RESEARCH ON HIGH TEMPERATURE PLASTICITY OF X70 PIPELINE STEEL IN CONTINUOUS CASTING

Tensile testing for X70 pipeline steels in 600~1 350 ℃ was carried out, and the fracture micrographs of samples in different temperature were examined with SEM and metallographic microscope. The effects of C, N content on area reduction (RA) were examined. The results show 700~900 ℃ is the embrittlement region III, where the RA is lower than 40%. The plasticity decreases in 1 000~1 250 ℃ with the increase of C and N, while the plasticity is improved slightly in region III. It's the contribution of pinning function of carbonitride of Nb, V precipitated in grain boundary.