EFFECT OF BORON ON THE MICROSTRUCTURE OF LOW-CARBON STEEL RESISTANCE SEAM WELDS

Small levels of boron (20-40 wt ppm) in steel were found to have a lar ge influence on the microstructure and hardness of resistance seam wel ds. The decomposition kinetics of austenite to ferrite were retarded a nd resulted in the formation of bainitic and martensitic microstructur es in the weld metal. The welds with low and high boron concentrations showed large differences in hardness. This microstructure development is in agreement with theoretical calculations of time-temperature-tra nsformation diagrams. This work stresses the importance of considering boron levels in steels on the weld properties.