Effect Of Vanadium And Heat Treatment Process On Microstructure And Properties Of High Strength Plastic Bainitic Steels

In recent years,ultra-high strength plastic nano-bainite steel?also known as super bainite steel?has attracted the attention of many scholars because of its excellent strong plastic matching.In order to obtain low temperature bainite structure of nanostructure,high carbon,which is not conducive to the improvement of welding performance.At the same time,the lower transformation temperature makes the bainite transformation time longer?even more than ten days?,which also limits the engineering application of this series of steel.How to improve the comprehensive mechanical properties of nano-bainite steel by alloy composition design and heat treatment process is particularly important.In this paper,two kinds of high carbon low alloy steels,62Mn2Si V and 60Mn2Si,were studied.By comparing with bainite steel without V,the effect of V on the carbon enrichment degree,rate,microstructure and mechanical properties of nano-bainite steel was studied.The results show that:The precipitation parameters of V in 62Mn2Si V steel were simulated by thermal Calc software.The austenitizing temperature corresponding to the full solution was1040?.The effect of V microalloying on the transformation of bainite steel is mainly as follows:the A_c1 and A_c3 points increase slightly,and the M_s point decreases.V suppresses the temperature range of high temperature transformation,and the transformation range of ferrite pearlite decreases.In addition,V increases the hardenability of austenite and the hardness of bainite steel.The results show that the TTT curve of V-bearing test steel is C-shape.Different from that of V-free test steel,there is no"Swing back"phenomenon in the temperature range close to M_s point,"nose tip"temperature is between 300-320?,and the incubation period of bainite transformation is obviously prolonged,V?in the form of solid solution and precipitation coexisting in austenite?can inhibit the transformation of bainite,reduce the diffusion coefficient of carbon in austenite,slow the enrichment rate of carbon in retained austenite,and thus slow down the transformation rate of bainite.Based on the investigation of carbon enrichment rate of BAT?bainitic austempering?,BQ&P?bainite-based quenching plus partitioning?and DBAT?disturbed bainitic austempering?processes,it is found that the expansion of BQ&P and DBAT processes changes abruptly after quenching.This is because part of martensite formed in quenching process accelerates the transformation process of bainite,from accelerating the bainite process.The carbon enrichment rate of both processes is higher than that of bat process,so BQ&P and DBAT processes can be used to make up for the effect of alloy element V on delaying bainite transformation,accelerating bainite transformation and saving heat treatment time.The results show that the strength and plasticity of V-microalloying steel are improved in different degrees under the same conditions.The results of TEM fine tissue characterization showed that V?C,N?The diameter of these particles is about 13?30nm.The V?C,N?particles with uniform and fine dispersion distribution can play the role of precipitation strengthening.It can not only nail the austenite grain boundary and prevent the rapid growth of austenite grain,so as to refine the austenite grain,but also hinder the movement of dislocation,so as to improve the strength of steel.