Quality Control: Steel Rod Raw Material
This application involved looking at steel rod raw material which was manufactured into steel cables to be used in suspension bridges.
This materials needs to have high strength, plasticity, toughness & torsion, but in some instances the rod was found to fail the torsion test.
As there were examples of both good and bad performance a comparison between the different materials was undertaken, in order to identify which of the materials characteristics on the microscale was influencing behaviour on the macro scale.
As such several properties were examined including grain size and structure and inclusion characterisation.
To fully characterise the rod required data collection over large sample areas – in order to demonstrate changes through the section of the rod, a quarter of the rod was analysed. This meant any systematic changes in chemistry, grain size or strain from the centre to the edge of the rod could be monitored.
In the initial analysis >500 individual fields were analysed. These were then montage together to generate the final map.
The diameter of the rod was >1cm. In order to analyse this quarter section in enough detail to then interrogate the data post acquisition Aztec large area mapping was used and the fields montage together.
This was combined with automated inclusion classification using the Pirelli method to indicate how clean the steel was.
By combining the results from EBSD and EDS it was possible to identify differences through the rod, and potential source for the torsion failure. This then enabled them to screen steel rod raw material before it was processed, i.e. the job to be done.