New guy, probably not a new mistake (HT)

G

Grogimus

New Member
Hardened and did 1 temper cycle on my first knife tonight, made from Aldo's 1084. I used a paint can forge with a MAPP torch. I used fire bricks to close the rear of the forge off and I think that led to the mistake. When I finished the first hour of tempering at 400F the beautiful straw coloring was clear as day... and stopped right in front of the plunge line. When I draw a file across the blade further down it skates across but near the choil it feels like it's biting more. I assume (eek) I didn't get the ricasso area to the same temp as the blade.

Do I need to normalize the blade after I rearrange things so I can pass the knife further through and get a more even heat or should I just harden again?

Thanks for any input.

P.S. On a different note, from watching multiple videos I thought getting the blade above nonmagnetic would take quite some time. It took about three or four (just a guess) minutes when I normalized and hardened. Should I back the torch flame down a bit or is this ok?
 
1084 being fairly forgiving in heat treat will make a decent knife as long as you get above non-magnetic. Where ever your file is biting could mean there is a layer of decarb that needs to come off or it didn't get hard. I used a single brick forge for my first couple and had passable results, read that as the blade got hard enough to take an edge and cut stuff. If the area near your choil is thicker than the rest of the blade it could take a little longer to get fully non-magnetic so backing down your heat source could help that. I assume this is a full tang since you didn't say so keep in mind that the handle and ricasso will act as a heat sink when you are only heating the blade. I suggest you bring your paint can up to temp and stick the blade in handle first to get it good and hot so it won't pull the heat out of your blade and the area near the choil has a good chance of getting hard.
 
A couple things.

The color out of the temper may be deceiving a little. Things like degarb and oil from your hands touching the blade or wiping it before putting it in the tempering oven will have an effect on the colors that show out of the temper.

A sharp file will bite after tempering. The file test is done after hardening but before tempering.

I agree with Barry in that you certainly get a heat sink effect although not only on full tangs. The same will happen on a hidden tang blade. Preheating the area behind the plunge is the way to counteract the heat sink effect but I wouldn't do it the way Barry does. In all likelihood by the time you take the blade out and turn it around to heat the blade side it will cool down enough that the heatsink problem will be the same.

I think your on the right track. Open up the back so you can pass the blade all the way through and use the map flame to preheat the thick area behind the plunge.

You should be able to just harden a 2nd time on 1084. You probably will not get a 3rd shot on 1084 without normalizing first though.

Don't back the flame down IMHO. Once you open the back of the forge it's not going to hold the heat as much so you'll be dealing with a much smaller volume of heated air to work with.

3 to 4 minutes is about right. No need to extend the hardening process any longer than required to get up to hardening temp.

-Josh
 
Thanks guys. I'll give this a whirl when I get home from work. Looks like I should be able to use a smaller hard firebrick in between the larger, softer fire bricks I was closing the rear of the forge with to make plenty of room to extend the blade through.

It is full tang, I forgot to mention that earlier.

Thanks again, I'll try to post some images once I get some more work done.
 
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