DELIVERABLE 2.8 - urban track

2.9. NEW DEVELOPMENTS
D0208_STIB_M24.doc
TIP5-CT-2006-031312 Page 21 of 44
URBAN TRACK Issued: August 13, 2008
Quality checked and approved by project co-ordinator André Van Leuven
Corus is fully aware of the importance of the weld restoration coating process as it is significantly more
cost effective that the renewal of embedded tracks.
The key requirements of the new system are:
the use of steels with higher carbon content than grades 700/800 to reduce wear;
a process for in situ restoration without destroying the surrounding jacket;
restore the worn face with a more resistant wear coating resulting in a composite rail;
repeated application of the coating process.
A new submerged arch welding process was developed that uses a specifically formulated flux, a cored
arc wire and flux powder.
Steps of the process:
1. Light grind cleaning of the worn face;
2. Preconditioning with a novel “chill removal” treatment in the area to be restored;
3. Weld deposition of the root pass;
4. Weld deposition with subsequent passes until the worn portion has been restored;
5. Deposition of a capping weld bead as a final sacrificial layer;
6. Grinding to remove the sacrificial layer and to impart the desired gauge corner profile.
The key to creating the hard weld is the pre-conditioning “chill removal” treatment, which results in:
a crack free root pass of the weld deposit;
a hard but tough tempered martensitic microstructure in all passes.
The removal of the sacrificial last pass leaves a tough wear resistant surface
A purposely designed welding unit achieved the following:
10 to 12 m in a 4.5 hour track possession;
Capability of restoring more than 10 mm;
Preference to 6 mm wear.
The process is under still under development and is applied in Sheffield.
The following problems still need to be addressed:
The “chill removal” process is difficult to execute on an embedded rail and needs enhancement.
Currently the experience is limited to only one restoration on a rail.
The conventional process can be repeated several times.
The preference is to restore after 6 mm of wear whereas the conventional process can rebuild after up
to 20 mm of wear and this can be repeated up to 6-8 times.
The technique is not yet used on a wide scale: prototype evaluation is on going.