The continuous cooling transformation ( CCT) curves of high carbon alloy steel 75Crl (/% : 0. 75C

0. 27Si

0. 85Mn

0. 010P

0.003S

0.60Cr) and the effect of cooling rate on phases and structure of steel are obtained by Gleeble-3800 thermal simulation testing machine to carry out first reduction 25% deformation with deformation rate 15 s"1 at 1 090 °C then with 20 °C/s cooling to 880 °C and second reduction 25% with deformation rate 20 s

-1

then with 0. 05 〜 45 ℃ /s cooling to ambient temperature. Results show that the critical points of phase transformation Ac

1

and Ac

3

are respectively 730 °C and 773 °C ; with cooling rate being lower than 1°C /s the main structure of steel is proeutectoid ferrite and fine pearlite

with cooling rate being 1 〜

10 °C/s

the structure of steel is pearlite and bainite; with cooling rate being larger than 10 °C/s the martensite occurs in structure and with increasing cooling rate the amount of martensite increases

and with cooling rate being larger than 18 °C/s the main structure of steel is martensite and has minor bainite.