Abstract
According to the concept of the bainite-based quenching and partitioning (BQ&P) process, we designed the online heat treatment routes of bainitic rail steel for heavy haul railway. The new heat treatment process reduced the fraction and size of the blocky martensite/austenite (M/A) islands formed during the conventional air-cooling process. The M/A islands are coarse and undesirable for mechanical properties. A new kind of 1380 MPa grade bainitic rail steel with more uniform microstructure and better mechanical properties was produced by the online BQ&P process. We characterized the multiphase microstructures containing bainite, martensite, and retained austenite of 1380 MPa grade bainitic rail steels via optical microscope, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometer. We investigated in-depth the relationship between the microstructure, retained austenite stability, and mechanical properties, particularly the resistance to wear and rolling contact fatigue, of the new 1380 MPa grade bainitic rail steels. Meanwhile, the conventional air-cooling bainitic rail steel was studied as a comparison.
Highlights
Railway transportation is one of the important modes of transportation in China, supporting the development of the national economy
Compared with conventional pearlitic rail steels, low-alloyed bainitic rail steels have a better combination of strength and toughness, wear resistance, and rolling contact fatigue (RCF) resistance [3,4,5]
The results found that the carbide-free bainitic steels provided superior mechanical properties in comparison with the conventional 880 MPa grade pearlitic rail steel and other bainitic steels of similar chemical composition
Summary
Railway transportation is one of the important modes of transportation in China, supporting the development of the national economy. Compared with conventional pearlitic rail steels, low-alloyed bainitic rail steels have a better combination of strength and toughness, wear resistance, and RCF resistance [3,4,5]. Hasan et al [11] designed two new carbide-free bainitic rail steels with minimal alloying additions and processed them to achieve high strength and toughness for application in heavy-haul rail tracks. It is necessary to develop a new generation of online heat treatment processes for the bainitic rail, aiming to accurately control the microstructure and performances of bainitic rail steel. The optimization of the microstructure and mechanical properties via online heat treatment could, improve the resistance to wear and fatigue and prolong the service life of bainitic rails. Stability of retained austenite, and mechanical properties, the resistance to wear and RCF, of the new bainitic rail steels. The relationship between microstructure, lpolaadstiocfd2e5fogrfmaantdioan,dawnedllmtiimcroe-ocrfa1c0kss.wTahseinrevleasttiiognastehdipubseintwg eSeEnMm(ZiceriossstrEuVcOtu1r8e,, 2p0laksVti)c. deformation, and micro-cracks was investigated using SEM (Zeiss EVO18, 20 kV)
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