Economic air-cooled dual-phase low yield ratio steel plate and production process thereof

The invention relates to an economic air-cooled dual-phase low yield ratio steel plate and a production process thereof. The steel plate comprises the following chemical components in percentage by weight: 0.07-0.09% of C, 0.70-0.90% of Si, 1.90-2.10% of Mn, less than or equal to 0.015% of P, less than or equal to 0.008% of S, 0.90-1.10% of Cr, and the balance of Fe and inevitable impurities. By controlling a Mn/C ratio at 21-25, Si+Mn+Cr content is 3.5-3.7%; through a low-temperature rolling process and by air cooling after cooling, a ferrite+martensite dual-phase structure is obtained; according to the prepared steel plate product, thickness is more than or equal to 15mm, yield strength Rp0.2 is less than or equal to 440MPa, tensile strength Rm is more than or equal to 690Mpa, percentage elongation after fracture is more than or equal to 14%, yield ratio (Rp0.2/Rm) is less than or equal to 0.64 and impact energy at minus 20 DEG C is more than or equal to 60J.