteriorate more than the ease of sharpening increase? I'm sure that companies that heat treat/create knives have done the research on diminishing returns, but it's not something that I ever hear talked about. I know that the metallurgical make up of the steel has an impact on edge retention, etc. so in my mind, increasing the ingredients to be more abrasion resistant but lowering the heat treat to make it more manageable seems appropriate.

 

[Obsessed with Edges]

I have very little experience or knowledge when it comes to any of the topics listed in the title of this thread, so I will be following closely. I will say this: I have a few knives in "tool steel", and I vastly prefer softer, "inferior" steels. I have no interest in taking more than 15 minutes to sharpen a knife, even if it means I have to sharpen more often. Even the diamond stones on my Sharpmarker take forever to make an impact on my D2 knives.

Thinking of heat treats and steel quality raised a question on my mind, though. If you were to heat treat a "super steel" to a couple/few points lower than typical (say 58, instead of 61), would the edge retention deteriorate more than the ease of sharpening increase? I'm sure that companies that heat treat/create knives have done the research on diminishing returns, but it's not something that I ever hear talked about. I know that the metallurgical make up of the steel has an impact on edge retention, etc. so in my mind, increasing the ingredients to be more abrasion resistant but lowering the heat treat to make it more manageable seems appropriate.

Changing the heat treat will have more of an effect on the steel's tendency to roll (lower RC) or chip (higher RC), no matter the steel type or it's carbide content. It won't have as much direct effect on the hardness of the carbides themselves, which are much, much harder and get most of their uber-hardness during the raw steel's manufacture (long before it's ever heat treated). Those carbides are what make the steel more difficult to sharpen with inadequate tools, or even impossible with some tools. If ease of sharpening is the priority, it's better to stick with simpler alloys or (even more simple) plain carbon steels without the carbide content. For example, a 1095 blade (contains no hard carbides at all) at 60 HRC will still be much, much easier to sharpen on simple tools than will another blade of D2, S30V, S90V or similar 'super' steel at the same hardness, because the carbides in the 'super steel' mix are what make the difference in ease of sharpening, for the most part. Keep in mind, the 'Rockwell' hardness measured in a given steel and largely determined by the heat treat, doesn't reflect the hardness of the super-hard carbides in the alloy, but only of the matrix steel (Iron + Carbon) supporting the carbides.

Put into perspective on the Knoop scale of hardness, simple steels like 1095 will usually be at ~600-800 Knoop; chromium carbides (as in D2 steel, or ZDP-189) are about ~1800 Knoop, and vanadium carbide (as in S30V, 90V, 110V, etc) will be around ~2800 Knoop hardness. Changing the heat treat by itself isn't going to significantly change that; not hardly at all, in fact. Lowering the Rockwell hardness a bit, via a change in heat treat of a carbide-heavy 'super steel', will likely only mean the blade won't resist edge-rolling or other deformation as well, and will still be nearly as challenging to grind or sharpen. And, going too soft will sometimes make most any steel more difficult to refine during sharpening, due to increased burring at lower hardness.


David

 

[5K Qs]

I have very little experience or knowledge when it comes to any of the topics listed in the title of this thread, so I will be following closely. ... I have no interest in taking more than 15 minutes to sharpen a knife, even if it means I have to sharpen more often. ...

What Shawn states is true of me as well. I know almost nothing about types of steels and heat treatments, but I have little interest in becoming a "steel expert". I'd like to learn how to sharpen a knife so that I can cut stuff; I don't need mirror polishes or even hair shaving, as long as I can cut the stuff I typically encounter that needs cutting, and can get my knives to that degree of sharpness relatively quickly. (I'm learning that getting knives profiled/sharpened for whittling is probably a different story that may have to wait until I retire! )

But I'm fascinated by the discussion so far in this thread, and wonder if my current sharpening capabilities are related to some of these topics. Basically, the only knives I can sharpen the way I'd like to are carbon steel Imperials and Colonials from about 1960 or earlier!
Is this related to steel, to blade geometry, to heat treat, to all of the above, or to none of the above (and it's all in my head just because I happen to like those old, inexpensive knives)?

For what it's worth, I can usually sharpen those old knives on the bottom of a coffee cup; if they're really dull to start, circular motion on a DMT Fine "credit card" seems to get me started, and then the coffee cup finishes the job to my satisfaction. (As far as I know, I've never raised a burr in my life so far.)

- GT

 

[knarfeng]

"steel snob" is not acceptable terminology.

A lot of folks have need of or just plain like high performance blade alloys. That does not mean they are snobs. It just means they have their own preferences, which may not match yours.

 

[Wurrwulf]

Thank you, David! I've taken rudimentary courses on metallurgy for work purposes but never enough to be able to make heads and tails of what affects what. Very informative!