water cooling at 720 ℃ with cooling rate 30~35 ℃/s
the ultra-low-carbon bainite steel-0.023C
1.63Mn
0.52Cu
0.25Mo
0.055(Nb+Ti)
0.0011B had compound structure consisting of lath bainite + minor granular bainite
and irregular ferrite. The bainite bunch colony size was 3~5 μm and the lump and irregular ferrite size was1~2.5 μm. Tempering at 650 ℃ and 700℃ weren't obvious influence on bainite grain orientation.