Patent ID: 8496763

Claim:
A seamless steel tube for an airbag accumulator characterized by having a steel composition consisting essentially, in mass %, of C: 0.08-0.20%, Si: 0.1-1.0%, Mn: 0.6-1.6%, P: at most 0.025%, S: at most 0.010%, Cr: 0.05-0.8%, Mo: 0.05-1.0%, Al: 0.002-0.10%, at least one of Ca: 0.0003-0.01%, Mg: 0.0003-0.01%, and REM (rare earth metals): 0.0003-0.01%, at least one of Ti: 0.002-0.1% and Nb: 0.002-0.1%, with Ceq which is defined by the following Equation (1) being in the range of 0.45-0.63, and a remainder of Fe and impurities, with the metallurgical structure being a mixed structure of ferrite+bainite having an area fraction of bainite of at least 10%, and having a tensile strength of 850 MPa or more and a vTrs 100 value of −20° C. or less: Ceq =C+Si/24+Mn/6+(Cr+Mo)/5+(Ni+Cu)/15 (1) wherein the symbol for each element in Equation (1) indicates the number expressing the mass percent of the element.