To what temperature must the weld metal and rail cool before allowing traffic to cross it?

The correct temperature for the weld metal and rail to cool before allowing traffic to cross is 700°F. This temperature ensures that the weld has reached a level of strength and stability necessary to bear the loads imposed by train traffic. Cooling to this specific temperature allows for the proper tempering of the weld metal, thus minimizing the risk of cracking or failure once the rail is put back into service.

This cooling protocol is critical in maintaining the integrity of the railroad infrastructure, as temperatures above this threshold can still lead to stresses in the weld that may compromise its long-term performance. The chosen temperature strikes a balance between ensuring safety and allowing for efficient operation on the railways.