4140 Cracking During Heat Treat
4140 Cracking During Heat Treat
(OP)
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
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





RE: 4140 Cracking During Heat Treat
RE: 4140 Cracking During Heat Treat
This sounds odd.
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: 4140 Cracking During Heat Treat
yield = 1460 MPa (212 ksi)
tensile = 1590 MPa (231 ksi)
elongation = 12.5%
impact = 15 J (11 lb-ft
I agree that it is strange to have so much warpage if oil quenching was used. Perhaps the quenchant was water or water + polymer and the higher quench intensity (faster cooling) caused the distortion. Perhaps parts cut out of sheet will respond better than those hogged out of bar.
RE: 4140 Cracking During Heat Treat
RE: 4140 Cracking During Heat Treat
I'm checking with our heat treater right now to see what they're doing (water or oil quench). We assumed oil because, as a few of you stated, that's what the specs call out to achieve that yield strength. But maybe they are using water. I'll post as soon as I hear back from them.
-Jesse
RE: 4140 Cracking During Heat Treat
RE: 4140 Cracking During Heat Treat
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: 4140 Cracking During Heat Treat
RE: 4140 Cracking During Heat Treat
We preheated to 1250 degrees F.
Raised temp. to 1520, water quenched in 120 degree water. Same process we used on first quantity of 6 that turned out good.
We did not notice the cracks at 1520, we believe during quench.
The very first ones we did, we oil quenched, we could not get the required hardness.
RE: 4140 Cracking During Heat Treat
RE: 4140 Cracking During Heat Treat
RE: 4140 Cracking During Heat Treat
You must consider more than the temperature of the quenchant. The heat capacity is another very important factor, and is one of the reasons to use oil instead of water.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: 4140 Cracking During Heat Treat
Kal
RE: 4140 Cracking During Heat Treat
4140 CS has a propensity to edge crack, die crack, and center crack during the heat treatment process.
I've checked all of my remaining reference books and none even give values for water quenching 4140.
If the part was a thick section and complicated I would normally normalize it prior to heat treatment, but your part shouldn't need this.
From Bethlehem's data to achieve 210 psi yield.
Oil quench from 1550°F into agitated oil.
Temper with out delay at 700°F. I would temper twice.
I don't care to use 4140 in this hardness range. We have developed information over the years that makes the toughness values suspect.
IMO if you had preexisting cracks in your parts they would have broken into pieces.
I think the warping will be mitigated by increasing the separation and using agitated oil of sufficient volume. I like 100::1 v/v.
RE: 4140 Cracking During Heat Treat
RE: 4140 Cracking During Heat Treat
I have lost many parts in heattreatment of 4140 grade!
RE: 4140 Cracking During Heat Treat
Of course, for cost reasons, we're opting not to use 4340...although that would be our preference, given the choice. :)
RE: 4140 Cracking During Heat Treat
Check also to see if they monitor the oil temperature prior to quenching. What is the acceptable temperature range that they have established for their oil quenching procedure?
Maui
RE: 4140 Cracking During Heat Treat
RE: 4140 Cracking During Heat Treat
Brine quenching is more severe than raw water quenching.
RE: 4140 Cracking During Heat Treat
What's the difference between 4140 and 4140H
Is 4140H the same as 4140HRA?
-Jesse
RE: 4140 Cracking During Heat Treat
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.
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: 4140 Cracking During Heat Treat
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).
RE: 4140 Cracking During Heat Treat
RE: 4140 Cracking During Heat Treat
For some reason, we're having a hard time finding any.
RE: 4140 Cracking During Heat Treat
http://www.emjmetals.com/