DEVELOPMENT OF LOW TRANSFORMATION TEMPERATURE (LTT) WELDING CONSUMABLES Tariq Alghamdi, Stephen Liu, and Faisal Alabbas Colorado School of Mines ABSTRACT Fatigue resistance of welded steel joints has grown to be one of the most important concerns of structural integrity. Undesirable tensile residual stress is observed in low carbon structural steel weld joints upon completion of solidification and after the weld is cooled to room temperature. This harmful stress makes the welded joints more prone to fatigue failure. Thus, the presence of compressive residual stress, instead of the typical tensile residual stress, improves the fatigue properties of the structural welded joint and makes the nucleation and propagation of the crack more difficult. Thermal post weld heat treatment (PWHT) and mechanical shot peening processes are known to reduce the tensile residual stress and possibly induce a compressive stress. However, both approaches are cost and time consuming methods. Considerable effort was made to create welding consumables that can induce compressive residual stresses near the weld toe regions via phase transformations. This compressive residual stress can be significantly bigger than the one generated by mechanical or thermal rework of weldment. Martensite transformation start (Ms) and finish (Mf) temperatures are essential parameters in structural steel welding because of their influences on residual stress development in the weld. It is preferred that the martensite transformation initiates at a temperature as low as possible and finish just above the final temperature to which the weldment is expected to cool. It is well established that alloy compositions affect significantly the temperatures of phase transformations. Yet the exact nature and extent of the effects of chemical composition on the metallurgically-induced compressive residual stresses has never been clearly evaluated. This work presents and compares several methods of calculating martensitic start temperature (Ms) reported in the literature. The key aspect of this research is to distinguish between newly developed Low Transformation Temperature (LTT) welding wires to specify leaner and more economical alloyed consumables. By means of leaner chromium, nickel and manganese additions, the new experimental wires can achieve high fatigue properties as the 10Cr-10Ni wire proposed close to a decade ago to mitigate tensile residual stresses in weld toes.