Steel plate for ultralow-temperature and high-pressure service delivery tubes, and its making method

The invention discloses a steel plate for ultralow-temperature and high-pressure service delivery tubes, and its making method. The chemical components of the steel plate comprise 0.03-0.07wt% of C, 0-0.30wt% of Si, 1.5-1.9wt% of Mn, 0.015-0.06wt% of Al, 0.05-0.11wt% of Nb, 0.010-0.018wt% of Ti, 0.10-0.30wt% of Cr, 0.10-0.30wt% of Cu, 0.10-0.30wt% of Ni, 0-0.30wt% of Mo, 0-0.015wt% of P, 0-0.004wt% of S, 0-0.005wt% of N, and the balance of Fe and impurity elements, wherein a weight ratio of Ca/S is not smaller than 2, a weight ratio of Ti/N is not smaller than 4, the equivalent C amount Ceq of the steel plate is not greater than 0.43, and the crack sensitive index Pcm of the steel plate is not greater than 0.21. The yield strength and the tensile strength (Rm) of the steel plate made in the invention are not smaller than 500MPa and not smaller than 600MPa respectively, the steel plate has the advantages of good low temperature toughness, good crack cracking stopping performance, good weldability and low cost, and the making method has the advantages of simplicity and easy control, and is also suitable for making large ships, ocean engineering, bridges, high-rise buildings and important structural members.