Maraging C300 Low Hardness

[novateague]

We just had some Maraging C300 parts come back from a standard aging process (6 hrs @ 900F, air cooled) with a 47.5 HRC hardness.

Typically it should be 50-55 HRC. What would be the best course of action to achieve higher through hardness without case hardening or nitriding?

 

[mfgenggear]

Op
Was this operation in house or outside supplier.

Run test samples run ar a longer time .
If in-house contact a consultant .
If outside discuss with your heat treater It's all about the recipe. Time vs temp,

 

[novateague]

Op
Was this operation in house or outside supplier.

Run test samples run ar a longer time .
If in-house contact a consultant .
If outside discuss with your heat treater It's all about the recipe. Time vs temp,

HT was done by a supplier that is normally very reliable. Could be a material issue as well.

My first thought is run it for 10 hrs, but I'm not a materials expert...I have no idea the effects of reheating the material.

Maybe a cryo treatment would convert more Martensite and harden it up too?

 

[mfgenggear]

Op
Was this run in a vacuum or inert atmosphere.
If not the surface will have been oxidized.
Is there stock in the outer surface.

 

[SWComposites]

Have you asked the supplier for their advice? Did you specify the details of the aging process or did the supplier select the process?

 

[novateague]

I don't have details on their equipment yet, but they heat treated C350 without issue. This is their first time with Maraging steel.

If it wasn't an inert gas or vacuum furnace, could the material have the scale removed and then reheat treated in a vacuum furnace?

 

[mfgenggear]

Op
Return the parts to vendor, have them section one part for metlab test, due micro hardness test from .005 from the surface . At increments of .010 or .020. For .250 depth or more.
The hardness may be acceptable at the core.
Regardless discuss with the vendor for options.

 

[novateague]

Op
Return the parts to vendor, have them section one part for metlab test, due micro hardness test from .005 from the surface . At increments of .010 or .020. For .250 depth or more.
The hardness may be acceptable at the core.
Regardless discuss with the vendor for options.

Thanks for the info @mfgenggear - that's interesting that the core hardness may be to spec but the surface drops off.

If that is the "case" (no pun intended), we may end up having the parts Ion Nitrided as we were considering testing the effects anyway.

My main concern is reduced strength at the lower hardness levels. I haven't found a good correlation between strength and hardness for C300.

 

[EdStainless]

Did you check the raw material?
Does the original MTR show aged property testing?
II also suspect that this is a surface issue.

 

[novateague]

Did you check the raw material?
Does the original MTR show aged property testing?
II also suspect that this is a surface issue.

We always solution anneal Maraging material once again before machining. I haven't checked the hardness results from that condition yet.

If it is a surface issue, that would be much easier to rectify.

Are "failed" heat treatments typically just reheated?

 

[mfgenggear]

Depending on the specification.
On the AMS spec I believe it allows 3 reworks. And generally it is rework due to to much distortion.