ATTEN: Manager Liu
ADD: Longhua Development Zone, Jing County, Hengshui City, Hebei Province
4.1 Influencing factors of steel bar strength-yield ratio 4.1.1 The strengthening mechanism of conventional elements of carbon, silicon and manganese on steel bar strength-yield ratio Jingxiang steel shows that the strengthening effect of carbon, silicon and manganese in steel is mainly solid solution strengthening. Although the effect of solid solution strengthening is much lower than that of precipitation strengthening, the effect of solid solution strengthening is better than that of pearlite strengthening. Elements have little effect on the formation of pearlite. Pearlite has good comprehensive properties and can greatly improve the tensile strength of steel. Both solid solution strengthening and pearlite strengthening can improve the yield ratio of steel. Among the three elements of carbon, silicon and manganese, carbon plays the most important role in improving the strength and yield ratio of steel bars; although silicon can improve the strength-yield ratio of steel bars, its effect on steel strength is not as good as that of manganese in the composition design, which should take into account the strength, plasticity and weldability of various indicators comprehensively, and determine the specific content of 4.1.2 V microalloying method to improve the strength-yield ratio of steel bars. The regression statistics of strength-yield ratio, tensile strength and yield strength of reinforcing bars under different vanadium microalloying modes are obtained through data analysis. The regression results of strength-yield ratio, tensile strength and yield strength of ammoniated ferrovanadium, argon vanadium and ferrovanadium to steel are shown in tables 3~5. The regression statistics results of strength-yield ratio and chemical composition of steel are shown in tables 4. Statistical results of regression between tensile strength and chemical composition of reinforcing bars Table 5 Statistical results of regression between yield strength and chemical composition of steel strand 2) Microalloying of ferrovanadium, vanadium nitride and ferrovanadium helium, which affects the strength-yield ratio of reinforcing bars, can play the role of solid solution strengthening, precipitation strengthening and fine grain strengthening in steels, but vanadium in steels with little nitrogen content. Only a small amount of vanadium in the steel forms carbonitride precipitation.
That is to say, in the case of low nitrogen content in steel, vanadium precipitation strengthening and fine grain strengthening have little effect, while precipitation strengthening and fine grain strengthening both greatly improve the yield strength of steel, and the increase of tensile strength is relatively much lower. Therefore, under the condition of a certain vanadium content in steel, vanadium ferroalloying has the lowest degree of strength-yield ratio of steel. When ammonia in vanadium steel increases gradually, argon and vanadium have strong affinity, which promotes the precipitation of_C and vanadium, and makes the vanadium in solid solution state more transformed into precipitation state, which plays a more precipitation strengthening role. Moreover, the increase of helium also promotes the precipitation of carbon (helium Austenite-ferrite interface) and effectively prevents the strengthening of ferrite crystal. The effect of vanadium precipitation strengthening in steel depends on the number and dispersion of precipitation phases. The more and finer particles disperse, the greater the effect of precipitation strengthening. Some studies have shown that the original helium content in the molten steel of Chengdu Iron and Steel Co. is higher than 70 ppm, and the ratio of vanadium to nitrogen has reached or exceeded the ideal value of /N=4:1 when added with the helium brought in by vanadium nitride or ferrovanadium heliide.
That is to say, whether the molten steel is alloyed with vanadium helium or ferrovanadium nitride, the effect of vanadium on fine grain strengthening is redundant in the steel. According to the regression statistical results in Tables 3-5 and the characteristics of molten iron in our company, the vanadium micro-alloying method for producing HRB500E high strength aseismic steel bow is determined. For small size steel bunkers, using ferrovanadium nitride alloying method, for large size steel bunkers, using ferrovanadium nitride + ferrovanadium composite alloying method 42HRB500E chemical composition design 4.2.1 conventional elements according to Table 4~Table 5 statistics, each increase of 0.0 yield strength and tensile strength in steel can increase 7MPA and 8M respectively to prevent excessive carbon equivalent. The addition of Mn can improve the solid solution strengthening effect, reduce the phase transformation temperature, refine the structure of steel and improve the strength and toughness. Moreover, Mn can improve the solid solubility product in austenite and enhance the precipitation strengthening effect, but the content of Mn can be increased.