Dear Rutvik,
What Hemant told is absolutely right. Since, when austenite is <50 wt.%, materials show net duplex microstructures. But when the austenite percentage is higher than ferrite, a diffusion interface appears at grain boundaries, which modifies all the properties. The objective of this work is to characterize this interface in order to identify its nature and predict the behaviour of the duplex stainless steel. For this purpose, a duplex stainless steel has been produced by mixing ferritic–austenitic stainless steel grade powders, compacting at 700 MPa and sintering in vacuum at 1250 °C for 30 min. The mentioned interface has been studied by SEM and light optical microscopy (LOM) and characterized by nanoindentation in order to determine the hardness and Young's modulus of each phase. Testing mechanical properties completes the study.
Yadav Shiva Chelliya,
Inspection Engineer,
Doha Qatar,
+974-6166465
On Tue, Mar 30, 2010 at 12:33 PM, hpi001 <pieper-qsi@kpnmail.nl> wrote:
Dear Rutvik,
You will always have differences in the distribution of austenite when
welding is involved. The dendritic austenite structure for the weld is
normal and mostly will have a little bit more austenite than ferrite.
In the heat affected zone always the opposite is present. During
welding and cooling down there will arise more ferrite in the heat
affected zone even when you take the necesary precautions regarding
interpass temp of max. 150 - 175°C. Important is that the base
material have a homogenous distribution of Austenite Islands in a
Ferritic matrix. The requirements for the Ferrite range of 35 - 65 %
is what you should keep in mind. In the weld it will be near to 35%
and in the HAZ near to the fusion line it will be near to the 65%.
The only way to prove that the present microstructure met the
requirements for the corrosion properties is to perform a corrosion
test on this WPS.
Best Regards,
Herman Pieper
On 30 mrt, 00:17, "pgoswami" <pgosw...@quickclic.net> wrote:
> 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-pgosw...@sympatico.ca
>
> Email-pgosw...@quickclic.net
>
> Tel-905-679-9677
>
> Date: Fri, 26 Mar 2010 17:58:21 +0530
> From: rutvikdi...@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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> 864KWeergevenDownloaden
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