Q345qNH耐候桥梁钢动态CCT曲线构建及其相变研究

Measurement of Dynamic CCT Curve and Transforation of Q345qNH Weathering Bridge Steels

利用Gleeble-1500热模拟实验机采用热压缩的方法,对Q345qNH试样的感应加热段压缩60%的变形量,然后以0.1℃/s、0.5℃/s、1℃/s等10个不同速度冷却至室温,并测定其相变温度和时间情况,检测了变形段易变形位置的金相组织和硬度,构建了Q345qNH钢的动态CCT曲线。试验结果表明,0.1~1℃/s冷速获得均匀铁素体+珠光体组织;1℃/s~5℃/s冷速组织中珠光体量逐渐减少,粒状贝氏体含量增多;随着冷速进一步增大至50℃/s,几乎全变为粒状贝氏体组织;100℃/s冷速下,组织中出现板条贝氏体,或极少数出现马氏体。硬度和微观组织的关系曲线可以分为3个阶段:铁素体细晶强化阶段、粒状贝氏体增量强化阶段和贝氏体板条形态强化阶段。根据动态CCT曲线和具体的组织状态,通过控制钢材的轧后冷却制度,获得预期的组织,为Q345qNH/Q370qNH钢生产工艺提供理论支撑和技术参考。

Gleeble-1500 thermal simulation machine was used to compress 60% of the deformation in the induction heating section of Q345 qNH the sample, and then the sample was cooled to room temperature at 10 different rates, such as 0.1℃/s, 0.5℃/s, and 1℃/s. The phase transition temperature and time were measured, and the microstructure and hardness of the deformation position in the deformation section were detected. The dynamic CCT curve of Q345 qNH steel was constructed. The results show that the uniform ferrite + pearlite structure is obtained at 0.1~1℃/s cooling rate. At 1℃/s~5℃/s cooling rate, the pearlite volume decreased gradually and the granular bainite content increased. With the cooling rate further increasing to 50℃/s, almost all of them become granular bainite structure. At the cooling rate of 100℃/s, lath bainite or very few martensite appeared in the tissue. The relationship curve between hardness and microstructure can be divided into three stages: ferrite fine grain strengthening stage, granular bainite incremental strengthening stage and bainite lath morphology strengthening stage. According to the dynamic CCT curve and the specific structure state, the expected structure is obtained by controlling the cooling system of steel after rolling, which provides theoretical support and technical reference for the production process of Q345 qNH/Q370 qNHsteel.