The Development of Manganese Steel Laser Additive Manufacturing as a Means of Special Trackwork Repair

摘要

Railroad special trackwork such as frogs and crossing diamonds have long been a challenge to maintain and repair in the field. Special trackwork frogs are manufactured out of cast austenitic high manganese steel (AMS or Hadfield steel) for its excellent work hardening characteristics and high toughness. However, this chemistry creates a unique challenge to repair in the field. Railroads report that traditional repairs often can only last weeks to six months before requiring additional repairs. The concept of using laser additive technology to repair high manganese steel castings was brought to Holland and Titanova by the Union Pacific Railroad. Based on the potential benefits of laser cladding with lower heat input, less dilution and near net shape deposits with a robotically controlled process, Holland and Titanova began working on a better solution for frog repairs. There are no industry material or test requirements for the parent or repair materials for frogs or diamonds, so with the assistance from the EVRAZ Pueblo Product Technology team members, Holland selected three test criteria and metallographic examinations to compare the performance of parent materials, current MIG welding repair materials, laser powder and laser hot wire materials and processes. The wear resistance, strength, ductility, and toughness of the materials were evaluated by use of disc-on-disc wear, Charpy impact, and tensile testing all performed at Evraz. The repair processes were also evaluated in terms of heat input to the parent material, the extent of porosity on the weld build-up and the resulting microstructure. The Evraz team provided metallurgical evaluations and recommendations to the Holland process development. The results of the testing led to the development of the laser hot wire process that was used to repair test frogs that have been tested on UP track and at the Transportation Technology Center in the Facility for Accelerated Service Testing high tonnage test loop.