I'm a little confused by the thread linked here. Both in the matter of a couple details, and in a general sense.
Detail: Quoting from Allen Blade's post:
"heat to cherry red
let cool to no color
heat to critical temp "using magnet to check"
Quench in oil edge down(mineral/olive mix oil)
put into pre heated oven at 400 Degrees for
let cool to room temp.
turn on oven back to 375 Degrees for 1 hr
turn back on at 350 Degrees for 1hr.
I know I get a bit mixed up about normalizing and annealing. So Allen's "recipe" is all the more confusing. When he says "heat to cherry red, let cool to no color", is this the hardening heat? Or the annealing heat? Or the normalizing heat? When he says "let cool to no color, heat to critical temp" does he mean that you proceed directly to the second heat as soon as no color from the first heat can be seen? I thought in oil quenching steels, you let it cool to room temperature after each heat, sometimes leaving it in the air, and others in the quenching material, or in ashes. Is this incorrect?
He also doesn't specify any length of time or degree of coolness between:
"Quench in oil edge down(mineral/olive mix oil)
put into pre heated oven at 400 Degrees for 1hr.
Does this mean he quenches only the edge? He doesn't edge quench to a level, then immerse the whole blade in the quenching oil til room temperature? Does he just wait after quenching the edge for the color to go out of the edge, and then move directly to the tempering heat in the oven?
He does specify letting the tempered blade cooling to room temperature after the first tempering heat. I assume then that when he says let cool in the 2 subsequent tempering heats he means the same level of coolness.
I'm curious about the changing temps for the tempering heats. I know Ed Fowler does his triple tempering at the same temperature for both 5160 and 52100. Why would one want to change the tempering temperature? Isn't either the highest or lowets temperature going to be the one that has the final impact on the steel?
In both Allen Blade's response and that of one or two other responses to the opening post in the thread, they talk about too much work. Do hardening, annealing, and normalizing heats all contribute to the quality of the steel? If so, why aren't they always done?
No mention is made of cryogenic tempering. Is this not done on O-1? Does it not help O-1?
Frankly, I don't get the feeling that doing the best possible job is the goal of the processes spelled out by Blade. I mean he does suggest a triple temper, which I understand to be necessary for best steel performance, but why does he skip one or two of the steps that Ed Fowler and Rick Dunkerly use in their heat treating of 5160 and 52100?
I'd sure appreciate help in understanding these things. Thanks.
I think we should go into basic theory at this point. Iorn(steel) has a memory, When you forge, cast,or weld you are introducing stress. normalizing seeks to realign the metal's molicules to it's present shape. If this is not done your work piece will not be stable. It will have a tendancy to move around as the molicules seek to realine themselves( that unexplainable warpage)
anealing is the process that if properly done will bring a piece of steel to it's soft state. (This changes from steel to steel it is best to look it up)
the simplest way to normalise is to leave it sit for 4-5 years. (this is standard practice for some of the better cast iorn)
another way is to run it through an anealing process. (there are many veriations of this, I'm sure that most of the makers have a favorite, and would be very happy to elucidate)
I hope this clears up the some of the confusion, EE
p.s. I don't understand that cryo stuff either, I have read somewhere that it is used to harden medium carbon steel. and now these guys are using it as a method of tempering? I've never needed it,
but just because I dont understand something does not mean I don't listen and try to learn?
Bugs, welcome to the club. I understand theory but to be honest, under the conditions we heat treat, we are much better to go back to the "what worked for me" process. There are many ways to normalize. I have never needed to bury it in vermiculite while raising an ash stake to the four winds. Heat it to cherry and let it cool slowley works for me.
Now the cryo treatment. Now for years I've said it was impractical to do at home. I've done it using liquid nitrogen and it just wasn't worth the trouble. A few days ago Bruce told me that he felt thet the knives he made in Winter held a better edge and he froze them between cycles. This is the "it works for him" procedure. I tried it in the freezer and for whatever reason, the moon lining up with the ice cream or whatever, it works.
Cryogenics has been shown to increase the performance of all steels to some extent,gun barrels,car/truck axles,gears,and of course knives.The "P" thing is all superstition,it only works,if it's from redheaded virgins.
Thanks, Eric, Peter, Mike et al. I appreciate the answers. As I said in my earlier post, I do get confused between the normalizing and annealing heats. I had it in my mind that heating the blade to a certain point/color, then letting it cool in the air, was annealing. And that heating the steel to the point of non-magnetism, then cooling it in vermiculite or ashes was normalizing. I also understood that heating for hardness was to a temperature higher than the normalizing heat, and that forgers heat treated 3 times, then tempered 3 heats and then did the cryogenic. Wait, guess the cryo came after the first tempering heat, and before the last one or two. I still don't understand in Blade's formula what hardening heat he uses. It sounds to me like he anneals the blade, then normalizes the blade, then commences tempering, without ever doing any hardening. I don't see how he could do all 3 with just 2 heatings.
Like Mike, I was pretty sure I'd read that cryogenic treatment essentially improved all steels. -- heck they even say that 420J2 that has been cryoed is almost steel-like. I thought that the really low temperature of the liquid nitrogen was more beneficial than a home freezer. Maybe not.
I understand what you mean by "works for me", but am quite curious about how much testing of blades Y'all do. I mean for instance, if a 4-12 hour bath in liquid nitrogen increased the ability to cut rope of a blade from say 100 cuts to 150 cuts, wouldn't that make it a worthwhile thing to do?
The other confusing thing to me, using different tempering heat levels, would seem to me to beg for comparison between blades tempered 3 times at each of the 3 temperatures used, and one done with the 3 different temperatures. I can't help but think that there would be measurable differences between the 4 methods. Guess it wouldn't hurt to reverse the order of the 3 different temperatures for another comparison.
Bugs- I don't know why, but I'm having trouble using the search feature here. Allen posted this same formula with a better explanation in another thread, but I didn't have it bookmarked and can't find it now. The first "heat to cherry red" is the normalizing cycle. The next "heat to non-magnetic" is the hardening cycle. In my attempts, after the oil quench a file will skate off the hardened blade. I don't know the explanation for the 3 tempering cycles at different temperatures, this just falls into the "works for me" category. The knives I've treated this way have been performing very well. Sorry we got off-topic, no disrespect intended.
I find that in practice, normalizing and anealing are the same procedure, just called by different names.
I don't forge many knives. I do forge blades; woodcarving gouges, chisles, plane irons, draw knives, inshaves, etc. some of these get a little tricky. All must hold a sharp edge, that will see a lot of use.
these are not show pieces.
in practice I find 30-45 min at 400 deg good enough and is my standard practice. all the rest of the processes are iceing on the cake, and they may well improve the blade, but are not necessary.(I do differentialy temper)
I find that simple is better,
those who work with me know that my blades cut
a simple techniche that is well understood and well practiced, will serve very well. learn the simple, progress from there.
Bill, maybe this will help. It's long but I've always felt every word was worth reading for the beginner.
HARDENING SIMPLE STEELS
All of the really low alloy steels have one feature which make them virtually foolproof when it comes to cooking them for hardening. When one of the low alloy steels reaches the critical temperature where it can be hardened by quenching, it turns non - magnetic. As the steel heats, check it with a magnet. At a certain point, the magnet won't stick. That's usually at a temperature ( color ) far lower than you would think. Once the magnet won't stick to the blade, give it a moment more in the fire and then into the quench it goes. ( An extra 50 degrees over the critical temperature insures better hardening and won't hurt the steel.)
The simple aloys can also be selectively hardened, not with a fancy temper line, but with a softer back that will make the spine and tang less susceptible to breakage. All you have to do is take the blade up to heat very quickly, getting the thin parts along the edge hot before the thicker spine. You could also just dip the cutting edge into the oil, allowing the spine to cool more slowly, not hardening it.
Should you err and get the spine too hot and inadvertently harden it, you can use a torch to partially anneal the critical areas. I recommend that all stick tang blades have a softer section where the tang joins the blade.
When the hot blade hits the oil, you will almost always get some fire. Don't leave the tang half out of the oil. It is near red hot, sticking out of the oil and acting like the wick of a candle to start a fire in the tank. NEVER use a small tank of oil to quench a lot of blades. Sooner or later, you'll find the flash point of the oil. That's where it starts burning all by itself, and you won't like that one little bit.
Forged blades will always have stress than needs to be worked out before hardening. They should be annealed, preferably several times before hardening. Some knife makers have had wonderful results by annealing their blade steel three times before hardening. It reduces grain size significantly, making a much tougher blade.
SERIOUS HEAT TREATING
1040 to 1050 steel Water quench from 1525 to 1550 F. Hardens to approx. RC 58. Very easy to get cracks with water quenching. Draw at 350 F. for spring temper, best for daggers, etc. Shallow hardening and can be done with beautiful, Japanese style temper lines.
1050 to 1095 steel Brine quench from 1475 to 1500 F. hardens to RC 60 to 65. Draw immediately. Oil quench at the same temperatures for slightly lower hardness. Shallow hardening and can be done in the Japanese style with a decorative temper line.
O-1, O-2, O-6, O-7 steel Preheat slowly to 1200 F. Oil quench from 1450 to 1500 F. Draw at about 350 F. O-6 reaches RC 65.
W-1, W-2, W-3 steel Preheat slowly to 1050 F. Water (brine) quench from 1400 to 1500 F. Draw immediately. May also be oil hardened if cross sections are radical, or simply for less chance of cracking. Shallow hardening and will work with Japanese temper lines.
L-6, L-7 steel Quench from 1450 to 1550 F in water or brine. Doesn't really need to be drawn. L-7 will give slightly more hardness.
D-2, D-7 steel Preheat at 1500 F. Harden from 1850 to 1875 F. Draw immediately.
A-2 steel Preheat at 1450. Air harden from 1700 to 1800 F. Draw at 350 F.
Water hardening is a mis-used term. In virtually all cases where a steel is referred to as water hardening, they're actually talking about quenching in brine, heated to a temperature of 170 degrees, (F) or above. Brine is made by dissolving non-iodized salt in water until a egg will float in it. Jim Hrisoulas uses bluing salts to make his brine. The whole idea is to raise the boiling temperature of the liquid and make it transfer heat better. Brine will eat right through an ordinary steel barrel in a very short time. Jim Ferguson just mixes in borax and detergent to reduce the surface tension.
Drawing is normally done for 30 minutes when one has the equipment to properly maintain the temperature. Flash drawing, that is, heating to show a certain oxide color on the metal surface and then letting it cool, is fine for softening a spine, but not best for the cutting edge.
Any steel which has a low draw temperature may be drawn to a softer temper along the spine to give it better shock resistance. If this is done, the blade will almost always curve a bit towards the softer part of the blade. This works better on shallow hardening steel than on others but can be done on 5160, 52100, A-2, 440-C and others.
Many of the low alloy steels, like 0-1 and 5160, will show a temper line if the blade is selectively hardened, but the line is rather plain, merely a division between hard and soft. A proper, decorative line, needs either the 10 series, or W series of steel. Oil quenching will produce a temper line in those steels, but water quenching is necessary if one desires the more intricate details of the Japanese style line.
SPARKS GIVE A CLUE TO COMPOSITION
The spark from a steel with .15 to.40 of one percent carbon will simply fork.
Steel with at least .45 of one per cent carbon will show a small but distinct secondary burst. This is considered the minimum for hardening into a useful knife.
Carbon over one per cent will give an intense and multiple bursts.
Moderate silicon makes a spark that is short and ends with a sharp white flash.
Nickel sparks have a small, very intense and bright white color.
Molybdenum gives a spark with a distinct, separate head.
Sparks are best judged by looking at the last third of the trail. Alloys with several additives will confuse the heck out of anyone.
OVEN DRAWING COLORS
If you want to do your own heat treating on some of the easier steel types, you will have to first harden the steel all the way, then draw its' hardness back a bit to keep it from being too brittle to use as a knife. You can do this in an ordinary kitchen oven, but most ovens have a crude thermostat that is not much better that taking an educated guess at the temperature. The scientific term is SWAG, scientific wild assed guess.
Oxide colors will form on clean steel as it is heated. You've seen them many times, as the steel got hot where you're grinding.
Contrary to some belief, these do not indicate that the steel has had its' carbon burned out. All it means is that the steel got hot, and if hardened, lost some of the hardness. ( Burning carbon out of a blade takes bright yellow heat applied for more than just a minute.)
The colors are a very precise indicator of temperature with simple carbon steel.
400 degrees, pale straw
425 degrees, straw
490 degrees, golden yellow
500 degrees, brown
525 degrees, brown purple
570 degrees, purple
600 degrees, bright blue
650 degrees, pale blue
There is one little catch when using the color with any steel more complex than 0-1. They don't all react to a given temperature with the same color. D-2, for instance, looks a lot different from 0-1 at 450 degrees. It's best to put a scrap piece of 0-1 or 1095 in with the complex stuff when running the draw cycle, and use it as a precise indicator.
RED HEAT TEMPERATURES
Faintest dull red 900F
Dull red 1200F
Cherry red 1400F
Orange red 1500F
Bright salmon orange 1600F
Brilliant orange 1640F
Temperatures should be judged in a dimly lit area. If you are working outside, colors will appear at least one or possible two steps too low, and you will severely overheat the steel. I have become intimately familiar with this problem. One fellow has a open barrel set horizontal beside the forge, providing a shaded spot to stick the blade into for judging steel temperature.
If you want the spine of a carbon steel blade drawn softer than the cutting edge, the process isn't nearly as difficult as you might think. All you need is an inexpensive wallpaper tray, filled with water, and a torch. A propane torch will work, but the oxyacetylene type works a lot better.
You hold the blade above the tray, edge down, and begin heating the spine until you start to see some color. You always start at the heaviest part of the blade. The first color will be a pale yellow.
At this point, try to keep at least half an inch of the cutting edge in the water. This will keep the heat from running down to the parts that have to stay hard. Work the heat only on the very spine, and work slowly towards the tip. Stop well back from the tip. It will heat easily and you want it to stay hard.
If you are using a acetylene torch. the flame must be aimed directly down at the spine of the blade. If you heat from the side, the blade will warp. This is not a problem with the slower heating L P torch. After you melt a tray or two, you'll also want to use a metal tank.
When the length of the spine has a rich blue color, it will be drawn to a high 40 or low 50 Rockwell, which is right where you want it. On stick tang blades, you should cook the junction of tang and blade to at least a good rich brown to prevent any brittle fracture at that point. The end half of a tang doesn't need to be hardened at all.
Some of the more complex alloys with low drawing temperatures, like 440-C and A-2 may also be treated to soften the back with this technique.
Sorry Bill but the system will only let me post half of it. If someone wants the whole thing, email me and I'll send it to them.
Eric, Richard, and Peter -- thank you very much for your responses. Especially all the info you provided, Peter. I am so glad to have all that info in one place. I've e-mailed you, and would appreciate the remaining info that goes with what you've written so far.
I think I'm understanding a lot more now, thanks to all your answers. I really appreciate them.