Forging Super Duplex Stailess Steel 2

[jimsan]

I understand that best forging practice for super duplex stainless steels (eg A182F55) requires water quenching immediately after forging is completed rather than air cooling even though the parts are subject to subsequent solution treatment.
Has anyone had experience of water quenching this material after forging and if so how was it done in a practical sense?

 

[metengr]

Having been exposed to this material at a Code committee level I never heard of such a "best forging" practice after hot forming. The F55 is readily hot formed and can be air cooled before a proper solution treatment as a separate processing step. Frankly, I see no benefit to be gained by such a forging practice.

I could envision after hot forging if the material is immediately reheated to the solution treatment temperature range and water quenched, as a single operation. Typically, soak time prior to forming is critical for these alloys.

 

[EdStainless]

The only advantage that I can think of is that if you air cool and form some intermetallics in heavy sections you will need a longer anneal later to remove them.
These alloys are very cooling rate sensitive.

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

 

[SJones]

Ed's reasoning is outlined in EEMUA 218 as a recommendation to quench after hot forming. Other documents, such as API 938-C, simply demand a water quench after final solution anneal.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[metengr]

I am not sure I would describe water quenching after hot forming as "best practice".

 

[BMKR]

Aren't you risking cracking when air-cooling Duplex steels as opposed to insulated slow cooling?

 

[metengr]

BMKR;
The duplex and superduplex steels are not to be slow cooled because, as mentioned above, intermetallic compounds will form. These alloys are designed for rapid cooling rates. Hot forming temperatures and maintaining the temperatures are more critical for these alloys.

 

[BMKR]

I meant to say post forging somewhere in there. Slow monday...

 

[BMKR]

Just wondering really if the intermetallics, mentioned above would pose as initiation points for cracking seeing as there will be quite a bit of internal stress post forging.

 

[metengr]

Depends on the cooling rate, forming temperature and complexity of the forging. If slow cooled, the volume fraction of intermetallic precipitates could be significant, and affect ductility.

 

[BMKR]

So the Forging/HT process of F55 (ASTM A182) would be as follows:

1) Forging operation (simple forging IE pancake)
2) Air-cool
3) Solution Treat
4) Quench (depends on desired results as far as polymer, oil, water go)

So the quench really controls how the intermetallics form?

 

[metengr]

Yes, correct. Quenching, if done properly, will provide a uniform duplex microstructure with very low volume fraction of intermetallic compounds.

 

[EdStainless]

The faster the cooling rate from forge the less time you will need at anneal temp to achieve clean microstructure.
The intermetallics will seriously lower the corrosion resistance long before you will see the impact on mechanical toughness.

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

 

[jimsan]

Thanks guys for all of your input.

EEMUA 218 does imply that water quenching is preferred immediately after forging (not air cool) even though the parts are subject to solution treatment and water quenching subsequently.

The reasons are that undesirable intermetallic phases may be present in the structure and may not be removed after the heat treatment.

I was kind of hoping someone had had some experience of how water quenching after forging is actually done in a practical sense.My assumption is that you need a facility similar to a heat treatment quench tank which is temperature controlled and monitored and water is constantly circulating.

 

[BMKR]

The press operator would most likely place the forging into a quench bucket

 

[abramb]

jimsan,
From my quite short experience, you don't need the same quenching equipment used for quality heat treatment when you perform water quenching after forging.
It's enough that the quenching bath has enough capacity to rapidly cool the forging, to avoid/limit the presence of intermetallic phases.

Superduplex (type 25Cr) material grades are more critical than Duplex (type 22Cr) material grades.
Superduplex grades have also the problem of carbide nitrides formation.


Attilio Brambilla
Material Engineer

http://it.linkedin.com/pub/attilio-brambilla/25/465/544

 

[EuroWeld]

After solution annealing the forging will be removed from the furnace at a temperature about 1050 degrees celsius. Within a minute the forging will be transported to the water quench bath and will be lowered there! In between about 985-550 degrees celcius intermetallics will grow! So in this phase rapid quenching is needed, see phase diagram! In this zone nitrides, sigma and chi will form! Quenching must be done in minutes! Phase diagram also shows that cooling rate is more critical for super duplex like F53 and F55!

Hope this help you to get an idea about how this work!

 

[DXM]

The main problem of water quenching after forming, without a previous solution annealing treatment, is the risk of craking ("clink") above all in hight diameters. How could this problem be solved?

 

[BMKR]

@DXM, I do not believe it can be avoided. We form, open air cool, solution treat, and quench.