Steel tube for airbags and a process for manufacturing same

摘要

A steel tube for an airbag which has a low alloy cost and a strength of at least 1000 MPa and vTrs100 of −80° C. or below and a process for its manufacture which can minimize the number of times that softening annealing treatment is performed in a cold drawing step are provided. Stable properties are obtained even when quench hardening is carried out by high frequency induction heating on a large scale. The steel tube has a steel composition which comprises, in mass percent, C: 0.05-0.20%, Si: 0.10-0.50%, Mn: 0.10-1.00%, P: at most 0.025%, S: at most 0.005%, Al: 0.005-0.10%, Ca: 0.0005-0.0050%, Nb: 0.005-0.050%, Ti: 0.005-0.050%, Cu: 0.01-0.50%, Ni: 0.01-0.50%, Cr: 0.01-0.50%, B: 0.0005-0.0050%, N: 0.002-0.010%, and a remainder of Fe and unavoidable impurities.

主权项

1. A seamless steel tube for an airbag characterized by having a quenched-and-tempered microstructure and a steel composition which consists of, in mass percent,
C: 0.05-0.20%, Si: 0.10-0.50%, Mn: 0.10-1.00%, P: at most 0.025%, S: at most 0.005%, Al: 0.005-0.10%, Ca: 0.0005-0.0050%, Nb: 0.005-0.050%, Ti: 0.005-0.050%, Cu: 0.01-0.50%, Ni: 0.01-0.50%, Cr: 0.01-0.50%, B: 0.0005-0.0050%, N: 0.002-0.010%, and a remainder of Fe and unavoidable impurities, and which satisfies the following Equation (1), the tube having a tensile strength of at least 1000 MPa, a yield strength of at least 960 MPa, and a high toughness such that vTrs100 is −100° C. or below:
Cu+Ni≧(M)2+0.3  (1) wherein M indicates Cr, and the symbols for elements indicate the contents in mass percent of those elements.