| 摘要 |
PURPOSE: A method for producing steel for a line pipe is provided to easily assemble pipes by having a yield ratio of under 85% while maintaining yielding strength of 50kgf/mm¬2 and to prevent the generation of HIC(hydrogen induced crack). CONSTITUTION: A steel slab is composed of 0.02-0.03wt% of C, 1.6-2.0wt% of Mn, 0.1-0.2wt% of Si, 0.02-0.50wt% of Al, 0.01-0.02wt% of Ti, 0.04-0.06wt% of Nb, 0.15-0.25wt% of Mo, 0.001-0.002wt%of B, under 0.01wt% of V, under 0.002wt% of S, under 0.02wt of P, 20-60ppm of N, 20-50ppm of Ca, and the remnant wt% of Fe and impurities. The steel slab is heated at a temperature of 1150-1250°C for being hot rolled at a finishing temperature of Ar3+(100-200)°C. Then, the steel slab is rapidly cooled at a cooling speed of 7-11°C/sec to the temperature of 450-510°C for being cooled to be a normal temperature.
|
