Is my heat treat OK?

B

Bamph

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Aug 9, 2015
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I just did my first couple of heat treats on my first knives. I'm working with O-1, making some small carving knives and a hunter. I'm using an old Paragon furnace.

I wonder if I got the steel hot enough. I programed a 20 minute soak at 1475. At the end, the knives only glowed with a dull red color, not a bright red-orange color like I've seen in some videos. I did check with a magnet, and the knives were non-magnetic.

Does the magnet test prove that they were hot enough?

Ben

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ok a few things you need to test your knives to see first and formost. every kiln can read a different temp. high and low

cameras auto aajust color temps of steel in the kiln and out often looking way over heated when quenched

the mag and watching the shadows will show when it passes the curie point and getts you in the ball park know full well you need to pass the shadow a bit and with O1 a slight soak is to your advantage before quenching
 
The color is far less bright than most people believe. At non-magnetic it is a dull cherry red. You want the steel just a shade brighter than that.

There are several ways to check the oven/blade temperature when getting used to using it. One of the simplest is a Tempilstik. It is a crayon like marker that will indicate the temperature of the blade. Get three sticks - 1450F, 1475F, 1500F ( you can get six that are 10° apart if you really want to fine tune things, but the 25° spread will work just fine for checking out your oven). These will allow a reliable check for the range the oven is at. Do some tests on a piece of 1/4" steel with a clean surface. Heat to 1430F and test, then ramp to 1450 with a 10 minute soak and test. Repeat for 1470, 1490, 1510. Record the results of the Tempil sticks at each test. Plot the results on a graph. This will give you a chart of your oven's approximate reading accuracy through the normal HT range. You can then make adjustments in the settings to compensate for any errors. If it shows that the oven pyrometer reads about 7° lower than the actual temperature as tested, subtract 7° from all setting numbers in your HT.


One good thing to do with a very old oven is install a new TC. They get inaccurate with age.
 
Years ago I did tests to find just how accurate I could by eye tell the temperature . About the best I could do was 25* F.This was all checked with instruments in a metallugical lab. Also "red" that one person sees may be different than the "red"someone else sees.
The change at the Curie temperature can be subtle and is different going up vs going down in temperature. As Butch found a camera is not the best indicator either .If you have problems check out everything !
Have you a hardness tester and use a test block ? Have you taken off all the decarb ?
The more complex the steel the more temperature and time control is important.
 
Do you rub the tempilstik on the steel and then place in oven. Will a 1450 stik melt at say 1400 if it's in there to long or only once it reaches 1450?
 
I know what you mean in the heat treat videos. The steel always looks way to hot. I would break some test pieces to check for grain growth to help see if your getting it to hot.
 
You make the marks on the cold ( or warm) steel. Then as each temperature is reached the indicating crayon melts. It is clear what that happens. If you have 1425, 1450, and 1475 on the steel, and the 1425 and 1450 are melted, the temperature is between 1450 and 1475. Then, raise the temp 10 degrees on the oven. If it now melts the 1475, the last reading was about 1460-1465, and the current one is 1475.

Tip, write the final digits with the crayon - 50 for 1450, 75 for 1475, etc. That way you can tell which is which when they melt.
 
Thanks for all the great information. I will work on getting a better idea of my actual furnace temperature.

It looks like the knives did harden because grinding in the bevel on my hunter, even with an extra-coarse diamond stone, seems to be taking forever. The knife seems much harder then my commercial folding knives.

I tempered at a lower temperature (400) because I want my carving knives hard.
 
butcher_block said:
ok a few things you need to test your knives to see first and formost. every kiln can read a different temp. high and low

cameras auto aajust color temps of steel in the kiln and out often looking way over heated when quenched

the mag and watching the shadows will show when it passes the curie point and getts you in the ball park know full well you need to pass the shadow a bit and with O1 a slight soak is to your advantage before quenching
Click to expand...

This is great, thanks for sharing! I've been meaning to ask about this for a while now, thanks for asking Bamph. While I've heated all my blades to just over non-magnetic for quench, I've doubted that I did it right even after testing the blade with a file after because the color in the YouTube videos is always so different than what I've seen in my garage. I never even thought about the camera adjusting the color. Makes sense why some video's make it look too cool or too hot at the quench... Thanks again! :)
 
They are for wood carving. Very small, with something approaching a full flat grind.
 
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