| 摘要 |
Provided is a high strength seamless steel pipe for use in oil wells which has excellent resistance to sulfide stress cracking. The seamless steel pipe has a composition containing, in mass%, C:0.20-0.50%, Si:0.05-0.40%, Mn:0.3-0.9%, P:0.015% or less, S:0.005% or less, Al:0.005-0.1%, N:0.008% or less, Cr:greater than 0.6% and less than or equal to 1.7%, Mo:greater than 1.0% and less than or equal to 3.0%, V:0.01-0.30%, Nb:greater than or equal to 0.001% and less than 0.01%, B:0.0003-0.0030%, and O (oxygen):0.0030% or less, and the material of the steel pipe has a tempered martensite phase of 95 vol% or greater, with the prior austenite grains thereof having a grain size number of 8.5 or greater. The segregation index Ps is less than 65 and is defined by a relational formula of XM, which is the ratio of the segregation content and the average content: Ps=8.1(XSi+XMn+XMo)+1.2XP (Here, XM: (segregation content (mass%) of element M)/(average content (mass%) of element M.). |
