[MW:4627] MW: -4617 uniform distribution of austenite in ferrite matrix

Hi Rutvik,

Typically duplex microstructures what we see, for products like, plates, pipes, fittings and other wrought products are lot refined and fine grained, through forming , and multiple heat treatments (heating and cooling cycles during forming operations). As a compared to a wrought product, micro structures of duplex S.S casting would definitely be coarse and chunky.

ASME SA 995 Gr.4A is the cast version equivalent of ASME SA240 S31803 duplex S.S. Properties of both alloys are comparable when SA 995 Gr.4A is properly heat treated after casting. In general weldabilty of cast alloys are poorer compared to a wrought alloy, due to coarser grains and segregation of alloying elements. If they are properly solution annealed after casting, the properties get lot better and are easier to weld.

Welding of castings require precautions required for welding a wrought alloy in the same degree or more..

I am not sure what your spec requirements were. NACE MR 0175 Part -7 applies tighter restrictions on duplex castings, which are similar to ASME SA 995, with supplementary requirements.-

Wrought and cast duplex stainless steels shall:-

· be solution-annealed and liquid-quenched,

· have a ferrite content (volume fraction) of between 35 % and 65 %, and

· Not have undergone ageing heat-treatments.

Looking at your query I would propose that you should look in to the following tests while qualifying weld procedure for welding of Duplex Castings:-

· PQR qualification as per ASME Sec-IX, which includes conventional mechanical tests, hardness, charpy impact(if required) and chemical analysis.

· Ferrite count as per ASTM E-562.

· Detection of Intermetallic (Sigma) phases as per ASTM E-923

· Pitting corrosion test or other tests as required by the specifications.

I have attached some references for you reading .Feel free to drop me a line.

Thanks.

Pradip Goswami,P.Eng.

Welding & Metallurgical Engineer/Specialist

Component Integrity Section.

Engineering amd Training Services

Ontario Power Generation Inc.

Res:-88,Garth Trails Crescent

Hamilton,Ontario, L9B2X1,Canada

Email-pgoswami@sympatico.ca

Email-pgoswami@quickclic.net

Tel-905-679-9677

Date: Fri, 26 Mar 2010 17:58:21 +0530
From: rutvikdixit@yahoo.co.in
Subject: [MW:4617] uniform distribution of austenite in ferrite matrix
To: materials-welding@googlegroups.com

Hi everyone,

I am having the WPS for the Duplex SS ( ASTM A 995 Gr.4A) The microstructure of weld shows the dendritic austenite in ferrite, HAZ and base metal shows no uniform distribution of austenite in ferrite.

The requirement is uniform distribution of austenite in ferrite matrix.

Can this pattern of microstructure cause adverse effect?

With Regards,
Rutvik

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