Ferrite test

[azizur447]

Hi,

We got a valve cast body from a foundry. The body made from SA-995 grade 4A they give the result of Ferrite content 52% tested I.A.W ASTM E 562 of the cast body. Our allowable ferrite range is 35% to 55%.

But after machining it and tested ferrite content on the machined surface with Fischer Ferrite Scope and shows the result above 60%. Ferrite Scope has been calibrated with standard sample.

Thanks

 

[metengr]

The ferrite scopes are not as accurate as you think with regards to duplex stainless steels. The 60% ferrite measurement may still be within the value stated for the ASTM E562 practice.

 

[XL83NL]

Some while ago I had an issue, where a 2205 DSS weld did not meet the ferrite content (it was too high).
The MFR decided to grind down some weld metal from the top layer (the excess external reinforcement). He then measured the FN again, and found a value that was lower (and within the acceptable range).

This seems to be a parallel to what azizur447describes in his second para. Any one who knows why/how this is caused?

 

[metengr]

Since the weld metal deposited within the weld groove, with the exception of the cap pass, normally has some dilution and cooling associated with base metal, could be part of the reason. Similar to a temper bead where the cap pass being the last pass is not tempered and must be removed.