Nihard residual stress

[Tmoose]

We are considering having rings 44 inch diameter cast from one of the nihards, then machined to create moderately accurate labyrinth grooves and a few tapped holes, and finally two saw cuts made to remove a section to allow installation.

One of the concerns is residual stress levels that would make the ring "spring" when saw cut. I see ASTM A532 -93a includes stress relieving as an option for both "hardened" and "as cast", without mentioning a process or resulting hardness. NIhard's low ductility (often described as NIL) makes installation of this part risky, and even more so if it must be spread to line up bolt holes.

Are we concerns justified?

thanks

Dan T

 

[EdStainless]

Yes,
Ask your vendor what stress relief he uses. If he doesn't know off the top of his head maybe you should search further.

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Plymouth Tube

 

[MOB1]

The information I have from Foundry Industry Research in Australia is that NiHard 1 and 2 may be heat treated at 250-300C for 4 to 16 hours or 4 to 6 hours at 425-475C followed by 4 to 16 hours at 250-300C. This treatmentis "designed to stress relieve the casting and temper the martensite formed in the as cast condition.."
NiHard4 is generally heat treated at higher temperatures and air cooled and may have a temper applied.

 

[arunmrao]

I am away from my desk on tour,you can find infomation onNiDI regarding machining and sess relieving.

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[arunmrao]

I wasreading your post yet again,I note,you need to saw cut for installation.My concern is more towards saw cutting,which can be risky, and you end up cracking the part. Can you consider,creating those pockets in the casting,thereby avoiding the need to saw cut.
You can thenuse a hand ginder and have an easy fit.

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr