Research On Deformation Resistance And Recrystallization Of Non-Quenched And Non-Tempered Microalloy Steel 40Mn2V

The research and application of microalloyed non-quenched and non-tempered steels simplified production process and saved energy, which is one of the most important product in modern industry and have great development space. In this paper, resistance of deformation, dynamic recrystallization and second-phase precipitation in high temperature deformation had been studied for microalloyed non-quenched and non-tempered seamless steel pipe 40Mn2V combining the actual production of Hengyang Steel Tube.Co.,Ltd., which had provided reliable theory data for actual production.Fourteen of deformation condition had been designed for approximatively simulating the actual production of steel tube 40Mn2v in this paper. Resistance of deformation and dynamic recrystallization had been researched according to true stress-strain curve in high temperature deformation tested by the Gleeble-1500 thermal simulation machine. The size of recrystal grain in deformation condition and original grain had been analyzed by microstructure observation, and the state of second-phase precipitation in high temperature deformation had been observed by TEM.The results show that the high temperature deformation process of steel 40Mn2V is a integrative process of work-hardening and high temperature softening, and the deformation resistance become smaller with higher temperature and lower deformation rate. The logarithm value lnσof deformation resistanceσlinearity reduce and increase respectively with the increasing of temperature T and deformation rate lnε, however the value of deformation resisitance and deformation degree comply to nonlinear relation. The fitting formula of deformation resistance of microalloyed non-quenched and non-tempered steel 40Mn2V had been gained by using Matlab soft to synthetically regress for the tested datas, according to the resistance of deformation model proposed by Jihua Zhou and Kezhi Hu, which fit degree is better for 0.9663. Only as the deformation degree is big enough, recrystallization behavior could occur and achieve, which become more easily with higher temperature and lower rate of deformation, according to the true stress-strain curve. The dynamic recrystallization activation energy Qd of microalloyed non-quenched and non-tempered steel 40Mn2V had been calculated for 382.2168KJ/mol by experiential formula and test datas, which is 95.2KJ/mol more than low carbon steel 287KJ/mol. As the Zener-Hollomen factor Z were adopted, it simplified the graph of dynamic recrystallization, which show that recrystallization behavior become more easily with smaller factor Z. There are smaller recrystal grain size and stronger effect of refinement with bigger factor Z. TEM observation show that the carbonitride of V and Ti precipitate in temperature range of 800℃～950℃, which not only strengthened the resistance of deformation, but also increased the dynamic recrystallization activation energy, and hampered dynamic recrystallization evidently.