Duplex Stainless Steel and Austenite / Ferrite Ratio
Duplex Stainless Steel and Austenite / Ferrite Ratio
(OP)
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.
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.





RE: Duplex Stainless Steel and Austenite / Ferrite Ratio
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
RE: Duplex Stainless Steel and Austenite / Ferrite Ratio
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
RE: Duplex Stainless Steel and Austenite / Ferrite Ratio
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdoweb/
RE: Duplex Stainless Steel and Austenite / Ferrite Ratio
S.
Corrosion Protection & Corrosion Control
RE: Duplex Stainless Steel and Austenite / Ferrite Ratio
gr2vessels
RE: Duplex Stainless Steel and Austenite / Ferrite Ratio
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdoweb/
RE: Duplex Stainless Steel and Austenite / Ferrite Ratio
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.