[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.