Determining optimal Rockwell hardness?

Dr Rez

Dr Rez

Pisser of the Couch
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Hello all, quick question about heat treating different steels.

How does the steel type or the knife-maker determine what the optimal hardness is? Is it simply based off the amount of carbon/chromium and the intended purpose for the blade? Am I missing anything with that, because I am sort of in the beginning stages of learning about the methods used to create different types of steel...particularly the modern super-steels that have not only very high carbon and chromium but lots of others elements added in for varying purposes.

Also as an add on question, what hardness do you prefer a super steel stainless like cpm 154 or cpm s30v to be at in a small folder vs the hardness for a 1095 or 3v larger survival fixed blade?

Any tips from some of you that are far more knowledgeable than myself would be great. Thanks for your time in helping me figure this out.
 
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Dr Rez said:
Hello all, quick question about heat treating different steels.

How does the steel type or the knife-maker determine what the optimal hardness is? Is it simply based off the amount of carbon/chromium and the intended purpose for the blade? Am I missing anything with that, because I am sort of in the beginning stages of learning about the methods used to create different types of steel...particularly the modern super-steels that have not only very high carbon and chromium but lots of others elements added in for varying purposes.

Also as an add on question, what hardness do you prefer a super steel stainless like cpm 154 or cpm s30v to be at in a small folder vs the hardness for a 1095 or 3v larger survival fixed blade?

Any tips from some of you that are far more knowledgeable than myself would be great. Thanks for your time in helping me figure this out.
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The first step a knifemaker asks himself is what is the purpose of the knife and how is it used?

that will help narrow down what the geometry of the blade is, shape, thickness and edge.

Then the knifemaker is limited by how its made and what equipment and experience he/she has for heat treatment. Is it forged? or stock removed? heat treated by digital oven? or by eyeball

Then the steel and hardness is chosen from there .

So you see that you can't pick a steel and hardness until the other factors are solved first, otherwise a nonsensical chose is made that can compromise the performance of the knife.

Its not just as simple as the hardness and steel either, its all about the underlying mircostructure of the steel.

We can have the same steel and same hardness but the microstructures can be very different

Why is this important?

Let's pretend we have the same steel, same hardness.


One will have a finer grain with the most martensite converted in the grain and a more even distribution of finer carbides throughout the steel, this one will be tougher, more edge stable, sharpen better-grind, apex and deburr best, and cut longer.

Meanwhile, if someone only knows how to get the steel hard without understanding the underlying mircostructure of the steel then they could overcook the steel and make massive grains which sharpens bad and hold a bad edge, mirco cracks from unevern heating and queching which can lead to chips and critical blade failure, too much Retained austenite, and a lower martensite conversation from a bad heat and quench which leads to bad edge taking and stubborn burrs in some cases, carbides oversaturated in the grain boundaries reducing toughness, mircochiping.

I could go on and on and they're even smaller details I am always learning about. hahaha most of the stuff can just be user error though too.


I generally want my knives as hard as possible with the most stable microstructure but I will make comprises depending on the design and use of the knife and will choose the appropriate steel and hardness for that.

I personally don't like knives that are comprised on the softer side for user error and improper sharpening technique, but I understand their place.

I wouldn't turn my nose down at them, I have plenty of family members that need that kind of knife so its fine,

Its just not for me, I really like knives and high performance, but its my obsession and main hobby so that's a given.

Some people just don't have the interest or time to take care of their knives and treat them like shovels, and I get it, there are plenty of things I don't have the time or interest in; like shovels lol
 
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My simple rule is that if I can't send out a knife with a edge hardness of at least 60Rc, I am not interested in that steel.Iif I ever decide to make a tactical tomahawk, I might let it slide at 58Rc. ;)
 
DeadboxHero said:
T
I personally don't like knives that are comprised on the softer side for user error and improper sharpening technique, but I understand their place.
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I don't understand their, even with knives made to a price point. IMO,if you have to leave your blades 53-55Rc, you are either using the wrong steel, even the wrong INEXPENSIVE steel, you are not treating it correctly or both.
 
Wowbagger said:
PS: I think they frown on (won't let you use) that particular "face" in this forum.
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True.
It is not a man scratching his head in thought. He is doing something else.
That emoticon is called a "jerkit" and is only allowed in Whine & Cheese.
I have removed it.
 
Many steel manufactures supply Technical Data Sheets which provide heat treat vs. property charts. Those serve as a starting point.

But above all, you are depending on the knife maker or manufacturer to have the expertise to choose proper temper. Partly, that will depend on the use for which the knife is designed. That knowledge is part of what you are paying them for.
 
jdm61, I agree, but I see users that are very upset with any type of chipping and refuse to understand the limits of steel or change how they use their tools, so they enjoy softer steels because the damage is less dramatic.

also, they embrace constant sharpening and low grit, low polish, thick edges on very rudimentary abrasives.

I see it as the flip side of the coin, but It would not perform for my preference and use. I would get annoyed since my edges dull from cutting not failure from abuse. So I would have to stop more frequently to sharpen.

also the soft steel can't support the acute geometries I like that sail through material.
 
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I work with one particular steel, Cru Forge V, which I have typically left at 61Rc. Adam Desrosiers who uses a lot, discovered that it can chip like 58-59Rc, but if you have it at say even 62-63 Rc, no chipping. His standard test is whacking moose antler. In the same vein, guys like Dan Keffeler and Nathan Carothers discovered that if you use the low temper on 3V, it doesn't microchip. Kevin Cashen played around with 52100, likely in part to debunk certain claims about it and discovered that if you used a lower austenizing temp, it gets really tough and hold a crazy fine edge. That probably explains, among other things, why Bob Kramers kitchen knives performed so well. I suspect that if you ever got to see Busse's HT recipe for SR101,you would probably discovery that the "modification" of 52100 was a similar devotion from the industry standard HT for bearings and the knifemaker standard hardness of say 59Rc which leaves you with big abrasion restart chromium carbides, but also with more RA. . We see similar results with people playing with the HT for simple steels like AEB-L and 15N20. Like you pointed out, its less about just the hardness and more about the microstructure which ALLOWS you to use a specific hardness..
DeadboxHero said:
jdm61, I agree, but I see users that are very upset with any type of chipping and refuse to understand the limits of steel or change how they use their tools, so they enjoy softer steels because the damage is less dramatic.

also, they embrace consistent sharpening and low grit, low polish, thick edges on very rudimentary abrasives.

I see it as the flip side of the coin, but It would not perform for my preference and use. I would get annoyed since my edges dull from cutting not failure from abuse. So I would have to stop more frequently to sharpen.

also the soft steel can't support the acute geometries I like that sail through material.
Click to expand...
 
Hardness is the by-product of prior microstruccture. Choose an appropriate steel and temperatures and the hardness will end up where it needs to be.
 
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