| 摘要 |
<p>A high strength steel plate is provided, wherein the high strength steel plate is low in strength deterioration even when performing a long stress relief annealing process after a welding process, and is excellent in weldability by preventing the generation of cracking when performing a welding process. A steel plate contains, by mass percent, 0.05 to 0.18% of C, 0.10 to 0.50% of Si, 1.2 to 2.0% of Mn, an 0.01 to 0.10% of Al, 0.05 to 0.30% of Cr, and 0.01 to 0.05% of V, and satisfies the following mathematical expression: 6.7[Cr]+4.5[Mn]+3.5[V]>=7.2% by mass, where [Cr], [Mn] and [V] represent a Cr content, a Mn content and a V content by mass percent, wherein cementite grains in structure of the steel plate have a mean grain size of 0.165 mum or less as a circle equivalent diameter. The steel plate further contains at least one of 0.05 and 0.8% of Cu and 0.05 and 1% of Ni. The steel plate further contains 0.01 and 0.3% of Mo. The steel plate further contains 0.005 and 0.05% of Nb. The steel plate further contains 0.005 and 0.05% of Ti. The steel plate further contains 0.0005 and 0.01% of B. The steel plate further contains 0.0005 and 0.005% of Ca.</p> |
