4140 Possible Distortion Quench/Temper?

[tharding247365]

Long story short, making a tube with internal splines, and some other geometry on one end. I require a hardness of about 52HRC through hardened for it's mechnical proerpties, just hoping it won't be too brittle.

For the broach to go through the part cannot be any harder than 32HRC. My plan was to do the machining in the annealed state, then quench and temper after. Anyway to minimize distortion?

 

[CoryPad]

Yes, you can make sure the chemical composition of the steel is towards the upper limits so that you don't need a severe quench to harden the part. You can use a lower austenitizing temperature and a higher quenchant temperature to lower severity. Look into hot oil quenching.

 

[tharding247365]

We don't have much control over the composition we receive. However, I've sent out what we get to see what composition we were currently getting. We recieved as follows:

Element Sample
C 0.48
Mn 0.76
P 0.017
S 0.019
Si 0.24
Cr 1.12
Ni 0.02
Mo 0.22
Cu 0.03

How does this look? I'll look into hot oil quenching. Never heard of that. That about the only other thing that we can control?

 

[CoryPad]

Your carbon concentration is very high for 4140, so that will provide high hardenability.

Hot oil quenching is also known as marquenching, you can search the Internet for more info. Another option for low distortion is austempering (to produce brainite) instead of quench hardening plus tempering. This also will be much tougher at 52 HRC than Q+T martensite would be.

 

[tharding247365]

I've talked to my heat treat vendor about the hot oil. Our parts were quenched in 156.8F oil, he said he can heat it up to 160F max. They don't do the 220F stuff. This might help a bit if I go this route.

However, austempering looks perfect for this application. Doing a little research it does look ideal for sure. I'll ask our vendor about that as well. You've been a big help CoryPad!

I do believe we actually use 4147, slight variant of 4140 which may help in my favor with the higher carbon content.