| 摘要 |
The present invention relates to a steel for a drill collar bar having high strength and high toughness. The steel comprises: 0.42-0.48 wt% of C, 0.15-0.35 wt% of Si, 0.85-1.20 wt% of Mn, 0.85-1.20 wt% of Cr, 0.030 wt% or less of P (exclusive of 0), 0.030 wt% or less of S (exclusive of 0), 0.25 wt% or less of Cu (exclusive of 0), 0.05-0.25 wt% of Ni, 0.25-0.35 wt% of Mo, 0.005-0.030 wt% of Al, 0.005-0.015 wt% of Ti, 0.010-0.040 wt% of Nb, 0.0035-0.0120 wt% of N, and the remaining consisting of Fe and inevitable impurities. The steel for the drill collar bar of the present invention has a tensile strength of 1000 MPa or more; a yield strength of 895 MPa or more; and an impact toughness of 54 J or more at -20°C by obtaining a fine grain size. Also, the drill collar bar manufactured by a continuous casting method of the present invention has excellent physical properties while showing uniform mechanical properties at all positions of a rod. |
