Effect of intermediate cooling on precipitation behavior and austenite decomposition of V-Ti-N steel for non-quenched and tempered oil-well tubes

The effect of intermediate cooling stop temperatures (Ts) during tube rolling and reheating on the precipitation behaviors of steel 33Mn2V was investigated on a real manufacture process of N80 grade non-quenched and tempered (non-Q&T) hot-rolling seamless oil-well tubes. The results show that the vanadium precipitation characteristics in austenite are of vital importance for the subsequent phase transformation in the manufacturing process of medium carbon non-Q&T seamless steel tube. The higher Ts results in complex precipitation of vanadium predominantly in the latter procedures, inducing the harmful bainite. Whereas, the lower Ts leads to the precipitation of fine V(C, N) in austenite before its decomposition starts in the final cooling process and promotes the formation of intragranular ferrite, resulting in optimized combination of toughness and strength.