Long (really long) Ramp Times

S

Surly

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Apr 26, 2000
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Guys, a heat treat oven question:

After reading this thread: http://www.bladeforums.com/forums/showthread.php?t=280164&page=8&highlight=rwl-34 concering heat treating RWL 34, I've got question:

I'd like to try HT'd some stainless steels. My oven takes roughly 180 minutes (that's right, 3 hours) to get up to 2000 deg F. It WILL get there though. Most of that time is going from 1000 to 2000.

Are there negative consequences of an extremely long ramp time? Is it a logical assumption that this would reduce the final soak time?

Thanks guys, I appreciate all the info that is here!


PS: I attempted to search, but the function didn't seem to be working.
 
Surly: That's a long time. In theory, the long soak time won't affect yur results. Problem is, unless you have a perfect seal on all edges of your foil pack, you risk some substantial decarb. So, check them real well.
I would recommend 1 of 2 approaches:

1) Heat your furnace to the Austenitizing temp, then add your foil pack. Start timing your soak when the furnace reaches the Austenitizing temp.

2) Add your blades at 100-200F over whatever the preheat temp is, usually around 1500F. By oershooting, the furnace will cool about that much when you add the blades.
This is a more cautious approach. Easier to do, because the furnace is cooler.
 
Thanks RJ, that makes a lot of sense. I couldn't find any data on oversoaking, but I was sure that there was something I was missing.

I hadn't thought about the effect re: foil packet. Is there way to make the edges air tight? Everything I've read just said to fold them together and use a small combustible.
 
How long does it take to go from 1500 to 2000F ? I'd wonder about possible grain growth. It still takes the high temperature to dissolve those carbides and distribute the carbon so you still have to soak at the high temperature.I'd rather do without the preheat..... Try to get as much of the air out of the foil packet as possible then fold three times and squeeze the seam in a vise or use a hammer.
 
Sheffield sells a little gizmo called a "seam roller" for $6.50 on page 60 of their catalog, P/N SSTR5. Works really nice; real crisp seams, so they seal well and are easier to double over.
 
fitzo said:
Sheffield sells a little gizmo called a "seam roller" for $6.50 on page 60 of their catalog, P/N SSTR5. Works really nice; real crisp seams, so they seal well and are easier to double over.
Click to expand...
yep handy little tool but there now made of plastic
thats what i have but it seems to do a good job. i was told they no longer the nice wood handle steel wheel tool
btw i fold 2 times and roll them good and flat with brown paper wraped around the blade i find this helps me get the blade out of the foil for quench
it kind of just slips out on all the ash
butch
 
That long soak time is very important once you reach the critical temperature.
For most stainless alloys it is around 1450 F give or take 50 F. Once that temp is reached the material transforms to austenite. Austenite allows more alloy to dissolve into the matrix of the steel. Even at the lower end this will throw off the material and dissolve too much alloy. Grain growth, as mentioned above is the other downside. Knife steels are too thin to worry about pre-heating. Get the oven to temp, put the blade in and estimate 10-15 minutes to get a 1/4 inch thickness up to temperature. Air pockets in the foil will increase the time a little. Soak at recommended times once the steel is up to temp.
 
Surly, may I ask what kind of oven you have, and does it operate on 120v or 240v?
 
You can use any radiused, hard tool to seal your edges. I use the handles on my foil cutting scissors. Wprk on a clean, flat, hard surface and the seams will be crispy. Pay special attention to the corners. Skip the combustible.

I have wallpaper seam rollers, but, you can lean on a 1 piece tool a lot harder.
 
Awww, c'mon, RJ, sure you can use the scissors handle, but then that's one less tool in the shop.....;) :D
 
fitzo said:
Awww, c'mon, RJ, sure you can use the scissors handle, but then that's one less tool in the shop.....;) :D
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I just got an even heat and i wonder if someone can tell me where to get the foil? Also, should i put paper in with the blade or not?

Thanks everyone
Michael
www.AdamMichaelKnives.com
 
When I said use a hammer I really meant to iron it with a hammer !
 
Mete, it looks like it takes about 115 minutes to go from 1500 to 2000.

Here is what my curve looks like:

heattreatovenchart8ek.jpg
 
SATRANG - Those temps you stated are for simple carbon steels,not stainless steels.Stainless steels will have to go to 1900-2000F.

RALENER - Yes,wrap the blade in the paper,then wrap the "packet" in the foil.The foil can be purchased from most HT suppliers and knife making suppliers.Be careful with the foil,it is wicked sharp.
 
Surly said:
You betcha--it's a "Cressi 100" 120v that's been retrofitted w/ a Bartlett digital pyrometer. It's also the subject of an earlier post: http://www.bladeforums.com/forums/showthread.php?t=371431

Thanks for all the info guys, I really appreciate it.
Click to expand...


Surly, I believe your long ramp times are a characteristic of your 120v power input. As your furnace reaches its upper limits, it's working incredibly hard to get enough electrons into the elements to make a rapid enough change in temperature. A higher current rushing in would certainly make for more current-exchange to heat. If there is a way to convert yours to 240v, I would recommend it.
 
Yes, You might want to consult the manufacturer and possibly an electrician to set you up with a higher amperage outlet.

Again, I do not recommend any type or amount of combustible to be added to the packet. If you make the foil package correctly, with sharp folds, there will be very little airspace left. Your blades will come out a nice silver grey color and will be very clean.

In the meantime, heat the kiln all the way up before adding your packets.
 
Bladsmth,
You are looking at hardening temps not critical temps. Steels transform to austenite below what is recommended for hardening. The higher hardening temeratures are needed for alloy containing carbide contents where some of these need to be dissolved also during the heat treat process. 440A has a critical temperture of 1475 vs a hardening temperature of roughly 1900.
 
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