Automobile body reinforcing steel pipe

Abstract

An automobile body reinforcing steel pipe having a wall thickness-to-outer diameter ratio, t/D, defined by: 0.09-4.8.times.10.sup.-5 .times.L.ltoreq.t/D.ltoreq.0.16-6.0.times.10.sup.-5 .times.L where L(mm) is a span of a bending load applied to the pipe. The pipe has a tensile strength of 120 kgf/mm.sup.2 or more and an elongation of 10% or more, and is preferably made of a steel consisting of 0.15-0.25 wt % C, 1.8 wt % or less Mn, 0.5 wt % or less Si, 0.04 wt % or less Ti, 0.0003-0.0035 wt % B, and the balance of Fe and unavoidable impurities including 0.0080 wt % or less N. A process for producing the steel pipe comprises: coiling a hot rolled steel sheet at a temperature of 600.degree. C. or higher; electric welding the adjoining edges of the sheet to form a steel pipe; and quench hardening the pipe.

Dependencies are inferred from the claim text.