An Efficient Welding Method to Control the HAZ Softening of Ultra Fine Grained Steel Weldment

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.

Effect of Weld Metal Microstructure on Cold Crack Susceptibility of High Strength Weld

Facing the practical difficulties in reducing the diffusible hydrogen content of fluxcontaining welding consumables like flux-cored arc welding (FCAW) wires, the present study investigated the microstructural aspect to improve the hydrogen-induced cold crack (HICC) resistance of multipass weld metal of 600MPa strength. Two FCA welding wires were prepared by controlling the Ni content to give different weld microstructure, but to have similar levels of hardness and diffusible hydrogen content. HICC susceptibility of those two consumables was evaluated by 'G-BOP test' and also by 'multi-pass weld metal cold cracking test'. As a result of this study, it was demonstrated that microstructural modification with decreased proportion of grain boundary ferrite (GF) improved cold crack resistance of weld metal. The detrimental effect of GF against HICC has also been addressed based on the characteristics of weld metal cold cracking.

Exothermic Additions in a Tubular Covered Electrode and Oxidizing Reactions Influence on Underwater Wet Welding

During Underwater Wet Welding (UWW), the water that surrounds the arc decomposes liberating large amount of hydrogen and oxygen. As a consequence of the presence of these gases in the arc atmosphere and weld pool, porosity in the weld metal occurs. In the past years, many research programs had been carried out with the objective to reduce or eliminate porosity in wet welds. A simple way to accomplish this goal is using chemical elements or ingredients to promote or avoid certain chemical reactions in the weld pool. In conventional stick (shielded metal arc - SMA) electrodes, it is possible to add alloying elements or other ingredients through the external covering. A tubular covered electrode (TCE) (a hybrid process between SMA and flux cored arc - FCA welding) allows the addition of reactive elements in the hollow rod, separate from the other ingredients used in the flux covering. This way, it is possible to use exothermic elements, placed inside the tube, to control the oxidation reactions, but limiting these reactions to the arc plasma and in the weld pool. Exothermic additions in welding consumables can promote desirable oxidation reactions, change the metal transfer mode, reduce the cooling rate, and decrease the electrical dependence of the welding process. Theoretically, the application of flux cored shielded metal arc (FC-SMA) welding with exothermic additions will permit better control the weld metal composition and reduce the porosity in wet welds. This paper describes underwater wet welding with tubular covered electrodes that contain exothermic additions such as (CaC2) and aluminum (A1), and the influence of these ingredients on weld metal composition and porosity.