ULTRAHIGH STRENGTH WELD JOINT EXCELLENT IN LOW TEMPERATURE CRACKING PROPERTY OF WELD METAL, ULTRAHIGH STRENGTH WELDED STEEL PIPE, AND THEIR MANUFACTURING METHODS

摘要

PROBLEM TO BE SOLVED: To provide a weld joint made of a steel plate, in which tensile strength of the weld joint made of the steel plate or the pipe body of the steel pipe is ≥ 800 MPa (over X100 in API standards) and which is excellent in low temperature cracking properties, a steel pipe which is made by forming a steel plate into a tubular shape and welding the edge parts each other, and their manufacturing methods.

SOLUTION: The ultrahigh strength weld joint and the steel pipe have a weld metal on the inner face which has an amount of a non-diffusible hydrogen of ≥0.01 ppm and is excellent in the low temperature cracking properties. Preferably, a ratio of the non-diffusible hydrogen amount to the whole hydrogen amount of the weld metal on the inner face is ≥ 0.5 % by percentage. Further, preferably, the weld metal on the inner face has Mo carbides of 1 piece/μm2or more. After the abutted part is welded from the inner face, the outer face is welded by setting the reheating temperature of the weld metal on the inner face to 500-700°C.

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