Jump to content
Sign in to follow this  
Toni

Heat Treating with very basic equipment.

Recommended Posts

I'm pretty new to this stuff, but what I have been reading about heat treating it seems like a very precise process. Yet a lot of guys seem to be doing it with very basic equipment. Especially normalizing and annealing seem to require very precise control. Is it possible to properly normalize and anneal stuff with a very basic forge and no heat measurment equipment? In what ways can you do it?

Share this post


Link to post
Share on other sites

A lot of this stuff can be done by eye and a magnet. Our ancestors didn't have computer-controlled HT ovens, and they were able to make some pretty good stuff with what they had. I can tell you what I do with normalizing and annealing in my coal forge. I have found that stepping down your heat is good for normalization. I heat it up past critical heat, let it air cool, then heat it up just a little past critical, let it cool, and lastly get it at or above (usually above to avoid being below critical) critical. I find that usually those 3 cycles make the crystal structure silky smooth. However, it is tricky because you need to heat up the spine before the edge. If you just put the whole thing on its side, the edge grain size will be obliterated. I check for critical heat by using a magnet, it's that simple. On many steels, critical is just past the nonmagnetic point, so use your magnet as a reference, not an indicator of critical heat. You can also wait until it is dark enough to actually see the recalescence/decalescence of the steel to determine when it is at critical. It is usually a shadowy line that runs across the blade when it is heating up or cooling down. As for annealing, I wouldn't do it unless the knife that you forged is extremely thin. I had to cover some of my kitchen knives in wood ash when they were cooling down from critical. I don't know how accurate this is, but I think that any thermal cycling before you anneal doesn't really matter. Annealing makes everything really soft, but the crystal size is all over the place regardless of what you do before.

  • Like 1

Share this post


Link to post
Share on other sites

The heat treatment of modern steel alloys really is an exact and precise process. If you know the make up of the steel alloy and it's intended purpose there is a controlled heat treating process for it that will yield highly predictable results. Of course, if every novice knife maker had to have precise heat treating equipment from the start there wouldn't be many novice knife makers. Very good results can be had with basic equipment and the simpler steel alloys. Ideally, choose a simple easy to heat treat steel like 5160 or the 10XX series, 1084 is my preference, and start small and learn what works (I think it is also important to learn at least the basics of why it works too).

 

As Wesley pointed out above one of the most influential things for me was learning to see recalescence/decalescence. I like holding a steel bucket up so that it is dark inside and sticking the heated steel up into so you can see when the shadows begin writhing across the steel with the momentary brightening and then pulling it out to gauge the color of the steel in ambient light levels. In my experiences playing around with files and 1084, in shaded daylight conditions it is inevitably closer to full red than orange, something that told me I had been overheating my early blades. A magnet is a good tool but it will only tell you when critical has been reached, not how far over it you have gone. Another exercise is to take a piece of steel, old files work great for this, and over heat it so that when quenched and then broken the grain is huge and easily visible. Then run it through a simple normalizing sequence with a quench from the proper temperature, if done properly, when broken again, you can see how the grain size has shrunk to become that silky smooth you want for a knife blade (break an old file first to see an example of that silky smooth grain too).

Share this post


Link to post
Share on other sites

I'd go as far as to say don't bother with the magnet. That will tell you the Curie Point (about 1417 F), which is below critical. Really focus on recalescence and decalescence. Many people using solid fuels use what is called a muffle pipe (I think, I use gas). Take a pipe, cap one end, crush it into an oval shape, put it in the fire and your blade it the pipe. You can now see your blade as it is heating up in a sort of oven. Search for all of these terms on the forum, but use a Google site search rather than the built in search tool.

 

Example:

site:bladesmithsforum.com muffle pipe

 

(Definitely check out the first post that shows up in that search, or just click here to get to it.)

Share this post


Link to post
Share on other sites

Another point is to select a steel alloy the matches the equipment that you have. Steel that has 0.85% carbon or less has less of a problem with retained austenite formation. Steel with a simpler alloy (no high temperature carbide forming metals) don't require a long soak at temperature. There is no such thing as too much temperature control when heat treating knives but if you stick with the simpler steels and pay attention to the basics you can still make a high quality blade.

 

Doug

Share this post


Link to post
Share on other sites

Jerrod I am going to disagree with you on that.

The magnet is extremely useful as a fixed point reference that is unaffected by light. In practice for a simple steel like 1084 quenching from 1400 will get reasonable hardness not full solution or hardness but reasonable. Ad to that the fact the most over shoot the temp in any case and 1450-1500 in 1084 will get full hardness. A magnet is also extremely useful in finding the lower transformation point as it lines up reasonably well with the return to magnetic. In practice for the thermo cycleing heating to just nonmagnetic and air cooling to regaining magnitisum.

I have never been able to see recollassaance a gas forge or in a shop with any light. Only in a dark shop in a erstwhile muffle furnace. (Capped pipe in a coal forge)decollassaance is easy to see and is useful and is one of the methodsi both teach and use, but I do this along with a magnet.

MP

Share this post


Link to post
Share on other sites

The use of magnets for judging critical temperature makes the metallurgist in me shudder a little on the inside. If you are going into it knowing that it is a point that is "almost hot enough, just need to go a little hotter", then it can be useful. On the other hand, recalescence and decalescence are perfect and will be at the perfect temperature for every steel, since it is actually the phase change that you are seeing and thus at different temperatures for different steels. I'd recommend taking the extra effort to make that a possibility (HT at night, a bucket or pipe in/next to the forge, whatever).

 

Side note: Judging temper temperature by oxide color makes the metallurgist in me cringe so hard it becomes visible on the outside too. Please don't do that. It is not accurate due to all the variables (atmosphere, alloy, surface contamination, surface finish, etc.).

Share this post


Link to post
Share on other sites

I agree with everyone!

Its all just tools, the better the tools the more predictable the results.

I think a magnet is a great tool, as is a portable dark space (i have a big bit of chimney). thermocouples and readers are awesome as are temp controlled ovens.

 

it is possible to get good results with very basic equipment, but they are unlikely to be optimal.

 

However I still have most of the tools I made at blacksmithing college in 94, heated to cherry red (whatever the hell that is) and quenched in used motor oil with the temper drawn back with the residual heat. like wise my first proper blade made at ABS school H'td with a oxy propane torch is still going strong.

It is very easy to dismiss everything that existed before modern best practice...........But its what has inspired most of us, all be it being inspired by the legends of the 7th century , the 17th century or the 1970's and 80's......

  • Like 2

Share this post


Link to post
Share on other sites

Owen great point, sometimes best is the enemy of the good.

Share this post


Link to post
Share on other sites

Yep!

 

I have made a knife from 5160 that passed the ABS performance test (for my own edification, I'm not going for a stamp) using only the pipe-in-the-forge method and a toaster oven with some chunks of firebrick to maintain even heat for tempering.

Share this post


Link to post
Share on other sites

Indeed, a smith's reasonably good efforts with good steel and the most basic of tools will likely well exceed many commercially available blades. "Optimal performance" is often over-rated. Especially when most users will never come close to needing better than "good" (relative terms here) and wouldn't even be able to tell the difference between "good" and "optimal", since really they are likely to be pretty close in performance.

 

I should also add that using a magnet with 1080/1084 is definitely effective, as the phase transformation occurs below the Curie point.

Share this post


Link to post
Share on other sites

Indeed, a smith's reasonably good efforts with good steel and the most basic of tools will likely well exceed many commercially available blades. "Optimal performance" is often over-rated. Especially when most users will never come close to needing better than "good" (relative terms here) and wouldn't even be able to tell the difference between "good" and "optimal", since really they are likely to be pretty close in performance.

 

I should also add that using a magnet with 1080/1084 is definitely effective, as the phase transformation occurs below the Curie point.

 

Reading that last line is reassuring. I consistently quench Aldo's 1075 in water from what my thermocouple says is 1415. I swore the phase transition was happening at about 1390 but I didn't know if my gear was off.

 

I use fairly basic equipment for my heat treat. I did make the jump to a thermocouple a few years back which was an amazing investment for adding consistency. I think the thermocouple, the ceramic sheath and readout was less than $100. That investment alone took me from nothing bigger than a pocket knife to making a katana.

 

Before that I only made smaller blades and I had little control over my heat. My technique was blade in the fire for 5 seconds out for 3 sec, do that until color appears. Then in for 4 out for 3 until non-magnetic. Then 3 and 3 until I could see recalescence. At that point I played with the timing until it recalescence started 3-4 seconds after removing the blade from the fire. At that point I would quench. It works and it's nice when starting out since you probably only have one forge. But it's stressful, and kind of exhausting.

 

Jared

Share this post


Link to post
Share on other sites

The use of magnets for judging critical temperature makes the metallurgist in me shudder a little on the inside. If you are going into it knowing that it is a point that is "almost hot enough, just need to go a little hotter", then it can be useful. On the other hand, recalescence and decalescence are perfect and will be at the perfect temperature for every steel, since it is actually the phase change that you are seeing and thus at different temperatures for different steels. I'd recommend taking the extra effort to make that a possibility (HT at night, a bucket or pipe in/next to the forge, whatever).

 

Side note: Judging temper temperature by oxide color makes the metallurgist in me cringe so hard it becomes visible on the outside too. Please don't do that. It is not accurate due to all the variables (atmosphere, alloy, surface contamination, surface finish, etc.).

Walter Sorrells touches on that point when he's using a backyard charcoal heat treating method. he said to keep it in there a good 20 to 30 seconds more once the magnet no longer attracts. he has quite a few vids for beginners.

Share this post


Link to post
Share on other sites

I got an Evenheat to heat treat modern stainless alloys, mainly AEBL and ATS-XX. I have done a lot of 1084/15n20 damascus, O1 and 1095 in there too. Tempering in there is much more consistent than tempering by eye. I still do all the HT on chisels, axes etc by eye though. Much less consistent, but usually good enough.

Share this post


Link to post
Share on other sites

I have found that a large furnace, a scaled down Don Fogg HT furnace, really, is very effective for austenitizing when used in conjunction with a thermocouple and reader. Adecent thermocouple is expensive, and with this set up I have to guard against draughts as my burner is atmospheric, but otherwise it seems it can hold a temperature indefinitely- cheap and best!

 

I've heard horror stories about high dollar electric HT rig elements pulsing or cycling or something like that, and the radiant heat queering the readings, which is off-putting.

 

Seems too that there is often confusion over HT specs and the dimensions of material they are referring too. I'd love to see a comparison, for instance, of HT specifications for O1 in 30mm thick pieces vs. 2mm pieces, done by a qualified metallurgist f course.

 

Best practice from my point of view is to do vigorous destructive testing on your steel of choice using your HT of choice.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...