The effects of hot-rolled three-stage cooling and temper-rolling processes on mechanical properties of 2.3 mm 700 MPa grade Nb-Ti micro-alloying S600MC high strength steel strip (/% : 0.07C

0.15Si

1.50Mn

0.015P

0.003S

0.025Alt

0.015Nb

0.08Ti) are studied. When end rolling at 870 as intermediate temperature decreasing from 670 X. to 580 °C

the yield strength increases from 577 MPa to 600 MPa

the tensile strength basically remaines unchanged (774 MPa to 784 MPa)

the elongation decreases from 24% to 21%

and the yield ratio increases by 0.04. When the coiling temperature increases from 150 °C to 250 °C

the mechanical properties remain unchanged. The yield strength of high strength steel with primary temper-rolling process increases by 20 MPa to 43 MPa

while the tensile strength changes slightly and the elongation decreases by 2-5 percentage point. The yield strength increases by the secondary temper-rolling process significantly to 101 MPa

while the elongation decreases by 8 percentage point

which is adverse to comprehensive properties.