multiple, multiple quenches - damage?

E

Edward SE

Joined
Oct 12, 2001
Messages
16
I don't want to scrap a blade which I've had trouble hardening and am wondering if a six'th quench will still harden the blade. I think the heater was off in the oil and I might have been down around 100 deg rather than the typical 130-160 I usually quench at. So, frustrated, I quenched a couple different ways for a four'th and fif'th time. I know that all other variables were ok - unless the leaf spring really isn't 5160.
I also tempered for two hours thinking to finish the knife anyway. But now I would like to go back and quench again. Does anyone see any problems?
Should I re-normalize (I normalized three times prior to these five quenches.)? Is it basically junk now?
Ed:mad:
 
While I am no authority on this I will relate my
past experance. Several times when quenchimg large
Bowies I have quenched more than 4 times because I
bent the blade, what I found was that I had surface
checks all over the blade, when grouned off thay
proved to be quite deep, some times thy would form
a pattern. The blades were not saleable because my
name would be on them. I broke several blades and
did not find any thing wrong with them. I still have
one of them I put a test handle on and have used it
on very ruff duty, trying to destroy or damage it
and it wont quit. Don't know if this helpes, I also
would like a answer. The steel was 5160 Gib
 
I had that too once.. out of pure frustration i water quenched it. Neat.. said ping right away.

In any case, most leafsprings are 5160, and if they are not, it's still a carbon steel, so usable as blade.

If I were you, I'd normalize the steel first, and while your doing that, get a few pieces of the same Leafspring to over non-magnetic (I found that leafsprings liked to be quenched from orange heat), and use several quench media (several oils at several temps). Then find out which makes a file skid. On the other hand, a file HRC 60 or over, make sure it is just barely fileable ( you don't want the feel of a solid piece of crystal).

On the other hand.. it could very well be that it is hardened already, but you are cutting with the decarbeurised parts. I'd keep that as backupplan, since it will require you to totally reprofile your blade, since lots of steel has got to come off. Some 5160 I forged was useless, as I lost more carbon then I tough, resulting in a $hitty blade.

Hope to help you a bit,

Bart.
 
While experimenting with multiple quench I went as high as 11 quenches with carbon steel blades. One time the fourth quench demonstrated a lowering of cut performance, the rest all resulted in very minor advances. Bart was correct in the thoughts on poor perfromanc in the outside of the steel, you need to grind off a few thousands to get to the better steel. This is providing that you had a fairly thick edge when you quenched.

I leave my blades at least 1/8 inch thick before hardening. I feel this provides a sort of 'thermal cushion' that serves to protect, what will become the cutting edge, from what I call excessive thermal shocks during the heating and quenching.-
 
I mistakenly thought that since I went down to a 120 grit finish before quenching, which looks very clean, that there was no carborized surface. Wrong! As good as it looked coming out of the quench, there was still a soft exterior. I took the edge down on the grinder and again brought the file against the edge and there it was. Beneath a good twenty thousandth's or so, the file skidded across it perfectly.
Thanks for sending me in the right direction guys,
Ed
 
A very good lesson. I used to almost finish the blade before Heat treating. The reasoning was that grinding after heat treating was bad. I found that I was grinding twice as much. I also read some of Ed's posts and found that as usual he was right on the money. I don't leave quite 1/8 but close to it.
 
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