Abstract: An object of the present invention is to provide a heat treatment device, a heat treatment method, and a rail steel which are suitable for preventing the occurrence of brittle fractures which originate in a base portion of a weld of the rail steel. A heat treatment device of the present invention includes a coil and heats a bottom surface of the base portion of the weld of the rail steel by induction heating. When a region in the weld which is heated to an Ac1 point or higher during welding is represented by HAZ, and the length of the HAZ in a length direction of the rail on the bottom surface of the base portion is represented by Lh, and a width of the rail steel is represented by W, the length of an outer region of the coil in the length direction of the rail is 1.2 times or more Lh and the length of the outer region of the coil in a width direction of the rail is 1.1 times or more W when viewed from opposite the bottom surface of the base portion.

Abstract: A stress-relief heat treatment method for stress-relief heat-treating a rail which is welded includes arranging at least one pair of an induction heating coil to face the rail at both sides of a welding center along the longitudinal direction of the rail while being separated from the welding center of the rail by 20 mm to 300 mm in a longitudinal direction of the rail and being an axial direction of the induction heating coil parallel to the longitudinal direction of the rail. The method further includes flowing a current to the induction heating coil arranged at one side of the welding center and to the induction heating coil arranged at the other side of the welding center being opposite to each other, and induction heating the rail to a heating temperature of 400° C. or higher and 750° C. or lower.

Abstract: A method of reheating a rail weld zone after rails were welded, a distance C between a reheating region P of a rail web portion 2 and a welding center Q is set to more than or equal to 0.2 times and less than or equal to three times a HAZ length Lh of the rail weld zone. A length B of the reheating region P may be more than or equal to 0.5 times and less than or equal to five times the HAZ length Lh of the rail weld zone. A height A of the reheating region P may be more than or equal to 0.2 times a height Hw of the rail web portion 2. A temperature Th reached in a reheating process at a center of the reheating region P may be higher than or equal to 400° C. and lower than or equal to 750° C.

Abstract: A stress-relief heat treatment apparatus according to the present invention for stress-relief heat-treating a rail which is welded includes an induction heating coil, and the induction heating coil is arranged at a lateral face of a web of the rail while being separated from a welding center of the rail by 20 mm to 300 mm in a longitudinal direction of the rail. The stress-relief heat treatment apparatus may include a plurality of the induction heating coils, and the induction heating coils may be arranged at both sides of the welding center. The stress-relief heat treatment apparatus may include a plurality of the induction heating coils, an axial direction of the induction heating coil may be vertical to a lateral surface of the rail, and a plurality of the induction heating coils, of which distances from the welding center along the longitudinal direction of the rail are the same, may be arranged to cover a whole circumference of the rail while being separated from each other.

Abstract: An object of the present invention is to provide a heat treatment device, a heat treatment method, and a rail steel which are suitable for preventing the occurrence of brittle fractures which originate in a base portion of a weld of the rail steel. A heat treatment device of the present invention includes a coil and heats a bottom surface of the base portion of the weld of the rail steel by induction heating. When a region in the weld which is heated to an Ac1 point or higher during welding is represented by HAZ, and the length of the HAZ in a length direction of the rail on the bottom surface of the base portion is represented by Lh, and a width of the rail steel is represented by W, the length of an outer region of the coil in the length direction of the rail is 1.2 times or more Lh and the length of the outer region of the coil in a width direction of the rail is 1.1 times or more W when viewed from opposite the bottom surface of the base portion.

Abstract: A stress-relief heat treatment apparatus according to the present invention for stress-relief heat-treating a rail which is welded includes an induction heating coil, and the induction heating coil is arranged at a lateral lace of a web of the rail while being separated from a welding center of the rail by 20 mm to 300 mm in a longitudinal direction of the rail. The stress-relief heat treatment apparatus may include a plurality of the induction heating coils, and the induction heating coils may be arranged at both sides of the welding center. The stress-relief heat treatment apparatus may include a plurality of the induction heating coils, an axial direction of the induction heating coil may be vertical to a lateral surface of the rail and a plurality of the induction heating coils, of which distances from the welding center along the longitudinal direction of the rail are the same, may be arranged to cover a whole circumference of the rail while being separated from each other.

Abstract: A method of reheating a rail weld zone after rails were welded, a distance C between a reheating region P of a rail web portion 2 and a welding center Q is set to more than or equal to 0.2 times and less than or equal to three times a HAZ length Lh of the rail weld zone. A length B of the reheating region P may be more than or equal to 0.5 times and less than or equal to five times the HAZ length Lh of the rail weld zone. A height A of the reheating region P may be more than or equal to 0.2 times a height Hw of the rail web portion 2. A temperature Th reached in a reheating process at a center of the reheating region P may be higher than or equal to 400° C. and lower than or equal to 750° C.

Abstract: The invention provides a method of cooling a rail weld zone. The method includes a first rail web portion cooling process of cooling a rail web portion cooling region of the rail weld zone in a part of a temperature range until the completion of transformation from austenite to pearlite, a second rail web portion cooling process of cooling the rail web portion cooling region after the entire rail web portion of the rail weld zone is transformed to pearlite, a foot portion cooling process of cooling a foot portion of the rail weld zone, and a head portion cooling process of cooling a head portion of the rail weld zone. When cooling time of the first and second rail web portion cooling processes is t minute, a k value satisfies an expression represented as ?0.1t+0.63?k??0.1t+2.33.

Abstract: A device for cooling a rail weld zone according to the invention includes a first cooler cooling a head portion of the rail weld zone, a second cooler cooling a rail web portion of the rail weld zone, and a control section controlling the first and second coolers. The first cooler includes a first temperature detecting section that detects the temperature of the head portion, and a first ejection section that ejects a first cooling fluid to the head portion. The second cooler includes a second temperature detecting section that detects the temperature of the rail web portion, and a second ejection section that ejects a second cooling fluid to the rail web portion. The control section individually changes the kinds, the flow rates, and the flow velocities of the first and second cooling fluids while cooling the head portion and the rail web portion.

Abstract: The invention provides a method of cooling a rail weld zone. The method includes a first rail web portion cooling process of cooling a rail web portion cooling region of the rail weld zone in a part of a temperature range until the completion of transformation from austenite to pearlite, a second rail web portion cooling process of cooling the rail web portion cooling region after the entire rail web portion of the rail weld zone is transformed to pearlite, a foot portion cooling process of cooling a foot portion of the rail weld zone, and a head portion cooling process of cooling a head portion of the rail weld zone. When cooling time of the first and second rail web portion cooling processes is t minute, a k value satisfies an expression represented as ?0.1t+0.63?k??0.1t+2.33.

Abstract: A device for cooling a rail weld zone according to the invention includes a first cooler cooling a head portion of the rail weld zone, a second cooler cooling a rail web portion of the rail weld zone, and a control section controlling the first and second coolers. The first cooler includes a first temperature detecting section that detects the temperature of the head portion, and a first ejection section that ejects a first cooling fluid to the head portion. The second cooler includes a second temperature detecting section that detects the temperature of the rail web portion, and a second ejection section that ejects a second cooling fluid to the rail web portion. The control section individually changes the kinds, the flow rates, and the flow velocities of the first and second cooling fluids while cooling the head portion and the rail web portion.

Abstract: In a method of automatically welding rails, welding of bottom portions of the rails is carried out as root pass welding of a first layer according to CO.sub.2 gas shielded arc weld technique, and as continuous multilayer welding of layers above the first layer according to CO.sub.2 gas shielded arc weld technique without discontinuing the welding of a second layer and upper layers. In welding of ankle portions (R2) of the rails, a flux is rapidly added to promptly shift to electroslag weld. Then, welding is conducted to head surfaces (R5) of the rails by continuing electroslag weld technique. This automatic welding method enables high efficiency field welding of rails, obviating the need for any complicated switching operation of the electric power source and use of several kinds of welding materials.