SA516Gr70 steel plate with excellent high-temperature strength at 200-400 DEG C and manufacturing method of SA516Gr70 steel plate

The invention relates to an SA516Gr70 steel plate with excellent high-temperature strength at 200-400 DEG C and a manufacturing method thereof. The steel plate comprises the following chemical components in percentage by weight: 0.16-0.20% of C, 0.20-0.40% of Si, 1.20-1.50% of Mn, less than or equal to 0.006% of P, less than or equal to 0.001% of S, 0.10-0.20% of Ni, 0.04-0.10% of Mo, 0.10-0.20% of Cr, 0.01-0.02% of Nb, 0.01-0.03% of V, 0.01-0.03% of Ti, 0.02-0.05% of Alt, less than or equal to 0.0005% of B, less than or equal to 0.0005% of Pb, less than or equal to 0.0005% of Sn, less than or equal to 0.0005% of As, less than or The structure is a mixed microstructure composed of, by area percent, 65%-80% of ferrite, 10%-15% of pearlite and 10%-20% of granular bainite, and the granular bainite structure is distributed in a cluster shape. Under the condition of 620 +/-10 DEG C * 12 h simulated postweld heat treatment, the allowance of yield strength and tensile strength of the steel plate is 30 MPa or above,