Thoughts on Heat Treating a blade

[kbaknife]

In spherodizing, you are basically pulling all the carbon into small "spheres", which allows for cutting instruments like drill bits and mills and taps to cut through the steel.
I spherodize my 5160 - 0.60%C, as well as the hyper eutechtoid steels.
My last step in thermal cycling at the end of forging is to bring the blade up to temp and quench for martensite, which also reduces grain size.
Sort of like jumping into a cold pool!
But now the blade is hard, or if it was 5160, without even quenching, it will air harden and smoke a good drill bit.
Most people take that blade up to some sort of real hot and then try to slow cool it in some media.
But why take it up hot after we've spent a whole bunch of time reducing grain size?
I don't want to risk endangering the grain size, but I still want to drill and mill with ease, so the blade gets soaked at around 1300 for an hour and slow cooled in the oven. It's this sloooooooooooow cool from a high sub-critical that spherodizes the carbides, making for easy machining, yet leaving ultra fine grain.
If a maker has a heat treating oven, it should really be put to use in this manner.  
This also leaves the carbon in the right spot to just JUMP! into the making of martensite.
When steel is annealed from above critical, you not only risk grain growth, but it's also more necessary to soak the steel for extended periods of time to pull all the alloy into solution so as to get completely dissolved when it comes time to quench.
When spherodized, about all you gotta do is get 'er hot! Everything is sort of set up already.
I have not burnt a drill bit, or had a tap hang up, etc., in spherodized steel, in , well, a really long time. Years.
And have kept grain size and carbon location right where it needs to be at all times.
I paid a thousand dollars for that oven I'm gonna use it!
This is just the basic concept, without going into everything else that, quite honestly I don't understand, but it's a basic guideline.

[Lin Rhea]

That's great Karl. Even I understand it the way you told it.

Something doug said reminded me of a point. Usually, a given color equals a temperature. If you can read the color, you can get pretty dang close. A pyrometer is best, but for some of us here on TG, we need to learn color.

One reason an oven is a such a good tool is that you can achieve EVEN heating throughout the thick and the thin areas of the blade. If all you have is a forge, you should do all you can to learn to control your heating so the whole blade is the right temperature/color for the intended operation.

[Ragnarok Forge]

I am one of those "color" guys.  With a wife in college and two kids to fund, I am still saving up to buy a knife oven.  

With practice using the steel color works great.  A hunting buddy was just raving last night about how a knife I made him has cleaned, skinned, and boned multiple animals now and is still razor sharp.

[kbaknife]

You know what, maybe what I've been doing is not even the best way to do it.
It's just how my knife making has evolved.
Lot's of good knives were made before heat treating ovens became so popular.
As a result of some recent "awakenings" and a few discussions I've had, I may even employ some more simplistic methods and see what happens.
Having a good heat source helps, and experience at failure is crucial!

[Ragnarok Forge]

There are a lot of ways to make a great knife.  Each smith learns what works best for them. The learning process is a big part of what I enjoy about creating knives and tomahawks.

[Lin Rhea]

Karl,
   I'd put my money on your way as far above average. Your understanding of heat treat and steel behavior is well known and respected so I dont recommend changing it. I have learned as much from our discussions as anywhere.

[Doug Campbell]

No doubt about that Lin, wish I could retain half what Karl says/shows. Just goes to show you what you can achieve when you live and breath steel.

I've learned more in the last four or five years than in the previous 15 after getting involved with guys like you, Karl, Jon, Ed and several others in the ABS. While experience, good and bad can teach you banging around in the shop mostly on your own isn't conducive to higher learning.

Thank you to all of you  

[Kevin Evans]

Karl don't forget to tell about the extra piece of steel in the oven.To let it even cool down slower.
After I did the steel in the bottom of the oven it takes a lot longer to cool down ,which I supose makes it even softer.??
By the way great job guys,I even understand what you guys are talking about nowadays.LOL  Boy it took a Long time.LOL

[kbaknife]

No, Kevin, it won't make it any softer, but what that does is keep the cycling range of the oven to only a few degrees and more steady/accurate.
But it will ensure that the slow cool takes as long as possible and everything is as evenly distributed as can be.
But you are right, it'll slow down that cooling off period forever!

Guys, I have a 1" thick floor of wrought iron in my heat treat oven. I bring it up to heat as well and let the oven soak at temp for about an hour before I ever put a blade in.
This really ensures that I have equal heat throughout the oven and helps to distribute the heat evenly.

[Doug Campbell]

Hey Karl, when your oven is running what range in temp is there? I assume probably just a few degrees with that being a pretty much closed environment and everything being automatic. Running my forge manually bout the best I can do is stay within a 15-20 degree range... If I get sidetracked for just a minute that goes out the window.  

[Lone Ranger]

great thread! damn I am confused now! LOL

time for a re-read~

L.R.  :D

[kansas stik man]

join the club lol i think being confused at first is some wierd  form of anitiation lol but really addicting, the more i learn the more i wanna apply my new knowledge to a new project, there is simply not enough time in the day.

[Roughcountry]

Great stuff guys, Thanks for starting this one Lin.

[JohnHV]

Many thanks to Lin, Karl, Doug and all the other skilled craftsmen on this forum for helping the rest of us improve.

I am just a hobbyist and make no claims of "expertise". However, I thought I'd share a few things I've learned from others on this forum that have helped me immensely with regard to heat treating.

1. As Karl has said repeatedly in the past, get some good quench oil. Until I did this, I was really struggling.

2. For me, the normalizing step is the most critical for achieving a quality blade.

3. I can only properly heat treat one blade at at a time.  Takes all of my attention to get it right!

3. As Lin says, test the blade before putting on the handle.  Much easier to repeat the heat treatment this way (Don't ask me how I know that!)

[Lin Rhea]

Bump for some of the new guys.

[Fallguy]

Thanks Lin, I have not started any make knives yet but this thread and Karl's video series have been very enlightening on all the details it thanks to get it right.