This research investigated 8.0 mm thick high strength weathering steel Q550NQR1 with relatively low -40℃ low temperature impact value

and multiple pearlite segregation bands were observed in core microstructure

although the segregation bands are narrow and discrete

the quantity is numerous and ratio reaches 5. 8% ; through test

the segregation band in core microstructure has little effects on mechanical performance of tested steel

which is considered to be resulted from the effects of fine grain strengthening and precipitation strengthening by Nb-V micro alloying； however

the interface of ferrite and pearlite is relatively weak

which facilitates generation and extension of crack

as well as the pearlite segregation band likely leads to increase of ductile-brittle transition temperature thereby deteriorating low temperature impact toughness of tested steel. The improved technologies that increasing heating temperature and assuring enough heating time

increasing cooling rate in laminar cooling section as well as controlling the contents of Nb and V were adopted to conduct rolling

and for the final product

grain refinement achieves

pearlite segregation band vanishes

mechanical performance satisfies requirement and the surplus is appropriate

as well as -40℃low temperature impact average value increases 84.3 J.