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通过升温、冷却和拉伸试验,对历经300~900℃高温后的Q690钢材在自然冷却和浸水冷却条件下的力学性能展开试验研究。结果表明:经高温冷却的Q690钢材在不同温度和不同冷却方式下有不同的外观特征;受热温度超过500℃时,高温冷却对Q690钢材的弹性模量影响很小,对其强度和伸长率影响较大;当受热温度不超过700℃时,Q690钢材高温后的强度和伸长率在两种冷却方式下具有基本相同的变化规律;在700~800℃之间,不同冷却方式对Q690钢材高温后强度和伸长率产生影响,且随温度升高差别愈加明显,自然冷却条件下强度降低且伸长率增大,浸水冷却条件下强度增大且伸长率减小。将Q690钢材高温后力学性能与Q235钢材和Q460钢材比较,认为不同强度等级钢材高温后的力学性能差别显著,在自然冷却条件下较高强度钢材(Q690)的强度衰减和延性增长大于较低强度钢材(Q235和Q460)的。根据试验结果,建立了不同冷却条件下的高温后各力学参数与受热温度之间的数学模型,该模型可用于火灾后Q690钢结构的承载能力的评估。
The mechanical properties of Q690 steel subjected to high temperature of 300 ~ 900 ℃ under natural cooling and immersion cooling were studied through the experiments of heating, cooling and tensile. The results show that the high temperature cooling Q690 steel has different appearance characteristics under different temperatures and different cooling methods. When the heating temperature exceeds 500 ℃, high temperature cooling has little effect on the elastic modulus of Q690 steel, and affects the strength and elongation When the heating temperature does not exceed 700 ℃, the strength and elongation of Q690 steel after the high temperature have basically the same change rule under the two cooling methods; between 700 and 800 ℃, different cooling methods on the Q690 steel after high temperature Strength and elongation, and the difference becomes more obvious with the increase of temperature. Under the condition of natural cooling, the strength decreases and the elongation increases. Under the condition of immersion cooling, the strength increases and the elongation decreases. The mechanical properties of Q690 steel after high temperature are compared with those of Q235 steel and Q460 steel. It is considered that the mechanical properties of steel with different strength grades are significantly different after high temperature. The strength and ductility of higher strength steel (Q690) under naturally cooled conditions is greater than that of lower strength Steel (Q235 and Q460). According to the experimental results, the mathematical model between the mechanical parameters and the heating temperature under different cooling conditions is established. The model can be used to evaluate the bearing capacity of Q690 steel structure after fire.