Steel rail for high speed and quasi-high speed railways and method of manufacturing the same

Abstract

The present discloses a steel rail for high speed and quasi-high speed railways and a manufacturing method thereof. The steel rail having a superior rolling contact fatigue property can be obtained by reducing content of carbon in conjunction with controlled cooling after rolling. The steel rail includes 0.40-0.64% by weight of C, 0.10-1.00% by weight of Si, 0.30-1.50% by weight of Mn, less than or equal to 0.025% by weight of P, less than or equal to 0.025% by weight of S, less than or equal to 0.005% by weight of Al, more than 0 and less than or equal to 0.05% by weight of a rare earth element, more than 0 and less than or equal to 0.20% by weight of at least one of V, Cr, and Ti, and a remainder of Fe and inevitable impurities. The steel rail manufactured according to the method of the present invention maintains the strength and hardness of the existing steel rail for the high speed railways, while enhancing the toughness, plasticity and yield strength, and an energy value required for initiating and expanding microcracks formed at the surface of the steel rail due to fatigue is increased, and thus under the same conditions, the rolling contact fatigue property of the steel rail can be improved, thereby finally improving the service lifetime and the transportation safety of the steel rail.

1 . A steel rail for high speed and quasi-high speed railways, comprising 0.40-0.64% by weight of C, 0.10-1.00% by weight of Si, 0.30-1.50% by weight of Mn, less than or equal to 0.025% by weight of P, less than or equal to 0.025% by weight of S, less than or equal to 0.005% by weight of Al, more than 0 and less than or equal to 0.05% by weight of a rare earth element, more than 0 and less than or equal to 0.20% by weight of at least one of V, Cr, and Ti, and a remainder of Fe and inevitable impurities,
 wherein a head portion of the steel rail has a uniformly mixed microstructure of pearlite and 15-50% of ferrite at a room temperature.   
     
     
         2 . The steel rail of  claim 1 , comprising 0.45-0.60% by weight of C, 0.15-0.50% by weight of Si, 0.50-1.20% by weight of Mn, less than or equal to 0.025% by weight of P, less than or equal to 0.025% by weight of S, less than or equal to 0.005% by weight of Al, more than 0 and less than or equal to 0.05% by weight of a rare earth element, more than 0 and less than or equal to 0.20% by weight of at least one of V, Cr, and Ti, and a remainder of Fe and inevitable impurities. 
     
     
         3 . The steel rail of  claim 1 , comprising at least one of 0.01-0.15% of V, 0.02-0.20% of Cr, and 0.01-0.05% of Ti. 
     
     
         4 . The steel rail of  claim 3 , comprising at least one of 0.02-0.08% of V, 0.10-0.15% of Cr, and 0.01-0.05% of Ti. 
     
     
         5 . The steel rail of  claim 1 , wherein the head portion of the steel rail has a uniformly mixed microstructure of pearlite and 15-30% of ferrite at the room temperature. 
     
     
         6 . A method of manufacturing the steel rail of  claim 1 , comprising smelting and casting molten steel, rolling steel rail, controlled cooling after rolling, and air-cooling,
 wherein the controlled cooling after rolling comprises making the steel rail stand upright on a roll table, transferring the steel rail to a heat treatment unit through rotation of the roll table, and blowing cooling medium onto the steel rail by the heat treatment unit to uniformly cool the head portion of the steel rail at a cooling rate of 1-4° C./s until a temperature of a top side of the head portion decreases to 350-550° C.   
     
     
         7 . The method of  claim 6 , further comprising after finishing rolling during the rolling steel rail, cooling the steel rail to a temperature lower than an austenitic phase zone, and then heating the steel rail to a temperature in the austenitic phase zone at a rate of 1-20° C./s, followed by the controlled cooling after rolling. 
     
     
         8 . The method of  claim 6 , wherein the cooling medium is at least one of compressed air, a mixture of water and air, and a mixture of oil and air. 
     
     
         9 . The method of  claim 6 , wherein the head portion of the steel rail finally obtained has a uniformly mixed microstructure of pearlite and 15-30% of ferrite at a room temperature. 
     
     
         10 . The method of  claim 6 , wherein the smelting and casting molten steel comprises smelting the molten steel by using a converter, an electric furnace or an open-hearth furnace, performing a vacuum treatment on the molten steel, casting the molten steel to a billet or a slab, and cooling the billet or the slab or directly transferring the billet or the slab to a heating furnace to increase a temperature thereof. 
     
     
         11 . The method of  claim 6 , wherein the rolling steel rail comprises feeding a billet or a continuous cast slab which has been heated to a certain temperature and kept for a certain period of time into a rolling machine to roll the billet or the continuous cast slab to a steel rail having a required cross-section. 
     
     
         12 . The method of  claim 11 , wherein during the rolling steel rail, the temperature of the billet or the continuous cast slab is increased to 1200-1300° C., and kept for 0.5-2 h. 
     
     
         13 . The method of  claim 6 , further comprising after the controlled cooling after rolling, placing the cooled steel rail in the air to be naturally cooled to a room temperature. 
     
     
         14 . The steel rail of  claim 2 , comprising at least one of 0.01-0.15% of V, 0.02-0.20% of Cr, and 0.01-0.05% of Ti.