Conventional fusion welding processes are reaching their applicability limits as far as the weldability of thin gauge, modern high alloy steels (i.e. UHSS, TRIP, CP, MS, DP and IF steels) is concerned. Weldability issues are also a matter of concern in Cr-containing steels employed in the energy and transport sectors due to micro-structural control, embitterment risks and environmental concerns.
The Friction Stir Welding (FSW) process, a low heat input, solid state joining method, offers a number of advantages likely to overcome weldability problems in difficult-to-weld steel grades. Moreover, FSW has also shown to be able to produce multi-material joints between steel and non-ferrous alloys. Starting from the present state of art in FSW of steels this project intends to focus on two lines of development: process technology and application to relevant steel grades and multi-material joints.
The process technology focus will aim at alternative tool materials and geometry, their respective process parameter fields as well as pre- and post-weld heat treatment methods viewing increased tool life and the cost effectiveness of the process. The suitability of the process to different steel grades will be investigated on modern high alloy and Cr-alloyed materials with emphasis on the microstructure development and joint performance.
This development work will be supported by modelling (temperature and deformation) and by an economic evaluation and concluded with the manufacturing of demonstration structures from the automotive, shipbuilding and energy sectors. In summary, the main objective of this project is to define the merits of FSW when applied to steels based on the achievable joint performance, applicability to structures and economics.