SEAMLESS STEEL TUBE FOR AN AIRBAG ACCUMULATOR AND A 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%, A1 : 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 : 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.