| 摘要 |
Disclosed are a method to manufacture a hot-rolled steel sheet with excellent heat-treatment properties, and a method to manufacture a steel pipe with excellent resistance to corrosion. According to the present invention, the method to manufacture the hot-rolled steam sheet is characterized by including a step of reheating a slab comprising: 0.1-0.2 wt% of C, 0.05-0.2 wt% of Si, 0.4-0.6 wt% of Mn, 0.01 wt% or less of P, 0.001 wt% or less of S, 0.1 wt% or less of Al, 0.01-0.05 wt% of Nb, 0.01-0.02 wt% of Ti, 0.1-0.4 wt% of Mo, 0.2-0.5 wt% of Cr, 0.001-0.003 wt% of Ca, 0.006 wt% or less of N, and the remainder consisting of Fe and inevitable impurities at a temperature of 1200°C or higher for at least two hours; a step of rough-rolling the reheated slab within an austenite recrystallization temperature range; a step of finish-rolling the rough-rolled slab within an austenite non-recrystallization range; and a step of air-cooling the slab after cooling the finish-rolled slab at an average cooling speed of 10 °C/sec or higher to be cooled below 650°C or less. |
