Q345冷成型钢高温蠕变性能试验研究

Experimental study on creep behavior of Q345 cold-formed steel at elevated temperatures

高温蠕变会加速热轧型钢构件受火失效,而对冷成型钢构件的高温蠕变性能研究有待深入。为此,对厚1.0 mm的Q345冷成型钢进行了8个试验温度(200~700℃)下的高温蠕变试验,每个试验温度设置2~8个应力水平(应力比0.10~1.1),总计41个试验工况,最长持时240 min。得到了不同温度和不同应力比下的蠕变曲线,并与已有的Q345热轧型钢高温蠕变曲线进行对比。结果表明:相同温度及应力比下,冷成型钢蠕变发展要快于热轧型钢,在实际工程中,应区别对待热轧型钢与冷成型钢的蠕变特性。基于高温下试件进入加速蠕变阶段的最小应力水平,给出了Q345冷成型钢在温度400~700℃下的蠕变断裂临界应力比,其中,温度为400~500℃和700℃时,蠕变断裂临界应力比高于屈服强度折减系数;而温度为550~600℃时,蠕变断裂临界应力比低于屈服强度折减系数,Q345冷成型钢可能会在达到高温屈服强度之前发生蠕变破坏,不利于结构安全。根据复合时间强化模型和稳态蠕变速率与应力比的定量关系,分别给出Q345冷成型钢高温蠕变曲线预测模型和稳态蠕变速率预测模型,预测值与试验值均较为接近,适用于预测Q345冷成型钢在温度200~700℃下的蠕变和稳态蠕变速率。

The high-temperature creep may accelerate the fire failure of hot-rolled steel members, but the impact on the fire resistance of cold-formed steel structures is unclear, because the research on the high-temperature creep performance of cold-formed steel is still scarce. For this reason, the high-temperature creep tests of 1.0 mm thick Q345 cold-formed steel were carried out under 8 temperature conditions(200-700 ℃), and each temperature condition was set with 2-8 stress levels(stress ratio 0.10-1.1), with a total of 41 test conditions and a longest duration of 240 min. The creep curves under different temperatures and stress ratios were obtained and compared with the existing high-temperature creep curves of Q345 hot-rolled section steel. The results show that the creep development of cold-formed steel is faster than that of hot-rolled steel under the same temperature and stress ratio. In actual engineering, the creep characteristics of hot-rolled section steel and cold-formed steel should be treated differently. Based on the minimum stress level at which the specimens enter the accelerated creep phase at high temperatures, the critical stress ratios of creep fracture of Q345 cold formed steel at 400-700 ℃ are given. The critical stress ratios are higher than the yield strength reduction coefficients at 400-500 ℃ and 700 ℃, while at 550-600 ℃, the critical stress ratios is lower than the reduction coefficients of yield strength, indicating that creep failure may occur before reaching the yield strength, which is not is not conducive to structural safety. According to the composite time hardening model and the quantitative relationship between the steady creep rate and the stress ratio, the prediction model of high temperature creep curve and the steady-state creep rate of Q345 cold-formed steel are given. The predicted values are close to the experimental values, and are applicable to the creep and steady-state creep rate prediction of Q345 cold formed steel at 200-700 ℃.