X65 clad with Inconel 625, closure welds

[twoheads]

Can someone please enlighten me as to why during the fabrication of 625 clad HSLA steels, the closure welds have to be made with a 625 filler right out and not say root and hot pass with 625 (which would take up the clad area of the joint) and the fill and cap made with a suitably matched carbon steel consumable.
I have been told in the past there may be chemical and mechanical issues at the joint when welding C/S to inconel but not when welding inconel to the steel.

Thanks again in advance.

 

[metengr]

I have been told in the past there may be chemical and mechanical issues at the joint when welding C/S to inconel but not when welding inconel to the steel.

This is true and those issues mentioned above are from dilution. Using an austenitic based filler metal for joining Ni-base alloys or stainless steel to CS is the correct approach. Using carbon steel electrodes directly on stainless or Ni-base metals will result in dilution that forms harmful phases in the weld region.

 

[twoheads]

Thanks again