Ruined knives by softening tangs? (no pics)

soundmind

Well-Known Member
#1
I had two full tang D2 blades from a supplier and softened the tangs in order to drill more holes before putting scales on. The process was: wrap blade in wet rag, then apply heat to the tang with a propane torch. I could only do a little at a time this way. I kept heat on until each part reached bright red/orange. I held it that color for a few moments, worked my way up to the ricasso, then back down....the other knife I was able to heat the same way but had much slower, overnight cooling. Both of the tangs were machinable after each process.

I thought softening the tangs to make them machinable would also make them tougher. But now I'm thinking did this process ruin the heat treat and weaken these knives?

These are finished. I'd like to give at least one away to a friend, but not sure if I can do that in good conscience, since these are field knives.
 

Johan Nel

Well-Known Member
#2
Do you have the ability to test the hardness of the blade?
I believe you should be safe on the process. I recently did the same on a blade, and had no problems.
 

Chris Railey

Well-Known Member
#3
Rough finish one and beat the crap out of it. If it survives, you can feel better about the other. Then you will know if your process was good or bad.
 

Doug Lester

Well-Known Member
#4
My concern would be with heating the steel up to a bright red to orange color. I know that color is a very rough gauge to go by but D2 is an air hardening steel. If you got the steel hot enough to austenize then you actually hardened the tang and left it as untempered martensite.

Doug
 

soundmind

Well-Known Member
#5
Do you have the ability to test the hardness of the blade?
I believe you should be safe on the process. I recently did the same on a blade, and had no problems.
No, no way to test hardness yet. But they were machinable.

My concern would be with heating the steel up to a bright red to orange color. I know that color is a very rough gauge to go by but D2 is an air hardening steel. If you got the steel hot enough to austenize then you actually hardened the tang and left it as untempered martensite.
The air hardening aspect surprised me. I came across that recently - reading the same book I've been reading before just missed that. When I reread that I'm thinking...oh no! Then I thought maybe I'm ok, b/c the result was they were machinable.

Is it only "untempered martensite" that would make it brittle, Nothing else? Or if it truly is annealed then these are good?
 

Doug Lester

Well-Known Member
#7
This is where an magnet would come in handy. Heat it until it has some color but not until it looses magnetism. If it's still magnetic you haven't changed phases in the steel. Yes, it would be the untempered martensite that would cause a problem but note that I stressed that it was if you had heated the steel enough to change phases.

Doug
 
#8
To anneal a hardened rifle receiver to drill for a scope mount, I use an acetylene torch with a small tip. I just heat the spot I want to drill/tap to red, let cool. It doesn't hurt the receiver. I need to try this on a tempered knife.
 
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