Solid steel tube welding execelent in low temperature rigidity, method for manufacturing steel tube welded excellent in low temperature rigidity, and steel plate for manufacturing thick welded steel tube.

摘要

Solid steel tube excellent in low temperature stiffness, method for making steel tube excellent thick soldier in low temperature stiffness, and steel plate to manufacture all of the thick welded steel. This invention refers to a welded steel tube that is executively thick at low temperature when the contents of M and M satisfy me (expression 1) below, the PCM obtained by (expression 2) below is 0,16 to 0,19, and a metal structure of a steel plate of BAS material And consists of ferrita being from 30 to 95% in an area ratio and a temperature EBA transformation structure,And in a metal structure of a rough grain HAZ, a zone -contour ratio of the ferrite grain is 1,5% or more, the total area ratio of the border of the ferrite grain and the intragranular Ferris no less than 11% or more than 90%,For area of Ma is 10% or less, and its balance is composed of bainite. 12325 (0,85 x [mn]) 15215...(expression 1) and PCM [[c] [si]/30 + ([mn] + [ass + [cr]]/20 [[ni]/60 + [mo]/15 [(v]/10...(expression 2)