Nickel-Iron Phase Stability

With nickel-iron alloys you have to watch that unwanted intermediate phases don't form during welding. They occur when you hold the material too long in the wrong temperature range or cool it too quickly. That makes the structure brittle and prone to cracking. Keep the interpass temperature in range and let the part cool slowly and evenly after welding, then the structure stays stable and you'll have no issues with corrosion resistance.