4340 vs A106 machining stability

[Tmoose]

We have the choice of machining a 60 inch diameter ring from a 4340 or A106 forged ring.
The forging house will deliver the ring stress relieved and normalized.

The ring will be cut into 6 identical segments after machining.

We are considering a second thermal stress relief after rough machining to reduce ( eliminate!) distortion/spring after cutting.

Is either material likely to offer better stability to reduce distortion after cutting?

Thanks,

Dan T

 

[EdStainless]

Nope, it is all in the stress relief (and how uniform the original HT is).
If you are that concerned you might add another one mid way through the roughing.

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P.E. Metallurgy, Plymouth Tube

 

[redpicker]

If your 4340 is ring-rolled, stress relieved, then normalized, it will probably move quite a bit after machining. 4340 can be slow to transform during normalizing, at relatively low temperatures (perhaps below 800F) and since the transformation products are considerably harder than the austenite, even with "still air" you can get quite a bit of residual stresses building up from the transformation.

The A106, on the other hand, will transform much more evenly, at higher temperatures, and you can expect quite a bit of stress relieving to occur after transformation. It still may move after machining, but I wouldn't expect as much as the 4340.

Stress relieving after normalizing would make the difference less, but I would still expect the 4340 to move more than the A106. If you stress relive after machining, you may get some movement during the SR, so the best shot would be a SR after normalizing.

 

[racookpe1978]

How accurate do you require the final machined part to be?

How much are you taking off of the original 60 inch dia ring - inside and outside?

 

[tbuelna]

4340 alloy steel and A106 carbon steel are very different materials. Both raw materials in bar form can be hot roll forged into a 60" diameter ring and be given a thermal stress relief. This would usually be followed by a rough machining to remove any defective surface material from the hot rolling operation. You did not mention what the cross section dimensions of the rough machined rolled ring are prior to splitting. These dimensions will have a significant effect on how much the shape changes after splitting. A heavy wall ring that has been stress relieved properly will probably not change shape much after splitting.

The most obvious consideration between 4340 and A106 is raw material cost. If the mechanical properties of A106 are acceptable for your application, then why would you consider using far more expensive 4340?