Laser cladding repair study on rail steels

• Main Author: Liew, Tat Fong
• Other Authors: Pang Hock Lye, John
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/141114
• Institution: Nanyang Technological University

Railway crossings are high-value components that are subjected to aggressive working conditions such as impact and wear during daily service operations. Failure would result in high costs and downtime due to maintenance & replacement thereby having a detrimental effect on rail network reliability. Conventional surface repair techniques such as welding and thermal spraying are not ideal in the application of rail repair as the quality and geometric profile of the repaired rail is highly dependent of the operator’s skills and hiring skilled operators are expensive in the long run. Laser cladding technology is an emerging repair technique that is fully automated and has the potential to mitigate the rate and cost of maintenance and increase the service life of the rail components, most importantly the crossing nose. Two main types of crossings are used in Singapore’s railway network and they are the common carbon crossing and cast manganese crossing. Currently, about 50% of the crossings on mainlines uses cast manganese crossing. In this report, the main focus is on evaluating laser cladding repair feasibility of the common carbon crossing. A repair methodology has been proposed involving Stellite 6 and Inconel 625 cladding materials. The metallurgical analysis was performed to study the clad materials’ compatibility with rail steel. Cross-section microscopic characterisation showed clear metallurgical bond achieved at the clad and rail substrate interface. Hardness profile distribution across the clad, HAZ and rail substrate was determined with the average hardness at clad region observed to be 425 HB approximately and maximum hardness of 764 HB at the HAZ. While the high hardness of the cladding promises for improved wear resistance, the significant peak in hardness at the HAZ is undesirable as it may lead to embrittlement and hence possible delamination of the cladding layer. Inconel 625 is then identified as a buffer layer between the premium Stellite 6 cladding and rail steel substrate to prevent the risk of cracks occurring at the cladding interface. It is evident from this study that laser cladding repair of the crossing nose is feasible with the capability for service life extension. Future work is to investigate laser cladding materials for the repair of cast manganese crossing nose.