Technical Reports

A Metallurgical Evaluation of two AAR M128 Steel Tank Car Head Plates Used in Switchyard Impact Tests

  • 01
  • Apr
  • 1981
AUTHOR: Federal Railroad Administration
SUBJECT: Hazardous Materials
KEYWORDS: Impact Properties; Rail Tank Car; Tensile Properties
ABSTRACT: The National Bureau of Standards correlated the mechanical properties and metallurgical characteristics of two steel head plate samples taken from tank cars subjected to switchyard impact tests. This metallurgical evaluation included determining whether the samples conformed with the appropriate specifications and to determine the impact test behavior of both plate samples. The results of check chemical analyses and ambient-temperature tensile tests indicated that both plates met the chemical, tensile strength, and tensile ductility requirements of AAR M128 steel. The results of metallographic analyses of both plates revealed extensive banding with alternate layers of ferrite and peralite, typical of carbon-manganese steel in the hot-rolled condition. One sample also contained a microstructural anomaly near the inside plate surface, possible related to prior thermo/mechanical processing of the plate. The nil-ductility transition temperatures were determined to be -20F and -40F for the plates, similar to the lowest values reported for a group of tank car plate samples. The results of Charpy V-notch tests established that the transition temperatures of these two plates are similar to one another, and are among the lowest of those measured for all other tank car plates tested at NBS. The comparatively low impact transition temperatures for both plates are related to the high manganese-to-carbon ratio and relatively fine ferrite grain size observed in the microstructures.