Development of high-strength chromium-molybdenum rail steel with improved weldability

TLDR: In this article, the authors modified the chromium-molybdenum (Cr-Mo) steel composition by reducing the manganese and chromium contents while maintaining the same as-rolled hardness.

Abstract: Chromium-molybdenum (Cr-Mo) steel rails have been in trial service since 1975, and favorable reports have been received from all test locations. These Cr-Mo rails, containing nominally 0.75% C, 0.85% Mn, 0.75% Cr, and 0.18% Mo, exhibit life expectancy equal to that of head-hardened and fully heat-treated rails. Rails of this composition require a special flash-butt welding cycle to delay the cooling rate of the weld to provide a uniform heat-affected zone microstructure. In this study, the Cr-Mo rail steel composition was modified by reducing the manganese and chromium contents while maintaining the same as-rolled hardness. The heating and cooling cycles used for making conventional flash-butt welds in carbon-steel rails were applied to the modified Cr-Mo steels. It was found that a 0.75% C, 0.60% Mn, 0.60% Cr and 0.21% Mo steel has heat-affected zones which are virtually martensite-free under the conventional flash-butt welding conditions. This lean Cr-Mo rail steel composition appears to be well-suited for heavy duty rail production.