MANUFACTURE OF HIGH STRENGTH RESISTANCE WELDED STEEL TUBE FOR AUTOMOTIVE USE EXCELLENT IN DUCTILITY AND THREE-POINT BENDABILITY

摘要

PURPOSE: To improve the strength and toughness of a steel tube by subjecting steel sheet stock contg. specified amounts of C, Si, Mn, P, S, Cr, Ti, B, Ca and N to resistance seam welding and executing high-frequency heat treatment of high-frequency heating and hardening. ;CONSTITUTION: Steel sheet stock contg., by weight, 0.15 to 0.27% C, 0.5% Si, 0.80 to 1.70% Mn, ≤0.02% P, ≤0.02% S, 0.1 to 0.7% Cr, 0.005 to 0.040% Ti, 0.0005 to O.0025% B, 0.0004 to 0.0100% Ca, ≤0.0080% N and the balance Fe with inevitable impurities is subjected to resistance seam welding. The obtd. steel tube is subjected to high-frequency heat treatment of high-frequency heating and hardening under the conditions of 850 to 1050°C heating temp. and ≥100°C/sec cooling rate. The above compsn. is incorporated with optimum amounts of one or more kinds among Nb, V and Mo according to necessary. By the addition of Ca, sound seam properties can be obtd., and by high-frequency heating treatment, the objective resistance welded steel tube having 150 to 190kgf/mm² class tensile strength and excellent in three-point bendability can be obtd.;COPYRIGHT: (C)1993,JPO&Japio