Summary for inconel 718 turns black during pickling Discussion
Inconel 718 turns black during pickling is the issue Mickie Davis raised after noticing that the same HF/nitric pickle that leaves untreated parts bright and unpitted caused heat-treated parts to darken to a black or dark gray finish. The thread explains that heat treatment changes the alloy’s surface condition and can make it much more reactive to the pickle, so the same soak time no longer behaves the same way. The practical takeaway is that heat-treated Inconel 718 may need a different pickling approach, tighter control, or a revised process rather than assuming the pre-weld pickle will work identically. The discussion is focused on why the appearance changes after heat treatment and on using material removal as a process-control check, but it does not provide a single universal chemistry fix in the excerpt shown.
Q. We pickle Inconel 718 before welding in HF/Nitric solution in preparation for welding. We measure material removal as a way to control the process (soak time).
Lately, I was asked to pickle some parts that had been heat treated already. The metal turned dark grey/black in the exact same pickling solution that leaves non-heat treated Inconel bright with no pitting.
Can someone explain what happens to this metal in heat treatment that would cause it to be sensitive to the pickling process and turn black?
Thank you for any info.
Mickie Davis
– Cookeville, Tennessee
July 28, 2021