Effects of Hot rolling Reduction on Microstructural Evolution and Mechanical Properties of 1.25Cr-1Mo-0.5V-0.3C Steel for High-Speed Rail Brake Discs

In this study, the effect of rolling of 1.25Cr-1Mo-0.5V-0.3C American Iron and Steel Institute 4340 modified steel for highspeed railway brake discs on the microstructure and mechanical properties was investigated. The materials were hot-rolled at 0%, 51%, and 66% reduction ratios, and then analyzed by optical microscopy, scanning electron microscopy, and electron backscattering diffraction (EBSD). needle-shaped ferrite block morphology in bainite varied with the rolling ratio. EBSD analysis reveals dynamic recovery and dynamic recrystallization, affected ferrite block boundaries and dislocation densities during rolling. Mechanical tests showed that hardness, toughness and elongation increase at higher rolling reduction ratio, while strength remained relatively constant. In particular, the impact toughness increased almost twice from the level of 70 J in S1 (0% reduction) to the level of 130 J in S3 (66% reduction). These results showed that the hot rolling can significantly improve the strength and toughness combination of cast brake discs material.

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The materials of this study was supported by the “Development Break Disk for KTX San Cheun Korean Type High-Speed Train” project of the Ministry of SMEs and Startups’ Purchase Conditional New Product Development Project [grant number SE210021]. And the analysis device and hire was supported by the “Development of 100 Ton or More Eccentric Drive Shaft Manufacturing Technology for Ultra-Large Industrial Machinery to Enter the Global Market” project of the Ministry of Trade, Industry and Energy’s Global Flagship Industry Quality Response Root Technology Development Project [grant number KM220140].