CARBON MIGRATION THROUGH THE WELDING JOINTS OF DISSIMILAR STEELS

Based on the concept of thermodynamical activity, carbon migration through the welding joint of dissimilar steels has been discussed. Apart from their difference in composition, their different crystal structures if exist may markedly influence the carbon migration and the effect of phase transformation must also be considered. The processes of the carbon migration may be classified as: 1. migration takes place quickly at high temperatures, the precipitation of preeutectold ferrite may given rise to violent migration; 2. migration takes place slowly at rather low temperatures, the diffusion rate of such elements as chromium which has a strong tendency to form carbide may be vital for carbon migration. Suggestion has been put forward on thermodynamic and kinetic considerations to retard carbon migration in either case cited above.