heat treating blues

[tomh]

I have been having a devil of a time figuring out how to heat treat.
on the edge quench are there any reliable visual indicators showing it was done right?
I just did 2 today, 1/2 blade height in the oil. I got a 1/4 inch line of black scale that fell off, but in the black scale was a small area of a lighter color scale. I am worried it will be a softer spot and won't be a nice clean temper line.
this has been driving me nuts and have been getting hit and miss on my heat treats.
any advice on what to look for.
i have bugged Ed enough on this issue!

[cdent]

Hi Tom,
Can you hit it with a quick belt clean up, not finish grind, just to better decide if the look you want is ok. I'd hope it's not actually a soft spot.

Sounds like the heat isn't even/consistent enough. Don't over cook the tip, but why not try your forge to get a more even heat. If it comes out better, then back to practicing with the torch to give the edge a similar look before quenching (while leaving the spine cooler).

Hopefully a real knifemaker will jump in and help, Craig

[Ed Caffrey]

Tom......if just gona take some time. Your gona have to break a few eggs if you want to make a cake. This is why I am always harping about taking the time/effort to experiment...and that means creating some blades, and then destruction testing them to make sure they are where you want them to be. There's no easy way around it.

Once you do some testing, and get a few more blades under your belt, you will know what to look for. Heck, even after 25 years of doing this, I still fall flat on my face sometimes..... Everything will "look" right, and "seem" right, but when I cut test the blade prior to finishing it out.......its crap. I just hang my head, toss that blade aside, and start another one. Thats just the way it is with what we do. If any knifemaker tells you that they have 100% success with every blade....chances are very good they are lying to you. As time goes by you will learn how to minimize your errors, but its very unlikely you will ever be able to eliminate them. Have some patience with yourself.......your already 5-7 years ahead of most "beginners."

[tomh]

Thanks guys.

Hey Ed are you sure the 5160 blade I forged at your place was not really mild steel? Ha!
Everything looked great on that one, when I did the edge flex on the brass rod the whole thing layed over like play do. I think I will grind the edge down thick on that one and try again. then test to destruction!!!

[tomh]

is where the scale blows off as far as the martensite extends up the blade?

[Ed Caffrey]

Actually, the line that you see in a finished blade is the "transition zone" where one formation ends and the other begins. Sometimes you will see blades that seem to have a very wide temper line......which means the transition zone is wider. Usually this comes from a cooling rate that is too slow to produce that clean/crisp transition from one formation to the other. Ideally, it is where the martensite ends, but I hesitated to say that because there are so many different structures that COULD be achieved.

[tomh]

so is the width of the scale not an indiacator of a good quench?

[Ed Caffrey]

Its not a fully accurate measure of exactly where the temper line will appear in the finished blade, but it is an indicator that the steel where its blown off has fully hardened.

[tomh]

i think I have been afraid of getting the blades too hot, and have been quenching too close to nonmagnetic.
today I had to re do the blades I did yesterday, and ended up doing a differntial/full quench, and it got me exactly the hardness levels I wanted.
so far I think I have only gotten a perfect edge quench once, and it was an accident since I dont know what was different.
it is dang hard to see the colors when you are staring at a bright flame!!