Microstructure-Fracture Behavior Relationships of Slot-Welded Rail Steels
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THE mechanical properties of bainitic rail steels and pearlitic rail steels were investigated.[1–6] These studies showed that the bainitic rail steels outperformed the pearlitic rail steels in all tests. Aglan et al. determined that the ultimate tensile strength, yield strength, and elongation to failure were all higher in the bainitic rail steel than the pearlitic.[1,4] It was also determined that when compact tension specimens were used, the plane strain fracture toughness of the bainitic steel was over 26 pct higher than the pearlitic steel.[4] Tested under the same conditions, the bainitic rail steel showed much higher fatigue lifetime and resistance to fatigue crack propagation than the pearlitic rail steel.[2] Laboratory wear tests performed on the bainitic steel showed that it was less prone to wear than the pearlitic steel.[6] These laboratory tests of pearlitic and bainitic rail steels show that bainitic rail steels should have a higher service lifetime in track, reduce frequency of maintenance, and also increase the rail’s safety. The higher percentage of alloying elements of bainitic steel that provided the superior mechanical properties ALDINTON ALLIE, Postdoctoral Student, and HESHMAT AGLAN, Associate Dean, are with the College of Engineering, Architecture and Physical Sciences, Tuskegee University, Tuskegee, AL 36088. Contact e-mail: [email protected] MAHMOOD FATEH, Program Manager/Track and Structures, is with the Federal Railroad Administration, Washington, DC 20590. Manuscript submitted October 14, 2010. Article published online March 29, 2011 2706—VOLUME 42A, SEPTEMBER 2011
created some weldability challenges, which can be assessed using the equivalent carbon content. Higher equivalent carbon content indicates that the steel is difficult to weld. The value of the equivalent carbon content is a function of the carbon content and the various alloying elements, as shown in Eq. [1]:[7] Mn þ Si Cr þ Mo þ V þ 6 5 Ni þ Cu þ 15
Equivalent carbon ¼ C þ
½1
The equivalent carbon content was calculated and found to be 1.2 and 1.5 pct for the pearlitic and bainitic rail steels, respectively. On this basis, it appears that the bainitic rail steel is more difficult to weld. In the present work, challenging issues related to the welding of bainitic steel will be undertaken. Welding is used in different industries to optimize their product design and to minimize their costs of production. Some of the applications of welding include joining of gas and oil transmission pipelines, welding of submarine hulls, hardfacing worn steels, and joining and repairing rail tracks.[8–14] In the railroad industry, mechanically jointed tracks were replaced by continuously welded rails and are now the accepted method for joining and repairing rail steels. The implementation of welded rails reduced the effects of impact loading and, hence, a reduction in the track inspection and maintenance requirements.[15] These continuously welded rails METALLURGICAL AND MATERIALS TRANSACTIONS A
also assist in noise reduction and vibrati
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