Toaster oven tempering

[gizamo]

Got a free toaster oven a while back. Decided to give it a try as a tempering oven for small knives. Ended up putting a firebrick inside and a piece of 1/4" plate steel on top of that. This acts as a heat sink to help even out the +/- degrees in cycling. Added a oven thermometer to the inside. Preheated to 425 and then added the knife for an hour.

It came out of the oven a perfect straw color. Really pleased with the results.

Thinking of cycling it one more time and letting it slowly cool off in the oven.  Is there a better way to slowly let the blade cool off?

[Bill Raby]

Brick and a steel plate is a great idea.With blade sitting on top it is not going to cool down any faster than the brick. Just leave it in there and turn it off and it will cool slow. Or turn down the temperature 50 degrees every hour or so and let it take all day.

[rich pierce]

Depending on the steel you're using that might be hard enough to use as a graver and not very tough. I made some knives from old files way back when and one snapped for no good reason except being too hard.

[gizamo]

Rich...

Tempering temp vary. I was told by a older and very experienced blacksmith that I needed to make a Tempering sample. Thin strip of material and only heat from one end. Try to break the sample at the differing color points . Where it broke was the area above the correct temper.

[rich pierce]

That is a great and simple test!  I will remember that one.

[tippit]

If you have mystery steel, then start your temper lower say 375F.  If file still skates go up 25 degrees each temper till file starts to cut.  You may need to go an additional 25 degrees for ease of sharpening.  I temper for 2 hours and cycle twice. Cooling doesn't have to be slow as your crystalline structure won't change as it does in a fast quench.  You can test your edge by rolling it over a round edge of a Bic lighter or brass rod.  You can watch the edge deflect.  If it stays deflected too soft, if chips too hard, if comes back you are in the range.  Or just skin a deer, hog, or bear too see if you blade holds an edge.

Newbie here...tippit

Couple of my knives...

[David R. Pennington]

With knives I like to harden edge only and leave spine softer and draw temper carefully along edge. They most generally won't break that way. You can do it ok in forge but easier to control heat with oxy/acetylene torch. Test edge after sharpening on a 20d nail or similar rod. I have a good knife made from an old junk file that is my favorite. It has dressed lots of deer. Another from railroad brake shoe spring clip made an awful good knife. Oven be good for springs and the like I suppose. For tools and knives I like to have temper run to the edge. Like on punches and chisels you want the edge harder than the end you strike. Couldn't do that in an oven. I like hatchets welded up out of wrought iron with steel bit. Then you can temper them a little harder than a normal axe and they will stand up. I like them to where a file just will cut. Oven OK if you want the whole piece tempered the same.

[tippit]

Another way to quench & temper is to quench the entire knife then blue back the spine by putting as much of the edge you want to stay hard in wet sand.  Heat the handle and spine with a propane torch till it turns blue/purple thus softening the spine. Then temper the entire knife. This is one way to pass your ABS journeyman test of bending a knife 90 degrees without the blade cracking.

[JCKelly]

For those who like to forge their blades, it is very important to normalize or anneal that forging. This refines some of those enormous grains developed during forging.

Big grains are bad.

You've heard the ancient (and incorrect) statement that "it crystallized, so it broke"

"IT" was always full of crystals. In steel they should be too small to see, unless magnified at least 100 times. If you can see them, they are too @!*% big and the thing will be brittle, regardless what else you do to it.

After normalize - at least heat the thing a nice red & lay it on the ground to cool. Grind off the scale AND A FEW THOU OF DECARBURIZED METAL before you harden it. Helps keep it from cracking in quench.

With respect to springs, a toaster oven is just not hot enough. IMHO. Might be good for heating horn to a good plastic temp, which I think is about 350F. Do check with hornmakers guild site on this.

[David R. Pennington]

I agree about annealing and normalizing. Learned hard way. How do you usually do it?

[Old Ford2]

Great topic!
Question:
Can I use pick-up leaf springs for blades?
I have several about  11" X 2 X 5/16
I heat with dry maple, and would use the coals.
I realize max temp is about 1100 degrees F.
Thank you for any help.
Fred

[Black Hand]

Can I use pick-up leaf springs for blades?

From my reading, some smiths avoid leaf springs (unless new) due to microfractures in the steel...