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采用OM、SEM和TEM等方法,对600 MPa级Nb-Ti微合金化高成形性元宝梁用钢的组织与力学性能进行了测试表征,并分析了强化机制。结果表明,终轧温度对实验用钢的组织与力学性能有显著影响,随着终轧温度的降低,钢中铁素体晶粒尺寸逐渐减小,位错密度逐渐增加,析出物尺寸逐渐减小、数量逐渐增多、Nb/Ti原子比逐渐增大,屈服强度与抗拉强度均呈现出单调上升的规律,而延伸率存在一个最佳温度,终轧温度为840℃时具有最优的力学性能,其屈服强度与抗拉强分别达到了541与615 MPa,延伸率为31.0%,-60℃冲击功为117 J。(Nb,Ti)C在奥氏体中析出的Nr T与PTT曲线表明,在实验温度范围内,均匀形核与位错线形核的形核率随温度的降低而提高,形核孕育时间随温度的降低而缩短,这与观察到的析出物尺寸随着终轧温度的降低而减小、析出物的数量随着终轧温度的降低而增多的规律相符。细晶强化与位错强化是实验用钢主要强化方式,细晶强化占总屈服强度的46%~48%,位错强化占总屈服强度的18%~25%,析出强化对屈服强度的贡献较小,约2%左右。
The microstructure and mechanical properties of 600 MPa grade Nb-Ti microalloying high-forming ingot beam steel were characterized by OM, SEM and TEM. The strengthening mechanism was also analyzed. The results show that the finish rolling temperature has a significant effect on the microstructure and mechanical properties of the experimental steel. With the decrease of the finish rolling temperature, the grain size of the ferrite in the steel gradually decreases, the dislocation density gradually increases and the size of the precipitate gradually decreases , The number increased gradually, the atomic ratio of Nb / Ti increased gradually, and the yield strength and tensile strength all showed a monotonically increasing law. However, there was an optimum temperature for elongation and the best mechanical properties were obtained when the finishing temperature was 840 ℃ , The yield strength and tensile strength reached 541 and 615 MPa respectively, the elongation was 31.0% and the impact energy at -60 ° C was 117 J. NrT and PTT curves of (Nb, Ti) C precipitated in austenite show that the nucleation rate of uniform nucleation and dislocation linear nuclei increase with the decrease of temperature in the experimental temperature range. The nucleation incubation time The decrease of the temperature is shortened, which agrees with the observation that the size of precipitates decreases as the finishing temperature decreases, and the amount of precipitates increases as the finishing temperature decreases. Fine grain strengthening and dislocation strengthening are the main strengthening methods for experimental steel. Fine grain strengthening accounts for 46% ~ 48% of total yield strength, dislocation strengthening accounts for 18% ~ 25% of total yield strength, and precipitation strengthening contributes to yield strength Smaller, about 2%.