STEEL PIPE FOR UNDERBODY COMPONENTS OF AUTOMOBILES, AND UNDERBODY COMPONENT OF AUTOMOBILES

摘要

A steel pipe for underbody components of automobiles, which has a chemical composition that contains, in mass%, 0.35-0.60% of C, 0.25-1.0% of Si, 0.05-2.0% of Mn, 0.1% or less of P, 0.0050% or less of S, 0.005-0.1% of Al, 0.01% or less of N, 0.01% or less of O, 0.20-1.5% of Mo, 0.01-0.05% of Ti, 0.0001-0.01% of B, 0-1.0% of Ni, 0-1.0% of Cu, 0-1.5% of Cr, 0-0.2% of Nb, 0-0.2% of V, 0-0.02% of Mg and 0-0.02% of REM, with the balance made up of Fe and impurities, while satisfying [5.0 ≤ Al × Ti/(Mn × S) × 10 ≤ 60.0] and [2.0 ≤ 3 × Si × Mo × B × 10⁴]. This steel pipe for underbody components of automobiles has a metal structure wherein the area ratio of cementite is 25-70% and the spheroidization rate of cementite is 70% or more.