4130 HRC45-49 3

[NickE]

Well in this thread {thread330-123117} I described a problem encountered in the production of a set of prototypes. Teh customer was informed of the problem with carburization. Engineering data was exchanged and the print was updated as far as the material call out.

Just to re-hash:
4130
50mmX15mmx6mm


is 45-49HRc too high of a spec for Q&T of this size of part? I would like an oil quench to reduce the severity, however normally all we do is supply the material type and the final required hardness.

thanks.
(yes I've checked the TTT curves this time.

 

[israelkk]

According to MIL-H-6875H 4130 can be treated upto 180-200ksi.

 

[Steve898]

Temper Hardness
300F 50-52 HRC
400F 47-48 HRC
450F 45-47 HRC
725F 40-43 HRC 180-200 ksi double temper
800F 36-40 HRC 160-180 ksi
1050F 27-33 HRC 125-145 ksi

In aerospace and military applications 180-200 ksi is maximum allowed for this steel.

Don't carburize unless you want over 53 HRC.
You can successfully harden this part in oil and temper to 45-49 HRC. It will harden about 1/4 inch deep all over.

 

[NickE]

Is the aerospace and military strength max for impact, or for SCC? Otherwise thanks for the info.

Do you suppose I need to specify the full heat treat requirement or can I just spec my final hardness? Or should I write a general internal specification (thats what was done for the raw material order)?

 

[israelkk]

The MIL-H-6875H does not explain why it just do not allow this alloy beyond this strength. However for 4340 it allows up to 200-220 ksi and then jumps to 260-280 ksi.

I not a metallurgist but I recall that between 220ksi to 260ksi the 4340 alloy is brittle. May be the same is for 4130 beyond 200ksi which limits it to the maximum 180-200 that MIL allows. Maybe one of the metallurgists in this forum can respond to this issue.

 

[metengr]

At 45-49 HRc you will have reduced toughness for 4130, and will have increased susceptibility to SCC in certain environments because of the higher strength.

I would specify the Q&T heat treatment in your general specification. I never like to specify just hardness.

 

[NickE]

Thanks guys, I'll buy a round of little purple stars for all.

I gues then I'll start writing the spec.

(on the toughness/SCC issue: This is the hot side of a specialized compressor, there is absolutely no chance of SCC, and any impacts should be relatively low energy since they can only occur at the initial start.)

 

[Steve898]

Check out 300M, an aircraft alloy that is a modified form of 4340. It is similar to 4340M. It is used at 280-300 ksi, 50-52 HRC and has very high impact strength. My 2 cents.

 

[NickE]

The problem Steve is that this part is going to be produced in a stamping press, then formed and heat treated, 4330, 4340, 300M are not generally available in HRPO coil form.

(4130 is really hard to find, but available; or should be, I think that the military is buying it all up for armor right now though)