Did I lose my temper? (a novice question)

G

Gauge7

Joined
Apr 13, 2006
Messages
264
Hi,

I have been making really basic knives for a couple years now. I have a couple knives that I am in a rush to get out as gifts. To reduce my time I didn't clean much of the scale off the knives as I usually do between the ht and the temper. Well, after two hours at four hundred I pulled the knives out to find that they were almost purple :( (yeah, like him). Well, I quickly pulled out some 220 grit and polished both blades and threw them back in to double check. After an hour I checked on them and they were the usual straw color :grumpy: (like him). So did I get them too soft on the first temper or was it an illusion due to me not removing much scale ( I soaked them in warmed vinegar to get some off, but I really didn't get them clean)? Should I play it safe and redo the ht?
Thanks.
Jeremy
 
I figure you are just fine. You can see most any color during the tempering process. Always use time at temperature and you can't go wrong.

Fred
 
Thank you Fred! After having performed my best hting to date on these two, I hated to think I had gone and flubbed it by doing a lousy temper. I had preheated my little tempering oven for twenty minutes (I had placed some old railroad iron to aide in temp rentention) and then place the two knives in the oven for the stated time and temp.
 
When you said you soaked them in vinegar, if this was before tempering and you didn't wash it off well that could lead to dark colors.
If your reported temperature of 400 (I assume F ) is accurate you are fine. The colors are surface oxidation and can progress to darker colors after a longer time.

What does a file say? if they file like you expect and hold an edge then color is irrelevent.

ron
 
I never clean the blades between heat treat and temper, except maybe to wash the oil off. No sense in subjecting them to the shock of a grinder, and I want to keep the time at such a high stress form to a minimum just in case I drop it or it decides to crack on its own. I use my household oven, and I use a cooking thermometer (one you can hang on the rack) to set the temperature by on my old analog oven (turns out to be ~375 on my oven control is actually 400). As long as you keep the temperature under control and temper for time, you're fine.

--nathan
 
I soaked them in warm vinegar for about four minutes just to loosen the scale enough so I could see some bare metal along the edge (also just to help wash any oil residue off before I placed them in the oven. I've had better luck using warm vinegar to remove oil residue than warm soapy water.) After the vinegar I hit it with some warm soapy water just to neutralize the vinegar. I use an old toaster oven that I have found to be pretty reliable. I just have to leave it at just under 400 on the dial as it tends to run about 25 degrees warmer than the dial. Thanks for the advice on the thermometer, Nathan. I'll pick one up just to be sure.

As far as testing the edge, all I did was to check to see if the file would begin to bite. Thanks Ron, I'll try to put an edge on them in the morning and see what they do.
 
If you're using tool steel, you probably want to put them into the tempering oven when they drop to 120'-150 degrees. There's really no need to wash anything off after heat treatment. Just take it out of heat treat oven/forge and wait a bit till you can hold it in your hand....might be somewhat uncomfortable and then just put it in.
 
Have you checked the cutting edge by doing the brass rod test?

Take a piece of 1/8" or larger brass rod and put it horizontal in a vice, run the cutting edge along it pushing down just enough to see the cutting edge flex. The edge should return to normal, if it stays deformed it's too soft, chips out it's too hard.
 
Since I'm just a novice I use mostly cheap metal a.k.a. U.S. files and springs (got a couple of great antique wagon bed springs I want to try). I don't have electricity to my shop yet (old MO stone building built in the 40's) so getting the post-quench still-warm blades to my oven is a bit tricky as to date the only method that works for me is to either place the blade in boiling water to carry it back to the over, or use warm ash from the "forge" to get the blades back.

I haven't tried the brass rod test. I will get some brass rod and try that too. Thanks
 
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