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TitleCharacterization of microstructure, tensile (23°C to 850°C) and Charpy transition curves of a current tank car steel (TC128B) circumferential weld
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorXu, SORCID logo; McKinley, J; Chen, J; Liang, J; Laver, A
SourceCanmetMATERIALS, Report CMAT-2018-WF 34540443, 2019, 27 pages, Open Access logo Open Access
Mediadigital; on-line
File formatpdf
SubjectsScience and Technology; Transport; welding; metals; spectroscopic analyses; chemical analyses; structural analyses; thermal analyses; Steel; Materials technology; Methodology; Rail transport
Illustrationsphotographs; tables; schematic diagrams; profiles; photomicrographs; schematic representations; plots
ProgramCanmetMATERIALS Advanced Materials Porcessing
Released2019 01 01; 2022 03 02
This report details experimental procedures and results of microstructure, tensile and Charpy properties of a current TC128B circumferential weld. The sample coupon was received from at DOT-117 tank car. The work included the determination of (i) chemical composition, microstructure and micro-hardness (ii) tensile strength and failure locations in the temperature range of 23°C to 850°C, and (iii) Charpy transition curves.
The weld was made using a double pass procedure. The combined weld and heat affected zone (HAZ) widths were approximately 14.8 mm close to the mid-thickness (the smallest), 22 mm at the inside surface and 24 mm at the outside surface (the largest), respectively. The HAZ width ranged approximately 2.3-4.2 mm. Weld metal (WM) and HAZ showed typical microstructures. The hardness values in the weld and HAZ were considerably higher than those of base metal (BM), i.e., demonstrating desired weld strength over-matching. The average and standard deviation of micro-hardness of BM, HAZ and WM were 164±8 (from 152 to 182), 191±17 (from 151 to 217) and 194±9 (from 163 to 217), respectively. Ultimate tensile strength (UTS) of cross-weld tensile specimens dropped sharply beyond 600°C as it did in all BM tests performed previously. All cross-weld specimens tested at 700°C and below failed at the BM. Two of the specimens tested at 700°C and one specimen tested at 800°C broke close to the weld region (probably in HAZ). Two cross-weld tensile specimens at 800°C failed in the WM. At 850°C, three cross-weld tensile specimens failed in BM. These indicated that the WM may become a weak link at high-temperatures approximately above 700°C to 800°C. However, in all cases, the UTS of the specimens were similar no matter where the specimen failure occurred. CVN (Charpy V-notch) values of WM were significantly lower than those of BM. CVN values of HAZ specimens were between those of BM and WM, and displayed larger scatter. CVN values for WM specimens at -46°C (average: 18 J, individual: 16 J, 24 J, 13 J) indicated that the weld toughness values were slightly lower than the specified values (i.e., 20.3 J minimum average for three specimens and 13.6 J minimum for one specimen at -46°C). The cross-weld tensile and Charpy test results indicated a need to optimize the current welding procedure.
The low toughness of the weld metal (CVN values) should be investigated further. CanmetMATERIALS's recommended course of action is to begin by verifying these results by testing another weld from the same tank car (e.g., a longitudinal weld). Additional welds from tank cars manufactured with TC 128B steels should be tested. This should be followed by reviewing the standard practice for TC128B welding and then development of an improved weld process. It may be possible to improve the weld toughness using minor changes to the welding parameters, heat treatment, or filler metal composition without making significant changes to existing procedures and equipment.
Summary(Plain Language Summary, not published)
In this work, a tank car TC128B circumferential weld was characterized to examine its microstructure, hardness, tensile, and Charpy testing ductile-to-brittle transition properties. Cross-weld (or transverse tensile) and all-weld-metal (AWM) tensile tests were performed to evaluate the weld joint performance, i.e., whether the weld is a weak location for failure and its strength is lower than the previously-assessed base material (BM) of the shell steel (Simha and McKinley (2017), Xu et al. (2017)). Charpy toughness tests of the weld metal (WM) and heat-affected zone (HAZ) were performed to establish Charpy transition curves. In order to examine general characteristics of the TC128B circumferential weld, and assist mechanical specimen preparation, metallography, micro-hardness, and micrography testing were performed and are described. Mechanical properties of the tank car steel weld were evaluated and are compared to those of BM.

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