Statistical Analysis Of High Strain And Low Cycle Fatigue Life Of Rebars And The Effect Of Vanadium Microalloying

Due to frequent earthquakes, the property of the buildings has an importantinfluence on catastrophic loss, therefore, the material used for construction is highlyrequired. This paper studied the rebars which reinforce the buildings, through thecomparison between HRB400V-N, HRB400V-Fe microalloyed, HRB400steel bars byquenching and self tempering (QST) and fine-grain bars, the effects on the anti-seismicproperties by Vanadium was studied. The four rebars was researched on high strain andlow cycle fatigue(HSLCF) property and the performace of carbonitride precipitating.All kinds of rebars have satisfied the current domestic criterion (GB1499.2-2007)for anti-seismic rebars. When researching the HSLCF life, because the low cycle fatiguelife data is dispersed, some kinds of mathematical statistics methods, such as Weibulldouble parameters probability function, normal distribution, lognormal distributionfunction and t-distribution function were used to statistically analyze the low cyclefatigue life data. The results indicate that, in all of the probability functions, the lowcycle fatigue life has the highest reliability by the t-distribution function method, thelow cycle fatigue life has the lowest reliability by the normal distribution method, andthe low cycle fatigue life has the highest safety by Weibull maximum likelihood method.Five mathematical statistics methods were applied to process initial fatigue data.According to the results of fatigue life，the cyclic toughness of Vanadium microalloyedsteel bars HRB400V-N， HRB400V-Fe, HRB400QST and fine-grained steel barsHRB400FG were compared and analyzed, combining with the analysis by Scanning andTransmission electron microscope, it is demonstrated that microalloy-vanadium caneffectively improve the low cycle fatigue properties of steel bars, but V\N should becontroled. Considering the factors of economic and technological in the practicalproduction, Vanadium micro alloyed steel bars are more suitable for application.It’s better to precipitate carbonitride when steel bars are rolled in the Nosetemperature, which is confirmed by production practice. In order to make full use ofvanadium’s effect, the stress relaxation was used for investigating the performace ofcarbonitride precipitating; the curves of PTT was drew. The results of the experimentsshow that at the same degree of deformation, the shape of precipitation-temperature –time is typical of C curve, and there exist a fastst precipitation temperature, about850℃~870℃.