Study on Chemistry and Process Optimization of V-microalloyed N80 Seamless Tube
The complex effects of different Nitrogen (N) contents and thermal routines on the microstructures and mechanical properties of 33Mn2V steel for N80-Class seamless tube application were investigated using Gleeble simulation technique. The results showed that the N additions of 140 or 210ppm in the steel for the in-line normalization process (ILNP) increased the strength while the toughness remained at a high level as compared with that of the low-N steel of 50ppm. It is also revealed that the N addition of 210ppm could enhance the performance combination of strength and toughness in the steel by using 700℃ as the cooling interrupted temperature (CIT) for the non in-line normalizing process (NILNP). It was further evidenced that the toughness was improved at expense of strength to some degree in all the steels by decreasing reheating temperature for the ILNP, while an increase of CIT for NILNP severely impaired the toughness and slightly improve the strength in the high-N steel of 210ppm. This can be attributed to the dissolution and precipitation behavior of V(CN). The optimization of V(CN) precipitation can be achieved by the enhanced N. The precipitation of V (CN) in austenite was promoted by cooling to a certain temperature lower than the Ar1 for the ILNP. The V(C,N) particles formed in austenite contributed to grain refinement by the VN-induced nucleation of intragranular ferrite, but as a result the effect of precipitation on strengthening would become weaker due to a decrease of the precipiation of V in ferrite.
Seamless tube; In-line normalizing; V(CN); Reheating; Mechanical properties; Gleeble simulation.
Tao Pan (1), Caifu Yang (1), Yongquan Zhang (1), Weibin Zong (2) and Chuanyou Zhang (2)
(1) Central Iron & Steel Research Institute, Beijing 100081, China
(2) Tianjin Pipe Co., Ltd., Tianjin 300300, China
International Conference: 3rd Thermomechanical Processing of Steels, 2008, Padua, Italy