STEEL PIPE FOR FUEL INJECTION PIPE AND FUEL INJECTION PIPE USING THE SAME

摘要

A steel pipe has a 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. As impurities, contents are Ca: 0.001% or less, P: 0.02% or less, S: 0.01% or less, and O: 0.0040% or less. The micro-structure is tempered martensitic or tempered martensite and tempered bainite, in which a prior-austenite grain size number is 10.0 or more. Tensile strength is TS 800 MPa or higher. Critical internal pressure is [0.3·TS·a] or more, a=[(D/d)2−1]/[0.776 ·(D/d)2], D: pipe outer diameter (mm), d: pipe inner diameter (mm).

主权项

1. A steel pipe for fuel injection pipe having 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 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 having 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 of 800 MPa or higher, and a critical internal pressure satisfying a following formula (i):
IP≧0.3×TS×α  (i)α=[(D/d)2−1]/[0.776×(D/d)2]  (ii) where, in the above formula (i), IP denotes a critical internal pressure (MPa), TS denotes a tensile strength (MPa), and a is a value represented by the above formula (ii), and where, in the above formula (ii), D denotes an outer diameter (mm) of the steel pipe for fuel injection pipe, and d denotes an inner diameter (mm) of the steel pipe for fuel injection pipe.