should be less than 1%
THANKS & BEST REGARDS
KG.PANDITHAN, AWS-CWI, CSWIP 3.1
CONSULTANT-WELDING & QUALITY
On Thu, Apr 3, 2014 at 7:43 AM, pgoswami <pgoswami@quickclic.net> wrote:
--Hi Sankaran,Gr 91 steel contains strong ferrite stabilizers e.g Cr,Mo & V. Forced air cooling imparts martensitic structure in wrought components .However same may not be true for castings. Generally industries allow "Delta Ferrite " up to 5%Max in cast Gr-91 steel. However lower numbers are still better. You do not experience the "ferrite" related problem in properly heat treated forging or pipes.Please see below the extract from API -TR-938B, Use of 9Cr-1Mo-V (Grade 91) Steel in the Oil Refining Industry and the attached paper for reference.Thanks.Pradip Goswami, P.Eng,IWEWelding & Metallurgical SpecialistOntario, Canada6.2.3.1 Chromium Equivalent (Cr
eq)To obtain a proper balance between facture toughness, creep-rupture strength and resistance to long-term embrittlement, the alloy composition and residual elements are typically controlled to provide a single-phase microstructure and avoid residual delta ferrite. Delta ferrite reduces toughness and creep resistance. By keeping Chromium Equivalent (Cr eq) below 10, the tendency to form delta ferrite is reduced. Even materials with Cr eq between 10 and 12 exhibited adequate toughness when the delta ferrite does not exceed five (5) percent.
The Chromium Equivalent is estimated by the following formula [2] (all elements in %):
Cr eq= Cr + 6Si + 4Mo + 1.5Mo + 1.5W + 11V + 5Nb + 9Ti + 12Al - 40C –30N - 4Ni - 2Mn– 1Cu.
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Sankaran Sp
Sent: Wednesday, April 02, 2014 8:13 AM
To: materials-welding@googlegroups.com
Subject: [MW:20466] Is it delta ferrite allowable in C12A/F91/P91 microstrucure?--Dear Experts,We are getting ASTM 217-C12A type valve body casting from foundries to make a high pr valves, while getting a Test certificate for body we are asking foundry to submit the microstructer of body castings.When they making a report ,specify that" micro structure is fully tempered martensite and delta ferrite <5% "Is it acceptable delta ferrite in this type castings? what is the correct micro structure of C12A casting or P91 pipe or F91 forging?Kindly clarify and send the accpetable microstructure photo for our reference.Regards,Sankaran.Spwelding& Metallurgy expertCoimbatore,India.
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