Hardening M42 tool steel salt bath media

Kjeksen · Jan 1, 2019

Hi there, good folks of Practical Machinist forum.

I am about to harden a M42 tool steel blank. It is finished machined and stress relieved.

Looking into recomandations. It is recomended to harden in salt bath media. What salt is preferred to use?
Anything available in a "general store" ?

Ox · Jan 1, 2019

Good luck.
I haven't found hardly anyone over here that still run salt baths.
Even those that have it on their websites have told me that they quit running them several years ago.
I can only imagine that Europe would be worse yet as it seems to be an environmental thing...

???

--------------------------

Think Snow Eh!
Ox

Kjeksen · Jan 1, 2019

Ox said:
Good luck.
I haven't found hardly anyone over here that still run salt baths.
Even those that have it on their websites have told me that they quit running them several years ago.
I can only imagine that Europe would be worse yet as it seems to be an environmental thing...

???

--------------------------

Think Snow Eh!
Ox

Hmm.. Okei, what other good alternative for the home shop is there? I do not have a vacuum oven at hand.

Does anybody have experience on letting M42 air cool after hardening? What HRC did you see compared to oil quenched?

Joe Gwinn · Jan 1, 2019

Kjeksen said:
Hi there, good folks of Practical Machinist forum.

I am about to harden a M42 tool steel blank. It is finished machined and stress relieved.

Looking into recomandations. It is recomended to harden in salt bath media. What salt is preferred to use?
Anything available in a "general store" ?

See the steel folk on this:

High Speed Steel | M42 Tool Steel | M42 Steel

The Basics of Molten Salt Quenchants | Metal Finishing & Heat Treating Products | Heatbath / Park Metallurgical

Kjeksen · Jan 1, 2019

Joe Gwinn said:
See the steel folk on this:

High Speed Steel | M42 Tool Steel | M42 Steel

The Basics of Molten Salt Quenchants | Metal Finishing & Heat Treating Products | Heatbath / Park Metallurgical

From what I read it is about salt media quenching. I am looking for salt media bath to harden in. To protect the M42 steel from de-carburozation

jz79 · Jan 1, 2019

as a backup option - at the place you got your steel blank from you can ask if they have stainless steel foil for this exact purpose, wrap it and seal as tight as possible around the part, add a piece of paper inside to consume the oxygen, I've had some punches and dies hardened this way (not HSS though), there was basically no scaling

Joe Gwinn · Jan 1, 2019

Kjeksen said:
From what I read it is about salt media quenching. I am looking for salt media bath to harden in. To protect the M42 steel from de-carburization

Yes. The first url covers both, the second quenching. The advice is more general - ask the steel suppliers.

And the stainless steel foil bag trick does work. How big are the parts you are trying to harden?

Kjeksen · Jan 1, 2019

jz79 said:
as a backup option - at the place you got your steel blank from you can ask if they have stainless steel foil for this exact purpose, wrap it and seal as tight as possible around the part, add a piece of paper inside to consume the oxygen, I've had some punches and dies hardened this way (not HSS though), there was basically no scaling

M42 is most commonly oil quenched so foil bag of stainless is a no-no according to the book I read from William Bryson. This is due to un-even quenching in areas that the foil does not touch and that in turn induces more stress, uneven hardness and possibly fudges up the grain structure.

But.. I wonder how much HRC I actually loose from letting it cool in still air rather than oil quenching. These are small parts 22mm in diameter and 100mm long.

Kjeksen · Jan 1, 2019

Joe Gwinn said:
Yes. The first url covers both, the second quenching. The advice is more general - ask the steel suppliers.

And the stainless steel foil bag trick does work. How big are the parts you are trying to harden?

Could ask the steel supplier, but the steel is imported through a 3rd party. Not many domestic suppliers of M42 steel in Norway i`m afraid.

MattiJ · Jan 2, 2019

Kjeksen said:
Hi there, good folks of Practical Machinist forum.

I am about to harden a M42 tool steel blank. It is finished machined and stress relieved.

Looking into recomandations. It is recomended to harden in salt bath media. What salt is preferred to use?
Anything available in a "general store" ?

High temp salt baths are ordinary natrium cloride (table salt) mixed with barium chloride. Not sure but natrium chloride might work at HSS hardening temps even alone. Sort of harmless composition compared to case hardening or nitriding baths with cyanide salts.

Crucible says that you might lose 1-2 HRC on hardness if quenched in air instead of oil. Crucible Selector - REX® M42
So after hardening you are probably somewhere 63...65 HRC hardness, tempering could bring that up to 70 HRC or lower a bit depending on temp and what you want. Still plenty of hard for most uses.

edit: barium chloride was nastier(poisonous) than I remembered. Since its still part of almost every high temp bath recipe I assume it's really needed...

DDoug · Jan 3, 2019

Kjeksen said:
These are small parts 22mm in diameter and 100mm long.

Mail them to a proper heat treating facility, and get the parts done right.

Mark Rand · Jan 3, 2019

I have used sodium chloride/household salt for hardening EN24/4340/34CrNiMo6 steel gears. It melts at 802°C so it was ideal for the required 850°C. It should be noted that any salt bath, especially sodium chloride, will cause a flash rust coating to form on any unprotected steel in the same room :eek:

.

This was in a home shop, so The only health and safety department was me!

Propane gas heated trial.
Electrically heated final run.

Ox · Jan 3, 2019

Mark Rand said:
I have used sodium chloride/household salt for hardening EN24/4340/34CrNiMo6 steel gears. It melts at 802°C so it was ideal for the required 850°C. It should be noted that any salt bath, especially sodium chloride, will cause a flash rust coating to form on any unprotected steel in the same room .

This was in a home shop, so The only health and safety department was me!

Propane gas heated trial.
Electrically heated final run.

Was this just a "Because I can" project, or what?
Shirley 60 quid min would have been better money spent at the commercial H/T'ers eh?

What fer wire did you use?

---------------------

Think Snow Eh!
Ox

Mark Rand · Jan 3, 2019

Ox said:
Was this just a "Because I can" project, or what?
Shirley 60 quid min would have been better money spent at the commercial H/T'ers eh?

What fer wire did you use?

---------------------

Think Snow Eh!
Ox

It was a 'I ain't got enough money to pay to get someone else to fix this 1952 basket case HLV' project. Hardening the gears and shafts was fairly trivial after making them.

The heating wire wrapped around the crucible was Kanthal A1, although it is also rather delicate and short lived in the presence of salt fumes. The wire that the gear hung from was .024" steel MIG wire.

And yes, a lot of it was the learning excercise. Not worth it at all commercially, but good value as training.

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