High-workability steel pipe and method of producing same

Details High-workability steel pipe and method of producing same High-workability steel pipe and method of producing same

B - Operations, Transporting

21

C

B21C 37/08 (2006.01) B21B 17/14 (2006.01) C21D 8/10 (2006.01) C21D 9/08 (2006.01) C22C 38/06 (2006.01)

Patent

CA 2403830

The invention provides a steel pipe being superior in workability, particularly in bending workability, in which an r-value in the axial direction of the pipe in a portion where melting or transformation of a steel material has occurred during seam welding is as high as comparable to that in a portion where melting or transformation of the steel material has not occurred, and a method of producing the steel pipe. In the high--workability steel pipe, an r-value in the longitudinal direction is not less than 1.2, more preferably not less than 1.6, over an entire area in the circumferential direction, including a seamed portion. The steel pipe is produced by a method comprising the step of performing diameter-reducing rolling on a steel pipe in a temperature range of from 600°C to Ac3 with a reduction in diameter of not less than 30%, preferably after heating the steel pipe to temperatures of not lower than Ac1, the steel pipe being produced by seam--welding strip steel, or a method further comprising the step of performing heat treatment of holding the rolled steel pipe in a temperature range of from 600°C to 900°C for a time of 1 second or longer during cooling subsequent to the diameter-reducing rolling or by reheating the rolled steel pipe after the cooling.

L'invention concerne un tuyau en acier à haute formabilité, dont la valeur r dans le sens longitudinal est supérieure ou égale à 1,2 et de préférence supérieure ou égale à 1,6 sur toute la partie comportant une zone de raccord. L'invention concerne également un procédé de fabrication correspondant, qui consiste à chauffer un tuyau de cercles d'acier assemblés par soudure électrique, à une température Ac1 ou supérieure, et à soumettre le tuyau échauffé à une opération d'étirage-réduction, selon une réduction de diamètre supérieure ou égale à 30 %, à 600 DEG C ou plus et jusqu'à une température Ac1, puis éventuellement à chauffer de nouveau le tuyau durant ou après le refroidissement qui suit l'opération susmentionnée, à une température comprise entre 600 DEG C et 900 DEG C, en maintenant la température pendant une seconde au moins. Ce type de tuyau à haute formabilité présente une partie fondue ou transformée en soudure par joints, avec une valeur r élevée dans le sens axial, équivalant à la valeur r d'une partie non soumise à la soudure, et la formabilité est particulièrement remarquable à la courbure.

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