It's been a while since we've even discussed anything sort of TECHNICAL, so, without a lot of talking, I thought I'd just show ya'll some pictures.
I had my camera handy yesterday when I was doing some post-forging thermal-cycling and grain reduction steps.
We've discussed these over and over again, but a picture is worth a, well, a bunch of words.
After we have over-heated and beat the living snot out of a piece of steel, the grain structure is wildly out of anything that could be called "normal".
So, we NORMALIZE.
We try to get it back to normal, which is a regular and homogenous atomic arrangement of atoms and alloys.
Keep in mind - the steel "WANTS" to be happy and regular, and we've just put it into a condition of chaos.
So, we're gonna help it out and get it back to where it should be.
This reminds me of an old blacksmith addage.
"We have FAR more opportunities to totally ruin a decent piece of steel, than we will ever have to improve it."
So, we need to do everything we can to get it BACK to where it was when we started.
Everybody's set-ups are different. I can only show you what I do.
I do a lot of take-down construction which involves threading of the tang, which I want to be absolutely as strong as possible, yet, still be able to thread.
We know that the strength in steel comes from its grain size. So, I always need to thermal cycle my tangs as well, but should be done regardless.
So I do it in two stages - first I thermal cycle the back 1/2, then do the front 1/2.
3-4 reducing heat cycles on each 1/2, followed by bringing to critical, quenching for martensite, then re-heating to a dull red.
I then do a controlled oven sub-critical anneal, but those without oven will just have to do without.
Here's what you look for:
After all straightening is completed, heat the steel ALMOST up to the temp at which the majority of the forging took place.
Get it EVEN!!!
Then, remove to a place with no moving air, so it cools on its own.
And watch the transformation take place. THis is what the ancients used to call the SPIRIT in the steel, because it moves all over.
What it's dong is going from one condition to another - a transformation.
But, this transformation is so violent - on an atomic scale - that it actually CREATES heat. Sort of like friction of all the components ramming into one another in an effort to go where they want to be - HAPPY!
But this also takes heat to accomplish, and since the steel is cooling off and losing heat, the transformation does not all take place in one cycle, so we do it three or four times, but each time, starting out at a lower heat - which is call reducing heat - so as not to lose all the gains acquired on the previous cycle.
But always remember, even though we're starting out a a lower heat each time we still need to be ABOVE non-magnetic on the last cycle!
So, here is a picture of the blade right out of the forge. Sorry about the focus on this one, not sure if it was the camera or me, but you'll see the entire front 1/2 is up bright and orange:
Here we are losing the heat in the tip and back by the tang where it started out the coolest. The tang is absorbing some of the heat.
Now keep in mind that even though the heat is the same throughout the blade, I have forged in distal taper to the point, and tapered down to the cutting edge. So we have differing thermal mass along the blade. The heavier portions will hold the heat the longest and will be last to respond to the process.
Here, we're getting cooler yet. The cutting edge is black, but there is still residual heat in the main meat of the blade.
Now, here, the main portion of the blade is cooling off to black, which by the way is about 950 degrees.
But notice that the cutting edge, and any area that WAS previously cooling off and going dark is now returning to orange and coming BACK up to heat!!
And now, look how bright the blade has returned. It has created a LOT of energy going through its phase transformation. The tip is nearly black, most of the time, but don't let that fool you. It's very thin there, and does not hold its heat well, so it goes through the very same transformation, but does it much more quickly.
Now here, the entire blade is cooling off. I will only let it go JUST TO BLACK!! in a lighted room.
I do these steps with the lights off so I can watch things, and once the majority of the process is complete, I turn the lights back on or walk over to the door and wait until the knife just goes black and then back into the forge for the next cycle.
On the next cycle, we heat up evenly again, but not as high as the first time.
And again, lower yet.
3-4 times.
Then on the last time, quench at critical for that steel and re-heat to a VERY dull red in a dark room.
I'll do another post after this one showing the tang process.
Topic: Isotropic Phase Transformation (Read 833 times)
