High tensile railway track section made of carbon-manganese steel - subjected to controlled quenching on leaving hot rolling mill

摘要

Railway track sections are made from steel contg. 0.55-0.8% C, 0.9-1.3% Mn, and 0.15-0.35% Si. On leaving a hot rolling mill, the track is immersed in an aq. bath which has a cooling capacity above that of boiling water but below that of water at room temp.; and the track section is kept in the bath until the rail head or mushroom has cooled to 625 degrees C at a point >=15 mm below the top surface of the mushroom. The bath pref. contains materials in soln. or suspension to improve heat transfer from the track to the bath, esp. 4% Na silicate; and the bath is agitated by nozzles immersed in the bath and fitted with recirculation pumps. Local quenching is pref. employed for the mushroom, and the cooling effect of the nozzles is pref. reduced when the allotropic transformation is complete. Used for mfr. of rails, esp. vignoles rails, with min. tensile strength 110 kg/mm2 and min. 12% elongation at fracture; good resistance to shock, flaking, wear and fatigue, a fine structure with uniform hardness, esp. in the mushroom; and good weldability.