Evolution of microstructure and mechanical properties of cold-drawn small-caliber 16MnNiV seamless steel tube

16MnNiV steel is developed from 16Mn and 16MnV steel. After hot-perforated rolling into tube, cold rolling, cold drawing and heat treatment are carried out to prepare high pressure tubes with high caliber. The microstructure and mechanical properties of 16MANIV seamless steel tube of small diameter were studied by means of optical microscopy (OM), scanning electron microscopy (SEM). electron backscattering diffraction (EBSD), transmission electron microscopy (TEM) and physicochemical phase analysis. The microstructure and the change of the second phase precipitation were revealed, and the strengthening increment was calculated. The relevant results can provide a reference for the material development and performance improvement of high strength high pressure tubes. The results show that the main structure of the experimental steel in the process of drawing the tube is ferrite and pearlite. In the case of precipitation, annealing after one pull increases the total amount of precipitation, and annealing after the second pull does not change the total amount of precipitation. It is known from EDS analysis that the precipitated second phase particle is VC. The tensile strength and yield strength of the experimental steel are gradually increased and the elongation rate decreases after cold drawing and different heat treatment processes. It can be seen that the increase of yield strength of experimental steel mainly comes from the contribution of fine crystal reinforcement due to the large deformation of cold extraction process. After heat treatment, the tensile strength, yield strength and elongation rate of $6.35 mm 3 mm round tubes reach over 950, 864 MPa and 15. 5%. Compared with other high pressure tubing products of 16Mn series, the mechanical properties are greatly improved and good strong plastic matching is obtained.