The 3 mm hot-rolled plate finishing rolling at 860 °C water-cooling of dual-phase steel DP780 (/% : 0. 09C

0. 17Si

1. 94Mn

0. 009P

0. 003 S

0. 23 Cr) is cold-rolled to 1mm sheet respectively with single pass reduction 1. 0% and 6. 0%

and annealed at 780 °C for 5 h. The distribution of surface residual stress and thickness direction residual stress after cold-rolling and annealing of dual-phase high-strength steel DP780 with different single pass reduction is analyzed respectively by using X-ray diffraction and peeling method. Test results show that the effect of single pass reduction on distribution of stress in dual phase steel DP78O is great

the surface residual stress of sheet with pass reduction 6. 0% is larger and with increasing the distance along thickness direction the stress gradually decreases

the surface residual stress of sheet with pass reduction 1. 0% is smaller and with increasing the distance along thickness direction the stress first increases then decreases

and the compressive stress of center of thickness for both reduction is up to maximum value. The residual stress of sheet reduces markedly by annealing

that is with pass reduction 1. 0% the surface residual stress of sheet decreases by 50% and with pass reduction 6. 0% the surface residual stress of sheet decreases by 75%

and after annealing the distribution rule of residual stress along thickness direction with both reduction percentages is about the same.