| 摘要 |
PURPOSE:To produce inexpensively an electric welded steel pipe for automobiles which has high quenched hardness, by subjecting the electric welded steel pipe formed of a steel contg. C, Si, Mn, etc. having a specific compsn. and compsn. relation to specific normalizing and hardening. CONSTITUTION:A hot-rolled steel sheet obtd. from the steel consisting of 0.30- 0.35% C, 0.10-0.30% Si, 1.40-2.00% Mn and the balance Fe and unavoidable elements and contg. <=4.0 or 5.5-7.0 Mn/C is formed to a tubular body, and the edges of the tubular body are welded by heating, thereby forming a steel pipe. The resultant electric welded steel pipe is normalized at 800-950 deg.X for 1-5min by a bright normalizing furnace or the like to relieve strain and to make the texture uniform and fine in grains. The steel pipe is allowed to cool after the normalizing. Such steel pipe is further quickly heated to 950-1,050 deg.C at >=50 deg.C/ min heating rate between Ac1-Ac3 by a high frequency heating coil or the like, and is immediately hardened at >=250 deg.C/sec cooling rate without holding, whereby the electric welded steel pipe having >=600Hv quenched hardness for automobiles is obtd. |
