4140 Cracking During Heat Treat 1

[Jboy333]

Can anyone provide any advice on a problem we're having with heat treating a 1/2" square 4140 rod.

We're shooting for a yield strength of 210 ksi. The first batch came back great, no problems.

The second batch, all but 2 of 15 came back terribly warped and with many cracks along the length of the rod. We sent samples of the cracked rods to the steel supplier's metallurgist and he said that there appeared to be a seam in the metal, and that was why it cracked...so we were reimbursed.

The next time we ordered a 6" wide sheet of 1/2" material and laser cut the parts out (instead of machining down a nominal 1/2" sq rod to 1/2"). We had a message from our heat treater, that these bars again cracked.

We've spoken with a few different heat treaters and they feel we should easily be able to hit 210ksi with 4140. Before we send out any more parts to be treated, I was wondering if anyone had any advice on what might be going wrong here.

Thanks,

-Jesse

 

[arunmrao]

BillPSU

Brine quenching is more severe than raw water quenching.

 

[Jboy333]

Hey guys,

What's the difference between 4140 and 4140H

Is 4140H the same as 4140HRA?

-Jesse

 

[EdStainless]

The H is material that meets restricted hardenability ranges. In otherwords it will come out the same twice.

I haven't worked in Q&T for years, but we used to test the quench rate of our quenchants to make sure that they still worked the way that we wanted them to. This along with temp control is heat treating 101.

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[TVP]

Heat-treatable grades like 4140 can be ordered to 3 different compositions/hardenability ranges. The standard composition is defined in SAE J404. The composition and hardenability of 4140H is defined in SAE J1268. The last type is "restricted" hardenability, 4140RH, which is defined in SAE J1868. In addition to the chemical composition, H and RH grades have requirements for hardenability as determined from a Jominy End-Quench test (SAE J406 or ASTM A 255). 4140 and 4140RH have the same chemical composition, but SAE J404 makes no specific mention of hardenability, and therefore there can be considerable variation in heat treating response. 4140H allows for a slightly larger range of C (0.37-0.44 instead of 0.38-0.43), Mn (0.60-1.00 vs. 0.75-1.00), and Cr (0.75-1.20 vs. 0.80-1.10) in order to allow steelmakers the opportunity to vary the composition but still maintain a guaranteed hardening response.

With regards to 4140HRA, this is not a standard designation. I would guess that this is supposed to mean someone measured the hardness using Rockwell scale HRA (same indenter as HRC but only 60 kgf instead of 150 kgf).

 

[unclesyd]

HRA can also mean Hot Rolled Annealed, especially when used with bsr stock.

 

[Jboy333]

Does anyone know of any suppliers that handle 4140H.

For some reason, we're having a hard time finding any.

 

[unclesyd]

You should give these people a call. You might also look at the 4142 materials.

http://www.emjmetals.com/