It's All About The Heat Treat

[Brock O Lee]

Hopefully some of you don't turn your critical eye toward all facets of your life or you'll never cross a bridge or enter a building ever again. Sometimes, you have to trust that the experts are experts and are doing their due diligence.

There is a lot of truth in this statement.

Often I don't care too much about the detail and blindly trust the experts, but for some facets of my life I want to "trust and verify" the experts!

[ladybug93]

but that's what they do on forged in fire...?!

[Brock O Lee]

The old ways are the best!

[Cl1ff]

I’m just interested in learning more about metallurgy, heat treat, and knife design.

When commenting on complex topics as a new enthusiast/amateur addressing or referring to those in the profession, and even if your grasp of the topic is quite solid, it’s best to be humble, respectful, and also know when it’s not your place to comment.
Sometimes things need to be “called out” or fairly criticized and questioned, but it’s not a good look to be a condescending noob, even if you’re right.

At least, that’s what I’ve learned in my time with other “communities” like paleontology (and adjacent fields of research) and what I aim to practice here.

[Bk.Obamah]

It's pretty simple for me. If I'm interested in a knife I look up the type of steel used and it's properties. If I'm still interested I look up what decent heat treat is for that steel.

Then I check the Manufacturers target. Hopefully they coincide.If I absolutely love the design I might buy the knife Regardless.

If it's a SpyderCo I can pretty much just pick a design and steel I like and not worry as it's going to have a better HT spec than pretty much anyone else.

[Stuart Ackerman]

For those that say a file that slides on the HTed blade is the test...

One question...What hardness is the file? :)

In my HT experiments, I tested a bunch of files to see the HRC.

Enough of a variance that is matters.

A file might give you a general idea between the difference of annealed and hardened steel, but not accurate enough to know how hard it actually is for sure.

[Stuart Ackerman]

An extract that I did in 2018 in EM...

.......I have Rockwell tested all my files, old and new, and the variance is scary.

They were tested at the brand mark and the tip of the file. Four indentations.

Nicholson, Bahco, Grober...and borrowed from other craftsmen and craftswomen that I know: Pferd, Vallorbe...

Two Vallorbe needle files, identical in shape and type, had a 4C difference.

Three Nicholson Second Cut ( all brand new and bought from the same hardware supplier) had a 6C difference.

That meant that a supposedly 58C Rockwell hardened O1 blade could be perfect.... or less than maybe 54C...

I do know that I have daily access to a Rockwell tester, and most folk do not.

So, it might be worthwhile to get a single file new Second Cut or Smooth file Rockwell tested, just for reference purposes for hardness checks.

Keep the file away from your normally used batch of files, so that it remains pristine.

I just did a Google random search for hardness testing files, and this was the first site that popped up...

http://www.flexbar.com/shop/pc…ESTING-F ... -p5383.htm

Yup, they cost a bit, but if you are serious about what you do, think about it?..............

[sidpost]

Just because it skates with a 54RC file doesn't mean it is hardened to 54RC. I do agree though that setting aside a 58RC file you have for this purpose is a good idea assuming you want knives in the high-50's to low-60's RC range.

[Bolster]

A file might give you a general idea between the difference of annealed and hardened steel, but not accurate enough to know how hard it actually is for sure.

Except for the hardness test files, as you mentioned. Can buy $27 each at McMC.





https://www.mcmaster.com/hardness-tester-files/

[TTFulltimer]

You can learn everything you need to know about heat treatment by watching "Forged in Fire"

[Michael Janich]

Dear TTFulltimer:

Actually, in most cases "Forged in Fire" doesn't show the tempering step that occurs after the quench and before the knives are hafted. On rare occasions, they include it, but usually not.

Stay safe,

Mike

[TkoK83Spy]

You can learn everything you need to know about heat treatment by watching "Forged in Fire"

Believing everything on that show is like believing everything you see on youtube.

[kennbr34]

but that's what they do on forged in fire...?!

Heh, to be fair I wasn't saying that oil-quenching a blade of a certain temperature and then tempering in an oven can't make for a great heat treat.

I was just trying to point out there's no way of telling if that's all someone did. I could TELL you that I annealed, normalized, thermocycled, and did cryogenic cooling... But you have no idea if I really did all that, or if it was just me out in the backyard with a fire pit, a tank of motor oil and mom's old oven.

But to be fair Brock O Lee was absolutely right to walk away from that deal. Depending on the steel, the temperature at quench, etc. those blades could have even been well up to 66-68 HRC! Basically way too brittle for most simple carbon steels and most use cases for them, particularly a pocket knife. Using a blade at it's quenched-hardness is almost never a good idea unless you just didn't get it hot enough to get very hard, and that raises all sorts of other issues with things like grain structure.

File-testing hardness goes down a lot on Forged in Fire because it's a really simple way to tell if the quench hardened the blade at all (not that it got as hard as it should), and it's a competition format. But as someone else mentioned they usually never show the tempering process, which is hugely important... Arguably much more important. I don't think the file test is actually that practical outside of that contex. There's also been a few times on that show where they will use steels that don't actually get harder than a file, or the smith neglects to remove forge scale, and their file skates on a hardened blade and they re-quench it unnecessarily thinking it wasn't hard. In my (very limited) experience the way to do it is to get it to its critical temp, quench it, then test the hardness after the temper.

But anyway, I studied a lot about heat treating 108* series carbon steels, and it's really not exactly rocket science to get a serviceable, hard blade with steels like that even without specialized equipment or processes; there's a few cool videos around showing you how to make blades with a campire that actually do work. BUT that's just the 108* carbon steel series; things even get trickier just going up to 1095. Other steels might be air quenching instead of oil, and there's differences between martensite and austenitic, etc. Especially when you start talking about highly-alloyed steels. All steel is technically an alloy of iron and carbon, but once you start throwing things like chromium, vanadium, tungsten, molybdenum, nitrogen, etc. things get really complicated. I'd be speaking out or turn if I commented on anything but doing simple oil quenches on low-alloy steels. And then there's things like annealing and normalizing...

Anyway I got sidetracked. Like I said before, without special testing equipment, verifying the quality of a heat treat isn't really that feasible for the average consumer. Even using some of those hardness testing files, or even a Rockwell machine, aren't going to really tell you anything about the grain structure. Only way for the end user to really verify is to have that equipment and/or do very controlled testing. It's pretty much all a game of trust for us. Personall, I think a lot of the qualities or shortcomings people tend to attribute to the heat treatment are more likely differences in blade geometry.

I should have linked to these videos before when I mentioned Shawn Houston talking about this stuff
https://youtu.be/abaR6fE3MUA
https://youtu.be/pgASlsQRDAo

So yeah, any time someone says a heat treat on one knife isn't as good as a heat treat on another, I think it should be taken with a real big grain of salt unless they're testing work identical geometry and have the calipers and goniometers to prove it.

[sidpost]

Again, I don't know what Newt Livesay of Wicked Knives did to those knives of his but, they are phenomenal performers for 1095 steel, and they have impressive rust resistance in my usage.

Heat treatment, quenching, tempering, Cryo treatments? Don't know what he did but, it sure does work well for me and my uses!