I accidentally replied to the wrong postThe crystalline shift from one atomic stacking to another requires extra energy to complete, this is what would be called an “endothermic” transformation in that it pulls heat in. The actual process is indeed known as decalescence. I teach this method of watching the shadows to all of my students that are heat treating in a forge, it is much more versatile and can even be more accurate than the magnet. The magnet merely measures the Currie point of iron, which is around 1414°F, but steel isn’t all iron, the bits that make alloys behave so differently do not care as much about the Currie point, but the shadow of decalescence allows you to actually see the beginning, middle and end of the austenization process. All of my students are well versed in how to gently heat to the beginning of decalescence, in a forge that is dialed back, working all the shadow out of the blade without overheating any thinner sections, and then applying high heat after the shadow is gone. They are often amazed at how evenly the steel will heat after decalescence regardless of how fast it is done. Steel is actually a very good conductor and the body of the blade wants to pull the heat out of edges and tips in order to equalize, but decalescence won’t allow it.
If you want to practice it, do it in a darkened room and wait to see what happens on the way back down. The reverse process, on cooling, is called recalescence, and it is very cool to watch because it is exothermic instead. At round 1100°F there will be a bright wave of energy that will start at the edges and move to the center of the steel as pearlite is formed.
You can temper for longer than 2 hours if you like, but nothing more will really happen until you get out to a few more hours. In watching the chatter on the internet in the last 5 years I have seen this two hour standard grow to two, or even three, 2 hour cycles, taking tempering out to 4, 6 or even more hours. I hope it wasn't a misunderstanding of anything that I wrote that has people doing these crazy long tempers, there is no real benefit in intentionally going this long, and there can even be some bad effects after a certain point. If one is not doing HRC testing and walking in the numbers, a two hour cycle, at your chosen temperature, is more than good enough.
I think a few of us were following the HT routine that is posted on this forum in the Knife Steel Reference section. In the routine it says to temper 2 times for 2 hours each cycle. If I can get away with 1 2 hour temper cycle that would be awesome!
Carbon = 0.80-0.94 Manganese = 0.70-1.00 Phosphorus = 0.40 Silicon = 0.50 This chemistry is just a reference, always check the source for exact chemistry. 1084 is a great steel that is often overlooked due to it being considered a beginners steel. It is a great steel for beginners but...
1084 is a great steel that is often overlooked due to it being considered a beginners steel. It is a great steel for beginners but experienced makers often consider it one of their favorites. It is very easy to heat treat which is one of the main reasons it is so popular and the main reason it is often suggested for beginners. Makers with minimal equipment will come closer to getting the most out of this steel. A consistent heat source, some fast quench oil (Parks #50, Canola, Mineral, etc.) and a little experience is all it takes to make a good knife. It makes good hunters, EDC's, etc.. It also does fairly well for choppers and some people even use it for kitchen knives. It may not be a Super steel but it makes good knives. If you're getting started you can't go wrong by starting with a few bars of 1084.
1. Heat to ~1500 degrees F.
2. Quench in oil.
3. Temper twice, for 2 hours each time, anywhere between 350 & 475 depending on the application of the blade.
This is just a starting point, you may need to adjust temps. & times to suit your needs and equipment"