The effect of austenizing time (30 - 100 s) at 850 °C on structure and mechanical properties of 1 mm sheet of DF78O cold rolled dual phase steel (% ： 0.15C

1.80Mn

0.08Ti

0.04Al) has been studied by using continuous annealing simulation machine. Results show that with conditions of austenizing at 850 X.

cooling to 460 °C with 24 Y/s

retention for 12 s then cooling to ambient temperature with 7 Y/s

the martensite content in steel and tensile strength of steel could be controlled by change austenizing time: with decreasing austenizing time the martensite is continuously banded distribution and with prolonging austenizing time the continuity of banded martensite is weakening； as austenizing for 30

45 and 100 s

the martensite content in the dual phase steel is respectively 13. 7%

21. 6% and 15. 6%

and the tensile strength of steel is respectively 800

840 and 805 MPa.