Surface Decarburization
Edge decarburization is the loss of carbon at the workpiece surface during annealing, leading to hardness loss.
Physical-Chemical Mechanism
During the annealing process, carbon reacts with the furnace atmosphere and loses its bond to the metal. This process can be particularly pronounced at the edge of the weld, since temperatures are higher there and the atmosphere is in direct contact with the metal.
Metallurgical Relevance & Welding Risks
Edge decarburization leads to a local loss of hardness on the workpiece surface. This can cause cracks, wear, and reduced strength in the edge zone of the weld. It also increases susceptibility to corrosion.
Workshop Practice & Actions
To avoid edge decarburization, the furnace atmosphere should be well protected and either inert (e.g., argon) or provided with a strong deoxidizing agent. The weld should be kept in the furnace until fully cooled to ensure an even carbon distribution.