Abstract
A new welding method, ultranarrow gap welding with constrained arc by flux band, is proposed to compensate for the low quality of rail thermite welded joints. This article presents the results of research on the microstructure and mechanical properties of ultranarrow gap welded joints of U71Mn rail steel made using three types of alloying composition content flux bands. Results indicated that the base metal metallographic microstructure consisted mainly of pearlitic, the HAZ was mainly composed of fine pearlite, and the microstructure of the welded bead was composed of acicular ferrite, while the weld grain size decreased as the alloy composition increased. The average hardness noticeably changed in weld metal as the alloy composition increased, and when the alloy composition reached 19%, the hardness was equivalent to the base material. The average hardness value of the HAZ (35.8 HRC) was higher than that of the base metal (24.8 HRC). The tensile strength increased, and the percentage elongation after fracture decreased with increasing alloying composition from 9% to 19%. The impact absorbing energies were decreased as the alloying composition increased. Consequently, all the mechanical properties of rail ultranarrow gap welding were higher than those of the standard requirements of the rail flash welding. And the optimal alloying composition of flux band was 19%.
Highlights
Nowadays, there are mainly two types of welding processes applied in continuous welded rails: electric flash-butt welding and thermite welding [1, 2]
Fracture and fatigue damage in thermite welded rail joints is a frequent source of service failures in railway infrastructure [11], which has a major impact on rail service reliability and safety [12]. us, it can be seen that the rail in situ welding is the weakest link in the overall welding quality of the seamless line
We intend to change the alloying composition content of flux bands to study the effect of this change on the microstructure and mechanical properties of ultranarrow gap welded joints of U71Mn rail steel
Summary
There are mainly two types of welding processes applied in continuous welded rails: electric flash-butt welding and thermite welding [1, 2]. Ultranarrow gap welding with a constrained arc by flux band is applied to rail in situ welding [13]. In this method, an I-shaped groove with a gap width of 4 mm is adopted to conduct multilayer single-channel ultranarrow gap welding by using a flux band to constrain the melting electrode arc. Erefore, it is of great significance to apply ultranarrow gap welding with a flux band constrained arc to the rail in situ welding. We intend to change the alloying composition content of flux bands to study the effect of this change on the microstructure and mechanical properties of ultranarrow gap welded joints of U71Mn rail steel.
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