Duplex Stainless Steel and Austenite / Ferrite Ratio 3

[Metcorr]

In general when duplex stainless steel is mentioned, it is understood that it will have a 50:50 ratio of austenite and ferrite. The welknown 2205 is an example.

But, for sake of definition, does duplex stainless steel can also have 20:80 or 30:70 ratio of austenite and ferrite or ratios other than 50:50. Are any such duplex stainless commercially available.

 

[gr2vessels]

Metcorr,
The issue of unbalanced content of austenite and ferrite, is in the welds, rather than the parent material you have purchsed. If the raise of ferrite in the weld is beyond approx. 70%. these welds may become brittle with the host of consequences. Lower than 30% ferrite would diminish the duplex properties.
The duplex corrosion resistant material deposited as weld overlay on carbon steel must be carefully monitored for the ferrite content, the problem is the accuracy of the estimate in absence of precise measurement. Many studies have been published, one from the AWS Weld Research is the following link:

http://www.aws.org/wj/supplement/wj0506-91.pdf

cheers,
gr2vessels

 

[EdStainless]

It is common to see the ferrite content in the range of 50% -65% for properly annealed material. After all the ferrite phase is the matrix.
The reasons sited by gr2 are why the duplex fillers have slightly higher Ni content (2209), to help keep the ratio in un-annealed welds.

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Plymouth Tube

 

[SJones]

Phase balance measurements for product acceptance are usually additional requirements specified by purchasers. 50:50 is an ideal nominal but practical tolerances have to be applied. The question then becomes: what are the practical tolerance limits which is probably the thrust of the thread.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[strider6]

usually the content is 40 - 60% of ferrite. Typically the 2205 contains 40-50% of ferrite. i don't see why there should be a commercial duplex with 30 or 70 percent.

S.

Corrosion Protection & Corrosion Control

 

[gr2vessels]

There is no commercial Duplex SS material with 30 - 70% ferrite. That wouldn't be Duplex grade and couldn't be sold as Duplex material. There is however, a 30 - 70% ferrite acceptable limit in the WELD material. There are welding consumable and welding procedures to ensure the compliance with the above limits.
gr2vessels

 

[SJones]

You won't know whether it's 30-70% ferrite if you, as a purchaser, don't look for it in the first place and it gets through mechanical testing.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[bruv]

I agree with gr2vessels - we often see 30-70% specified in the weld metal. I have seen base material specified at 40-60%, 35-55% and 35-50% by different people.

Purchasers should specify what values they want and ask for ferrite count by ASTM E562, or estimated content by calculation (or Ferritscope) using ASTM A800.

Some years ago we made some duplex to a French spec(NF A 32-055 grade Z 6CNDU 20.08-M), specified with 15-40% ferrite.