NEW PLATES IN THERMOMECHANICAL STEELS - A N OUTSTANDING EXAMPLE - THEREMOULINS BRIDGE

Until now normalized heavy plates have been used for bridge constructi on. The normalized delivery condition cart be achieved by normalizing hear treatment or by normalizing rolling. The mechanical properties of the normalized plates (N steels) mostly depend on the chemical analys is. The development of powerfull rolling mills and accelerated cooling equipments associated with extremely accurate control devices enable the plate manufacturers to achieve specific rolling sequences which le ad directly to enhanced metal properties without any subsequent normal ization heat treatment. This process is the thermomechanical controlle d process : specific rolling sequences are achieved within specific te mperatures ranges in order to promote a very fine grained metallurgica l structure ; Accelerated Cooling may also be implemented, depending o n plate thickness, in order to achieve a fine grained structure and su bsequent hardening through adequate micro-alloying precipitation. Taki ng into account this particular rolling procedure, the TM plates exhib it excellent properties in comparison with those of the normalized pla tes : with equivalent chemical analysis TM plates will show higher ten sile and roughness properties than N plates, with lighter chemical ana lysis, TM plates will exhibit tensile properties equivalent to those o f N plates. The above leads naturally to better fabrication properties of the TM plates in comparison with those of the N plates. This paper emphasizes the TM plates production route, standards, fabrication pro perties and an example of application of these TM plates for the const ruction of the Remoulins bridge (located on the Garden River, South of France) and resulting savings.