The test interstitial-free steel IF(/% : 0.0036-0.0049C

0.005-0.007Si

0.11-0.12Mn

0.007P

0.005S

0.007-0.011Alt

0.047-0.051Ti

0.0030N

0-0.0037Ce) is melted by a 10 kg vacuum induction furnace

and forged to 30 mm x 25 mm billet

finishing forging at 950 ℃

air cooling. With using Gleeble-1500D thermal simulation testing machine the tensile test on the testing steel with strain rate 0. 1 s

-1

at 750-1150 ℃ has been carried out to study the effect of micro rare earth (RE) element Ce on high temperature tensile properties of the IF steel. As compared with IF steel non-containing Ce

the hot plasticity ( reduction of area-Z value) and hot tensil

e strength ( Rm value) of IF-Ce steel containing 0. 0037%Ce increase obviously

but with increasing temperature the increment decreases ； the reduction of area and tensile strength at elevated temperature of IF steel and IF-Ce steel respectively are 77.62% -110 MPa for IF and 88.65%-160 MPa for IF-Ce at 750 °C ； 87.35% -85 MPa for IF and 92.88% -100 MPa for IF-Ce at 950 ℃: and 85.68% - 55 MPa for IF and 90.62% -58 MPa for IF-Ce at 1150 °C. The main reasons to increase hot plasticity and hot tensile strength of IF steel by adding RE element are that the element Ce improves structure of steel

fines grain size

and segregates and clusters at grain boundary to increase the strength of grain boundary.