what happens if you quench at 1550 instead of 1450?

M

MCoughlin

Joined
Feb 1, 2005
Messages
471
Hi guys,
Thought I'd fire off a quick question to the experienced.
I recently got myself a nice digital thermocouple for my forge. I found the lower end of my temp settles out at about 1550-1560F. Critical temp is around 1450ish for most carbon steels as far as I know. Would quenching at 1550 be harmful as opposed to 1450? Can anyone tell me what happens to steel at 1550? Is there a mayor transformation in grain size in that temp range? I've been using a magnet with exceptional results. With a piece of 1084 I made a test blade with clay coating. I bent it 90 successfully. I had the edge and spine tested for rockwell which were 59.5ish for the edge and 35ish for the spine. We did several tests along each and that would be about average. So I guess what I'm saying is I'm happy with how things are going for me with carbon steels but it would be nice to have the control of soaking at temp as well. I think this thermocouple will help me there and I think I may widen the chiminey a bit to cool it off a little more. 1550 was about my minimum though. Is 1550 too far from the ideal quenching range? Thanks in advance if I don't get back to you guys right away. My wife is having contractions as we speak. hee hee hoo hee hee hee hoooooooo...lol
Mike
 
Short answer - 1550 won't destroy the blade.
Longer answer - Each steel has its own quench temperature.For most carbon steels that range is from 1395 to 1450. As the temperature rises above Ac1 the austenite grows larger grains.Carbon starts to oxidize faster as temperature rises,too.In a controlled soak,for 5-10 min. there is little problem with a few extra degrees,as long as you stay below Ac3.My recommendation is 50-100 degrees above Ac1. Austenitizing occurs at about 50 degrees above critical temp,which for 1080 is 1350.Thus 1395 would be optimal,and 1450 max.
The main reason you want to be able to lower the forge temp is to do other HT things like sheroidization.
Stacy
 
Might want to add some mass to the thermocouple to see if the steel temps are really that high.
I add a nut and bolt to the thermocouple junction to make the response time slower.
This way it gives a better read of the temps of the steels, rather than the flame temperatures...
 
This is a little off the original post but:
I am trying to build my own thermocoulpe. I was planing to use a multimeter and conect it to a store bought probe.
What sort of probe are you useing. The saleman selling these things had a wide range if probes,ranging from a twisted wire to some rod like ones, some quite pricie. He told me that a propane forge would oxidize the probe and a thin wire one would not last long. :confused: Is this true? And how long do you have to have the probe in the heat to get a reading? Do you leave it in all the time or just do spot readings? I was thinking I could make a small hole in the side of the forge and slide it in when needed, and plug the hole when not in use.
Any thoughts on this topic would be helpfull.
Cheers Ron.
 
best thermocouple is a long wire covered in ceramic - forge temperatures can be very uneven.



This should be an interesting discussion. I have my knee-jerk answer prepared...but am waiting to see what others have to say (especially those more experienced than I).
 
Mungo Park said:
This is a little off the original post but:
I am trying to build my own thermocoulpe. I was planing to use a multimeter and conect it to a store bought probe.
What sort of probe are you useing. The saleman selling these things had a wide range if probes,ranging from a twisted wire to some rod like ones, some quite pricie. He told me that a propane forge would oxidize the probe and a thin wire one would not last long. :confused: Is this true? And how long do you have to have the probe in the heat to get a reading? Do you leave it in all the time or just do spot readings? I was thinking I could make a small hole in the side of the forge and slide it in when needed, and plug the hole when not in use.
Any thoughts on this topic would be helpfull.
Cheers Ron.
Click to expand...

First of all I got mine through Omega here in canada. Somewhere in quebec I think. I ended up calling and I talked to a specialist in thermocouples and he recommended the one I got. I told him I wanted something fairly inexpensive but decent as far as accuracy etc. Very helpfull. All said and done I paid about 170CDN I think. That gave me the digital controller the wire/probe(which is a foot long and quite robust) and the plug for the probe to fit in the controller. Accurate to 2000F. I wish it went a bit higher because I'm not sure what damascus will take for temp and I hope I didn't buy one that's no good for that. I'm not forging blades yet but will be when I get an anvil and hammers. I have most everything else now. I still like to play with carbon steels though through stock removal. I do know my forge would easily have maxed out my thermocouple if I hadn't turned down the pressure on the propane tank. As far as oxidizing the probe? I haven't had any problems with mine I know of. I leave mine in all the time because it takes a bit for the probe to come to the temp in the forge. In other words the forge goes up in temp very fast. The probe will follow but it will only show increments as it's rising until it starts to slow down and settle out a bit. What a great thing to have though. I will be able to exercise much more control now. I drilled a hole straight into the back of my forge so the probe is very close to where the blade sits. I hope this helps. Just type in omega thermocouples in google and that should lead you to the'r phone number. Let me know if you have troubles and I'll dig up my reciept with all the info.
Mike
 
Daniel Koster said:
best thermocouple is a long wire covered in ceramic - forge temperatures can be very uneven.



This should be an interesting discussion. I have my knee-jerk answer prepared...but am waiting to see what others have to say (especially those more experienced than I).
Click to expand...

Hey long time no talk! This probe I got is 1/4" thick and seems to be quite accurate but who's to say right. I guess the blades will determine. The long wire will still only reflect the temp near the end of the wire though right? Or am I wrong. I found by moving my probe in and out I can determine the temps in various points in the forge. I was told the front inch is the most sensitive point on my probe...as bad as that sounds lol. You're right though an interesting discussion could definitely happen here.
Mike
 
The only temperature that will affect the readings are the temperature at the thermocouple, where the two dissimilar metal wires are fused together. (at the end on the probe, or the middle of the two wires, depending on how you look at it...)
Properly sheathed, a thermocouple should last a very long time, as they are not directly exposed to the oxidizing atmosphere.
Even an exposed large wire thermocouple should last a good while.
mikxx1, did you get a type k thermocouple?
If so, it should be good to 2500°F or so. Maybe the limitation is in the range of the controller?
 
howiesatwork said:
The only temperature that will affect the readings are the temperature at the thermocouple, where the two dissimilar metal wires are fused together. (at the end on the probe, or the middle of the two wires, depending on how you look at it...)
Properly sheathed, a thermocouple should last a very long time, as they are not directly exposed to the oxidizing atmosphere.
Even an exposed large wire thermocouple should last a good while.
mikxx1, did you get a type k thermocouple?
If so, it should be good to 2500°F or so. Maybe the limitation is in the range of the controller?
Click to expand...
Maybe, I will look into it and get back to you. If that's the case I may only have to upgrade the controller in the future.
mike
 
Thanks guys I was able to get the forge down to around 1400ish so I should be good. My burner flutters but I'm closer to where I want to be for hardening.
MIke
 
Sorry not able to spend time to read all replies and I guess what I will say has already been covered but just in case....

If your steel is specified to soak at 1450 F or there-abouts I would suggest chances are that soaking at much higher than that, and 100 F higher is much higher, you should expect grain enlargement which can cause embrittlement. As an example, I would not soak O1 tool steel that high - at least for knife blade purposes. Using my Even Heat I normally set it for 1475 F.. That is not to say that my Even Heat is working at 1475 F. but that through trials I have found that setting on my particular furnace (oven) to work well for that steel. 1550 F is too high for O1 for the purposes we heat treat O1 for. I might get called on that but I thinkst me correct.

rlinger
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To dampen the effect and fluctuation of the flame, put a piece of two inch pipe in your forge and heat treat in it. It is a more even heat and your thermocouple readings will be dampened inside the pipe as well.

Craig
 
No need to close off the end,Using a muffle (the pipe) will keep the flames off the blade and evenly distribute the heat.Stick the pipe out the back door hole of the forge(if your forge has one) and put the thermocouple in from the back.If you have a one door forge,then I guess closing the back of the pipe would be of some advantage,but not mandatory.
 
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