The production flow sheet for Nb-Ti microalloying pipeline steel X65 (/%: 0. 07C

1. 60Mn

0. 35Mo) is 130 t top and bottom combined blown converter-ladle argon blowing-LF-RH-250 mm X 1 500 mm slab casting-continuous rolling to 30mm plate-control cooling process. The effect of beginning rolling temperature (890 ~940 °C) in II rolling passes

cooling temperature (780 ~ 850℃) and cooling speed (8 ~ 20 ℃/s) after rolling on tensile properties

drop-weight tear test (DWTT) performance and structure of X65 steel heavy plate has been studied. Results show that with beginning rolling temperature 940 ℃ in II rolling passes and cooling speed 20 ℃/s after rolling the main structure in X65 steel heavy plate is acicular ferrite and granular bainite

the tensile strength and yield strength of plate are respectively 665 ~ 695 MPa and 495 〜520 MPa and the DWTT fibre structure ratio of plate is about 92% to meet the requirement of standard.