PDA

View Full Version : Need D2 HT for blade and slippie spring



Bruce Bump
09-25-2010, 12:04 AM
D2 heat treating at home is new to me. Does anybody have the procedure for the blade and spring for a slip joint? Thanks in advance for your proven method.

LRB
09-25-2010, 05:49 AM
I can't tell you anything about the blade, but as far as I know, a spring from about any steel needs to be in the mid to lower 40's in Rc hardness, so if you have a temper heat chart, it should tell you the heat range to get that.

murphda2
09-25-2010, 05:52 AM
Rusty McDonald makes a slippie or two from D2 if I'm not
mistaken. I'm sure he can help you out Bruce.

Bruce Bump
09-25-2010, 09:15 AM
I can't tell you anything about the blade, but as far as I know, a spring from about any steel needs to be in the mid to lower 40's in Rc hardness, so if you have a temper heat chart, it should tell you the heat range to get that.

I have always heard that springs need to be 48-49 rc for most all steels.

LRB
09-25-2010, 11:52 AM
Probably be fine. My info came from a metallurgist/longrifle maker who on occassion builds his own locks, but even metallurgists opinions vary.

LRB
09-26-2010, 05:13 AM
Bruce, here is the info given to me. It covers more than spring tempering that may interest you.
http://www.lrml.org/technical/gunsmithing/heattreatml.pdf

Rusty McDonald
09-26-2010, 06:53 PM
Bruce Ive been using D2 alot lately, I HT the springs with the blades and then temper the springs at 1200 for 2 hrs once, and the blades at 900*F for 2 hours twice. My blades have been comming out at 59-61 springs vary some from 46-49 I dont know why this is but they all work well.

Bruce Bump
09-26-2010, 08:09 PM
Thanks much guys!

Rusty, would you give me the entire run down. Times, soaks, temp, cyro? quench method? Come on buddy.

Rusty McDonald
09-26-2010, 08:26 PM
Ok,
My complete D2 run down
First I do my blades I usualy do batches of 3 - 4 knives.
Run up to 1200 soak for 20 min
then Run up to 1880*F soak 20 min - 30 min depending on thickness of the blades.
Then Plate quench, or Oil if they are small parts. But normaly I plate Quench with blown air.
I dont let my blades get below 125* before temper
then Temper for 2 hours at 900*F, 2 Times
Cryo after first Temper cycle

Then I do the springs
Same as above except the temper is at 1200*F Two hours ONE time.
I dont cryo the springs.

Bruce Bump
09-26-2010, 08:32 PM
Thanks Rusty. I knew some arm twisting would make you spill it all.
Its appreciated buddy.

Nathan The Machinist
10-03-2010, 05:38 PM
Dang Bruce. I wish you would have asked this on the other forum. I don't get time to come around here as much as I would like.

D2 is my pet steel. Has been for years. I have some hard earned experience that I'll share. Some of it contradicts information in earlier posts. So y'all please understand I'm just trying to be helpful.

The thing to understand about D2 is its tendency to retain austenite. In more current literature that value is frequently as high as 20%. This is due to the high chrome and high carbon and high austenitizing temperatures. That RA number has been revised up in more recent literature. It was worse than they originally thought. Something to think about.

The RA is a non-issue in stamping dies (what this steel was designed for), but it undermines fine edge stability in a knife edge where it acts kind of like perforations in a paper stamp.

There are more than one way to address the RA, but the two most common are a high temperature temper which decomposes it, or cryo as a part of the quench which converts it.

All steels are austenite when the quench starts. And ideally they're martensite when the quench stops. But the Mf for D2 is generally given as around -100F, so your quench isn't finished until you reach that. If you're stopping short of that before going into temper you're going to have a lot of retained austenite. It will stabilize during temper and at that point, even cryo won't budge much of it. At that point all you can do is the high temperature tempering to convert it.

Reasons why the high temperature tempers are not good for knife blades:
First you have to consider what the rockwell hardness reading actually measures. It is the depth a diamond penetrator penetrates the steel, and there are more than one mechanism that can affect this. In steels with a secondary hardening hump, what is actually happening is the carbon is leaking out of the martensite and forming carbides with surrounding alloys. It is these carbides that give the higher rockwell measuremement. But the martensite is losing carbon and thus becoming weaker. So you end up with weaker carbon lean martensite with a larger carbide fraction. Which, again, act like perforations in a paper stamp. It works fine in a big stamping die, but not a knife edge. Also, consider what alloy all that carbon is combining with - your free chrome. So, the high temperature tempers reduce fine edge stability and reduce corrosion resistance. I believe this is true for all steels.

RA and/or carbon lean martensite probably improve impact strength and/or metal fatigue resistance, which would be great in die. But the trade off probably isn't worth it in a knife.

Tempering a spring to 1200 will surely decompose most any remaining RA, which will convert to untempered martensite at room temp. All that untempered martensite (which could easily be 20%) needs to be tempered. In fact, most high temperature tempers in that range are done three times. One is probably not enough for your springs.

A simple D2 recipe that is proven to perform with the best (Dozier etc):

Austenitize at 1850, soak 30-40 min

Rapid quench (plate quench or slow oil, pull around 500 to straighten any bends)

Cool in water, dry off, continue quench to Mf in dry ice. Soak in dry ice 2-4 hours. Technically this is not cryo, it is simply finishing the quench. There are some theories about why the quench time at low temps is not instantaneous, but I don't really know.

Temper two time between 425-500 (450-475 is my normal range) for a target hardness HRC 60-63. This knife will be stronger than most any stainless, hold an edge longer than about anything I've tried, and has very good stain resistance.

In semi scientific tests, otherwise identical blades that received high temperature tempers, snap tempers before cryo and no cryo at all did not compair to this HT in fine edge stability and subsequent edge retention.