Low-compression-ratio and thick-specification X70-grade
gas transmission pipeline steel is prepared from, by weight percent, 0.03-0.075% of C, 0.15-0.35% of Si, 1.30-1.90% of Mn, not larger than 0.015% of P, not larger than 0.002% of S, not larger than 0.006% of N, 0.035-0.065% of Nb, 0.025-0.05% of V, 0.015-0.025% of Ti, 0.1-0.40% of Cr, 0.1-0.2% of Ni and 0.10-0.25% of Mo. Production steps include heating of
casting blanks with the thickness
ranging from 225 mm to 235 mm, rough rolling, high-pressure water descaling, fine rolling, cooling, straightening and standby application. According to the low-compression-ratio and thick-specification X70-grade
gas transmission pipeline steel, the X70-grade pipeline steel with the thickness being 30 mm or above can be produced through the
continuous casting blanks with the thickness being 230 mm, the Rt0.5 of the product ranges from 500 MPa to 580 MPa, the Rm of the product ranges from 600 MPa to 650 MPa, the ratio of the Rt0.5 to the Rm is not larger than 0.90, and the elongation A50 is not smaller than 24%; at -20 DEG C, the
impact energy KV2 is not smaller than 250 J; at -15 DEG C, the DWTT fracture
surface shear rate SA is not smaller than 95%; and HV10 <=235.