STEEL PIPE FOR HIGH-PRESSURE FUEL PIPE AND HIGH-PRESSURE FUEL PIPE COMPRISING IT

摘要

A steel pipe for fuel injection pipe has a chemical composition consisting, by mass percent, of, C: 0.12 to 0.27%, Si: 0.05 to 0.40%, Mn: 0.3 to 2.0%, Al: 0.005 to 0.060%, N: 0.0020 to 0.0080%, Ti: 0.005 to 0.015%, Nb: 0.015 to 0.045%, Cr: 0 to 1.0%, Mo: 0 to 1.0%, Cu: 0 to 0.5%, Ni: 0 to 0.5%, V: 0 to 0.15%, and B: 0 to 0.005%, the balance being Fe and impurities, and the contents of Ca, P, S, and O in the impurities being Ca: 0.001% or less, P: 0.02% or less, S: 0.01% or less, and O: 0.0040% or less, and has a metal micro-structure consisting of a tempered martensitic structure, or a mixed structure of tempered martensite and tempered bainite, in which a prior-austenite grain size number is 10.0 or more, wherein the steel pipe has a tensile strength TS 800 MPa or higher, and a critical internal pressure is [0.3 × TS × ±] or more, wherein ± = [(D/d) 2 -1]/[0.776 × (D/d) 2 ], D: steel pipe outer diameter (mm), and d: steel pipe inner diameter (mm).