Decomposition mechanisms of continuously cooled bainitic rail in the critical heat-affected zone of a flash-butt welded joints

Abstract

The joining process of bainitic rails is significant in terms of their industrialization in high-speed and heavy-loaded railways. This paper demonstrates the microstructure changes in the critical zone of the welded joint, which is responsible for the greatest deterioration in mechanical properties. Extensive progress in the decomposition of the retained austenite and bainitic ferrite occurs in the low-temperature heat-affected zone (LTHAZ) of the flash-butt welded joint of low-carbon bainitic rail. The decomposition products of the retained austenite were mainly a mixture of cementite and ferrite. The cementite was mainly precipitated at the boundary of the bainitic ferrite laths, which indicates lower thermal stability of the filmy austenite. Moreover, it was found that a part of the refined blocky retained austenite was decomposed into the ferrite and nanometric cementite, while another remained in the structure. The decomposition mechanisms are rather heterogeneous with varying degrees of decomposition. A relatively high proportion of dislocations and stress fields prove the occurrence of residual stresses formed during the welding process.

The Influence of the Hot Working Tool Steel Substrate Material on the Element Distribution, Microstructure and Hardness of Gas Metal Arc Welding Hardfaced Layers

“…6f). The first process is similar to the changes occurring during rapid tempering [32]. This resulted in a decrease in hardness which is described later.…”

Evaluation of cracking risk of 80MnSi8-6 nanobainitic steel during hot forging in the range of lower temperature limits

“…The phenomenon of intensive abrasive wear is encountered in many branches of industry, most prominently the extractive, concrete, ceramic, and metallurgical industries [1,2]. Abrasion is also a very important consideration during the performance of machines and devices for earthworks, which applied in agriculture and construction [3,4]. Additionally, because of progress in the development of environmental protection, much research is conducted with the aim of prolonging the operation time of machines in direct contact with the materials used in waste recycling, e.g., metal shredder blades, transportation containers, and so forth.…”

“…This microstructure can be uniformly generated in large-scale forgings, such as steam turbines, or in selected areas of the product, for example, as a result of surface treatment leading to increased wear resistance [3]. Recent studies have indicated that comparing the mechanical properties of bainitic steels with those * E-mail: graca@agh.edu.pl of conventional steels is favorable [4]. It has also been observed that the properties of this type of steel depend on the size of the phase components.…”

“…For these reasons, researchers have focused on developing an economical composition of elements, such as Fe-C-Si-Mn-Cr. Bainite subunits thinner than 100 nm are most commonly obtained through isothermal heat treatment in the temperature range of 200-400 • C [4]. In the initial studies dedicated to the design of nanobainitic steels, the theory of bainitic phase transformation was employed, with the primary objective of achieving nanobainite at the lowest possible temperature.…”

Advanced Heat Treatment of Pearlitic Rail Steel

“…Studies referring to the properties of pearlitic steels used in railway engineering have already been conducted in the second half of the 20th century [1]. In time, together with the technical progress and the general need of building new railway lines according to the technical interoperability standards [2], a necessity occurred to standardize the steel grades used to make the railways as well as to determine standards for their production [3]. It should be mentioned that there is also research into bainitic steel for application in rails [4].…”