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Also, keep reading Kevin's stickies. They take more than once to fully grasp.**
I will have to eventually find a way to take care of that problem
QUOTE]
Why? Good information takes effort to assimilate. The random junk everywhere else on the interweb sticks in your head whether you want it to or not.
I will have to eventually find a way to take care of that problem
For the sake of technical accuracy it is better to drop the use of the word molecular from your memory when discussing metals. Annealing is perhaps the oldest of heat treatments and was born of the world of cold worked metals, non-ferrous first and then ferrous. Its main purpose was to remove the strain hardening effects of deformation; it accomplishes this by first erasing the stored strain energy in a lower temperature are of the process known as recovery. Next it erases the other effects at the recrystallization temperature by making all new grains. And then via slow cooling it allows all the carbon to separate out so that the steel stays in this new and soft condition. But carbon the carbon that is put into solution above the recystallization temperature will separate out into banded sheets when slow cooled. This is not a problem with lower carbon steels, but high carbon stuff will form larger sheets that will be difficult to machine, so
another type of softening operation known as spheroidizing is used on higher carbon steel. This operation still goes through the recovery process and eliminates the strain energy, but it does not go high enough in temperature for recrystallization so the established grain size is totally unaffected. But most importantly it does not put eh carbon into solution but instead separates it out into countless tiny spheres that easily move out of the way of machining operations.
Because of these differences some sources do not use spheroidizing and annealing interchangeably, but if we wish to treat them as the same then the more generally accurate description for annealing would be for the purpose of softening the steel.
Normalizing may or may not result in s totally stress free or softer steel depending on the alloy and its main function is to bring the internal structure to normal and even conditions. Carbide, grain size, various segregation and even strain effects are all equalized by normalizing. It is not necessarily a lower temperature thing and is actually described as a fairly high temperature (1700F) operation in industry. Bladesmiths however have the freedom work with a variety of ranges and often use cycles at much lower temperatures and call it normalizing. But the ideal would be to start high with one cycle to equalize everything and then follow it up with lower temperature cycles to refine the homogenized structures.
Then, as mentioned, there are pure stress relieving operations done only in the recovery range (around 1200F) which will remove the strain effects in the steel and nothing more.
For the most part- no, but this could depend on the steel you are working with. If it is really good stuff, the chances of you detracting from its good condition get better with every unnecessary cycle. However if you got some steel that is particularly prone to nasty segregation these days (1095, 5160, cheap O1 etc ) then a few high temp cycles couldnt hurt.
Not necessarily, it could take up an entirely new thread but soft spines are not necessarily the best option for strength or overall blade toughness and present some issues of its own, despite the prevailing beliefs, but the facts of how strengths and toughness in steel works are at definite odds with those beliefs. If you are really attracted to differential heat treatments for performance and not aesthetics then a differential temper instead of a differential hardening is well within your means by simply reheating the spine while protecting the edge after the normal full heat treatments.
I hope this helps clear things up.
., for the other folks – iron carbide), coarse pearlite (banded iron carbide) will offer a tougher machining material than spheroidized (think of shoveling a pile of shingles versus a pile of marbles). After forging reheat the steel as evenly as possible (evenly is the key word in normalizing, evenly heated and evenly cooled) to a nice orange heat, (1600- 1700F). This will, evenly redistribute the carbon and equalize the grain size (uneven grain size is actually worse and a little larger grain size) and undo much of the havoc you inflicted in the forging process (hand hammer faces have a hard time moving steel perfectly even). Allow to air cool evenly (put the tang in a vice don’t’ lay the blade flat on anything). Follow this up with a heat just beyond magnetic to refine the even structures you now have. This can also be followed by another heat a hair lower or even another heat to nonmagnetic and a quench to room temp to really refine things and set it up for the last normalizing heat which can actually double as spheroidizing as long as you stay below nonmagnetic, and if attempting to spheroidize you should try to hover in that magnetic red range for a little while by cycling it in and out of the forge.
Kevin, really informative. Sorry to dig up an old post for my first comment, but I have been curious/slightly confused about when to anneal or if it is necessary if you are normalizing.In a perfect world with a pure iron/carbon system that temperature would be around 1335F, but…
Almost every steel we work with has some sort of elements other than carbon which moves that temperature around, so each steel will have its own unique temperature that will fall near that range. In an average shop without equipment able to read exact temps for the given steel the magnet will suffice for ballpark figures. If the magnet quits sticking you have definitely began making new crystals, but not necessarily moving the carbon around as you may need for other heat treating operations. The new crystalline phase opens the pathways for the carbon to move it then requires time or temperature for that to happen, but in stress relieving and annealing this is not as critical.
Simple spheroidization involves keeping things below recrystallization so the magnet should not stop sticking during the process. It may be easier just to think of this type of spheroidizing as very high temperature tempering, and is effective enough for very simple steels to make very fine spheroidal carbides that will allow grinding and some machining.
Steel above .8% carbon will have excess carbide that will get into mischief on you if you allow it to with a slow cool from solution. As mete pointed out it will naturally want to go for the grain boundaries where it will not only burn up your mills and drills, but it will also cause embrittlement issues if not removed from those grain boundaries. But even without grain boundary cementite (I threw that big word in for mete
1084 is right on the borderline to where you would really need spheroidizing and if the most you may do is drill it, then the extra effort of spheroidizing may not be necessary. The old standard anneal among bladesmiths and blacksmiths is to heat to nonmagnetic and then stuff it into wood ash or vermiculate for a long slow cool, this is known as a “full anneal” or more precisely as a “lamellar anneal” due to the lamellar pearlite it forms.
Spheroidizing on the other hand does not rely on the cooling but instead on the temperature at which it is held (red but still magnetic) to do all of the work.
After forging reheat the steel as evenly as possible (evenly is the key word in normalizing, evenly heated and evenly cooled) to a nice orange heat, (1600- 1700F). This will, evenly redistribute the carbon and equalize the grain size (uneven grain size is actually worse and a little larger grain size) and undo much of the havoc you inflicted in the forging process (hand hammer faces have a hard time moving steel perfectly even). Allow to air cool evenly (put the tang in a vice don’t’ lay the blade flat on anything). Follow this up with a heat just beyond magnetic to refine the even structures you now have. This can also be followed by another heat a hair lower or even another heat to nonmagnetic and a quench to room temp to really refine things and set it up for the last normalizing heat which can actually double as spheroidizing as long as you stay below nonmagnetic, and if attempting to spheroidize you should try to hover in that magnetic red range for a little while by cycling it in and out of the forge.
The full anneal would then be as described above with heating to above nonmagnetic (kind of undoing any grain refinement accomplished in normalizing) and burying in an insulating medium. But if you follow the above normalizing steps you should be able to move on to grinding without the full anneal with 1084.