Joining nichrome wire within 1140 celsius kiln
The bulk conductivity of steel is not your problem, it will be far better than nichrome. However at 1200 C, it will oxidise fast and you'll lose the metal surface. You need to use an alloy that will withstand the temperature without surface oxidation. Maybe stainless steel? If you can use it to hold one nichrome wire in contact with the other, you may get away with it.