Annealing question

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Pete Allan

Joined
Oct 29, 2003
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I have a small electric HT oven and at the moment I am annealing some small 6150 gun parts. I put the parts in a tin can and mix and cover them with sand or cat litter which seems to keep the scale to almost nothing. I run the oven to around 1600 and hold for an hour then just shut off the power. The problem is it usually is about 24 hrs before I can handle the can. I know there is a point at which I could take the parts out of the oven and air cool them without messing up the anneal -- any one know at what temp this would be safe? It would be nice to use the oven before 24 hrs.
Thanks
 
Pete, I expect I'll get my wrist slapped but I almost never leave them that long. I bring it up to heat and take it out to air cool. It will still take a few hours for it to cool.

What on earth are you using the 6150 for ....springs?
 
Pete. Good thinking on the can with sand. The magic temp is only 1325f for 3o minutes. Its called "spherodizing" Let it cool down to 900f and open the can. I do it all the time but not in a can, there is only a trace of scale but sands right off.
 
Yep Im sure. Call Devin Thomas. He taught me this trick. Ive done it for years on my blade steels including damascus. It doesnt work with L6 or 15n20 though because of the chrome I think. 1550 may work for them.
 
I am putting together flint locks. I make the tumbler,sear,fly,main spring and frizzen spring in 6150 and the frizzen in 1095 every thing else is 8620. Most of the parts get a lot of taped holes and as cast you can't drill 6150 or 1095 let alone tap it.

I am sure getting some good use out of the knife grinder I built last year. I have made some good holding jigs to hold the small gun parts for degateing.
Yesterday I degated 40 tumblers in less than 4 min. and every thing is smooth and straight. What an improvment from the way we did it 30 yrs ago.

Thanks Don and Bruce
 
There's actually two different kinds of annealing with slightly different methods. Bruce mentioned "spherodizing" which uses a lower temp, but doesn't ramp down immediately, you need to hold for about half an hour like he said. The other is "lamanilar" (sp?) which takes a higher temp but doesn't require a hold, just a ramp down over a longer period of time.

Kevin C or Mete can clairify the details.
 
Yep, 1300 - 1325 degrees F. is about right for a spheroidizing anneal on simple carbon steels. That's what I use on all my 10xx series steels. A "sub-critical" anneal will render the softest, easiest working steel you ever saw. What happens is the carbides pool up into little globules (spheres) and leave larger spaces of the softer ferrite, so the steel is easier to grind, drill, file, etc.

On the 10xx steels I always normalize, then take the steel up 1450 - 1475 degrees F. and quench. The resulting Martensite structure is more responsive to the spheroidizing than Pearlite. After quenching the oven is set in my case at 1310 degrees F. and the steel is soaked for about 1 hour.

I have tried both removing the blades after an hour and letting them air cool, and just shutting the oven off after an hour and letting them slow cool -- taking them out the next day. No problems either way. The steel is still dead soft.

I've also left them at 1310 degrees F. for 3 hours with no ill effects. You are afterall holding the steel at a temperature that is not causing grain growth. As long as I get about 1 hour on blade sized pieces everything comes out right. On blades there's one thing to remember. You will probably require some soak time from the spheroidized state when you harden. I hold them at temp for about 8 - 10 minutes.

As Bruce mentioned, the alloy steels don't respond the same way to the aforementioned method. I just use this specific procedure on the 10xx series steels. For example, I have a completely different procedure for 5160.

The sand idea sounds intriguing. I'll file that one away for a special case. In my case the just forged and normalized blades are not cleaned up prior to annealing anyway, so I don't concern myself with scale.

After the annealing I clean them up different ways depending on the time of day and/or my mood. If it's the end of the day I just put the cooled down blades in a container of vinegar and let them soak overnight. It eats away the scale. The next day I just take them out and scrub them down with a steel brush. If I'm in a bit more of a hurry I'll put them in Ferric Chloride for a while then scrub them down with a steel brush. Sometimes I just clamp them up and go over them with an angle grinder Harvey Dean style.

H-m-m, I'm getting off topic here. Sorry for rambling.
 
I hadn't thought it about for tumblers Pete. I've been using O1 for the tumblers and sears. The reason I asked about the springs is that someone, maybe Chambers, is using it for springs now.

The grinder is nice for working those parts, isn't it. That's one of the reasons there are so many cross overs. The techniques are so much alike.

I built a little variable speed 6", 120 volt DC, disk grinder today. This one has a table that allows me to use jigs. It will be for sharpening, final finish and precision grinding of gun parts. BTW...if you know any elevator repair people, they use these little DC motors all the time. Just rectify 120 AC and use a dimmer switch on the DC side to control the speed.
 
You can get two different structures , spheroidized [carbide in little balls] or lamellar [pearlite]. I assume you're starting out with martensite or maybe pearlite . Spheroidized would be the easiest to machine and the easiest way to get that [minimum scale and distortion] would be to heat at 1200F [subcritical anneal]. You would have to try different times ,1,2or 3 till you get what you want .Subcritical anneal does not have to be cooled slowly. Once you anneal just let it air cool.
 
Bruce Bump said:
Yep Im sure. Call Devin Thomas. He taught me this trick. Ive done it for years on my blade steels including damascus. It doesnt work with L6 or 15n20 though because of the chrome I think. 1550 may work for them.
Click to expand...

Typical lameller anneals will work with 15n20 (it doesn't have the chrome like L6), perhaps even the 1500F+, but L6 almost necessitates spheroidal anneals, it simply does not like to make pearlite. One does have to be careful on how they do the L6 spheroidizing, since it hardens so easily.

I have been using spheroidizing for many years now, and really like it for the completely stress free and dead soft characteristics. Also, since it is subcritical, one can refine grains to whatever level they wish and not mess with it in the subsequent anneal, recrystalization is not completed. This is why I do all of my grain refinement at the end of the forging operation.

In steel that is not hypereutectoid, there really is not much of the tell-tale spheroidal carbides because there is not enough carbon to ball up, in the time we have to work with, but things still get very soft all the same. Hypereutectoid steel will really respond to it, and if there are carbide forming elements present the effect will be more so. Going from a bainitc or martensitic structure will get the job done in no time because the carbon is allready in solution and can ball up quite readily.

Pearlite has the carbon and iron layered out in alternating lamellae of ferrite and cementite, this is why it is referred to as lamellar. The higher the soak temp and the longer the time the coarser the pearlite, due to greater seperation of the two. The process by which it forms on cooling is quite fascinating but a bit aside from the topic at hand. Lower soak temperatures, with less time will result in finer pearlite, due to the lesser degree of separation. normalizing 1084 will get you plenty of fine pearlite. Stuffing 1084 at 1500F. into vermiculite or wood ash will get you the course stuff. Coarse pearlite is softer but actually not as tough (kind of reverse of what is normally expected).

Trying to spheroidize pearlite will take a little longer than what most of us would care to spend, but then if it is pearlite, it is already annealed ;) There are always catches though, if you have a spheroidal microstructure you will need to increase your soak time to get all the carbon back into solution. I can get pearlite completely austenitized within 3 minutes in the salts, but I need 4-5 minutes after rebound to complete the job on spheroidized steel.
 
Sounds like you and I are in agreement Kevin. Spheroidizing gets it dead soft without jacking with the grain refinement one has carefully worked to achieve.

I wish I could say that I came up with my procedure on my own, but truth be told it's based on info I picked up from Howard Clark a few years ago. I've tweaked it a bit here and there, but Howard was definitely the one who set me on the right path and gave me a real appreciation for spheroidizing.

The first big "aha" was going to the sub-critical anneal from Martensite instead of Pearlite. But then upon hitting a true dead soft spheroidizing anneal I was briefly somewhat disappointed with the results after the heat treating. The results were good, but not as good as my old methods.

The second big "aha" was something I picked up from you shortly thereafter, and that was giving the spheroidized steel an increased soak time to get the carbon back to solution. That was the ticket.

I've shared the idea of achieving Martensite first, then going with a sub-critical anneal with a few people, but I generally get a blank look like I'm speaking a foreign language. :D
 
I can't claim any great discoveries in the field myself, but then it is a fairly standard proceedure in industry. It was well over 10 years ago that Tim Zowada described his spheroidal annealing method to me. For some time we both used the same industrial method, since we both worked with L6 (however Tim prefers Carpenter, while I have always been partial to Crucible), that consisted of heating to 1375F. and then cooling no faster than 50 degrees per hour to below 1000F. This produces extremely spheroidized structures but also requires rampable controllers and results in heavy decarb. My answer has always been to leave all the scaly forging skin on and do plenty of grinding afterwards.

I have since played with other spheroidizing methods, I like the method of cycling around Ac1, because it produces finer dispersion and results in less decarb. Even without the decarb, I like quicker methods because of the way the kilns spin my electric meter. Just a simple soak at 1275F for 1 hour will produce around 26-30HRC in Crucible L6.

The advantage of going from martensite to spheroidal is why it works so well for me. I work mostly with O1 and L6 so all I really need to do is a good series of normalizations after the forging, the air cooling alone sets things up very well for spheroidizing.
 
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