D2 heat treat ?

S

Shipshores

Joined
Apr 2, 2016
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I'm conflicted about the heat treat time for d2. Most of the info I found says to heat to 1850f for 20-30 minutes. The spec sheets say it haves to soak a minimum of 45-60 minutes even when under 1". I would think that would enlarge the grain.
 
SS
If you haven't finished a blade yet, you might want to experiment a little.

There seems to be a great variance in how long a soak is needed to disolve all the carbides and how much advantage is gained by disolving more. The more carbon pulled from the carbides, the more carbon to enrichen the austinite prior to the quench; at which time you re-form carbides and martensite (if done correctly). The object supposedly is to get a nice even distribution of carbides in a nice uniform martensite matrix. The question is how even do you need the distribution in a knife blade and at what cost. Longer soak times supposedly increases the decarb which isn't good.

This being said, try soaking at 1450°F for until the blade is heated evenly (3 minutes should do for anything thinner than .25") then ramp up to 1875°F as fast as your oven will heat. Hold at 1875 for three minutes then quench in 130°f Oil. Yea forced air will work but I always get better results with oil.
If you want to experiment, try a 10 minute soak at 1875°f and quench in oil. You can also repeat the process for air quench at different soak times.
Hope this helps
Jim A.
 
D2 needs a long soak at temp to dissolve carbides and distribute carbon. The carbides are big and spheroidized. Otherwise you get a weak and uneven structure. It needs 30-35 minutes at temp for the carbon to dissolve and even out. You don't need to worry about grain growth from a long soak in D2, there are so many things in there pinning grain boundaries you could soak it an hour and the only problem would be too much carbon in solution, not grain growth.

Unless you have two ovens I suggest skipping the presoak (it doesn't do much for a knife) and going directly into an oven at full temp. This is because cheap knifemakers ovens tend to over heat areas in the oven and on the blade due to radiant heat from exposed coils so close to the work during an extended ramp up.

A simple HT for D2 that works pretty reliably:
Soak at 1880 30 min
plate quench to under 400F
Straighten any little bends with gloved hands while still hot if possible
go directly into subzero
temper twice in the range of 400-500. You can fixture to correct any bends during temper.




Edit to add: Small and poorly insulated ovens tend to loose a lot of heat when you open them and put in work, which still leads to a ramp up to temp and the risk of overheating spots. When I have to use a cheap knifemaker's oven I'll soak the oven empty 100F hotter than I plan to use it. Then I turn it off, put in my work, and turn it on again at the correct temperature. This minimizes extended time with the coils blazing.
 
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Thanks for the replies. I have several small knives ready for testing purposes. Ill try both ways to see which works best with my equipment. Do I need to use a foil pouch or can i leave plenty of extra meat to grind off due to decarb. I have a evenheat oven.
 
Stainless steel and air hardening steels are used as-is. Normalization and annealing are not in the normal skill set for most knifemakers.
 
Using the proper definition of Normalizing , air cooling won't work on air hardening steel as the steel will be hardened in the process. Don't worry just harden it and give it a sub-critical anneal [ 1200F for 2 hours ] giving you nice fine spheroid structure .

In general there is always a temperature gradient in a furnace . Don't crowd things . Near a heating element also creates problems. Try tricks like Nathan does or use barriers such as knife in a tube .
 
Nathan the Machinist said:
D2 needs a long soak at temp to dissolve carbides and distribute carbon. The carbides are big and spheroidized. Otherwise you get a weak and uneven structure. It needs 30-35 minutes at temp for the carbon to dissolve and even out. You don't need to worry about grain growth from a long soak in D2, there are so many things in there pinning grain boundaries you could soak it an hour and the only problem would be too much carbon in solution, not grain growth.

Unless you have two ovens I suggest skipping the presoak (it doesn't do much for a knife) and going directly into an oven at full temp. This is because cheap knifemakers ovens tend to over heat areas in the oven and on the blade due to radiant heat from exposed coils so close to the work during an extended ramp up.

A simple HT for D2 that works pretty reliably:
Soak at 1880 30 min
plate quench to under 400F
Straighten any little bends with gloved hands while still hot if possible
go directly into subzero
temper twice in the range of 400-500. You can fixture to correct any bends during temper.




Edit to add: Small and poorly insulated ovens tend to loose a lot of heat when you open them and put in work, which still leads to a ramp up to temp and the risk of overheating spots. When I have to use a cheap knifemaker's oven I'll soak the oven empty 100F hotter than I plan to use it. Then I turn it off, put in my work, and turn it on again at the correct temperature. This minimizes extended time with the coils blazing.
Click to expand...


What would you consider a "cheap oven"? Are you saying that the typical oven/kilns that we can purchase from the primary makers aren't up to snuff? If so, what are the choices, a home built with better insulation and shielded elements? I've noticed temp differentials in my oven and am concerned about the effects on my blades. My customers are asking for longer and longer blades and the tips are getting closer to the rear elements.
 
Nathan pointed out very spot on advices!!! A very neat trick to make the oven behave nicely ;)
I use a forge that i specifically built for HT, and the array of small venturis + a thick iron pipe muffle gives me even temp all over the blade consistently for any timing soak.
If i were to rely on an electric kiln i would check all the inside of the chamber with a proven TC to understand the different zones and to rig something accordingly to even out the temperature...key point is you should rely on the even heat from the chamber, not the one direclty coming from the elements, and the control TC should read as close as possible to the blade, not in i.e. the upper back corner.
 
Justice4all said:
What would you consider a "cheap oven"? Are you saying that the typical oven/kilns that we can purchase from the primary makers aren't up to snuff? If so, what are the choices, a home built with better insulation and shielded elements? I've noticed temp differentials in my oven and am concerned about the effects on my blades. My customers are asking for longer and longer blades and the tips are getting closer to the rear elements.
Click to expand...

You could have four Evenheat ovens for the cost of a single industrial or lab grade oven. It's a good value, but it has some shortcomings. A Lindberg Blue has covered coils and the door telescopes much deeper into the chamber when it closes. The 18" model is 5,600 watts, so it gets to temp much faster, and the entire chamber is heated very evenly without direct radiant heat from the coils or hot spots.

You can do a good heat treat with an Evenheat, but you can't just assume the entire chamber, and the work in it, is the temperature shown on the display. <-- people make that assumption and it's crazy.

There was a thread a little while back about a new EH with a fancy new touch screen and all these programs and even a cell phone control app? I just shook my head because they're giving the illusion of control (and making something simple unnecessarily complex).

I think it would help if they added coils to the door or eliminated them at the back of the oven. As it is, I wouldn't go longer than 16" in an 18" oven, and then only if you take precautions.
 
Yep, sort of like putting a PID controller on a 2BF. Whistles and bells don't equal the quality level on most equipment.

The degree of control is almost always a factor of the amount of mass on most tools.

A large drill press with a 2" quill and regulated by changing the belt position will be a lot more precise than a table top with VS.
A big, heavy mill with a massive quill will have much better control than a 75 pound mini mill with all sorts of lights and dials.
A 300+ pound HT oven with 4" thick walls and a stepped door will have better temperature control than a table top unit with a fancy controller.
2" of wool and 3/4" of refractory will be much more even in heating for a forge.

Yes, more mass equals more cost - but you usually get what you pay for.

A friend had an old massive industrial burnout oven. I have no idea what it weighed, but I suspect it was in the 300-400 pound range. It was analog, and had embedded coils. The chamber was about 16X20X12", and the unit was about 36X30X30". All the controls had was an ON switch, a dial that controlled the on/off cycle time, and a high quality pyrometer gauge. You set it by eye, and once at temperature and soaked it would stay at temperature all day long with almost no creep. By keeping a log of previous runs, you could determine the number on the dial to set it at. We would set it and go home. In the morning, the flasks were at exactly 1350F.
When he died, I never moved it because it was too big, and only went to about 1500F.
 
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Nathan the Machinist said:
You could have four Evenheat ovens for the cost of a single industrial or lab grade oven. It's a good value, but it has some shortcomings. A Lindberg Blue has covered coils and the door telescopes much deeper into the chamber when it closes. The 18" model is 5,600 watts, so it gets to temp much faster, and the entire chamber is heated very evenly without direct radiant heat from the coils or hot spots.

You can do a good heat treat with an Evenheat, but you can't just assume the entire chamber, and the work in it, is the temperature shown on the display. <-- people make that assumption and it's crazy.

There was a thread a little while back about a new EH with a fancy new touch screen and all these programs and even a cell phone control app? I just shook my head because they're giving the illusion of control (and making something simple unnecessarily complex).

I think it would help if they added coils to the door or eliminated them at the back of the oven. As it is, I wouldn't go longer than 16" in an 18" oven, and then only if you take precautions.
Click to expand...

First, thank you for the info. I've noticed even in the relatively small chamber of my 22.5 EH that there are differences in temperature. I'm getting busy enough just with simple word of mouth that better equipment would be worth the cost. I want to know that every knife I make is done properly before it goes to a customer. So far, I seem to be in the proper ranges - at least for CPM 154.

I was thinking of at least adding baffles to my current oven for the time being. Will the reflected energy from the brick I'm going to add be damaging to the elements? Also, since the thermocouple is located at the top, and is what drives the unit, should I move my knives up in the chamber, off of the floor ( knives sit edge up, in a ceramic fixture)?

It's funny, I just start to think I have a grasp of sorts, then bam, turns out I don't know sh*t. LOL Thank goodness for those that have the experience and are willing to share.
 
There is no reason on god's green earth that you can't get quality HT in a consumer HT oven. Heck, there are guys that do HT in a forge by judging color temperature alone (Hanson), but of course it takes years of experience to be successful doing something like that. The controls on an electric HT oven are for reference only, just like color temperature. And just like HT'ing in a forge, after gaining some experience your knife will come out properly heat treated. If you find you have hot spots, then use a muffle, problem solved. There are hot spots in forges as well, and also in industrial grade HT ovens yet these problems are overcome, also with experience. The bottom line is that it makes no difference how you generate the heat in a HT operation as long as you have the ability to generate enough of it for the proper periods of time. Taking good notes along the way will help with the experience curve and Rc hardness testing will provide the needed feedback.
 
TonyRV2 said:
There is no reason on god's green earth that you can't get quality HT in a consumer HT oven. Heck, there are guys that do HT in a forge by judging color temperature alone (Hanson), but of course it takes years of experience to be successful doing something like that. The controls on an electric HT oven are for reference only, just like color temperature. And just like HT'ing in a forge, after gaining some experience your knife will come out properly heat treated. If you find you have hot spots, then use a muffle, problem solved. There are hot spots in forges as well, and also in industrial grade HT ovens yet these problems are overcome, also with experience. The bottom line is that it makes no difference how you generate the heat in a HT operation as long as you have the ability to generate enough of it for the proper periods of time. Taking good notes along the way will help with the experience curve and Rc hardness testing will provide the needed feedback.
Click to expand...

Yeah, after thinking about it for a bit, seeing the prices of the lab quality ovens and my own testing of my blades, I'm thinking I'm fine with my current oven. Thanks.
 
Shipshores said:
If using a pipe in the oven should it have a end cap on the back side due to the rear element?
Click to expand...

All your trying to do is keep the coil from radiating directly upon the knife tip, so it really depend on the geometry...how long is the pipe, how long is the knife, the angle of the coil relative to the pipe opening, etc. I would say though that putting a cap on the end of the pipe would not be a bad idea in so much as it does add mass to the muffle which would even the heat out on the inside. I think a good rule of thumb would be not to have the tip of the knife closer than 2" away from a heating element, when not using a muffle.
 
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