Assessment of the weldability of historic steels: from sulphur-print and metallography to real welding tests and welding CCT diagrams
Source: BAM
In Germany, there are more than 6000 steel bridges and steel skeleton structures made of old mild steel that are more than 80 years old and need to be repaired in the next few years. However, welding as a particularly economical joining process has hardly been used to date for value-preserving and value-enhancing restoration work on existing old mild steel structures. Rivet and screw connections, on the other hand, are often uneconomical. For repairs, existing and damaged material often must be replaced with new material and welded with old mild steel. Sustainable, resource-efficient repairs can be achieved by using modern structural steels. In addition, modern controlled MAG processes allow a precise, adapted introduction of heat into the weld seam and to utilise the broad portfolio of approved welding fillers. Heat input and dilution in the HAZ and stresses are minimized. This avoids degraded microstructures, which cause high risks of cracking in old mild steels during production and operation as well as reduced load-bearing capacities. With the help of a steel database, practical welding tests and analyses, welding concepts are being developed to produce stress-optimized old-new steel mixed joints. This should enable the sustainable and resource-saving maintenance of existing infrastructure in Germany.
Challenges in the evaluation of the weldability of old mild steels for future use
Schroeder, N., Uhlig, M., Kromm, A. et al.
Weld World, 2026