1084: how much longer after non-magnetic?

Zuluninja

Zuluninja

Joined
Aug 25, 2009
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First, let me apologize for asking as I bet this question has been done probably to death in here. For the same reason, a search was on it was baffling...

Quite simply, assuming there is no pyro available, how much longer do I keep on heating 1084 after the magnet doesn't stick anymore? If I remember, the steel becomes non-magnetic at around 1420 F , still 80 short of 1500. Any trick? count to ten? different color? I have been sending blades to Peter's but want to do some ht myself, in a rather crude ceramic brick setup. I do have a pyro, but not sure exactly where to place it and dubious that a temp reading on a part of the blade will be the same as on another part.

Again, my apologies and sincerest thanks for the replies.
 
You don't need a magnet. Watch for decalescense.....the "shadows" that appear as the heat of the steel
increases from dark red to bright red. As the steel approaches transformation, it will actually loose heat
...that's why it will look darker as you pass "dark red", and just before the steel becomes bright red.
The shadows are the indication that transformation from ferrite to austenite is taking place. When the shadows
disappear, transformation has completed.....about 1472f.
 
That's a wise advice, but if your forge port is not big enough it could be difficult to catch that visual....watching the tang from behind.
If you could actually have a view at the whole blade it is indeed a valid method.
If your heat source is pretty steady andnot too hot you may want soak a bit the blade after decalescence, to allow even diffusion within the formed austenite.
 
The advice I normally give is to heat it about one full shade of red brighter than it was at non-magnetic. Color is subjective, but whatever it looks like when the magnet stops sticking....just a noticeable shade brighter.
 
Russ Andrews said:
You don't need a magnet. Watch for decalescense.....the "shadows" that appear as the heat of the steel
increases from dark red to bright red. As the steel approaches transformation, it will actually loose heat
...that's why it will look darker as you pass "dark red", and just before the steel becomes bright red.
The shadows are the indication that transformation from ferrite to austenite is taking place. When the shadows
disappear, transformation has completed.....about 1472f.
Click to expand...

Just a quick note, the steel doesn't loose the heat per se, it stores it as it goes through the phase transition. It will release the heat as the temperature drops back down past the recalescense point.
 
Bo T said:
Just a quick note, the steel doesn't loose the heat per se, it stores it as it goes through the phase transition. It will release the heat as the temperature drops back down past the recalescense point.
Click to expand...

Close -

As steel crosses the critical point, it absorbs heat in an endothermic change of atomic structure. At the moment the atoms rearrange from face centric cubic to body centric cubic, they draw in heat faster than the heat source can provide it. This momentarily lowers the internal temperature of the steel a few degrees. Decalescence is seen as shadows dancing and flickering across the blade, and is often called the "shadow dance" by older smiths.

As the blade cools down from above the critical point, the reverse happens, and an exothermic change causes the steel to heat up a bit. Recalescence is seen as bright flashes and flickers on the black surface of a cooling blade.

Decalescence and recalescence do not happen at the same temperature, BTW. Recalescence happens at a lower temperature. In metallurgical speak - Ac1 is not the same as Ar1.
 
well, I'm so glad I just have to watch color shading, and don't need to get a unicorn's horn or virgin's blood :D
 
dang. Do I need to fix a compass to the spine?? wouldn't the carbon steel make the needle point to a different dimension?

but seriously, thanks. I ordered some 1084 and other stuff from Aldo yesterday.
 
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