Experimental Basic Research Of V-N Microalloying For HRB400 High Strength Reinforcing Bars

V-N microalloying technology is the main route which adopted by countries all over the world to produce high strength rebars. Adding nitrogen in vanadium steel can accelerate V(C, N) precipitating in steel which will exert the function of fine crystal strengthening and precipitation strengthening to enhance the strength of rebars.Aiming at the problems of higher costing, higher energy consumption, longer production period of nitrided ferrovanadium, there is lacking feasibility research to the new method adding ferrovanadium and bottom-blowing N2, and lacking research that how does operation sequence affect the size, distribution, dispersity of V(C, N). So we will discuss above contents by means of contrastive experiments, and compare with the method of adding nitrided ferrovanadium directly.Consequences showed that blowing N2 can increase [%N] rapidly and it enlarges by the time. Adding ferrovanadium firstly is beneficial to absorb N2; the volume fraction of pearlite enlarges by increasing [%N]; and higher [%N] can decrease volume fraction of grains whose sizes are over 50?m and increase that of grains whose sizes are 15?50?m.V(C, N) can precipitate in the surface of MnS to enhance function of inducing ferrite transformation and it also can precipitate alone to exert this function after it becomes bigger. The TEM observations indicate that precipitations can be mostly found at dislocations, ferrite/cementite and ferrite/ferrite boundaries, but less in the grains.By analyzing the size, distribution, dispersity of V(C, N) between the contrast experiments, we know that more precipitations and higher dispersity can be gotten if the nitrogen content is higher, which can be also found in experiments of adding ferrovanadium firstly. Besides, there are more precipitations at the grain boundaries and dislocations which have better strengthening effect. Comparing the experiments adding ferrovanadium first and adding nitrided ferrovanadium directly we know that the effects are much the same, which illustrates the means of adding ferrovanadium and bottom-blowing nitrogen is feasible and can get an excellent effect.