A nickel-based buttering layer is often used when welding austenitic stainless steels to carbon steels...

In TR 942-B and API RP 582, it is emphasized:

“Nickel-based buttering is often used as an intermediate layer to reduce thermal stress mismatch during welding of ferritic and austenitic materials.”

“Nickel alloys have a coefficient of thermal expansion closer to that of both stainless steels and carbon steels, reducing stress concentrations and mitigating dissimilar weld cracking.”

“This technique also assists in achieving metallurgical compatibility and mitigating solidification cracking.”

Hence, option C is correct as it directly relates to minimizing thermal expansion mismatches.