What's new
What's new

Heat Treating D2 Tool Steel

I've done 2" diameter with a forced air quench. 6" diameter will almost certainly need an oil quench to get any hardness. It's just too large for air quench alone you need a minimum 30°C per minute quench rate down to 475°C. Use a separate, pre-heated oven/kiln for the temper if at all possible, since the wait for the first kiln to cool down may be long enough to allow cracking in the work piece if there are any sharp corners or stress raisers. The tempering is important with D2. It's not verysensitive to too much soak time, but very sensitive to over-temperature. Don't allow it to exceed 1040°C.

PS:- If you haven't found it yet, this is an excellent site for steel hardening information and comparisons. https://steelnavigator.ovako.com/heat-treatment-guide
(y) all I'll add to this is that with forced air you need to control localised accelerated cooling. For example if an edge stops glowing and goes black while the rest is still bright, this will likely be a failure point. If you are going to try this consider one or more baffles to create Eddie's and keep the direct air flow off any particular part.

I've tried oil quench too, and I found that if you use peanut oil and boil it first it gives good results without risking cracking. Smells like take- out too. Remember though that this was on much smaller material, so you'll likely need a lot of oil to make this work for you. I also tried using a diesel pump and injector to atomise oil in front of a fan/blower , with the D2 turning on a rotisserie. This gave fast cooling, coated the steel with oil and kept the oxygen off it (once coated in oil). The downside is that if you don't want the black finish then you need to refinish it.
 
Good morning everyone.
Trying my hand at heat treating D2 for the first time. The parts are rollers for a tube mill - 6" diameter, 4.5" high with a 1.8" bore down the middle. I attached the process I intend to follow, put together from a few resources online. I will be using a ceramic furnace like this - KILN and my part is wrapped in SS foil. How does my process look to guys with experience doing this?

Stress Relieving
After rough turning in the lathe, heat to 600C(1112F) slowly, hold at this temp for 1 hour – cool in air to room temp.

Hardening
Preheat parts to 775C(1427F) and allow to fully soak, 1 hour. Heat furnace slowly to 1000C(1832F) and hold for 30 minutes per inch of ruling section.
My parts are 6” diameter rollers. So hold for 3 hours?
Cooled in air after hardening.

Tempering
Start tempering immediately once tools have reached 50C(122F)
Heat furnace to 250C(482F), hold for 2 hours. Hardness desired: 58-61RC
Repeat this process for double tempering.

Thanks in advance.
Thanks for posting this. We recently started getting a lot of D2 stuff in our shop and it all needs repairs. Granulator/bed/fly knives. Definitely need to understand this process before welding, so all this info posted by you and commenters is excellent!
 
Please post the results. May help someone in the future.
One thing I learned through my experience is the formula for time and temp are general. like a food recipe. Make it work for you and the part. It doesn't have to be exact, especially when you get into oddball parts used in dies and molds. It was hard for me to wrap my head around at first with a machinist/engineer mindset. When in doubt just add a little time and/or temp. D2, A2 and S7 are nice to work with when it comes to heat treating. 60-65RC is pretty easy to hit on a consistent basis.
If i needed every question answered that i have and could have a reference available at any time for D2, O2, A2, etc, what would be a great place to start? I understand the O means oil hardening and A means air, and that D2 needs to be annealed before it can be welded, then rehardened, but thats about it. Any great books or PDF's out there you would recommend that covers all if not most? Basically just need to be able weld repair and surface grind D2 and O2 granulator, bed, fly, chipper, etc. blades
 
It actually does have a programmable ramp controller, this is the oven I am using: https://www.soundingstone.com/colle...mt1018-3-pottery-ceramic-kiln-208-or-240-volt
But would the oven internal temp and the test part itself have different temps? The part was still hot to touch this morning and the oven was cooled off already, so thats why I'm wondering.
My reading is that D2 has to be removed from the oven and quenched in still air. You may want to place it on a grate for full circulation.
 
If i needed every question answered that i have and could have a reference available at any time for D2, O2, A2, etc, what would be a great place to start? I understand the O means oil hardening and A means air, and that D2 needs to be annealed before it can be welded, then rehardened, but thats about it. Any great books or PDF's out there you would recommend that covers all if not most? Basically just need to be able weld repair and surface grind D2 and O2 granulator, bed, fly, chipper, etc. blades

Chuck nailed it on the book.^ There is a lot of conflicting info online so I experimented a lot. I have tig welded hardened D2 successfully with small welds and peening. Tool should be annealed and hold 500-700 degrees through the part while welding and cool very slowly, in a kiln with temp control is best. Used to burry it it warm sand and let it cool but depending on the size and shape sometimes that cools it too fast.
 
I believe I recall a guy writing in complaining that he ruined a part made of D2 with improper HT. https://hudsontoolsteel.com/technical-data/steelD2 has some interesting info. For your large part they suggest a double preheat. First slowly (<400F/hr) to around 1200F. Soak, then to ~1425F. Then to 1860F. Air cool from 1625F to get through-hardening. This does suggest that a ramp programmable controller would be useful. At about a grand per foot for 6” D2, suggest checking with the supplier for mfr’s HT recomendations. Good luck.
 
I made the mistake of assuming the oven temperature is the same as the part temperature. Result were soft parts.

Bryson recommends a window and look to see if the part is the same color as the oven walls. He does not like opening and closing the door of the oven to check.

This can be tricky if the time at temperature is short.

How do the professional heat treater's do this?


Chuck
 
Never do a hardness test on an untempered part. It can explode, with possible painful to life changing results.
 
I made the mistake of assuming the oven temperature is the same as the part temperature. Result were soft parts.

Bryson recommends a window and look to see if the part is the same color as the oven walls. He does not like opening and closing the door of the oven to check.

This can be tricky if the time at temperature is short.

How do the professional heat treater's do this?


Chuck

It is just trial and error. There is no way to read the part temp internally. When in doubt, always add time
 
It is just trial and error. There is no way to read the part temp internally. When in doubt, always add time
We've drilled holes in parts before to add thermocouples. Did it on 14" thick steel.

Parts were sacrificed, of course. Did it on already scrapped parts to verify what we had predicted. The entire heating cycle was charted out with samples every minute for 12+ hours.
 
We've drilled holes in parts before to add thermocouples. Did it on 14" thick steel.

Parts were sacrificed, of course. Did it on already scrapped parts to verify what we had predicted. The entire heating cycle was charted out with samples every minute for 12+ hours.

I like that kind of testing. What kind of steel was it? Were the holes for the thermocouple plugged or open during the test?
 
Would a non-contact thermometer be of value in determining part temperature? Of course it would be the surface temperature of the foil covering the part but might be better than guessing?

I like the thermocouple approach especially for large parts with lots of cross section.

1690915529839.png
This one reads up to 2400F.

Chuck
 
I don't think an IR thermometer would get you the accuracy needed.

When austenitizing steels, your target temperature window is about 50 degrees F. If you undershoot, you won't get the proper hardness, and if you overshoot, it'll delay your air quench at best with potentially worse effects.

(Edit to add: pulling a part out of the furnace to check temperature might be no-go anyway as it'll begin cooling immediately as you open the furnace door).

You can get a thermocouple that plugs into a multimeter, IF you don't trust your furnace's thermostat. That said, furnaces are generally accurate enough. A common issue is that your ramp up time is too fast and your parts don't have enough time to reach proper temp. Best to ramp up a bit more slowly and add a delay somewhere before you reach max temp. Don't go overboard though. Going too slow has detrimental effects as well.
 
Last edited:
I like that kind of testing. What kind of steel was it? Were the holes for the thermocouple plugged or open during the test?
It was a very high grade of maraging steel requiring high hardness and toughness thru the entire section. Core samples were machined out later and sent in to a lab for destructive testing.

Yes, the thermocouples were plugged using some sort of insulating grout-like material.
 








 
Back
Top