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TitleStrength, creep, and toughness of two tank car steels, TC128B and A516-70
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorMcKinley, J; Xu, SORCID logo; Gesing, M; Williams, BORCID logo; CanmetMATERIALS
Source 2019, 92 pages Open Access logo Open Access
PublisherTransport Canada
Mediaon-line; digital
File formatpdf (Adobe® Reader®)
SubjectsScience and Technology; Transport; temperature; thermal analyses; Materials technology; Steel; Rail transport; Fire
Illustrationstables; bar graphs; photomicrographs; schematic representations; graphs; photographs; schematic diagrams; digital images; models
ProgramCanmetMATERIALS Pipelines Program
Released2019 04 01; 2019 08 01
CanmetMATERIALS (CMAT) conducted literature reviews on the fracture toughness and high-temperature performance of rail tank car steels in 2015 and 2016 at the request of Transport Canada. The objective of this work was to gain an understanding of the material parameters affecting tank car performance in accident scenarios such as tank punctures and pool fires. This work identified deficiencies in the available literature and recommended experiments to close the gaps. From 2016 to 2018 CMAT conducted a comprehensive experimental program on two common tank car steels, TC128B and ASTM 516 grade 70 (A516-70). The tests performed included; composition and microstructure, tensile testing at temperatures from -80°C to 800 °C, creep rupture testing, Charpy impact, dynamic fracture toughness using drop weight tare tests (DWTT) measuring crack tip opening angle (CTOA), and fracture toughness using single edge notched bending SE(B) and tension SE(T) specimens. Detailed results from this work are included in CMAT technical reports [1]-[6]. The main results of the work are summarized in this combined report.
The compositions of the TC128B and A516-70 steel tested in this work meet Association of American Railroads (AAR) 2014 specifications. The low sulphur and phosphorous contents are consistent with current steelmaking technology. The constituent phases are ferrite and pearlite in a heavily banded structure. Tensile properties of longitudinal and transverse samples are very similar and consistent. Tensile strengths decreased with increasing temperature. Discontinuous yielding (Lüders band formation) was found between temperatures of -80 °C and 200 °C. Lüders strains of up to 2.93% were observed and decreased with increasing temperature. Discontinuous yielding was not observed at temperatures above 200°C. The tensile test data was fit to a temperature dependent constitutive material model to be implemented in finite element code.
Both steels have Charpy absorbed energy values (CVN) that are substantially higher than the AAR specification at -46°C. Fracture propagation toughness values, CTOAB/2, are in the low/middle range in comparison with typical pipe steels. The results of B×2B SE(B) tests, representing baseline conservative fracture toughness values, were acceptable for structural applications but relatively low in the range of typical modern pipe steels. Fracture toughness tests revealed some differences between the tank car steels compared with pipe steels (i.e., later attainment of maximum loads, small load drops during tests before maximum loads, and anomalous effects of constraint on fracture toughness) and these should also influence tank car structural performance. The results provide a fracture toughness dataset that can be used for the low-temperature integrity assessment of current tank car steels and for steel development.
Creep was observed at the test temperatures between 500 °C and 800 °C. Both steels demonstrated the typical creep response of metallic alloys with primary, secondary, and tertiary creep deformation. As expected, the rate of creep increased with temperature and applied load. For most creep tests the rupture time was within 100 minutes which is much shorter than a standard creep test. Shorter tests were performed to match the timeframe of a tank car failure. The creep rupture data will be fit to an appropriate creep model. Finite element simulations of tank cars in pool fire

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