Non-magnetic properties of Hadfield manganese steel

[DAVIDSTECKER]

I am working on a project that has cast Hadfield manganese steel (ASTM A128 Gr. A) parts.
One of the main properties required is that the magnetic permeability needs to be less than 1.2mu.
The foundry that is casting the parts for me has experience with casting Hadfield for wear resistant parts, but they informed me today that the castings are not passing the permeability test.
What processes affect the magnetic properties of the Hadfield?
The castings have been heat treated but I do not know what temperature or how long it they were held at temperature. I am assuming (dangerous word) that the heat treating procedure in the MIL specification was followed.
If the heat treat was done correctly, what else could affect the magnetic properties?

 

[arunmrao]

What parts and application please. Hadfield steel,as you might know is work hardenable. Any factor contributing to raise of Ms temperature will make it magnetic. Please check the heat treatment cycle and also the microstructure. However,I stress once again that this alloy being nonmagnetic is short lived. any impact on the part,will tend to harden it therby rendering it magnetic.

 

[EdStainless]

They may have 'fixed' their shot blasting and are now working the material too much.
They may also be shaving the chemistry too much. It might be inadvertent as there are other austenite stabilizers other than Mn (Ni, Cu, N, C) and reduction in these could result in higher perm.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[DAVIDSTECKER]

arunmrao; the end prouct is a boat anchor.
It appears that heat treat did play a role in this.
A keel block was poured and sections were cut off for testing the physical properties. The cut off sections did go throught heat treat with the rest of the parts.
The problem is that the remaining keel block that the founrdy was testing for the internal section permeability properties had not been heat treated.
Hopefully the issue has been resolved.
Thank you for your input.
Best regards, David

 

[arunmrao]

David,can you please explain why you need nonmagnetic properties for a civilian boat? Also how will the work hardening happen in this alloy for it to be exploited?

I have been involved with military applications where magnetic permeability ,is of extreme concern.

 

[DAVIDSTECKER]

These are for the military. Minesweepers I would guess.

 

[arunmrao]

That answers all my concerns. Thanks

 

[TemperedMartensite]

Another possibility is segregation during the solidification process. This can lead to "hot spots" during testing.

Cold work or strain hardening in general is a prime suspect. As it was pointed out that the introduction of strain could cause the formation of martensite... which is magnetic.

 

[mcguire]

I'm a little late here, but isn't delta ferrite present in as-cast high Mn steel?

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[metengr]

If you look at the Fe-Mn-C phase diagram it is possible to have ferrite - austenite - carbide at RT. Most likely, during solidification, the carbides precipitate out along grain boundaries versus ferrite and this results in poor ductility until heat treatment is performed - solution anneal and quench.