It depends on the grade. F1554 grade 36 is mild steel and is weldable. Grade 55 is a modified mild steel and is weldable, provided it meets the weldability requirements as described in Supplementary Requirement S1 of the F1554 specification. Grade 55 material that does not meet the S1 carbon equivalency parameters is not weldable. Grade 105 is not weldable since the heat generated during welding could alter the mechanical properties of the medium carbon alloy quenched and tempered material.