The HAZ softening of the ultra fine grained steel weldment occurs when welding heat input is higher than the critical value. The critical welding heat input was found to be about 10kJ/cm for the steel studied. The lowest hardness value and the width of the softened HAZ are dependant on the applied welding heat input. For obtaining high productivity with the low heat input, less than 10kJ/cm, a high speed FCA welding process with 2 electrodes was developed and verified to be an efficient method for the ultra fine grained steel. The weldment made by this process did not have the softened HAZ; and thus, satisfied the tensile strength required.