Thick grey band after searing a sous vide ribeye in cast iron Searing

Two minutes a side is far too long, and the fix is to make the sear violently short rather than to make the pan cooler.

What works for me on a 1 inch steak:

• rest the bagged steak, then take it out, pat it dry and leave it uncovered on a rack in the fridge or freezer for 10 to 15 minutes. A cold, dry surface buys you time before the interior notices
• get the pan to the point where a drop of high smoke point oil is shimmering and just starting to smoke
• 45 to 60 seconds total per side, flipping every 20 seconds rather than leaving it still
• finish with butter off the heat, not during

That gives a proper crust with a grey band you have to look for. Flipping often sounds fussy but it genuinely keeps the sub surface cooler while the surface still browns.

Surface moisture is doing more damage than you think. Any water on the steak has to boil off before browning starts, which means the first 40 seconds of your sear were steaming, not searing, while the heat kept travelling inward. Pat dry, then pat dry again, then give it five minutes in front of a fan if you are being serious.

Honestly a 1 inch steak is the hardest case. There is simply not much distance between crust and centre, so a small band is close to unavoidable. Buy them thicker, 1.5 to 2 inches, and the same sear technique produces a band you cannot see.

A torch straight onto the surface, or a torch plus the pan, gets you a crust with almost no heat penetration at all. Faff to set up, and there is a knack to avoiding a fuel taste by keeping the flame moving and not lingering, but it is the most controllable option I have tried.