Did I goof up my heat treat?

FlaMtnBkr

FlaMtnBkr

Joined
Oct 20, 2004
Messages
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I turned on the oven to let it warm up for the first temper and threw the blade in so it could be warming as well. I walked out to the shop for a 'minute' and was gone for probably 10...when I got back in the thermometer read 450 and I was shooting for 385. I took it out after an hour and it has a purple/blue color all over it. Does this mean it got too hot? Do I need to normalize and harden again? Oh its 1080 btw. Thanks!

Ryan
 
Yes primarily because the colors indicate a much higher temperature than your reported 450 F. Blues and purples are a sign of the 500+ F range and is normally advised to avoid when tempering tool steels. I suggest re-doing the heat treat.

RL
 
I figured that was going to be the case. Makes you wonder how I dont burn more food...The oven was set at 400 and I put a thermometer in there because I know they are not accurate and it read 450. Guess I need a new thermometer as well.


Ryan
 
Another problem here is the fact that three people will look at your blade and call it three different colors.A good pyrometer is invaluable for HT.As you are learning,the temperature in a home oven can vary as much as 50+ degrees from the setting. Purchasing a controlled HT oven is a good investment.
 
bladsmth said:
Purchasing a controlled HT oven is a good investment.

He is absolutely right on, however; if you do not have the funds to do so, go buy a couple of the oven thermometers in the kitchen department at Walmart. Why 2 you ask? Because one alone might not be quite accurate, but if you take two readings and average them, you will come mighty close. That way you can use your kitchen oven, providing the little lady doesn't mind. Good luck.
 
The other "knifemaker wisdom" is that the toaster ovens one can find at yard sales have very good temp control when overwrapped with a blanket of forge-style ceramic fiber insulation.

Still, one has to measure the set versus actual temps with an outside measurement, but everyone says they are repeatable and steady.

Welcome to the world of home heat treat blooz..... :D NEVER put a knife into heat that hasn't been "profiled" and tested for repeatability. Why in the hell do you think so many cakes get burned??? ;)
 
Thanks for the replies guys. I will just normalize and re-harden. There are actually a few colors going on...its mainly blue-purple with some gold close to the edge where it is thin and there was no clay. I thought I was good with the oven setting and 1 thermometer but apparently it was way off. I will get a couple, more expensive thermometers and try that. Ive got a multimeter that has a thermometer so if it will go that high maybe I'll try that...hopefully a thermocouple will be more accurate than the wound up piece of metal in the cheapie oven thermostat I have.

Also, this is my second knife I have made and heat treated so the heat treating oven is a ways down the road.

Fitzo: thats actually what I used was a toaster oven but I guess mine has seen too much freezer junk food to work properly :D . I had to put it on about 300 to reach the desired 385 on my apparently non-accurate oven thermometer.

Should probably start a new thread for this but I have another question:

I used satanite and made it real watery and put on the blade to prevent scale. After it bakes on is there an easy way to get it off besides sanding? I tried sprinkling borax on but it just popped off...maybe I didnt let it get hot enough. Thanks!

Ryan
 
Try boiling it, Ryan. That's what you do to get borax-based PBC antiscale off.
 
Thanks for the tip fitzo. Do you know why the borax would fall off? I got the blade hot and sprinkled it on and it started to bubble and melt and then I put it in the forge to heat it up and let it melt and coat the blade and it just got puffy and fell off :confused: . I've heard that borax makes a good anti-scale but could not get it to work right. Thanks!


Ryan
 
Plain old borax can be a very big PITA. Some people seem to have excellent success with it. Anhydrous borax does the puffy-thang a lot less. If you use 20 Mule team, that "puff and flake" routine is more common than not. I have also tried making a very thick solution of the stuff and applied repeated coats. That sucked, too. There's a liquid coating sold by K&G called "Turco" that serves this purpose and a powder called PBC that's available from Brownells. Look up Terry Primos's website for a tutorial on PBC. The problem with PBC is it turns acidic if overheated and will pit a blade faster than a badger can dig a hole if it goes much past 1600F.
 
Ryan
Two things you are going for straw/gold color on the blade
Make a holder of some type and keep it spine down in the oven
Next
Look up MSC website for some 'Keepbrite"
Coat the blades at 500deg F and then finish the HT
With a little practice they will come out whistle clean but ALWAYS leave enough extra steel to grind off any pinholes that may occur.
I have used it for 7yrs great stuff up to 1550deg
Easiest way is an old spice shaker to dispense, DON'T breath the fumes
wear a mask
 
More than one oven thermometer is also good for monitoring different areas of the oven cavity. Chances are great the entire blade area will not be subject to the same temperature. Your goldish color about the edge may indicate the edge was exposed to a lesser degree of heat (edge down perhaps?).

RL
 
Yeah I am using the '20 mule team' and not the anhydrous. Its a lot easier to swing by the grocery than ordering it. Maybe I'll try to play with it some more but the satanite seemed to do a good job, just a pain to get off.

I put the blade on the wire rack in the toaster oven so I'm not sure about the heat since its so small. I thought that the blue and purple were from a higher temp than gold and I thought it was weird the edge was the gold and not the spine so I guess the heat does vary quite a bit.

I have heard of the pbc stuff but it was fairly expensive and had to be ordered. I am on my second knife and I have already spent a ton of money between steel, forge supplies, good belts, wood, etc but I guess thats the nature of the beast. (BTW I just got some good ceramic belts in, and what a night and day difference...if any newbies read this do yourself a service and order some good belts!)

On a side note, and I'm trying not to get pi$$sed, I drank a few glasses of wine and thought I would do a little testing...so I sunk the tip in some wood and turned it a little and snapped about 1/8" off the tip :mad: . I knew better as I put a pretty good taper on it, as it was to be a slicer. So now I guess I will have more belly than I was going for after I reprofile...so another heat treat is in order for more than one reason now.

Thanks for the replies guys...If it weren't for this site and your help I wouldn't be developing the addiction.

Ryan
 
FlaMtnBkr said:
Thanks for the replies guys...If it weren't for this site and your help I wouldn't be developing the addiction.

Ryan
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Don't blame us! You found your own way here! :p There are a boatload of great people here. And then there's me and Indian George (IG).... ;)

Enjoy the journey, Ryan. It can be as rich or as simple as you desire, a great artisan craft. :)
 
Another thing I didn't notice mentioned, make sure to preheat the oven for a while before you put the blade in. It will cycle at higher temps at the begining as it's getting up to heat, once the heat is up there it does this much less and not as hot.
 
FlaMtnBkr said:
Thanks for the tip fitzo. Do you know why the borax would fall off? I got the blade hot and sprinkled it on and it started to bubble and melt and then I put it in the forge to heat it up and let it melt and coat the blade and it just got puffy and fell off :confused: . I've heard that borax makes a good anti-scale but could not get it to work right. Thanks!


Ryan
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The bubbling of the "20 mule team" borax is the water leaving the borax. You are exxentially making the borax anhydrous. If the area the borax on the blade looks glassy, there is a thin coat of anhydrous borax left on the blade and what fell off was excess. It only takes a thin coat to prevent scale.
 
Ryan, I apologize for not saying this last night, and I didn't even drink any wine! ;)

Try holding the 20 Mule Team coated blade in the flame/heat outside the forge mouth. If it doesn't heat up quite as fast, it will puff and fall off alot less. After it melts, go for it. That is what I do for damascus billets.
 
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