The tested steel 32CrNiMoNb (/% ： 0.32C

0. 30Si

0. 30Mn

0.012P

0. 004S

1.25Cr

1.20Ni

0. 36Mo

0. 05Nb) is melted by a 200 kg vacuum induction furnace and cast to 130 mm x 135 mm billet. And in laboratory the billet is rolled to 12 mm plate by a 550mm medium-heavy mill using two stage controlling rolling and cooling and direct- quenching process. The effect of beginning rolling temperature (950°C and 1000°C )

finishing rolling temperature (900°C and 950°C ) and direct-quenching end cooling temperature (150~350 °C ) at second stage on structure and mechanical properties of tested steel has been tested. Results show that at second stage with beginning rolling at (950 土 10)°C

finishing rolling at (900 ± 10)°C and direct-quenching end cooling t

emperature (250 土 10)°C

the matching of mechanical properties (R

p0.2

- 1 515 MPa

R

m

- 1 805 MPa

A- 8% and at -40 °C impact energy KV2- 24 J) and bending performance (180° ) of plate

structure (fine martensite) and precipitated phase ( NbCN) is best.