Ultralow-carbon bake-hardened steel plate blank and control method of solid solution carbon content thereof

The invention relates to an ultralow-carbon bake-hardened steel plate blank which comprises the following chemical components in percentage by weight: 0.0015-0.0030% of C, at most 0.03% of Si, 0.30-0.60% of Mn, 0.030-0.050% of P, at most 0.015% of S, 0.015-0.060% of Alt, 0.005-0.025% of Nb, at most 0.0050% of N, 0.0005-0.0020% of B and the balance of Fe. The invention also relates to of a control method of the solid solution carbon content of the ultralow-carbon bake-hardened steel, which comprises the following steps: sequentially carrying out pre-desulfurization and slag removal treatment on molten iron to obtain first molten iron with the sulfur content of at most 0.003%; smelting the first molten iron to obtain first molten steel with the carbon content of 0.025-0.050%; refining the first molten steel by a vacuum refining furnace to obtain second molten steel; sending the second molten steel into a continuous casting procedure, injecting into a carbon-free tundish, and casting the molten steel to obtain the ultralow-carbon bake-hardened steel plate blank, wherein the carbon increase amount of the second molten steel in the continuous casting process is at most 0.0003%. The control method shortens the smelting time in the vacuum refining furnace, enhances the production efficiency, and enhances the primary smelting hit rate of the plate blank composition.