@frank_lima and I are interesting in heat treating S7 tool steel. Is it possible to do this at the Makerspace, and would someone be willing to teach us? We have purchased a 0.5"x1.0"x18" oversized rectange.
Thanks,
Phil
1 Like
The steel should be annealed, heat treated, quenched, and then tempered. Unless very thick, it should air-quench.
The pottery kilns can support those temps and timing (Cone 6 is over 2200 degrees F and the high heat phase for S7 is 1725 degrees F), but I don’t know if they’d be available/permitted for that use - that’s a Fired Arts @Team_Fired_Arts question.
Quenching might be a problem if the tool is “large”, but based on the blank size you are starting with air-quenching is probably fine.
Here is a link to the heating profiles for hardening S7:
https://www.hudsontoolsteel.com/technical-data/steelS7
(From the site):
Heat Treating Instructions
Hardening
Critical Temperature:
Ac1: 1460°F (793°C) Ac3: 1540°F (838°C)
Ar1: 1390°F (754°C) Ar3: 1310°F (710°C)
Preheating: Heat at a rate not exceeding 400°F per hour (222°C per hour). For complex and large tools, heat to 1150-1250°F (621-677°C) and equalize. Then heat to 1300-1400°F (704-760°C) and equalize. For simple geometries, use only the second preheating temperature range.
Austenitizing (High Heat): Heat slowly from the preheat. Furnace or Salt: 1725°F (941°C). Soak for 30 minutes for the first inch (25.4 mm) of thickness, plus 15 minutes for each additional inch (25.4 mm) of thickness.
Quenching: Air, pressurized gas, or warm oil to 150-125°F (66-51°C). Note: Sizes over 2½ inches (63.5mm) in cross section will not achieve full hardness by cooling in air. It is necessary to increase the quench cooling rate between 1400 to 900°F (760 to 482°C) by using pressurized gas or an interrupted oil quench. For the oil quench, quench until black, about 900°F (482°C), then cool in still air to 150-125°F (66-51°C).
Tempering: Temper immediately after quenching. Hold at temperature for 1 hour per inch (25.4 mm) of thickness, 2 hours minimum, then air cool to ambient temperature. The typical tempering range for cold work tools is 400 to 500°F (204 to 260°C).
To minimize internal stresses in cross sections greater than 6 inches (152.4 mm) and to improve stability in tools that will be EDM’d after heat treatment, a soaking time of 4 to 6 hours at the tempering temperature is strongly recommended.
For hot work tool applications, tempering at a temperature in excess of 900°F (482°C) is recommended, and double tempering is required.
Cryogenic Treatment: Some prefer to do cryogenic treatment as an extension of the quench from the austenitizing treatment. Others prefer to cryogenically treat after tempering.
Annealing
Annealing must be performed after hot working and before re-hardening.
Heat at a rate not exceeding 400°F per hour (222°C per hour) to 1550°F (843°C), and hold at temperature for 1 hour per inch (25.4mm) of maximum thickness; 2 hours minimum. Then cool slowly with the furnace at a rate not exceeding 50°F per hour (28°C per hour) to 1000°F (538°C). Continue cooling to ambient temperature in the furnace or in air. The resultant hardness should be a maximum of 223 HBW.
2 Likes
One big difficulty with using the pottery kilns for this is that they are top-loaders. So, to pull the metal out to quench it means sticking your arm rather deep through 1725F…
1 Like
No metal is allowed in the pottery kilns*. The carbon off gassing is bad for the heating elements.
I think metal shop has their own kiln now, I would ask there. @Team_Metal_Shop
*I’m not speaking as an authority with Fired Arts, but I’m pretty sure @cmcooper0 would agree.
2 Likes
We have one kiln in the metal shop that is currently operational (though you have to drag it a few feet over to the plug) until I drop some better power). It is on loan from @Kriskat30 and she can tell you what it’s operational specifications are.
Cheers,
-Jim
1 Like
Chris W is the resident expert at metal annealing to my knowledge speaking from practical experience. He is the head of @Team_Machine_Shop. You are welcome to use the kiln for this with Chris’ help.
5 Likes
Aside from all of those concerns, you also can risk cracking the lid by lifting it while too hot. Pottery kilns, conceptually, can be used for annealing metals but it is not particularly safe for you or the kiln. The construction of the kiln in metal shop is much more suited to the effort (it’s a custom glass kiln, it’s designed to be opened while toasty).
1 Like
The one in the metal shop should work for what you want to do. Do you have experience using and programming a kiln?
I’ve used the kiln in metal shop to heat treat S7 before actually, and it works fantastic.
I recommend tying wire to your peice and using the long bar with a hook that should be hanging on the shelf by the kiln to lift it out for the air quench.
Other then that just follow through formula @HankCowdog posted
With @Chris_Wischkowsky and @hon1nbo help.
@Luetchy and I were able to heat treat the S7 tool steel last night.
Using the hardness testing files we have in Machine shop we think we got it about between 50 and 55 HRC.
1 Like
Folks I have a small burnout kiln that I have never use I was told it was working wjem ot
was given to me I know that it needs a little repair with some refacoy
cement
No electronic controller on it, I am willing to dig it out of my storage building and donate it to any committe that wants it, It is front loading
At one time I planned to use it for enameling
Let me know, I need to have a cooler day to dig for it
Science may be interested in repairing it. We are looking to make our own YCBO superconductors.
1 Like
They would be welcome to it, it is not real large but I
know I will never use it
I really need to destash a lot of craft items that I will not use
We only need something about 5x5x5 or so. Do you think you can find it this week or next? Not trying to be pushy in any way but don’t want to loose momentum.