THICK HOT ROLLED STEEL PLATE FOR STEEL PIPE AND STEEL PIPE PRODUCED THEREFROM HAVING EXCELLENT IMPACT TOUGHNESS AND METHOD FOR MANUFACTURING THEREOF

摘要

The present invention relates to a thick hot-rolled steel plate for a steel pipe having excellent impact toughness and a method for manufacturing the same. More specifically, the present invention relates to a high-strength and low-yield ratio hot-rolled steel plate having excellent impact which can be used as a steel pipe for oil wells, a steel pipe manufactured by the same, and a method of manufacturing the same. A hot-rolled steel plate according to an embodiment of the present invention comprises 0.3 to 0.5 wt% of C, 0.5 to 2.0 wt% of Mn, 0.05 to 0.5 wt% of Si, 0.01 to 0.05 wt% of Ti, 0.008 wt% or less of N (exclusive of 0), and 0.02 wt% or less of P (exclusive of 0), with the reminder thereof being Fe and inevitable impurities, wherein microstructure consists of ferrite of 5 to 15 area% and remaining pearlite, and an average packet size of the ferrite is 5 m or less (exclusive of 0). Therefore, the hot-rolled steel plate has, after making a pipe, yield strength of 379 to 552 MPa, tensile strength of 655 MPa or more, a yield ratio of 0.75 or less, and impact toughness of 50 J or more at 0C even at the thickness of 16 mm.