The effect of quenching temperatures on microstructure and mechanical properties of 780 MPa grade hydroelectric steel(/% ：0. 09C

0. 10Si

l.50Mn

0.009P

0.002S

0. 90Cr

0.20Ni

0.023Ti

0.004Nb

0.0010B) was investigated. The results showed that the tested steel can transform into lath bainite microstructure when the steel was quenched at different temperatures

and the average grain size of prior austenite grows from 9.1 μm to 16.6 μm with increasing quenching temperature from 910 °C to 950°C

the microstructure of the tested steel after tempering is basically maintained a lath structure after quenching. When the quenching temperature is between 910 °C and 950°C

with increasing quenching temperature

the strength of the tested steel increases firstly then decreases and the maximum value reaches at 930 °C

and variation of the impact toughness and elongation of tested steel are identical compared with the strength. The optimum mechanical properties are obtained when quenching at 930°C. and tempering at 610 °C

the yield strength is 802 MPa

tensile strength 858 MPa and elongation 19% with the Charpy impact energy 238 J at -40 °C .