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Re: [MW:19882] Duplex microstructure

By Materials & Welding
Goswami,

As per Psuedo binary diagram also, it transforms from delta ferrite to austenite and remains as delta ferrite + austenite at lower temperature [i.e. in the alloy composition of duplex].But duplex stainless steel contains Molybdenum, which is a ferrite stabilizer.

 Why alpha ferrite should form embrittle phase at 250degC. If thats case every carbon and low alloy steels should embrittle at 250degC. 

 


On Thu, Jan 16, 2014 at 8:04 AM, pgoswami <pgoswami@quickclic.net> wrote:
Sudharsan,
 
The ferrite in DSS/SDSS is alpha-ferrite, not delta ferrite. Delta ferrite is a high temperature phase (often referred to as precipitate) is related to austenitic stainless steel. On this attachment if you draw a vertical line to any Cr level between 20-25% and Ni content -5-10%, you'll know the phases occurring at various temperatures. These phases(ferrite +austenite) are stable phases at varying compositions and temperatures.
 
Read this document, which is self explanatory.
 
Regards.
 
Pradip Goswami, P.Eng,IWE
Welding & Metallurgical Specialist
Ontario, Canada
 
 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of sudhakar kuppuswamy
Sent: Wednesday, January 15, 2014 10:20 AM
To: materials-welding@googlegroups.com
Subject: Re: [MW:19866] Duplex microstructure

Hi Sudharsan,


The ferrite in DSS is Delta ferrite,


During DSS metal or weld metal solidification, initially 100 % Ferrite is formed and then further transformed to Austenite, for this transformation to occur sufficient austenite stabilizer especially Nitrogen is added  to the Steel .

 

The ferrite that formed at high temperature are retained as such during solidification , hence ferrite formed is DELTA FERRITE NOT APLA FERRITE.

 

 

Regards,

Sudhakar.K



On Tue, Jan 14, 2014 at 9:14 PM, sudharsan s <sudharsan.inspection@gmail.com> wrote:
Dear members,

Duplex structure in Duplex stainless steel [DSS] is 50% Austenite and 50 ferrite appx. The ferrite mentioned here is alpha ferrite or delta ferrite?. Because in many of the solidification diagram for DSS refered in this forum, the alpha ferrite symbol is used. 

Sigma phase conversion of delta ferrite is one of the major issue in DSS, that is why ASME code restrict its use below 350degC.

Please claify...

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With Regards,
Sudharsan

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With Regards,
Sudharsan

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