[MW:20472] RE: 20466] Is it delta ferrite allowable in C12A/F91/P91 microstructure?

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,IWE

Welding & Metallurgical Specialist

Ontario, Canada

pgoswami@quickclic.net

pradip.goswami@gmail.com

pradip_goswami@yahoo.ca

 

6.2.3.1 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.Sp

welding& Metallurgy expert

Coimbatore,India.

--
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
http://www.linkedin.com/groups/MaterialsWelding-122787?home=&gid=122787&trk=anet_ug_hm
 
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
---
You received this message because you are subscribed to the Google Groups "Materials & Welding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to materials-welding+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.