High strength steel pipe for an air bag and a process for its manufacture

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In order to manufacture a steel pipe for an air bag which can cope with increase in the pressure of gas blown into an air bag and decreases in the wall thickness of an accumulator, a steel having a composition, mass %, of : C : 0.05-0.20%, Si : 0.1-1.0%, Mn : 0.20-2.0%, P : at most 0.025%, S : at most 0.010%, Cr : 0.05-1.0%, Al : at most 0.10%, if necessary at least one of Mo : at most 0.50%, Ni : at most 1.5%, Cu : at most 0.5%, V : at most 0.2%, Ti : at most 0.1%, Nb : at most 0.1%, and B : at most 0.005%, and also if necessary, at least one of Ca : at most 0.01%, Mg : at most 0.01%, and REM (rare earth elements) : at most 0.01%, and a remainder of Fe and impurities is used to produce a steel pipe, and the pipe is then subjected to cold working to predetermined dimensions, then to heating to a temperature of at least the Ac1 transformation temperature followed by quenching, and then to tempering at a temperature no higher than the Ac1 transformation temperature.