Modelling and design of new stainless-steel welding alloys suitable for low-deformation repairs and restoration processes

Abstract

The plasticity associated with low-temperature martensitic transformation can be exploited to reduce the stresses developed due to thermal contraction of the weldments. The key feature of stress-mitigating welding alloys is their transformation from austenite to martensite at low temperatures e.g. ideally close to ambient temperature. Thermodynamics databases (MTDATA and SGTE) were used to model and design new welding alloys with low martensitic transformation temperatures (Ms) around 200 °C. The modelling, conducted in this work, was based on this assumption that martensitic transformation starts at a certain temperature when the free-energy change for austenite to transform to ferrite reaches a critical value. Since martensitic transformation is a diffusion-less process, the change in free-energy vs. temperature was calculated for the austenite and ferrite phases with the same composition.Three prototype welding alloys, CamAlloys 4 & 5 and OpenAlloy 1, were successfully designed and made in the University of Cambridge (UK) and the Open University (UK). The design of these alloys was purely based on thermodynamics equations. Comprehensive characterisation, examinations and mechanical tests showed this family of alloys could substantially reduce contraction-induced deformations in stainless steel weldments. One of the applications of these alloys is in the repair and restoration of damaged stainless-steel components.