4140 heat treating questions

[Borealis]

We have some 4140 parts that we plan to heat treat next week in our electric atmospheric heat-treating oven. These parts are one-offs for internal r&d, so we won't disappoint any customers if we get this wrong on the first try.

These parts are roughly 4" diameter and 1.75" thick. The ASM heat treating handbook is clear on the temps, soak times, and tempering conditions. A friend said we should wrap these parts in heat treating foil for the long high-temp soak but I've never used the stuff with O1 or A2. Is foil necessary with 4140? I see nothing in the handbook discussing quenching parts wrapped in foil. Do we rip the foil off fast and then quench? Or just dunk the wrapped part? Or just forget about the wrap altogether? I left the diameter about 0.012" oversize for the grinding allowance.

 

[Freedommachine]

It will get super scaley if you don't wrap it. Other than that, it won't hurt anything at all to omit the foil.

Make sure it is free from oil and that will help a bit.

 

[Covenant MFG]

The only point in using foil usually is so you don't oxidize it or decarb the surface. With that oversize though I think you'll be fine, especially if you don't overheat it for the soak.
Foil might act as an insulator if you're doing an oil quench- most guys who use foil are plate quenching a stainless.

 

[EmGo]

We have some 4140 parts ....

These parts are roughly 4" diameter and 1.75" thick.

You know you're not going to get your target hardness all the way through with that alloy, right ?

 

[gbent]

With only .010 for clean up I think you will have decarb in the finished surface if not wrapped in foil.

 

[dgfoster]

You may want to water quench parts of this thickness assuming they are more or less hockey puck shapes.

Bill Bryson has an excellent text for folks doing small quantity heat treating. He discusses 4140 in some detail. Also when to use water vs oil.

Amazon.com

Denis

 

[Borealis]

You know you're not going to get your target hardness all the way through with that alloy, right ?

Yessir, only aiming for Rc 48-50 on the exterior after tempering.

With only .010 for clean up I think you will have decarb in the finished surface if not wrapped in foil.

If you use foil, do you quench the part in the foil or does the part need to be taken out beforehand?

You may want to water quench parts of this thickness assuming they are more or less hockey puck shapes.

Bill Bryson has an excellent text for folks doing small quantity heat treating. He discusses 4140 in some detail. Also when to use water vs oil.

Amazon.com

Denis

Thanks for this recommendation. I've seen other people mention the book before but I just ordered a copy.

 

[technocrat]

Some people add something like paper or a sliver of wood in the foil to scavenge the oxygen in the package. I have never tried it, but it is supposed to reduce scaling. I can't see that there would be any negative effects.

 

[William Lynn]

Are you using 4140 annealed or pre-hardened? What Rockwell hardness are you shooting for?

 

[sfriedberg]

If you use foil, do you quench the part in the foil or does the part need to be taken out beforehand?

For air hardening parts, leave them in the foil. I don't believe you will get a a remotely good thermal transfer if you leave the part in the foil while quenching in oil or water. But maybe someone has experience to the contrary.
For oil or water quench, it's much better to cut the foil envelope open with a set of shears directly over your quench tank and let the part drop in. Spending any amount of time messing around with the part is just asking for an ineffective, too-slow quench.

 

[EmGo]

For air hardening parts, leave them in the foil.

It's 4140, not a chance. But he's got his own (electric ?) oven, yes ? Maybe try flooding it with nitrogen, that's cheapish, and skip the whole foil wrap thing. It's hard enough to get chicken out of that stuff, much less a red hot piece of steel.

 

[dgfoster]

For air hardening parts, leave them in the foil. I don't believe you will get a a remotely good thermal transfer if you leave the part in the foil while quenching in oil or water. But maybe someone has experience to the contrary.
For oil or water quench, it's much better to cut the foil envelope open with a set of shears directly over your quench tank and let the part drop in. Spending any amount of time messing around with the part is just asking for an ineffective, too-slow quench.

Yup, that part has enough mass to alow for a little fumbling. But, I make sure I have everything at hand when I, wearing welding gloves and using a vise-grip, snag the bag out of the furnace with a bucket of oil at my feet. You will need to slash the foil which, btw, gets less less flexible (sort of brittle) in the heat treat, and grasp the part or have wire already twisted on through a hole or drop it into a coarse mesh basket. Just dropping it into the oil or water does not provide essential-to-success aggitation. You have to VIGOROUSLY and rapidly move the part up and down in the quench to keep cool quench in contact with the surface. Bryson covers this in his book.

With a little pre-planning and practice it works fine.

Denis

 

[Borealis]

If the foil is sort of a hassle, what do you gents think about anti-scaling compounds like this:

Anti-Scale Coating for Heat Treating ATP 641

Liquid anti-scale compound can be sprayed, flow coated, brushed or dipped onto your knife blade to minimize the formation of oxide scale and drastically reduce pitting and decarb loss during heat treat. Reduce re-work time after heat treat with the fantastic option to foil wrapping. Has a hot...

knifemaking.com

or

PBC (regular) Anti-scale powder 1lb

PBC Regular Anti-scale compound This PBC anti-scale compound protects your blade from decarb and scale damage to 1650F degree during your heat treat with out tool wrap (heat treat foil). Directions: Pre-heat your steel dies, tools, or parts to about 450°F (varies per application), ensuring...

usaknifemaker.com

I'm sorta leery of borrowing techniques from the knifemaking crowd but these seem interesting if they in fact perform as claimed.

 

[EmGo]

If the foil is sort of a hassle, what do you gents think about anti-scaling compounds

Hobbyists. All the commercial heat treaters I have used just flooded the oven with an inert gas. Nitrogen is cheap.

 

[gbent]

I have seen where anti-scaling compounds should not be used in electric ovens with exposed elements.

 

[sfriedberg]

I've used PBC occasionally in a Thermolyne burnout furnace without getting into too much trouble.
I mostly heat-treat A2, and it mostly goes in a foil wrapper.

 

[Borealis]

Yup, that part has enough mass to alow for a little fumbling. But, I make sure I have everything at hand when I, wearing welding gloves and using a vise-grip, snag the bag out of the furnace with a bucket of oil at my feet. You will need to slash the foil which, btw, gets less less flexible (sort of brittle) in the heat treat, and grasp the part or have wire already twisted on through a hole or drop it into a coarse mesh basket. Just dropping it into the oil or water does not provide essential-to-success aggitation. You have to VIGOROUSLY and rapidly move the part up and down in the quench to keep cool quench in contact with the surface. Bryson covers this in his book.

With a little pre-planning and practice it works fine.

Denis

Received the book yesterday. It's an easy read and by far the most practical and concise book on heat treating I've ever come across. When Bryson gives instructions about tempering, it gets a little scary, though. Things go all caps and he writes, "IT IS CRITICAL THAT TEMPERING TAKES PLACE AS SOON AS THE PARTS REACH 125 TO 150 DEG F. IT'S A MATTER OF LIFE OR DEATH--life or death of the tool or parts."

I never recognized how important it is to temper immediately after the quench. Now I've bought another oven that will be preheated to the tempering temperature so we can follow Bryson's advice to the letter. The more you learn, the more money you get to spend

 

[dgfoster]

Received the book yesterday. It's an easy read and by far the most practical and concise book on heat treating I've ever come across. When Bryson gives instructions about tempering, it gets a little scary, though. Things go all caps and he writes, "IT IS CRITICAL THAT TEMPERING TAKES PLACE AS SOON AS THE PARTS REACH 125 TO 150 DEG F. IT'S A MATTER OF LIFE OR DEATH--life or death of the tool or parts."

I never recognized how important it is to temper immediately after the quench. Now I've bought another oven that will be preheated to the tempering temperature so we can follow Bryson's advice to the letter. The more you learn, the more money you get to spend

Yes, I’m not quite sure where, all that enthusiasm for a immediate temper comes in. It may be possible that things could spontaneously, crack or shatter, if they were not immediately tempered, but I certainly have never seen that or anything approaching it.

Glad you like the book.

Please report on your findings and any suggestions that you might come up with.

Denis.

 

[lr harner]

Normally i would foil and plate quench but with that thickness you should have the thremal mass to allow for cutting the pouch and dropping into something like parks 50 quenching oil. what hardness are you shooting for? ive never been a fan of high tremp tempering. so to clean up any RA i do a LN cryo treatment before tempering and then temper at 400 (knife alloys) im not sure if 4140 really would have much RA or even benefit from a cryo cycle. i found a HT that puts 4140 to 55Rc that uses 400f temper