Development of In-line Heat Treated DHH Rails

Recent progress in rail lubrication and grinding techniques and increase in axle load of freight cars have led to demand for more than ever excellent rails. To produce rails suitable for changing conditions of application, Nippon Steel developed and constructed an in-line slack quenching facility at the rail mill of Yawata Works in 1987. Deep head-hardened (DHH) rails produced by the in-line heat treating process have a hardened head area of greater case depth than obtainable by the conventional off-line head hardening process and can cover medium to high strength regions. The combination of microalloying and controlled cooling also helps to produce high-quality welded joints in these rails.