This presentation provides an overview of research that has been (and is being) carried out at The University of Manchester, with a focus on the role that phase transformations play in the development of stress in steel welds. There are several motivations for this research. Residual stresses play a significant role in affecting the long-term structural performance of safety-critical components in many power plants. They can also contribute to the driving force for crack growth and, in nuclear environments, they can activate material degradation mechanisms such as creep and stress-corrosion cracking even in the absence of operating stresses. This is significant because many safety-critical components in a nuclear plant undergo welding during manufacture, and welding is known introduce substantial levels of residual stress. Solid-state phase transformations affect the development of stresses in steels because these transformations have associated strains, which in turn affect the development of stress upon heating and cooling. Residual stresses also tend to be limited by the yield stress of the material, so the mechanical properties of transformation products will have a direct bearing on the development of stress. Some of the topics that will be covered in this presentation include the development and assessment of low-transformation-temperature filler materials for the mitigation of residual stresses, assessments of the effects of particular welding processes on the development of stresses, work towards understanding the mechanisms contributing to the development of transformation strains, and the incorporation of phase transformation effects into finite-element models for the prediction of residual stresses in steel welds.