Seamless Steel Tube for an Airbag Accumulator and Process for its Manufacture

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A seamless steel tube for an airbag accumulator which can be manufactured by heat treatment of normalizing without quenching and tempering and which has a tensile strength of at least 850 MPa and resistance to bursting at −20° C. has a stee; composition comprising, in mass %, C : 0.08-0.20%, Si : 0.1-1.0%, Mn : 0.6-2.0%, P : at most 0.025%, S : at most 0.010%, Cr : 0.05-1.0%, 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, with the metallurgical structure being a mixed structure of ferrite+bainite : [in-line-formulae]Ceq=C+Si/24+Mn/6+(Cr+Mo)/5+(Ni+Cu)/15  (1)[/in-line-formulae]wherein the symbol for each element in Equation (1) indicates the number expressing the mass percent of the element.