Spheroidize anneal process question

D

deker

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Nov 14, 2005
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I want to make certain that I understand the complete process of the approximation of a spheroidize anneal that Kevin recommends for simple carbon steels. I'm using mostly 1084/1095/15n20. Is this the correct recipe? (all I have is some very bad notes I took at Ashokan)

- Thermally cycle to reduce grain size
- Heat to critical and quench
- Soak @ 1275F for one hour

Now, another question. How important is the cooling cycle after the hour at 1275F? Should it be a "turn off kiln and let cool slowly" or would cooling in still air be sufficient? Since I only have limited access to other people's kilns to do this right now, so I'm hoping that just a regular cooling in still air would be sufficient so that an entire night of kiln cool down can be avoided. It seems to me that the heat to 1275 is kind of like a "super tempering" and so once the carbon is allowed to relax out of the matrix it should be about as soft as it's going to get and so a regular cooling in still air would be sufficient. Is this a correct line of thought?

Thanks,

-d
 
You could do them all by heating to sub-critical at around 1375-1400. Hold for about an hour.
According to my specs, they say:
"Furnace cool to 1200 degrees at a rate not exceeding 50 degrees per hour. From 1200 to ambient temperature, cooling rate is not critical".
I always do mine at night, and ramp my temp down at about 40 degrees per hour, then have the oven shut off. By the time I open the oven up in the morning, it has cooled down almost all the way.
As well, 5160 would hold at the same temp, but that cools to 1200 at only 10 degrees per hour! that spherodizing anneal take me about 12 hours.
 
Karl,

Isn't that for a full process anneal? I'm hunting for info on Kevin's "quickie spheroidize approximation". I don't have the luxury of letting a kin cool overnight since it's not my kiln :)

Thanks,

-d
 
No, that's not a full anneal - it's a sub-critical spherodizing anneal.
Here's something you can do, and what I used to do before I got my oven:
Make a box like pictured here and fill with lime, the really finely powdered lime. About the best insulator you will find.
Heat up two large pieces of steel that are through and through heated to a dull red in low light - maybe a little bit bright.
Bury them on edge in the lime about an inch or so apart.
Then heat up your blade to a dull red and place between the bars. Cover with lime and place lid on container.
I've had a knife blade still too hot to handle with bare hands the next morning!
You never really got up past critical, so this is NOT a full anneal, and your blades can still be like BUTTER!
anneal.jpg


anneal1.jpg
 
Karl I don't understand your method at all. Deker , what you're trying to do is form fine spheres rather than the large spheres formed from full anneal. This has a number of benefits as Kevin has explained. It is a matter of forming martensite [ heat to critical and quench ] then temper at ~ 1200 F [not called a soak] .This is 'subcritical anneal' and results in ferrite and fine spheroidized carbides. You might want to do it longer , perhaps 2 hours.
 
mete said:
Karl I don't understand your method at all. Deker , what you're trying to do is form fine spheres rather than the large spheres formed from full anneal. This has a number of benefits as Kevin has explained. It is a matter of forming martensite [ heat to critical and quench ] then temper at ~ 1200 F [not called a soak] .This is 'subcritical anneal' and results in ferrite and fine spheroidized carbides. You might want to do it longer , perhaps 2 hours.
Click to expand...

Ok, that's what I thought. So, how important is the cooling from that tempering cycle?

Thanks,

-d
 
mete said:
Karl I don't understand your method at all. Deker , what you're trying to do is form fine spheres rather than the large spheres formed from full anneal. This has a number of benefits as Kevin has explained. It is a matter of forming martensite [ heat to critical and quench ] then temper at ~ 1200 F [not called a soak] .This is 'subcritical anneal' and results in ferrite and fine spheroidized carbides. You might want to do it longer , perhaps 2 hours.
Click to expand...


For example, for 5160, right out of the Heat Treater's Guide:
"For a predominately spherodized structure, heat to 1380 degrees F. then cool rapidly to 1300 degrees F., then cool to 1200 degrees F. at a rate not exceeding 10 degrees F. per hour."

Out of the same guide are the directions as I quoted above. Only slightly different for 1080/1084/1095 in the cooling rate.

It's not my method.
 
If you go above 1335F then the cooling becomes the critical factor as you will actually begin to dissolve carbide and will have to be cooled through the Ar1 range very slowly to ball up the carbide instead of it going lamellar. Spheroidizing is not really for simple carbon steels but instead best for anything above .8% carbon, particularly if there are carbide formers, if you wish to do machining.

If you stay below 1300F then it is just a matter if time at temperature to spheroidize things. The time will depend on prior microstructure due to teh distances the carbon will need to travel. Course pearlite will take some time to ball up due to the segregated condition it already has, but martensite will precipitate carbides very quickly and ball them up nicely at 1200F - 1275F. That is why the quench right before will make things easier. How hot and how long will effect how much carbon moves and thus the coarseness of the spheres. Coarser spheres will be the softest for machining, while finer spheres will go into solution quicker when it comes time to heat treat.

I have a whole series if microgrpahs that I dug out of my files that touches very well on this topic and a few other topics that have been of interest lately but I will not be able to post them until next week since I am elbows deep in preparation for a bladesmithing metallurgy class this weekend.
 
Thanks for weighing in Kevin. I think I have a bit of a better understanding of what I'm shooting for now. Really, all I want to do is to get some pattern welded billets soft enough to easily bandsaw cut, but I wanted to make sure I understood what I was doing before doing it.

I look forward to micrographs in the future, pictures always help me :)

Thanks,

-d
 
2 questions for Kevin.
1. When do you do this?
and
2. Does it leave the steel soft enough to grind?
 
1. - after you forge you normalize which yields pearlite. You then anneal [ regular or subritical] ....2.- Yes , that's the whole point of doing it !!
 
mete said:
1. - after you forge you normalize which yields pearlite. You then anneal [ regular or subritical] ....2.- Yes , that's the whole point of doing it !!
Click to expand...
Just axin'..lol. I have been doing the "heat it to critical and stuff it in the trash can full of vermiculite overnight" thing. Now I have a Paragon and have become interested in weird things like accuracy and consistency:D
 
It is really only necessary with steel that will give you grief from carbide or stuff you want to easily machine, if all you want to do is grind some 1070, 1080 or 1084 then one could normalize after forging and call it good, unless you started experiencing more distortion in the quench. The more metallography I do on steel that has undergone typical baldesmithing treatments the less I like full lamellar anneals, that is heating above critical and then stuffing it into vermiculite, wood ash or the hot forge.
 
Kevin, so you're saying that this spheroidization (or w/e you want to call it) process isn't really necessary for simple carbon steels? That normalizing after forging is fine unless you're experiencing weirdness after quench?

Are you finding benefits in multiple normalizing cycles in simple steels? The reason I'm asking this follow on question is that I tried experiments with 3x normalizing versus a single normalizing cycle and couldn't find improvements in my simple cutting and edge hardness testing (I cut cardboard and hammered blade edges through nails.) Not fancy but I don't have a lot of fancy testing equipment.
 
I'd like to see some formal tests of machinability and grindability of the different structures. With a .80 C steel the normalized structure will be 100 % pearlite. Machinability [lathe,milling machine] of this structure will be lower than speroidized carbide of the same material ! I suppose a simple grind might be ok on this type of steel. Maybe Kevin can elaborate on this. The more complex the steel, with other carbides the more important it is for sure.
 
Doing a spherodization on my 5160, W1 and W2, I have discovered that I get virtually NO distortion upon quenching after a soak time prior to quenching.
 
I will reiterate that “simple carbon steel” is not the determining factor in whether great advantages will be obtained by spheroidizing, the amount of carbides that will give you problems otherwise is. 1095 is a simple carbon steel but it will spheroidize very nicely while you will barely notice the effects in 1070 or 1080, even under the microscope. Adding alloying only makes it more important because course pearlite will be harder to obtain and carbide will be even more ornery.

If all you have to heat treat is a forge and your soak time is the few seconds it takes to determine the magnet is not working anymore, then spheroidizing could be a lot more trouble than it is worth, however not nearly as much trouble as heating above critical and then stuffing it in the gas forge or vermiculate for the night. Instead, if you are working with a steel that really isn’t going to make large spheroids anyhow (1070, 1080, 1084) and all you want to do is grind it (no drilling or milling) or file it, then you may be better off just normalizing a couple of times and calling it good after a final lower temperature cycle. The resulting fine pearlite will grind well enough with zirconia and other such belts, but more importantly will go back into solution very quickly in that few second soak time.

If done right there should be gains in carbide size and distribution as well as grain refinement in a few good normalizing cycles, even one good normalizing cycle should give you better conditions than the forging heats left you with.

If you have enough carbon to make proeutectoid cementite (the stuff you get above .8% C) and you do a lamellar anneal, not only will there be grain growth, but while the steel is making pearlite, anything above the eutectoid will be gathering in the grain boundaries. After all my observations I am convinced a lot of the odd practices that bladesmiths claim make super blades is just a matter of finally defeating this huge liability, which didn’t need to be there to begin with. We really need to stop assuming that the latest blade is the pinnacle of steel performance long enough to ask why that blade before it sucked so badly that this one is that much better. Progress is always good, but so is perspective, +5 is not as spectacular when you started out at -8 ;).


mete, grinding pearlite is not too much of a problem with the fancy new abrasives, in fact I think one may get better belt life than with a spheroidal structure since the pearlite would offer enough resistance to fracture and expose fresh new cutting surfaces, while spheroidized steel can be like grinding non-ferrous. I always write off a belt when I am touching up some non ferrous parts since it will kill zirconia as it doesn’t have the oomph to shatter the particles and give fresh cutting. Milling or drilling lamellar structures, even in 1084 just plain sucks! Chatter, chipping, squeeling and dulling! I don’t care if it is wrought iron, if it has to be milled it is going to be put through the spheroidizing treatment in my shop, end mills aren’t free!
 
Kevin R. Cashen said:
Milling or drilling lamellar structures, even in 1084 just plain sucks! Chatter, chipping, squeeling and dulling! I don’t care if it is wrought iron, if it has to be milled it is going to be put through the spheroidizing treatment in my shop, end mills aren’t free!
Click to expand...

Aye! There the rub! This was my initial concern. The piece that brought this question out is a billet of mosaic that I need to bandsaw cut to unfold. First cut went fine, second cut went 1/2" and stopped cutting. Then I remembered this little spheroidizing conversation I had with Kevin...

Now I'll just hope that the existing cuts won't blow things apart when I have to quench this one before the kiln....

Thanks!

-d
 
Kevin, "fancy new abrasives" I forgot that I'm still in the dark ages !! I do have experience in personally machining pearlite and solving many machining production problems caused by improper HT !
 
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