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Friction Stir Processing of Steel

Project Code: 0904-07


Develop a better understanding of the latest generation of FSW tool materials.

Understand FSW processing and weld characteristics/performance.

Optimise friction stir welding tools for friction stir processing/modification of arc welds.

Understand the changes in residual stresses introduced by friction stir processing.

Quantify the improvement in the fatigue lives of fusion welds resulting from friction stir processing.

Project Outline

Initial work will focus on using the most promising generation of FSW tools and tool materials established in the 2007-09 CRP and assessing how these might most effectively be applied to welding of steel. This work will include developing process parameters, optimising process control techniques to extend tool life, increase the predictability of tool behaviour and also assessing the weld performance.

Having established a better understanding of the best operating conditions and optimum tool materials, these will be applied to friction stir processing of arc welds.

The initial trials will be conducted on relatively high strength alloys such as pipeline and structural steels, after bead-on-plate weld runs have been made on the plates. This will enable the initial FSP tool designs to be assessed, and the effect of the FSP on the weld microstructure to be evaluated. Thereafter welded plates with sound and partial penetration root passes will be processed, and selected welds will be sent for residual stress analysis.

Microstructural examination of the welds will be conducted throughout the project, and will be used to as a comparison with the hardness and residual stress data obtained from selected welds, by identifying the heat affected zones from both the arc and FSP welds for example. The residual stress analyses will be conducted by the University of Manchester, using its time allocation on the test facilities at the Rutherford-Appleton Laboratory in England and the CERN site in Grenoble.

The top beads of many arc welds are dressed after completion of the welding, to minimise the number of stress raisers by grinding or other techniques, prior to service use. It may be possible to design the FSP tool to achieve this at the same time as modifying the residual stresses and microstructure of the weld, and this may be applicable to the top weld bead as well as the root pass.

The results of the first residual stress analyses will be evaluated by the NMO department at TWI, in order to predict the probable effects of FSP on the fatigue life of the arc welds. Further welding trials will then be performed on full thickness arc welded plates, some of which will be sent for residual stress analysis, and others will be fatigue tested in order to quantify the improvement made by FSP, working with the FGM department at TWI.

Relevant Industry Sectors

Aerospace, Oil and Gas, Power Generation, Automotive and Construction and Engineering

Technical and Economic Benefits

Potential of predictable tool behaviour and increased tool life.

Potential to widen the applications of high temperature FSW.

Enhancement of fatigue life in arc welded steel components for critical applications.

Reduced costs of root pass remediation in arc welded components.

Replacement of current dressing techniques for top beads of arc welds, with simultaneous improvements to weld microstructure.


Industrial Member Reports

Access the Industrial Member Reports resulting from this programme:

Friction Stir Welding of Steel


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