Threading Nimonic 80A bolts

[Gem1]

Hi All,

We are trying to source Nimonic 80A bolts for a steam feed pump, to replace some that are approaching their end of life.

One supplier is proposing to machine the threads after heat treatment, as per the material spec sheet, but the other supplier is insisting that 80A bolt threads are commonly machined prior to heat treatment. I'm wondering if this is true, or if the second supplier is just trying to get away with the reduction in machining cost on the unheatreated material.

Has anyone else purchased Nimonic 80A bolts that were machined prior to HT?

Thanks,
Gemma

 

[TVP]

A typical production sequence for Alloy 80A bolting consists of the following:

Initial bar extrusion at 1125-1150 C followed by water quenching
Cold stretching 10% minimum
Solution annealing at 1080 C for 8 hours followed by air cooling
Thread rolling or cutting with single point tool
Precipitation treatment at 850 C/24h/AC then 700 C/16h/AC

I would clarify with your suppliers the exact production sequence that they are proposing, because there are a number of "heat treatment" steps for this alloy.

 

[Gem1]

Thanks for the information TVP, I'll ask the suppliers for more information.