CR-containing steel pipe for pipe for excellent conduction in resistance to crevice corrosion cracking in heat-affected welded zone

摘要

Cr-containing steel pipe for pipe for excellent conduction in resistance to cracking corrosion under intergranular stress in thermally affected welded zone. The present invention relates to a steel tube containing cr for high strength conduction pipe of class x-65 to x-80 and being excellent in toughness, corrosion resistance and resistance to cracking by sulphide stress corrosion, and It also excels in resistance to cracks cracking under intergranular stress in a thermally affected welded zone. to be more specific, the composition of the cr-containing steel tube in% masa; 0.001 to 0.015% c; 0.05 to 0.50% of itself; 0.10 to 2.0% min; 0.001 to 0.10% al; 15.0 to 18.0% of cr; 2.0 to 6.0% ni; 1.5 to 3.5% mo; 0.001 to 0.20% and v and 0.015% or less of n, to satisfy the following ratio of cr + mo + 0.4w + 0.3si-43.5c - 0.4mn-ni-0.3cu - 9n: 11.5 to 13.3. A thermally affected welded zone that is heated to a ferrite single phase temperature region of 1300 ° C or more at the time of welding and is cooled has a microstructure in which 50% or more of the previous ferrite grain boundaries are occupied by one phase. martensite and / or an austenite phase in a ratio to the total length of the previous ferrite grain boundaries. accordingly, the formation of an exhausted carbide zone is suppressed, thereby providing a steel pipe that markedly improves resistance to cracks cracking under intergranular stress in a thermally affected welded zone. Due to such steel pipe, it is possible to achieve an advantageous effect in which it is unnecessary to carry out post-weld heat treatment, thereby greatly shortening the construction period of the welded steel pipe structure.